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Cool spring, late summer reduced local glacier recession

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Melt season in Whistler's glaciers ended in late August with cooling temperatures, cloudy skies and snowfall in the alpine on several occasions. The logbook at the Russet Lake cabin records snowfall on two nights of the Labour Day weekend.

We arrived on Sept. 7 with the snowline well above the cabin, but it was definitely cool. The ensuing overnight freeze-up all but ensured little melting on nearby Overlord Glacier.

The following morning we began measurements from baseline to its forked snout. The snout closest to the cabin revealed a half-metre advance from last year's position. Eureka! "Global warming arrested!" we said in jest. The other snout, however, brought on reality - a 2.5 metre recession from last year's position. Yet the miniscule amount was encouraging, especially when the two results were combined to yield a scant 1.0 metres of recession.

So what brought on the 20-fold reduction from last year's result? Certainly the cold spring and cold early summer helped; the snowpack was very slow to melt away, and in fact the trail to Russet Lake still has a few winter snow patches over it. And the short distance between the moraines pushed up by the ice movement to the present ice tongues is short, corroborating the hypothesis.

However, there are a few other factors. Weighing most on our mind is the century-ending climax winter of 1998-99 - a record-buster for snowfall. Taking 11 years for that record pack to generate a surge of ice from accumulation zones to glacier terminus is about the right time interval for a glacier of Overlord's dimensions.

But why did one snout advance and the other not?

The other factor is the blanket of rock debris on the ice surface, which acts as an insulator, blocking the penetration of atmospheric heat. The advancing snout is covered with rocky debris whereas the recessed snout is of clean ice and exposed to solar rays. Thus, a quirk of nature (rockfall onto the glacier) likely prevented a 2.5 metre retreat of that snout.

But even that amount of recession is miniscule compared to the long-term picture. Gross recession was arrested in 2010 - another Olympic victory!

On the following wet and snowy weekend (Sept. 11-12), the annual Wedgemount Glacier Survey was carried out with the Geomatics Division of the B.C. Institute of Technology joining in. Their report on last year's investigation was presented at the site, showing very significant down-wasting of the glacier surface over the last 32 years - 40 metres was the average loss.

Recession of the glacier in the up-valley direction from the lakeshore continues, 6.2 metres since the 2009 survey, though significantly less than the 28.4 metre recession recorded between 2008 and 2009. The small reduction is encouraging, but other features on the ice surface near and at its margins indicate significant recession in forthcoming years. A rock ridge is emerging through the ice on its left side, which is reducing the width of the glacier. On the right side a large ice cave has opened up on the ice margin, floored by a pond. Collapse of the ice roof of the cave will generate significant change in the outline of the terminus. How much will the cave continue to enlarge before this epic event takes place?

On the flipside there is a scheduled La Nina year in the Pacific oceanic circulation. A cold winter is on the books. Will it drag on into the spring to provide another assist to reduced glacier recession?

We will let you know a year from now.

Surveys this year also assisted by Doug Wylie (for Overlord), Rob Tupper (the son of the now deceased founder of the Wedgemount project, beginning in 1973), Dave and Graham Lyon (father and son of Don Lyon, was also assisted the first few years of surveys at Wedgemount). That makes three generations of helpers at Wedgemount.

 

 

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