Streams of Warm Ground Water Under the Ice
Shelburne Pond is one of our most popular skating ponds. About 20 years ago I found a peculiar narrow (2 feet wide) finger of thin ice that stuck about 100 feet out into Shelburne Pond in Vermont. I have looked for this ever since withouit success. This year we found six of them.
The bands appear to be related to groundwater flow from shore, perhaps injuected under the ice as a shore based spring. Their occurance appears to be related to a warm January with little frost in the ground. The following appear to be factors in their occurance.
- Warm conditions (little frost in the ground to inhibit ground water flow). This can be either early in the season or mid-winter warm spells or at the end of the ice season.
- Rocky ledges next to the ice (or nearby) and rock that has ground water passages. Rock layers that dip toward the ice sheet. Also swamps that have ground water moving through them can create underice streams.
- They are wider at the shore and extend up to 100 feet from shore, nearly perpendicular to the shore.
- They are likely to occur at the same places when the conditions are right.
There is well over a mile of rocky and swampy shoreline around Shelburne Pond. We only found thin ice from these streams in four places, three of them within 1/8 mile of each other.
I got the following from Doug, a friend, on January 29, 2017
Doug wrote:I headed over to Shelburne Pond this afternoon to check the ice and get in a quick skate with my wife and son. Access onto the ice requires ginger steps for the 1st 3', but once on it the plate was solid. A group of 3 fisherman was heading out as we were clipping our skates on. They relayed that a group that just left the ice reported 6"-8" of thickness.
Just as we were getting our skates on we heard a commotion and looked to see one of the party had fallen through. Moments later, another one of them fell through as well. The third person, who was trailing the other two, stopped and pushed his plastic tote-sled toward the hole for his partners (turned out to be his brother and his father) to grab. I pulled of my pack, got my throw rope, and started toward them, but they were both out of the ice, lying on it scootching toward the launch before I was needed.
The men were surprised and cold, but able to stand and walk off the ice once they felt it was solid. They were only about 300' from the launch access, directly North of it. It appeared that the rock bluffs may have warmed in the sun and weakened the ice near them.
I tested the ice and found I could not poke through with 4-6 stabs, it was at least 3" thick. I found a couple of recently frozen over fishing holes and found the ice thickness to be 4-6". The surface was a 5-6 grade. My wife was spooked by the fishermen's plunge and decided to hike the nearby woods trail. My son and I skated the Southern end of the lake for 20 minutes or so.
When we left the fisherman had changed and were still by their trucks warming up. I asked if they had ice claws. They did not, but admitted that they'd be a good idea. Fortunately, they will live to fish another day.
If you decide to skate Shelburne Pond, turn East (to your right) once you get onto the ice. Do not proceed due North from the launch. Give the rocks on the Western Shore at least 300' of space. As always, proceed with caution
End of Doug's report
When I got to the ice on January 30th the ice was still near breakthrough thickness in the area where the breakthroughs took place. The thin ice was a straight band of thin ice that was perpendicular to the shore. The three on the Southwest side of the pond origionated at the sloped limestone ledges. They ranged from two to 10 feet wide. The forth thin ice band origionated on the east side in a swamp that drains a nearby limestone ridge. As the ice was going out two more of the streams melted out before the near by thicker did giving a total of 6 streams found.
The weather leading up to end of January showed a long spell when temperatures stayed close to freezing, both night and day. December also did not have much cold weather.
Temperatures in December (above)
Temperatures in January 2016. The swims took place on the 29th.
The following are a couple picures of