Volcanoes: Powerful Forces of Nature
1991 Mount Pinatubo blast
Second largest eruption in the 20th century
On June 15, 1991, a slumbering giant awakened. Mount Pinatubo, a volcano on the Philippine island of Luzon, erupted after lying dormant for 500 years.
The mammoth eruption was the second largest volcanic outburst of the twentieth century. A series of huge explosions darkened the skies that day and created a column of ash that rose 21 miles (34 kilometers) in the atmosphere. On the way down, the ash mixed with rain from a typhoon and fell across 2,500 square miles (6,475 square kilometers). Although hundreds of people died, thousands of islanders living near the volcano were evacuated.
Mount Pinatubo is just one of about 600 volcanoes throughout the world that have had known eruptions during recorded history. About 50 to 70 volcanoes erupt each year, making these giant powerhouses one of the most destructive forces on Earth. Not all of them reside in tropical climates such as the Philippines. The largest volcanic outburst of the twentieth century occurred in Alaska, near the Arctic Circle. The powerful blast from Novarupta sent 3 cubic miles (12.5 cubic kilometers) of hot, liquefied rock and ash into the air. Falling ash measured more than a foot (0.3 meters) deep in a 3,000-square-mile (7,770-square-kilometer) area, roughly the size of Delaware.
The blast felt around the world
Pinatubo's effect on Earth's atmosphere
Volcanic eruptions have consequences beyond the regions around them. They can also affect the entire planet. The Mount Pinatubo blast sent millions of tons of pollutants into the air. Air currents spread the particles around the world, causing average global temperatures to drop by roughly 1 degree Fahrenheit (0.56 degrees Celsius) for about three years. The dip in temperature was caused by the layers of volcanic particles in the atmosphere, which blocked sunlight and cooled the planet. Sulfur dioxide from the eruption also enlarged the hole in Earth's ozone layer in the Antarctic.
Some volcanic eruptions have caused crops to fail, creating famines. Volcanic blasts also can disrupt air travel. The outburst from Iceland's Eyjafjalkjokull volcano in 2010 grounded airplanes for several days as ash from the eruption swept across Europe. The volcano sits directly under the jet stream, which carried the ash into European airspace. The air travel disruption was the largest since the Second World War.
Io: The volcano capital of the solar system
These violent outbursts are not just confined to Earth. Scientists have observed volcanic eruptions on Jupiter's moon Io.
Imagine living on a world roughly the size of Earth's moon where volcanic eruptions are almost a daily part of life. Welcome to Io, the volcano capital of the solar system. More active volcanoes reside on Io than on any other world in the solar system. Io's surface is pockmarked with active volcanic craters called calderas. These hot craters thrive in a world where the average surface temperature is a frigid minus 202 degrees Fahrenheit (minus 130 degrees Celsius). The heat near the volcanoes, however, can reach 3,000 degrees Fahrenheit (1,649 degrees Celsius), hot enough to keep liquid lava flowing. But once hot sulfur dioxide ash from volcanic blasts hits the moon's surface, it turns to snow.
Io eruption: Hubble's view
The Voyager 1 spacecraft was the first observatory to discover active volcanoes on the volatile moon in 1979. Since then, astronomers have been using satellites, including NASA's Galileo spacecraft and Hubble Space Telescope, and ground-based observatories to monitor Io's turbulent, chaotic activity. The satellites spotted about 150 active volcanoes on Io. Astronomers, however, think the moon may have as many as 400 active volcanoes.
Astronomers hit the jackpot
In 2013 astronomers struck a gold mine when they witnessed three volcanoes on Io blasting material into space during a two-week period. Astronomers observed two of them on the same day in Io's southern hemisphere. Using the W.M. Keck Observatory in Hawaii, astronomers calculated that the brightest outburst produced a lava flow that was 30 feet (9 meters) thick and spanned 50 square miles (130 square kilometers) – enough to cover Manhattan Island, the heart of New York City. The other eruption produced flows covering 120 square miles (311 square kilometers). Both eruptions generated what looked like "curtains of fire" as lava blasted from long gashes in Io's crust.
Io eruptions: Gemini's view
However, the third eruption two weeks later from yet another volcano was the most dramatic. The event, captured by the Gemini North telescope and NASA's Infrared Telescope Facility, both in Hawaii, was brighter than the previous two eruptions and hotter than any volcanic eruption seen today on Earth. Astronomers compared the outburst to the destructive eruptions on our planet when it was young.
A violent past
Mercury: Messenger's view
In fact, the rocky planets — those planets closest to the sun — and many moons in our solar system show evidence of past volcanic activity. Mercury contains ash deposits. Mars is home to many extinct volcanoes, including Olympus Mons, the largest volcano in our solar system. These features formed millions of years ago when our solar system was much younger and its objects were much hotter.
Many recipes for volcanic eruptions
Although volcanoes are plentiful in the solar system, the forces that produce them vary.
On Earth, the continents that make up our planet are part of massive "tectonic plates" located beneath our planet's surface. These plates are always in motion, and volcanoes typically form where they collide or spread apart. Volcanoes can also occur at a "hot spot" in the middle of a plate. Volcanoes form when liquid rock, called magma, from within the Earth travels up to the surface. At the surface, the liquid rock erupts to form lava flows and ash deposits. The volcano continues to grow, getting bigger over time, as it continues to erupt.
Io: The big squeeze
On Io, the volcanic activity is driven by Jupiter's powerful tidal forces of gravity, which squeeze the moon's interior and heat it up. Like Earth's volcanoes, molten rock is then forced through Io's surface, erupting as volcanoes. In fact, Io is the only place in the solar system, other than Earth, where active volcanoes have been observed ejecting extremely hot lava.
Io, however, has a lower surface gravity than Earth. So material can leave Io's surface more easily and travel far into space. For that reason, many Io eruptions can blast debris high above the moon. One such eruption shot plumes of material more than 300 miles (483 kilometers) high, forming a huge umbrella of hot material.
Mars: Land of the giant volcanoes
Olympus Mons on Mars
The volcanoes on Mars were active long ago and are now extinct. These dead volcanoes, however, are much larger than any volcano on Earth. For example, Mars' Olympus Mons, the largest volcano in the solar system, is up to 100 times larger than Mauna Loa, Earth's biggest active volcano. In fact, the entire chain of Hawaiian Islands (from Kauai to Hawaii) would fit inside Olympus Mons.
One reason for the Martian volcanoes' monstrous size is that Mars does not have tectonic plates beneath its surface that move the way they do on Earth. On our planet, as a plate drifts over a hot spot of magma, a new volcano forms. As the plate moves away, the volcano is separated from the magma, stops growing, and becomes extinct. The hot magma, however, finds another place in the surface to break through, and another volcano is formed. This process continues, creating a chain of volcanoes, like those that formed the Hawaiian Islands. Instead of building one large volcano, the erupting lava forms many smaller volcanoes.
Olympus Mons close-up: From Viking 1 Orbiter
The surface on Mars, however, remains stationary over a hot spot of magma, and the erupting lava piles up in one place, making one giant volcano. Olympus Mons spans 374 miles (602 kilometers) across at its base and reaches an elevation of 16 miles (26 kilometers), more than twice as tall as Mauna Kea, a dormant volcano in Hawaii that is Earth's tallest mountain as measured from its base, deep in the Pacific Ocean, to its peak.
Like Io, Mars also has a lower surface gravity than Earth, which helped to produce tremendous eruptions long ago. The lava flows on Mars also lasted longer – many weeks – and were more widespread, than those on our planet. Observations have captured a vast lava flow the size of the state of Oregon on Mars' surface. In fact, volcanic features cover most of the planet's surface. The Martian volcanoes are extinct because the planet's core has cooled. The volcanoes, therefore, have no heat to power them.
Shaping our solar system
Volcanic activity has helped shape the landscape of Io and our other solar system neighbors. Spacecraft that have flown by Io since 1979 have observed numerous surface changes as a result of Io's volcanic activity. Material launched by eruptions create large lava flows and paint the surrounding surface of Io in shades of yellow, red, white, black, and green. The volcanic material also is found in Io's patchy atmosphere. The smooth plains are dotted with tall mountains, some rising higher than Mount Everest in Nepal, one of the tallest mountains on Earth. Unlike other solar system worlds, Io does not have any craters from asteroid impacts. Scientists think that new impact craters are buried by the frequent flow of volcanic material.
Volcanoes are a tremendous force of nature, but thanks to ground-based observatories, space telescopes, and Earth-observing satellites, scientists have a better understanding of the impact of volcanoes on Earth and on our solar system neighbors.
Scientists use satellite observations to keep vigil on volcanoes all over our world. With their perspective from space, satellites have a unique view of changes to Earth's surface and atmosphere. Their heat-sensitive detectors, for example, reveal when and where lava appears, and help scientists predict where the lava will flow – alerting people to evacuate when a volcano awakens near towns and cities. Using satellites to track the ash spewed by Iceland's Eyjafjalkjokull volcano in 2010, scientists mapped the location of the ash in the sky, keeping planes and passengers out of harm's way.
Satellite data also have helped researchers develop new techniques for monitoring eruptions. Scientists, for example, used instruments and techniques developed by studying the eruptions of Mount St. Helens in Washington and other volcanoes in the 1980s to accurately predict the Mount Pinatubo outburst. By forecasting the impending eruption, scientists warned people living in the volcano's shadow to move to safety, which saved thousands of lives.
Although our solar system neighbors are far away, astronomers are using space-based and ground-based observatories to monitor geologic activity produced by active volcanoes on these nearby worlds.
From death to life
Twenty-five years later: Crater lake forms
The saying "time heals all wounds" is certainly true regarding the destructive power of volcanic eruptions on Earth. Falling ash, flowing lava, mudslides, and deadly gases create a wasteland around the erupting volcano, wiping out towns, tearing apart highways, and killing wildlife and vegetation. In time, however, life begins to take hold again. Mount Pinatubo, for example, is green again 25 years after the huge eruption, and its volcanic crater has become a lake. More than 3,000 tourists a year climb the volcano and enjoy the beautiful view or swim in the lake. In Hawaii, coffee plantations thrive in the rich soil produced by lava flows from the Mauna Loa volcano.