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THE THERMO-MECHANICAL BEHAVIOR OF FROST-CRACKS OVER ICE WEDGES: NEW DATA FROM EXTENSOMETER MEASUREMENTS.
Session: John Ross MacKay Symposium - Permafrost III / Symposium John Ross MacKay - Pergélisol III
Denis Sarrazin, Centre d'études nordiques (Canada)
Michel Allard, Centre d'études nordiques, Université Laval (Canada)
Specially adapted extensometers were deployed across eight frost cracks over ice wedges on Bylot Island in order to measure the timing of cracking and width variations of the open cracks over the winter. The cracking-contraction-expansion data were correlated with atmospheric and ground thermal temperature data acquired by automated meteorological stations and thermistor cables. Analysis of the data shows that narrow, sub-millimeter-size cracks first open abruptly early in winter when the active layer is frozen back. The cracks abruptly expand later when permafrost temperature falls below -10 °C. They keep enlarging over the winter, reaching widths between 6.8 and 18.2 mm by the end of March when permafrost temperatures oscillate around -18 to -20 °C. Short and small width variations in winter are associated with warmer spells of a few days duration. The cracks narrow by the end of the winter with warming ground and air temperatures. But they stay open at about half of their maximum width for several weeks in May-June, at the time of snowmelt.
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