Snow Shadows

February 01, 2012

Ss2Web

Photographer: Stu Witmer
Summary Author: Stu Witmer

What’s going on here? I’ve asked around and received some interesting possibilities, but so far no one I've talked to has ever seen this particular effect before. I took these photos on a recent trip to Iceland. It was about 9 a.m. on September 11, 2011 after a light snowfall. Temperatures were right around freezing. GPS on my camera gives the image location as 65.767733, -17.169181 and the altitude at 1,434 ft (437 m). This is just off the west side of the Holasandur volcanic sand desert in the island’s north. The mountain in the background is the Gaesafjoll volcano and the camera is facing east (ENE). I can say that it had been very windy for several days. On one of those days, we were on Breidamerkursandur, the black sand beach on Iceland's south coast. The wind was so strong it knocked me over. Down on the deck I was relentlessly buffeted by intensely blowing sand. When I stood up again I noticed that the sand was not blowing much higher than my knees. I wondered if something similar was going on with the snow. A strong wind, blowing consistently from upper left, might then explain the shadows. i.e., the snow-laden wind would carry streaks of load Ss2closeupWebpast the rock on either side, and the shadows would reflect simple interruptions in that sheet of blowing granular material. In the "close-up", you can see that the snow is pretty wet (though it need not have been so when it fell). Wet snow can still be redistributed if winds are sufficiently strong. Looking closely it appears that some of the "shadow" track have melted and then partially re-frozen with water glazing the surface. Click here or on the related link below for the details of other possibilities.

Photo details: Top - Camera Maker: HTC; Camera Model: PC36100; Focal Length: 4.9mm; ISO equiv: 117; Color Space: sRGB. Bottom - Camera Maker: Canon; Camera Model: Canon PowerShot SD1300 IS; Focal Length: 17.3mm; Aperture: f/5.6; Exposure Time: 0.0020 s (1/500); ISO equiv: 125; Exposure Bias: none; Metering Mode: Matrix; White Balance: Auto; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB. Software: GIMP 2.6.1.