Is Hawaii’s Biggest Volcano About to Blow?

Mauna Loa, the largest active volcano on Earth, is showing signs of unrest.

Is Hawaii’s Biggest Volcano About to Blow?

Mauna Loa, Hawaii’s largest active volcano, during a quiet moment.

Photo by Anish Patel/Flickr

The soaking winds of Tropical Storm Darby stole headlines this weekend in Hawaii, but seismologists have been monitoring another potentially devastating situation: Mauna Loa, the largest active volcano on Earth, is showing signs of unrest.

Over the past few months, researchers monitoring the volcano recently have recorded up to 40 earthquakes per week—four times what had become the “usual” number of tremors. In late May, the uptick prompted scientists at the U.S. Geological Survey Hawaiian Volcano Observatory to elevate the Volcano Alert Level for Mauna Loa from the base level of “normal” to “advisory” (there are four levels in all).

Since the alert-level upgrade, Mauna Loa activity has continued between three and seven miles beneath the surface at consistent frequency. Researchers also have used GPS beacons to record changes in the magma reservoir beneath the 13,679-foot summit and upper Southwest Rift Zone.

A story in West Hawaii Today quoted officials as saying that while this increase in subterranean activity is alarming, it does not mean an eruption is imminent.

Still, particularly for those in the tourism industry, the spike is cause for concern.

When Mauna Loa last blew in 1984, it sent lava inching across Highway 11 and within 4.5 miles of Hilo, which is in the northeast and is the island’s second-largest city. Kilauea, another volcano in the southeast corner of the island (and the centerpiece of Hawaii Volcanoes National Park), has been erupting steadily since 1983, and has caused entire towns to evacuate over the years.

All told, Mauna Loa has erupted 33 times since its first documented eruption in 1843. Data from the weeks leading up to the 1984 eruption and the one before that, in 1975, show that researchers recorded about 100 earthquakes each day.

Researchers behind that study noted that, based on data from the two most recent eruptions, Mauna Loa’s next eruption, if it were to occur, likely would start at the summit (as opposed to one of the “radial vents” on the flanks of the mountain).

Frank Trusdell, a geologist with the USGS, told the local newspaper that if data suggests another eruption is imminent, scientists would have ample warning of this event and would give locals and visitors plenty of time to take evasive action.

“As we get closer, we will see characteristic signatures of volcanic tremor and earthquake swarms—those both say that the molten material is migrating,” he was quoted as saying. “At that point, when the earthquakes start building to hundreds per day, we will issue press releases and let emergency managers know that Mauna Loa looks like it’s starting to get closer to an eruption.”

For all of the latest updates about Mauna Loa, visit the official Hawaiian Volcano Observatory site run by the USGS. And if all this talk of volcanic eruptions makes you nervous about an upcoming trip to Hawaii Island, consider trip insurance, just to be safe.

Matt Villano is a writer and editor based in Healdsburg, California. To learn more about him, visit
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