Thursday, June 26, 2008

Tarr Inlet

I picked up a copy of John Muir's Travels in Alaska at the lodge and started reading his accounts of visiting Glacier Bay in the 1800s. Everything in these photos was still under thousands of feet of ice at that time. The glacier named after him is now hidden, having retreat far up it's valley (Muir Inlet), and our boat didn't pursue it.

Two glaciers still emerge from the Fairweather Ice Field into the head of Tarr Inlet - the Margerie and the Grand Pacific. The former is the classic calving glacier, a face of blue ice several hundred feet high with relatively little rocky debris except at its margins. The Grand Pacific, at least from this perspective, is an enormous load of dirt being carried to the sea by the ice. It also appears to have retreated far enough so that it is barely qualifies as a tidewater glacier.

As you head up Tarr Inlet, you are following the retreat of the ice. 20 miles from the glacier, the landscape is many decades old, the geology has begun to settle down and the forest has moved in. As you approach the glacial front, the landscape gets younger - alder thickets on highly unstable rocky slopes. And in front of the ice, the land is only freshly exposed and there is no obvious vegetation.

In the photo up the alluvial fan into the mountain valley, you can see sloping lines (they are subtle) in the trees to the right of the stream showing a series of terraces developed as the stream has rapidly cut down into the ravine. The photo of the kayaks on the beach contains an intriguing feature. The beach, although it is a very young feature, is a fairly ordinary gravel beach (as far as I can tell from the boat), but it is backed by a higher terrace - something I did not see widely exposed elsewhere on the inlet. I'm guessing this is a remnant of a backbeach formed many decades ago, after the glacier retreated past this point, but before significant rebound had occurred. It has now been lifted beyond the reach of the waves and tides. In most places, this feature would be eliminated by subsequent erosion, but here it has been preserved - at least for another decade or so until the beach erodes back across it.

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