Long Island: Home Sweet Home• You know that Long Island is an island, but do

you know about the origin of Long Island and the coastal features that surround it?

Great South Bay

Peconic BayLong Island Sound

Shinnecock Bay

www.loving-long-island.com

In the beginning…

• The Atlantic Ocean basin originated ~200-135 million years ago (mya) as the supercontinent Pangaea began drifting apart from seafloor spreadinghttp://upload.wikimedia.org/wikipedia/commons/8/8e/Pangea_animation_03.gif

The geological history of Long Island• When Pangaea broke apart, it separated what

is now South America and Africa, leaving the Appalachian Mountains* as the western border of the emerging Atlantic Ocean basin

* themselves created ~480 mya from plate collisions that culminated in the construction of Pangaea; once volcanoes

http://www.fossilmuseum.net/fossilrecord/Appalachian-Orogenyb.htm

http://en.wikipedia.org/wiki/Allegheny_Plateau

The geological history of Long Island

• 200 million years of weathering drastically reduced these mountains in size and deposited large amounts of sediment along the edge of the expanding Atlantic Ocean

• Gradually, Long Island originated as a river valley as sediments were supplied by the erosion of these coastal plains and the Appalachian Mountains– served as a foundation for present-day Long Island

The Last ‘Ice Age’

• ~110,000 - ~10,000 years ago marked the last (most recent) glacial period

• During this time, much of the Northern Hemisphere (and to a lesser extent, the Southern Hemisphere) was covered in glaciers

• Under the extremely cold conditions, these glaciers grew, or advanced

And you thought this winter was cold…

• Glaciers originating from Canada advanced southward toward present-day Long Island

• This extensive ice sheet reached Connecticut ~26,000 years ago and the river valley of (now) Long Island ~21,000 years ago

• This glacier (commonly called the Wisconsin Ice Sheet) covered CT and the surrounding area, widening and deepening the river valley that eventually became Long Island Sound

Stuck between a rock and a hard place

• As the glaciers spread southward, they scraped up sediment (including bedrock!) and carried it along with them, depositing the accumulated material as they traveled and receded

Wisconsonian Glacier

Stuck between a rock and a hard place

• The melting of the Wisconsin ice sheet ~20,000 years ago deposited rocks and sediment from within the rocks forming glacial moraines

• Forms LI’s north shore and ‘backbone’

*Moraines

**

• The water melting from the giant ice sheet formed Lake Connecticut (where LIS now stands)

• As more and more of the ice sheet melted, sea level rose and eventually covered over the coastal plain creating Long Island Sound (saline) ~12,000 years ago

The origin of glacial deposits

Ice Age: The Final Meltdown• Long Island is now surrounded by unique

marine environments, but is still changing• Currents transport sediments creating barrier

beaches, and salt marshes line its estuaries

• Storms (hurricanes, in particular) are constantly reshaping the profile of Long Island, and even occasionally creating new inlets!

Shinnecock Bay; June 1938

Shinnecock Bay; September 1938 after the Great Hurricane

Storm surge carved out a large section of the barrier island separating Shinnecock Bay from the Atlantic Ocean

Shinnecock Inlet

The geological future of Long Island

• As sea levels rise, more and more of Long Island will become submerged (why you need flood insurance if own a house on the south shore…)

• Alternatively, if sea levels decline, more and more of Long Island would be exposed

• Earthquakes from isostatic rebound and ancient faults continue to occur