Margaret M. Loos
If time and circumstances permitted several other visits to sites in the harbor itself and on its Western shore would be useful, but we will have to settle for our view of these areas, visual material, and maps for background.
A.
The Harbor’s Formation
Our New Haven harbor, the single most recognizable feature of the Connecticut shoreline, was formed as a result of the drowning of the coastal plain after the ice-ages, and its low placement at the end of a rift valley. Geologists refer to that valley as the tip of the Triassic Lowlands. Triassic identifies the period during the Mesozoic era when this low section of our state resulted from a vertical movement along faults that existed to the East and West of the valley. The vertical movement caused the bedrock beneath this rift valley to sink. Earthquake activity can be responsible for such vertical movements. The valley itself is composed chiefly of larger amounts of red sandstone which justifies the area being termed weak lowlands. The valley also has prominent ridges of trap (igneous) rock formed by protruding edges of uplifted layers of resistant volcanic rock.
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These were caused when three lava sheets intruded on the red sandstone layers. The lava could invade the earlier material because it was a very dense, molten material. Much later in our valley’s history the sediments above the cool molten material were removed by erosion and West Rock Ridge and East Rock were uncovered. If the rift valley were wider at the tip our harbor would be wider, but the Eastern and Western Highlands are composed of materials highly resistant to the rivers which drain them and only slight submergence has taken place resulting in a small harbor.
Students may be interested to learn that at the time of New Haven’s settlement the harbor reached to the Green or Mall and that if the sea level here were only 100 feet higher the shoreline would be at the foot of West Rock. If we dipped the land under more the ridges of trap rock to the East of West Rock would make a series of lovely islands. (See maps on next page.)
The lowlands at the edge of the harbor cover our entire area of study and are only five miles across, but they widen to about 20 miles across as they reach the Massachusetts border. The highest points in the Lowlands are only 100 feet above sea level, whereas the Eastern and Western Highlands have many places ranging up to more than 1,000 feet. Probably the whole of the rift valley between the two border faults was at one time filled with river and lake deposits.
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The lowlands are also often referred to as the Redlands and New Haven was at one time Rottenberg (Redrock).
B.
The Harbor’s Waters
The Quinnipiac River, the Mill River which joins it near the harbor, and the West River are the chief contributors of fresh water to the harbor. These rivers deposit some sediments but they are not the chief source of the sediments in the harbor that would eliminate its economic advantages if they were not periodically removed. The natural reaction between fresh and salt water present at the mouth of rivers explains the chief source of sediments. We must discover by measuring the density of fresh and salt water that salt water is the denser and therefore salt water will sink when the two meet and a lighter layer of fresh water will ride on top of the salt. An area where this meeting occurs is called an
estuary
. Since the layer of salt water is heavier it can invade the fresh water. This contributes to the river being affected by the tides and therefore it is termed a
tidal
river
. The Connecticut River is tidal as far north as Hartford but the tidal invasion into the Quinnipiac, etc., is slight. The salt layer is at the bottom of the harbor and deposits much of the sediment it moves into the harbor from the Sound. The harbor bottom is dredged regularly. If we consult our surficial map we can trace the channel that is maintained for the traffic of the large oil tankers and cargo ships that serve this part of the state. The contour lines in the harbor indicate the depths of the bottom. Besides discovering the channel for shipping we will also find an area of much greater depth on the recent surficial maps (1965+) near the Eastern shore of the harbor. This was believed to be the source of much of the fill material that was used for the landfill site of Long Wharf on the West shore.
C.
The West Shore of the Harbor
We should consult our maps from earlier years to discover how the Long Wharf landfill section appeared before the man-made expansion. Much of the area may have been marshland, because there is still a small remnant of marsh West of the landfill. Marshes often fill in because the marsh grasses trap sand and sediments when the marsh is protected from the action of the sea. However, in our area it appears that the face of the marsh was eroded and material removed. Normally that would result in the marsh invading the inland area but man has, in fact, prevented this action by landfill, highways and construction. There really is no natural shoreline left in this section. However, if we consult the map we see a very low-lying arm of sand reaching into the harbor from the Western end. It is very low because it consists of sand that has been moved and deposited by shore drift. It is termed a
spit
. This process can create new land, in the form of spits and as islands when they are cut off by water.
D.
The Horizon
,
Long Island
A last observation on the formation of the harbor itself is that Long Island Sound did not exist as a body of water prior to the glaciation. We’ve learned that Long Island was formed by the glacier, but subsequently the water level rose when the glaciers melted, and Long Island was partly drowned. The glacier had by this time retreated farther inland leaving a fairly flat depression between Long Island and the mainland which was filled when the sea level rose, thus supplying the waters for the Sound. The sea level dropped again and Long Island was left across the Sound from New Haven harbor. The sea level is now rising at the rate of 3 mm a year which translates into a continual annual drowning of a foot of shoreline per year.