|PHOTO INDEX OF|
Volcanic Ash Flows
|Target Name: ||Earth's Volcanos|
|Produced by: ||International Association of Volcanology and Chemistry of Earth's Interior (IAVCEI)|
|Copyright: ||© 1995, International Association of Volcanology and Chemistry of Earth's Interior (IAVCEI)|
|Date Released: ||1995|
This video clip was taken from "Understanding Volcanic
Hazards", © 1995, International Association of Volcanology
and Chemistry of Earth's Interior (IAVCEI). The following was
extracted from the video:
In addition to clouds of ash that rise above a volcano, some explosive
eruptions produce avalanches of hot ash, rock and gas that move at high
speeds down the slopes of a volcano. Ash flows are the most destructive
type of volcanic activity. They are extremely hot and can move across
the ground as fast as several hundred kilometers per hour. Ash flows
knock down and burn everything in their path. Few living things can survive
an ash flow. The eruption of Mount St. Helens in 1980 generated an
extremely large ash flow that completely devastated an area of
600 square kilometers.
Close to Mount St. Helens forests were striped
completely from hills. Trees two meters in diameter were mowed down like
blades of grass twenty five kilometers from the volcano. Logging
equipment was tossed about like toys. Everything in the path of the
ash flow was destroyed. Cars not mangled by the ash flow were buried
with rock debris. Ash flows are difficult to observe because they are
extremely dangerous and move quickly. An ash flow cannot be outrun.
As an ash flow moves down the side of a volcano, it usually pours into
canyons and river valleys, but at the bottom of the volcano it can
spread out across the land into populated areas.
One of the most destructive ash flows this century swept through the
city of St. Pierre only seven kilometers from Mount Pele volcano. The
city was completely destroyed. Twenty nine thousand people died. The
ash flows knocked down buildings and homes. The hot ash started fires
that burned through the city for hours. Pictures of St. Pierre before and
after the eruption show its complete destruction.
Only two men survived and even they
were badly burned. The deaths caused by the eruption of Mount Pele
shocked the world and alerted people to the dangers of ash flows. But
this type of tragedy is repeated at some other volcano every few years.