Local recession has accelerated
Whistler Naturalist Society
Annual surveys of the positions of the termini (snouts) of Overlord Glacier and Wedgemount Glacier were carried out on Sept. 8 and 16 respectively. Due to knee surgery the surveys were omitted in 2004, though a spot check on Wedgemount was carried out by a helpful day hiker in that year, thus providing a position for the 2003 to 2004 interval as well as 2004 to 2005.
For Overlord the data is for the two-year interval only, with no monitor in place to position the glacier snout in 2004.
Surprisingly, the two glaciers showed almost identical distances of recession for the two-year interval: 33.3 metres for Overlord, and 31.0 metres for Wedgemount. For the latter, the recession for both years was nearly the same: 15.4 m for 2003-2004, and 15.6 m for 2004-05.
For both glaciers, the recent annual recession rate is above the long-term average, which had been 12.6 m/year for Wedgemount, and 10.3 for Overlord, although the latter had been at a much slower rate since 1951, and actually advancing at about 5 metres/year for the 1951 to 1986 time span. The increase in recession rates no doubt reflects the impact of a series of El Niños which inundated western North America in the 1990s, culminating in the unusually warm winter of 1997-98, notwithstanding the recent outburst added in 2005.
However, it is what happens to the head of the glacier (accumulation zone) that determines the position of its down-valley snout many years hence. That is, there is a lag in action, controlled by glacier length, slope, sub-glacial water flow, etc., that regulates when the terminus responds to precipitation variations at the glaciers head. In this regard the heavy snowfall in the winter of 1998-99, with its prolonged summer residual presence, has not yet slowed down the recession of either glacier, but it should happen at the shorter and higher Wedgemount Glacier within the next couple of years. For Overlord it could be another five or six years before the snout returns to its oscillating behaviour as witnessed before 1993.
How much of this surge in glacier wastage is due to mankind-induced global warming, as opposed to natural fluctuation, is unknown. Over 5,000 years ago our glaciers suffered a similar if not a more severe demise a sobering fact which alarmists to date have failed to recognize.
During the two-year period outwash gravel from the Wedgemount pushed out the delta into the lake by 3.1 metres; that is the lake is slowly shrinking in areal extend as well.
The goats are still visiting the terminus of the Overlord Glacier but some of the trails stamped out by the herd of 12 or more in 2003 have not been used this year, and dust bath basins are fewer, suggesting that the herd is either spending less time at the Overlord terminus or that their numbers have been reduced. This herd requires some active monitoring and management to ensure its continued presence in the Overlord and adjacent alpine basins.
Saturday, Oct. 1st, 8 a.m. Monthly Bird Walk. Meet at the bottom of Lorimer Road near the Catholic Church. Everyone welcome. Please note the later, more humane, starting time.
Oct. 14-15. "Fungus Among Us" Mushroom Festival. Join the Whistler Naturalists for two days of fungal fun. The event includes a slide presentation on Friday night, a foray on Saturday morning, and a cooking show with Ophra Buckman on Saturday afternoon. Watch this column for more details next week.