Tia Ghose reports that a view of Halema'uma'u lava lake at the summit of Kilauea is draining rapidly after a dramatic magnitude-5.0 earthquake caused a lava eruption in the east rift zone of the volcano. Officials say the lava lake could fuel dramatic steam explosions that spew 10-ton ballistic rocks if the lava levels drop below the water table underground. Rockfalls and trapped lava could launch 10-ton "ballistic rocks" at Hawaii's fiery Kilauea volcano, officials at the Hawaiian Volcano Observatory said yesterday. That's because a lava lake near the summit of Kilauea is draining, setting the stage for a steam explosion.
The volcano has been undergoing big changes over the past few weeks, culminating in a dramatic eruption following a 5.0-magnitude earthquake and a subsequent magnitude-6.9 earthquake last week. That powerful outburst occurred after rockfalls caused the collapse of the PuuOu crater at the summit of Kilauea, which had been puffed up like a soufflé filled with red-hot lava. That lava had to go somewhere, and it oozed underground to the east rift zone of the mighty volcano, where magma doesn't usually travel. New volcanic fissures or cracks opened up ito the surface allowing lava and toxic gases to escape into the surrounding residential areas, called Leilani Estates and Lanipuna Gardens. A side effect of all these shifts is that a lava lake on the summit called Halema'uma'u has been draining like a bathtub; as of May 6, it had dropped 722 feet (220 meters), according to the U.S. Geological Survey. As it continues to descend, the magma column could drop below the water table, the depth below which groundwater occurs to great depths, unless the lava heats up the groundwater. If lava cover the water table and groundwater is trapped bellow (and heated to the boiling point, that could spell danger for the surrounding areas. Unless the pressure drains away (which it commonly does in volcanic rocks of cooled lava), the hot water could break through the overlying lava, turning to steam in the process with explosive power. Also, with the lava in Halema'uma'u, the walls surrounding the dwindling lake are now steep and unstable, and rockfalls are inevitable, said Don Swanson, a geologist with the Hawaiian Volcano Observatory, said at a news conference yesterday.
"When you remove that support from the conduit and the crater, it causes instability and causes material to fall in," Matt Patrick, a geologist with Hawaiian Volcano Observatory, said at the news conference. In turn, there will be an increased risk that falling rocks will plug the conduit for Halema'uma'u; as lava heats the groundwater, steam will form but will have nowhere to go. As pressure builds, eventually the main Kilauea vent could explode with steam, hurling any loose rocks with it — a phenomenon known as a phreatic explosion, Tina Neal, a geologist with the Hawaiian Volcano Observatory, said at the news conference.
The volcano could eject rocks weighing as much as 10 to 12 tons over a distance of half a mile (1 kilometer) and launch pebble-size rocks across a couple of miles, according to geologists from the observatory. This explosion could also eject dangerous amounts of ash, sulfur dioxide and acid rain. The clock begins to tick when the magma drops below the water table, which is likely to happen in mid-May, Swanson said.
Kilauea has been erupting continuously for decades, but it hasn't spewed rocks in such an explosive manner since 1924, according to the Associated Press. While the surrounding areas will be affected, the whole island is unlikely to see dramatic effects, Swanson said. "Past explosive eruptions at Kilauea have been comparatively small on a worldwide scale," Swanson said. "We don't anticipate there being any wholesale devastation or evacuation." Meanwhile, the lava in the east rift zone is inching dangerously close to the Puna Geothermal Venture plant that houses 50,000 gallons (190,00 liters) of pentane, a volatile gas. But all of the pentane is expected to be removed by the end of the day today (May 10), the Associated Press reported.
Early signs that pressures could build in the subsurface (and then drain away) came from the blow-out of geothermal wells at the Puna plant 30 years ago, see (more).
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