Last month WC posted a 1975-2015 comparison shot of Worthington Glacier. Mrs. WC came across an older photo of Worthington Glacier recently. The photo is undated. The Richardson Highway is in pretty good shape in the photo, which suggests mid-1930s to mid-1940s. If any reader has better information of the photo’s date, WC invites you to share in a comment.
The angle of the photo is a little different, but let’s compare this earlier shot to WC’s photo in July 2015:
The changes are even more dramatic than shown in WC’s 1975 photo. The south lobe is much thinner and narrower; most of th north lobe is simply gone. The lowest rock peak against the skyline is much more exposed, and the main body of the glacier, which bulged up in the old photo, has mostly collapsed in 2015. The width of the snouts of both lobes are a fraction of what they were. The rock ridge dividing the two lobes is exposed another quarter mile or so up the glacier.
Apart from the ice, note in the old photo there is no vegetation on the glacier moraine – the piles of rubble – in front of the glacier. That area is covered with 10 foot high alder, now. More evidence of Worthington’s retreat.
Glaciers advance an retreat for all kinds of reasons. But the physics is well understood: if the rate of accumulation of snow falls below the rate of melt, the glacier retreats and, eventually, vanishes. If the accumulation line climbs above the ridge line, the glacier will vanish. Plainly, the melt rate of Worthington Glacier has exceed the accumulation rate for the last century. The reason why is where it gets complex. But warming temperatures are a factor. Even if warmer temperatures mean more moisture in the air, and more snowfall at higher altitudes, it does a glacier no good if the snow all melts in the summer. It’s total accumulation – the amount left at the end of autumn, at first winter snowfall – and not the amount of snow that falls each winter, that builds and maintains a glacier.
Which is why WC thinks climate change is the primary culprit in the shrinking Worthington Glacier.