Using an electronic distance meter to measure deformation of Mauna Loa Volcano, Hawai`i
Mauna Loa: A Caldera Widens
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.
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.
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.