Lava lake seen on Halemaumau floor
HILO » For the first time since a voggy, sputtering vent opened near the bottom of Halemaumau Crater on March 19, scientists have been able to look far enough inside to see a pool of sloshing lava.
Scientists from the Hawaiian Volcano Observatory obtained the views of the lava lake during two helicopter flights yesterday, they said. They described it as a "roiling pond with multiple bursting bubbles."
The center of the 160-foot-wide pond repeatedly rose in a circular motion, fell and rose again, they said. The phenomenon is known as "gas pistoning," comparable to the rise and fall of a piston in an automobile engine.
The lava "pistons" are believed to be caused by gas pushing up through lava from below and releasing into the air, making the lava rise and fall.
The pond is somewhat difficult to see in photos because it is about 330 feet below the floor of Halemaumau, and fumes from the vent partially obscure the view. Scientists had speculated for several months that there was a pond inside the vent but had not been able to get a good view until yesterday.
The better look into the interior was made possible by the vent doubling in size since March to about 215 feet wide. Previously its width was 115 feet, said geologist Janet Babb.
The widening has also meant the vent opening has spread onto Halemaumau's floor. The original, smaller vent was on the east wall of Halemaumau, about 55 feet above the crater floor. The floor is about 300 feet below ground level.
Small pieces of lava had been ejected from the vent many times, believed driven by bursting gas bubbles.
Since March, six significant explosions from the vent have taken place, blasting out lava, rocks, and dust. The most recent explosion occurred Tuesday.
At the time, 8:13 p.m., the vent was almost completely dark, suggesting a crust had formed on the interior lake.
Eight hours after Tuesday night's explosion, instruments indicated more magma was entering the shallow region from deeper inside the earth.
Then instruments showed repeated bursts of seismic tremor, which coincided with pulses of bright glowing inside the vent, scientists said. The periods of tremor and glowing suggested gas pistoning, later confirmed by the helicopter flights.