Small Debris Flow Event off the Gower Peninsula, Wales

October 07, 2012

Debris_Flow_3Da (Large) (2)

: Brian Barrett; Brian's Web site
Summary Author: Brian Barrett

Having braved a swim in the chilly water off the Gower Peninsula, Wales, I saw this wonderful example of a small-scale debris flow on my return walk. I jogged about 1/3 mi (500 m) to get my camera and back again to find the same spot. Fortunately, only one footstep had been added to the scene. The photo was taken at low tide (12:30 p.m.) at Three Cliffs Bay -- this stereo pair allows the scene to be viewed in 3-D. It actually shows a double landslide/debris flow event and nicely illustrates the changing cohesiveness of sand as it dries or dewaters. The capillary action of water on the sand grains provides suction and cohesive strength, known as the sandcastle effect. However, as the sand has dried, this apparent cohesion has been lost, and a failure occurred. What's especially interesting here is that as the material continued to dry a second failure event occurred with basically the same run-out path. The two objects at left center are shown for scale. The pair can be viewed by "free viewing" and by using a stereo viewer such as the OWL. Click here for instructions on how to view using both of these methods. Photo taken on September 1, 2012.

Photo details: Camera Maker: Canon; Camera Model: Canon EOS 550D; Lens: Canon EF 18-55mm 3.5-5.6 kit lens; Focal Length: 35mm; Aperture: f/8.0; Exposure Time: 1/1250 s; ISO equiv: 400; Exposure Bias: none; Metering Mode: Matrix; Exposure: aperture priority (semi-auto); White Balance: Auto; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB; Software: GIMP 2.8.0.