Big Island recalls 'eerie' but 'nifty' Mauna Loa eruption 20 years ago

By Christie Wilson
Neighbor Island Editor

Scientists monitoring the ongoing inflation of the 13,680-foot summit of Mauna Loa paused yesterday to recall the volcano's most recent eruption 20 years ago that threatened homes and businesses in Hilo.

Frank Trusdell, a Hawaiian Volcano Observatory geologist with the U.S. Geological Survey, was a 25-year-old graduate student at the University of Hawai'i-Manoa when the eruption began March 25, 1984. He flew to the Big Island to help study the event and said he was awestruck by the massive volume of lava pouring forth from the world's largest volcano.

"When I was working around Kilauea I never felt threatened, but the Mauna Loa magma stream was so large," he said. "If the lava jumped out of the stream, it was very, very dangerous."

"On Mauna Loa, the scale of everything is much larger. It literally was a river of lava."

The eruption, which lasted until April 15, was preceded by three years of increasing seismic activity, with a marked rise in the number of earthquakes six months before lava began surging out of fissures on the mountainside, generating mile-long curtains of fountains that shot 160 feet in the air.

The earthquakes came after a period of inflation at the summit region, as magma accumulated inside the volcano.

That's exactly what has been happening at Mauna Loa since April or May 2002, when — after nearly 10 years of slight deflation — Hawaiian Volcano Observatory instruments showed the summit area was rising and the caldera widening, indicating swelling of the magma reservoir within the mountain.

Although scientists say Mauna Loa is sure to erupt again, low seismic activity suggests an eruption is not imminent.

Less than three hours before the eruption on March 24, 1984, the tremors were coming at a rate of two or three per minute. Just before 1 a.m. on March 25, the constant groundshaking increased to the point that the telescopes on Mauna Kea, 26 miles away, could not be stabilized.

"At 1:25 a.m., a military satellite recorded a strong infrared signal from the summit of Mauna Loa, indicating that the eruption was under way. Within just a few minutes, people all over Hawai'i were reporting an intense red glow above the volcano," according to the Hawaiian Volcano Observatory Web site.

Dante Carpenter, an Office of Hawaiian Affairs trustee, was driving to Ka'u with his wife that day and had stopped at the Volcano Golf Course for lunch.

"We saw the eruption on the flanks of Mauna Loa and we said, 'Wow, that's something you don't see often,' " said Carpenter, who would be elected Big Island mayor later that year. "You could see orange fingers of lava shooting up in the air.

"We'd seen Kilauea many different times but this was a new one, and we said, 'Uh-oh.' "

The eruption had begun in Moku'aweoweo, the summit caldera, and spread rapidly down the southwest rift zone. Lava flows quickly advanced downslope, and by daybreak of March 26, Kulani Prison was put on alert for possible evacuation because lava was approaching within two miles.

Meanwhile, Hilo residents anxiously watched clouds of smoke rise from burning vegetation and the intense glow at night, according to the observatory account. Loud explosions were heard, caused by methane gas along the advancing flow front.

At night from Carpenter's Hilo home, it looked as if the town would be consumed, he said. "The glow of orange filled the valley overlooking Hilo and it was like it was right on top of Hilo," he said. "That was chicken skin.

"It was eerie, spooky, but it was very nifty. We were all on pins and needles."

State Sen. Lorraine Inouye, D-1st (Hamakua, S. Hilo), said Hilo residents, who had survived tsunami and other natural disasters, took the threat of lava inundation seriously.

"We had never experienced that type of sensation on the east side (of the Big Island) in my lifetime," she said. "There was grave concern, particularly for those on the Saddle Road area and Kaumana that it could occur anywhere and cause devastation."

Families were preparing to move out and stay with relatives outside of the hazard zone, she said.

Trusdell said the flow front eventually was slowed by the more gently sloping terrain, heavy vegetation and the declining eruption. Several smaller flows that diverted lava from the main channel further stopped the advance.

On April 15, the eruption ended, with the longest flow extending to within four miles of Kaumana on the outskirts of Hilo.

Trusdell said scientists learned from both the 1984 event and a brief summit eruption that occurred July 5 and 6, 1975, that the run-up to future Mauna Loa eruptions likely will include a period of inflation and seismic activity that builds to a crescendo. The 1984 eruption also provided valuable data on the dynamics of lava flows, he said.

Reach Christie Wilson at (808) 244-4880 or cwilson@honoluluadvertiser.com.

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