Wednesday, February 13, 2013

More on the Toandos Landslide

When I posted on one of Toandos landslide complexes landslide-complex-on-toandos, I forgot to add the oblique aerials I had of the slide area.


1994 (WDOE)

The 1994 image is pre the big slide event. Small shallow slides along the shore are evident at several locations and trees have been removed for a view on one of the narrow properties above the slide. Otherwise most of the shoreline bluff and slide complex is forested. However, this slide complex had already been identified by Jefferson County in 1983. Note the small kettle lake in the upper part of the picture. The land in the upper part of the image is underlain ice wasting deposits and glacial till.

2001 (WDOE)

As can be seen in 2001 nearly all the trees on the lower portion of the bluff have been removed. Note the relatively fresh headwall scarp marking the extent of upper slide complex. The land at the headwall dropped about 20 feet. The upper half of the bluff moved like a glacier with trees on the slide surface with the lower part of the upper deep slide cascading over the steep bluff to the shore below. That is what took out nearly all of the trees.

2006 (WDOE)

By 2006 most of the lower bluff is tree covered again with a stand of red alder. A good example of one of the challenges of reading the landscape - the trees get in the way.

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