Friday, December 19, 2008

From Mt. Lafayette towards the Presidential Range, 2006

I'm using this photo I took from the summit of Lafayette in January ‘06 again because it has an enormous amount of geological and ecological history plainly visible in it. It shows examples of “fluvioglacial” outwashing. mass wasting (as in erosion), and containment, all the stuff that was going on as the continental glacier ablated. It also shows clearly how trees get selected by specific soil types and drainage patterns.

In the lower center of the photo you can see the long tongue of outwash, probably as a result of glacial outwash and, technically, it could be termed a “fluvioglacial landform” meaning that it was formed by glacial meltwater that was under pressure and had the energy to move a the heavy gravels and stones. If you study the picture for a moment you can see where the mountains actually moved. From Garfield, the peak on the left, you can almost feel where the east flank slid down towards Franconia Brook as did that large area that washed down from the ridge between Garfield and Galehead Mountain towards the valley.

It makes some sense that the southward moving glacier pushed non-resistant crustal matter, soil, gravel, small to fairly large sized rocks and boulders proglacially, or in front of it, so a lot of what we see in the photo is glacial till. But there would have been a separate process occurring as the glacier melted back northward in its retreat. The remaining movement of water and till after that would be as nominal erosion and mass wasting caused by melt water flowing as rivers and streams.

The photo shows how the hardwoods, paper birch and yellow birch primarily, like the well drained glacial till and lower elevations in the center of the photo. In higher zones where drainage is mixed the conifers, balsam and spruce, predominate. We'll focus on the herbaceous plants a little later.

Richard Goldthwait presented a paper in 1966 titled "Soil Development and ecological succession in a deglaciated area in Muir Outlet, southeastern Alaska" that I am trying to get a copy of. It's rare, but I'd like to read it and see what is salient for the White Mountains in terms of the actual chronology of soil development and ecological succession here between 11,000 and 5,000 years ago.

No comments: