Deformation (volcanology)

It can be caused by magma withdrawal (related to intrusion or eruption), volatile escape, thermal contraction, phase changes during crystallization, and tectonic extension.

This is particularly true for subglacial volcanoes, which may undergo inflation or deflation due to size variations of the overlying ice cap.

Global Position System (GPS) measurements can be used to estimate the location and amount of magma accumulating beneath the surface via both vertical and lateral movement.

Because InSAR detects deformation over broad areas, it is an excellent tool, often in conjunction with GPS, for mapping both large- and small-scale changes.

In addition to the previously stated techniques of monitoring ground deformation, varying frequencies of seismic energy may be recorded in order to infer magma movement.

Lower frequency volcanic earthquakes, a result of resonation (physical oscillation from seismic waves) in cracks due to magma movement, may also be detected by seismograms.

Summit inflation at Mauna Loa , as indicated by GPS measurements between June 2004 and April 2005.
A cryptodome developed on the north side of Mount St. Helens prior to its 1980 eruption as magma pushed up within the peak.
USGS GPS Station, The Husband, Three Sisters, Oregon.
Interferogram produced with the Italian Space Agency's (ASI) constellation of COSMO-SkyMed radar satellites over Kilauea, Hawaii, showing ground deformation after an eruption on 5 March 2011.