Connecticut Water Trails Association
|
|
|---|
|
Connecticut Water Trails Association |
|
Connecticut Water Trails Program
Estuaries
How An Estuary Is Formed
Crash! Thunder rumbles overhead. Raindrops fall, collect in a twisty, turning stream and dash downhill. Salmon flash and splash, struggling against the tugging current to spawn upstream. Fresh water swirls over a mossy green log, then flows into a broad, sweeping river. The river swells from incoming creeks and streams following a well-worn channel. Paddling ducks dash into a stand of cattails seeking shelter. Off in the distance, a lone seagull cries out. The river flow slows down, churning and twisting in its banks. This wide water road carries fresh water to its final destination – the coastal inlets and bays of a salty sea. Estuaries are places where rivers meet the sea.
An estuary begins where fresh river water flows into
coastal bays and inlets. These areas of transition between the land and
the sea are driven by tides, like the sea, but sheltered from the full
force of ocean wind and waves, like a river. When fresh water meets
salty seawater, both liquids combine turning into a brackish mixture.
Estuaries can be called interior bays, lagoons, sounds or sloughs
How Was The Long
Island Estuary Formed? What we now know as Long Island Sound (LIS) began to
develop many millions of years ago with the rupturing of the great
supercontinent Pangaea. Pangaea formed about 500-250 million years ago
by collisions of other continents and survived for about 50 million
years. About 200 million years ago, Pangaea began to separate into other
landmasses and Africa, North America and the Atlantic Ocean began to
form. These same forces also began to form LIS. The great mountains, which formed during the
movement of these landmasses, weathered for 200 million years producing
enormous amounts of sediment and leaving the Applalachin Mountains. Much
of this sediment was deposited along the edge of the expanding Around 3 million years ago, a seaward-thickening
wedge of sediment buried most of the hard, crystalline, Appalachian
Mountain rocks that formed the eastern flank of North America forming
the above water Atlantic coastal plain. The submerged portion of the
plain became the Continental Shelf and extends out into the Atlantic
Ocean over 100 miles at its thickest point. The next major force acting on the coastal plain was
stream water flow from the North American glaciers about 3 million years
ago. This stream action over time was able to erode land and solid rock
making channels, streambeds and riverbeds and wider geographical areas.
Low-lying areas were affected both by stream flow as well as the erosive
effects of the advancing glaciers. These forces reshaped the coastal
plains and redistributed eroded material. The foundation of LIS was
formed in this way. Much more recently, in the last great ice age about
85,000 years ago, glaciers formed in Canada (the Wisconsinan Glacier)
and advanced toward the Atlantic Coast reaching the Connecticut
Coastline about 26,000 years ago. The Wisconsinan Glacier began to
recede about 21,000 years ago leaving behind it a wall of debris (i.e.,
the terminal moraine) which was a collection of rocks and sediment
pushed ahead of the advancing glacier (much like the ring of soap scum
left in the tub after a bath). This wall of debris is now found in the
middle of LIS. Present studies suggests that sea levels during the
Glacier were about 300 feet below what it is today, which means that the
coastline was about 70 south of where it is today. The Glacier began to recede about 21,000 years ago
because it was melting faster than new ice was pushing southward. This
wasn't a smooth continuous process, there were stops and starts, where
the ice melted for many years and then pushed south again. During each
of these changes, a pile of debris was left behind (recessional
moraines) which make up most of the above water portions of Fishers
Island, Plum Island and northernmost Long Island. The Wisconsinan
Glacier acted to hollow out the basin of LIS and the material pushed
forward made an ideal dam for collecting melting water from the glacier.
As the glacial ice continued its retreat northward, glacial Lake
Connecticut formed north of the moraine dam. The glacial lake continued to expand as the ice
melted eventually growing to be about the same size as present-day Long
Island Sound. The fairly shallow depth (20 meters or 64 feet) of today's
Long Island Sound is attributable to the fact that Lake Connecticut was
nearly filled in by clay sediments brought southward by the glacier. Around 15,000 years ago, the glacier had retreated
out of the State and glacial Lake Connecticut had just about completely
drained to the sea through an outlet in the moraine dam at the Race
(between Fishers and Long Islands). Changes in land and sea levels over
the next few thousand years resulted in seawater refilling the LIS basin
through the Race. Initially there was a shallow sea, with a depth of
40 meters, from around 13,500 years ago to around 9,000 years ago.
Current evidence indicates that the rate of relative sea-level rise
decreased about 5,000 to 3,000 years ago leaving More recently, sedimentation flow into LIS has kept pace with changes in sea level, and marshes developed along the margins changed much in the past centuries because the wave energy is fairly low in the Sound. If you want experience an example of this, compare the waves which impact on the Eastern Coast of Long Island during a storm with those that impact Connecticut beaches.
|
|||||||||
 |
|
