Frequent quakes at Loihi no threat to island, HVO says

  • Loihi is about 19 miles off the southeastern coast of the Big Island.

An increase in seismic activity around the youngest Hawaii volcano poses no immediate danger to the Big Island, geologists report.

According to a report from the USGS Hawaiian Volcano Observatory, more than 100 earthquakes have been detected around Loihi Seamount, the underwater volcano off the southeast coast of Hawaii Island, between Monday and Tuesday mornings — a significant increase for a volcano that typically has fewer than three daily.

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Of those earthquakes, 79 were magnitude-2.0, while another 19 were magnitude-3.0 or higher. Most Loihi earthquakes fail to reach as high as magnitude-2.0.

The quakes originated at approximate depths of between 0.6 miles and 6 miles beneath the volcano’s surface, or 2.2 miles to 7.7 miles below sea level.

As of midday Tuesday, the quake rate had dropped to less than four per hour.

Tina Neal, HVO scientist-in-charge, said similar “earthquake swarms” are not uncommon in volcanically active areas, and can range in length between mere hours or months. The last recorded eruption of the volcano occurred in 1996, which preceded a nearly monthlong swarm of more than 4,000 earthquakes.

Neal said the most likely cause of the recent swarm is a subterranean movement of magmatic fluids within the volcano, although she added that they could also be caused by gas or fluid escaping from Loihi.

If the earthquakes were to become shallower, it could indicate the beginning of a submarine eruption, Neal said, which could cause summit collapses that could, in turn, cause tsunami waves to reach the island. However, she emphasized that the volcano is likely too deep under the surface to generate any noticeable impact on the Big Island.

“In 1952, there was a report of a tsunami in Kalapana,” Neal said. “But we don’t have a lot of data on an event from so long ago.”

Jackie Caplan-Auerbach, a professor at Western Washington University who has studied Loihi for decades, said its periodic earthquake swarms are “interesting, but not alarming.”

While the 1996 eruption did cause a summit collapse at Loihi — a 100-meter-high cone called Pele’s Vent collapsed into a 300-meter-deep pit — Caplan-Auerbach said that collapse was both too small and too incremental to be noticeable from the Big Island.

Caplan-Auerbach compared the collapse to the summit collapse at Kilauea’s Halemaumau Crater in 2018: In both cases, change occurred over long spans of time, with each earthquake accompanying only extremely small topographical shifts at once.

“But, even had it happened all at once, I don’t think it would have been big enough to do anything to the Big Island,” Caplan-Auerbach said. “In a relative sense, it’s too small. You think of the really damaging tsunamis, like the ones that hit Japan in 2011, and those were caused by the movement of literally thousands of kilometers (of tectonic plate) at once.

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“I think Loihi would have to split in half to create a damaging tsunami,” Caplan-Auerbach concluded. “And we don’t think that’s going to happen anytime soon.”

Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.

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