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Water Levels in the Sierra

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Water Levels in the Sierra

Postby austex » Tue Jul 30, 2013 12:01 pm

Ice Age/Ice Age gone/Global warming/what's next? No way a political statement.

Submerged Forest Suggests Sierra Drought

Associated Press Published: Sep 12, 2012, 4:01 PM EDT Associated Press


RENO, Nev. — 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 endures 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."



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Re: Water Levels in the Sierra

Postby LightRanger » Tue Jul 30, 2013 12:09 pm

That time period coincides with a substantial dry period(s) elsewhere in the Southwest that is believed to have led to the collapse of the Hohokam and perhaps other cultures.

There's still a ton we don't know about the climate of the West. As another example, the Colorado River Compact of 1922 was based on flow measurements gleaned during the first 20 or so years of the 20th-Century. Climatologists now know that on average that time period was substantially wetter than normal. So the River was oversubscribed from the outset.

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Re: Water Levels in the Sierra

Postby Wandering Daisy » Tue Jul 30, 2013 12:21 pm

A lake is not necessarily a sign of excessively wet conditions (conversely a submerged forest may not necessarily be an indication of severe long term drought). Many lakes are formed by natural dams. Say a rock fall plugs the lower end of a valley. Water still enters the upper end and just piles up. Forest gets submerged. It does not necessarily take a change in climatic conditions. The article cited does not discuss this.

In the Wind Rivers there is a lake (Scott Lake) that has an incredible 10-foot high bathtub ring. I suspect that an ice dam blocked the outlet until quite recently, and then broke. There also is a big lake that sits at the head of the Grasshopper Glacier, that melted through the glacier, and caused a sudden flood in 2003, and has subsequently re-filled.

At the peak of an ice age (glaciation), things get really dry. So dry conditions do not even indicate warming conditions. And excessively dry conditions in one place, is not necessarily an indication of dryer conditions globally. Nevertheless, quite interesting to find a submerged forest!
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Re: Water Levels in the Sierra

Postby LightRanger » Tue Jul 30, 2013 4:11 pm

WD,

That wasn't the best news coverage I've seen about this study. See here:
http://www.tahoedailytribune.com/news/6 ... mega-basin

The full study is reproduced here:
http://www.nvwra.org/storage/newsletter ... kleppe.pdf

In this case, the evidence does indeed suggest a massive drought.
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