Glacial Pothole in the City EarthCache
Glacial Pothole in the City
-
Difficulty:
-
-
Terrain:
-
Size: 
(other)
Related Web Page
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
Waypoint 8 of 10 on Going Coastal’s NY-NJ Harbor Estuary EarthCache Discovery Trail in Inwood Hill Park, caches developed by Going Coastal, Inc. (www.goingcoastal.org) as a special project in affiliation with Groundspeak and support from the NY-NJ Harbor Estuary Program and the New England Interstate Water Pollution Control Commission.
The NY-NJ Harbor Estuary Earthcache Discovery Trail is meant to help visitors develop a better understanding of the Estuary, make connections between earth and environmental science, and foster stewardship.
A glacial pothole bored through a massive seven-foot tall rock! (visit link) The pothole is located on the eastern face of the sloping rock. Boring through rock is no easy task. Manhattan schist is a hard rock. It is also a very old rock. The pothole formed during the last ice age. The tops of the glaciers were 1,000 feet high; meaning the top of the glacier was 1,000 feet higher than where we are now standing!
What did the tops of the glaciers look like? The tops of the glaciers were not just solid ice (like an ice skating rink), but the tops of glaciers also had rivers and streams running over them. On the bottom of the rivers and streams were small cracks and holes in the ice. When water flows rapidly down a hole it swirls around just like when a toilet is flushed. The water in the rivers also carried with it small rocks. The swirling water with rocks acted like a grinder that slowly bored a hole through the 1,000 feet of ice, and then bored a hole through the underlying bedrock (visit link) The glacier melted about 10,000 years ago and we are now left with the glacial pothole you see before you.
The glacial pothole is a small piece of nature in which a world exists. Once the pothole is created it begins to collect fresh water. (visit link) Freshwater is defined as water that contains very little salt. The pothole fills with rainwater, dead leaves, branches and other detritus creating a micro lentic zone or standing body of freshwater that is home to numerous organisms. Micro algae phytoplankton are the principle photosynthesizers in pothole.
Occasionally swimming insects will take a dip in the pothole pool. Its micro size and limited water movement characterize this small, simple freshwater ecosystem. Heavy rain and runoff might cause the water to overflow in a mini waterfall. Like the Earth’s biosphere and all ecosystems, interactions among biotic and abiotic factors control conditions in the glacial pothole.
Because of the dampness and low light there are lichens, like a mat of green felt growing on nearby rocks and trees (substrate). A lichen is a plant. It has no leaves, stems or roots, but like other plants it makes its own food using energy from sunlight. Lichen form when fungus meets algae and they are compatible. It is a symbiotic relationship, algae are the photosynthesizers that produce food and fungus forms a body that houses both.
The south side of the rocks and trees will generally have more lichens than other sides. This is because the south side gets more sunlight for photosynthesis to occur. When a lichen is wet from rain or dew it grows actively, but when it dries out in summer, it stops growing. However, the lichen does not die, but instead lies dormant until the next rain starts it growing again.
Lichens are important in many ways in the habitat. Some make the nitrogen in the air usable to plants, They are homes for spiders, mites, lice, and other insects. All are important in the nutrient cycle in the places where they grow. Lichen (visit link) are very sensitive to pollution in the air and can be used to measure the effects of pollution on an environment.
This pothole is one of the most unique sights of the Inwood Hill Park. In addition to Inwood Hill, 40 foot deep glacial potholes over 110 feet below the streets have been reported by engineers at the World Trade Center site. We hope you enjoyed exploring one of nature’s most interesting natural formations.
Logging Tasks:
1. Geologists have a theory about how the combined actions of glacial melt, flowing water and rocks made the pothole. Which rock was younger, the pothole rock or the rock that cut through it?
2. Take a close look at the rock. Is the inside of the pothole smoother texture than outside rock? Why do you think that is?
3. Estimate the circumference of the glacial pothole.
4. (Optional) Look for the lichen on the rock faces and nearby trees. Is the lichen dormant or in a growing stage? The weather will help determine the answer. Please include date, time of day and weather conditions in your answer.
To log a find on this earthcache, email the cache owner (DO NOT POST IN YOUR LOG). Use your GPS device to locate the next cache - GC2RWQK. (visit link)
Remember, to upload a photo and let us know in your log ways we can improve the trail.
Data Sources:
• Lichenland: (visit link)
• NY Botanical Gardens: (visit link)
• NYC Department of Parks & Recreation: (visit link)
• Wikipedia: Giant’s Kettle, Lichen, Mosses
Data Collected: September 26 – April 15, 2011
Name and Type of Land
Inwood Hill Park
W 218 Street & Seaman Avenue, Manhattan
Phone: (212) 304-2365
www.nycgovparks.org
Additional Hints
(No hints available.)