Gather round, folks, and brace yourselves for a wild ride through the geological wonders of Long Island! Forget what you thought you knew about this seemingly serene stretch of land because beneath its surface lies a treasure trove of absurdity that'll make your head spin faster than a Long Islander merging onto the LIE during rush hour.
Long Island’s Basement Bedrock
- Long Island's geological history includes pre-glacial events such as the formation of ancient metamorphic bedrock, which is over 400 million years old, serving as the island's foundation
- Approximately 70 million years ago, during the late Cretaceous period, sands and clays were deposited on this bedrock
- While surface exposures of the bedrock are widespread in Manhattan and the Bronx, they are limited on Long Island
- Long Island's bedrock is 230 to 350 million years old, composed of metamorphic rock
- The bedrock slopes down to the south and east beneath the rest of Long Island, without forming significant landforms
- Underlying nearly all of Long Island is a substantial wedge of Cretaceous sediments, comprising sands, clays, and gravels
- This wedge, over 2,000 feet thick under Fire Island, thins towards the north shore and western end of the island, eventually disappearing under Long Island Sound, western Queens, and Brooklyn
- Despite reaching elevations above sea level in northern Nassau and northwestern Suffolk counties, the Cretaceous sediments are largely covered by younger glacial deposits
The Glacier That Made Long Island
- Long Island formed during from the melting of the Laurentide ice sheet, specifically the Wisconsin Glacier, around 60,000 years ago
- The glacier left behind gravel and rock, shaping Long Island's distinctive fish shape
- Throughout history, Long Island has transitioned between being an island and a peninsula multiple times, often persisting in one state for decades
- Fossils are not very common on Long Island, likely due to its formation by glaciation
Post Glacier Evolution
- Post-glacial changes on Long Island are most evident along its extensive coastline
- Waves, currents, and wind have actively eroded and reshaped the soft glacial sediments, resulting in various sandy shoreline features
- Additionally, less dramatic changes occur on the upland surface, influenced by numerous streams and small rivers
- These water bodies gradually erode the land and transport sediments to the coast, contributing to ongoing landscape changes
- Post-glacial changes on Long Island are most evident along its extensive coastline, particularly the south shore
- The Ronkonkoma terminal moraine deposits near Montauk Point have experienced significant erosion from the powerful waves of the Atlantic Ocean
- The south fork of Long Island has shortened by several miles due to wave action since the glacier's retreat
- Currents have transported substantial amounts of material westward from the eroding moraine, contributing to the formation of sandy barrier beaches like Fire Island, Jones Beach, and Long Beach
- These barrier beaches, constructed by wave action and currents, feature offshore bars formed by waves acting on the shallow sea bottom and extended westward by drifting currents
- Fire Island has expanded westward by five miles since the construction of its lighthouse in 1844
- Barrier beaches are stabilized by wind-blown sand forming dunes away from the wave zone, with grasses and shrubs helping to hold the sand in place
- The elevation of the dunes and vegetation aids in resisting erosion during storms and prevents the beach from washing away
The Inlets
- Barrier beaches are interrupted by inlets allowing tidal waters to flow in and out of shallow, marsh-filled lagoons behind the beaches
- Through a natural process of silting and marsh formation, these shallow bays or lagoons gradually fill in, connecting barrier beaches with the Long Island mainland
- This filling process is observable in the bays behind Long Beach, where narrow channels separate marshy islands
Stormwater Runoff and Drainage
- Surface drainage on Long Island primarily consists of small streams due to its relatively small land area
- Freshwater runoff typically flows directly into the sea without forming large rivers
- The Peconic River is the largest river on Long Island and serves as the only major east-west draining stream
- Other small rivers, such as the Carmans, Connetquot, and Nissequogue, may appear significant near their mouths because the lower portions of their valleys have been flooded and widened by the rising post-glacial sea
- Such flooded and widened river valleys are known as estuaries, where estuarine waters are characterized by a brackish mixture of salty seawater and fresh stream water
Elevation
- Long Island has a relatively low elevation, with its highest point at Jayne's Hill reaching 401 feet above sea level
- Due to this low elevation, the island is susceptible to flooding, and continued sea level rise could potentially lead to total submergence
Earthquakes
- Long Island has had its fair share of earth rockers over the years, click here for a list.