The Harbor Hill Moraine, in the

geography of Long Island Long Island is in southeastern New York, United States, separated from the rest of the state by the East River and from Connecticut by Long Island Sound. Long Island contains four counties, of which the western two are boroughs (Queens and Broo ...

, forms the northern of two ridges along the "backbone" of

Long Island Long Island is a densely populated island in the southeastern region of the U.S. state of New York, part of the New York metropolitan area. With over 8 million people, Long Island is the most populous island in the United States and the 18 ...

Description

The Harbor Hill Moraine, skirting the North Shore, represents the

terminal moraine A terminal moraine, also called end moraine, is a type of moraine that forms at the terminal (edge) of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, has been pushed by the front edge ...

of the most recent advance of the

Wisconsinian glaciation The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cord ...

, which reached its most southward advance about 18,000 years ago; the earlier

Ronkonkoma Moraine The Ronkonkoma Moraine, in the geography of Long Island, forms the southern of two ridges along Long Island's "backbone." Description The Ronkonkoma Moraine, a terminal moraine, predates the Harbor Hill Moraine (which reached Long Island during ...

, much cut through by outwash streams from the Harbor Hill Moraine, lies to the southeast. The Harbor Hill moraine is represented by the North Fork of eastern Long Island and in three disjunct sections farther east, Plum Island, Great Gull Island, and

Fisher's Island Fishers Island (Pequot: ''Munnawtawkit'') is an island that is part of Southold, New York, United States at the eastern end of Long Island Sound, off the southeastern coast of Connecticut across Fishers Island Sound. About long and wide, it ...

. The Harbor Hill Moraine, named for its prominence at Harbor Hill,

Roslyn, New York Roslyn ( ) is a village in the Town of North Hempstead in Nassau County, on the North Shore of Long Island, in New York, United States. It is the Greater Roslyn area's anchor community. The population was 2,770 at the 2010 census. History Ros ...

, the highest point in Nassau County, resulted from a lingering equilibrium stage in the glacier's episodic retreat, creating a stationary melting front; the Long Island area became permanently free of glacial ice in the range of 13,000 to 12,000 YBP (Years

Before Present Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Beca ...

). The Harbor Hill Moraine intersects with the earlier Ronkonkoma Moraine at Lake Success: east of the lake the two moraines may be seen, but west of Lake Success the Harbor Hill moraine overrode and effaced the Ronkonkoma moraine.Garvies Point Museum and Reserve: the Geology of Long Island
/ref> South of the moraines is a broad

outwash plain An outwash plain, also called a sandur (plural: ''sandurs''), sandr or sandar, is a plain formed of glaciofluvial deposits due to meltwater outwash at the terminus of a glacier. As it flows, the glacier grinds the underlying rock surface and c ...

sloping towards the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

, much of which has been submerged as ocean levels rose in the post-glacial period. The Harbor Hill Moraine forms the major drainage divide in Nassau County: streams to the northwest of the moraine flow into

Long Island Sound Long Island Sound is a marine sound and tidal estuary of the Atlantic Ocean. It lies predominantly between the U.S. state of Connecticut to the north and Long Island in New York to the south. From west to east, the sound stretches from the Eas ...

, whereas those to the south empty into the series of bays or sounds behind the barrier islands and so into the Atlantic.

References

{{Commons, Harbor Hill and Ronkonkoma Moraines, Harbor Hill and Ronkonkoma Moraines Geography of Long Island Moraines of the United States Landforms of Suffolk County, New York

Description

See also

References