Tectonic Cracks

 A roughly 12" wide tectonic crack

Tectonic cracks are usually associated with pressure ridges.    Whenever a ridge terminates in the middle of an ice sheet there is a tectonic crack continuing onward.  They also occur by themselves.  The have a characteristic irregularity about their shape.  If they are refrozen there are usually several vertical white freeze lines from previous openings. They are also one form of what is called wet cracks (wet cracks also includes contraction cracks).

3" tectonic crack with many refreeze lines. Picture taken in mid March.

They range in width from an inch to over a foot.  Often they are reasonably easy to see from a moderate distance but sometimes they are not.   They are a hazard to iceboaters for catching runners and, possibly, causing a crash.   They are generally not a problem for skaters who can step across them fairly easily.

Tectonic crack wiith some buckling of the ice sheet. Burlington Harbor 2005

In the spring they may take a different character.   They take over the role of accommodating the expansion and contraction in the ice sheet (See Spring Tectonic Cracks)

Frozen tectonic crack. The little dark stars are refrozen small infiltration holes (roughly a foot appart)