Friday, May 14, 2010

A Few Friday Fun Fotos: A Fluvial Forest?

For our highly irregular Friday Fun Fotos Feature, I offer a Fluvial Forest, and a bit of a mystery. These are Jeffrey Pine trunks, in the middle of the West Walker River in the eastern Sierra Nevada east of Sonora Pass.
Why were these trees growing in the middle of the river, and how did they die??

Speculations are welcome in the comments section!


Lockwood said...

They appear to top out at about the same height as the terrace. I'm guessing there was a forest on a valley floor a bit deeper, which was inundated by a debris flow. The trees died, and the portion above the new ground level decayed. The portions below ground, with less oxygen, and possibly saturated with ground water, were preserved. As the river has eroded down, these trunks have been exhumed.

That's my guess, and I'm sticking with it.

Gaelyn said...

Those pines must have been growing pre-fluvial. Wonder how long ago that was. Or what Lockwood said.

Roy said...

I actually did a research project on a similar situation.

When glaciers surge, they often truncate trees almost exactly the way you have photographed. It typically happens when a sandur buries a forest which is later overrun by the ice.

Seeing as my experience was in Alaska at an active ice margin, and yours is in California; I do not suspect them to be the same process, but possibly similar (along the lines of what Lockwood mentioned.)

If you're interested, I can explain my experience in greater detail or send you some images.

Anne Jefferson said...

Is there a mining history in this region?

Here's my totally speculative idea: The trees grew on the valley floor or toe slopes. Mine spoils in the stream caused it to aggrade, raising the streambed, burying the tree roots, and drowning them with a raised watertable and more frequent flooding. Following the end of mining, the river may now be incising again and will eventually leave these behind as a cut and fill terrace.

Sue Campbell said...

I vote for Lockwood's guess.