The following is an example illustrating how deformation during a simplified inflation-deflation cycle of a magma reservoir is measured using tiltmeters and GPS stations. Inflation begins Inflation begins as magma rises into the summit reservoir. Tiltmeters measure changes in slope of the ground. As the magma reservoir becomes inflated, the ground around it cracks to accommodate its increasing volume.
Many small earthquakes occur in the area surrounding the magma as the rocks break.
As the surface of the volcano changes shape, tiltmeters record tiny changes in slope, distances increase between benchmarks on opposite sides of the caldera, and elevations of the stations increase. In order to correctly interpret tiltmeter data, it is important to note the location of the tiltmeter in relation to the magma reservoir. For example, on Mauna Loa, tiltmeter station MOK is northwest of the summit magma chamber. A tilt to the northwest recorded at this station is, therefore, a tilt away from the magma chamber and is usually indicative of magma reservoir inflation. However, if the same tilt were recorded at a tiltmeter located on the southeast side of the magma chamber, this would be a tilt toward the magma chamber, indicating a deflation of the magma reservoir.