Ground Deformation

The Island Today

The deformation of the surface of the Earth reflects the processes happening at depth. Methods such as GPS (Global Positioning System) or EDM (Electronic Density Measurement) can measure small displacements of the surface, for example along faults before and after an earthquake, or even of entire tectonic plates. GPS and EDM are also used to monitor the change of shape of volcanoes, for example if their surface bulges or deflates, giving an indication of magma movements within the crust.

Electronic Distances Measurement (EDM) instruments emit beams of infrared light which is reflected by a prism or target on the volcano. Because the speed of the light beams is known, the distance to the target can be measured very precisely. Credit: MVO Archive.

This global positioning system (GPS) instrument receives continuous signals from several satellites, to calculate very precisely (~1cm error) its position and how it varies with time. Credit: MVO Archive