Mauna Kea has experienced more than one million small seismic tremors since 1999, but don’t worry—the volcano is just a little gassy.
A new report published in the journal Science this month presents evidence that the mountain’s frequent rumbling is the result of magma cooling deep underground, Carolyn Gramling reports for Science News. As the magma cools and crystalizes, it pushes out gas, which builds up in the free space around it. When the pressure gets to be too much, the rocks shift to release it, causing tremors about every 7 to 12 minutes.
The United States Geological Survey team collected the seismic signals by accident in 2013. Aaron Wech, a volcanologist at USGS’s Alaska Volcano Observatory, tells Science News that the team was applying an algorithm to seismic signal data from a neighboring, active volcano, Kilauea.
“We decided to apply this technique across the whole island, because why not? And then we started seeing these [signals] beneath Mauna Kea — which in itself was odd,” says Wech to Science News. The signals came from about 15 miles below the mountain. “When you see deep seismicity, there’s a temptation to assume it’s a sign of unrest. These signals can still mean magma ascent, but the point here is that doesn’t have to be your first interpretation.”
The researchers also note in their paper that signals like this might be overlooked because they are so slight that researchers require very sensitive equipment to sense them, reports Nina Pullano at Inverse.
Mauna Kea, the tallest volcano on the Big Island of Hawai’i, hasn’t erupted in about 4,500 years. The summit is respected in Hawai’ian culture as a most sacred place on the archipelago. It is considered the home of the goddess Poli’ahu and is also associated with dieties Lilinoe and Waiau, and in ancient times only chiefs and priests were allowed to the top. The dormant volcano is also the site of several observatories, and plans to build the Thirty Meter Telescope at its summit have been met with protests.
Seismic activity around a volcano is often a cause for concern. The 1991 eruption of Mount Pinatubo in the Philippines was preceded by the same kind of deep, low magnitude tremors as the volcanologists observed under Mauna Kea, per Science News. But tremors before an eruption usually come in clusters, not a consistent pattern like what’s coming from Mauna Kea.
But the USGS team’s conclusions are not set in stone. In a perspective published in Science that accompanies the research paper, University of California, Santa Barbara volcanologist Robin Matoza writes that the study is “impressive” and the results are “surprising,” and suggests that the team’s hypothesis—that the tremors are a result of cooling magma—“should be tested at other volcanoes in different tectonic settings worldwide,” reports Cosmos’ Nick Carne.
University of Southern California in Los Angeles seismologist John Vidale, who wasn’t involved with the new study, tells Science News that the small seismic signals are common among volcanoes but the signal under Mauna Kea is unusual. He isn’t convinced that the release of gas by cooling magma is the only explanation for the signals.
“I don’t think it’s proof, but it’s good evidence. They identify something that’s clearly an ongoing process that’s been happening for years at regular intervals.” he says to Science News. “There are probably several mechanisms involved.”