(I) When disasters occur near populated areas, they
are likely to cause death and social and economic
catastrophe. (II) Volcanologists use seismographic
devices and other instruments to monitor geophysical
signs that may indicate when a volcano is getting ready
to erupt. (III) These signals include earthquake activity
and swelling of the ground beneath the volcano.
(IV) Volcanologists can usually determine if a volcano
will produce a minor or major eruption on the basis of
the volcano’s earlier activity. (V) A larger eruption, for
example, would be preceded by a long period of
vigorous earthquakes and a change in the shape of the
volcano due to underground swelling of magma.