All around the deserts of Utah, Nevada, southern Oregon, and eastern California, ancient shorelines line the hillsides above dry valley floors, like bathtub rings — remnants of the lakes once found throughout the region. Even as the ice sheets retreated at the end of the last ice age, 12,000 years ago, the region remained much wetter than it is today. The earliest settlers of the region are likely to have encountered a verdant landscape of springs and wetlands.
So just when and why did today’s desert West dry out?
Researchers from MIT and elsewhere have now determined that the western U.S. — a region including Nevada, Utah, Oregon, and parts of California — was a rather damp setting until approximately 8,200 years ago, when the region began to dry out, eventually assuming the arid environments we see today.
The team identified this climatic turning point after analyzing stalagmites from a cave in Great Basin National Park in Nevada. Stalagmites are pillars of deposited cave drippings that form over hundreds of thousands of years, as water slowly seeps down through the ground, and into caves. A stalagmite’s layers are essentially a record of a region’s moisture over time.
The researchers used a dating technique to determine the ages of certain layers within two stalagmites, then analyzed these layers for chemical signatures of moisture. They dated stalagmite layers ranging from 4,000 to 16,000 years old, observing that moisture content appears to drop dramatically in samples that are less than 8,200 years old.
Photo shows graduate student Elena Steponaitis taking notes while collecting stalagmite and drip water samples in Lehman Caves, Nevada. Photo credit: Christine Y. Chen
Read more at MIT.