form a hypothesis to explain the earthquakes that precede the eruption

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Erik Klemetti

What's Up With the Quakes Before a Volcano Erupts?

Earthquakes and volcanoes are intimately linked. They are both products of the plate tectonic process that is constantly reshaping the surface of the Earth. But even beyond that, earthquakes are some of the best clues we have that a volcano might be heading towards an eruption. So, why are there earthquakes in the days-months-years before a volcano erupts and why do some earthquakes lead to an eruption and some don't? Well, it is a little more complicated than it seems.

When we're talking about earthquakes that are leading up to an eruption , the key reason they occur is magma on the move. Most magma that is the source of volcanism in places like Iceland, the Cascades , Sicily and almost every volcano on the planet is initially formed by melting the mantle, many (8-80) kilometers beneath our feet. That magma is buoyant because it is hot, chock full of gases and made of less dense material than the rock around it, so it rises.

Although we tend to think about magma as a liquid, it is a very dense and viscous liquid compared to something like water . This means it can exert a lot of force on the rocks around it as it rises its way through the crust. This is what generates much of the earthquakes that occur in volcanically active areas: the fluid pressure from the rising magma cracking the rock, making space for itself as it rises.

The earthquakes causes by this don't tend to be large—rarely are they larger than magnitude 5 and usually they less than magnitude 3. You might be hard pressed to notice them at all if you were standing on the volcano itself. However, if magma is rising steadily, the location of the earthquakes in the crust will change. They will become shallower and they might even move laterally as the magma tries to find the easiest path out of the crust. By locating the earthquakes in the crust, volcanologists can map out the pathway and location of the magma as it rises. These earthquakes generated by magma cracking the rock along the way upwards are called volcano tectonic (VT) earthquakes .

You also get long-period (LP) earthquakes under volcanoes as bubbles form and escape from the magma during its ascent. Unlike VT earthquakes, LP earthquakes gradually begin and then fade away rather than being abrupt events. So, if a swarm of earthquakes under a volcano is a combination of VT and LP events, it is a pretty good sign that the earthquakes are being caused by magma moving into shallower parts of the volcano. However, as the magma gets closer to the surface, VT events tend to go down as LP events increase. They can also occur as hybrid (or mixed) earthquakes that have some of the VT and LP characteristics.

A third type of shaking can occur under volcanoes and that is harmonic tremor . This is small but constant shaking possibly caused by the turbulent motion of the magma in the conduit. Typically when volcanologists are watching a volcano that is restless, the onset of harmonic tremor is a good sign that an eruption is likely to occur in minutes to days.

These three types of earthquakes—VT, LP and harmonic tremors—are the clues that volcanologists use to determine if the volcano is heading towards an eruption (along with the suite of other volcano monitoring tools). All of these earthquakes can occur at a volcano that does not end up erupting , so putting all the clues together is vital for an accurate forecast. Volcanologists also use seismic information to look for eruption events like explosions and lahars (mudflows) as they can also produce their own, distinct earthquakes.

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And if that wasn't tricky enough, earthquakes can occur under volcanoes that have nothing to do with magma. Places with abundant volcanoes also tend to be riddled with faults, so earthquake swarms that are merely tectonic are common. What volcanologists look for to determine if an earthquake is potentially related to magma movement or just fault motion is if the earthquake was caused by dilation (opening) of the crust (magma movement) or some other type of motion (tectonic).

Earthquakes can also be generated in the shallow crust (a few kilometers below the surface) by hot fluids in the volcano's hydrothermal fluids . All the water that percolates through the crust over volcanoes can heat up (sometimes to the point of becoming a supercritical fluid ) and as those fluids move, the accompanying change in pressure can fracture the rocks around the fluid. If you look at places where geothermal energy is being tapped or at a restless caldera like Yellowstone , earthquake swarms are common from hydrothermal fluids.

If you watch webicorders that volcanologists have installed at many volcanoes, you can see the different types of earthquakes as they occur. However, seismometers like these also pick up earthquakes that happened all over the world or even non-geologic shaking like truck, people or wind. Although it is easy to watch these near-realtime records of volcanic shaking, it takes training to interpret all those blips into a forecast for a volcano.

So, earthquakes are a great tool for understanding what might be going on under a volcano, both during times that it might be heading towards an eruption or periods when all is quiet. The earthquake record at Mount St. Helens in Washington shows how even during times before and after eruptions (2002-2012), the earthquakes deep under the volcano don't stop—that's because magma is always moving, cooling, degassing and recharging with new magma. Calling a volcano "dormant" is a bit of a misnomer as the only part that is quiet is the top and really, volcanoes spend most of their life not erupting. Those earthquakes remind us that volcanoes are always rumbling .

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How do scientists forecast eruptions?

Scientists use a wide variety of techniques to monitor volcanoes, including seismographic detection of the earthquakes and tremor that almost always precede eruptions, precise measurements of ground deformation that often accompanies the rise of magma, changes in volcanic gas emissions, and changes in gravity and magnetic fields. Although not diagnostic individually, these techniques, when used in combination at well-monitored volcanoes, have resulted in successful predictions. At Pinatubo volcano (Philippines) in 1991, a successful forecast saved thousands of lives. The USGS Volcano Hazards Prgram notes that the key to an accurate short-term eruption forecast is being able to recognize when such monitored data show consistent changes from normal background levels of activity.

Monitoring-based forecasts are becoming much more reliable, but they remain imperfect. If scientists are fortunate, precursors to an eruption follow the same course as they followed before previous eruptions. Patterns often change, though, and wholly new behavior is observed. The best forecasts will be based on an integration of geologic history, realtime monitoring, and a deep understanding of the internal plumbing processes of the specific volcano. Even with the best of monitoring and interpretations, reliable forecasts are rarely possible more than a few days in advance of an eruption.

Some forecasts of volcanic eruptions are based on eruption recurrence intervals, but these are notoriously unreliable for two reasons: 1) few volcanoes are sufficiently well studied to provide an accurate eruptive history over the many hundreds, or tens of thousands, of years necessary to establish a reliable recurrence interval; and 2) few volcanoes maintain the same behavior for long (more often than not, as soon as a repetitive pattern becomes apparent, the volcano changes behavior).

Volcano observatories make forecasts with great caution as they can have huge impacts on the affected populations, in some cases forcing people to leave behind homes, farms, and livestock. Inaccurate forecasts can lead to unnecessary obligation of scarce resources and/or undermine residents' confidence in future forecasts.

Reliable forecasts, however, can be made by volcano observatory staff, who have the experience to interpret their monitoring that detects eruption precursors. Most nations with volcanoes have tasked an established observatory, run by the government or by a university, to provide eruption forecasts to the public. All of these observatories are members of the World Organization of Volcano Observatories (WOVO) .

List of Questions

Global Volcanism Program, 2024. [Database] Volcanoes of the World (v. 5.2.0; 6 Jun 2024). Distributed by Smithsonian Institution, compiled by Venzke, E. https://doi.org/10.5479/si.GVP.VOTW5-2024.5.2

November 29, 1999

What Causes a Volcano to Erupt, and How Do Scientists Predict Eruptions?

Volcanologists cannot yet predict a volcanic eruption

By Attila Kilinc

Kilauea erupting.

Douglas Peebles Getty Images

Editor’s Note (6/4/18): This story is being re-posted in light of the deadly eruption of Guatemala’s Fuego volcano on Sunday (June 3), which covered nearby villages in fast-moving ash flows.

Attila Kilinc, head of the geology department at the University of Cincinnati, offers this answer. Most recently, Professor Kilinc has been studying volcanoes in Hawaii and Montserrat.

When a part of the earth's upper mantle or lower crust melts, magma forms. A volcano is essentially an opening or a vent through which this magma and the dissolved gases it contains are discharged. Although there are several factors triggering a volcanic eruption, three predominate: the buoyancy of the magma, the pressure from the exsolved gases in the magma and the injection of a new batch of magma into an already filled magma chamber. What follows is a brief description of these processes.

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As rock inside the earth melts, its mass remains the same while its volume increases--producing a melt that is less dense than the surrounding rock. This lighter magma then rises toward the surface by virtue of its buoyancy. If the density of the magma between the zone of its generation and the surface is less than that of the surrounding and overlying rocks, the magma reaches the surface and erupts.

Magmas of so-called andesitic and rhyolitic compositions also contain dissolved volatiles such as water, sulfur dioxide and carbon dioxide. Experiments have shown that the amount of a dissolved gas in magma (its solubility) at atmospheric pressure is zero, but rises with increasing pressure.

For example, in an andesitic magma saturated with water and six kilometers below the surface, about 5 percent of its weight is dissolved water. As this magma moves toward the surface, the solubility of the water in the magma decreases, and so the excess water separates from the magma in the form of bubbles. As the magma moves closer to the surface, more and more water exsolves from the magma, thereby increasing the gas/magma ratio in the conduit. When the volume of bubbles reaches about 75 percent, the magma disintegrates to pyroclasts (partially molten and solid fragments) and erupts explosively.

The third process that causes volcanic eruptions is an injection of new magma into a chamber that is already filled with magma of similar or different composition. This injection forces some of the magma in the chamber to move up in the conduit and erupt at the surface.

Although volcanologists are well aware of these three processes, they cannot yet predict a volcanic eruption. But they have made significant advances in forecasting volcanic eruptions. Forecasting involves probable character and time of an eruption in a monitored volcano. The character of an eruption is based on the prehistoric and historic record of the volcano in question and its volcanic products. For example, a violently erupting volcano that has produced ash fall, ash flow and volcanic mudflows (or lahars) is likely to do the same in the future.

Determining the timing of an eruption in a monitored volcano depends on measuring a number of parameters, including, but not limited to, seismic activity at the volcano (especially depth and frequency of volcanic earthquakes), ground deformations (determined using a tiltmeter and/or GPS, and satellite interferometry), and gas emissions (sampling the amount of sulfur dioxide gas emitted by correlation spectrometer, or COSPEC). An excellent example of successful forecasting occurred in 1991. Volcanologists from the U.S. Geological Survey accurately predicted the June 15 eruption of the Pinatubo Volcano in the Philippines, allowing for the timely evacuation of the Clark Air Base and saving thousands of lives.

Pu‘u ‘Ō‘ō, the easternmost of Kilauea's volcanic vents, spews molten lava on the Big Island of Hawaii.

Can earthquakes trigger volcano eruptions? Here's the science.

Possible links between these two geologic titans have long fascinated—and divided—scientists. Here’s what the latest studies have to say.

Tectonic earthquakes are among the most powerful natural phenomena on the planet. It’s no surprise, then, that they are sometimes suspected of being able to trigger volcanic eruptions .

Earth’s volcanoes are often located in seismically excitable parts of the world. Just take the so-called Ring of Fire , which is technically a horseshoe-shaped region that traces the edges of tectonic plates around the Pacific basin. This area hosts 90 percent of the world’s recorded earthquakes and 75 percent of all active volcanoes.

In such seismic hotspots, eruptions and earthquakes are often taking place at roughly the same time—but that’s exactly what you would expect. Despite frequent breathless speculation online, you can’t automatically assume that there’s a connection between a given quake and a subsequent eruption.

“The volcano may have already been preparing to erupt, or it’s already been erupting for a long time,” says volcanologist Janine Krippner .

Still, the question of whether earthquakes can cause volcanic eruptions is a serious research topic that experts have been investigating for centuries. And multiple lines of evidence from recent studies suggest that a connection could potentially exist in certain situations. So, where do scientists currently stand on the issue? We’ve got you covered.

Joining up some dodgy dots

Atsuko Namiki , associate professor of geosciences at Hiroshima University, highlights a few geophysical studies with data that suggest a connection. A 1993 paper, for example, links a magnitude 7.3 quake in California to volcanic and geothermal rumblings immediately afterward. And a 2012 study reckons that a magnitude 8.7 earthquake in Japan in 1707 forced deeper magma up into a shallow chamber, triggering a huge blast at Mount Fuji 49 days later.

Even the ever-cautious U.S. Geological Survey says that sometimes, yes, earthquakes can trigger eruptions. The agency suggests that some historical examples imply that an earthquake’s severe ground shaking, or its ability to otherwise change the local pressure surrounding the magmatic source nearby, can trigger volcanic unrest. They cite the magnitude 7.2 earthquake on Hawaii’s Kilauea volcano on November 29, 1975, which was quickly followed by a short-lived eruption.

But there are problems. First, as the USGS stresses, the triggering mechanisms for such events are not well understood, and papers linking quakes to later eruptions can really only speculate.

Second, it’s possible that the timing in all these examples was just a coincidence. Geologists must understand the specific triggering and rule out chance before a connection can be definitively made–and Earth’s geological complexities make both extremely difficult.

Darwin’s accidental deception

Statistical analyses are attempting to tackle the chance problem head-on. A 1998 Nature paper investigated whether magnitude 8.0 or larger quakes could trigger explosive volcanism up to 500 miles away from the epicenter within five days. Using data from the 16 th century to the present, its authors found that these types of eruptions happened four times more often than chance alone could explain.

Similarly, a 2009 paper used historical data to show that that magnitude 8.0 quakes in Chile are associated with significantly elevated eruption rates in certain volcanoes as far as 310 miles away. The problem is that these sorts of historical data aren’t exactly great.

Related Photos: Learn More About the World’s Volcanoes

“Major earthquakes and large volcanic eruptions are both relatively infrequent events, and scientists have only been reliably keeping these records for the last half century or more, depending on the region,” says Theresa Sawi , an undergraduate researcher in geophysics at the University of California, Berkeley.

Many data points in the past come from fairly ambiguous news reports and journal entries. David Pyle , a professor of volcanology at the University of Oxford, points out that one of the earliest writers to link earthquakes and eruptions was none other than Charles Darwin .

In 1840, Darwin gathered eyewitness information on some minor changes at Chilean volcanoes following the powerful quake there in 1836. It’s unclear if any eruptions took place, but “nonetheless, all of these 'events' ended up in the catalog of volcanic eruptions and now appear to offer evidence for earthquake triggering,” Pyle says.

Squeezing out toothpaste

Sawi is a coauthor on a more recent statistical analysis in the Bulletin of Volcanology that tries to circumvent this issue. This study focused only on more scientifically robust data from 1964 onward, and it looked at smaller quakes of at least a magnitude 6.0 that took place 500 miles from a volcanic eruption.

Sawi’s study found that there was a 5 to 12 percent increase in the number of explosive eruptions two months to two years following a major quake.

The team identified 30 volcanoes that may have at some point undergone a potentially triggered eruption. On a scale of days, the team found no evidence for triggering that couldn’t be explained by chance alone. That result actually goes against one of the findings of a 2006 review featuring Michael Manga , a coauthor on the new paper.

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“It's nice to see researchers not being afraid to make conclusions that go against their previous work,” said Oliver Lamb , a volcanologist at the University of North Carolina at Chapel Hill. “This is how science should work, really.”

Curiously, Sawi’s study found that there was a 5 to 12 percent increase in the number of explosive eruptions two months to two years following a major quake. This jump is both surprising and interesting, according to Lamb, but it’s also pretty small.

Jackie Caplan-Auerbach , an associate professor of seismology and volcanology at Western Washington University, says that the paper “actually highlights how unlikely it is that a quake could trigger an eruption.”

How, then, could this long-term trend be explained? What may happen during those months is that ruptures caused by quakes open up new pathways for viscous magma to follow, gradually, to the surface. The shaking, over time, could also create additional bubbles in the magma, which increases its pressure–a bit like shaking up a can of soda.

Perhaps the movement of rock can squeeze magma bodies like a tube of toothpaste, Sawi says, slowly forcing the magma out via volcanic exit routes. Or the quake may stretch the rock around a volcano’s magma reservoir, which would prompt gases to bubble out of the molten rock and increase the pressure in the reservoir.

Honey, I shrunk the volcano

Caplan-Auerbach suspects that if a quake does trigger an eruption, then the volcano has got to be primed and ready to go when it strikes. But while it might seem “intuitively reasonable that large earthquakes might trigger activity at a volcano that is poised to erupt, the empirical evidence for this link is rather thin,” Pyle says.

Some scientists, like Namiki, are hoping to find such evidence. She and her colleagues design models of volcanic systems in the lab and shake them about to examine how triggering could physically take place.

In a 2016 study , his team used syrups with varying crystal numbers, bubble quantities, and so forth to simulate various magma reservoirs . They found that at the resonant frequency, the frequency at which an object can naturally vibrates, the back-and-forth sloshing of the “magma” was most prominent. Bubbles joined up, and the frothy foam atop collapsed. In a real volcano, this would allow hot gases to readily escape from the magma, increasing the reservoir’s pressure and potentially pushing the volcano to erupt.

In 2018, the team also published a study of a gel model of a volcano injected with fluids simulating different types of magma. They found that shaking the model caused the fluids to move around faster than they otherwise would. However, where the fluids went was tied to their buoyancy and storage depths. Less buoyant fluids moved sideways or downward, which in a real volcano would make an eruption less likely. But bubbly fluids at shallow depths ascended, something that could lead to an eruption.

Keeping their eyes to the ground

It’s certainly not straightforward, and Namiki notes that skepticism about eruptions triggered by earthquakes is perfectly natural. However, Eleonora Rivalta , group leader of earthquake and volcanic physics research at GFZ Potsdam, suggests that the mood may be slowly shifting toward the possibility of a connection.

“While the wider scientific community may still be a bit skeptical, many volcano geophysicists are now convinced volcanoes may indeed react to earthquakes with a variety of responses,” she says. She emphasizes, however, that the smoking gun is still missing–specifically, a clear demonstration of how exactly an eruption was triggered at a specific volcano by a specific earthquake.

There are other avenues to explore outside statistics and lab simulations. Pyle suggests that if certain volcanoes are thought to be triggered by quakes, then the volcanic debris they eject could hold clues about the state of the magma reservoir prior to their outburst. That may reveal if the quake really did make a significant difference, or it may show that they were primed to erupt anyway and the quake just accelerated the countdown.

For Sawi, the way forward is clear: “Increased monitoring of volcanoes worldwide, especially those historically under-studied volcanoes, would help provide the data needed to begin recognizing patterns and, yes, triggers that could indicate a heightened probability of eruption.”

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When Volcanoes Erupt

Volcanoes have various impacts.

Erupting volcanoes are powerful forces of nature that both build and destroy. For example, undersea volcanic eruptions created the Hawaiian Islands, and to this day the Hawaiian volcano Kilauea oozes lava into the sea, creating new coastland on the southeastern side of the Big Island of Hawaii. On the southeast slope of the Big Island is a growing submarine volcano called Loihi, which will not breach the ocean’s surface for tens of thousands of years.

Kilauea has been continuously erupting since 1983, often emitting lava flows. In contrast, other types of volcanoes erupt quickly and violently, in huge explosions that can send up large columns of gas and ash, rain down rocks, spew lava, and unleash pyroclastic flows – large masses of hot rock fragments and gas that speed down a volcano’s slopes. These eruptions can destroy lives and property. In the continental United States, the most recent and deadly volcanic eruption came on May 18, 1980, when Mt. St. Helens blew its top–and one whole side of the mountain–killing 60 people and leveling 600 square kilometers (232 sq. miles) of forest.

The most powerful volcanic eruption observed in recent history was in 1815 at the Tambora  volcano in Indonesia, which produced huge pyroclastic flows and ejected large quantities of fine ash and gases into the stratosphere. The eruption killed an estimated 60,000 people and the resulting volcanic cloud lowered temperatures around the globe by as much as 3 degrees Celsius (5.4 degrees Fahrenheit). In parts of Europe and North America, 1816 was known as the “year without a summer,” due to the cooler temperatures.

The Science of Volcanoes

Volcanic eruptions are vivid reminders that our planet is a geologically active and dynamic place. On any given day, scientists estimate 20 volcanoes worldwide are erupting on the land. Still more are probably erupting underwater, but scientists don't have enough instruments to detect them. Many of these submarine eruptions theoretically occur along mid-ocean ridges, where an estimated 80 percent of Earth's magma erupts unnoticed.

An erupting volcano is like a window into the depths of the Earth, because lava and other erupted material provide clues to the mystery of what is going on far below the surface. For example, scientists can use these materials to learn about the composition, temperature and history of Earth’s interior.

To help understand the components of Earth’s interior, Smithsonian volcanologist Dr. Elizabeth Cottrell simulates the conditions deep under volcanoes by using special machines to generate the immense pressure found many kilometers under the Earth’s surface. The machine compresses and melts rock samples, essentially recreating the magma from which the rock sample came. She uses her findings to understand how the interior of the planet has evolved over many millions of years.

Dr. Benjamin Andrews , another Smithsonian volcanologist, performs similar experiments on erupted volcanic rocks in order to understand the geological conditions deep underground that preceded the eruptions. This information can help scientists better predict future eruptions.

Volcanoes of different ages can provide insight into scientific fields beyond geology. Smithsonian scientist Dr. Helen James explores lava tubes and other volcanic caves, searching for fossils of extinct animals, mainly birds. She conducts most of her research in the Hawaiian Islands, which were formed one at a time over millions of years, as the Pacific Plate moved over the Hawaiian hotspot, with the youngest island to the southeast, and oldest to the northwest. This makes the islands a great place to study the evolution of biodiversity over time.

The Hawaiian Islands were created by volcanoes and Hawaiians believe the volcano goddess Pele lives in Kilauea volcano. A traditional epic story about Pele and her sister Hi'iaka is a main source of Hawaiian poetry, music and dance. Smithsonian anthropologist Dr. Adrienne Kaeppler studied Hawaiian hula dance and how it relates to, and honors, Pele.

Forecasting Volcanic Eruptions

Volcanoes and humans have an uneasy coexistence, because volcanic eruptions can cause severe destruction. More than three dozen historical eruptions have each caused more than 1,000 fatalities. Yet they provide myriad benefits as well: Volcanic soils are very fertile for agriculture, for example, and support habitats for wildlife. Also, many ore deposits, from gold to diamonds, are closely associated with volcanoes.

Scientists use a wide variety of techniques to monitor volcanoes, including seismology (detection of the earthquakes and tremors that almost always precede eruptions), precise measurements of ground deformation (such as bulges) that often accompanies the rise of magma, changes in volcanic gas emissions, and changes in gravity and magnetic fields. These techniques, when used in combination at well-monitored volcanoes, have resulted in successful predictions. At Pinatubo volcano (Philippines) in 1991, a successful forecast saved thousands of lives.

Monitoring-based forecasts are becoming much more reliable, but they remain imperfect. If scientists are fortunate, precursors to an eruption follow the same course as seen and recognized before previous eruptions. Patterns often change, however, and wholly new behavior is observed. The best forecasts will be based on an integration of geologic history, real-time monitoring, and a deep understanding of the internal plumbing processes of the specific volcano. Even with the best of monitoring and interpretations, reliable forecasts are rarely possible more than a few days in advance of an eruption. 

The Smithsonian Institution’s Global Volcanism Program is devoted to a better understanding of the Earth’s 1,600 known active volcanoes and their eruptions during the last 10,000 years. The program documents both current and past volcanic activity; its website contains more than 7,000 activity reports.

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Plate tectonics, volcanoes and earthquakes.

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The Earth rumbles and a hiss of steam issues from the top of Mt Ruapehu. Are these two events related? Is the earthquake caused by the volcano? Or is the steam caused by the earthquake?

Tectonic plates

When Alfred Wegener first proposed the idea of continental drift (the precursor idea to plate tectonic theory), it didn’t quite explain the full story. While he correctly showed that Africa and South America fitted together, his model wasn’t able to explain the violent forces that occur around the Earth’s crust.

It wasn’t until the 1960s that a full explanation began to develop – the theory of plate tectonics. This theory explained many pieces of the puzzle that scientists had observed, for example, continental fit, matching geology, past glaciation, movements of the ocean floor and the location of fossils of ancient animals and plants.

Scientists now believe that the crust of the Earth consists of rigid interconnecting plates (6 major plates and a few smaller ones). Plates are thought to float on the partially molten mantle, moving away from oceanic ridges where new plate material is produced and moving past each other or colliding along plate boundaries. Earthquakes and volcanoes are related to this movement.

Explore plate tectonics further.

Colliding plates

Where plates come into contact, energy is released. Plates sliding past each other cause friction and heat. Subducting plates melt into the mantle, and diverging plates create new crust material.

Subducting plates, where one tectonic plate is being driven under another, are associated with volcanoes and earthquakes. This activity is focused along the edge of the plate boundary where two plates come into contact, forming regions such as the Pacific Ring of Fire – a chain of earthquake and volcanic activity around the edge of the Pacific Ocean – which generates 75% of the world’s volcanoes and 80% of the world’s earthquakes.

Diverging plates

When plates move away from each other, the space between them gets filled with material, which rises to the surface, cools and forms mid-oceanic ridges. The Pacific Ocean is growing wider by about 18 cm per year as the plates diverge and the mid-oceanic ridge is built up.

Subducting plates and volcanoes

Plate material that is produced along the ocean floor is generally quite dense and relatively heavy. Continental plates don’t tend to get subducted. When oceanic plate is pushed from the mid-ocean ridge towards a plate boundary with a continental plate, it tends to subduct or dive below the continental crust. In this process, water is also being subducted with the oceanic plate. Friction increases the heat along such boundaries, which causes this material to melt and mix the oceanic plate material, the continental plate material and the water.

Andesite volcanoes tend to form at these subduction boundaries. This may have something to do with differences in plate densities and the release of gases, such as water vapour. As more heat is being produced through the subduction process, the mix of more and less volatile ingredients causes changes in density and pressure, which are linked to volcanic activity.

Volcanoes and earthquakes

Volcanoes and earthquakes are often found in the same place, but are they related? Does one trigger the other? The answer seems to be yes – but not always. They are sometimes linked but are often independent events.

When a volcano erupts, the pressure of the rising magma forcing its way through the crust to the surface will often trigger earthquake activity. Scientists have been able to demonstrate this link and also know what type of earthquake to look for.

Conversely, an earthquake may trigger subsequent eruptions. As the crust changes and moves in a major earthquake, fissures or cracks can form that may act as pipelines for magma and future volcanoes. This is harder to monitor and test and is an area of active research.

Related content

Use the teaching resource Earthquakes New Zealand to learn about seven activities designed to help students develop an understanding about earthquakes in New Zealand, including why we get them and how we measure them.

There are many volcanoes in the Pacific, including the very large Hunga Tonga–Hunga Haʻapa underwater one. Read about the devastating Hunga Tonga–Hunga Haʻapa volcanic eruption in January 2022, the tsunami that followed, and what we might expect next? This article looks at what we’ve learnt a year later about this violent eruption and predicting future submarine volcanic eruptions.

Realistic contexts connect students to authentic scientific processes and purposes, it's all explained in:

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(NAS Colloquium) Earthquake Prediction: The Scientific Challenge (1996)

Chapter: hypothesis testing and earthquake prediction.

This paper was presented at a colloquium entitled “Earthquake Prediction: The Scientific Challenge,” organized by Leon Knopoff (Chair), Keiiti Aki, Clarence R.Allen, James R.Rice, and Lynn R.Sykes, held February 10 and 11, 1995, at the National Academy of Sciences in Irvine, CA.

Hypothesis testing and earthquake prediction

(probability/significance/likelihood/simulation/Poisson)

D AVID D.J ACKSON

Southern California Earthquake Center, University of California, Los Angeles, CA 90095–1567

ABSTRACT Requirements for testing include advance specification of the conditional rate density (probability per unit time, area, and magnitude) or, alternatively, probabilities for specified intervals of time, space, and magnitude. Here I consider testing fully specified hypotheses, with no parameter adjustments or arbitrary decisions allowed during the test period. Because it may take decades to validate prediction methods, it is worthwhile to formulate testable hypotheses carefully in advance. Earthquake prediction generally implies that the probability will be temporarily higher than normal. Such a statement requires knowledge of “normal behavior”— that is, it requires a null hypothesis. Hypotheses can be tested in three ways: (i) by comparing the number of actual earthquakes to the number predicted, (ii) by comparing the likelihood score of actual earthquakes to the predicted distribution, and (iii) by comparing the likelihood ratio to that of a null hypothesis. The first two tests are purely self-consistency tests, while the third is a direct comparison of two hypotheses. Predictions made without a statement of probability are very difficult to test, and any test must be based on the ratio of earthquakes in and out of the forecast regions.

Hypothesis testing is an essential part of the scientific method, and it is especially important in earthquake prediction because public safely, public funds, and public trust are involved. However, earthquakes occur apparently at random, and the larger, more interesting earthquakes are infrequent enough that a long time may be required to test a hypothesis. For this reason, it is important to formulate hypotheses carefully so that they may be reasonably evaluated at some future time.

Single Prediction

The simplest definition of earthquake prediction involves specification in advance of the time interval, region, and magnitude range in which a future earthquake is predicted to occur. To be meaningful, all of these ranges should be defined in such a way that any future earthquake could be objectively judged to be either inside or outside the range. In addition, some definition should be given for the “location” of an earthquake, since an earthquake does not occur at a point, and the region should be specified in three dimensions, because deep earthquakes may be different in character from shallow earthquakes. An example of a testable earthquake prediction is as follows:

“An earthquake with moment magnitude equal to or greater than 6.0 will occur between 00:00 January 1, 1996, and 00:00 January 1, 1997, with hypocenter shallower than 20 km, within the latitude range 32.5 degrees N and 40.0 degrees north, and within the longitude range 114 W to 125 W. The moment magnitude shall be determined from the most recent version of the Harvard Central Moment tensor catalog as of July 1, 1997, and the hypocenter shall be determined by the most recent version of the Preliminary Determination of Epicenters (PDE) catalog as of July 1, 1997. All times are Greenwich Mean Times.”

This definition illustrates the difficulty of giving even a simple definition of a predicted event: there are different magnitude scales, different listings of hypocenters, and different time zones. If these are not specified in advance, one cannot objectively state that some future earthquake does or does not satisfy the prediction. An earthquake that meets the definition of a predicted event may be called a qualifying earthquake. In the discussion to follow, I will usually drop the adjective; the term earthquake should be interpreted as a qualifying earthquake. The example illustrates another problem: the prediction may not be very meaningful, because the area is fairly large (it includes all of California) and fairly active. The occurrence of an earthquake matching the prediction would not be very conclusive, because earthquakes satisfying the size and location conditions occur at the rate of about 1.5 per year. Thus, a single success of this type would not convincingly validate the theory used to make the prediction, and knowing the background rate is important in evaluating the prediction. One can then compare the observed earthquake record (in this case, the occurrence or not of a qualifying earthquake) with the probabilities for either case according to a “null hypothesis,” that earthquakes occur at random, at a rate determined by past behavior. In this example, we could consider the null hypothesis to be that earthquakes result from a Poisson process with a rate of r= 1.5/yr; the probability that at least one qualifying earthquake would occur at random is

p 0 = 1 − exp (−r*t) .

For r =1.5/yr and t =1 yr, p 0 = 0.78. [1]

What can be said if a prediction is not satisfied? In principle, one could reject the prediction and the theory behind it. In practice, few scientists would completely reject a theory for one failure, no matter how embarrassing. In some cases, a probability is attached to a simple prediction; for the Parkfield, California, long-term prediction ( 1 ), this probability was taken to be 0.95. In such a case the conclusions that can be drawn from success depend very much on the background probability, and only weak conclusions can be drawn from failure. In the Parkfield case, the predicted event was never rigorously defined, but clearly no qualifying earthquake occurred during the predicted time interval (1983–1993). The background rate of Parkfield earthquakes is usually taken to be 1/22 yr; for t = 10 yr, p 0 =0.37. Thus, a qualifying earthquake, had it occurred, would not have been sufficient evidence to reject the Poissonian null hypothesis. Most scientists involved in the

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Parkfield prediction have responded to the failed prediction by modifying the parameters, rather than by abandoning the entire theory on which it was founded.

Some predictions (like Parkfield) are intended to be terminated as soon as they are satisfied by a qualifying earthquake, while others, such as those based on earthquake clustering, might be “renewed” to predict another earthquake if a qualifying earthquake occurs. Thus, when beginning an earthquake prediction test, it is helpful to describe in advance any conditions that would lead to a termination of the test.

Multiple Predictions

Suppose there are P predictions, either for separate regions, separate times, separate magnitude ranges, or some combination thereof. To simplify the following discussion, we refer to the magnitude-space-time interval for each prediction as a “region.” Let p 0 j , for ( i =1,…, P ), be the random probabilities of satisfying the predictions in each region, according to the null hypothesis, and let c i for ( i =1,…, P ), be 1 for each region that is “filled” by a qualifying earthquake, and 0 for those not filled. Thus, c i is 1 for each successful prediction and zero for each failure. According to this scheme only the first qualifying earthquake counts in each region, so that implicitly the prediction for each region is terminated as soon as it succeeds. A reasonable measure of the success of the predictions is the total number of regions filled by qualifying earthquakes. The probability of having as many or more successes at random is approximately that given by the Poisson distribution

where λ is the expected number of successes according to the null hypothesis. The choice of the rate parameter λ requires some care. If multiple events in each region are to be counted separately, then λ is simply the sum of the rates in the individual regions, multiplied by the time interval. If, instead, only the first earthquake within each region counts, then λ is the sum of the probabilities, over all regions, of success during the time interval t . The difference between the two approaches is small when all rates are small, so that there is very little chance of having more than one event in a region. The difference becomes important when some of the rates are high; in the first approach, the sum of the rates may exceed P/t, whereas this is prohibited in the second approach because each region may have only one success. The first approach is appropriate if the physical hypothesis predicts an enhanced rate of activity that is expected to continue after the first qualifying event in each region. The second approach is more appropriate when the hypothesis deals only with the first event, which changes the physical conditions and the earthquake rates. An advantage of the second approach is that it is less sensitive to treatment of aftershocks. Under the first approach, aftershocks must be specifically included in the prediction model or else excluded from the catalog used to make the test. Whether aftershocks are explicitly predicted or excluded from the catalog, the results of the test may be very sensitive to the specific algorithm used to predict or recognize aftershocks.

Eq. 2 is approximate, depending on λ being large compared to one. There are also a few other, more subtle, assumptions. A more robust, but also approximate, estimate of the probabilities may be obtained by simulation. Assume the second approach above, that the prediction for each region is either no earthquake, or at least one. Draw at random a large number of simulated catalogs, also represented by c i for ( i =1,…, P ). For each catalog, for each region, draw a random number from a uniform distribution between 0 and 1; if that random number is less than p 0 j , then c i =1; otherwise, c i =0. For each synthetic catalog, we count the number of successes and compile a cumulative distribution of that number for all synthetic catalogs. Then the proportion of simulated catalogs having N or more events is a good estimate of the corresponding probability. Simulation has several advantages: it can be tailored to specific probability models for each zone, it can be used to estimate other statistics as discussed below, and its accuracy depends on the number of simulations rather than the number and type of regions. Disadvantages are that it requires more computation, and it is harder to document and verify than an analytic formula like Eq. 2.

The “M8” prediction algorithm of Keilis-Borok and Kossobokov ( 2 ) illustrates some of the problems of testing prediction hypotheses. The method identifies five-year “times of increased probabilities,” or TIPs, for regions based largely on the past seismic record. Regions are spatially defined as the areas within circles about given sites, and a lower magnitude threshold is specified. TIPs occur at any time in response to earthquake occurrence; thus, the probabilities are strongly time dependent. The method apparently predicted 39 of 44 strong earthquakes over several regions of the world, while the declared TIPs occupied only 20% of the available space-time. However, this apparently high success rate must be viewed in the context of the normal seismicity patterns. Most strong earthquakes occur within a fairly small fraction of the map, so that some success could be achieved simply by declaring TIPs at random times in the more active parts of the earth. A true test of the M8 algorithm requires a good null hypothesis that accounts for the spatial variability of earthquake occurrence. Constructing a reasonable null hypothesis is difficult because it requires the background or unconditional rate of large earthquakes within the TIP regions. However, this rate is low, and the catalog available for determining the rate is short. Furthermore, the meaning of a TIP is not explicit: is it a region with higher rate than other regions, or higher than for other times within that region? How much higher than normal is the rate supposed to be?

Probabilistic Prediction

An earthquake prediction hypothesis is much more useful, and much more testable, if probabilities are attached to each region. Let the probabilities for each region be labeled p j , for j =1 through P. For simplicity, I will henceforth consider the case in which a prediction for any region is terminated if it succeeds, so that the only possibility for each region is a failure (no qualifying earthquake) or a success (one or more qualifying earthquakes). In this case, several different statistical tests are available. Kagan and Jackson ( 3 ) discuss three of them, applying them to the seismic gap theory of Nishenko ( 4 ). Papadimitriou and Papazachos ( 5 ) give another example of a long-term prediction with regional probabilities attached.

(i) The “ N test,” based on the total number of successes. This number is compared with the distributions predicted by the null hypothesis (just as described above) and by the experimental hypothesis to be tested. Usually, the null hypothesis is based on the assumption that earthquake occurrence is a Poisson process, with rates determined by past behavior, and the test hypothesis is that the rates are significantly higher in some places. Two critical values of N can be established. Let N 1 be the smallest value of N, such that the probability of N or more successes according to the null hypothesis is less than 0.05. Then the null hypothesis can be rejected if the number of successes in the experiment exceeds N 1 . Let N 2 be the largest value of N, such that the probability of N or fewer successes according to the test hypothesis is less than 0.05. Then the test hypothesis can be rejected if N is less than or equal to N 2 . If N 1 is less than N 2 , then there is a range of possible success counts for which neither hypothesis can be rejected. According to classical hypothesis testing methodology, one does not

accept the test hypothesis unless the null hypothesis is rejected. This practice is based on the notion that the null hypothesis is inherently more believable because of its simplicity. However, there is not always uniform agreement on which hypothesis is simpler or inherently more believable. The method presented here gives no special preference to the null hypothesis, although such preference can always be applied at the end to break ties. If N 1 exceeds N 2 , there will be a range of possible outcomes for which both hypotheses may be rejected.

Under a few simple assumptions, L will be normally distributed with a mean and variance readily calculable from Eq. 3. Alternatively, simulated catalogs c j may be constructed as described above, and the distribution of L may be estimated by the simulated sample distribution. The hypothesis test is made by comparing the value of L, using the actual earthquake record, with the distribution of simulated catalogs. If L for the actual catalog is less than 95% of the simulated values, then the hypothesis should be rejected. The L test may be applied to both the test hypothesis and the null hypothesis separately. Either, neither, or both might be rejected.

(iii) The “ R test,” based on the ratio of the likelihood value of the test hypothesis to that of the null hypothesis. The log of this ratio is

R is the difference between two log-likelihood functions, with the test hypothesis having the positive sign and the null hypothesis the negative sign. Thus, positive values favor the test hypothesis, and negative values favor the null hypothesis. The hypothesis test involves calculating the distributions of R for the test hypothesis (that is, assuming that c j is a sample of the process with probabilities p j ), and for the null hypothesis (assuming the c j correspond to p j ). The log-likelihood ratio will be normally distributed if the log-likelihood functions for both the test and null hypotheses, calculated using Eq. 3, are normally distributed. Alternatively, the distributions may be calculated as follows: First, generate simulated catalogs using the probabilities p j . Then compute the log-likelihood ratio for each catalog using Eq. 4 and compute the sample distribution of log-likelihood values. Now generate a suite of simulated catalogs using p 0 j , the probabilities for the null hypothesis. For each of these, calculate R from Eq. 4 and compute their distribution. Again, two critical values may be calculated. Let R 1 be the least value of R, such that less than 5% of the catalogs simulated using the null hypothesis have a larger value of R . Then the null hypothesis can be rejected with 95% confidence if the actual value of R exceeds R 1 . Let R 2 be the largest value of R, such that 5% or less of the catalogs simulated using the test hypothesis have a smaller value of R . Then the test hypothesis can be rejected with 95% confidence if the actual value of R is less than R 2 . As in the other tests, either, neither, or both of the two hypotheses may fail the test.

Let us now revisit the topic of predictions in which no probability is given for the test hypothesis. These might be interpreted as identifying regions for which the probability of an earthquake is larger than that for other regions or in which the ratio of probability according to the test hypothesis to that of the null hypothesis is especially high. These predictions are often discussed in terms of a trade-off curve, in which the fraction of earthquakes predicted is compared to the fraction of space-time for which “alarms” are active. As more of time-space is covered by predictions, more earthquakes will be successfully predicted. Success of a prediction scheme is measured by comparing it with a hypothetical scheme which occupies the same proportion of space-time. An optimum threshold can be calculated if costs can be assigned to maintaining a state of alert and to unpredicted earthquakes. However, if probabilities are given for each region, then a prediction scheme can be tested using all of the probabilities, and there is no need to establish a threshold for declaring alerts. This separates the problem of testing scientific hypotheses from the policy problem of how to respond to predictions.

Predictions Based on Rate-Density Maps

Predictions based on subdividing magnitude-time-space into regions have the disadvantage that probabilities may differ strongly from one region to another, so the success or failure of a hypothesis may depend strongly on small errors in location or magnitude estimates. Furthermore, earthquakes that occur just outside the boundaries of a high probability region pose a strong temptation to bend the boundaries or adjust the earthquake data. Statistical procedures should account for uncertainty in measurement and for imperfect specificity in stating hypotheses. One way to achieve these goals is to formulate hypotheses in terms of smaller regions, allowing for some smoothing of probability from one region to another. In fact, many prediction hypotheses lend themselves to description in terms of continuous variables, such as functions of distance from previous earthquakes or locations of geophysical anomalies. Let us consider a refinement of the “region” concept to include infinitesimal regions of time-space, in which p j =∧ (x j , y j , t j , m j ) dx dy dt dm. Here dx, dy, dt, and dm are small increments of longitude, latitude, time, and magnitude, respectively. The function ∧ is often referred to in the statistical literature as the “conditional intensity,” but I will use the notation “conditional rate density” to avoid confusion with the seismic intensity. The term “conditional” is used because earthquake prediction usually refers to a temporal increase in earthquake likelihood inferred from the existence of some special geophysical circumstance. If dx dy dt dm is made arbitrarily small, then 1− p j approaches 1, and log(1− p j ) approaches −pj . After some algebra, we then obtain

where N is the number of earthquakes that actually occurred, N' is the total number of earthquakes predicted by the test hypothesis, and N′ 0 is the total number of earthquakes predicted by the null hypothesis. The sum is over those earthquakes that actually occurred.

A consequence of shrinking the regions to an infinitesimal size is that there is no longer any reason to distinguish between the first and later earthquakes in a region; all of the regions are so small that the probability of a second event in a given box is also infinitesimal. Another consequence is that aftershocks must be dealt with carefully. No longer is it possible to assume that they will be unimportant if we consider only the first

qualifying earthquake in a region. Now it is virtually certain that the aftershocks from an earthquake in one region will occur in another. One way to deal with aftershocks is to use a declustered catalog in making the test. Another is to build aftershock prediction into both the test and null hypotheses. Kagan and Knopoff ( 6 ) offer an algorithm for modeling the probability of earthquakes following an earlier quake. Testing a hypothesis on “new data”—that is, using a hypothesis formulated before the occurrence of the earthquakes on which it is tested—now requires that the hypothesis be updated very quickly following a significant earthquake. Rapid updating presents a practical problem, because accurate data on the occurrence of important earthquakes may not be available before significant aftershocks occur. One solution is to specify in advance the rules by which the hypothesis will be updated and let the updating be done automatically on the basis of preliminary information. A more careful evaluation of the hypothesis may be carried out later with revised data, as long as no adjustments are made except as specified by rules established in advance.

Introducing aftershocks into the model makes it more difficult to compute confidence limits for the log-likelihood ratio than would otherwise be the case. Because the rate density may change dramatically at some time unknown at the beginning of a test period, it is very difficult to compute even the expected numbers of events analytically unless the aftershock models are very simple.

Rhoades and Evison ( 7 ) give an example of a method, based on the occurrence of earthquake swarms, in which the prediction is formulated in terms of a conditional rate density. They are currently testing the method against a Poissonian null hypothesis in New Zealand and Japan. They update the conditional rate calculations to account for earthquakes as they happen. As discussed above, it is particularly difficult to establish confidence limits for this type of prediction experiment.

A fair test of an earthquake prediction hypothesis must involve an adequate null hypothesis that incorporates well-known features of earthquake occurrence. Most seismologists agree that earthquakes are clustered both in space and in time. Even along a major plate boundary, some regions are considerably more active than others. Foreshocks and aftershocks are manifestations of temporal clustering. Accounting for these phenomena quantitatively is easier said than done. Even a Poissonian null hypothesis requires that the-rate density be specified as a function of spatial variables, generally by smoothing past seismicity. Choices for the smoothing kernel, the time interval, and the magnitude distribution may determine how well the null hypothesis represents future seismicity, just as similar decisions will affect the performance of the test hypothesis. In many areas of the world, available earthquake catalogs are insufficiently complete to allow an accurate estimate of the background rate. Kagan and Jackson ( 8 ) constricted a global average seismicity model based on earthquakes since 1977 reported in the Harvard catalog of central moment tensors. They determined the optimum smoothing for each of several geographic regions and incorporated anisotropic smoothing to account for the tendency of earthquakes to occur along faults and plate boundaries. They did not incorporate aftershock occurrence into their model, and the available catalog covers a relatively short time span. In many areas, it may be advantageous to use older catalogs that include important large earthquakes, even though the data may be less accurate than that in more recent catalogs. To date, there is no comprehensive treatment of spatially and temporally varying seismicity that can be readily adapted as a null hypothesis.

Binary (on/off) predictions can be derived from statements of conditional probability within regions of magnitude-time-space, which can in turn be derived from a specification of the conditional rate density. Thus, the conditional rate density contains the most information. Predictions specified in this form are no more difficult to test than other predictions, so earthquake predictions should be expressed as conditional rate densities whenever possible.

I thank Yan Kagan, David Vere-Jones, Frank Evison, and David Rhoades for useful discussions on these ideas. This work was supported by U.S. Geological Survey Grant 1434–94-G-2425 and by the Southern California Earthquake Center through P.O. 566259 from the University of Southern California. This is Southern California Earthquake Center contribution no. 321.

1. Bakun, W.H. & Lindh, A.G. (1985) Science 229 , 619–624.

2. Keilis-borok, V.I. & Kossobokov, V.G. (1990) Phys. Earth Planet. Inter. 61 , 73–83.

3. Kagan, Y.Y. & Jackson, D.D. (1995) J. Geophys. Res. 100 , 3943–3959.

4. Nishenko, S.P. (1991) Pure Applied Geophys. 135 , 169–259.

5. Papadimitriou, E.E. & Papazaehos, B.C. (1994) J. Geophys. Res. 99 , 15387–15398.

6. Kagan, Y.Y. & Knopoff, L. (1987) Science 263 , 1563–1567.

7. Rhoades, D.A. & Evison, F.F. (1993) Geophys. J. Int. 113 , 371–381.

8. Kagan, Y.Y. & Jackson, D.D. (1994) J. Geophys. Res. 99 , 13685–13700.

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Reservoir induction

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A separate type of earthquake is associated with volcanic activity and is called a volcanic earthquake. Yet it is likely that even in such cases the disturbance is the result of a sudden slip of rock masses adjacent to the volcano and the consequent release of elastic strain energy. The stored energy , however, may in part be of hydrodynamic origin due to heat provided by magma moving in reservoirs beneath the volcano or to the release of gas under pressure.

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There is a clear correspondence between the geographic distribution of volcanoes and major earthquakes, particularly in the Circum-Pacific Belt and along oceanic ridges. Volcanic vents, however, are generally several hundred kilometres from the epicentres of most major shallow earthquakes, and many earthquake sources occur nowhere near active volcanoes. Even in cases where an earthquake’s focus occurs directly below structures marked by volcanic vents, there is probably no immediate causal connection between the two activities; most likely both are the result of the same tectonic processes.

Artificial induction

Earthquakes are sometimes caused by human activities, including the injection of fluids into deep wells, the detonation of large underground nuclear explosions, the excavation of mines, and the filling of large reservoirs . In the case of deep mining , the removal of rock produces changes in the strain around the tunnels. Slip on adjacent, preexisting faults or outward shattering of rock into the new cavities may occur. In fluid injection, the slip is thought to be induced by premature release of elastic strain, as in the case of tectonic earthquakes, after fault surfaces are lubricated by the liquid . Large underground nuclear explosions have been known to produce slip on already strained faults in the vicinity of the test devices.

Of the various earthquake-causing activities cited above, the filling of large reservoirs is among the most important. More than 20 significant cases have been documented in which local seismicity has increased following the impounding of water behind high dams. Often, causality cannot be substantiated , because no data exists to allow comparison of earthquake occurrence before and after the reservoir was filled. Reservoir-induction effects are most marked for reservoirs exceeding 100 metres (330 feet) in depth and 1 cubic km (0.24 cubic mile) in volume. Three sites where such connections have very probably occurred are the Hoover Dam in the United States , the Aswan High Dam in Egypt, and the Kariba Dam on the border between Zimbabwe and Zambia . The most generally accepted explanation for earthquake occurrence in such cases assumes that rocks near the reservoir are already strained from regional tectonic forces to a point where nearby faults are almost ready to slip. Water in the reservoir adds a pressure perturbation that triggers the fault rupture. The pressure effect is perhaps enhanced by the fact that the rocks along the fault have lower strength because of increased water-pore pressure. These factors notwithstanding, the filling of most large reservoirs has not produced earthquakes large enough to be a hazard.

The specific seismic source mechanisms associated with reservoir induction have been established in a few cases. For the main shock at the Koyna Dam and Reservoir in India (1967), the evidence favours strike-slip faulting motion. At both the Kremasta Dam in Greece (1965) and the Kariba Dam in Zimbabwe-Zambia (1961), the generating mechanism was dip-slip on normal faults. By contrast, thrust mechanisms have been determined for sources of earthquakes at the lake behind Nurek Dam in Tajikistan . More than 1,800 earthquakes occurred during the first nine years after water was impounded in this 317-metre-deep reservoir in 1972, a rate amounting to four times the average number of shocks in the region prior to filling.

In 1958 representatives from several countries, including the United States and the Soviet Union , met to discuss the technical basis for a nuclear test-ban treaty . Among the matters considered was the feasibility of developing effective means with which to detect underground nuclear explosions and to distinguish them seismically from earthquakes. After that conference , much special research was directed to seismology , leading to major advances in seismic signal detection and analysis.

Recent seismological work on treaty verification has involved using high-resolution seismographs in a worldwide network, estimating the yield of explosions, studying wave attenuation in the Earth , determining wave amplitude and frequency spectra discriminants, and applying seismic arrays. The findings of such research have shown that underground nuclear explosions, compared with natural earthquakes, usually generate seismic waves through the body of the Earth that are of much larger amplitude than the surface waves. This telltale difference along with other types of seismic evidence suggest that an international monitoring network of 270 seismographic stations could detect and locate all seismic events over the globe of magnitude 4 and above (corresponding to an explosive yield of about 100 tons of TNT).

Effects of earthquakes

Earthquakes have varied effects, including changes in geologic features, damage to man-made structures, and impact on human and animal life. Most of these effects occur on solid ground, but, since most earthquake foci are actually located under the ocean bottom, severe effects are often observed along the margins of oceans.

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How Scientists Forecast Volcanic Eruptions

Volcanic eruptions are impressive demonstrations of the activity of our planet. While some eruptions may be safely observed from distance, many eruptions, especially if explosive, may be hazardous to the populations and the environment around the volcano, including the animals, plants, and manmade structures. To reduce harm caused by eruptions, scientists called volcanologists attempt to forecast eruptions. Although volcanoes commonly provide several kinds of warnings before erupting, there is no single warning signal that allows volcanologists to accurately predict every eruption. Instead, data from various types of monitoring instruments are combined to help scientists forecast eruptions at least a few days in advance. In the next decades, as volcanologists improve monitoring systems and better understand the processes happening inside volcanoes, more precise eruption forecasts will be possible.

Volcanoes: A Natural Hazard

Our planet experiences several types of natural hazards, including earthquakes, volcanic eruptions, landslides, tsunamis, hurricanes, and tornadoes. Volcanic eruptions can vary in size, with the largest being the most devastating of natural hazards, capable of impacting the entire planet ( Figure 1 ). Luckily, these destructive events are rare—usually occurring approximately once every 100,000 years—whereas the most frequent eruptions, occurring approximately every week, are mild and impact only small areas.

• Figure 1 - (A) The Mount St. Helens volcano (USA) before (left) and after (right) the 1980 eruption (Image credit: USGS).
• The explosive eruption destroyed the top and a side of the volcano; it also destroyed the surrounding forest, including the trees in the foreground, leaving a blanket of ash formed by the exploded magma 1 . (B) The eruption of the Usu volcano (Japan) in 2000 changed the ground below the house, covered the roof with volcanic ash, and pierced the roof with falling bombs of magma.

There are ~600 active volcanoes on Earth, mainly along the boundaries of the mobile tectonic plates that make up the outer shell of our planet. It is estimated that about 800 million people—one-tenth of the world’s population—live near active volcanoes. Volcanic activity has claimed the lives of nearly 300,000 victims in the last four centuries [ 1 ]. The last major destructive event was the Nevado del Ruiz eruption in Colombia, in 1985. This eruption was only of moderate size, but it caused more than 23,000 casualties in a matter of minutes. Even if they do not cause human deaths, eruptions can impact the environment, including animals, plants, and man-made structures like buildings, roads, railways, airports, factories, and power plants. During the Eyjafjallajokull eruption in Iceland in 2010, for example, the ash cloud from the eruption spread through the atmosphere and halted the air traffic over Europe for several days, stranding 10 million passengers and resulting in the loss of $5 billion (US).

To reduce the impact of volcanic eruptions on humans and the environment, scientists called volcanologists must be able to forecast when and where volcanoes are going to erupt. Forecasting volcanic eruptions allows people to be alerted so they can evacuate, reducing the negative impact of eruptions on human populations.

How Volcanoes Work

To forecast eruptions, volcanologists must first understand how volcanoes work.

Volcanoes are usually in a silent, “resting” state, when the magma below them does not move or accumulate. Sometimes the magma rises toward the surface and, when it stops rising, it accumulates within the rock that makes up the Earth’s crust. This accumulation of magma eventually forms a magma chamber. The magma chamber can change the shape of the surrounding rock and create fractures in the Earth’s crust that can cause earthquakes. Earthquake activity is called seismicity . The fractures also serve as pathways that allow gases to escape from the magma into the air. This is called degassing . The accumulating magma slowly enlarges the volcano through deformation .

When the volcano passes from a silent phase to an “excited” phase when seismicity, degassing and deformation occur, this is called unrest . The unrest phase can last from days to months, and it is considered a warning from the volcano it is unstable and that there may be an eruption. Most eruptions are preceded by unrest, but not every unrest episode ends in an eruption—sometimes after unrest a volcano may become silent again. So, although unrest does not always precede eruptions, its appearance is the main clue for volcanologists to forecast eruptions.

To make a reliable eruption forecast, volcanologists must understand what exactly happens during unrest, by analyzing the signals sent out by the volcano. Unrest is usually detected and studied using a precise monitoring system, consisting of a group of sensitive instruments that record the real-time activity inside a volcano, particularly the movement of magma. Therefore, monitoring the seismicity, degassing, and deformation produced by the moving magma allows volcanologists to understand what is happening in a volcano during unrest ( Figure 2 ). Mathematical models use this monitoring information to define the size, shape, and location of magma producing the unrest [ 1 ].

• Figure 2 - Frequently used volcano monitoring techniques include GPS, InSAR, and tiltmeter, which are techniques to measure deformation; surveying, in which volcanologists directly examine the volcano; thermal imaging, which detects temperature variations on the volcano (Image credit: US Geological Survey, USGS; https://volcanoes.usgs.gov/vhp/monitoring.html ).

While many volcanoes are monitored, several volcanoes, especially in remote areas, are monitored poorly or not at all. Forecasting eruptions obviously depends on the availability of a monitoring system that can detect unrest.

Current Forecasting Approaches

Volcanologists have used two kinds of approaches to forecast eruptions. First, they have tried to predict for sure (yes or no) whether an eruption is coming. This is called a deterministic approach. More recently, they have been trying to forecast whether an eruption is likely or not, using a percentage of likelihood. This is called a probabilistic approach.

Only when monitoring data collected during unrest show linear behavior eruptions can be predicted by a deterministic approach. The large eruptions of Mount St. Helens (USA) in 1980 and Pinatubo (Philippines) in 1991 were predicted days in advance. Linear behavior means an increase in the volcano’s signals, and both the Mount St. Helens and Pinatubo unrest episodes showed this linear behavior.

Unfortunately, the unrest that precedes many eruptions shows non-linear behavior : an increase in the intensity of the signals is followed by one or more decreases and finally by eruption. Under these erratic conditions, predicting an eruption in a deterministic way is impossible. Non-linear behavior shows us the complexity of the volcanic system, in which many processes, only some of which are detectable by monitoring, happen at the same time. Because of this complexity, forecasting eruptions is usually made using a probabilistic approach, in which the possibility for eruption is expressed as a percentage [ 2 , 3 ]. This approach, which is also used in weather forecasting, more accurately accounts for the erratic behavior of volcanoes. So, to avoid errors, a wise volcanologist should forecast (probabilistic approach) rather than predict (deterministic approach) eruptions.

In recent decades, some eruptions have been successfully forecasted, while others have not been. Successful forecasting has led to successful evacuations, while inaccurate forecasting has led to evacuations followed by no eruption or to missed evacuations, when eruptions occur before people are evacuated. As a result, volcanology has experienced both successes and confidence in forecasting eruptions, as well as disasters and frustrations. Our capability to forecast eruptions is still limited, with ~20% of eruptions accurately forecasted. Only moderate improvements have been made in the last few decades, despite the wide use and continual improvement of monitoring instruments [ 4 ].

Volcano Type Affects Forecasting

There are two types of volcanoes that affect the way eruptions are forecasted: closed-conduit volcanoes and open-conduit volcanoes ( Figure 3 ). Closed-conduit volcanoes have solidified magma in the path through which the magma travels to the surface, which separates the molten magma from the Earth’s surface. This causes magma to accumulate inside the volcano, which increases the pressure and breaks the surrounding rocks, generating fractures and earthquakes, and deforms the surface of the volcano. In closed-conduit volcanoes, unrest consists of seismicity, and surface deformation. Conversely, open-conduit volcanoes, which are less common, have molten magma filling the volcanic conduit, almost reaching the surface. The continuous supply of magma from inside the volcano prevents solidification of the conduit, causing frequent eruptions. In open-conduit volcanoes, magma does not accumulate inside the volcano, so pressure does not build up to fracture the surrounding rock or deform the volcano, although there is frequent degassing through the open conduit. This results in weaker unrest indicators. Therefore, given the stronger signals, forecasting eruptions is usually easier for closed-conduit volcanoes. Nevertheless, some well-monitored and frequently erupting open-conduit volcanoes may still provide enough data for a reliable forecast, such as Mt. Etna (Italy), whose eruptions are currently predicted with a 97% success rate. Since the global forecasting success rate for all volcanoes is ~20%, the forecasting of Mt. Etna is extremely successful.

• Figure 3 - (A) Closed-conduit and (B) open-conduit volcanoes show different unrest behaviors.
• A single volcano can switch from closed- to open-conduit during its eruptive history.

Volcanologists are constantly looking for new approaches to improve forecasting, by combining monitoring data with knowledge of volcanic processes. To identify the start of an eruption, recent studies focus on the appearance of specific monitoring signals that are directly related to the rise of magma, rather than its accumulation. This will help researchers to better forecast times when eruption is likely to happen soon. As some volcanoes have multiple eruptive craters scattered over wide areas, researchers also try to forecast the possible locations of future craters, to reduce the impact of eruptions in inhabited areas [ 1 ]. These efforts will certainly improve future eruption forecasting, providing more reliable probabilistic estimates and reducing the level of uncertainty or error. Nevertheless, we must remember that uncertainty is a part of any forecast, so future eruption forecasting will be similar to weather forecasting [ 5 ].

In summary, while forecasting eruptions is currently a difficult although not impossible task, future studies and research, as well as increased availability of monitoring data, will allow better understanding of how volcanoes work. This in turn will allow a more reliable eruption forecasting, reducing the adverse impact of volcanic activity on the population and environment.

Seismicity : ↑ Occurrence of earthquakes in an area.

Degassing : ↑ Release of gases, usually related to the magma below, from the crater or other portions of a volcano.

Deformation : ↑ Change of shape; the part of the volcano above the Earth’s surface or the rocks below it may deform.

Unrest : ↑ State of a volcano with seismicity, degassing and deformation that can precede eruption.

Deterministic : ↑ Exact prediction (yes or no) of whether an event (like an eruption) will occur.

Probabilistic : ↑ An uncertain forecast, defined as a percentage expressing how likely the event is to occur.

Linear Behavior : ↑ When a system (such as a volcano) behaves in an expected way.

Non-Linear Behavior : ↑ When a system (such as a volcano) behaves in an unexpected way.

Conflict of Interest

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

1. ↑ Visit https://pubs.usgs.gov/gip/msh/catastrophic.html to see what happened between the two images shown here.

[1] ↑ Acocella, V. 2021. Volcano-Tectonic Processes . Berlin: Springer.

[2] ↑ Sparks, R. S. J., and Aspinall, W. P. 2004. Volcanic activity: frontiers and challenges in forecasting, prediction and risk assessment. State Planet Front. Challenges Geophys. Geophys. Monogr . 19:359–73. doi: 10.1029/150GM28

[3] ↑ Marzocchi, W., and Bebbington, M. S. 2012. Probabilistic eruption forecasting at short and long time scales. Bull. Volcanol . 74:1777–805. doi: 10.1007/s00445-012-0633-x

[4] ↑ Winson, A. E. G., Costa, F., Newhall, C. G., and Woo, G. 2014. An analysis of the issuance of volcanic alert levels during volcanic crises. J. Appl. Volcanol . 3:14. doi: 10.1186/s13617-014-0014-6

[5] ↑ Poland, M. P., and Anderson, K. R. 2020. Partly cloudy with a chance of lava flows: forecasting volcanic eruptions in the twenty-first century. J. Geophys. Res . 125:e2018JB016974. doi: 10.1029/2018JB016974

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• Review Article
• Published: 22 June 2021

The build-up and triggers of volcanic eruptions

• Luca Caricchi   ORCID: orcid.org/0000-0001-9051-2621 1 ,
• Meredith Townsend   ORCID: orcid.org/0000-0001-8846-1466 2 ,
• Eleonora Rivalta   ORCID: orcid.org/0000-0001-8245-0504 3 , 4 &
• Atsuko Namiki   ORCID: orcid.org/0000-0002-1321-3780 5  

Nature Reviews Earth & Environment volume  2 ,  pages 458–476 ( 2021 ) Cite this article

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• Volcanology

More than 800 million people live in proximity to active volcanoes and could be directly impacted by potential eruptions. Mitigation of future volcanic hazards requires adequate warning of a pending eruption, which, in turn, requires detailed understanding of the fundamental processes driving volcanic activity. In this Review, we discuss the processes leading up to volcanic eruptions, by following the journey of magma from crustal storage zones to the surface. Magma reservoirs can feed volcanic eruptions if they contain sufficiently hot and mobile magma and are able to supply sufficient energy for the magma to reach the surface. Young volcanic plumbing systems favour volcanic activity, whereas storage becomes more likely in mature volcanic systems with large reservoirs (hundreds of cubic kilometres). Anticipating volcanic activity requires a multidisciplinary approach, as real-time monitoring and geophysical surveys must be combined with petrology and the eruptive history to understand the temporal evolution of volcanic systems over geological timescales. Numerical modelling serves to link different observational timescales, and the inversion of data sets with physics-based statistical approaches is a promising way forward to advance our understanding of the processes controlling recurrence rate and magnitude of volcanic eruptions.

The thermal evolution of magmatic systems influences the physical properties of magma and the rocks surrounding the volcanic plumbing system, which, over the long term, favours magma storage over eruption.

Magma recharge is the primary driver of magma reservoir pressurization and destabilization. Second boiling can trigger reservoir failure, although it is less likely to cause repeated eruptions.

Only when volcanoes are in a critical state (close to eruption), small variations of stress or rock strength caused by external phenomena can help to initiate a volcanic eruption.

Magma can become arrested on its way to the Earth’s surface because a lack of pressure or insufficient volume do not allow the magma to overcome stress barriers.

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Acknowledgements

L.C. received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant no. 677493 - FEVER) and additional support from the Swiss National Science Foundation (grant no. 200021_184632). E.R. received funding from the Deutsche Forschungsgemeinschaft (DFG – German Research Foundation; grant no. 634756). A.N. was supported by the Japan Society for the Promotion of Science (JSPS) grant KAKENHI 17KK0092. We are grateful to Andrew Harp for sharing his version of the Summer Coon dike map with us.

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• Luca Caricchi

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Meredith Townsend

GeoForschungsZentrum, Potsdam, Germany

Eleonora Rivalta

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L.C. focused on the thermal evolution of magmatic systems and interaction between magmatic fluids and magma; M.T. took the lead on the discussion of the processes of magma reservoir pressurization; A.N. led the sections on internal and external triggers; and E.R. led the sections on magma transfer through the crust. All authors contributed equally to the remaining sections of the manuscript and edited the final version.

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The explosive vaporization of rapidly heated fluids.

Pressure in excess of the lithostatic pressure.

The percolation and chemical interaction between externally sourced magmatic fluids and magma, sometimes also referred to as fluid fluxing.

Volatile phases such as H 2 O and CO 2 stored in bubbles suspended in the magma.

A measure of the relative decrease of magma volume in response to an increase of pressure.

Minimum temperature at which a melt phase can coexist with crystals in thermodynamic equilibrium.

Volatile exsolution that occurs as a result of the increased concentration of water in silicate melt during crystallization.

Steeply dipping tabular or gently curved intrusions.

Arcuate intrusions with a geometry like the segment of a downward-pointing cone.

Arcuate or circular intrusions associated with caldera ring faults.

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Caricchi, L., Townsend, M., Rivalta, E. et al. The build-up and triggers of volcanic eruptions. Nat Rev Earth Environ 2 , 458–476 (2021). https://doi.org/10.1038/s43017-021-00174-8

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How are volcanoes and earthquakes interrelated?

• Updated 17/11/22
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Both volcanoes and earthquakes occur due to movement of the Earth’s tectonic plates. They are both caused by the heat and energy releasing from the Earth’s core. Earthquakes can trigger volcanic eruptions through severe movement of tectonic plates. Similarly, volcanoes can trigger earthquakes through the movement of magma within a volcano. Therefore, one aspect of how are volcanoes and earthquakes interrelated is the cyclical relationship where earthquakes cause volcanic eruptions and magma movement causes earthquakes.

Earthquakes and volcanic eruptions in itself are dangerous natural phenomena which poses risk to humans. Furthermore, tsunamis are an equally deadly secondary effect caused by underwater disturbances such as earthquakes, volcanic activity, landslides, underwater explosions or meteorite impacts which pose significant danger to human lives.

What are tectonic plates and how do they explain volcanoes and earthquakes?

The outer layer of the Earth is made up of solid rock, called lithosphere. The lithosphere is broken up into 17 major separate pieces that fit together like a bad jigsaw puzzle. A piece of the puzzle is called a tectonic plate . The plates are horribly placed, with overlapping pieces, gaps, and are forced to fit with each other even when they don’t. Because the tectonic plates don’t go well together, it creates earthquakes and volcanic activity when two plates collide, diverge or slide past each other.

There are three types of boundaries caused by tectonic plates on Earth: first, transform boundaries when two plates slide or grind past each other. Transform boundaries are horizontal movements of plates and do not create or destroy plates. Second, divergent boundaries when two plates create a gap in between each other. Divergent boundaries create ocean basins when plates move apart from one another. Third, convergent boundaries when two plates crash towards each other and overlap to form a subduction zone.

Tectonic plates are extremely large and can encompass both land and ocean. These tectonic plates interact with one another because of the Earth’s internal heat. This heat causes movement of material beneath the Earth’s crust and releases energy in the form of earthquakes and volcanic eruptions. Interactions between the tectonic plates occurs in three main places: first, oceanic-continental convergence, where the continent meets the ocean. Second, continental-continental convergence, where two continents meet. Last, oceanic-oceanic convergence, where two oceans meet.

So, how are volcanoes and earthquakes interrelated? Both volcanoes and earthquakes are caused along the boundaries of tectonic plates due to their movements and interactions.

How dangerous are volcanoes and earthquakes to humans?

How many deaths there are and how severe a natural disaster is depends on the interactions we have as humans with our environment. A strong earthquake can be completely overlooked if it happens in the middle of land where hardly any people live in, for example in December 2003, when a 6.5 magnitude earthquake in Central California killed two people. Consequently, a similar earthquake in a densely populated metropolitan area can cause many deaths, injuries and destruction of property, for example, a 6.6 magnitude earthquake in Bam, Iran killing 30,000 people, injuring 30,000 more and destroying 85% of property.

The same goes for volcanic eruptions, if an underwater volcano erupted in the middle of the ocean, it would have little impact to humans living far inland. However, if the volcano had been dormant for a significant amount of time and humans started populating the land close to the base of a volcano it would be devastating should it ever erupt. Further, indirect consequences of a volcanic eruption can have a greater impact than the eruption itself. For example, volcanic ash can induce climate change that have serious agricultural, economic, and sociological impacts on people’s lives.

Read these articles to learn more about the structure of the volcano and the internal structure of the volcano .

To find out more about where the next volcano will erupt in Australia, read this article.

Tsunamis as a result of earthquakes or volcanic activity

Tsunamis are giant waves that occur when a large volume of water is displaced. The most common causes of underwater disturbances that lead to tsunamis are earthquakes and volcanic eruptions, especially because most volcanoes are underwater. Although tsunamis can also be caused by landslides, meteorite impacts and underwater explosions. Tsunami waves travel extremely fast, with wave speeds reaching up to 900 km/h in deep water. The waves get taller the closer they reach the shoreline because of rapidly decreasing depth of the sea floor, and slow down to 20 – 50 km/h.

We can deduce that volcanoes and earthquakes are caused by tectonic plate movements, they both pose a significant danger to humans, and result in deadly secondary effects like tsunamis.

Additional Reading

https://web.archive.org/web/20120913041924/http://www.enviroliteracy.org/nsfmod/NaturesFury.pdf

https://australian.museum/blog-archive/science/earthquakes-and-tsunamis/

https://australian.museum/learn/minerals/shaping-earth/plate-tectonic-processes/

https://media.australian.museum/media/dd/Uploads/Documents/4645/volcano_structure.134d97b.pdf

https://australian.museum/learn/minerals/shaping-earth/structure-of-volcanoes/

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Image credit: gadigal yilimung (shield) made by Uncle Charles  Chicka  Madden

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Latest Earthquakes |    Chat Share Social Media  

Can earthquakes trigger volcanic eruptions?

Sometimes, yes. A few large regional earthquakes (greater than magnitude 6) are considered to be related to a subsequent eruption or to some type of unrest at a nearby volcano. However, volcanoes can only be triggered into eruption by nearby tectonic earthquakes if they are already poised to erupt . This requires two conditions to be met:

• Enough "eruptible" magma within the volcanic system. 
• Significant pressure within the magma storage region.

If those conditions exist, it's possible that large tectonic earthquakes might cause dissolved gases to come out of the magma (like a shaken soda bottle), increasing the pressure and possibly leading to an eruption.

Learn more:

• What's with all these earthquakes? And will they affect Yellowstone?
• Can a nuclear blast trigger a Yellowstone eruption? No. But how about an earthquake? Also no.
• Monitoring Volcano Seismicity Provides Insight to Volcanic Structures

Related Content

• Publications

Can an eruption at one volcano trigger an eruption at another volcano?

There is no definitive evidence that an eruption at one volcano can trigger an eruption at a volcano that’s hundreds of kilometers/miles away or on a different continent. There are a few historic examples of simultaneous eruptions from volcanoes (or volcanic vents ) located within about 10 kilometers (6 miles) of each other, but it's difficult to determine whether one eruption caused the other...

Do volcanoes affect weather?

Yes, volcanoes can affect weather and the Earth's climate. Following the 1991 eruption of Mount Pinatubo in the Philippines, cooler than normal temperatures were recorded worldwide and brilliant sunsets and sunrises were attributed to this eruption that sent fine ash and gases high into the stratosphere, forming a large volcanic cloud that drifted around the world. The sulfur dioxide (SO2) in this...

How Do Volcanoes Erupt?

Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Since it is lighter than the solid rock around it, magma rises and collects in magma chambers. Eventually, some of the magma pushes through vents and fissures to the Earth's surface. Magma that has erupted is called lava. Some volcanic eruptions are explosive and others are not. The...

How many active volcanoes are there on Earth?

There are about 1,350 potentially active volcanoes worldwide, aside from the continuous belts of volcanoes on the ocean floor at spreading centers like the Mid-Atlantic Ridge . About 500 of those 1,350 volcanoes have erupted in historical time. Many of those are located along the Pacific Rim in what is known as the " Ring of Fire ." In the United States, volcanoes in the Cascade Range and Alaska...

How much of the Earth is volcanic?

More than 80 percent of the Earth's surface--above and below sea level--is of volcanic origin. Gaseous emissions from volcanic vents over hundreds of millions of years formed the Earth's earliest oceans and atmosphere, which supplied the ingredients vital to evolve and sustain life. Over geologic eons, countless volcanic eruptions have produced mountains, plateaus, and plains, which subsequently...

What are some examples of supervolcanoes?

Volcanoes that have produced exceedingly voluminous pyroclastic eruptions and formed large calderas in the past 2 million years include Yellowstone in northwest Wyoming, Long Valley in eastern California, Toba in Indonesia, and Taupo in New Zealand. Other 'supervolcanoes' would likely include the large caldera volcanoes of Japan, Indonesia, Alaska (e.g. Aniakchak, Emmons, Fisher), and other areas...

What are some benefits of volcanic eruptions?

Over geologic time, volcanic eruptions and related processes have directly and indirectly benefited mankind: Volcanic materials ultimately break down and weather to form some of the most fertile soils on Earth, cultivation of which has produced abundant food and fostered civilizations. The internal heat associated with young volcanic systems has been harnessed to produce geothermal energy . Most...

What is the "Ring of Fire"?

Most earthquakes and volcanic eruptions do not strike randomly but occur in specific areas, such as along plate boundaries. One such area is the circum-Pacific Ring of Fire , where the Pacific Plate meets many surrounding tectonic plates. The Ring of Fire is the most seismically and volcanically active zone in the world. Learn more: USGS Volcano Hazards Program

What is the difference between "magma" and "lava"?

Scientists use the term magma for molten rock that is underground and lava for molten rock that breaks through the Earth's surface.

What kind of school training do you need to become a volcanologist?

There are many paths to becoming a volcanologist. Most include a college or graduate school education in a scientific or technical field, but the range of specialties is very large. Training in geology, geophysics, geochemistry, biology, biochemistry, mathematics, statistics, engineering, atmospheric science, remote sensing, and related fields can be applied to the study of volcanoes and the...

What was the most destructive volcanic eruption in the history of the United States?

The May 18, 1980 eruption of Mount St. Helens (Washington) was the most destructive in the history of the United States. Novarupta (Katmai) Volcano in Alaska erupted considerably more material in 1912, but owing to the isolation and sparse population of the region, there were no human deaths and little property damage. In contrast, the eruption of Mount St. Helens caused loss of lives and...

Where does the United States rank in the number of volcanoes?

The United States ranks third, behind Indonesia and Japan, in the number of historically active volcanoes (that is, those for which we have written accounts of eruptions). In addition, about 10 percent of the more than 1,500 volcanoes that have erupted in the past 10,000 years are located in the United States. Most of these volcanoes are found in the Aleutian Islands, the Alaska Peninsula, the...

Kīlauea Volcano — Sunrise Over Lava Channel

Early morning view of the open  lava channel  during helicopter overflight of the lower East Rift Zone.

Kīlauea Volcano — Fissure 8 Lava Fountain

Lava  continues to erupt at a high rate from  Fissure  8 and flow within the established channel to the ocean. No channel overflows were observed during this morning's overflight.

Kīlauea Volcano — UAS Survey of Halema‘uma‘u Crater Rim

A UAS mission on June 13, 2018, filmed details of the dramatic changes occurring within Halema‘uma‘u crater at Kīlauea's summit since  explosive eruptions  of  ash  and gas and ongoing wall collapse beg

Lava Lake Spattering at Halema'uma'u Crater

21 January 2014 Lava Lake Spattering at Halema'uma'u Crater The lava lake in the Overlook crater, within Halema'uma'u Crater at Kilauea's summit, undergoes frequent periods of spattering. The spattering is normally at the lake margins, and the surface crust often flows towards, and is consumed at, the spattering source.

A gas plume arising from Augustine Volcano during it's eruptive phase 2005-06.

A gas plume arising from Augustine Volcano during it's eruptive phase 2005-06. This photo was taken during  a FLIR/maintenance flight on January 24, 2006.

Comparison of earthquake early warning systems and the national volcano early warning system at the U.S. Geological Survey

2018 update to the u.s. geological survey national volcanic threat assessment.

When erupting, all volcanoes pose a degree of risk to people and infrastructure, however, the risks are not equivalent from one volcano to another because of differences in eruptive style and geographic location. Assessing the relative threats posed by U.S. volcanoes identifies which volcanoes warrant the greatest risk-mitigation efforts by the U.S. Geological Survey and its partners. This update

U.S. Geological Survey Volcano Hazards Program—Assess, forecast, prepare, engage

The novarupta-katmai eruption of 1912 - largest eruption of the twentieth century; centennial perspectives, eruptions in the cascade range during the past 4,000 years, volcano hazards: a national threat.