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Areas around volcanoes are at risk from a number
of different hazards. Lava flows produced during an
eruption can flow overland or down stream valleys
and destroy everything in their path. The risk areas
for lava flows are determied by the terrain - where
the land surface is flat, lava flows will spread out
over broad areas, but where the terrain is hilly the
lava flows will move down stream valleys. A study
of where lava flows have advanced during past eruptions
can provide good information of their potential future
path and travel distance. These areas can be plotted
on maps and such maps can serve as important educational
and land-use planning tools.
Lahars are mudflows produced during or after a
volcanic eruption. They are the greatest threat to
people and property around many volcanoes. If a volcanic
eruption flash melts the snowcap on a volcanic peak
the meltwater can quickly mix with ashfall debris
and soil to produce a swift- moving mudflow. Lahars
generally follow stream valleys, and can move at speeds
over 50 miles per hour. They are deadly and very destructive
and can travel over 50 miles downstream from the volcano
that produced them. Heavy rains during or following
an eruption can also produce lahars. Again, a study
of historic eruptions can reveal where past lahars
have travelled and the distance that they have reached
beyond the base of the mountain.
Ashfalls, pyroclastic flows and landslides are
additional hazards that can be shown on a volcanic
hazard map. An overview of these types of hazards
can be found at the US Geological Survey's Volcanic
Hazards website. The map above is one of many
produced by USGS for the Mount Rainier area. For more
details on the map above visit their Volcanic
Hazards from Mount Rainier webiste.
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