Most volcanoes provide warnings before an eruption. Magmatic eruptions involve the rise of magma toward the surface, which normally generates detectable earthquakes. It can also deform the ground surface and cause anomalous heat flow or changes in the temperature and chemistry of the groundwater and spring waters. Steam-blast eruptions, however, can occur with little or no warning as superheated water flashes to steam.
Notable precursors to an eruption might include:
- An increase in the frequency and intensity of felt earthquakes
- Noticeable steaming or fumarolic activity and new or enlarged areas of hot ground
- Subtle swelling of the ground surface
- Small changes in heat flow
- Changes in the composition or relative abundances of fumarolic gases
These precursors do not indicate the type or scale of an expected eruption (that information is best obtained by mapping previous eruptions). Precursors can continue for weeks, months, or even years before eruptive activity begins, or they can subside at any time and not be followed by an eruption. Italy’s Campi Flegrei volcano has been showing signs of unrest for over 60 years.
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Instruments to measure sulfur dioxide and carbon dioxide can be mounted in aircraft to determine the quantity of gas being emitted on a daily basis. Such instruments can also be used in a ground-based mode. An instrument that detects carbon dioxide can be installed on a volcano and configured to send data continuously via radio to an observatory. Sulfur dioxide in volcanic clouds can also be...
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Volcanoes are inherently beautiful places where forces of nature combine to produce awesome events and spectacular landscapes. For volcanologists, they're FUN to work on! Safety is, however, always the primary concern because volcanoes can be dangerous places. USGS scientists try hard to understand the risk inherent in any situation, then train and equip themselves with the tools and support...
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Hot lava samples provide important information about what's going on in a volcano's magma chambers. We know from laboratory experiments that the more magnesium there is in magma, the hotter it is. Chemical analysis, therefore, provides the means not only to determine the crystallization history of lava but also to establish the temperature at which it was erupted. For example, Kilauea's 1997 lavas...
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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...
Do earthquakes large enough to collapse buildings and roads accompany volcanic eruptions?
Not usually. Earthquakes associated with eruptions rarely exceed magnitude 5, and these moderate earthquakes are not big enough to destroy buildings and roads. The largest earthquakes at Mount St. Helens in 1980 were magnitude 5, large enough to sway trees and damage buildings, but not destroy them. During the huge eruption of Mount Pinatubo in the Philippines in 1991, dozens of light to moderate...
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...
Which volcanoes in the conterminous United States have erupted since the Nation was founded?
Excluding steam eruptions, these volcanoes have shown activity: Mount St. Helens, Washington - Eruptions and/or lava dome growth occurred in the late 1700s, 1800-1857, 1980-1986, and 2004-2008. Lassen Peak, California - A series of steam blasts began on May 30, 1914. An eruption occurred 12 months later on May 21, 1915. Minor activity continued through the middle of 1917. Mount Hood, Oregon -...
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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...
What is the largest sinkhole in the United States?
There are some very large, ancient, ‘inactive’ sinkholes in some areas of the U.S. that are thousands of years old. Alabama claims to have the largest recent collapse sinkhole. It is called the “Golly Hole” and is located in Shelby County in the central part of the state. It collapsed suddenly in 1972. The sinkhole is about 325 feet long, 300 feet wide, and 120 feet deep. Learn more: USGS Water...
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 of...
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- FAQ
How are volcanic gases measured?
Instruments to measure sulfur dioxide and carbon dioxide can be mounted in aircraft to determine the quantity of gas being emitted on a daily basis. Such instruments can also be used in a ground-based mode. An instrument that detects carbon dioxide can be installed on a volcano and configured to send data continuously via radio to an observatory. Sulfur dioxide in volcanic clouds can also be...
Is it dangerous to work on volcanoes? What precautions do scientists take?
Volcanoes are inherently beautiful places where forces of nature combine to produce awesome events and spectacular landscapes. For volcanologists, they're FUN to work on! Safety is, however, always the primary concern because volcanoes can be dangerous places. USGS scientists try hard to understand the risk inherent in any situation, then train and equip themselves with the tools and support...
Lava sampling: Why do we do it?
Hot lava samples provide important information about what's going on in a volcano's magma chambers. We know from laboratory experiments that the more magnesium there is in magma, the hotter it is. Chemical analysis, therefore, provides the means not only to determine the crystallization history of lava but also to establish the temperature at which it was erupted. For example, Kilauea's 1997 lavas...
Why is it important to monitor volcanoes?
There are 161 potentially active volcanoes in the United States. According to a 2018 USGS assessment, 57 volcanoes are a high threat or very high threat to public safety. Many of these volcanoes have erupted in the recent past and will erupt again in the foreseeable future. As populations increase, areas near volcanoes are being developed and aviation routes are increasing. As a result, more...
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...
Do earthquakes large enough to collapse buildings and roads accompany volcanic eruptions?
Not usually. Earthquakes associated with eruptions rarely exceed magnitude 5, and these moderate earthquakes are not big enough to destroy buildings and roads. The largest earthquakes at Mount St. Helens in 1980 were magnitude 5, large enough to sway trees and damage buildings, but not destroy them. During the huge eruption of Mount Pinatubo in the Philippines in 1991, dozens of light to moderate...
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...
Which volcanoes in the conterminous United States have erupted since the Nation was founded?
Excluding steam eruptions, these volcanoes have shown activity: Mount St. Helens, Washington - Eruptions and/or lava dome growth occurred in the late 1700s, 1800-1857, 1980-1986, and 2004-2008. Lassen Peak, California - A series of steam blasts began on May 30, 1914. An eruption occurred 12 months later on May 21, 1915. Minor activity continued through the middle of 1917. Mount Hood, Oregon -...
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...
What is the largest sinkhole in the United States?
There are some very large, ancient, ‘inactive’ sinkholes in some areas of the U.S. that are thousands of years old. Alabama claims to have the largest recent collapse sinkhole. It is called the “Golly Hole” and is located in Shelby County in the central part of the state. It collapsed suddenly in 1972. The sinkhole is about 325 feet long, 300 feet wide, and 120 feet deep. Learn more: USGS Water...
What are some benefits of volcanic eruptions?
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