Frost‐cracking conditions, Bylot Island, eastern Canadian Arctic archipelago

The meteorological and ground temperature conditions under which frost cracking takes place in an ice‐wedge polygon site were inferred from electric cables that were probably severed by ground thermal contraction. Between 1997 and 2002, the severing of cables in the active layer occurred mostly in January. The daily mean air temperature when the cables broke ranged from −25 to −40°C, with a mean of −34.3°C. They generally broke after a drop in air temperature of about 7.9°C over a mean period of 18 h, at a mean atmospheric cooling rate of −0.5°C/h. The breaks occurred a few hours to a few days after the arrival of persistently cold temperatures, the daily mean ground temperature being −22.9°C at 2 cm under the surface (1997–2002) and −18.6°C at the permafrost table (2000–2002). The mean thermal gradient in the active layer at the time of breakage was −10.9°C/m. Maximum ground cooling rates during breaking episodes were located in the active layer or at the top of permafrost. Copyright © 2005 John Wiley & Sons, Ltd.