This edition of the photo of the week highlights something I feel that I should have explained a long time ago: my banner photo. The banner photo above is more than just a pretty picture. It actually illustrates, very beautifully, a truly interesting phenomenon that can be encountered in Arctic watersheds. I speak of the aufeis, pronounced oh-fyse, which is the giant sheet of ice covering the river. Aufeis form in one of two ways. The first is when an ice dam forms in a river and water piles up behind it and then overflows and freezes upward creating an aufeis. The second is when aufeis occur at points of groundwater discharge into a river. Groundwater, which has a much higher temperature than surface water during the winter can discharge year-round. Therefore, it continues to discharge even when temperatures are well below freezing. However, when it discharges into the frigid temperature of an Arctic winter it rapidly freezes causing the development of an aufeis at the discharge point, which is the case in the pictures below. It is possible to distinguish the two types of formation by analyzing the stable isotopes of 18O and 2H in the ice to determine its source: groundwater or river water.
These aufeis are relatively small. Only a few sqaure kilometres max. However, they can grow into massive ice bodies. The largest known is at the Moma River, Siberia and is between 70 and 110 km^2 (Clark and Lauriol, 1997).
Clark, I. D., & Lauriol, B. (1997). Northern Aufeis of the Firth River Basin, Northern Yukon, Canada: Insights into Permafrost Hydrogeology and Karst. Arctic and Alpine Research, 29(2), 240–252.