Geology Reference
In-Depth Information
Fiery Explosions of Molten Rock: Volcanic
Eruptions
As geologic hazards go, volcanic eruptions make for good photo ops, with fiery red lava
and large ash clouds flowing from mountaintops. The nature of a volcanic eruption and,
thus, the hazards it presents vary depending on the type of volcano and the composi-
tion of the molten rock inside. Some volcanic eruptions include slow flowing lava pour-
ing out, while others are explosive, sending massive amounts of gas, ash, and broken
rock materials miles into the air and down mountainsides.
While the lava that flows from volcanoes is extremely hot and dangerous, it
moves slowly and doesn't present an immediate danger to nearby towns. The real
hazards from volcanic eruptions are in the form of ash clouds and pyroclastic
flows. Ash clouds from volcanoes can travels for miles in the air. The ash can
block the sun, reduce visibility for drivers, and damage airplane engines. Pyroclast-
ic flows are debris flows of intensely heated rock and ash that move down moun-
tains through the valleys. Unlike flowing lava, pyroclastic flows move very quickly
(almost 450 mph) and destroy everything in their path.
And finally, volcanic eruptions can release large amounts of poisonous gases into the at-
mosphere, which endanger the health of people in nearby communities.
Melting Ice with Fire: Jokulhlaups
The Icelandic term jokulhlaup (sometimes pronounced yer-kul-hyolp ) refers to a flood
from sudden melting of a glacier. In Iceland, where glaciers cover a volcanic landscape,
small jokulhlaups often occur when the ice is heated by volcanic activity, melts, and
rushes to the sea. These “glacial outburst floods” cause all the damage associated with
massive flooding and occur with the unpredictability of a volcano.
Jokulhlaups, while first named in Iceland, are not restricted to Iceland. Any region where
glaciers form is in danger of experiencing a jokulhlaup. A jokulhlaup can occur when a
glacier that dams a lake shrinks enough that the lake water spills out suddenly. The
eruption of glacier-covered volcanoes, such as Mount Rainier, Washington, would result
in jokulhlaup-type flooding, as well as debris flows from the combination of meltwater
and volcanic debris produced during the eruption.
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