Mauna Loa still showing signs of unrest but slowing down of late

  • Aerial view of Mauna Loa erupting on the morning of March 25, 1984, the first day of the volcano’s most recent eruption. The lava flow was advancing southeast, toward Kilauea, from fissure vents at an elevation of about 11,200 feet on Mauna Loa’s Northeast Rift Zone. Mokuaweoweo, Mauna Loa’s summit caldera, is visible at top left. (USGS photo by P.W. Lipman)
  • USGS Hawaiian Volcano Observatory Geologist Frank Trusdell gives an update on Mauna Loa at Thursday evening's West Hawaii Community Forum at the West Hawaii Civic Center. (Laura Ruminski/West Hawaii Today)
  • The 1984 Mauna Loa flow is seen from the Hilo National Guard station. (HVO/USGS/Special to West Hawaii Today)
  • An erupting fissure on Mauna Loa's Northeast Rift Zone is seen March 25, 1984. (USGS/Special to West Hawaii Today)
  • Simplified map of historical lava flows at Mauna Loa volcano from USGS-HVO. (USGS/Special to West Hawaii Today)
  • On March 25, 1984, at 6:20 p.m., ‘a‘ā lava flows from vents near Pu’u Ha’a. (USGS/Special to West Hawaii Today

  • IMG0082 - March 26; lava erupts from the main vents on ML’s northeast rift zone; referred to as the 2,900-m (9,500 ft) vents, they were 19 km (12 miles) east of the original outbreak point that began within Moku`aweoweo caldera about 36 hours earlier.
  • Residents peruse charts pertaining to Mauna Loa provided by the USGS Hawaiian Volcano Observatory at Thursday evening's West Hawaii Community Forum at the West Hawaii Civic Center. (Laura Ruminski/West Hawaii Today)
  • USGS Hawaiian Volcano Observatory Geologist Frank Trusdell gives an update on Mauna Loa to a full house at Thursday evening's West Hawaii Community Forum at the West Hawaii Civic Center. (Laura Ruminski/West Hawaii Today)
  • USGS Hawaiian Volcano Observatory Geologist Frank Trusdell gives an update on Mauna Loa at Thursday evening's West Hawaii Community Forum at the West Hawaii Civic Center. (Laura Ruminski/West Hawaii Today)
  • Hawaii County Civil Defense Director Talmadge Magno outlines the agency plan in case of a lava flow at Thursday evening's West Hawaii Community Forum at the West Hawaii Civic Center. (Laura Ruminski/West Hawaii Today)
  • HELCO President Jay Ignacio talks about the electric company's plans in case of a lava flow at Thursday evening's West Hawaii Community Forum at the West Hawaii Civic Center. (Laura Ruminski/West Hawaii Today)
  • HELCO President Jay Ignacio talks about the electric company's plans in case of a lava flow at Thursday evening's West Hawaii Community Forum at the West Hawaii Civic Center. (Laura Ruminski/West Hawaii Today)

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.

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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.

All of Mauna Loa’s eruptions have commenced at the summit, with about 48 percent staying within the caldera. Outside the caldera, an estimated 24 percent occurred along the Northeast Rift Zone and 21 percent occurred along the Southwest Rift Zone, according to Trusdell.

Six percent — or three eruptions — have occurred from radial vents on the volcano’s north, northwestern and western flanks. In 1877, an eruption started at the summit phase, migrated to a radial vent near Kealakekua Bay resulting in reports of “floating rocks that were too hot to carry,” discolored water and sulfur gases. In 1859, an eruption on the northwest flank sent lava all the way to Kiholo Bay in just eight days.

“That black pahoehoe flow where everybody likes to go swimming in the lagoon that’s a Mauna Loa flow from 11,000 feet up on the mountain,” Trusdell told attendees.

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.

For Mauna Loa’s most recent eruptions, scientists were able to provide warning that lava would break the surface of the volcano to the tune of about 30 minutes in 1975 and about an hour in 1984.

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.”

Magno covered the various means Civil Defense has to communicate an emergency to the public, including the mass notification system used in the false missile alert on Jan. 13, radio messages, warning sirens, Nixle, Blackboard and recorded messages to land lines in areas where demographics and connectivity may be an issue in spreading the word.

Weeks stressed practicing evacuating and keeping a three-day “Go Kit” and a two-week “Shelter in Place Kit” packed and ready to go.

Ignacio reassured the company’s 86,000 customers that it is prepared should Mauna Loa erupt and that HELCO will keep electricity on as long as possible, so long as it is “prudent,” he said.

His biggest concern about a Mauna Loa flow is damage to the island’s four basic transmission lines that carry electricity from east to west with one each along the island’s northern and southern coasts and two through the Saddle between Mauna Loa and Maunakea. Should more than one line be damaged by a flow “there may be a situation where we may not have enough power” and HELCO would have to work with agencies like Civil Defense to manage where electricity goes.

“I think the biggest threat to our power grid would be for a lava flow to impact the Saddle,” he said.

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HELCO has also been working on improving lava barriers for its poles after an attempt during the 2014 Kilauea lava flow was unsuccessful when after three days of being surrounded by lava, the wooden pole dropped and burned.

“It was a delay tactic, but it didn’t fully succeed in protecting the pole,” he said. To do that, they’ve replaced the wooden pole with a steel one and used the same barrier. “We are pretty sure our combination of the barrier and steel will actually work.”