Editor’s note: Over the next few weeks, West Hawaii Today will be taking a closer look at each of the volcanoes on and around Hawaii Island. This week is Mauna Loa.
You can see the imposing mass of Mauna Loa from space. It encompasses more than half of Hawaii Island, rises 13,680 feet above the Pacific, and is so heavy it depresses the ocean floor below it almost 5 miles. It’s the world’s most massive volcano that has broken the ocean’s surface, and, when measured from its true base below the seafloor, is actually 26,971 feet taller than Mount Everest.
Scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory have been monitoring activity on Mauna Loa for decades. On Sept. 17, they upgraded Mauna Loa’s Volcano Alert Level from normal to advisory for the first time in almost five years because of an increase in the number of shallow earthquakes and surface deformation on the volcano.
HVO volcanologist Frank Trusdell was present for Mauna Loa’s most recent eruption in 1984 and continues to monitor its activity.
“Since Mauna Loa last erupted, we have better monitoring capabilities and better, new equipment. It will be an exciting time if the volcano actually erupts,” he said. “Because these volcanoes (Mauna Loa and Kilauea) change fairly often compared to most volcanoes, this is the perfect laboratory to check novel techniques.”
The latest equipment on Mauna Loa includes GPS and tilt stations that indicate their precise location on Earth down to a few millimeters horizontally and a few centimeters vertically. If magma is moving below the surface of the volcano and shifting the Earth’s surface, researchers are able to triangulate the location changes between tilt and GPS stations. From there, they can begin to determine how much molten material could be accumulating within the volcano to create the motions displacing the Earth’s surface.
Readings from these stations, as well as mountainside digital seismic stations, helped to signal that magma within Mauna Loa is stirring.
“We can watch the migration of earthquakes in a vertical sense toward the surface,” said Trusdell.
This is useful because most volcanic earthquakes are below magnitude 3.0, the level where most people are able to feel them. Though tiny earthquakes can impact sensitive atmospheric equipment, Mauna Loa’s Observatory’s instruments are mostly atmospheric.
“We have some (instruments) that are sensitive to alignment, but nothing nearly as sensitive as astronomical telescopes,” said MLO station chief John Barnes. “We built a lava barrier above the observatory in 1985. It has never been tested and hopefully won’t for a long time.”
Trusdell has a theory about Mauna Loa in relation to Kilauea, the island’s other infamous active volcano.
“Just because Kilauea has been erupting a lot doesn’t mean that its stealing lava from Mauna Loa,” he said. “But, if you look at the long-term picture — the last 2,500 years or so — there is a nominal correlation that says when one is active, the other is less active.”
Trusdell explained that this could be because the two volcanoes buttress against each other. When Kilauea is erupting, it inflates away from Mauna Loa, leaving it un-buttressed. Mauna Loa then shifts to backfill that space. When Mauna Loa moves into that space, it creates more room in its magma chamber. The larger magma chamber requires more magma to fill and pressurize it.
But the recent increase in Mauna Loa’s seismic activity doesn’t mean the volcano will erupt — or that Kilauea will stop erupting.
“Between 2002 and 2005, the volcano showed similar patterns to what we’re seeing now in terms of inflation and slight earthquakes,” said Trusdell. “It raised up and then went into quiescent. It retreated from yellow (advisory) back to green (normal).”
If Mauna Loa does erupt, said Trusdell, it’s interesting to look at the precedent of historical flows.
“Forty-eight percent are summit eruptions and stay in the summit, 24 percent go down the Northeast Rift (toward Hilo), 21 percent go down the Southwest Rift (in Ka‘u), and 6 percent happen in the neighborhood of radial vents (scattered near the summit and in the Kona region).”
There’s always a possibility that lava from an erupting Mauna Loa could impact West Hawaii residents. In fact, according to a USGS slope map, if the eruption were to occur high on the volcano in the Southwest Rift Zone, lava could speed down its steep slopes and reach the ocean off Ka‘u or South Kona in as little as three hours. If an eruption were to occur high on the volcano’s northwest flank, lava could reach the waters off Waikoloa within eight days. In comparison, because of the shallower slopes on the island’s eastern side, it would take weeks to months before lava from a Northeast Rift Zone eruption would reach the Hilo area. In 1984, it took lava 22 days to reach within 4.5 miles of Hilo.
If Mauna Loa does send lava down its flanks, “The impacts could be islandwide,” said Trusdell. “People should realize that Mauna Loa is still an active volcano and should become acquainted with the hazards that the volcano poses.