Using an electronic distance meter to measure deformation of Mauna Loa Volcano, Hawai`i

Mauna Loa: A Caldera Widens

Mauna Loa volcano, Hawai`i

Mauna Loa: largest volcano on Earth
Photograph by J. Griggs on 10 January 1985

Northeast flank of Mauna Loa.

Mauna Loa volcano rises nearly 9 km above the ocean floor, which makes it largest volcano on Earth. It is also one of the most active volcanoes with more than 30 eruptions since its first well-documented historical eruption in 1843. More than half of the volcano is covered with lava less than 1,500 years old; almost 90 percent of the volcano is covered with lava less than 4,000 years old.

Mauna Loa summit caldera, Hawaii

Mokuaweoweo caldera, summit of Mauna Loa
Photograph by R.B. Moore on 22 November 1977

Mauna Loa summit caldera.

This view of Mauna Loa's summit caldera shows gases and steam rising from fumaroles along a fissure that erupted on July 5-6, 1975. One to two times a year, scientists from the USGS Hawaiian Volcano Observatory measure the distance between various benchmarks on opposite sides of the caldera using an electronic distance meter. The caldera is about 3 km wide (east-west) and 5 km long (north-south). View is to the north; Mauna Kea Volcano in background.

Graph of distance (in meters) across caldera between 1966 and 1985

Rising magma wedges caldera apart

The distance between two benchmarks located on the east and west rim of Mokuaweoweo increased during the 1975 and 1984 eruptions of Mauna Loa. During the onset of both eruptions (red lines), rising magma forced the caldera apart by about 50 cm. More was learned about the extension and eruption processes of Mauna Loa during this time period than in all earlier historic eruptions.

More information about Mauna Loa volcano


Lockwood, J.P., Dvorak, J.J., English, T.T., Koyanagi, R.Y., Okamura, A.T., Summers, M.L., and Tanigawa, W.R., 1987, Mauna Loa 1974-1984 -- A decade of intrusive and extrusive activity, in Decker, R.W., Wright, T.L., and Stauffer P. H., (eds.), 1987, Volcanism in Hawaii: U.S. Geological Survey Professional Paper 1350, 1667 p.