7 Explosive Facts about Volcanoes

The word volcano comes from the Roman name Vulcan—the Roman god of fire

Volcanoes are some of Earth’s most fascinating features. They are both creators and destroyers: Their lava cools and builds new land while their eruptions of ash and rock have buried cities such as Pompeii and even blocked out the sun’s rays. Volcanoes have also inspired artists, writers, and scientists for centuries. Read on for some explosive examples of how volcanoes have changed the world.

Lassen Peak, Lassen Volcanic National Park, California © Rex Vogel, all rights reserved

1. There are three main types of volcanoes

The simplest type of volcano, cinder cone aptly describes how this type of volcano forms: As lava bursts out of the earth, it cools and falls back to the surface as pebbly textured cinder piling up around the original site of the eruption. The cinder eventually forms a dark, smooth-sided cone. When looking at a map, you will find that thousands of cinder cones exist in western North America and in other volcanic areas of the world.

Some of the Earth’s grandest mountains are composite volcanoes—sometimes called stratovolcanoes. They are usually tall with steep even sides and are formed by repeating layers of lava flows, volcanic ash, cinders, blocks, and volcanic bombs. These mountainous volcanoes often result in huge eruptions of thick lava and tephra (small rocky fragments) that build up over time. About 60 percent of the world’s volcanoes are stratovolcanoes and they include Mount St. Helens and Mount Rainier in Washington, Mount Hood in Oregon, Mount Garibaldi in British Columbia, and Mount Shasta in California. Some composite volcanoes rise over 8,000 feet above their surroundings.

Shield volcanoes are built almost entirely of fluid lava flows. Lava erupts or pours out of multiple vents in all directions and spreads out over land. Shield volcanoes build up slowly by the growth of thousands of lava flows that spread widely over great distances and then cool as thin sheets. Crater Lake was formed when a massive shield volcano Mount Mazama collapsed in on itself. Snow filled the crater with water, creating a lake. Further eruptions created a small island in the middle of the lake. The Hawaiian Islands are made of a chain of shield volcanoes including Kīlauea and the world’s largest active volcano, Mauna Loa. 

Mount St. Helens, Mount St. Helens National Monument, Washington © Rex Vogel, all rights reserved

2. Eruptions are measured by the volcanic explosivity index

The power of a volcanic eruption is measured on a scale from 0 to 8 called the Volcanic Explosivity Index (VEI), according to the amount of lava, tephra, and ash that spews forth. An eruption with a VEI of 0 is basically dormant; each subsequent number indicates a tenfold increase in ejected material. The 1980 eruption of Mount St. Helens was a VEI 5. The most recent megacolossal eruption took place in 2022 at Hunga Tonga Ha’apai: The blast destroyed 90 percent of the South Pacific island and merited a VEI of 6.

>> Related article: See Steaming Volcanoes at This Eerie National Park

El Malpais National Monument, New Mexico © Rex Vogel, all rights reserved

3. The Ring of Fire is Earth’s most active volcano zone

About 1,350 potentially active volcanoes dot the Earth today and about 75 percent of them can be found along a 25,000-mile-long horseshoe-shaped ribbon that borders the Pacific Ocean. This Circum-Pacific Belt, more commonly known as the Ring of Fire is home to some of the most volcanically active areas in the world including Southeast Asia, New Zealand, Japan, Chile, Alaska, and parts of the contiguous United States. 

The volcanoes are clustered near subduction zones—unstable areas where one of Earth’s heavy tectonic plates slides under a lighter one. The movements trigger earthquakes as well as a buildup of magma (molten rock) where the plates scrape together. Magma often escapes through the lighter plate as a volcano.

Lassen Volcanic National Park, California © Rex Vogel, all rights reserved

4. The U.S. has a surprisingly high number of volcanoes

Three volcanoes in the Lower 48 have erupted since the Declaration of Independence was signed: Mount St. Helens in Washington, Mount Hood in Oregon, and Lassen Peak in California. Mount St. Helens: Eruptions and/or lava dome growth occurred in the late 1700s, 1800-1857, 1980-1986, and 2004-2008.

Lassen Peak: 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: After being dormant for over 1,000 years, Mount Hood had an eruptive period beginning in 1781 that lasted for about a decade. In the mid-1800s, local residents reported minor explosive activity.

>> Related article: Celebrate Volcano Week!

Due to the statehoods of Alaska and Hawaii in 1959, the U.S. now ranks first in the world in the number of potentially active volcanoes per nation with 162. They include the planet’s largest active volcano, Hawaii’s Mauna Loa which rises 2.5 miles above sea level and 10.5 miles above its base on the bottom of the ocean. Alaska’s Novarupta volcano in present-day Katmai National Park and Preserve had the biggest eruption of the 20th century beginning on June 6, 1912 with a VEI of 6.

El Malpais National Monument, New Mexico © Rex Vogel, all rights reserved

5. Volcanoes can change Earth’s climate

The biggest eruptions can shoot tons of ash and gas high into the atmosphere where they can block some of the sun’s radiation and be dispersed around the world by air currents. These aerosols can actually change Earth’s climate for a few years.

In April of 1815, the eruption of the volcano Mount Tambora rocked modern-day Indonesia. The blast, nearly 100 times as large as that of Mount St. Helens in 1980 sent a massive cloud of miniscule particles into the atmosphere. As the particle cloud blew its way around the globe it reflected sunlight causing a meteorological phenomenon to which we now refer as the year without a summer.

In June 1991, Mount Pinatubo’s eruption in the Philippines sent ash into the stratosphere and cooled the globe for about two years.

>> Related article: Rivers of Ancient Fires: El Malpais National Monument

When the Hunga Tonga-Hunga Ha’apai volcano erupted in January 2022, it sent a tsunami racing around the world and set off a sonic boom that circled the globe twice. The underwater eruption in the South Pacific Ocean also blasted an enormous plume of water vapor into Earth’s stratosphere—enough to fill more than 58,000 Olympic-size swimming pools. The sheer amount of water vapor could be enough to temporarily affect Earth’s global average temperature.

Mount St. Helens, Mount St. Helens National Monument, Washington © Rex Vogel, all rights reserved

6. A volcano made the loudest sound ever recorded

When Krakatau blew its top in August 1883, it released a boom that geologists believe was the loudest sound in recorded history. The 310-decibel cataclysm was heard over 2,000 miles away in Australia where ranchers thought it was a rifle shot; people 3,000 miles away thought it was a cannon blast from a nearby ship. In addition to the eardrum-busting noise, the volcano released 6 cubic miles of material into the atmosphere, triggered tsunamis that killed 36,000 people and coated the sea in layers of floating pumice.

The closest we’ve come to a repeat of Krakatoa was the Hunga Tonga-Hunga Ha’apai eruption near the Polynesian island of Tonga in January 2022. Sonic booms were felt as far north as Alaska and researchers more than 6,000 miles away at Boise State University in Idaho recorded subterranean frequencies equivalent to about 100 decibels.

Fortunately, this blast wasn’t nearly as deadly with three fatalities recorded. Still, it wreaked a lot of havoc. Tonga was largely cut off from the rest of the world for days, ash blanketed large swaths of the surrounding area, and tsunamis caused major damage along the coastlines. On one of the closer outlying islands all the homes were destroyed. The volcano had created its own new island several years before; that was entirely obliterated along with large chunks of two nearby islands.

Petroglyph National Monument, New Mexico © Rex Vogel, all rights reserved

7. Volcanoes are erupting, spewing ash on three continents

Active volcanoes prompted ash warnings and set nerves on edge in Italy, Mexico, and the Democratic Republic of Congo earlier this month. 

Mount Etna showered ash over Catania in eastern Sicily on Sunday, May 21, 2023 and forced the temporary suspension of airport operations. Lava flows were reported in January and an explosion on May 14 produced an ash admission. Activity at Mount Etna has been observed and recorded for more than 2,500 years, making it one of the oldest continuously monitored volcanoes.

>> Related article: On the Road to Mount St. Helens

Volcanic ash from Popocatépetl triggered the temporary closure of Mexico City’s Benito Juárez International Airport on Saturday, May 20. Flight delays related to the presence of ash also were reported Monday. People were urged not to travel within a 7.5 mile radius of the volcano and to avoid the crater “due to the danger of falling ballistic fragments,” according to Mexico’s National Center for Communication and Civil Protection Operations. The volcano has experienced explosions, tremors, and exhaled vapor, gas, and ashes for weeks, according to monitoring reports from the national center and the National Autonomous University of Mexico. 

Lassen Volcanic National Park, California © Rex Vogel, all rights reserved

The Nyamulagira volcano in the Democratic Republic of Congo also continued ongoing eruption and lava flow. Nyamulagira is Africa’s most active volcano. An eruption began in the summit crater on March 14 and active flows were seen on May 7 and May 12, according to the Smithsonian’s Global Volcanism Program. The volcano has been active since April 2018.

As of April 14, 2023, 49 volcanoes around the world were in continuing eruption status, according to the Smithsonian’s Global Volcanism Program. Last week, 24 were in some stage of active eruption, according to the program’s latest weekly report.

The Popocatepetl volcano reputedly 730,000 years old is the second-highest peak in Mexico; Citlaltépetl is roughly 500 feet higher. It is the second-highest volcano in North America; Hawaii’s Mauna Loa, the largest active volcano in the world soars roughly 30,000 feet over the ocean floor.

The Mauna Kea volcano on the island of Hawaii is the tallest mountain on Earth if you measure its height from its bottom on the ocean floor; it rises to a height of over 33,000 feet.

Worth Pondering…

Each volcano is an independent machine—nay, each vent and monticule is for the time being engaged in its own peculiar business, cooking as it were its special dish which in due time is to be separately served. We have instances of vents within hailing distance of each other pouring out totally different kinds of lava, neither sympathizing with the other in any discernible manner nor influencing other in any appreciable degree.

—Clarence Edward Dutton, Report on the Geology of the High Plateaus of Utah (1880)