27 November 2007

"Stripes:" A Type of Patterned Ground in Gelisols

Posted by John Freeland

Shegar_18 by Thibaut Cheytion
Photo credit: Thibaut Cheytion (Tibo)

Update: 12-14-2007
Received an email from Tibo, who thinks the stripes might be wind-generated. My first impression of the picture had me thinking dune ripples, as well. The odd thing, seems to me, is the thin mantle of vegetative cover on what looks like smooth dune sand. I wouldn’t expect the shifting dune sands to be stable enough for such a uniform covering of moss, or whatever the plant cover is. It might take a another field trip to solve this mystory. Here is a photo of periglacial stripes taken by someone at the University of Regina Geography Department.

In the world of soil taxonomy, the most recently “minted” soil order is the Gelisol order. Gelisols are found in very cold climates that support permafrost. Two major processes associated with Gelisol formation are solifluction (or gelifluction), and cryoturbation.

Solifluction occurs when the saturated (or nearly so) upper part of the soil thaws in summer and flows over the top of the permafrost below, creating low ridges and swales that look like “stripes.”

Since the volume of water expands about 10-percent when turned to ice, cryoturbation is a process of soil mixing, heaving, and buckling due to freeze-thaw cycles. Sometimes frost thrusting creates polygons, such as those shown in the valley here in an earlier post.

The photo above was taken by Thibaut Cheytion (Tibo), a young MBA and CFO of a company in China. Whether he knows it or not, he’s got an eye for soil geomorphology. This photo, I think, shows an especially beautiful example of patterned ground.

Because organic decomposition is slowed by cold temperatures, Gelisols are generally high in organic matter and, therefore, an important global carbon sink.