© Hollyn Johnson/Tribune-HeraldMauna Loa is seen Saturday morning from West Hawaii. -
An eruption isn't imminent, and no warnings are being issued, but the towering 13,678-foot mountain is going through the same motions that it did before its 1984 and 1975 eruptions, said Wes Thelen, HVO seismologist. The activity includes faint, shallow earthquakes to the west of the summit and "deep long period" temblors 28 to 31 miles below the surface, both of which point to the intrusion of magma.
"All the signs are there that tells us that magma is moving into the shallow system," Thelen said. He said monitoring equipment, much more sophisticated than what was in place in the 1980s, is continually detecting magnitude 0.5 quakes about 4 miles below the surface in the same areas where activity was detected in the years leading up to the last eruptions. Thelen noted he is confident the small earthquakes are a recent development.
He said HVO is seeing the same type of activity "in the same place at the same depth, and that leads us to believe, even though those earthquakes are smaller, it's probably the same process that's going on as was occurring before the 1975 and 1984 eruptions."
According to HVO's website, the rate of shallow earthquakes at the summit has increased over the last few months. Earthquake activity remains elevated on the upper southwest rift zone and west flank.
The website notes that deep long period quakes occurred in 2004 and 2005 before subsiding.
The volcano is potentially more destructive than Kilauea, and can threaten a much larger territory. Roughly half of the Big Island rests on past flows from Mauna Loa, including Hilo, which was threatened in 1984.
But there might not be a reason to worry just yet.
In the past two eruptions, magnitude 3 to 5 earthquakes were recorded before magma reached the surface, Thelen said.
Temblors of such scale have not been detected.
"We really expect based on those two eruptions to see a big increase in seismicity, in earthquakes, and increased inflation before we see any activity at the surface," he said.
"Those precursors began up to a year before the eruptions actually happened. That's why we haven't done anything dramatic in terms of raising the code."
With Kilauea erupting, there's no reason to believe that it will prevent Mauna Loa from doing the same. Both can be active at the same time, as was the case in 1984, Thelen said.
"They are not obviously connected" underground, he said, though he noted it's "curious" that Mauna Loa has stayed relatively quiet over the past three decades while Kilauea has been anything but.
In the past 3,000 years, Mauna Loa has erupted on average every five to six years, Thelen said.
But that may just mean we are due.
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