Hempstead Harbor Woods - Port Washington’s Least Known Secret!
Hempstead Harbor Woods in Autumn Colors & at Serendipity Pond
The HHW is the ecological heart of Port Washington. It is a gem for field biology, wildlife, and geology!
See here for a presentation on the HHW by Guide, David Jakim, with TTPW.
Join us as we immerse ourselves in the geology of the Hempstead Harbor Woods, a 200-acre geological treasure located on the Port Washington Peninsula.
As the glaciers receded approximately 20,000 years ago, they deposited thick layers of sand, till, and clays, including thousands of boulders. Sand mining on the west shore of Hempstead Harbor that began in the mid-19thcentury exposed layers of glacial and pre- glacial sediments that have been studied by geologists for well over 100 years. Comprehensive Professional Papers on Long Island’s geology and groundwater resources published by the U.S. Geological Survey in 1906 and 1914 described the sand pit strata and used them as important resources in interpreting the glacial history of Long Island. In the ensuing years many papers have been published updating and expanding upon the early work.
Today, although the mining is done, many interesting geological features remain. These include:
Beneath the glacial deposits on the surface of Long Island are ancient sediments (sand, clay & gravel) that are about 75 million years old and date from the late Cretaceous Period. These sediments were deposited in a near-shore, estuarine environment. They are important today because they hold Long Island’s underground water supply. The sand pits are one of very few sites where they are exposed at the surface.
Interesting features found in the Cretaceous beds include iron-oxide concretions (Indian paint pots), pyrite (fool’s gold) nodules, lignite, and plant fossils in red shale.
Thousands of boulders and large cobbles (called glacial erratics) were transported to Port
Washington during two glacial advances. Today, these rocks are scattered across the peninsula’s land surface and in the sand pits they are concentrated in large piles where they were dumped during the sand mining operation. Most of these boulders were plucked by the advancing glacier from bedrock in the Bronx and Westchester. Occasionally, one can find an erratic that travelled in the ice from as far north as the Adirondack Mountains. They provide an outdoor laboratory for the study of regional geology of southern NY and New England.
Layers of glacial outwash (sand and gravel) were deposited by meltwater streams adjacent to the glacier margin. These are the high quality “Port Washington Sands” that were of greatest value to the mining companies. Also, two distinct glacial till layers mark the overspreading of the peninsula by ice. The till was of little commercial value but it is of great importance for geologists because each till layer marks a glacial advance. The Port Washington glacial sequences serve as a model for the glaciation of Long Island.
There is clear evidence of faulting and folding of frozen Cretaceous and glacial sediments by an advancing glacier that occurred when the last Ice Age neared its maximum 22,000 years ago. Thick layers of white Cretaceous sand are seen high in the cliffs where they were shoved by the moving ice creating Beacon Hill. Also, a spectacular, 50 foot high pinnacle of resistant glacial till is a remnant of a glaciation, dating back over 50,000 years, that later was deformed by the powerful final advance 22,000 years ago.
Excellent examples of erosion and deposition are found where loose sediments have been eroded from the high cliffs and deposited in many shallow basins. Wetlands form in these basins creating the substrate for much of the biodiversity found in this unique area. Finally, if one has sharp eyes, they may find a sand-blasted quartz rock, called a ventifact, that was sculpted by powerful “katabatic” winds near the edge of a glacier.