VOLCANOES NATIONAL PARK — The recent appearance of water at the bottom of Halemaumau, a crater at the summit of Kilauea Volcano, has attracted wide attention and generated many questions.
To understand the significance of this water, we must first gather accurate information on its behavior. Similar to our monitoring of ponded lava in Halemaumau in 2008-2018, USGS Hawaiian Volcano Observatory (HVO) scientists are now relying on both direct observations and modern tools to monitor the water.
During regular visits to Kilauea, HVO staff observe, measure, and document changes in the water in Halemaumau through photographs, videos, and thermal images.
As shown in HVO’s website photos, the ponds are milky turquoise, or greenish, in color, indicative of dissolved sulfur and metals from magmatic gases or surrounding rock mixing into the water. Thermal images show water surface temperatures of approximately 70 degrees Celsius (158 degrees Fahrenheit). Tracking both color and temperature of the ponds will help us identify changes in chemistry and heating.
The water in Halemaumau is not visible from publicly accessible areas of Hawaii Volcanoes National Park, but this past week, HVO moved one of its existing webcams to a site that provides a direct view of the ponds. This temporary webcam doesn’t have high enough resolution to discern small scale changes in the water level but will nevertheless be valuable for identifying larger scale events.
To measure the level of water in the ponds, HVO scientists use a long-range laser rangefinder. These daily measurements show that the water level has slowly risen, enlarging the ponded water area over the past week.
Future helicopter overflights will allow us to map and precisely measure the area and volume of the changing ponds. Using oblique photographs, we can create 3-dimensional models of the crater floor. Comparing these updated models with the lidar (light detection and ranging) data collected in July 2019 will help us estimate water volume. High-resolution satellite images, which are routinely collected at Kilauea’s summit, can fill in observational gaps between HVO’s overflights.
Unmanned aircraft systems (UAS), or drones, a tool used during the 2018 events, could also provide aerial imagery and precise measurements of pond area and volume.
In addition to surface observations, HVO also monitors for subsurface changes. Fortunately, Kilauea’s summit hosts one of the densest volcano monitoring networks on Earth. Seismic, deformation, and gas instruments, can help determine if magma is rising closer to the surface. Seismic monitoring may be able to detect instabilities in the hydrothermal system (the zone where groundwater and hot gases interact) that, at other volcanoes, have been precursors to eruptions.
Direct sampling and chemical analyses of the water in Halemaumau would provide insight into its source — if it is a shallow accumulation of rainwater or the surface expression of a deeper-seated layer of groundwater. Some of the water could also be from condensed water vapor directly released by the magma.
Knowing the water’s source will help us better understand the possible hazards associated with it. For instance, if the water is from the extensive zone of groundwater around the crater, it could be more likely to interact with rising magma and result in explosive activity.
Given the hazardous location of the water, however, direct sampling is tricky. Walking down to the ponds is not advised due to the possible accumulation of carbon dioxide on the crater floor. Other dangers include frequent rockfalls from the steep, unstable slopes.
In recent media interviews, HVO scientists have discussed how the presence of water could increase the potential for explosive activity given the right set of conditions. At the current time, however, monitoring data do not indicate any signs of imminent unrest at Kilauea’s summit. Magma continues to quietly recharge the summit magma reservoir.
The historically unprecedented appearance of water in Halemaumau is a reminder that, even in the absence of a lava lake, Kilauea’s summit remains a highly dynamic place. HVO continues to keep a close eye on the volcano and will post updated photos and videos to our website (https://volcanoes.wr.usgs.gov/hvo).
Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.