Explosive Volcano? Just Add Water


Scientists are warning of “ballistic rocks” hurled from Kilauea’s crater. So, steer clear of the erupting volcano, people. (Nat Geo News)

Use our resources to learn more about craters and the lava lakes they sometimes hold.

This explosion at Halema’uma’u was likely triggered by a rockfall, not steam.
Photograph by U.S. Geological Survey

Discussion Ideas

Halema’uma’u is a crater in the Kilauea caldera. The lava lake sits in Halema’uma’u’s pit crater.
Image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team
  • Scientists warn that if the lava lake at Halema’uma’u falls below the water table, the generally gentle Kilauea volcano may get explosive. What is a lava lake?
    • A lava lake is just what it sounds like—a large pool of molten and semi-molten lava. Lava lakes are either the result of lava spilling into a broad basin or being continuously fed by magma vents. The lava lake at Halema’uma’u is the second type. It is fed by vents from the Kilauea volcano.
    • Lava lakes are found in volcanic craters. Halema’uma’u is a large crater located in the caldera of the Kilauea volcano. Halema’uma’u’s current lava lake first formed in 2008.
      • The lava lake at Halema’uma’u reached high levels in April of this year, prior to the current eruption. Since April 30, however, the lava levels have fallen a whopping 220 meters (722 feet). See the videos below!



  • What is the water table? Look through our reference resource for some help.
    • An area’s water table describes the boundary between water-saturated ground and unsaturated ground. Beneath the water table, pockets of water are trapped in areas called aquifers. (The top of a water table is called the phreatic zone, by the way. Remember that vocabulary.)
      • An area’s water table can fluctuate based on precipitation, extraction from wells, or the changing landscape.


  • The mantle plume fueling the Hawaiian hot spot, which in turn feeds Halema’uma’u’’s lava lake, already goes a lot deeper than the water table. So, how do Hawaii’s water table and the Kilauea volcano normally interact?


At Kilauea, when the lava column drops below the water table, groundwater may come into contact with with magma or hot rocks, causing violent steam explosions.
Illustration by U.S. Geological Survey



Click above for a webcam of Halema’uma’u crater.


Nat Geo: Will the Eruptions From Hawaii’s Kilauea Volcano Turn Explosive? Get the Facts.

Popular Science: If Kilauea’s lava lake falls below the water table, the results could be explosive

USGS: Webcams—Kilauea Volcano, Summit

Nat Geo: What is a volcano?

Nat Geo: What is a water table?

Nat Geo: What is a crater?

Nat Geo: What is magma?

Smithsonian Institution: Global Volcanism Program—Magma Meets Water

USGS: Volcanic Hazards Program—Kilauea

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