Water Has Appeared at the Bottom of a Crater in Hawaii's Kīlauea Volcano and Scientists Don't Know Why

An unusual pool of water has appeared in the Halema'uma'u crater of Hawaii's Kīlauea volcano, scientists have announced. The water was first spotted at the end of July, with an aerial image showing a "green pond" at the bottom of the crater that was estimated to be about the size of a pickup truck.

The image was intriguing as there are no written observations of water inside the volcano: "The presence of a pond would be unusual," Don Swanson, Hawaii Volcano Observatory scientist emeritus, explained in a statement.

Halema'uma'u is one of the most active craters within the caldera of Kīlauea volcano—the most active of the five volcanoes that make up the islands of Hawaii.

After the first image was sent in, a helicopter collecting data on Kīlauea took another picture of the pond to try to confirm the initial observation. This showed a "smooth green patch looked like water" but the team onboard did not see a reflection—a key indicator that would strongly suggest it was a pool of water.

green pond volcano
The green pond as seen on July 25 (left) and an observational flight on August 1 (right). Ron Chapelle, Quantum Spatial/S. Conway.

A third image taken from high altitude also showed the mystery green pond, but scientists were still unable to confirm the presence of water. "Another possibility is that the smooth, green color comes from a flat surface underlain by ash or rock-fall dust blown from the wall of Halema'uma'u and trapped in the bottom of the crater," Swanson said. "The green color could result from sulfur minerals or algae. A weak point of this idea is that large rocks adjacent to the supposed pond are not coated with ash, much less green ash."

On August 1, scientists with the HVO flew over the crater to see the pond for themselves. On this trip they saw reflections on the surface, showing it was water. They also found the pond had "clearly enlarged" in the week between their visit and the initial aerial photo.

The pond sits in an extremely inaccessible spot deep inside the volcano and it cannot be seen from most of the rim. Scientists with the HVO are now attempting to get more observations and to install a camera to monitor the new pond.

Swanson said the next question will be to work out the source of the water. "Until we better understand where the water is coming from, it's impossible to understand its significance," he wrote. "At this time, there is no reason to think hazards at the summit have increased or decreased because of the presence of water."

Halema‘uma‘u crater, which is part of the larger Kīlauea Volcano. USGS Hawaiian Volcano Observatory