Posted on 08/28/2003 9:40:09 PM PDT by blam
Glaciers Dominated L.A. Skyline Larry O'Hanlon, Discovery News
The San Gorgonio Mountains
Aug. 27, 2003 — Despite its palm-lined boulevards, Hollywood was just miles from glaciers as little as 5,000 years ago, according to California geologists.
Using a new technique to measure how long glacier-strewn boulders have been ice-free, geologist Lewis Owen of the University of California at Riverside and colleagues have discovered there were several glacial periods on San Gorgonio Mountain immediately northeast of Los Angeles.
"The ultimate aim is to determine the fluctuation of the ice sheets and climate during the last glacial period," Owen said. That, in turn, might help sort out how future global climate changes could play out on local climates.
On TV: Get a reminder to watch "Discovery Spotlight", Discovery Channel's current events program.
Get a dose of history on our "Unsolved History fansite!"
Among the more puzzling aspects of the Los Angeles area glaciers is that they existed at a time when the much higher, colder and more northern Sierra Nevada mountain range was glacier-free, according to Alan Gillespie, a Sierra Nevada glacier specialist at the University of Washington in Seattle.
"Glaciers on San Gorgonio may define a different chronology of glacier advances than in the Sierra Nevada, only 250 kilometers north," Gillespie explained.
The seemingly contradictory existence of glaciers in Southern California at a time when the Sierra Nevada had none probably had a lot to do with the temperatures and where the jet stream funneled storms, according to Owen.
"The jet stream was being pushed further south (during the colder epoch)," Owen said. "That brings in very high moisture supply."
Combined with the six- to eight-degree cooler temperatures, conditions were enough to allow pile-up after pile-up of snow on the cool, shady northern slopes of San Gorgonio that lasted year-round. Eventually that snow compacted into glaciers that carved out steep valleys on the mountainside.
It wouldn't take much additional moisture because perennial snows have been seen on San Gorgonio even recently during wet El Nino years, according to Owen.
"This result, if true, suggests that California experienced strong regional variations in climate on the scale of a few hundred kilometers," Gillespie said, "variations that do not occur to the same degree today."
Owen and his team conducted their research by first mapping out the glacial moraines — the piles of rocks and boulders dropped by the glaciers when they melted. They then employed a dating technique that relies on cosmic rays breaking down elements in the rocks when they are exposed to the open sky.
The longer a rock is ice-free and exposed to the sky, the more elements are broken down by cosmic rays. The amounts of changed elements, and hence the time the rock has been sitting ice-free, can be measured with modern laboratory instruments.
Let me know if you wish to be added or removed from this ping list.
'Arlington Springs Woman' 13,000 Year Old Human Skeleton, California, Island
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.