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Earthquake activity beneath a volcano almost always increases before an eruption because magma and volcanic gas must first force their way up through shallow underground fractures and passageways. When magma and volcanic gases or fluids move, they will either cause rocks to break or cracks to vibrate.
Magmatic gas is the driving force of volcanic eruptions. As the magma rises to lower pressure it causes the magma to expand rapidly (think agitated champagne being released from the pressure of the bottle). A primary objective in gas monitoring is to determine changes in the release of certain gases from a volcano, chiefly carbon dioxide and sulfur dioxide. Such changes can be used with other monitoring information to provide eruption warnings and to improve our understanding of how volcanoes work.
Measuring Deformation and Tilt with GPS
Volcano deformation can provide clues about what is happening deep below the surface. Two techniques used to monitor deformation include Tiltmeters and GPS. Like a carpenter’s level, an electronic tiltmeter uses a small container filled with a conducting fluid and a “bubble” to measure a change in slope. Tiltmeters measure the amount of tilt in microradians, which is the angle turned by raising one end of a beam one kilometer long the width of a dime (equivalent to 0.00006 degree!). GPS measures the distance between two points to determine if they are moving further apart, as they might if magma was entering the system.
Animations and videos are made in partnership with Earthscope, USGS, and Volcano Video & Graphics.
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