Pele slipping upslope to Mauna Loa, pumping magma, USGS raises caution level yellow

Peleʻs Kilauea home Halema`uma`u. Credit: USGS

Is Madame Pele shifting residences, slipping upslope from her Kīlauea playground to her mountain palace at Mauna Loa?

It seems that way because thatʻs where sheʻs rumbling now.

After last yearʻs dramatic destruction on Kīlaueaʻs East Rift Zone, destroying homes by the hundreds and forests by the thousands of acres, Kīlauea has been quiet. That quietness, according to the USGS Volcano Hazards Program, has now continued for some months.

What of the other Hawaiian active volcanoes?

Haleakala remains quiet, as well. Hualalai too. Mauna Kea, which hasnʻt erupted in 4,600 years, shudders now and then, but mainly remains serenely calm. Lo`ihi, the undersea volcano building off the Hawai`i Island coast, shakes occasionally, but doesnʻt appear ready to erupt.

But seismic observations indicate thereʻs new activity now under massive Mauna Loa—the biggest active volcano on the planet. Not that itʻs ready to release raw lava in the short term. But right now, it is the most active of the Hawaiian volcanoes.

Magma—the term for molten rock underground—is moving. The volcano stores magma in different places, and one of them is a fairly shallow reservoir beneath the summit. Earthquake activity around that reservoir indicates that thereʻs movement in that region.

The Hawaiian Volcano Observatory uses a range of equipment to take, as it were, Peleʻs pulse. There are seismic monitors, and tilt meters, and even satellite measurements. You can see the observatoryʻs reporting on Mauna Loa here.

So far, the geologists are using very careful language, clearly intending to inform but not alarm.

"For the past several months, earthquake and ground deformation rates at Mauna Loa Volcano have exceeded long term background levels. An eruption is not imminent and current rates are not cause for alarm. However, they do indicate changes in the shallow magma storage system at Mauna Loa," the observatory reports.

It has upped Mauna Loaʻs alert level from placid green to cautious yellow. That means thereʻs stuff going on but the experts donʻt think an eruption is imminent. For perspective, the next two levels would be orange (eruption possible in as little as two weeks) and red (eruption likely within 24 hours.)

Weʻre nowhere near those more fiery color levels, but again, thereʻs something going on. It started with a significant earthquake "swarm" in October 2018. Since then, quake level and the actual swelling and shrinking of the mountain have been above background levels.

Theyʻre not yet a big deal, but this is the kind of activity that has led to eruptions in the past.

"Seismic stations have recorded an average of at least 50 shallow, small-magnitude earthquakes per week beneath Mauna Loa's summit, upper Southwest Rift Zone, and upper west flank. This compares to a rate of fewer than 20 per week in the first half of 2018. 

Shallow earthquakes are occurring in locations similar to those that preceded Mauna Loa's most recent eruptions in 1975 and 1984," the observatory wrote.

The near-surface magma storage area seems to be inflating, filling with molten rock, they say. That said, the volcano has had similar activity twice since 2000, without an eruption...so this is not a countdown.

"As has happened before, it is possible that current low-level unrest will continue and vary in intensity for many months, or even years without an eruption. It is also possible that the current unrest is an early precursor to an eventual eruption. At this time, we cannot determine which of these possibilities is more likely," the observatory reported.

If an eruption nears, there should be plenty of warning signs: "These signs could include further increases in rates of earthquakes and ground deformation, increases in the sizes of earthquakes, an increase in surface temperatures, or an increase in visible steam plumes or sulfur dioxide emissions."

Mauna Loa erupted 33 times since 1843. That works out to once every five years, although some of those were quite small. Among larger eruptions—ones whose lava covered 10 square kilometers or more, there were 16—one every 11 years.

The last eruption was in 1984, meaning itʻs been 35 years without a Mauna Loa eruption.

Kīlauea was erupting during much of Mauna Loaʻs recent quiet period. For many years, some scientists argued that a connection between the volcanoes prevented one from erupting while another was spewing lava. You can still see this information on websites, but the 1984 double eruption proved this wrong. Hereʻs a New York Times storyon that. 

© Jan TenBruggencate 2019