Newspaper article The Christian Science Monitor

What Keeps Nature's Sandstone Arches from Falling? Oddly, It's Gravity

Newspaper article The Christian Science Monitor

What Keeps Nature's Sandstone Arches from Falling? Oddly, It's Gravity

Article excerpt

Photos of graceful sandstone arches, villages set deep into natural alcoves in cliffs, or gravity-defying rocks perched atop pedestals are staples for summer-vacation uploads to Flikr or Instagram.

Wind may have freed these pillars and arches from their surrounding rock or carved out the alcoves. But gravity is the ultimate "glue" that ensures these spectacular landforms stand for hundreds to thousands of years, according to a new study.

For tourists visiting places such as Arches National Park in Utah, that's good news. For gravity, it's a major role reversal, notes a research team led by Jiri Bruthans, a geologist at Charles University in Prague.

Gravity long had been seen as a force that worked to tear down these landforms. But lab experiments and modeling studies the team conducted suggest that for these features quite the opposite is the case.

In effect, as erosion eats away at the surrounding rock, the rock that remains has to bear the weight of any overlying sandstone. This stress increases as erosion shrinks the rock formation until the compression is intense enough to lock the sandstone grains together. Wind has a much tougher time chipping away at this scrunched sandstone. Facing a vastly slower rate of erosion, what remains - arch, pillar, pedestal, or alcove - becomes a fixture on the landscape.

"A lot of textbooks need to have some adjustments made to them now," says Alan Mayo, a geologist at Brigham Young University of Salt Lake City and a member of the research team.

The team first uncovered clues to this mechanism at Strelec Quarry in northern Czechoslovakia, a source of sand for highly valued Bohemian glass.

Chunks of the sandstone removed from the quarry readily disintegrate even when rubbed between fingers, Dr. Mayo explains. But to mine it, the sandstone has to be blasted free - a testament to the interlocking nature of the grains when subject to the pressure of overlying rock formations. …

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