We recently expanded our network of continuously recording global positioning system (GPS) stations on Mauna Loa, shown on the map above. The current network can detect changes in the shape of the ground surface due to inflation of both the relatively shallow magma reservoir at the summit and a deeper magmatic system. Several of the new GPS stations are positioned to monitor the potential movement of magma into the northeast and southwest rift zones and into the area of radial vents on the northwest flank. The network is also designed to monitor stress changes in the seismically active Ka`oiki fault zone on the southeast flank.

GPS data are usually processed about 24 hours after collection using the rapid satellite orbit information distributed by the Jet Propulsion Laboratory. Final orbits are released about two weeks later and the GPS data are then re-processed. Consequently, the data on the graph for the past two weeks or so should be considered preliminary.

Plotted below are the changes in distance between stations MOKP and MLSP, located on opposite sides of Moku`aweoweo, Mauna Loa's topographic caldera, and MOKP and ELEP, located on opposite sides of  the structural caldera (beyond the outermost faults of the caldera). Over the last several decades, various surveying techniques have shown that an increase in the distance between MOKP and MLSP is a good indicator of inflation of the summit magma reservoir. In May 2002, the distance between these two stations abruptly began extending, reversing an almost decade-long trend of contraction. Survey GPS measurements of a large network of benchmarks on Mauna Loa, as well as tilt surveys at the summit, have confirmed that this extension is due to influx of magma into the summit reservoir.