Travel Reference
In-Depth Information
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Volcanoes are formed over millennia as a result of the normal shifting processes of the
earth's crust. For example, when oceanic crust slides against continental crust, the
higher-density oceanic crust is pushed into a deep region of the earth known as the as-
thenosphere. This process, along with friction, melts the rocky crust to form magma,
which rises through weak areas in the continental crust due to its comparatively light
density. Magma tends to collect in a chamber below the earth's crust until increasing
pressure forces it upward through a vent and onto the surface as lava. Over time, lava de-
posits can form large, conical volcanoes with a circular crater at the apex from which
magma can escape in the form of gas, lava and ejecta.
Although our understanding of volcanoes has greatly progressed in the past few dec-
ades, scientists are still unable to predict a volcanic eruption with certainty. However, it is
possible to monitor three phenomena - seismicity, gas emissions and ground deforma-
tion - in order to predict the likelihood of a volcanic eruption. Seismicity refers to the on-
going seismic activity that tends to accompany active volcanoes. For example, most act-
ive volcanoes have continually recurring low-level seismic activity. Although patterns of
activity are difficult to interpret, generally an increase in seismic activity (which often ap-
pears as a harmonic tremor) is a sign that an eruption is likely.
Scientists also routinely monitor the composition of gas emissions as erupting magma
undergoes a pressure decrease that can produce a large quantity of volcanic gases. For
example, sulfur dioxide is one of the main components of volcanic gases, and an increas-
ing airborne amount of this compound is another sign of an impending eruption. Finally,
scientists routinely measure the tilt of slope and changes in the rate of swelling of active
volcanoes. These measurements are indicators of ground deformation, which is caused
by an increase in subterranean pressure due to large volumes of collecting magma.
Volcán Arenal is still considered by scientists to be active, despite its recent appear-
ance to the contrary, and comprehensive monitoring of the volcano occurs frequently.
Sleeping & Eating
Arenal Observatory Lodge
LODGE
d/tr/q without bathroom US$97/$112/127, with bathroom from US$133/147/176;
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