Finger rafting on the Weddell Sea
When thin ice floes collide, spectacular fractures result.
Sea ice comes in many forms. One rarer form is the blocky geometric patterns created by “finger rafting”, which occurs when two thin ice floes collide.
Blocks of ice from the two floes slide above and below each other in a pattern that resembles a zipper or interlocking fingers. Saltwater expelled from the ice forms a solution that acts to lubricate the sliding chunks.
Finger rafting can only occur when the floes are very thin – calculations suggest that 20 centimetres is the upper limit on thickness. Any thicker and the ice will be unable to bend enough. Collisions between thicker floes often result in big pile-ups, known as “ridging”.
This photo was taken on 14 November in the Weddell Sea, off the Antarctic Peninsula, by Operation IceBridge scientist John Sonntag.