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Hawaii's Mauna Loa volcano last erupted between March 25 and April 15, 1984, following nearly two years of increased seismic activity.
The biggest active volcano on Earth, which rises 13,000 feet above sea level—has again been rumbling to life in recent weeks, entering a state of heightened unrest.
According to the most recent update from the U.S. Geological Survey (USGS), issued on October 30, there were 27 earthquakes detected below the summit and four to five miles beneath its upper-elevation northwest flank. Since mid-September, the amount of earthquakes at the volcano has increased.
The volcano is currently under a yellow advisory status. The color is a step above green, which indicates normal behavior. The next level above yellow is orange, indicating that the activity is being watched, and then it moves to red, which constitutes an active warning.
Officials are continuing to stress that the activity doesn't mean an eruption is imminent. But they are telling residents in the nearby areas to remain prepared, just in case an eruption does occur.
What Will Happen When It Next Erupts?
When the volcano next erupts, the hazard to communities on the downslope will "depend entirely" on where the eruption occurs, Scott Rowland, a volcanologist at the University of Hawaii at Manoa's Department of Earth Sciences, told Newsweek.
"Almost immediately after the 1984 eruption ended, Mauna Loa's magma storage system started to re-fill, preparing for its next eruption, whenever that will be. Since then there have been times of what appear to have been excursions of magma from deeper parts of the magma storage system into the shallower parts," Rowland said.
"These have been accompanied by increased shallow seismicity and surface deformation. So far, none of these have been voluminous enough for the magma to actually make it to the surface. Eventually that will happen and there will be an eruption. The hard part, of course, is knowing when that will happen, which volcanologists are unable to do; volcanic plumbing systems are very complex."
The good news is that Mauna Loa eruptions aren't as dangerous as those at many other volcanoes.
"Mauna Loa eruptions are not explosive eruptions like Mt. St. Helens. So generally there is no concern of the mountain top blowing off and affecting communities or burial of communities with thick piles of ash like the AD78 Mt. Vesuvius eruption," Rajeev Nair, a University of Calgary earth science professor, told Newsweek.
Nair said that the primary danger from a Mauna Loa eruption would be lava flows.
"In the case of Mauna Loa eruptions, historic lava flows originating from its two rift zones have entered Hilo, South Kona and Kau districts of the big island. So should eruptions occur on those rift zones those communities can be affected if the eruption is prolonged with significant lava flow volumes," Nair said. "Should eruptions occur in the lower SouthWest or NorthEast rift zones of Mauna Loa, the communities of Hilo and South Kona could likely come in the path of lava flows. But if the eruption is contained within the summit caldera, it should not affect the communities in a detrimental way."
Is an Eruption Likely?
Mauna Loa is one of the best monitored volcanoes in the world, but eruptions remain hard to predict.
"This is because while volcanic eruptions follow certain patterns, which of course is what scientists try to establish from a prediction point of view, those patterns can change. In the case of Hawaiian volcanoes earthquake swarms precede eruptions but not every period of earthquake swarms are followed by eruptions," Nair said.
While Mauna Loa is causing earthquake swarms such as this, Nair said a volcano can continue like this for a long period of time without an eruption happening.
This means an eruption at Mauna Loa isn't necessarily imminent.
"Scientists at the [Hawaii Volcano Observatory] have made significant strides in informing the communities during recent eruptions. The 2018 eruption of Kilauea was a case in point where the knowledge gained from long term observations of the patterns of the volcanic processes that connect the summit region and east rift zone of Kilauea was used to warn the communities in the lower East Rift zone that eruption could be on the way. But the current activity of Mauna Loa has not reached the stage where such pending eruptions can be predicted," Nair said.
About the writer
Robyn White is a Newsweek Nature Reporter based in London, UK. Her focus is reporting on wildlife, science and the ... Read more