1. 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 Bay
Long Island Sound
Shinnecock Bay

2. In the beginning…
The Atlantic Ocean basin originated ~ million years ago (mya) as the supercontinent Pangaea began drifting apart from seafloor spreading

3. 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
Driving on coastal plain eroded from the mountains; only their core is left (once volcanoes)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. The origin of glacial deposits

13. 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!

15. Shinnecock Bay; June 1938

16. 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
Storm surge carved out a large section of the barrier island separating Shinnecock Bay from the Atlantic Ocean

17. 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