Winter moraines and glacier monitor 2002
By Karl Ricker, Whistler Naturalists
Observations on the position of the termini of Overlord and Wedgemount Glaciers were carried out at the close of melt season September, or so we thought. Melting continued on a lesser scale during the warm and dry spell of October which, although not completely unexpected, was not appreciated by any skier or glaciologist.
Last year, NatureSpeak reported on a recession of 7.0 and 12.0-15.0 metres respectively for the above two glaciers. The main cause of withdrawal was a low snowpack over the preceding winter, followed by a hot, late summer. Happily, the snowpack last winter was near or slightly above average, and was followed by a very helpful late spring, that was not appreciated by any resident between here and Inuvik! So, reduced retraction of our glaciers was to be expected, but the ringer was the two hot spells in July and August.
On Sept. 14th, the long, slow hike to Overlord Glacier provided good news. The survey revealed only 2.8 metres of retraction over the year, as compared to the 1990-2002 average of 9.0 metres of recession per year. The bad news was revealed in the Sept. 20th survey of Wedgemount 18.8 metres of retraction over the year! The snout is now 24 metres above and 159 metres from the lakeshore. In 1991 it was at the lakeshore, although 21 metres of delta growth has taken place since, courtesy of the outwash kicked out by the receding glacier. Thus, 138 metres of recession over 11 years yields an average annual retreat of 12.6 metres, suggesting that year 2002 was 50 per cent above the norm. Whereas Overlord Glacier was 69 per cent below the norm.
The above quite opposing sets of observations are perplexing to say the least. Both glaciers appear to have a sufficiently large accumulation zone lying above the critical elevation of 2,100 to 2,150 metres. This is the so-called "equilibrium line" which separates exposed glacier ice from covering snow at the end of the summer melt season. Those that have dont have this situation, for example, the recently disappeared glacier in Saudan Couloir, are doomed to extinction. Both glaciers face an advantageous shading aspect of northwest, but to make it more perplexing, the terminus of Overlord Glacier is 200-225 metres lower and therefore in a zone of warmer and prolonged summer temperatures. So, the cause of excessive melting on Wedgemount appears to be a lack of sufficient snowfall during winter; that is, it appears to be in a local rainshadow. This is also borne out by the disappearance of one upper arm of the glacier altogether over the last century. The southeast basin below the summit of Mt. Weart is now virtually bone dry, and the residual ice at its lower end no longer joins the glacier.