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


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.


Date published: October 22, 2020

Volcano Watch — Charcoal, a game changer for understanding processes in young volcanic terraines

One of the fundamental premises of geology is that the "key to understanding the future is to understand the past."  In order to forecast how a volcano will behave, geologists must map the deposits from past eruptions and determine the ages of those deposits. Radiocarbon dating is our principal tool of use.

Date published: September 17, 2020

Volcano Watch — HVO camera network reconfiguration and upgrades coming soon!

Over the past two decades, the USGS Hawaiian Volcano Observatory (HVO) has set up a camera network system to monitor visual changes at Kīlauea and Mauna Loa volcanoes. This network was designed for the volcanic activity of the time and captured the two long-lived eruptions of Kīlauea at the summit and East Rift Zone up close.

Date published: September 8, 2020

New USGS Data Release - Campaign GPS measurements on the Island of Hawai‘i collected by the Hawaiian Volcano Observatory in 2019

The USGS has recently published a "Campaign GPS measurements on the Island of Hawai‘i collected by the Hawaiian Volcano Observatory in 2019." This data release includes all 2019 campaign survey GPS sites on Kīlauea and Mauna Loa on the Island of Hawai‘i; it also includes semi-permanent stations in Kīlauea's Middle...

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