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Movement on the Surface Provides Information About the Subsurface
Deformation is created by inflation of a magma reservoir and an intrusion
Surface deformations provide important information about the internal structure and functioning of volcanoes. Each eruption is preceded by a slow swelling (inflation) of the volcano and a rapid deflation during the eruption. The primary source of deformation is magnatic.
Deformation monitoring
Changes to a volcano’s ground surface (volcano deformation) appear as swelling, sinking, or cracking, which can be caused by magma, gas, or other fluids (typically water) moving underground or by movements in the earth’s crust due to motion along faults. Often, this deformation is very small in magnitude—a few centimetres (inches) or less—and so can only be detected and monitored with very sensitive instruments.
How is deformation monitored?
The Volcano Hazard Programme installs and maintains networks of instruments around volcanoes to monitor changes in the earth’s surface over time. Ground-based measurements are made at specific points on the Earth’s surface using Global Positioning System (GPS) receivers. Large-area space-based observations are made using satellite technologies such as InSAR. By combining this data with other monitoring techniques (geological observations, earthquake and gas detection), scientists can better understand what is happening under the ground, know when a volcano is behaving out of “context” and give a warning when a volcano is showing signs of eruption.
Bulge on the north side of Mount St. Helens developed as magma pushed up within the peak before May 18, 1980. View from the northeast.
Temporary GPS stations collect data to analyze area deformation at Three Sisters, Oregon.
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