EGU Blogs

Geology Photo of the Week #45

This weeks photo is once again related to permafrost and the Arctic….something tells me I miss being there.

Anyway, the gorgeous photo below shows a terrific example of polygonal patterned ground from Siberia. Patterned ground is a phenomenon that occurs frequently in cold regions and is caused by the seasonal freeze-thaw of the active layer/soil. This process can produce a phenomenon called ice wedges that extend deep into the permafrost (see my photo of a large ice wedge below) as water infiltrates into a crack freezing it and expanding it. This repeats annually as the ice cracks due to the extreme cold and is then filled by new meltwater from the active layer, which freezes.

Ice wedges have excellent potential as a climate research tool as they can be very old and preserve the isotopic signature of each new year’s water. In fact, my research group has an MSc. student working on this exact thing.

Sorting of sediments by the freeze thaw of groundwater also creates patterned ground as the process forces larger sediments upward and lets smaller sediment settle eventually creating little piles of rocks on the ground surface. However, in the case of the photo below, which is in a poorly drained peatland, there are likely lots of ice wedges.

Wet Sedge Polygons on Samoylov Island with Stolb Island in the background - Samoylov Island - Lena River Delta - 20.08.2010 - Sebastian Zubrzycki

Wet Sedge Polygons on Samoylov Island with Stolb Island in the background – Samoylov Island – Lena River Delta – 20.08.2010 – Sebastian Zubrzycki

Ice wedge along the Dempster Hwy. in the Yukon.

Partially collapsed ice wedge in cross section along the Dempster Hwy. in the Yukon. (Photo: Matt Herod)

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Matt Herod is a Ph.D Candidate in the Department of Earth Sciences at the University of Ottawa in Ontario, Canada. His research focuses on the geochemistry of iodine and the radioactive isotope iodine-129. His work involves characterizing the cycle and sources of 129I in the Canadian Arctic and applying this to long term radioactive waste disposal and the effect of Fukushima fallout. His project includes field work and lab work at the André E. Lalonde 3MV AMS Laboratory. Matt blogs about any topic in geology that interests him, and attempts to make these topics understandable to everyone. Tweets as @GeoHerod.