Submerged forest suggests massive Sierra drought
September 11, 2012
RENO – A forest submerged on the bottom of a Sierra Nevada lake holds evidence of a massive drought hundreds of years ago, scientists said.
And as Nevada and much of the country endure one of the worst drought years in recent memory, scientists continue studies of a Sierra drought they say likely dwarfed any event of modern times.
Scientists examined stands of trees rooted more than 100 feet beneath the current surface of Fallen Leaf Lake – evidence that a drought serious enough to drop lake levels by that amount and long enough to allow mature trees to grow occurred during medieval times or earlier, the Reno Gazette-Journal reported.
The dry period has come to be called a “megadrought.”
“The lake is the canary in the coal mine for the Sierra, telling the story of precipitation very clearly,” said Graham Kent, director of the Nevada Seismological Laboratory and member of a team of researchers who studied the trees and ancient submerged shoreline of Fallen Leaf Lake.
Their conclusions, published in scientific journals last year, could offer the best evidence yet of a Sierra drought lasting hundreds of years, Kent said.
Evidence suggests that about 800 years ago, a protracted period of drought occurred during which precipitation was less than 60 percent of normal.
“That’s what the Dust Bowl was, or maybe a little more severe, but you’re going to do it for 200 years,” Kent said.
Evidence that something was under the surface of Fallen Leaf Lake emerged years ago when deep-water fishing lines kept encountering unseen obstacles. The trees were discovered in the late 1990s by John Kleppe, an engineering emeritus professor at University of Nevada, Reno, with the aid of scuba divers.
Some suspected the trees might have been deposited on the lake bed by a landslide, but recent research using high-tech sonar gear and remote and manned submersibles indicates the trees grew where they stand, preserved in the biting cold of Fallen Leaf’s depths for centuries, Kent said. About 80 more trees were discovered lying on the lake bottom.
Scientists at UNR are continuing studies to determine how many such lengthy droughts may have occurred, but it appears they occurred multiple times over the last 12,000 years, Kent said.
It begs the question: Is what we consider normal when it comes to climate and precipitation really normal?
Maybe not. Maybe a much drier normal is really normal.
“Perhaps we’ve decided to sit in the wettest period of time and decided to call it normal,” Kent said. “That’s OK, but we may have to be ready for a new normal.”