Can you explain how the latest volcanic prediction of measuring
"bulges" and a consequent rise of the volcano body works?
Jo Davies
Dear Jo,
Think of blowing up a balloon. As it inflates the top of the balloon
rises higher and the distance between points increases. The same thing
happens on a volcano (except the source of inflation is a few kilometers
below the surface). Volcanologists can measure the increase in the
height of the volcano at different locations or the increase in distance
between two points on the top of the volcano. Once they have their data
they can model the size and location of the magma body and the center of
the uplift. They will compare the new information to how the volcano has
behaved in the past (if they are fortunate enough to have information on
past eruptions). For example, maximum uplift prior to many eruptions on
Kilauea is about 5-10 cm. If the volcanologist observed this much uplift
they would probably feel confident if predicting an eruption. Another
method to detect how much a volcano is bulging is called tilt. It
measures the change in the slope of the flank of the volcano. The tilt
increases as more magma moves into the summit of the volcano. If enough
magma accumulates to crack the overlying rocks there is an eruption and
then the tilt decreases as the magma is erupted (like someone letting the
air out of a balloon). Sometimes tilt can be used like a pressure
gauge. At a certain amount of tilt enough magma (and pressure) has
accumulated to trigger an eruption.
I hope this answer your question. If not, write us again.
Steve Mattox, University of North Dakota
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