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Volcanic Hazards

Lava fissure and flows from northeast rift zone of Manua Loa, Hawai`i, 1975
July 6, 1975

"It is profoundly significant that the Hawaiians of Ka`u did not fear or cringe before, or hate, the power and destructive violence of Mauna Loa. They took unto them this huge mountain as their mother, and measured their personal dignity and powers in terms of its majesty and drama."

Pukui and Handy, 1952

Historical Eruptions Spotlight
Potential Lava-Flow Inundation Areas

Thirty-three eruptions of Mauna Loa since 1843 have produced lava flows covering 806 km2 (310 mi2) of the Island of Hawai`i. Five eruptions generated lava flows that reached the west coast of Hawai`i and one flow poured into the sea from the southwest rift zone 15 km away in less than 3 hours! On the northeast side of the volcano, land now within the city limits of Hilo was covered by lava in 1880-81, and in 1984 a lava flow reached to within 6.5 km (4 mi) of the outskirts of the city.

Since 1984, more than $2.3 billion have been invested in new construction on the slopes of Mauna Loa, and the amount increases daily. But it is well to remember that Mauna Loa will certainly erupt again, most likely within a few years to a few decades. Areas covered by the volcano's historical lava flows are clear reminders of the general pathways that the next lava may travel--that is, down nearly any side of the volcano depending on the where the next eruption occurs.

The Next Eruption: Where Will the Lava Flow?

Based on Mauna Loa's historical eruptions and detailed geologic maps of the volcano's surface, we have identified relative lava-flow hazard zones on the volcano and throughout the island of Hawai`i. Six zones were recognized on Mauna Loa. Until the next eruption begins, however, we cannot determine with certainty which areas will be inundated by lava during the next eruption.

Lava fissure and flows from northeast rift zone of Manua Loa, Hawai`i, 1984
Photograph by R.W. Decker on March 25, 1984.
Fissure eruption and lava flows on the upper northeast rift zone of Mauna Loa about 10 hours after the start of the 1984 eruption. The eruption began from vents in the summit caldera (top) and then migrated about 10 km down the rift zone to the fissure shown here.

The high rate of eruption typical of Mauna Loa, combined with the volcano's steep slopes, means that flows can move far and fast. Hence our monitoring efforts to identify areas threatened by lava in the first few hours of the next eruption assume great importance.

Lava-Flow Directions Depend on Four Key Factors

The actual areas that will be covered by lava flows, and the warning time that can be given before lava reaches a specific area, depend on several key factors that only become apparent when an eruption begins: As shown by the1984 eruption that sent lava flows toward Hilo, scientists must monitor these factors constantly during an eruption to provide specific warnings about areas likely to be inundated and to identify areas immediately threatened by moving lava.

Summary of historical eruptions


Trusdell, F., A., 1995, Lava flow hazards and risk assessment on Mauna Loa Volcano, Hawai`i, in Rhodes, J.M., and Lockwood, J. P. (eds.), Mauna Loa revealed: structure, composition, history, and hazards: Washington D.C., American Geophysical Union Monograph 92, p. 327-336.

Pukui, K., and Handy J., 1952, The Polynesian family system in Ka`u, Hawai`i, Bishop Museum Press, Honolulu, 300 p. skip past bottom navigational bar

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Updated: 2 February, 2006 (pnf)