Ice on Swamps
Swamps account for a lot of break throughs relative to the amount of travel on them. Many of of the breakthroughs are into a muddy bottom but, as described below, they can be in deep water. Two occurred in 2012 on thinly skinned holes a few feet from the edge of Shelburne Pond, VT. It has cattail swamps on about half its perimeter. The thin ice over the holes was hard to spot as the ice had been through at least one snow-thaw cycle. One fall, by a friend in a dry suit, resulted in a bopped chin and couple of stitches as a result of his forward momentum. The other was a solo person who was staying close to the shore so he would be over shallow water in case he fell through (in this case that worked: it was waist deep where he went through). A test pole would have most likely avoided his getting wet and ice claws would have made getting out easier, especially if it had been deeper. In a follow-up on these accidents we found a few similar skinned-over holes as far as 50 feet from the edge of the cattails. Most of the time we do not find holes like this, especially this far from the edge.
Another friend, as a teenager, took a short cut across an ice covered swamp on his way home. He thought the very cold temperatures of the day would assure the ice was thick enough. There was some snow on the ice. He broke through into water over his head. He had great difficulty getting back on the ice because it kept breaking. He finally made it back onto thick enough ice about the time he figured his life was soon to be over. He said the walk to the first house he came to almost got him as well. Thirty years later I ran into him as we were about to go out skating on the lake. As we stood there in dry suits, helmets and inflatable life-jackets, he told us, in no uncertain terms, that we were nuts. His teenage experience obviously left a lasting impression.
My experience walking across ice covered swamps is the likelihood of finding thin ice is much higher than on a lake. As my friend found, swamps often have deeper areas that you might not expect.
I believe there are few reasons swamps are a problem.
- Ground water flows through the swamp toward the lake in complex paths that can bring warmer, deeper water up to the bottom of the ice sheet.
- Swamps often catch and hold more snow to insulate the ice, making it harder to get thicker and easier for under-ice erosion to take place.
- The vegetation absorbs sunlight more effectively than ice, heating the ice directly or warming on the water and bottom underneath it. The vegetation also reflects infrared radiation from the ice surface, inhibiting radiational cooling.
Swamps should always be approached as though they are dodgy ice. Take ice claws, a test pole, a buddy or two, throw ropes and flotation. Expect them to have thick mud at the bottom and to be over your head in places.