In 1950 Mauna Loa erupted consistently for nearly three weeks. Liquid lava poured out of a 12-mile-long fissure that opened along the Southwest Rift Zone. A 2-mile-high plume of smoke rose from the large opening. A different set of fissures then opened lower on the mountain. Lava poured out southward and westward into the ocean. The three-week total volume of lava produced by the Mauna Loa 1950 eruption was estimated at 376 million cubic meters of lava.
The most recent eruption at Mauna Loa occurred in 1984. The eruption began to spew liquid lava at the summit in the Moku'aweoweo crater. The eruption then continued beneath the summit at the upper Southwest Rift Zone and the Northeast Rift Zone as well. Large pools of lava formed flow systems, which ran down the sides of the mountain. The longest river of liquid lava covered an expansive area of 27 km. The total volume of lava produced in the 1984 eruption was estimated at 220 million cubic meters of lava.
Mauna Loa has erupted at least 39 times since 1832. However, recent years have seen a decline in Mauna Loa's volcanic activity. Prior to the current dormant phase (1984 to present), the U.S. Geological Survey estimates that Mauna Loa erupted on average at least once every six years for the past 3000 years.
Recent geological signs indicate that Mauna Loa's dormant stretch may soon be coming to an end. Between 2002 and 2005, the summit of Mauna Loa began inflating. When this happens in a shield volcano, it usually suggests that magma reservoirs within the volcano are swelling. Earthquake activity also increased beneath Mauna Loa in 2004.
