On August 1, 2019, USGS Hawaiian Volcano Observatory (HVO) scientists confirmed a growing pond of water inside Halemʻumaʻu crater during a helicopter overflight. Similar to the monitoring of ponded lava in Halema‘uma‘u in 2008‒2018, HVO scientists now rely on both direct observations and modern tools to monitor and document any changes to the water. How Big Is It?Within the massive Halemaʻumaʻu crater, it can be hard to get a sense of scale. Though it may look small, as of October 2020, the lake is an astounding 153 feet (47 m) deep, nearly the height of a ten story building. It is approximately 430 feet (131 m) wide by 885 feet (270 m) long, with a volume of nearly 125 million gallons and growing. Where Is The Water Coming From? Why Now?Water level is rising gradually, suggesting groundwater seepage, not surface runoff. However, testing indicates that the lake water was originally rain that percolated into the subsurface where it became groundwater and the chemistry changed.The lake is appearing now due to the massive summit collapse that occured in the summer of 2018. When magma drained from the summit of Kīlauea, Halemaʻumaʻu crater collapsed nearly 1,600 feet (500 m), with the bottom of the crater falling below the water table. The water table is slowly "bouncing back", filling the crater floor. Watch a video from the USGS Hawaiian Volcano Observatory that discusses the appearance of the lake. How Deep Will It Get?USGS provides monitoring data on water depth. If the lake equalizes with the nearby water table, it could reach a depth of about 230 feet (70 m). In its first year of existence, the lake rose several inches per day, but is likely to slow down as it approaches equilibrium.ColorEarly photographs of the lake in August 2019 showed water that was a bright blue color. Over time, it has transitioned to turquoise, yellow, and brown, likely due to the precipitation of iron-sulfate minerals and SO2 being dissolved into the water. The appearance of the water can even shift during the course of a single day.Photographs show areas of swirling, blue-green color in parts of the lake, likely indicating an influx of new water. 
TemperatureHigh-resolution thermal images indicate that the lake has maximum water temperatures of around 80–85 degrees Celsius (176–185 degrees Fahrenheit). AcidityWater samples taken in October 2019 indicated that the lake has a pH of 4.2, similar to most fruit juices. This puts the lake in a unique position in relation to other volcanic lakes around the world. Volcanic lakes elsewhere on Earth tend to be bimodal on the pH scale, either very acidic or alkaline, with very few lakes in the mid-range. A pH of 4.2, however, places this lake in the lonely middle of this distribution. Read a USGS "Volcano Watch" article on the chemistry of the water.
Water SamplingIn October 2019, the USGS Hawaiian Volcano Observatory took the next step in unlocking the secrets of this body of water. They launched a specialized unmanned aircraft system, UAS, that gathered photographs, gas measurements and a water sample from its scalding hot surface. Has This Happened Before?This is the first time in modern history, at least 200 years, that water has been visible in the Kīlauea caldera in the form of a lake. In that time period there have been small, ephemeral water features, but nothing on this scale.Over the long geological history of Kīlauea, it is possible there were water lakes in previous eras. Native Hawaiians have told several stories over the centuries in which the volcanic deity Pelehonuamea faced the threat of water drowning her volcanic fires at Kīlauea. Risk of Explosive ActivityWhenever magma interacts with water, there is the potential for explosive activity. The USGS Hawaiian Volcano Observatory has noted that at the Kīlauea summit, any explosions would likely be small, only affecting the immediate caldera floor. While explosive activity is a possibility, there are many factors at play and there would be likely be noticeable precursors prior to any such activity.Hazards at Kīlauea in the near term have not significantly changed because of the discovery of water. Will The Lake Be Named?There are currently no plans to assign a name to this new body of water.Growth of the Water Lake in Halemaʻumaʻu
Halemaʻumaʻu Crater on August 7th, 2019 (USGS/D. Swanson)
Halemaʻumaʻu Crater on April 21st, 2020 (USGS/M. Patrick)
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Last updated: October 22, 2020