The pressure inside a volcano still cannot be measured
The United States Geological Survey (USGS) scientists have developed an early warning system for volcano eruption called the USGC Volcano Hazard Program. This program operates in conjunction with federal, state and local government agencies, as well as with the private sector, in the operation of five volcano observatories. These stations are located in the states of Alaska, Hawaii, Utah, California and Washington. Although there are potential signs of pending volcanic activity, these activities can occur weeks, month or even years before an eruption. In fact, these signs can be "false positives," meaning that the eruption may not happen at all.
Seismic Activity
Although seismic activity is a sign of potential volcanic activity, it is not a definitive sign.
Increasing seismic activity is probably the most common warning sign that a volcano is likely to erupt. One seismometer can pick up movement under a usually quiet volcano, but three or more seismometers, strategically placed, can triangulate so as to pick up magma movement, an Oregon State University report explains.
Release of Gasses
Escaping gasses and changes in ponds and plant life are potential signs of a volcanic eruption.
Most active volcanoes have fumaroles (holes in the ground near a volcano) from which gasses within the ground escape. Elevated temperatures of these gases or an increased amount of gas escaping could be signs that hot magma is migrating toward the surface. The composition of the gasses can also be analyzed with correlation spectrometers (COSPECS), but this kind of data is more difficult to interpret. Some visual indicators are nearby plants dying suddenly and changes in the color of nearby ponds or lakes.
Ground Deformation
Changes in the surface of a volcano can indicate an upcoming eruption.
As magma migrates to the surface, it pushes the surrounding rock outward, causing the surface of the volcano to deform. Tiltmeters and geodimeters can measure even subtle changes in rock formations, according to Annenberg Learner. The amount of deformation can be measured using leveling and distance-measuring techniques. These measurements can be a matter of millimeters over a distance of several hundred meters, but they can also be drastic and happen very quickly. For instance, the dome of Mt. St. Helens expanded from 16 feet high and 82 feet in diameter to 164 feet high and 606 feet in diameter in just 24 hours prior to its eruption, NASA says.
Thermal Mapping
Hot magma near the surface can indicate an eminent eruption, or it can cool beneath the surface.
Satellites can provide thermal images of areas around volcanoes. By comparing these images on a monthly or bi-weekly basis, changes in temperature can be monitored. Increases in temperature can indicate magma rising to the surface.
Emerging Technologies
Volcanologists believe that satellite technology will increase their ability to predict volcanic eruptions.
NASA has developed the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) that was launched aboard the Terra satellite in December 1999. It can provide 3D digital elevation models of volcanoes and detect hot spots, pyroclastic flows and debris flows from a volcanic dome including the temperature, texture and chemistry of the dome surface. Volcanologist Michael Ramsey, the Assistant Professor of Geology and Director of the Image Visualization and Infrared Spectroscopy Laboratory, believes that ASTER's power of observation will enable him to even examine bubbles in the lava that indicate the potential explosivity of a pending eruption and mitigate volcanic hazards.
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