KAILUA-KONA — Mauna Loa continues to show signs of unrest, but activity at the world’s largest active volcano appears to be slowing down.
Two years ago, scientists at the Hawaiian Volcano Observatory upped the Volcano Alert Level for Mauna Loa from “normal” to “advisory” after seeing increased seismicity within the volcano and deformation across its flanks.
Today, those levels have diminished some, but not enough to reduce the alert level, said Frank Trusdell, a geologist with the U.S. Geological Survey Hawaiian Volcano Observatory with a lengthy history of studying Hawaii Island volcanoes, particularly Mauna Loa. Deformation — or ground surface changes that can indicate movement of magma within the volcano — has also shown signs of tapering off.
“That says Mauna Loa is not sleeping yet,” Trusdell told dozens of attendees of the monthly West Hawaii Forum Series presented by Community Forums Thursday night. Many came out to the meeting, which was scheduled in part in the wake of a newspaper article containing incorrect information about where lava could reach, just to get the latest update on Mauna Loa and Hualalai.
“The gentleman that explained everything is fantastic because he was doing very complicated things and explaining — not talking down to us — but making us understand. I thought it was excellent,” Edgar Frame, of Kailua-Kona, said after the presentation.
Last week, Trusdell said, 11 earthquakes were measured at Mauna Loa, which covers 51 percent of Hawaii Island. The current HVO weekly update for Mauna Loa said those earthquakes occurred at shallow depths of 8 miles or less.
“At the highest point, when we changed the level, it was about 40 earthquakes per week,” he said. Normal background levels are about one to three per week.
Prior to eruptions in 1975 and 1984, about 100 earthquakes were recorded each day. Increased activity persisted for about a year prior to the 1975 episode and 18 months before the 1984 eruption.
“We’re missing the intermediate depth earthquakes and the larger magnitudes. We have to have more consistent and persistent seismicity in order for us to feel like we should forecast the next coming eruption,” Trusdell said. “And, we should have increasing rates of deformation and seismicity.”
In all, Mauna Loa has erupted 33 times since 1843, which is when written records of volcanic eruptions began, following European contact. Over the last 3,000 years, Trusdell said, Mauna Loa has erupted once every six years. Since written records began, the volcano has erupted about once every five years.
But, 1950 marked probably one of the “most spectacular eruptions to happen from Mauna Loa,” Trusdell said, adding that the volcano put out “copious amounts of lava per unit of time.” Compared to Kilauea, the 1950 eruption put out about 1,200-1,800 meters per second versus Kilauea’s 1 meter per second.
That volume of lava erupted from Mauna Loa’s Southwest Rift Zone at nearly 10,000 feet, sent red hot rock down the volcano’s steep flanks, crossing Highway 11 in three places and reaching the South Kona shoreline where it destroyed structures. One made that trek in about three hours.
“Things can happen quickly,” Trusdell said.
Though Trusdell stressed an eruption is not imminent and it appears from data that Mauna Loa’s activity is waning, a cycle that’s been seen before, he and Hawaii County Civil Defense Director Talmadge Magno, Hawaii County Director of Red Cross Disaster Services Debbie Weeks and Hawaii Electric Light Co. President Jay Ignacio stressed during Thursdya’s meeting the importance of being prepared.
“Our mantra has been preparation for anything,” said Magno. “Whether it’s hurricanes, lava flows, tsunamis — anything that we can face on this island, we want you guys to be prepared.”