What likely effect will a volcanic eruption have on a nearby city of
approximately one million people?
David Leavy
Dear David,
The effect an eruption will have on a nearby city could vary from none at
all to catastrophic. For example, atmospheric conditions might carry ash
away from the city or topography might direct lahars and pyroclastic
flows to unpopulated areas. In contrast, under certain atmospheric,
eruption and/or topographic conditions, lahars, pyroclastic flows, and/or
ash fall could enter the city causing death and destruction.
Your scenario brings up several interesting problems. How do you
evacuate a large population if there is little warning before the
eruption? Where do these people go? If an eruption is highly likely yet
hasn't happened yet how long can people be kept away from their homes and
businesses?
I should point out that in most volcanic crises geologists advise local
civil defense authorities. The civil defense authorities decide what to
do concerning evacuations, etc.
The IAVCEI has a program to promote research on "Decade" Volcanoes.
Decade volcanoes are likely to erupt in the near future and are near
large population centers. Mount Rainier in Washington and Mauna Loa in
Hawaii are two Decade volcanoes in the U.S. Other Decade volcanoes
include Santa Maria, Stromboli, Pinatubo, and Unzen.
If you have a specific volcano in mind, send another question and I'll
see what I can find.
Steve Mattox, University of North Dakota
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