Saturday, July 11, 2015

Medano Creek

Shorelines and geomorphology, but instead of coastal processes, the story here is the interaction of fluvial and aeolian processes. The broad San Luis Valley gathers sediment eroded off the surrounding mountain ranges, particularly the San Juan range to the west. Like so many western valleys, this one was once (probably more than once?) filled with a large lake and sand and silt accumulated on its bottom. When the lake dried up, southwesterly winds remobilized the sandy material and blew it across the valley, piling it up against the base of the Sangre de Christo Mountains and creating this large dune field. Storm winds coming down the hill from the east further shapes the dunes, creating the landscape we see today.


Medano Creek flows out of the Sangre de Christosand is deflected southward when it encounters the dune field. In spring, when it is flowing, it erodes the forward edge of the dunes and carries sand southward into the valley, where it is probably picked up again by the wind when the creek dries up.

The braided nature of the broad shallow creek is a result of its being maxed out with sandy sediment. It was fun to see the channels and riffles shifting around, even over short periods of time, and to watch the rapids surge as the flow fluctuated.

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