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Pattern formation in permafrost

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Lunch in the open plan area at 12.30

Polar regions of both the Earth and Mars are host to a surprising variety of surface patterns, which form in soils which are permanently frozen (permafrost). These patterns form, in large part, due to the complex interactions between soil, ice, and in some cases, liquid water. This talk will focus on two such common geomorphologies: polygonal terrain, and patterned ground. Polygonal terrain occurs in areas of ice-saturated permafrost which see large temperature variations over the year. The winter cooling creates a large strain in the ice component, leading to fracture. These cracks remain open for some time, and snow and detritus can fall into them. In the summer, when it warms, the cracks heal, but there is a net addition of material. Over thousands of annual cycles, the crack networks can thus grow and develop into beautiful regular polygons, which cover vast areas of circumpolar terrain. Patterned ground relies, instead, on instabilities that occur during the freezing of water-rich permafrost, which leads to horizontal variations in ice content. These variations cause differential frost heave, as areas that accumulate more ice are forced to expand more to accommodate it. When the ice melts, the soils deflate, but they do not return completely to their original state. Over many cycles, repeated heaving can churn up the active layer of permafrost in a convection-like way. This leads to landscapes covered with gently undulating stripes, as if from a giant’s plough, or sorted circles of stones. I will report on recent field observations, from Antarctica and Greenland, which attempt to study the rates at which these processes occur. I will also discuss further plans for experiments to investigate these intriguing pattern formation problems.

This talk is part of the BPI Seminar Series series.

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