Lake Hitchcock: Pingo Scars EarthCache
Lake Hitchcock: Pingo Scars
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Lake Hitchcock was a glacial lake that formed approximately 18,000 years ago in the Connecticut River Valley. After the Laurentide ice sheet retreated, glacial melt water was trapped behind a large sediment dam which blocked up the Connecticut River, creating the long, narrow lake. The lake existed for approximately 4,100 years. At its longest, Lake Hitchcock stretched 250 miles long and up to 20 miles wide from the moraine dam at present-day Rocky Hill, Connecticut, to West Burke, Vermont.
A pingo, is a mound of earth-covered ice found in the Arctic and subarctic regions. Pingos can reach up to 70 metres (230 ft) in height and up to 600 m (2,000 ft) in diameter. A pingo is a periglacial landform, which is defined as a nonglacial landform or process linked to colder climates. Periglacial suggests an environment located on the margin of past glaciers.
The dam at Rocky Hill eventually breached and the lake began to drain. The climate, however, remained cold most of the year. Temperatures in the region remain below freezing for many years. Evidence of this arctic/subarctic climate can be seen in the formation of Pingos and ice wedge casts. Pingos are ice-cored mounds or hills developed in permafrost. Permafrost or cryotic soil is soil at or below the freezing point of water 0 °C (32 °F) for two or more years. As the ground froze downward it created pressure on the water table beneath. Under this pressure, areas of water pierced this permafrost layer and began to create mounds of ice. As the ice mound grew, it pushed the old lake bottom silt and clay upward and out. Once the ice melted, the crater where the ice began left a depression, surrounded by a small mound.
Here in the Connecticut River Valley, we no longer have Pingo Formations, but their remains. This is what is known as a Pingo Scar.
see Pingo Formations by Janet Stone, USGS
Wintergreen Woods is a 110 acre forest with vernal pools (Pingo Scars) and hiking trails of chipped wood, gravel and wood bridges. It is underlain by silt and clay sediments from Glacial Lake Hitchcock. The remnants of rare post-glacial features, Pingos, are a prominent feature throughout the southern section of the park.
See pages 16 & 17 of Town of Wethersfield Trail Guide.
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Stroll along the Blue or Red trail. Take notice of two individual Pingo Scars. Send the cache owner your answers to the following:
1) Are the depressions water filled or dry?
2) If dry, estimate the depth.
3) Do you note a berm or mound around the perimeter of the Pingo Scar? Estimate its height.
4) Understanding that the passage of time and multiple layers of vegetation have accumulated in and around these structures, discuss how existing vegetation may contribute to the changing shape of the pingo scar.
5) OPTIONAL: photos are always a great treat.
References and additional information:
AN INVESTIGATION OF POTENTIAL PINGO REMNANTS IN THE SOUTHERN CONNECTICUT VALLEY. 2007 GSA Denver Annual Meeting (28-31 October 2007) Paper No. 27-13
https://gsa.confex.com/gsa/2007AM/finalprogram/abstract_125233.htm
Dinosaurs, Dunes, and Drifting Continents:the Geohistory of the Connecticut Valley Richard D. Little, 1986, 2nd edition, 107 p. ISBN 0-9616520-0-4
The Rise and Fall of Lake Hitchcock - New England's Greatest Glacial Lake, Richard D. Little, 2000 ISBN 961652055 9780961652050
Stone, J.R., and Ashley, G.M., 1992, Ice-wedge casts, Pingo scars, and the drainage of Glacial Lake Hitchcock, Trip A-7 in Robinson, Peter, and Brady, J.B., eds., Guidebook for fieldtrips in the Connecticut Valley region of Massachusetts and adjacent States, New England Intercollegiate Geological Conference 84th Annual Meeting, Amherst, Mass., Oct. 9-11, 1992: University of Massachusetts, Geology and Geography Contribution 66, v. 2, p. 305-331.
Additional Hints
(Decrypt)
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