The May 29, 2020, overflight provided updated aerial photographs of Kīlauea summit, covering the caldera floor and showing the size of the water lake in Halema‘uma‘u crater. The label "downdropped block" shows the large portion of the caldera floor that subsided, along with the Halema‘uma‘u region, during the 2018 eruption.  (Credit: USGS HVO. Public domain.)

1. What's happening at Kīlauea Volcano’s summit? 

No major changes have been observed recently at Kīlauea's summit water lake, and the water level continues to slowly rise. On October 12, 2020, the lake was measured to be approximately 46 m (153 ft) deep. USGS photo by M. Patrick. (Public domain.)

Kīlauea is currently erupting. Following the 2018 lower East Rift Zone eruption and summit caldera collapse, long-term ground deformation trends at the summit of Kīlauea indicated that magma is being supplied to the volcano’s shallow magma reservoir.  

Water first appeared at the base of the deepest collapsed area of Kīlauea’s summit, within the Halemaʻumaʻu crater, at the end of July 2019. The body of water grew into a lake, as it saught equilibrium with the surrounding groundwater. 

On the evening of December 20, 2020, an eruption began in Halema‘uma‘u Crater. Lava quickly vaporized the water lake, which has been replaced by a growing lava lake. For information about the ongoing eruption in Halema‘uma‘u at Kīlauea's summit, see the current eruption webpage. 

The lake was continuously monitored by visual camera and thermal cameras, which allowed HVO to track color, circulation, and water temperature. HVO staff also measured the water-lake level at least twice a week. 

For information on the current  status of Kīlauea, please visit: https://volcanoes.usgs.gov/volcanoes/kilauea/status.html  

2. What was the source of the water in Kīlauea's summit water lake? 

Groundwater was filling the lowest elevations of Kīlauea’s summit, within the Halemaʻumaʻu crater. 

Hot groundwater was present below the surface of Kīlauea’s summit before the 2018 events (176–278°F or 80–137°C water was measured at the base of a well extending to 1.2 km or 0.7 mile depth); however, this was the first time in at least 200 years that water ponded on the surface at Kīlauea’s summit.

Geophysical surveys, which can map the surface of the groundwater table, show that water is present beneath the surface throughout most of the summit area. 

A groundwater well was drilled in the southern part of Kīlauea’s caldera in 1973. The water level within the well is approximately 55 ft (17 m) above the surface of the current water lake in Halemaʻumaʻu, or approximately 1640 ft (500 m) below the ground surface. 

Comparison of images showing growth of Kīlauea's summit water lake over one year. The left image, taken on August 2, 2019, shows a small green pond that was approximately 6 ft (2 m) deep. The right image, taken on July 21, 2020, shows a lake more than 130 ft (40 m) deep with shades of tan to brown and a sharp color boundary often cutting across the lake. Hawaiian Volcano Observatory scientists continue to monitor the lake, and Kīlauea's summit. (Credit: USGS. Public domain.)

3. What did the level, temperature, color, and chemistry of the water in the lake tell us? 

This compilation of photos of the water lake at Kīlauea's summit shows the dynamic nature of colors and patterns on the water surface. The color boundaries can shift over minutes to tens of minutes. Greenish areas appear to be zones of hot water influx at the lake margins.

The light-colored boulder (see arrow on June 30 image) provides a reference point for the lake rise. On June 30, 2020, the boulder was well above the water surface. On August 25, 2020, it was at the shoreline. And on September 15, 2020, it was submerged. Laser rangefinder measurements indicate that the lake rose approximately 5 meters (16 feet) over this time span (June 30-September 15). (Credit: M. Patrick, USGS. Public domain.)

The lake level rose at a rate of about 2.5 ft (0.75 m) each week. This rate decreased as the lake reached the level of the water table (the underground boundary below which soil and/or rock is saturated with water). To see a graph of the water lake depth visit: https://www.usgs.gov/media/images/water-depth-plot-kilauea-volcano-summit-water-lake.

The surface temperature of the lake was between 70–85°C (158–185°F). These temperatures indicate that the water was being heated by the volcano’s magmatic system. 

The color of the lake varied with different shades of green, yellow, orange and brown. Tan-brown shades were the dominant color in the latter part of 2020. The lake color was likely the result of minerals from crater wall rocks dissolving in or mixing with the water or is from new minerals produced when the lake water reacted with rocks in the crater walls. 

The chemistry of water samples collected from the lake, determined through isotopic analysis, confirmed that the water is meteoric in origin. In other words, it originated as rainwater rather than as water condensed from magma at depth. Some of it was rainwater that fell directly into the crater, but most was from rainwater that percolated into the ground to become groundwater, which then flowed below the ground surface into the lake. 

Analyses of the water samples also showed that the lake was mildly acidic, with a pH of around 4. This is about the acidity of tomato juice. For context, rainwater is mildly acidic with a typical pH value of around 5.5. 

The water chemistry of the lake was related to the surrounding rocks and minerals, as well as volcanic gases (carbon dioxide—CO₂, sulfur dioxide—SO₂, hydrogen sulfide—H₂S, hydrogen chloride—HCl, and hydrogen fluoride—HF) that are released from magma. As these gases travel toward the surface, some fraction of them likely dissolved in the lake and groundwater—this process is referred to as scrubbing. If it occurred, scrubbing could result in HVO's SO₂ emission rate measurements underestimating the total amount of SO₂ outgassed at Kīlauea. 

The water chemistry of the lake reflected minerals that are common on the slopes and crater walls of Halemaʻumaʻu. The contribution from magmatic degassing appears to have been less important. 

For additional information on the summit water lake, please visit: https://www.usgs.gov/volcanoes/kilauea/k-lauea-summit-water-resources.

4. What eruption styles are possible at Kīlauea’s summit? 

A helicopter overflight this afternoon (April 23) of Kīlauea Volcano's Halema‘uma‘u crater showed the extent of the largest overflow (silver gray) of the lava lake from approximately 6:30-9:30 a.m. this morning. The overflow covered much of the April/May 2015 and October 2016 overflows, but a section of the 2015 overflow is visible on the south (upper edge) of Halema‘uma‘u crater floor. At the time of the flight, multiple spattering sites were active around the margin of the lava lake, and the lake surface was a few meters (yards) below the rim. (Public domain.)

Based on past activity at the summit of Kīlauea, HVO geologists know that both effusive and explosive eruptions are possible. 

Effusive eruptions are those that produce lava flows and lava lakes. 

• Lava flows erupted along Kīlauea’s lower East Rift Zone in 2018 are the most recent example of an effusive eruption. A lava lake was most recently present at the summit of Kīlauea from 2008–2018 and resulted in effusive eruptions of lava flows across the floor of Halemaʻumaʻu. 

Explosive eruptions are those in which material is thrown into the air, sometimes violently. 

• Gas driven eruptions occur when pressurized gases from the magma cause explosions without involving hot magma or external water. Such explosions are poorly understood, but one took place in Halema‘uma‘u on March 19, 2008. 

• 

  The series of explosive eruptions in May 1924 followed the withdrawal of lava from lava lake in Halema‘uma‘u Crater that began in February and the ensuing collapse of its crater floor in late April. Scientists infer that the lava had drained to a depth below the water table at the summit, currently about 500 m (1,640 ft) below the floor of the caldera. Rock falls from the collapsing walls of Halema‘uma‘u Crater dammed steam rising from the water table, causing pressure to build, and triggering the explosive eruptions. The largest rocks ejected by the explosive activity weighed 14 tons and were hurled as far as 1 km (0.6 mi) from the crater rim. Note the dark plume of ash and gas blown south (far distance) of the crater by the prevailing trade winds. (Credit: Maehara, K. Public domain.)

  Gas driven eruptions, perhaps such as the May 1924 Kīlauea summit eruption, can be moderately to highly explosive. More than 50 explosive eruptions took place in May 1924 as magma drained from a lava lake and its conduit system. It has long been thought that these explosions were driven by steam from heated groundwater, in part because very little fresh lava was erupted. However, this concept is currently under review, and it may be that rising magmatic gas, rather than heated groundwater, was responsible for the explosions. Such uncertainties illustrate our limited understanding of explosive processes at Kīlauea and why ongoing research is so important for assessing the future explosive hazards of the volcano. This type of eruption can happen with little or no warning, but explosions would likely only impact the immediate vicinity of the summit caldera based on comparable events at other volcanoes. Larger explosions are possible but less likely. 

• Phreatomagmatic eruptions occur when violent or sudden interactions between hot magma and external water cause an explosion. The heat from magma flashes water to steam that rapidly expands in a confined space and ejects fresh lava fragments as well as overlying rocks. Many phreatomagmatic eruptions occurred at Kīlauea during the prehistoric Keanakākoʻi tephra period (1500 to early 1800s C.E.), the deposits of which can be found around the summit area. 

• Phreatic eruptions are steam-driven explosions that occur when groundwater or surface water flashes to steam that rapidly expands in a confined space. This type of explosion, caused by the heat from ascending magma or hot solidified rocks, ejects older, previously cooled fragments of lava or other rocks. Many phreatic eruptions also occurred during the Keanakākoʻi Tephra period. 

• Some geologists consider lava fountains, in which volcanic gases throw lava fragments into the air, as explosive eruptions. The 1959 Kīlauea Iki eruption, which remains the tallest recorded lava fountain in Hawaiʻi (at 1900 ft or 580 m high), was a mildly explosive eruption. However, fragments from lava fountains can retain their heat and flow as an effusive eruption after falling to the ground. 

5. What did the water lake atop Kīlauea mean for future eruptions and hazards at the summit of Kīlauea? 

Clear weather allowed another water pond measurement to be made on April 6, 2020. Results show continued slow rise of the water level. No major changes were observed. Note the former HVO observation tower can be seen above the geologist's helmet. (Credit:USGS. Public domain.)

Hazards could occur at Kīlauea summit with little or no warning.  Geophysical surveys show that water is present beneath the surface throughout most of Kīlauea’s summit area and it was present before the 2018 events; however, this was the first time in at least 200 years that water ponded on the surface at Kīlauea’s summit. Changes in Kīlauea’s summit water lake temperature, color, circulation, and chemical composition could have preceded impending changes in volcanic activity. In addition to those parameters, HVO continues to monitor other Kīlauea data streams, including seismicity, ground deformation, and volcanic gas emissions.

Hazard zones on Kīlauea have been assigned by HVO geologists using the record of past eruptive activity derived from geologic mapping and dating.  

The most frequent type of summit eruptions in Kīlauea’s recent past have been effusive. Alternatively, explosive eruptions may occur if magma, or heat rising above magma, interacts with surface or ground water to form steam that rapidly expands, violently fragmenting any magma and/or overlying rocks. Explosive eruptions can result in fast-moving pyroclastic flows and surge deposits that are not likely to travel far beyond the summit area. For more information on explosive eruption hazards, please see the “Explosive Eruptions/Tephra” hazards webpage or the “Volcanic Ash/Tephra” FAQs. 

Gas emissions (primarily water—H₂O, carbon dioxide—CO₂, and sulfur dioxide—SO₂) can be released in large amounts during eruptions and more passively when there is no eruption. Abundant SO₂ emissions can result in poor air quality downwind of Kīlauea through the formation of vog, sometimes known as volcanic smog. For more information, please see the “Volcanic Gas” hazards webpage or the “Volcanic Gas” and “VOG, or volcanic smog” FAQs.

Earthquakes can occur at Kīlauea during eruptions and during times of no eruption. For more information, please see the  “Damaging earthquakes” hazards webpage and the “About earthquakes in Hawaii” webpage. 

6. What did HVO do to monitor the water lake and greater Kīlauea summit area? 

The purpose of the UAS flights was to collect water samples and gas data to assess ongoing volcanic hazards. HVO's work in a culturally sensitive area closed to the general public was done with permission of Hawai‘i Volcanoes National Park. After a sample was collected, HVO team members transferred water from the sampling device to plastic bottles. The scientists wore protective gear, including hardhats in case of rockfall hazards near the crater rim, as well as aprons, goggles, and gloves to shield them from the hot, acidic water. USGS photo by S. Warren. (Credit: USGS. Public domain.)

HVO installed two cameras, one visual and one thermal, to monitor the surface appearance (color and circulation patterns) and temperature of the water lake. Feeds from these cameras can be accessed from the HVO website at https://www.usgs.gov/volcanoes/kilauea/summit-webcams  

HVO conducted laser-ranging measurements twice a week to monitor the elevation of the lake surface and calculate both water depth and the rise rate of the lake. A plot of the summit water depth can be found on the HVO website: https://www.usgs.gov/media/images/water-depth-plot-kilauea-volcano-summit-water-lake.

HVO, in cooperation with Hawaiʻi Volcanoes National Park, conducted sampling missions of the water lake using unoccupied aircraft systems (UAS). These samples were used to investigate lake water pH, chemical composition, and temperature. 

The nearby summit well, which is monitored and sampled quarterly, provides a baseline for comparison with local groundwater. 

HVO conducts helicopter aerial surveys of Kīlauea’s summit to capture aerial and thermal imagery. This imagery is used to construct visual and thermal maps to monitor changes at Kīlauea’s summit. 

HVO created a webpage dedicated to Kīlauea’s summit water resources: https://www.usgs.gov/volcanoes/kilauea/k-lauea-summit-water-resources.

HVO continues to monitor the summit of Kīlauea via a dense network of instruments, including 14 seismometers, 4 tiltmeters, 10 Global Positioning System (GPS) stations, 14 gas-monitoring instruments, 5 visual webcams, and 1 thermal webcam. If any significant changes in volcanic activity are detected, HVO will alert the authorities and the public. 

Subscribe to the Volcano Activity Notification Service to receive messages about volcanic activity: https://volcanoes.usgs.gov/vns2/.