Another Look at Nubansuit Lake, NH
November 6, 2012
In early January 2011 four fisherman returning to the launch on the east end on two snowmobiles broke through thin ice. One of them drowned (See Nabansuit Lake Tragedy). I visited the lake two days later and found large amounts of thin ice near a reef (see map below). At the time I speculated that it was related to warm, deep water from the east up-welling on the reef from the east. I did a follow-up visit in January 2012.
This map is from the New Hampshire Fish and Game Department website. They have an excellent selection of depth maps for many New Hampshire lakes and ponds.
The second visit was in early February 2012 to see if there was evidence of the reef hole that I thought I found 2011 year. I found no evidence of thin ice other than on the reef itself where sun warming of the shallow and exposed rocks resulted in some small ice free or thin areas. The large areas of thin ice that I found in 2011 were not there.
In the spring of 2012 I noticed that the google map/earth images of the area were taken on April 15, 2011; three months after the tragedy. The ice was a fairly advanced state of thaw and it shows three large open or thin areas (see below). The yellow thumbtack is where the tragedy took place.
My GPS track from Jan 9, 2011 closely followed the edge of the thin ice on its east side so there it is clear that these thin/open areas visible in mid-April were in place when the accident happened. I am surprised at how close the the track is to the edge thee months later.
During 2012, we had a similar persistent open water/thin ice formation on Shelburne Pond in Vermont. It was present the first time the ice was thick enough for us to get to the north end of the pond and stayed open until a week or two before the ice went out. At times it had wide areas of open water and the old ice was thinned for up to 100 feet back from the edge. Those wide areas were similar to the shapes seen on Nubansuit. It was a double ended, folded pressure ridge. This is the first time we have identified this sort of ice feature on Shelburne Pond in 30 years. Although we think they are uncommon, I expect we will find more, now that we know what to look for.
I think this is what occurred on Nubansuit Lake in 2011. The influence of the reef and the deep water to the on both sides is not clear but the lack of similar features in 2012 suggests they may not be the main causative factor. Based on just two visits to Nubansuit Lake and limited discussion with local fishermen, it is not clear how often something like the 2011 situation occurs. Our experience on Shelburne Pond suggests that it may not be all that often. However, anyone traveling anywhere near the this section of the lake should check things out carefully and stay reasonably close to the shore. Looking over the Google Map image might be helpful (in 2011 there was more room on the north side the thin ice than the south side). Keep in mind that when this happens again it is likely to be different than 2011.
We are continuing to look at data from Shelburne Pond and the Inland Sea (Lake Champlain) on the behavior of double ended folded ridges with hopes of getting a better understanding this source of persistent open water/thin ice. I have posted a more detailed report on Shelburne Pond.