SCIENCE

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.

Discussion Ideas

• 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?
  • They don’t, at least not much. Temperature takes care of that. “Normally, the heat of the magma keeps water from intruding into the parts of the ground near the lava lake.”
  • The rocks of the Halema’uma’u crater are fairly unstable, however, and regularly fall into the lava lake. (See that beautiful top photo!) There, they explode spectacularly but rather harmlessly, with some volcanic ash, water vapor, and steam. These volcanic products aren’t usually serious volcanic hazards at Halema’uma’u.

 

• So, how might the current interaction of water table and a lava lake create an explosive situation? Take a look at the diagram above for some help.
  • The hazard comes with the hundreds of feet of fragile rock left exposed by the retreat of the lava lake. “If enough rocks fall through, they could plug up the vent where the lava lake sits, barricading it below ground … all that steam could build up underground, increasing the pressure until suddenly …. boom.”
  • “The hazards are ballistic rocks around the summit area, and ash fall can occur in areas depending on wind strength and direction and the size of the eruption,” says one volcanologist.

 

• Will Kilauea’s explosive eruption mimic major explosive eruptions like Vesuvius, Mount St. Helens, or Pinatubo? Skim our reference resource to “Surtseyan” eruptions for some help.
  • No. “We are looking at the possibility of a steam-driven eruption at the summit, which is not as large as magmatic eruptions that we see at volcanoes like Mount St. Helens,” says one volcanologist.
    • In other words, those stratovolcanic eruptions are still way worse. Impress your friends with this related vocabulary:
      • phreatomagmatic: The sort of explosive events that characterized Vesuvius, Mount St. Helens, and Pinatubo are phreatomagmatic eruptions. Phreatomagmatic eruptions involve the interaction of surface water (such as the ocean or a crater lake) and underground magma. These are magmatic events.
      • phreatic: Any explosive eruption at Halema’uma’u would be a steam-driven event, or phreatic eruption. Phreatic eruptions are largely surface-level (phreatic zone) events driven by steam and surface rocks, and are generally not as catastrophic as their phreatomagmatic cousins. (Not always, though! The incredible 1883 eruption of Krakatoa may have been a phreatic event.)
    • Although officials warn visitors to steer clear of the erupting volcano, a Halema’uma’u eruption should not be a life-threatening event. Just avoid the 10-ton boulders falling from the sky.

 

TEACHERS TOOLKIT

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