The Big Melt:Western Canada's Glaciers Hit 7000-Year Low*

by Staff Writers
Boulder CO (SPX) Oct 31, 2007

Tree stumps at the feet of Western Canadian glaciers are providing new
insights into the accelerated rates at which the rivers of ice have been
shrinking due to human-aided global warming. Geologist Johannes Koch of
The College of Wooster found the deceptively fresh and intact tree
stumps beside the retreating glaciers of Garibaldi Provincial Park,
about 40 miles (60 km) north of Vancouver, British Columbia. What he
wanted to know was how long ago the glaciers made their first forays
into a long-lost forest to kill the trees and bury them under ice.

To find out, Koch radiocarbon-dated wood from the stumps to see how long
they have been in cold storage. The result was a surprising 7000 years.

"The stumps were in very good condition sometimes with bark preserved,"
said Koch, who conducted the work as part of his doctoral thesis at
Simon Fraser University in Burnaby, British Columbia. Koch will present
his results on Wednesday, 31 October 2007, at the Geological Society of
America Annual Meeting in Denver.

The pristine condition of the wood, he said, can best be explained by
the stumps having spent all of the last seven millennia under tens to
hundreds of meters of ice. All stumps were still rooted to their
original soil and location.

"Thus they really indicate when the glaciers overrode them, and their
kill date gives the age of the glacier advance," Koch explained. They
also give us a span of time during which the glaciers have always been
larger than they were 7000 years ago - until the recently warming
climate released the stumps from their icy tombs.

Koch compared the kill dates of the trees in the southern and northern
Coast Mountains of British Columbia and those in the mid- and southern
Rocky Mountains in Canada to similar records from the Yukon Territory,
the European Alps, New Zealand and South America. He also looked at the
age of Oetzi, the prehistoric mummified alpine "Iceman" found at
Niederjoch Glacier, and similarly well-preserved wood from glaciers and
snowfields in Scandinavia.

The radiocarbon dates seem to be the same around the world, according to
Koch. It's important to note that there have been many advances and
retreats of these glaciers over the past 7000 years, but no retreats
that have pushed them back so far upstream as to expose these trees.

The age of the tree stumps gives new emphasis to the well-documented
"before" and "after" photographs of retreating glaciers during the 20th
century.