74 Years Since Mauna Loa's Big Show - The 1950 Southwest Rift Zone Eruption
Maunaloa, recognized as the largest active volcano on Earth, is a monument to the power of our Hawaiian volcanoes. It gained its immense size through its extensive history of eruptions, unlike many of the other largest mountains on the planet that acquired their size through plate tectonics. This colossal volcano has shaped its surrounding landscape through frequent and dynamic geological activity, with 34 eruptions cataloged since 1843 and countless eruptions going back several hundred thousand years, telling the story of Earth's fiery natural processes.
74 years ago today, Maunaloa was on the verge of its largest eruption in modern recorded history, the legendary 1950 eruption. Maunaloa typically erupts at its summit first before migrating to one of its two rift zones, areas of easily fractured rock that stretch for many miles from the summit through which lava is able to surface. Many separate lava fountains emerge through weak points in a line, with the result referred to as a ‘curtain of fire.’ However, the transition between eruptive phases can range from as little as a few hours to as long as a year before activity progresses. The leading edge of a lava flow down the steeper section of the Southwest Rift Zone has reached speeds as high as 6 mph, giving little time for evacuations to proceed once an eruption begins.
Following a summit eruption in early 1949, instruments detected building pressure within the volcano's magma reservoirs, signaling that further eruptions were potentially on the horizon. As the months progressed, seismic activity around Maunaloa increased, escalating with a powerful M6.4 earthquake just two days before the eruption. Then on June 1, 1950, at 9:04 PM, Maunaloa erupted spectacularly, with large fissures erupting to form a "curtain of fire" over a 12-mile span. This eruption was not only remarkable for its sheer scale but also for the speed at which it unfolded, with branches of lava that extended down the mountain all the way to the ocean in just 3.5 hours for the Honokua flow, 14 hours for the Ka'ohe flow, and 17 hours for the Ka'apuna flow.
The 1950 eruption lasted 23 days, producing 376 million cubic meters of lava, with 90% of that volume erupted in the first six days. This makes the 1950 eruption one of the most vigorous eruptions in modern times. Like most Hawaiian eruptions, no lives were lost, but the lava destroyed about two dozen buildings and cut off the only highway in three spots. However, today many more people live on the exposed slopes of Maunaloa than in 1950, and the recent 2022 eruption showed how quickly traffic can accumulate on the only highway between Captain Cook and Ocean View. For those living in the Ocean View, Miloliʻi, and Kona Palisades communities, the 1950 sequence showcases how quickly an eruption on Maunaloa can transition into large lava flows that inundate communities.
Having a plan for what to do when Maunaloa erupts next, which you share with your family, can make a real difference.
We suggest also connecting to Hawai'i County's Civil Defense Everbridge alerts ( https://member.everbridge.net/index/371914103062563#/signup ), subscribing to the updates from the USGS Hawaiian Volcano Observatory, and upping your volcano knowledge here with us at the Hawaiian Volcano Education and Resilience Institute, to help you be prepared the next time Maunaloa threatens communities.
Video credit to the USGS Hawaiian Volcano Observatory
