NYC is located at the souther edge of the last glacier to come this way. the giant ice sheet, advanced, and pushed before it, loose rocks and dirts, the same way a push brooms does. as it came to NY, is ground to a halt, and stopped. slowly, it receded, and melted. the land below was compressed and sunken as a result of the weight of the glacier. the ridge of rocks, sand, and dirt, (a moraine, and in this case, a terminal moraine, since it marks the end point of travel) acted as a dam for the melt water. a giant lake began to form. the weight of the melt water helped keep the land compressed. for several thousand years, the water melted, the lake grew, until finally, a weak point in the moraine failed. Today, this weak point is called "The Narrows"-- and it is the site of the Verranzano
Narrows bridge, which marks the entrance into NY Harbor. on the brooklyn side, you have
Bay Ridge, named for the characterist high rigde of land (the moraine!) on the Staten Island side, you can actally see the sheared moraine!
with the dam broken, the water poured out of the glacial lake. and slowley the land emerged. but technically, the Hudson river is a fjord-- a sunken river. the old river bed is several hundred feet below the surface. (how ever, the river has silted up, and the silt is hundreds of feet deep, and the Harbor nowdays required dredging to keep a deepwater channel open.) but at Bear mountain (a hours drive, and a state park,) the river is narrow, and runs swiftly, and the water is 265 feet deep, and the surface is about 100 feet below ground level, in a gorge. Even in NYC, the side of the Hudson are (starting at about 23rd street in Manhattan, but on the NJ side, and at 150th Street Manhattan side) high cliffs. the area in NJ is know as Palisades-- since it resembled one. (and some of us old folk remember the pop hit of the early 60's
Palisade's Park, for an amusement park there)
the NY area still has pleanty of
Kills-- a dutch word for meadow, marshy remnats of the old glacial lake
Fresh Kills in Staten island is really a continuation of the NJ Meadowland-- home of a large sports complex. the same meadow continue (but in many places it has been "improved" out of existance!) to queens-- as "Fresh Meadows". Fresh Kills is now one of the highest point of land in NYC-- home to one of three "Mount Garbages" (the others being in Pelham (Bronx) and Flatbush (Brooklyn)) most of these areas are between the newest moraine, (North Hils Moraine,) and an older one--Ronkonkama Moraine.
All of Long Island is Moraine.. the fish shape, with the split tail at the east end, are remnants of the moraine. North Hills make the southern tail (Montawk Point, and crosses the Ronkonkama moraine in queens. it then runs diagonal through queens, to Brooklyn, and staten island.
any one who has flown into NYC, and gone to Manhattan, will have noticed that the trip to Manhattan is through a necropolis-- the moraines are not good farm land, and large parts of them became cemetaries.
i have take many local tours with geologists from AMNH
http://www.amnh.org/ -- and learned many details about NY. i know the same glacial mass covered most of Michigan-- and formed gorges in upstate NY, (watkins glenn, etc). but mostly i know NYC geology.
Visiters to NY can see, in central park, the bedrock of Manhattan (schist) and in many places, it is scarred, and bears deep parallel groves, as if some giant claw dug in and gouged the rock. the "claw" was the last glaicer!
glacial erratica-- about all over the area. some even remain!
