Current Activity | update | gps | seismicity | long-term monitoring data

We maintain several continuously recording electronic tiltmeters on Mauna Loa. The graph below shows two components of tilt recorded at MLO over the last month. Positive changes on the plot indicate tilting of the ground at the tiltmeter site toward the north and east. The tiltmeter is located northwest of the summit magma chamber, so tilt toward the northwest would indicate inflation of the magma reservoir. Electronic tiltmeters are highly sensitive instruments designed to detect minute changes in a volcano's shape. Unfortunately, this sensitivity makes electronic tiltmeters respond to signals that have nothing to do with volcanic processes -- temperature, for example. As the ground heats and cools it deforms slightly, resulting in a measurable tilt. Consequently, the tilt record contains a diurnal signal corresponding to the daily temperature fluctuations, and an annual signal corresponding to seasonal temperature changes. This makes tiltmeters less useful than GPS receivers for tracking relatively slow, long-lived processes. Rather, tiltmeters excel at imaging fast, short-term events in real-time, giving us the earliest possible warning of changes that could lead to eruption.

For more information on how electronic tiltmeters help monitor the deformation of Mauna Loa and Kilauea volcanoes, see a summary of the inflation-deflation of summit magma chambers.

Following a swarm of deep earthquakes centered just south of the caldera in late April 2002, seismicity was at a barely elevated level until July 2004, far lower than those of the months prior to the 1975 and 1984 eruptions. Starting in July 2004, however, a swarm of small (magnitude less than 3), deep (>40 km), long-period earthquakes occurred below the southern part of the caldera and adjacent areas. This swarm appeared to be over by the end of December 2004. Deep long-period earthquakes continue but at a much lower rate. Note that the date of the earthquake plot below may not be today's date. The plot date reflects that of the last earthquake plotted and not the date of the plot itself. If no earthquakes occur within this mapped area, that plot date won't change until another earthquake is plotted.