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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.

A scientists observes a volcano crater
Clear weather allowed HVO geologists to make observations and take measurements of the water pond at Kīlauea's summit. No major changes were observed, and the water level continues to slowly rise. Note the former HVO observation tower can be seen above the geologist's helmet. 

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.

Unoccupied Aircraft System is inspected by pilot just before take off
The sampling mechanism (on blue tarp) is prepared and the Unoccupied Aircraft System (UAS) is inspected just before take off to collect water from the Halema‘uma‘u crater lake. Brightly colored flagging tape tied to a cable attached to the UAS indicated depth as the sampling tool was lowered into the water. 

USGS scientists had utilized the unique capabilities of UAS flights at Kilauea before. In fact, the 2018 eruption marked the first time the federal government used UAS to assist in an eruption response in the United States. UAS flights into hazardous areas allowed USGS scientists to provide 24/7 real-time situational awareness at the volcano’s summit and lower East Rift Zone and to safely view, document and better understand what was happening with Kīlauea's rapidly changing eruption.

After months of planning, logistics and obtaining permission from Hawai‘i Volcanoes National Park, the sampling team finally got their chance to collect water. The team, with decades of combined experience, included scientists and pilots from the Hawaiian Volcano Observatory, the Volcano Disaster Assistance Program, Hawai‘i Volcanoes National Park and the Department of the Interior‘s Office of Aviation Services. The UAS pilots flew an initial reconnaissance flight carrying only a camera to get a sense of what things looked like down in the crater and how the winds would affect flying during sampling.

HVO scientists then attached a water sampler and temperature probe to the UAS via a 30-foot cord. The UAS was also equipped with a dual thermal and color camera to detect the temperature of the lake and capture video of the mission. The pilot lifted off smoothly, with the sampler rising vertically while a scientist stabilized the sampler so it wouldn’t swing on lift off. Flagging was attached to the cord at 5-foot intervals so the pilot, who was operating through a first-person viewer on a tablet screen, and visual observers using stabilizing binoculars, could tell how deep the sampler was in the water.

The sampler, which includes a long, durable plastic sleeve with a funnel-like cone on top, stayed closed as the pilot lowered it into the water. When it was pulled back up, water flowed into the sampler through the funnel, filling the sleeve. The October sample was collected at a depth of about 8 to10 feet below the surface of the pond and was enough fill a wine bottle, or about 750 milliliters.

After sampling the water, the drone returned and hovered near the scientists waiting at the collection point. Researchers wore safety goggles, thick rubber gloves and safety smocks to make sure that if any water spilled, no one would be injured or burned by the potentially very acidic water. The sampler was stabilized, and the drone pilot released the sampling cord. Scientists were then able to process the sample into sterile containers on-site in a makeshift field lab. They were also able to determine on-site that the water had a pH of 4.2, which is mildly acidic.

Four scientists work on samples at a volcano
After a sample was collected, HVO team members transferred water from the sampling device to plastic bottles. Team members took notes, measured water pH and evaluated water temperature data for each sample collected.   

The sample was then shipped to the USGS California Volcano Observatory for advanced chemical analyses, which showed the water originated as rainwater, but hadn’t fallen directly into the lake. Rather, the rainwater had made its way below ground and then flowed as groundwater into the lake. The analysis also indicated that as suspected, there is a significant amount of SO2 being dissolved by the lake water.

Most volcanic crater lakes around the world are routinely sampled to track changes that may indicate a change in hazards and it is no different here at the Kīlauea Volcano lake. In January 2020, the team of scientists and pilots conducted a second sampling mission, making further innovative improvements to the sampling payload. While the January chemistry was similar to the October sample, HVO scientists will continue to work with the National Park Service and other cooperators to do additional sampling to monitor the chemistry and determine what it might mean for degassing and hazards at the summit. In the meantime, Kīlauea is one of the best-monitored volcanoes on Earth with an extensive network of geophysical instruments and other monitoring tools to keep an eye on any changes in the volcano’s activity.

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