Under-ice Streams


Introduction

Shelburne Pond is one of our most popular skating ponds in the Burlington Vt area.  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. It appeared to origionate in the cattail swamp on the south end of pond.  I have looked for this ever since withouit success  until this year when we found six of them. 

Shelburne Pond with the under ice streams marked in red. The width in the red lines is exadurated.

 

 

The under ice streams erode the bottom of the ice with bands of thin ice or open water that  appear to be related to groundwater flow from shore, perhaps injuected under the ice as a shore based spring or stream.  Their occurrence appears to be related to a warm January with little frost in the ground.  The following factors appear to be somw of the factors in their occurrence.

 

  • 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.
  • 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 lots of bedrockor or 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.  

Details:

 I got the following from Doug, a friend,  on January 29, 2017