The body of water in Halemaʻumaʻu crater (USGS Photo/M. Patrick)

On August 1st, 2019, USGS Hawaiian Volcano Observatory (HVO) scientists confirmed a growing pond of water inside Halema'uma'u crater during a helicopter overflight. Similar to the monitoring of ponded lava in Halema‘uma‘u in 2008‒2018, HVO scientists are now relying on both direct observations and modern tools to monitor and document any changes to the water.The water in Halema‘uma‘u is not visible from publicly accessible areas of Hawai‘i Volcanoes National Park, but HVO now has webcams that provide a direct view of the lake. To measure the level of water in the lake, HVO scientists use a long-range laser rangefinder.Water samples indicate that the lake has a pH of 4.2 (moderately acidic, in the range of many fruit juices) and high concentrations of dissolved sulfur and magnesium. The lake is an astounding 128 feet (39 m) deep, nearly the height of a ten story building. It is approximately 430 feet (131 m) wide by 800 feet (244 m) long, with a volume of nearly 125 million gallons and growing. The water has a maximum temperature of about 80–85 degrees Celsius (176–185 degrees Fahrenheit). Learn more about the summit lake.