Block Island Sound
The Race
Long Island Sound
Block Island
Atlantic Ocean
Figure 2-1. Long Island Sound region bathymetry
The south shore and north shore of Long Island differ significantly. The south shore
is an outwash plain characterized by sand-sized sediments and a gentle slope. The gentle
slope found on the south shore is a controlling factor in the observed large bay sizes and
the presence of barrier islands. In contrast, the proximity of the north shore to the Harbor
Hill moraine is a controlling factor in the coarser sediment, steeper slope, and absence of
barrier islands found here. The Harbor Hill moraine begins in the west end of Long
Island and extends in a northeasterly direction to form the northern fork of Long Island
with its terminus at Orient Point. A second terminal moraine, the Ronkonkoma Moraine,
begins in the western portion of Long Island and extends to the southeast (Figure 2-2).
The western extent of the north shore of Long Island is characterized by a series of
narrow bays that extends south to the Harbor Hill Moraine. These bays are believed to
have been formed by protruding lobes of ice attached to the Wisconsin stage glacier that
advanced upon the region. The ice lobes carved the valleys that form the bays and thrust
the material southward, forming the steep bluffs found there. A secondary factor may
have been the action of "spring sapping," where underground springs loosen the sand
found in these valleys, allowing for rapid erosion (Fuller 1914).
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Chapter 2 Study Area and Physical Setting
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