Science Support
Frequently Asked Questions About Kīlauea Volcano's Summit Water
Water appeared in the summit area of Kīlauea Volcano in late July 2019; since then, the body of water has slowly risen and grown in size.
1. What’s happening at Kīlauea Volcano’s summit?
Kīlauea is not currently erupting. Following the 2018 lower East Rift Zone eruption and summit caldera collapse, long-term ground deformation trends at the summit of Kīlauea indicate that magma is being supplied to the volcano’s shallow magma reservoir. However, there are no monitoring signals to suggest that an eruption is imminent.
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. Since then, the body of water has grown into a lake, which continues to rise as it seeks equilibrium with the surrounding groundwater.
The lake is continuously monitored by visual camera and thermal cameras, which allow HVO to track color, circulation, and water temperature. HVO staff also measure 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 is the source of the water in Kīlauea's summit water lake?
Groundwater is 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 is the first time in at least 200 years that water has 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.
3. What does the level, temperature, color, and chemistry of the water in the lake tell us?
The lake level is currently rising at a rate of about 2.5 ft (0.75 m) each week. This rate is expected to decrease as the lake reaches 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/volcanoes/kilauea/past-year (scroll to the bottom of the page).
The surface temperature of the lake is between 70–85°C (158–185°F). These temperatures indicate that the water is being heated by the volcano’s magmatic system. However, molten magma remains at much greater depths.
The color of the lake varies with different shades of green, yellow, orange and brown. Tan-brown shades have been the dominant color over the past several months. The lake color is 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 reacts with rocks in the crater walls.
The chemistry of water samples collected from the lake, determined through isotopic analysis, confirm that the water is meteoric in origin. In other words, it originates as rainwater rather than as water condensed from magma at depth. Some of it is rainwater that falls directly into the crater, but most is from rainwater that percolates into the ground to become groundwater, which then flows below the ground surface into the lake.
Analyses of the water samples also show that the lake is 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 is 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 may dissolve in the lake and groundwater—this process is referred to as scrubbing. If occurring, scrubbing could result in HVO's SO2 emission rate measurements underestimating the total amount of SO2 outgassed at Kīlauea.
To date, the water chemistry of the lake reflects minerals that are common on the slopes and crater walls of Halemaʻumaʻu. The contribution from magmatic degassing appears to be less important at this time. Continued monitoring of lake chemistry will allow HVO to identify if/when magmatic degassing begins to have a greater influence.
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?
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.
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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.
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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.
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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.
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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.
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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.
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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 does the water lake atop Kīlauea mean for future eruptions and hazards at the summit of Kīlauea?
While an eruption is not imminent, hazards could occur 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 is the first time in at least 200 years that water has ponded on the surface at Kīlauea’s summit. Changes in Kīlauea’s summit water lake temperature, color, circulation, and chemical composition could precede 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, to detect any magmatic intrusions into the shallow subsurface beneath the summit that are likely to occur prior to an eruption.
Future eruptions at Kīlauea’s summit could be effusive (lava flows) or explosive. 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 is HVO doing to monitor the water lake and greater Kīlauea summit area?
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 conducts 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 at the bottom of this webpage: https://www.usgs.gov/volcanoes/kilauea/past-year.
HVO, in cooperation with Hawaiʻi Volcanoes National Park, conducts sampling missions of the water lake using unoccupied aircraft systems (UAS). Thus far, these samples have been 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.
As of November 2020, HVO has conducted four 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 and to characterize the growing lake. Future aerial surveys are planned.
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 and its water lake 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/.