Tuesday, March 26, 2013

Alluvial Fans and Glacial Moraines, Lehmi Range

Before spotting the cinder cone hiding in the crop circles crop-circle-cinder-cone, I had a great view Idaho's Lehmi Range. I was admiring the alluvial fans built up on the southeast side of the range. I have done a fair number of alluvial fan projects as a geologist and have been on the policy making and money spending side of a few alluvial fans as well - hence my enthusiasm.
But in the image below there is more than just alluvial fan deposits on the lower slopes of the range. The first image has three glacial moraines extending onto the lower slopes beyond the mountain front. These alluvial fans are visible in Google Earth as well as other satellite images. But the new, just-the-right-amount of snow and sun angle allowed for a very excellent and obvious view.
Glacial moraine in center of picture is built out on top of the main bulk of the alluvial fan.
There are two other moraines in the image. on the far right and far left 

Another angle showing two of the moraines

Closer view of the south moraine
The road is Idaho Highway 28
The southern moraine includes an older subdued moraine well out from the mountain front that has been at least partially breached by stream erosion and partially buried by alluvial sediments. I am outside my understanding of Rocky Mountain glaciation. The Pinedale Glaciation is associated with the last continental glaciation that brought glacial ice into what is now the Puget Sound region and the entire northern tier of Washington. Dort Wakefield gsa/2003RM/finalprogram/abstract correlates some of the glaciation that reached the valley as Bull Lake age - a much older glacial period in the Rocky Mountain ranges. Perhaps, the outer moraine is the older Bull Lake variety.  
These alluvial fans have a lot more history than the very young fans I have worked on in western Washington. Lots to figure out regarding past climate, uplift history and erosion history.


Geoffrey Middaugh said...

A fault scarp from the 1983 Challis quake is in this general area, named after Idaho's most famous horned dog, William Borah.

Dude Diligence said...

Look like faceted spurs along the front of that range.