Alluvial Fan, Kenai Peninsula, Alaska

September 09, 2012

Alluvial Fan (3)

Photographer: Russell Losco
Summary Author: Russell Losco

Pictured above is an alluvial fan at the base of a seasonal waterfall on the Kenai Peninsula in south-central Alaska. Alluvial fans are caused by rapid deposition of the suspended load of a stream when its gradient shallows to the point where it can no longer keep the material in suspension. The material deposits in accordance with Stoke’s Law, which states that particles drop out of suspension at a rate that's related to their diameter. Material is therefore sorted, with coarser grained sediments at the apex of the fan, closer to the source, and finer materials down-slope near the base. Note that growth that is more luxuriant occurs on the finer material. Photo taken on August 18, 2008.

Photo Details: Camera: KODAK EASYSHARE C743 ZOOM DIGITAL CAMERA; Focal Length: 6.0mm (35mm equivalent: 36mm); Aperture: f/2.7; Exposure Time: 0.0069 s (1/146); ISO equiv: 80.