ice flowers form only on very cold nights. Photo by Jeff Peneston (PolarTREC 2008/2009), Courtesy of ARCUS
Even at temperatures well below zero you can punch through river ice. Alaskan Natives, sled dogs, and veteran fur trappers all know this. And in the wrong place at the wrong time, it can kill you.
As an Alaskan winter wears on, river ice thickens, often to a depth that can support heavy vehicles. But all ice, regardless of thickness, is prone to cracking due to currents beneath it as well as expansion and contraction from daily temperature changes. And when cracks occur, water seeps upward on top of the ice. This layer of overflow can remain slushy if it mixes with snow, or it can form its own ice creating an ice-overflow water-ice sandwich.
Sometimes regions of open water can form as river ice shifts or, more rarely, warm weather spells melt it. In either case, the normally frigid temperatures quickly refreeze the top layer. But if snow falls soon after refreezing, it can insulate this thin ice and keep it from thickening further. This thin ice is almost impossible to detect until its too late.
This is where our training takes place.
Two full days of indoor trainings had left me thirsty for some fresh air. Even if it was subzero out. Andre joined me for an evening walk before rendezvousing with other PolarTREC-ers for a Thai dinner. Just before leaving the hotel Lisa warned us about thin ice on the Chena River - our intended destination. She had heard of patches of dangerous holes out there.
Upon reaching the river Andre and I proceeded cautiously, walking either on shore or just offshore, in case Lisa's warning proved accurate. About a quarter mile downriver we had just crossed under a bridge when Andre, normally a couple inches taller than me, dropped from view. His right leg had plunged knee deep through the ice into the river. His reactions were lightning-quick: he rolled on his back toward shore - the better to distribute his weight more evenly - and quickly stood up on solid ground. So fast did he do this that the water never made into his boot, it simply froze to the outside of his pants.
Picture Practice Day in the hotel conference room
Andre thawed his pants while enjoying a red curry dinner. It pays to be cautious and know what to do in a crisis.
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