Hawaiian Volcano Observatory
How Hawaiian volcanoes 

Simplified inflation-deflation cycle
of magma reservoirs at Hawaiian volcanoes

Scientists use a variety of techniques to measure deformation caused by rising magma. 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. The Global Positioning System (GPS) is used to measure the position of benchmarks. In order to determine the deformation caused by an episode of inflation, scientists must install and survey the benchmarks and install tiltmeters and GPS receivers (if continuous measurements are desired) before magma moves.

Diagram of Hawaiian volcano magma reservoir and deformation-monitoring stations before inflation begins
Rising magma inflates the magma reservoir

Peak inflation

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. 

Diagram of Hawaiian volcano magma reservoir and deformation-monitoring stations as a result of inflation
Inflating magma reservoir results in deformation that is measured on the surface

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.

Eruption usually leads to deflation

The summit magma reservoir begins to deflate when magma moves laterally into a rift zone and either erupts or is stored there. At the summit, tiltmeters record tilt toward the magma reservoir, and GPS stations move toward the reservoir. Near the eruption or intrusion, however, tiltmeters record local ground inflation and GPS stations move away from the erupting vent or intrusion.

Diagram of Hawaiian volcano magma reservoir and deformation-monitoring stations as a result of deflation
Deflating magma reservoir

Case example

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Updated: 28 May 2010 (pnf)