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Forces of the Wild
Flowers Lava A wave

Volcanic Action
To those of us who live far from these angry mountains, eruptions from volcanoes might seem like once-in-a-blue-moon natural catastrophes, affecting only the few rural farmers who favor their fertile soils. In fact, in just the last 15 years, volcanic eruptions have killed more than 29,000 people and caused billions of dollars in damage. Because more people are building homes near volcanoes, some 500 million people, by one estimate, will soon be at risk of volcanic hazards.

Lava
Lava can be hundreds of feet thick.
Even so, very few potentially deadly volcanoes are monitored for changes that could warn residents of impending disaster.

How do volcanoes harm so many people? When most people think of eruptions, they imagine a river of red lava flowing down a mountain, devouring everything in its path. Such dramatic flows are seen on the flanks of the Hawaiian volcano Kilauea in FORCES OF THE WILD. Lava flows, however, are actually the least dangerous output of an erupting volcano. They often move very slowly, allowing people to get out of their way.

Far more dangerous are explosive eruptions and their aftermath. In a pyroclastic flow, for example, hot clouds of ash, gas, and rock fragments spew forth from the mountain, rising into the air above and speeding down hillsides.

A pyroclastic flow can reach 1832 degrees F, incinerating everything in its path. Another big hazard is a lahar, which is similar to a pyroclastic flow. Lahars are essentially fast-moving mud flows; as they race down valleys, they transport huge boulders, destroy houses, and bury structures from buildings to bridges. During one eruption, a lahar filled the entire first floor of a hospital with mud. Pyroclastic flows and lahars have killed more people than any other volcanic hazards.

Also hazardous are the rock fragments that volcanoes shoot into the atmosphere. Larger fragments are known as blocks and bombs, and can travel long distances at high speed. The smaller particles, or ash, can remain in the atmosphere for months, disrupting electricity and telephone lines, damaging machinery, creating visibility and respiratory problems, and even causing airplane engines to fail. Active volcanoes also pose serious hazards from debris avalanches, landslides, tsunamis, volcanic earthquakes, gas releases, and more. It's enough to make a lava flow look almost tame.

How dangerous can volcanic events be? Here's a list of some of the deadliest volcanic eruptions in history, along with some more recent eruptions, and the numbers of people killed:

Volcano and Location
Year
Death Toll
Mount Pinatubo, Philippines
1991
350
Lake Nyos, Cameroon
1986
1,700
Nevado del Ruiz, Colombia
1985
25,000
Mount St. Helens, Washington
1980
57
Mont Pelee, Martinique
1902
30,000
Krakatau, Indonesia
1883
36,000
Tambora, Indonesia
1815
92,000
Unzen, Japan
1792
15,000
Laki, Iceland
1783
9,000
Kelut, Indonesia
1586
10,000
Mount Vesuvius, Italy
79 A.D.
3,360






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