A mystery in the stone
Sunlight shines through the mysterious volcanic columns being studied by researchers on the shore of Crowley Lake.
The strange pillar-like formation emerged after Crowley Lake reservoir was completed in 1941: Stone columns up to six metres tall connected by high arches, as if part of an ancient Moorish temple.
They had been buried and hidden for eons until the reservoir’s pounding waves began carving out the softer material at the base of cliffs of pumice and ash.
In the ensuing decades, the columns were regarded as little more than curiosities along the eastern shore of the Los Angeles Department of Water and Power reservoir, which is best known as a trout fishing hot spot about 16 kilometres south of Mammoth Lakes.
But now answers are emerging from a study at the University of California, Berkeley. Researchers have determined that the columns were created by cold water percolating down into — and steam rising up out of — hot volcanic ash spewed by a cataclysmic explosion 760,000 years ago.
“These columns are spectacular products of a natural experiment in the physics of hydrothermal convection,” said Noah Randolph-Flagg, 25, a PhD candidate and lead author of the study.
The blast created the Long Valley Caldera, a massive 16-by-3-kilometre sink that includes the Mammoth Lakes area. It covered much of the eastern Sierra Nevada range with a coarse volcanic tuff, or ash fall.
Randolph-Flagg said researchers not only discovered the origin of the columns but also learned a great deal about the surrounding landscape. “They have a lot to tell us about what the region was like before and after the caldera exploded, and about how volcanoes can change local climate,” he said.
The columns began forming as snowmelt seeped into the still hot tuff. The water boiled, creating “evenly spaced convection cells similar to heat pipes,” according to the study to be presented next month in San Francisco at an American Geophysical Union meeting, the world’s largest conference in geophysical sciences.
Analyses by X-rays and electronic microscopes of samples of the columns found that tiny spaces in these convection pipes were cemented into place by erosion-resistant minerals.
Randolph-Flagg estimates that as many as 5,000 columns exist within a five- to seven-square-kilometre area east of the lake. They appear in clusters and are diverse in size and shape. Many are grey, straight as telephone poles and encircled with horizontal cracks about 30 centimetres apart. Some are reddish-orange in colour. Some are bent, or all tilting at the same angle. Still others are half-buried and resemble the fossilized backbones of dinosaurs.
Next year, the Department of Water and Power will begin ferrying students to the site as part of an “effort to further educate the public about these invaluable natural resources,” said Amanda Parsons, a spokeswoman for the utility.
More analysis could help scientists better understand how quickly the columns solidified.