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Naturespeak

Good news and bad news, but a brighter horizon for our glaciers?

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Predictions of positive outlooks for our glaciers were rampant among our citizenry because of the inclement spring and summer.

But they forgot about the basics of glacier movement, and so what was measured in early September of 2011 may be a surprise to many.

The "health" of a glacier is controlled by the amount of snow received in its accumulation zone, and what happens to it there takes its time to translate to whether the glacier expands or recedes thereafter.

All glaciers have a summer-induced ablation zone, which melts away the winter snow cover. Yes, even this summer Wedgemount and Overlord Glaciers were reduced to exposed ice below the equilibrium line; that is, the boundary between accumulations of leftover snow to ablation below it, providing exposed ice.

If there is excessive accumulation, the snows will eventually metamorphose to ice, which in turn drives the glacier forward, over and above its usual rate of movement that occurs every day of the year. The time lag between receipt of excessive accumulation at the head of the glacier and an advance of its tongue (terminus) in the ablation zone is variable. The length of glacier, the slope of the bed of the glacier, the irregularities of the bed, the amount of water on the bed, amongst other lesser factors, will all dictate the pace for each glacier.

An accumulation zone that far exceeds the area of the ablation zone is another big item.

Overlord Glacier, for example, has a large accumulation zone, whereas Horstman Glacier's zone is miniscule. Wedgemount Glacier is on a relatively steep slope and hence a change above will quickly translate to a change at its terminus.

If we recall, the 1998/1999 winter was a century-ending record snowfall, but it was not until 2007 that Wedgemount responded with a much-reduced recession of its ablation zone. Unfortunately, it did not advance, but there was a four to six fold reduction in recession (2.5 metres). Thereafter melting at the terminus increased and this year it was 17.3 metres.

So, the crystal ball says: 15-plus metres' recession each year until 2018/2019 when, hopefully, last year's second greatest snowfall, followed by the third coolest spring/summer, will show an advance of the glacier tongue. By this time the ice cave, now developing near its snout with a shallow lake beneath it, will be fully-developed, if not again shrinking in size.

Overlord Glacier is in its second year of response to the 1998/99-winter snowfall.  Last year it recessed one metre, this year it was 0.7 metres or less, and next year - who knows?

In 1922/23 this past season's influx at glacier head might provide a significant advance.

However, there are devils in the interim: For example a very warm summer, which reduces the snow pack in the accumulation zone, or a colder and cloudier than normal summer, which leave a blanket of snow on the entire ablation zone.

And, I might add, each glacier has a mind of its own! Wedgemount's loss this year was much greater than expected at 6.2 metres from September 2009 to September 2010. Yes, we were sideswiped at (-) 17.3 metres!

 

 

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