Earth’s largest active volcano still breathes every few decades
Mauna Loa—“Long Mountain”—is one of five volcanoes building Hawaiʻi’s Big Island and Earth’s largest active volcano by mass and volume, though submarine Tamu Massif and Pūhāhonu outrank it overall. Its latest eruption ran from 27 November to 13 December 2022, the first since 1984.
The shield has probably been active for 700,000 years or more and likely rose above the waves roughly 400,000 years ago; certain dated samples reach 470,000 years. Pacific Plate drift over the Hawaii hotspot built the Hawaiian–Emperor chain across roughly seventy million years and 6,000 kilometres; within about 500,000 to a million years Mauna Loa will ride off the hotspot. It covers 5,271 square kilometres of land, up to 120 kilometres wide, with roughly 65,000–80,000 cubic kilometres of rock—more than half the island’s surface. Measured from its submarine base, the mountain climbs about 9,170 metres, more than Everest stands above the sea, and its weight presses the crust down roughly another 8 kilometres, giving a total relief near 17,170 metres.
Slopes rarely steepen past about twelve degrees because lava is so fluid. A magma chamber model places a 1.1-kilometre-wide reservoir about 4.7 kilometres deep near Mokuʻāweoweo’s southeastern rim. Thirty-four eruptions are well documented since written records began; 1926 and 1950 flows destroyed villages, and parts of Hilo rest on late-nineteenth-century lava. The Hawaiian Volcano Observatory has watched it since 1912; Decade Volcanoes listing flags the risk to towns. The summit caldera, Mokuʻāweoweo, measures about 6.2 by 2.5 kilometres and collapsed between 1,000 and 1,500 years ago after a big northeast-rift eruption drained the shallow reservoir beneath it.
Chemically separate from neighbouring Kīlauea despite looking like a flank bulge, Mauna Loa still shares a restless island with Mauna Kea, Hualālai, and submarine Kamaʻehuakanaloa. Mauna Loa Observatory samples the atmosphere near the summit while a solar observatory watches the Sun. Buffalo Soldiers helped cut a summit path in 1915 that researchers still use.
The two neighbours often seem to take turns: Mauna Loa was busy while Kīlauea slept from 1934 to 1952, and the pattern flipped from 1952 to 1974, though the 1984 and 2022 eruptions overlapped with Kīlauea activity.
Source: Mauna Loa
