How long island sound was formed

As, Tom Anderson, writes in his excellent book entitled This Fine Piece of Water , the Sound is not only the most heavily used estuary in North America, it is also one of the most beautiful waterways, with picturesque seascapes and landfalls.

Unfortunately, centuries of pollution and other abuse have gradually been killing off its marine life and have pushed the Sound to the brink of disaster. This is especially true in the Western Basin, which encompasses Fairfield CT and Westchester NY Counties, along with the North Shore of Long Island where, even though our shoreline development is mostly residential, the population density is heaviest while the water is extremely shallow and the passage narrow. This destroys percent of the original marshes in Connecticut.

It quickly focuses on hypoxia after multi-year studies show the severity of the problem. These efforts provide essential data to understand the severity and causes of hypoxia and implement management programs to address the problem.

By , the nitrogen reduction rate reaches 3, tons per year. As a result of the ecological and economic impacts, Congress, at the requests of the governors of New York and Connecticut, provides funds to investigate the potential causes, and gives economic relief to lobstermen.

Trading changed the relationship of the natives with the land. Instead of taking what they needed to survive, they now took more animals to trade. Over , beaver pelts were shipped to Europe and by the late s they had been exterminated from the region.

Traders also caused something new, inflation, when they discovered they could create their own wampum discs of drilled shell used as currency much faster than natives with metal drills. Other trade goods were products both practical like metal cookware and decorative like the notorious beads bartered for Manhattan Island. When colonists arrived in numbers, clearing of the land began on a massive scale to create farmland.

Without habitat, animals began to disappear or be pushed into remoter areas. Natives had to compete with colonists for the same natural resources. The Europeans also brought a host of diseases against which the natives had no immunity; smallpox, measles, flu, diphtheria, even bubonic plague. By the mids the native population was reduced to a tiny remnant, stripped of their ability to provide for themselves.

Figure 3B , unconformity uf2 forms the top of the coastal-plain deposit and, where coastal-plain strata are absent, it continues as the top of the crystalline bedrock. Glacial drift e. Figure 3F as thick as m unconformably overlies bedrock and coastal-plain strata.

The drift varies in acoustic character and, based on its stratigraphic position and relationship to onshore geomorphic features, is thought to represent outwash, till, ice-contact stratified drift, drift deformed by overriding ice, and glaciolacustrine sediment. Outwash is characterized by flat-lying and gently dipping reflectors. Drift that exhibits highly irregular and discontinuous internal reflectors is thought to be till, ice-contact drift, and or ice-deformed drift.

Deposits of outwash and ice-contact stratified drift unit Qd, Figure 3D , 3E , and 3F are usually preserved as local deposits on both bedrock and coastal-plain valley floors and walls. In most cases, these deposits are overlain by glaciolacustrine or moraine and till deposits.

These deposits are positive relief features and are identified in the subbottom records by a well-defined surface reflector that obscures underlying reflectors. The unit designation "end moraine deposit" Qtm is used to differentiate features that are obvious offshore extensions of known onshore moraines.

The till designation is used for similar deposits where the detailed morphology is less certain. In some places where seismic profiles show moraine and till deposits to be exposed at the seafloor Figure 3C , 3D , and 3F , bottom sediments are composed of boulders and gravel U.

Department of Commerce, ; these coarse materials are inferred to be lag deposits derived from till that caps and or makes up the moraine and till deposits. Drift that is characterized by laminated acoustic reflectors that mimic the underlying unconformity is inferred to be sediment deposited in proglacial lakes. The glaciolacustrine deposits unit Qgl, e.

Figure 3F are the most extensive and the youngest of the deposits within the glacial drift. Core data Figure 4 and previous studies Frankel and Thomas, ; Bertoni and others, indicate that the glacial lake deposits are composed primarily of laminated probably varved silt and clay, with local lenses of coarser sediment.

Since the laminations appear to mimic the shape of the underlying surface, we infer that they are the result of extensive, quiet-water deposition on the bottom of the lake. A complex surface that was initially cut by post-glacial streams Figure 3C , unconformity ufl and later greatly modified by wave and current action Figure 3F , unconformity um forms the top of the glaciolacustrine and other glacial deposits.

Prominent and continuous acoustic reflectors mark this smooth to very irregular surface Figure 3F. Where the fluvial unconformity ufl is preserved, it can be distinguished from the marine unconformity um because it is overlain by thin sediments of inferred fluvial and estuarine origin unit Qfe, Figure 3C , 3E , and 3F.

The fluvial and estuarine deposits are recognized by their internal cut-and-fill structures. Similar deposits, inferred to be composed of fluvial gravel and sand; estuarine sand, silt, and clay; and fresh- and salt-water peat, have been recognized in Block Island Sound Needell and Lewis, The marine unconformity um, e.

Figure 3F is represented by a strong, continuous reflector. It cuts the fluvial unconformity ufl and truncates the fluvial and estuarine deposits as well as the drift. It is overlain by complex Holocene marine sediments unit Qm, e. Figure 3F , which make up the bulk of the post-glacial deposits.

The marine sediments exhibit continuous, flat-lying, and gently dipping internal reflectors, cut-and-fill structures, constructional features, and in some areas a mottled appearance that results from a lack of distinct internal structure.

Postglacial marine deposits recovered in all four cores Figure 4 consist of silty clay, silty sand, sand, gravel, large pebbles, shell fragments and in core number one, peat. Figure 5 presents a synopsis of unit descriptions together with a surficial geologic map and interpretive geologic cross sections that show where the various units are thought to crop out at or very near the sea floor.

The morphology of the glacially modified fluvial surface uf2 that forms the top of the crystalline bedrock and the coastal-plain strata is shown on Figure 6. The distribution of the coastal-plain strata has been delineated using heavy dashed lines, which approximate the bedrock and coastal-plain contact. In general, the bedrock surface dips southward from the Connecticut coast, but it is incised by ten prominent valleys, having 50 to m of relief, that trend generally southward. The bedrock interfluves between these valleys extend as identifiable features south-southwestward to the mid-portion of the Sound.

Many outliers of coastal-plain strata are inferred to overlie bedrock north of the main coastal-plain cuesta remnant. Several of these outliers appear to have been preserved on the south side of the bedrock interfluves. At the toe of the north-facing cuesta slope, the bedrock and coastal-plain contact heavy, generally northeast-trending dashed line in Figure 6 is very irregular.

Its depth varies from a minimum of about 60 m below sea level in the east to a maximum of about m in the west. Northwest of Shelter Island, N.

East of Orient Point, Long Island, four prominent valleys incise the cuesta. These four valleys are separated from their western counterparts by a large interfluve or divide that nearly bisects the study area. The lowest point on this divide is about m below sea level Two of the four eastern valleys one between Orient Point and Plum Island, and the one associated with the Thames River also appear to deepen southward, but they are not as deep to m or as narrow as the western valleys.

The less severe morphology of the eastern valleys may be attributable to their more northerly position north of 41 o 10'. Figure 7 shows the thalwegs of the major valleys and the apparent preglacial drainage pattern. Our ability to reconstruct this pattern indicates that glacial modification of this area was not extensive. The thickness up to m and distribution of the aggregated glacial drift deposits is shown on Figure 8. Aside from limited interfluve areas along the Connecticut coast and a curved strip southeast of Niantic Bay, where modern erosion has probably exposed bedrock and coastal-plain strata Figures 5 and 8 , glacial drift is present throughout the eastern Sound.

A separate mapping of the localized outwash and ice-contact stratified drift deposits was not possible, but they are inferred to crop out at the sea floor in several places unit Qd, Figure 5. Figure 9 shows that end-moraine deposits occur along the north shore of Long Island and continue northeastward between Orient Point and Fishers Island Figure 1.

Just north of the main body of these deposits, a line of smaller features stretches from the vicinity of Orient Point, Long Island, northeastward to the mid-sound area south of the Thames River.

A few miles to the east of this line, the Clumps moraine Goldsmith, occupies a similar position north of Fishers Island. Two sub-parallel, northeast-trending bands of moraine and till deposits also occur off the Connecticut coast between Niantic Bay and Clinton Harbor. Some of these deposits are probably related to the Old Saybrook moraine. In most of the study area, the moraine and till deposits are less than 40 m thick, except east of Plum Island, where they are as much as 90 m thick.

The extensive glaciolacustrine deposits Figure 10 fill the inner lowland and valleys of the bedrock surface and fill the valleys and depressions in the coastal-plain strata. These deposits are thickest up to m in the deep valleys; they thin over the bedrock and coastal-plain interfluves and terminate against shallowing coastal-plain and moraine deposits in the southern half of the study area.

Along the Connecticut shore, the glaciolacustrine deposits pinch out against shallowing bedrock and moraine deposits. End-moraine, till and glaciolacustrine deposits are inferred to be exposed at the seafloor units Qtm, Qt, and Qgl, Figure 5 along both coasts and in the easternmost Sound. The shape of the glacial drift surface Figure 11 supports the concept that a considerable amount of material has been removed from the easternmost end of Long Island Sound.

As mentioned above, glacial drift is locally absent and bedrock and coastal-plain strata are probably exposed at the seafloor southeast of Niantic Bay. Surrounding these exposures, outcroppings of glaciolacustrine, and to a lesser extent, the other glacial deposits look scoured on the seismic records Figures 3D and 3F. In more protected areas, the drift is better preserved, and truncated reflectors within the drift remnants provide evidence that relatively thick glacial deposits originally extended throughout the eastern end of the basin Figures 3C and 3F.

Their sizes are dependant upon the size of the original ice blocks and vary from a three-fourths mile diameter for lake Ronkonkoma to ponds only twenty to thirty feet across.

The most noticable post-glacial changes on Long Island have occurred along the many miles of coastline. The action of the waves and currents aided by the wind have eroded and reshaped the soft glacial sediments to form numerous sandy shoreline features. Less dramatic changes have taken place on the upland surface caused by the numerous streams and small rivers that slowly cut away the land and transport the sediments to the coast. On the south shore, the Ronkonkoma terminal moraine deposits in the vicinity of Montauk Point have been extensively eroded by the powerful waves of the Atlantic Ocean.

The south fork of Long Island has been shortened many miles by wave action since the retreat of the glacier. Large amounts of material have been carried westward from the eroding moraine by long shore currents to supply much of the sand for the south shore barrier beaches Fire Island, Jones Beach, Long Beach, etc.

These long strips of sand are constructed by wave action and long shore currents. The waves act on the shallow sea bottom to form off shore bars. While the westerly drifting currents bring in more sands which extends the bars westward. Fire Island has grown five miles to the west since the lighthouse was built in Barrier beach, inlet and lagoon. Fire Island beach and inlet, and Great South Bay. The barrier beach is stabilized by wind blown sand which piles into dunes away from the wave zone. Grasses and shrubs grow on the dunes and hold the sand.

The elevation of the dunes and the plants help the beach to resist severe erosion during heavy storms, and prevent it from washing away. The barrier beaches are cut in several places by inlets that permit tidal waters to sweep in and out of the shallow, marsh-filled lagoons behind the beaches. Through a natural process of silting and marsh formation these shallow bays, or lagoons, will fill in, thereby joining the barrier beaches with the mainland of Long Island.

This filling process is easily seen in the bays behind Long Beach, where narrow channels separate the many marshy islands. Waves and currents in Long Island Sound and Peconic and Gardiners Bays have acted in a similar way to those in the open ocean, but on a reduced scale. Numerous sand features such as spits, tombolos and baymouth bars have formed from the erosion and drifting of material from the shoreline cliffs.

Spits are projections of current-drifted that extend out into open water. Sometimes the end of the spit may curve back towards the land, to form a hook. A spit which reaches across a bay to the etent that it closes, or nearly closes the mouth is called a baymouth bar. Sand that drifts across open water to connect an island to the mainland, or an island with another island, is called a tombolo.

The North Shore of Long Island is also an excellent example of the process of shoreline evolution. Waves and currents continually work to remove projecting points of land, while indentations and bays fill with sediments.