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-- A
seismometer
(or seismograph) is a sensor that detects the
intensity of earthquakes caused by magma that is
moving. It has been around for almost 2,000 years.
The first seismograph was invented by a Chinese
scientist. It looked like a large jar with dragon
heads on every side. Each dragon had a metal ball
in its mouth, and when an earthquake struck, one of
the balls would drop into the open mouth of a toad
sculpture below. By looking at which ball dropped,
Heng (the inventor) said he could tell from which
direction the earthquake came. (Actually he
couldn't but it was a good guess!)
Luigi Palmieri
invented a seismograph in 1856 while working near
Italy's Mt. Vesuvias. He wanted a way to predict
eruptions, and knew that tremors were usually felt
before an eruption. The seismograph uses a pendulum
to record movement of the ground below it. The
squiggly lines recorded on paper by a seismograph
are called a seismogram.
-- Since magma
gives off electric currents, electric meters are
used tospot rising magma levels by measuring its
electric current. Gravimeters
can also detect flowing magma.
-- Scientists also
take temperatures and gauge gas by using a
Landsat
satellite. The satellite uses infared sensors to
detect temperatures and changes in volcanoes.
Aircraft monitors the amount of gas released from
the ground. An increase in sulfur dioxide and other
gases usually means that there could be volcanic
eruptions.
-- The
tiltmeter
is a sensor that uses a laser beam to find the
rising or lowering of magma levels by measuring
changes in ground elevation.
--
GPS(Global
Positioning System)
is a method to determine position of locations on
Earth. It uses satellites that broadcast a signal
and receivers that pick up and record the signal.
GPS uses the relationship between velocity,
distance, and time (velocity equals distance
divided by time). With GPS, the velocity is the
speed of light. Knowing the velocity and time (and
the position of the satellite) allows the distance
to be calculated. As magma moves up into a volcano
the volcano swells and distances between points on
the volcano increases (think of dots on a balloon)
and the elevation at specific points increases.
Such a change is a common occurrence prior to an
eruption.
Volcanologists use
these instruments to successfully predict eruptions
which saves many lives. Scientists are trying to
develop new ways to predict future
eruptions.
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