A glacier known as the Wisconsin Ice Sheet covered this area 25,000-21,000 years ago to a depth of several thousand feet. Before the glacier, the water throughout the Finger Lakes region drained in a southerly direction. The advancing ice gouged out the north-south valleys pushing huge amounts of rock along with it. When the ice melted and receded, it left even more rock it had been holding in huge piles, especially at the locations where the flow of the ice coming south was nearly the same as the rate of melting, so the edge of the glacier was in more of less the same place for a very long time.
Those piles of glacial debris, something like what the snow plow piles leave behind in the spring, but on a grand scale, are called moraine. The edge of the Winsonsin Ice Sheet apparently lingered in a line that stretches across the southern edge of the Finger Lakes, and left the Valley Heads Moraine, a kind of natural dam that fills the valleys of this region. Near the location of this EarthCache you can see the dramatic impact of the glacier as the floor of the valley rises from around 600’ above sea level in West Danby, to over 1100’ only a few miles to the south.
Here is a brief description of some of the most visible effects that remain from the glaciers of the great ice ages:
Drumlin – A hill of sand and gravel, known as till, pushed ahead of a glacier and then streamlined by the flow of the advancing ice into a shape more or less like an overturned boat hull.
Erratic – An unusually large chunk of rock carried far enough by a glacier to rest where the bedrock is significantly different than where the boulder came from.
Esker – A snaking ridge of glacial deposits formed by a stream of meltwater flowing through tunnels in the receding glacier, carrying stones and sand and ultimately leaving them behind along its path.
Hanging Valley – A valley running perpendicular to the advance of a glacier, and thus not gouged deeper by the ice, where it runs into the much deeper valley the was oriented in the direction of the glacial flow. The newly carved depth of the glacial valley causes drainage from the hanging valley to drop dramatically as can be seen in gorges throughout the Finger Lakes region.
Kame – Deposits of sand and gravel left by glacial lakes that are characterized by their washed and sorted nature. This is in contrast to till, which is deposited as it is pushed ahead of the glacier and is not well sorted.
Kettle Lake – A depression left behind when a portion of glacial ice remained behind for some period, causing less material to be deposited there than in the surrounding area. These deposits have lots of clay so don’t drain very well, and the contours of the land are irregular, causing the depressions to fill and form small lakes.
Moraine – Is a thick cover of glacial till. The contour of moraine is often described as “humocky” and is typically pocked by kettle lakes.
Striation – Is the marking left by ice and the rocky debris it carried where it scratched and gouged the bedrock as it flowed past. Glacial striation is often weathered away but can be strikingly vivid in some places, resembling huge claw marks in the solid rock.
Logging Requirements:
- OPTIONAL – Your post will be received with giddy geocaching excitement if you include an optional photo of your visit to this unique area.
- Looking roughly SE from GZ, what is the dominant glacial feature you observe, and how big is it?
- Describe at least one other glacial feature you can observe from GZ or in the surrounding area.
Please don’t include your answers (other than the optional photo) in your online post so others can enjoy making their own observations. Send answers by message or email to CO.
Credits
Many thanks to Bradford B. Van Diver’s “Roadside Geology of New York” (Mountain Press Publishing Company, 1985) for many years of wonder at the evidence of enormous spans of rock and time, and the inspiration for this cache. It was from this book I first learned about the Valley Heads Moraine and I recommend it to anyone who travels the roads of New York.
This cache was placed with permission of the Finger Lakes Land Trust, under their permit #LPBP01. Please visit www.fllt.org for general information, and http://www.fllt.org/content/uploads/2014/12/lpbd_revised.pdf for a trail map of the Lindsay-Parsons Biodiversity Preserve.