Surficial Geology: Sand Dunes

Albany has a rich and complex geologic history that we really do not know all that much about. When the glaciers were retreating to the north of the Capital Region at the end of the last ice age (about 15,000 years ago), melting water from the glaciers formed a series of large and deep glacial lakes, known as glacial Lake Albany that extended from Glens Falls, NY to at least Catskill, NY. As the glacial ice shifted back and forth Lake Albany water levels dropped or were raised. Eventually the lake drained and exposed a broad plain of sand and gravel where the Mohawk River emptied into the lake just west of Schenectady. At first the flat plain was un-vegetated and the wind could easily blow fine sand around and form large Linear and Parabolic dunes. At present, we have no exact idea when all of this transpired.

It now turns out that due to a new technological development we can actually date the sand that is buried just below the soil horizon on the top of the dunes. The dunes themselves are comprised of sand grains whose last exposure to sunlight can be calculated by using Optically Stimulated Luminescence (OSL) dating. Additionally, sometimes the low spots adjacent or between the dunes form wet spots that collect and retain organic matter (leaves, twigs, and insects) that can be carbon dated (Radiocarbon dating). Combining these two dating procedures will assist us in constructing an accurate chronology of the regional dunes formation. Once we have an understanding of the age of the sand dunes we will have a better context for the glacial lake history.

In order to obtain samples for the procedures described above, a dune and its immediate area must not have been significantly altered over time. These conditions are very rare, especially in and around the Capital Region where development has been significant. Fortunately, several of these undisturbed dune sites have been located and are currently being investigated by the New York State Geological Survey.

 


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