This month marks the second anniversary of the largest rift zone eruption and summit collapse at Kīlauea Volcano in 200 years. In 2018, scientists at the U.S. Geological Survey Hawaii Volcano Observatory monitored more than 60 collapse events at the summit that caused the floor of Halema‘uma‘u crater to drop about 1600 feet, or more than five times the height of the Statue of Liberty.
In July 2019, yet another change occurred at the summit—water was seen at the bottom of the crater. Kilauea Crater, in which Halema`uma`u is located, is a sacred place in Hawaiian culture. Inquiries into oral histories of the volcano, however, found no mention of past water bodies forming for long periods in the crater.
The pond, now more properly called a lake, has been present for 9 months, with the water level slowly rising about 3 feet per week. Today, it is larger than five football fields combined, and the total depth is about 100 feet. It has a yellowish color that is not uniform over the surface. Some patches near the edges are a clear green, presumed to be places where fresher groundwater flows into the lake. Other patches are variable shades of rusty brownish-orange, likely due to the presence of iron sulfate minerals in the water. Another common feature is steam rising off the water’s surface, a testament to the fact the lake is scalding hot, roughly 160 degrees Fahrenheit, as measured by a thermal camera.
Initially, USGS scientists weren’t sure if the water was ponded rainwater or groundwater, so scientists needed a sample to chemically determine where the water was coming from. They also needed chemical analysis to help determine the total amount of sulfur dioxide (SO2) being released from the magma below the lake. The amount of SO2 emitted by a volcano can indicate how active a volcano is or how active it might become. Normally, such measurements only quantify the sulfur released to the atmosphere. However, SO2 is easily dissolved in water, so the new water pond could have been absorbing, or ‘hiding,’ a significant portion of the volcano’s released sulfur in the form of dissolved sulfur (e.g. sulfuric acid or sulfate).
For the first few months after the pond formed, scientists were unable to conduct important chemical measurements and were limited to remote observations of the lake’s size, color and surface temperature. Access to the pond more than 1500 feet below the crater rim was impossible on foot and considered too risky by helicopter. In October 2019, following the tradition of innovative field methods started by HVO founder Dr. Thomas A. Jaggar, researchers brought in Unoccupied Aircraft Systems (UAS) to collect samples deep within Kīlauea’s collapsed summit crater.