Volcanic Landforms

Volcanic Hazards and Episodes

Volcanic activity and the landscape that results is a natural, and rejuvenating process. It's only when humans seek to inhabit these precarious situations that they become a "hazard". Over human history, volcanoes and human beings have maintained a deadly relationship with one another. Death comes swiftly from scorching lava flows, fiery clouds of poisonous gases, burial by mudflows and tsunamis following an eruption. 

Lava flows burn and bury much in their path. Humans have relatively little influence on the path that these molten rivers of rock take. When hot pyroclastic material and ash rains down and melting snowpacks, mudflows called lahars rush downslope wreaking devastation on the countryside. In 1985 the eruption of Nevada del Ruiz in Columbia created a lahar that buried 23,000 inhabitants of the valley below. Glowing avalanche clouds of noxious gases and incandescent ash stream down mountain slopes enveloping all in their deadly path. Yellowstone National Park is noted for its hot springs and geysers which reflect the active volcanic forces beneath. Much of Yellowstone resides in the caldera of a reoccurring "supervolcano" that could explode and devastate a massive region. 

Pinatubo, Philippines, 1991

On June 15, 1991 Mt. Pinatubo, a stratovolcano on the "Ring of Fire" exploded hurling two cubic miles of tephra into the air and sent a cloud of sulfur dioxide 25 miles into the stratosphere. Pyroclastic flows swept down the sides of the mountain filling valleys and extending 11 miles from the site of the eruption.

Figure 16.15 Mt. Pinatubo, first eruption
Click image to enlarge
Image courtesy USGS DDS21

Pinatubo's toll was devastating: nearly 900 dead, 42,000 homes destroyed, 100,000 acres of cropland covered in ash and billions of dollars in economic losses. Ash and dust injected into the stratosphere spread across the globe depressing global temperatures by .5^oC. [ For more see: Astronauts Photograph Mount Pinatubo, Earth Observatory, NASA]

Explore Mt. Pinatubo with Google Earth

Mt. St. Helens is a stratovolcano found in southern Washington that on May 18, 1980 erupted with a violent fury wreaking devastation over thousands of square kilometers. For weeks the volcano had been venting steam and ash for weeks. A huge bulge on the side of mountain warned scientists that a major explosion was about to occur. When Mt. St. Helens erupted, four hundred meters (1,300 feet) of  the north summit blew away. A cloud of ash, hot steam and poisonous gas raced down the side of the mountain at speeds approaching 320 km per hour (20 mph) destroying forests, lakes, and camping sites as far away as 32 kilometers (20 mi.).

Figure 16.16 Mt. St. Helens prior to eruption
Click image to enlarge
Image courtesy USGS Cascades Volcano Observatory

Huge mud flows choked streams and valleys. Hundreds of homes were buried or damaged and a thick covering of ash coated nearby cities. Sixty people and an untold numbers of animals were killed as a result of the eruption.

 
Figure 16.17 Mt. St. Helens after eruption
Click image to enlarge

Image courtesy USGS Cascades Volcano Observatory

Explore Mt. St. Helens with Google Earth

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For Citation: Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography.
2006. Date visited.  http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/title_page.html

© 2003-2011
Michael Ritter (tpeauthor@mac.com)
Last revised 10/1/09