HVO's network of continuously recording Global Positioning System (GPS) stations, electronic tiltmeters, and strainmeters located on Mauna Loa are shown on the map below. These instruments detect changes in the shape of the volcano due to inflation of the relatively shallow summit magma reservoir and/or the deeper magmatic system.
Mauna Loa Monitoring Network
Global Positioning System (GPS)
Continuously recording GPS stations on Mauna Loa, shown on the map above, are positioned to monitor accumulation of magma beneath Mauna Loa's summit, as well as the potential movement of magma into the volcano's northeast and southwest rift zones, and into radial vents on its northwest flank.
Plotted in the graph below are changes in distance between two GPS stations—labeled MOKP and MLSP—that are located on opposite sides of Moku`aweoweo, Mauna Loa's summit caldera. Over the last several decades, various surveying techniques have shown that an increase in distance between MOKP and MLSP is a good indicator of inflation of the volcano's summit magma reservoir.
In May 2002, the distance between MOKP and MLSP abruptly began to lengthen. This extension reversed an almost decade-long trend of contraction on Mauna Loa. GPS measurements, as well as tilt surveys, confirmed that the extension was due to influx of magma into the summit reservoir.
The continued extension of the distance between MOKP and MLSP is a clear indication that Mauna Loa is slowly inflating.
GPS data for MOKP-MLSP over the past two years. Since 2009, the distance between MOKP and MLSP stations has decreased, as shown by the downward trend on this graph. Note: Data shown for the past two weeks are generally subject to greater error than older data.
For more information on how GPS is used to monitor deformation of Mauna Loa and Kilauea volcanoes, see the explanation for inflation-deflation cycles of summit magma chambers in How Hawaiian Volcanoes Work.
HVO maintains a network of continuously recording electronic tiltmeters on Mauna Loa (see Monitoring Network map above). Tiltmeters are highly sensitive instruments designed to detect minuscule changes in slope on the surface of the volcano. Unfortunately, their great sensitivity causes electronic tiltmeters to also respond to signals that have nothing to do with volcanic processes.
For example, as the ground heats and cools, it deforms slightly, which results in measurable tilt. Consequently, tilt records contain diurnal signals corresponding to daily temperature fluctuations, as well as annual signals corresponding to seasonal temperature changes. Tiltmeters can also be affected by rainfall, so rain gauges are commonly located with them to help determine when a tilt change is so affected.
Although electronic tiltmeters are less useful than GPS receivers for tracking relatively slow, long-lived processes, they excel at imaging fast, short-term events in real time and providing the earliest possible warning of changes that could lead to an eruption.
The graph below shows two components of tilt recorded at MOK, an electronic tiltmeter on the northwest edge of Moku`aweoweo, Mauna Loa's summit caldera. Positive changes on the plot indicate an increase in slope down toward the north and east, respectively.
Tilt data for MOK over the past two months. Tilt shown by the two components is sometimes related to changes in ground temperature at this high elevation (4,000 m) station. HVO scientists watch for abrupt departures from seasonal trends, which may indicate volcanic tilt.
For more information on how electronic tiltmeters help monitor deformation of Mauna Loa and Kilauea volcanoes, see the explanation for inflation-deflation cycles of summit magma chambers in How Hawaiian Volcanoes Work.
Earthquake activity almost always increases before an eruption, so HVO has established a seismic network to monitor Hawai`i's active volcanoes, including Mauna Loa.
Most volcanic earthquakes are small (magnitude less than 3) and shallow (depth less than 10 km). However, in July 2004, a swarm of deep (more than 40 km) earthquakes occurred south of Moku`aweoweo, Mauna Loa's summit caldera. This unprecedented swarm ended in December 2004.
Since 2005, Mauna Loa's seismicity has remained near background levels, with an average of two earthquakes per month.
The plot below shows the location, depth, and magnitude of earthquakes beneath Mauna Loa that occurred in the last two weeks. For more information, please go to HVO's map of recent earthquakes in Hawai`i.