Sunday, March 23, 2008

The quiet volcano gets explosive

The world's great drive-in volcano showed its darker side this week—and not for the first time.
Kīlauea is known for its calm eruptions and flows, which visitors often can approach close enough to feel the heat.
But as the week's activities showed, the volcano also has a history of violence, of catastrophic explosions capable of destroying property and taking lives.
Earlier, the firepit within the Kīlauea began producing prodigious amounts of nasty fumes. On March 19, 2008, a blast just before 3 a.m. strewed rocks and gravel over an estimated 75 acres. It followed several days of concerns over toxic sulfur dioxide gas emissions from the volcano, including the discussion that Volcano Village might need to be evacuated if gas clouds moved in its direction.
Parts of Crater Rim Drive continued to be closed due to danger from the gas, and the Hawaiian Volcano Observatory said further explosions—driven by steam or underground gas—were possible.
Elevated toxic gas levels continued after the explosions, and parts of the region remained closed to human activity several days after the explosion.
For many folks, the violence of the volcano seemed uncharacteristic, but it certainly was not unheard-of.
In its multi-day events of May 1924, the Halema'uma'u firepit rumbled and roared, its activity punctuated by powerful blasts that threw rocks from the size of sand grains to small cars. They landed, sizzling in the rain, hundreds and occasionally thousands of feet from the edge of the pit. Showers of yellow mud fell 25 miles away.
That event ended in a spectacular eruption. During the events, one observer, a photographer, was killed by rocks and hot mud.
Scientists said much of the pre-eruption activity was steam-driven—the result of water underground meeting magma. In these conditions, water flashes to steam, expanding dramatically in volume, and creating immense pressures that can drive explosive results.
And the 1924 events were predated by an even more catastrophic explosion.
In 1790, another explosion of ash from Kīlauea trapped the passing army of Keoua, and killed 80 or more people who were trapped. It has been suggested that it was the toxic gas rather than the ash that overcame the Keoua supporters. The volcano observatory said the ash eruption dumped 100 million cubic yards of ash on the landscape, some of it more than 35 feet thick.
For updates on what's happening at the volcano, see
© 2008 Jan W. TenBruggencate