Monitoring the deformation of the surface of the volcano (bulging, sinking, fractures) gives information on the magmatic system architecture, and reflects movements of magma, gas or other fluids, or movements along faults, within the earth crust.

While the surface displacements can sometimes reach meters and be observed with the naked eye, they are most of the time subtle (mm – cm/year).

MVO has, since the beginning of the eruption in 1995, been using several volcano-deformation monitoring methods, including Global Navigation Satellite System, Strain, and Electronic Distance measurements.

Global Navigation Satellite System (GNSS)   

The GNSS method uses several satellites constellations (amongst which the USA’s Global Position System constellation, (GPS)) to calculate the positions of several locations on and around the volcano with a mm-cm accuracy, and how these positions change through time (ie ground deformation). MVO maintains a network of permanent GNSS stations, where data are recorded continuously and retrieved daily (or at a higher frequency if necessary), and a network of campaign GNSS stations, occupied every few weeks.

Electronic Distance Measurements (EDM)

The EDM method calculates distances and angles, measuring the return travel-time of an infra-red wave between the instrument (‘Total Station’) and a reflector. It is a relatively simple monitoring method, faster and cheaper to deploy than GNSS stations, and requiring less processing time, while still being accurate (cm). MVO surveys regularly, usually weekly, several baselines to measure the displacements of stations located relatively close to the dome. 

Strain Measurements

Strainmeters are installed in boreholes at approx. 200 m depth. They measure strain, that is the extension, compression and shearing of the crust, related in particular to pressure changes due to the magma filling the magma chamber, or moving out of the magma chamber towards the surface. Strainmeters are extremely sensitive instruments and can detect deformation – related to magmatic activity but even due to tides, passing weather front, etc.- that would not be observed by other instruments such as GNSS or EDM.

Tilt Measurements

Changes in slope angle, or tilt, can indicate magma accumulating in the magma chamber (inflation) or propagating towards the surface (deflation). Like strainmeters, tiltmeters can detect very small changes in shape of the volcano, however they often have to be installed relatively close to the volcano conduit. Because of this, MVO’s network of tiltmeters was destroyed within few years after the start of the eruption, however it did give some very valuable data, showing cycles of inflation and deflation corresponding to the rise of magma within the magmatic conduit.