Witnessing the Birth of a Crater Lake Where Lava Just Flowed


The magma mysteriously drained from the crevice last year, and now scorching pools of water are bubbling up from below.

ImageWitnessing the Birth of a Crater Lake Where Lava Just Flowed
A view of Halema‘uma‘u from the summit of Kilauea, where a bright pool of lava at the center of the crater had existed for nearly 10 years.CreditCreditC. Parcheta/U.S. Geological Survey

Last spring, Hawaii’s Kilauea volcano began its most destructive eruption in recorded history. On May 2, as its underlying magma supply headed to the mountain’s lower east rift zone, a lava lake within the Halema’uma’u summit crater that had been there for 10 years began to rapidly drain. A week later, this pool of molten fury had vanished from sight.

Now, long after the last embers of that eruption faded, the lake is being replaced by water that is likely rising from below.

A single green pool was spotted at the base of the gargantuan crater in late July. As of now, there are three pools, each growing in size and likely to coalesce. Only time will tell, but it’s possible that we are witnessing the birth of a full-blown crater lake in a pit once ravaged by fire.

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Some Hawaiian oral histories may suggest that water was present in Halema’uma’u around the year 1500, and again around 1650, says Don Swanson, scientist emeritus at the United States Geological Survey’s Hawaiian Volcano Observatory. But written observations of the summit crater only go back to 1823, so this is the first time it can be definitively said to contain water in the last couple of centuries.

The water was first spotted toward the end of July, when helicopters passing over Halema’uma’u saw a green anomaly. Some thought it might be an illusion created by sulfur minerals or algae. But an Aug. 1 flyover by scientists at the observatory confirmed a pool of water.

ImageWitnessing the Birth of a Crater Lake Where Lava Just Flowed
Water at the bottom of Halema‘uma‘u, where three small ponds have begun to merge. The pond in the foreground, the largest, is about 50 feet across.CreditM. Patrick/U.S. Geological Survey
A view of the bottom taken with a thermal camera. CreditM. Patrick/U.S. Geological Survey

Although the rocks there are now cool enough to permit liquid water to exist, they remain scorching hot. The water, acidified by escaping magmatic gas, is about 158 degrees Fahrenheit. It is flanked by several fumaroles, vents unleashing volcanic gas at temperatures as high as 392 degrees.

It may seem intuitive that an empty crater is simply filling up with rainwater, but Dr. Swanson says that’s unlikely. “We’ve had a year with a lot of rain and the pond only showed up recently,” he said.

Crucially, the crater floor, which progressively collapsed during the 2018 eruption, is now 167 feet below the water table. That means the liquid here is probably groundwater, migrating in sideways and collecting within the crater.

To confirm its provenance, the scientists will need to gather samples. If the water is old, that would suggest it had been underground for a considerable length of time and hasn’t recently fallen from the sky.

Getting those samples will require someone with a good aim, because it’s too dangerous to obtain them on foot. Scientists want to fly a helicopter over Halema’uma’u and scoop some up using a bucket attached to a 1,640-foot-long rope.

Dr. Swanson, who reported the discovery in a blog post on the Hawaiian Volcano Observatory’s website this month, explained that this crater filled with lava where the water is now pooling has come and gone in the past. From 1823, it existed until the late-1890s, when it disappeared before springing up again in the early 1900s. Then, it was present until explosions rocked the summit in 1924. It vanished yet again until 2008, after which it grew and persisted until last year.

“There are no facts about the future,” said Dr. Swanson, but there is a good chance that magma will slowly rise up the volcano’s throat, reoccupy the crater and form a new lava lake. Based on its past behavior, if it does return, it will only take a few years to do so, and the pooling water won’t last long.

“Eventually,” said Dr. Swanson, “the volcano will win the battle.”

Right now, the depth of the water isn’t known, but if it’s dozens of feet below the surface, there could be fireworks. Water and magma can make for an unpredictable, explosive mixture, and a deeper water column makes that violent interaction more likely.

Fortunately, any blasts will be confined to the summit crater itself. “There is a greater potential for explosions than we’d realized before,” Dr. Swanson said, “but this is not going to affect public safety.”

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