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| Ground
Deformation |
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| Upward pressure from
rising magma deforms the volcano. |
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Pressure
from rising magma deforms the volcano. The ground can change shape
by rising up, subsiding, tilting, or forming bulges. Scientists monitoring
an active volcano will often measure the tilt of the slope and track
changes in the rate of swelling. An increased rate of swelling is
a sure sign of an impending event.
The newest and most accurate system of measuring ground deformation
is the Global Positioning System (GPS). This involves using a number
of satellites and radio waves. A receiver is set up close to the volcano
then data can be transmitted between satellites orbiting the earth
and the receiver. Data is obtained in just a few minutes and is extremely
accurate. |
| Another method
involves measuring tiny changes in the slope angle or "tilt"
of the ground with tiltmeters. An electronic tiltmeter is very accurate
and can detect tiny changes in the slope. Five electronic tiltmeters
record ground deformation around the flanks of the Soufrière
Hills Volcano. |
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