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Rising gradually to more than 4 km (13,100 ft) above sea level, Mauna Loa is the largest active volcano on our planet.


Summary

Its long submarine flanks descend to the sea floor an additional 5 km (16,400 ft), and the sea floor in turn is depressed by Mauna Loa's great mass another 8 km (26,200 ft). This makes the volcano's summit about 17 km (55,700 ft) above its base! The enormous volcano covers half of the Island of Hawai‘i and by itself amounts to about 85 percent of the area of all the other Hawaiian Islands combined.

The Hawaiian name "Mauna Loa" means "Long Mountain." This name is apt, for the subaerial part of Mauna Loa extends for about 120 km (74 mi) from the southern tip of the island to the summit caldera and then east-northeast to the coastline near Hilo.

Mauna Loa is among Earth's most active volcanoes, having erupted 33 times since its first well-documented historical eruption in 1843. It has produced large, voluminous flows of basalt that have reached the ocean eight times since 1868. It last erupted in 1984, when a lava flow came within 7.2 km (4.5 mi) of Hilo, the largest population center on the island. Mauna Loa is certain to erupt again, and with such a propensity to produce large flows, we carefully monitor the volcano for signs of unrest.

Read our Frequently Asked Questions about Mauna Loa.

News

Date published: May 6, 2021

Volcano Watch — Tiny changes at Mauna Loa’s summit hold big clues

Although Mauna Loa is Earth’s largest active volcano, it has lived in the shadow of Kīlauea since it last erupted in 1984.  The geologic record shows that Mauna Loa erupts every seven years on average; however, 37 years have passed since lava flows from the volcano’s Northeast Rift Zone came within 7 km (4 miles) of Hilo. 

Date published: April 22, 2021

Volcano Watch — How measuring gravity on Mauna Kea helps us monitor Mauna Loa

Gravimeters, essentially extremely precise pendulums, can measure a change in the force of gravity to one-in-one billionth of the force you feel every day. This force varies based on the distance and the amount of mass between the instrument (or you) and the center of the Earth.

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