It’s common for plumes of steam to drift from the summit of the Kilauea volcano in Hawaii Volcanoes National Park, as hundreds of curious visitors peer onto a blackened, lava-covered land.
But rangers have now closed down most the park, as top volcanologists at the U.S. Geological Survey warn that there’s a good chance Kilauea will erupt explosively, something the volcano hasn’t done for over half a century.
For 35 years, this volcano has oozed lava from the ground, with the molten rock mostly flowing into the ocean. But after an abrupt shift in how Kilauea’s magma rises to the surface, the volcano might now be on the verge of an explosive eruption.
And scientists have a pretty good idea for why that is.
What causes a non-explosive volcano to explode?
Hawaiian volcanoes aren’t typically capable of deadly, explosive events thanks to the quality of the molten rock, or magma, that lies beneath its surface.
Unlike the exceptionally thick magma trapping a large amount of gas beneath infamous, explosive volcanoes like Mount St. Helens, Hawaiian volcanoes have less viscous magma that won’t trap as much gas within it.
Mount St. Helens’ sort of eruptions can result in massive pressure releases with ash clouds thrown miles into the air, and horrifying 1,000-degree Fahrenheit avalanches of volcanic rock, ash, and gas.
“This is not like St. Helens,” Janine Krippner, a volcanologist at Concord University’s Department of Physical Sciences, said in an interview. “This is completely different.”
On May 6, the summit lake had dropped around 220 meters (720 feet).
But something unique is still happening in Hawaii — though it’s happened before.
Specifically, the famous lava lake that sits in Hawaii Volcanoes National Park is dropping — a lot.
After overflowing for the first time in three years in April, the lava has now dropped down about 1,000 feet beneath the rim of the Halema‘uma‘u vent, also known as the “overlook crater” in the park.
After hundreds of early May earthquakes, this molten rock appears to now be taking other routes to the surface, having (as of May 14), opened up 17 confirmed lava-spewing fissures in the nearby Leilani Estates neighborhood.
A lake of lava
Like any land, Hawaii has a water table — a depth beneath the surface where rock and soil is saturated with water. And in tropical Hawaii, there’s bounties of water that collect down there.
But the lava lake may soon, if hasn’t already, drop beneath the top of the water table, allowing water to enter into the volcano’s empty pit and seep into the lava. As one might expect, this will create a lot of steam.
The problem, however, develops when this steam becomes trapped, allowing a considerable amount of pressure to build up.
As the lava lake drops, it exposes unstable rocks, which could fall in and plug up the vent, allowing steam and gas to become trapped underneath.
“This could cause an explosion,” Krippner said.
Most of the park remains closed due to the non-life-threatening anticipated steam-powered explosion at the summit of Kilauea. Kahuku Unit and Highway 11 are open as usual.
— Hawaii Volcanoes NPS (@Volcanoes_NPS) May 13, 2018
Enough rocks are already tumbling down into the lava to stir up gases and create thick plumes of steam, which astronauts can even see from space.
An eruption in 1924
That said, this isn’t the first time Kilauea has threatened to erupt explosively.
In February 1924, scientists watched the lava lake within Halema‘uma‘u drain. By May of that year, the vent began to erupt explosively.
This time around, it’s unknown when exactly the explosive eruption might happen, only that conditions are prime for another series of explosions — so it’s wise to stay away.
“When there’s hot rocks flying out at you, it’s not a good idea to be there,” Krippner said.
Kilauea erupts explosively on May 18, 1924.
The May 1924 explosive eruption lasted for two and a half weeks, launching chunks of rock weighing as much as 14 tons from the crater, along with thick columns of ash.
Similar events can be expected this time — if the explosive eruptions do actually occur.
Plumes of rocky ash are created when volcanic rocks are blown apart, and blasted rocks the size of pebbles can also be ejected into the air.
“It’s just like you put dynamite into a mine,” said Krippner.
The ash plume traveled over five miles into the sky in 1924, though where it goes and how it affects islanders is dependent on the wind.