Home / 90 Frequently Asked Questions About Volcanoes and Their Answers

Given that active volcanoes can remain active for centuries and are often unpredictable as to their explosions, it's important to know what they are, the risks of being near one, and how to respond to a volcanic eruption event. According to the United States Geological Survey, such a unique natural formation as this is defined as follows: “Volcanoes are openings, or vents where lava, tephra (small rocks), and steam erupt on to the Earth's surface. Volcanic terrain, however, is built by the slow accumulation of erupted lava. The vent may be visible as a small bowl shaped depression at the summit of a cone or shield-shaped mountain. Through a series of cracks within and beneath the volcano, the vent connects to one or more linked storage areas of molten or partially molten rock (magma). This connection to fresh magma allows the volcano to erupt over and over again in the same location."

Inside the Earth's core, there is a red-hot liquid rock called magma. Volcanoes form when that magma rises to the surface of the Earth and pushes its way out of a vent in the Earth's crust. When the magma reaches the Earth's surface, it cools and hardens. As this happens over countless millennia, a volcano is formed.

A volcanic eruption can last from just a few hours to several years, making it almost impossible to categorize what is considered "normal" in terms of the duration of a volcanic eruption. However, according to the Smithsonian Global Volcanism Program, the median length of time for a single volcanic eruption is seven weeks. An eruption can be fast and sudden or slow and barely noticeable.

Mt. St. Helens is called a “dacite volcano.” It is considered an explosive structure with a complex magmatic system. In fact, the deadliest and most economically destructive volcanic event in U.S. history occurred when Mount St. Helens erupted in 1980. Located in Skamania County, Washington (just 52 miles northeast of Portland, Oregon), the eruption was so violent that the summit of the mountain was completely blown off, reducing the height of the mountain from 9,677 ft to 8,363 ft above sea level. The volcanic event killed 57 people, destroyed 200 homes, and took out 47 bridges, 15 miles of railway, and 185 miles of highway.

(However, there have been other eruptions that were even worse than the 1980 Mt. St. Helens eruption. In 1912, Katmai Volcano in Alaska erupted, a more forceful volcanic event with wider-reaching damage than Mount St. Helens. However, because the region was sparsely populated, there were no human deaths due to the event).


Volcanoes erupt because of pressures occurring below and inside of them. When molten rock called magma rises to the surface, this causes an eruption. As the magma rises, bubbles of gas form inside of it. The result? Runny magma erupts through openings or vents in the earth's crust (often at the peak of the volcano) before flowing onto its surface as lava.

The Yellowstone Caldera, a supervolcano, is located in Wyoming.

It is massive! The huge caldera measures 80 kilometers long, 65 kilometers wide, and hundreds of meters deep. It extends from outside Yellowstone National Park into the central area of the park.

This is a broad, domed structure with gently sloping sides. It looks much like a shield, hence the name. Such a structure is formed by the eruption of fluid, basaltic lava.

Volcanoes usually form at the boundary of the Earth's tectonic plates. That's why, in the United States, most of the country's 160+ active volcanoes are located in California, Oregon, Washington, Alaska, and Hawaii. However, "active" is a loose term. For example, ten active volcanoes in this region include:

  • Kilauea, Hawai'i – Last erupted: 2018.
  • Redoubt, Alaska – Last erupted: 2009.
  • Mount St. Helens, Washington State – Last erupted: 2008.
  • Mauna Loa, Hawai'i – Last erupted: 1984.
  • Lassen Volcanic Center, California – Last erupted: 1917.
  • Mount Hood, Oregon – Last erupted: About 200 years ago.
  • Mount Shasta, California – Last erupted: About 300 years ago.
  • Mount Rainier, Washington – Last erupted: About 1,100 years ago.
  • South Sister, Oregon – Last erupted: About 2,000 years ago.
  • Yellowstone, Wyoming – Last erupted: About 70,000 years ago.

There are five such structures in the state of Hawaii. Two of them are still active, Kilauea and Mauna Loa.

We normally associate such natural structures with the Tropics and with various islands in the Pacific Ocean. But of the more than 160 active volcanoes in the United States, most of them are in the Pacific Northwest, including northern California, Oregon, Washington State, and Alaska! According to American Geosciences, “There are about 169 volcanoes in the United States that scientists consider active. Most of these are located in Alaska, where eruptions occur virtually every year.”

There are approximately 1,500 such structures in the world, hundreds of which are in the United States.

According to the NOAA, “In geology, a hotspot is an area of the Earth’s mantle from which hot plumes rise upward, forming volcanoes on the overlying crust. In much the same way that plumes rise buoyantly in a lava lamp, plumes of mantle magma (molten rock) are theorized to rise buoyantly from a source within Earth’s deep mantle. When such a plume rises into the shallow mantle, it partially melts and the melt may then rise to the surface where it can erupt as a hotspot volcano. Hotspot volcanism is distinct in that it does not originate from processes that produce the more common submarine volcanism that occurs at boundaries of Earth’s tectonic plates.”

The largest active volcano on the planet, Mauna Loa is a shield volcano. The name is Hawaiian for “Long Mountain.”

There has been a great deal of speculation on this, with some answers being more legitimate than others. Quoting the credible scientists over at the United States Geological Survey, “If another large, caldera-forming eruption were to occur at Yellowstone, its effects would be worldwide. Such a giant eruption would have regional effects such as falling ash and short-term (years to decades) changes to global climate. Those parts of the surrounding states of Montana, Idaho, and Wyoming that are closest to Yellowstone would be affected by pyroclastic flows, while other places in the United States would be impacted by falling ash (the amount of ash would decrease with distance from the eruption site). Such eruptions usually form calderas, broad volcanic depressions created as the ground surface collapses as a result of withdrawal of partially molten rock (magma) below. Fortunately, the chances of this sort of eruption at Yellowstone are exceedingly small in the next few thousands of years.”

Most such structures are found along a belt called the Ring of Fire that encircles the Pacific Ocean. Some, like the hotspots in the Hawaiian Islands, occur in the interior of plates.

Many of the world’s active volcanic structures are located around the edges of he Pacific Ocean, in the Ring of Fire. They can be found along the West Coast of the Americas; the East Coast of Siberia, Japan, the Philippines, and Indonesia; and in island chains from New Guinea to New Zealand.

Like mountains, volcanoes vary greatly in size. The world's largest volcano is Mauna Loa, in Hawai'i. Mauna Loa is about 55,770 feet from its base beneath the ocean to the summit, which is 13,681 feet above sea level. Conversely, the smallest volcanoes in the world look more like large boulders than actual volcanic mountains.

There are about 1,500 active, volcanic structures in the world today.

According to the United States Geological Survey, “Some of the Earth's grandest mountains are composite volcanoes – sometimes called stratovolcanoes. They are typically steep-sided, symmetrical cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet above their bases. Some of the most conspicuous and beautiful mountains in the world are composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, and Mount St. Helens and Mount Rainier in Washington.”

Volcanoes are categorized based on the frequency of their eruption. Those that erupt frequently are called "active," and those that have not erupted in many, many years are called "dormant." However, dormant volcanoes could become active again. While there is no scientific consensus on what exactly counts as an active or inactive volcano, the Smithsonian Global Volcanism Program defines a volcano as active only if it has erupted in the last 10,000 years. Using that definition, there are about 500 active volcanoes on Planet Earth here in the 21st century, with more than 160 of them existing in the United States.

Mount Fuji is a Composite Cone, i.e., a stratovolcano. It is a massive mountainous structure and is formed from layers of rock, ash, and lava.

The three types are composite, shield, and cinder cone. There are also supervolcanoes. Following are three quotes from the United States Geological Survey that clearly and concisely define each type:

“Some of the Earth's grandest mountains are composite volcanoes – sometimes called stratovolcanoes. They are typically steep-sided, symmetrical cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet above their bases. Some of the most conspicuous and beautiful mountains in the world are composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, and Mount St. Helens and Mount Rainier in Washington.”

“Cinder cones are the simplest type of volcano. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world.”

“Shield volcanoes, the third type of volcano, are built almost entirely of fluid lava flows. Flow after flow pours out in all directions from a central summit vent, or group of vents, building a broad, gently sloping cone of flat, domical shape, with a profile much like that of a warrior's shield. They are built up slowly by the accretion of thousands of highly fluid lava flows called basalt lava that spread widely over great distances, and then cool as thin, gently dipping sheets. Lavas also commonly erupt from vents along fractures (rift zones) that develop on the flanks of the cone. Some of the largest volcanoes in the world are shield volcanoes. In northern California and Oregon, many shield volcanoes have diameters of 3 or 4 miles and heights of 1,500 to 2,000 feet. The Hawaiian Islands are composed of linear chains of these volcanoes including Kilauea and Mauna Loa on the island of Hawaii-- two of the world's most active volcanoes.”

The process is complex, but it can be simplified. Inside the Earth's core, there exists a red-hot liquid rock called magma. Volcanoes form when that magma rises all the way up to the surface of the Earth and pushes its way out of a vent that has formed in the Earth's crust. When the magma reaches the Earth's surface, it cools and hardens. As this happens over countless millennia, a volcano is formed.

From the USGS: “Cinder cones are the simplest type of volcano. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world.”

Kīlauea, on the Island of Hawai'i, is an active shield volcano. Its most recent eruption occurred in 2018. That eruption created a massive lava flow covering 13 square miles of the island, boiling Hawaii's largest freshwater lake and destroying 700 homes. While Kīlauea is known for its activity and is therefore closely monitored so that residents have time to evacuate before an eruption, it's only a matter of time before this volcano experiences another significant volcanic event.

Impressive and imposing, Mount Rainier is a stratovolcano.

This structure is quite unique. According to the experts at Volcano Discovery, “Present-day Vesuvius is a medium-sized typical stratovolcano volcano reaching a height of 1,281 m a.s.l. It comprises the older volcano, the Somma, whose summit collapsed (likely during the 79 AD eruption), creating a caldera, and the younger volcano, Vesuvius, which since then has re-grown inside this caldera and formed a new cone.”

Yellowstone is a supervolcano. According to one source, “It (Yellowstone) has had three massive eruptions, all of which created calderas. The first eruption occurred some 2.1 million years ago, and the second took place about 800,000 years later.” Though Yellowstone National Park is famous for resting atop a massive volcano, the geysers that reside at the Earth's surface in Yellowstone are not, themselves, volcanic. The big difference between a geyser system and a volcano system is that a geyser emits hot water and steam. In contrast, a volcano emits dust, fine rock particles, larger rocks, and lava.

These structures are build almost entirely from fluid, ongoing, and recurrent lava flows. Flow after flow after flow after flow pours out in all directions from a central summit vent, or from a group of vents, building a broad, gently sloping cone that takes on a flat, domical shape. It has a profile much like that of a warrior's shield, hence the name.

Very hot! The temperature of molten lava coming up out of a vent can vary anywhere from 700 to 1,200 degrees Celsius, or 1,300 to 2,200 degrees Fahrenheit.

Volcanic eruptions are more common than one might think. Dozens of volcanoes erupt each year in the United States alone, several of which erupt multiple times. Quoting the American Geosciences Institute: “There are about 169 volcanoes in the United States that scientists consider active. Most of these are located in Alaska, where eruptions occur virtually every year. Others are located throughout the west and in Hawaii. Kilauea volcano in Hawaii is one of the most active volcanoes on Earth. It has been erupting almost continuously since 1983.”

There have been at least 404 volcanic eruptions since 1883, almost 200 of which have occurred since the year 2000. But the big question on everyone's minds is this. Will volcanic eruptions become more frequent and more intense in the future? According to the Scientific American, it's likely that volcanic activity will increase as the planet warms. Researchers found that, historically, volcanic eruptions have increased as planet temperatures rose and glaciers melted. As the Earth is currently going through a warming phase, it's safe to assume that volcanic activity will become more common.

It is not. Mount Everest was formed by he clashing of two tectonic plates, the Indo-Australian and Eurasian plates. But there was no volcanic activity involved, hence Mount Everest is jus a very, very tall mountain.

It was Mount Vesuvius that destroyed the city of Pompeii. The eruption took place in A.D. 79, killing about 2,000 people.

Simply put, when molten rock called magma pushes its way to the surface of the Earth’s crust and expels out into the open air, this is a volcanic eruption. In most eruptions, runny magma erupts through openings or vents in the earth's crust before then flowing onto its surface as lava. If the magma is thick, gas bubbles cannot easily escape and pressure builds up as the magma rises. That’s what creates the trademark explosion that volcanoes are known for.

Subduction is simply the collision of continental and oceanic crusts. The oceanic crust melts and migrates upwards, until it ultimately erupts on the surface, creating a volcanic explosion.

There are 20 such structures in the state of California.

There are a little more than 450 such structures in the Ring of Fire.

Such a mountainous structure is formed of hot molten rock, ash, escaped gases, and lava. All of the above solidifies as it cools, following an eruption. What’s left behind is the building blocks for the structure itself.

Most such structures look quite like mountains, but others may look like shields or cones.

Such a geologic feature is a chain of volcanic structures that form above and along a subduction plate. They often spring up in an arc-like pattern, hence the name.

According to the National Geographic, “The Ring of Fire, also referred to as the Circum-Pacific Belt, is a path along the Pacific Ocean characterized by active volcanoes and frequent earthquakes. The majority of Earth's volcanoes and earthquakes take place along the Ring of Fire.”

Volcanoes and mountains are certainly similar. But they are different in that a mountain results from various geological processes (like the movement and collision of tectonic plates). On the other hand, volcanoes form around a vent in the Earth's crust when magma flows up and out of the vent, reaching the surface of the Earth.

When tectonic plates collide, volcanoes often form. This usually occurs when a thin, heavy oceanic plate “subducts,” or moves under, a thicker continental plate of heavy, solid rock. Then, when enough magma builds up in the magma chamber, it forces its way up to the surface and then erupts, often causing volcanic eruptions.”

Simply put, such structures change the surface of the Earth by allowing molten rock (magma) to escape from inside the Earth, come to the surface, and from various rock formations and even mountains.

The temperature of lava flow is usually about 2,000 degrees Fahrenheit. In other words, very, very hot!

There are about 1,500 such structures that qualify as active.

It is mineral-like, but not a true mineral. This is mostly because it’s composition is too complex and intricate to be classified as a single mineral.

Indonesia has the most by far. With over 13,000 islands within its boundaries, many of them formed by volcanic activity, this country has the most such structures of any country in the world.

Such an eruption has both warming and cooling effects. For example, released ash and sulfur dioxide have a cooling effect, because such particles reflect sunlight. However, such structures also release CO2, causing a warming effect.

This is another term for volcanic activity or phenomenon.

Kilauea is the most active by far! It is almost always erupting to some degree.

Vesuvius is considered the most dangerous. It’s eruptions are very explosive and sudden, and while it has been dormant since 1944, about 3 million people live within close proximity to it, suggesting the possibility for a great deal of destruction were it to erupt again.

Ojos Del Salado is the tallest, in the Andes Mountains, coming in at 22,615 feet above sea level.

According to the National Geographic, “Volcanic ash is a mixture of rock, mineral, and glass particles expelled from a volcano during a volcanic eruption. The particles are very small—less than 2 millimeters in diameter. They tend to be pitted and full of holes, which gives them a low density. Along with water vapor and other hot gases, volcanic ash is part of the dark ash column that rises above a volcano when it erupts.”

They are wider because of the difference in how they are formed. Composite structures are formed by upwards and outwards explosions, whereas shield structures are formed by constant, steady, ongoing lava flow.

Yes, particularly along the East African rift.

Yes. Because volcanic activity causes vibration within the earth’s crust and interior layers, this can set off earthquakes.

Eruptions can have a warming effect, as co2 is released into the atmosphere during an eruption.

There are four basic types: composite, shield, super, and cinder cone.

Magma, lava, gases, and ash.

The word is Latin in origin. According to the USGS, “The word ‘volcano’ comes from the little island of Vulcano (with a U) in the Mediterranean Sea off Sicily. Centuries ago, the people living in this area believed that Vulcano (with a U) was the chimney of the forge of Vulcan – the blacksmith of the Roman gods.”

An extinct volcanic structure, a dormant one, and an active one are all different and unique. According to Volcano Discovery, “An active volcano is a volcano that has had at least one eruption during the past 10,000 years. An active volcano might be erupting or dormant. An erupting volcano is an active volcano that is having an eruption. A dormant volcano is an active volcano that is not erupting, but supposed to erupt again. An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.” And can inactive volcanic structure become active again? Yes! A volcano can go for millions of years without erupting and then suddenly become active again.

Both plate boundaries and convergent plate boundaries can cause volcanic activity.

It is highly fertile because it is composed on many non-crystalline minerals, such as allophone. In simple terms, these minerals create strong bonds with organic matter, and that leads to the accumulation of organic matter in the soil.

There are two crucial ways to respond to a volcanic eruption, and how you react to such a natural disaster will depend on the type of volcanic eruption.

  • If the volcanic eruption involves ash fall but not lava flow, it's important to stay inside.
  • If the volcanic eruption involves lava flow, it's important to leave the area immediately.

Before and during a volcanic event, listen to the advice of local officials. They will tell you if you should take shelter in your home or if you should evacuate. If the eruption does not involve lava flow, stay indoors and:

  • Close all windows, doors, and fireplace or wood stove dampers.
  • Turn off all ceiling fans and all heating and air conditioning systems.
  • Bring pets and livestock into closed shelters and keep them there.

During an eruption, wear goggles and an N-95 respirator if they are available to you. If your eyes, nose, or throat become irritated from volcanic gases and fumes, move away from the area immediately. If you are caught outside during an eruption, seek shelter indoors. During volcanic activity, stay apprised as to what local officials and emergency responders are saying. If officials initially tell you to shelter inside but then change the recommendation later on to evacuate the area, follow their instructions immediately, as that likely means the volcanic event changed to one that involves dangerous lava flow.

Such is simply an opening, varying in size, out of which can escape magma, lava, gases, and volcanic debris.

Olympus Mons is the largest by far, located on Mars. According to NASA, “The largest of the volcanoes in the Tharsis Montes region, as well as all known volcanoes in the solar system, is Olympus Mons. Olympus Mons is a shield volcano 624 km (374 mi) in diameter (approximately the same size as the state of Arizona), 25 km (16 mi) high, and is rimmed by a 6 km (4 mi) high scarp. A caldera 80 km (50 mi) wide is located at the summit of Olympus Mons. To compare, the largest volcano on Earth is Mauna Loa. Mauna Loa is a shield volcano 10 km (6.3 mi) high and 120 km (75 mi) across. The volume of Olympus Mons is about 100 times larger than that of Mauna Loa. In fact, the entire chain of Hawaiian islands (from Kauai to Hawaii) would fit inside Olympus Mons!”

This is relatively infrequent, but yet, volcanic activity can cause impulsive disturbances in the ocean, displacing a great volume of water and causing a tsunami as a result.

Yes they do.

They are formed by volcanic activity on the seabed, often near the boundaries of tectonic plates.

This is partially dependent on the speed of eruption. While the United States Geological Survey has systems in place to detect volcanic eruptions, volcanic activity can still occur very quickly, with a volcano going from inactive to active overnight. One example of rapid volcanic activity was Paricutin, a volcano that appeared in a Mexican cornfield in 1943. Within a week, it was five stories tall! Ultimately, lava cools and hardens following an eruption. But how long it takes to do that is dependent on how rapidly and with how much intensity the volcano is erupting.

Such a structure is called a Submarine Volcano.

Scientists use seismographs to measure the tremors that begin shortly before a volcanic eruption occurs.

It is a mixture of rock, mineral, and glass particles. The particles are small, usually less than two millimeters in diameter. It is very irritating to the throat, lungs, eyes, and nose, so people who are near an eruption should take cover or evacuate and do everything they can not to breathe the ash.

It is called extrusive rock or igneous rock.

Not really. Mountains can be formed by volcanoes, and volcanic activity can change mountains, but a mountain cannot suddenly become a volcano. However, volcanoes are actually types of mountains.

Yes, sometimes. It usually takes a large earthquake, but this has been known to occur.

These are created when a narrow stream of hot mantle rises up from deep inside the earth and melts a hole in the plate, all so that the magma can ooze upwards. The Hawaiian Islands are an example of such a formation.

According to one source, “The Richter scale measures earthquake strength. Volcanoes have a similar scale called the Volcanic Explosivity Index (VEI).... It measures how much volcanic material is ejected, the height of the material thrown into the atmosphere, and how long the eruptions last.”

They are usually thousands of feet deep, with their bottommost sector being difficult to find.

It usually takes millions of years for such structures to form.

There are six such structures that we know about, in the world today.

Such an event is an electrical discharge caused by a volcanic eruption, rather than by an ordinary thunderstorm. It comes about as a result of colliding, fragmenting particles of volcanic ash. Such ash generates static electricity, leading to electrical discharges in the form of lightning.

There are 12 states that have active volcanoes. They are as follows:

Alaska: 141

California: 18

Oregon: 17

Washington: 7

Hawaii: 5

Utah: 4

Idaho: 4

New Mexico: 3

Arizona: 2

Nevada: 2

Colorado: 1

Wyoming: 1

In the Ring of Fire.

They are often located in the Ring of Fire, along the borders of the Pacific Ocean.

Though most volcanic activity that occurs each year in the United States is not that extreme, there is the potential for massive destruction from a volcanic eruption. Fast-moving lava can kill people, and falling ash can make it difficult to breathe. Lava can destroy homes, roads, livestock, farms, and infrastructure. Volcanic eruptions can also cause fires and earthquakes, leading to famine and immense loss of local resources and the capacity to sustain human life.

Not only does Alaska have a huge number of volcanic mountains, but many of the state’s volcanic structures are active! Alaska contains over 130 volcanoes and volcanic fields. The volcanoes in Alaska make up well over three-quarters of U.S. volcanoes that have erupted in the last two hundred years.

Yes! There are several. Currently, only two of them are active, Mount Erebus and Deception Island.


Sources

https://www.usgs.gov/natural-hazards/volcano-hazards/about-volcanoes

https://www.americangeosciences.org/critical-issues/faq/how-many-active-volcanoes-are-there-united-states#

https://www.britannica.com/place/Yellowstone-Caldera

https://www.volcanodiscovery.com/volcanoes/faq/active_erupting.htm

https://www.usgs.gov/volcanoes/mount-st-helens

https://avo.alaska.edu/volcanoes/about.ph

https://www.bbc.co.uk/newsround/44100737

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https://oceanexplorer.noaa.gov/facts/volcanic-hotspot.htm

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https://pubs.usgs.gov/gip/volc/types.htm

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https://www.nationalgeographic.org/encyclopedia/volcanic-ash

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https://mars.nasa.gov/gallery/atlas/olympus-mons.html