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Volcano Watch is a weekly article and activity update written by scientists and affiliates at the U.S. Geological Survey’s Hawaiian Volcano Observatory.
Now that we’ve reached the fifth anniversary of that pool of water’s appearance, we wanted to take this opportunity to remind you about the lake and tell you what we’ve learned in the nearly year and a half that it’s been there.
Monitoring and understanding the lake is important because the presence of water increases the likelihood of violent steam explosions should Kilauea erupt again, as it has in past eruptions.
During the lake’s existence, the U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) closely monitored the lake’s color, level, and temperature; at other volcanoes, sudden color changes or boiling can be a precursor to an eruption.
Water levels measured by HVO staff showed that the lake was rising steadily, regardless of rainfall, which meant that the lake was fed by groundwater. Thermal imaging camera measurements also showed that the water temperature was very high (up to about 80°C, or 175°F), and that at least half of the groundwater that flowed into the lake evaporated rather than remaining in the lake.
The lake is inaccessible on foot, and sampling by helicopter was deemed too dangerous. So, after careful planning and discussion with Hawaii Volcanoes National Park, HVO used an unmanned aircraft system (UAS, or drone) to collect water samples from the lake—the first on October 26, 2019, and the second on January 17, 2020.
In 2020, travel and fieldwork restrictions due to the COVID-19 pandemic prevented us from sampling again as quickly and frequently as we would have liked, but we ultimately managed to conduct a third sampling campaign on the one-year anniversary of our first, on October 26, 2020. Interestingly, the lake chemistry changed very little in the year between the first and third sampling campaigns.
The water is acidic (pH around 4), but not as acidic as most of the world’s acidic volcanic lakes (pH around 1), and contains large amounts of dissolved iron, magnesium, and sulfur.
We determined that iron and magnesium were leached from Kilauea’s basalt. Iron is also responsible for the many colors of the lake. The initial green color is due to the form of iron present in Kilauea’s basalt. As the iron in the water spent more time in the lake and came into contact with oxygen from the atmosphere, it converted to another form of iron, forming orange and brown minerals, similar to how rust forms on metal objects. This explains why the color of the lake changed from green to brown over time; the frequent presence of green water near the lake is another piece of evidence that tells us the lake has been fed by groundwater that contains green iron.
Initially, HVO thought that the sulfur in the water might be the result of sulfur gases dissolved in the lake water, such as sulfur dioxide (SO2) was released from the magma below—a process known as “scrubbing.” However, a closer look at the type of sulfur in the water, as well as the acidic but not too acidic pH mentioned above, shows that the lake’s sulfur actually comes from sulfate alteration minerals—deposited over the years on nearby rocks—that then dissolved into the water.
Ultimately, the lake showed no signs of change until the December 2020 eruption, and luckily the lava was erupting alongside the lake rather than across it, so no major steam explosions occurred. Instead, all the water that had accumulated over the past year and a half was evaporated by the lava flow in just over an hour!
Since then, Halemaumau has mostly filled with lava, and groundwater at Kilauea’s summit is much deeper than the current crater floor and well below the surface. So while it’s not impossible for another water lake to appear at Kilauea in the future, we don’t expect one anytime soon. But if we do find one, we’ll have a better idea of it right away based on our measurements of the 2019-2020 lake.
Volcano Activity Update
Kilauea volcano is not erupting. The U.S. Geological Survey volcano alert level is “warning”.
Seismic activity and ground deformation continue to occur at the summit and in the upper and middle East Rift Zone of Kilauea following the July 22-25 intrusion event. Over the past week, approximately 525 earthquakes were detected beneath the East Rift Zone in the upper part of Kilauea, and approximately 125 earthquakes were detected between Maunaulu and Pu’u’ō’ō in the middle of the East Rift Zone in Hawaii Volcanoes National Park. Over the past week, Kilauea’s summit and the middle East Rift Zone have exhibited slow expansion. Unrest may continue to wax and wane as magma input to these areas changes; changes could occur quickly, and so could the potential for an eruption.
Mauna Loa is not erupting. The U.S. Geological Survey volcano alert level is normal.
Three earthquakes were reported in the Hawaiian Islands over the past week: a M4.0 earthquake struck 13 km (8 mi) north-northeast of Oceanview, Hawaii at 2:00 a.m. on August 6, Hawaii Standard Time, at a focal depth of 7 km (4 mi); a M3.4 earthquake struck 6 km (3 mi) south of the volcano at 2:35 p.m. on August 4, Hawaii Standard Time, at a focal depth of 1 km (1 mile); and a M3.8 earthquake struck 6 km (3 mi) south of the volcano at 11:49 p.m. on August 2, Hawaii Standard Time, at a focal depth of 1 km (1 mile).
HVO continues to closely monitor Kilauea and Mauna Loa.
Visit the HVO website for past volcano monitoring articles, the latest news on Kilauea and Mauna Loa, volcano photos, maps, recent earthquake information, and more. Please email questions to askHVO@usgs.gov.
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