Alert level raised for world’s largest active volcano

Federal officials this week upped the alert level for the world’s largest active volcano — Mauna Loa in Hawaii — which last erupted in 1984.

The US Geological Survey made the shift from “normal” to “advisory” Tuesday following a steady increase in earthquakes and ground swelling at Mauna Loa that began in March — with 50 to 75 quakes each week.

The bulging of the ground, known as deformation, indicates that magma is entering the volcano’s plumbing system.

While an eruption isn’t imminent, scientists are keeping a close eye on Mauna Loa because it’s known for “evolving very quickly” and spouting lava far distances, USGS research geophysicist Ingrid Johanson said last month.

“Lava can go from the rift down to the ocean on the west side of Mauna Loa on the order of a couple hours,” Johanson said. “The rate of the eruption is just really fast.”

“Advisory” is the second of four alert levels, which indicates that scientists have detected elevated activity or unrest. The next level, “watch,” signals heightened activity with a greater chance for eruption, or that an eruption is ongoing but poses little threat. A “warning” — which is issued when a dangerous eruption is imminent or underway — is the highest level.

Level changes are not made lightly, according to Janet Babb, a geologist and spokeswoman for the USGS.

“A lot of discussion goes into it because it has ramifications,” Babb said.

Mauna Loa has erupted 33 times since 1843 — with lava flows stretching to the south and west coast eight times, and nearing Hilo, on the east side, seven times.

The last eruption sent lava flowing within 4.5 miles of Hilo, the largest city within the Big Island.

Gas emissions from the volcano have been low and steady in recent months, which “tells us that there isn’t magma rising to very shallow depths,” according to Johanson.

And scientists would normally expect to see 50 to several hundred earthquakes each day — not per week — before an eruption occurs, USGS volcanologist and geologist Frank Trusdell said.

“It’s above background, but it isn’t the amount of earthquakes we would expect to see prior to an eruption,” he said.

Meanwhile, Mauna Loa’s smaller neighbor to the south, Kilauea, long the world’s most active volcano — stopped erupting for the first time in more than 30 years last year, following one of its largest eruptions in recorded history. Trusdell said there’s historical evidence of a “general correlation” between the two hot spots.

“If you look at the long-term eruptive history of both volcanoes, when one volcano in the past was active, it seems like the other volcano was quiet,” he said.

But “it is not as if Kilauea is stealing Mauna Loa’s volume,” he added. “It has more to do with the interaction and the buttressing of the volcanoes.”

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