Halemaumau's vent small on top, gaping at bottom


POSTED: Tuesday, July 21, 2009

Scientists at the Hawaiian Volcano Observatory and the University of Hawaii used lasers to look inside and measure the depth of the vent in Halemaumau Crater.

The laser technology revealed that the vent has a cavernous interior that dwarfs the size of the opening at the surface and that the cavern is about 650 feet below the surface of Halemaumau and 935 feet below the overlook area at the rim of the crater, according to last week's “;Volcano Watch”; issued by the observatory.

UH researchers used a technology called Light Detection and Ranging, or LiDAR, for short. By bouncing pulses of lasers off objects, LiDAR can determine the distance to out-of-reach objects.

It is a similar technology to laser range-finders used by golfers, hunters and construction companies.

Scientists using LiDAR can produce entire images, or models, of distant surfaces based on thousands of individual laser bounces.

The image produced revealed a deep pit crater with overhanging walls near the surface. It is different from the steep and vertical walls of Halemaumau and Kilauea caldera.

Scientists believe that both Halemaumau and Kilauea are “;pit craters”; or “;collapse craters”; created when the overhanging walls of a vent collapsed, leaving the vertical walls.

That appears to be what is happening now within the vent in Halemaumau crater. The occasional pulses of ash plumes rising from the vent appear to be caused by the collapse of the overhanging rim.