Hummocky Ice Cover on the Athabasca River near Fort McMurray, AB (Canada), Feb 18, 2004
This photo shows the height of the hummocks on the winter ice cover on the Athabasca River in the steep reach upstream of Fort McMurray (the person in the photo is about 6′-4″ tall). An ice jam formed at this location during freeze-up, creating these particularly large hummocks in the ice surface topography. The ice was grounded in places and the water was under pressure elsewhere; when we drilled our first hole, water gushed out and flooded the ice cover.
(photo by UofA River Ice Group: Nikon E950, f/6.6, ISO-80, FL 19 mm, 1/61 sec. exposure)