Earthquakes are associated with volcanic eruptions. Abrupt increases in
earthquake activity heralded eruptions at Mount St. Helens, Washington;
Mount Spurr and Redoubt Volcano, Alaska; and Kilauea and Mauna Loa,
Hawaii. The location and movement of swarms of tremors indicate the
movement of magma through the volcano. Continuous records of seismic and
tiltmeter (a device that measures ground tilting) data are maintained at
U.S. Geological Survey volcano observatories in Hawaii, Alaska,
California, and the Cascades, where study of these records enables
specialists to make short-range predictions of volcanic eruptions. These
warnings have been especially effective in Alaska, where the imminent
eruption of a volcano requires the rerouting of international air
traffic to enable airplanes to avoid volcanic clouds. Since 1982, at
least seven jumbo jets, carrying more than 1,500 passengers, have lost
power in the air after flying into clouds of volcanic ash. Though all
flights were able to restart their engines eventually and no lives were
lost, the aircraft suffered damages of tens of millions of dollars. As a
result of these close calls, an international team of volcanologists,
meteorologists, dispatchers, pilots, and controllers have begun to work
together to alert each other to imminent volcanic eruptions and to
detect and track volcanic ash clouds.