The New York Times did a recent story on How the Ice Age Shaped New York with a tagline Long ago, the region lay under an ice sheet thousands of feet thick. It terminated abruptly in what are now the boroughs, leaving the city with a unique landscape.”  This resonated with me and reminded me of posts about Minnesota’s Lake Agassiz, as well as the Waterlines presentation last year by Dr. Stan Chernicoff on Seattle’s own geological history and how the ice age covered the city with a deep layer of ice ground away over time and as it melted 10-20,000 years ago, influenced and left many traces on cities.

New York City experienced similar issues, with a two-mile thick ice layer forming over two million years back, covering the area region encompassing much of the city and all of Manhattan, with the terminal moraine reaching the zone bisecting parts of Staten Island and Long Island, until warming and retreat 18,000 years ago.

The story of many areas is the same, the depth and weight of ice shifting bedrock, and creating waterways, kettle ponds and lakes, as well as retreat leaving glacial erratics and other rubble strewn through the zones.  However it’s more distinct in New York City, as pointed out in the article:  “While the line of glacial debris across the northern United States is often poorly delineated, the hilly ridge around New York City tends to be quite prominent. Its maximum height is roughly 200 feet, about that of a tall apartment building.”

The ridges and hills determined where people settled, as they avoided these areas and found flatter ground, and I remember the specific outcrops left in place in Central Park as features, but perhaps also to avoid having to blast or remove them. (see header image above)  The article mentions that many place names are derived from this rises, appended with Hills, Heights, and Slope and also its usage in local building materials.  The proximity of the terminal moraine to New York City is unique, but that glacial history has been forgotten over time.  As mentioned:

“Despite the ridge’s prominence and early allure for scientists, it turned out to be no rival for skyscrapers and urban distractions. The moraine that shaped the city was all but forgotten. “Clearly, it’s not on the radar,” said David E. Seidemann, a professor of geology at Brooklyn College. “The educational system here doesn’t emphasize earth science. And there’s so much else to do. I’ll go to a Yankees game over geology any day.”

But the hidden remnants paint a fascinating picture, capture by geologist and environmental educator from the American Museum of Natural History, Sidney Horenstein, who also does tours of these phenomena.  He found documents showing that geologists working in the 1800s found in terms of the variation of hill to flatland geology: “Ridges, mountains and even flatlands are typically rooted in rocky strata, such as the bedrock that underlies Manhattan and makes it ideal for erecting skyscrapers. But early investigators found the hilly ridges to be composed of clay, silt, sand, pebbles, cobbles and boulders, all jumbled up together.”

The walk through reports (such as the fascinating Natural History of New York published in 1842) established a chronology of more focused work on things like history of glacial floods, and fills in gaps on geological processes, even showing the emergence of terms to describe processes, like ‘Ice Age’ which was starting to be more widely used in the 1880s.

A 1902 USGS large-format map provided some spatial information as well

The maps used colors to show variations of geology amidst the emerging city grid, and identified the terminal ridge. As the article points out:

“At first, the city used the stony ridge for woodlots and rain catchments. Slowly, the uses expanded to reservoirs, recreational areas and, in time, neighborhoods in which buildings and houses were built on strong footings and foundations for stability.  Today, despite the wide development of the ridge’s lower slopes, a Google Earth view of New York City — a composite of images from April, June and September — shows the glacial relic as an intermittent band of green.”

A larger image of one of the maps  from the folio is seen below, via NYC99 gives an indication of the rich data available – click to enlarge (image source from Texas A&M Library).

Similar to the Missoula Floods that broke through a massive ice dam and carved out the Columbia River basin, New York also had a flood termed ‘biblical’, as glacial retreat happened around 13,000 years ago, where a “... towering wave of destruction crashed down through the Hudson gorge and proceeded to smash the southern end of the local moraine to smithereens.”

It’s interesting to draw parallels between how the glacial impacts are similar on the east and west coasts, but also how they differ due to variations of geology and topography.  The hidden history isn’t just hydrology, but a combination of physical and biological processes working in tandem, over millennia. We’ve done much to erase and obscure, but traces remain, indications of these long and large processes are tucked away under our feet, waiting to attract our gaze.

“…millions of people live on or near the glacial ridge. In all, it runs for roughly 30 miles beneath New York City. Invisibly, it links three boroughs, offering mute testimony to the power of vanished ice.”

 


HEADER:  Umpire Rock in Central Park – this and all other images, unless noted, via NY Times  

4 thoughts on “Ice Age: New York

  1. There is a morraine surrounding suburban Chicago too. The ice retreated to Lake Michigan.

    1. Thanks Jim. I’m imagining a map that I’ve yet to see out there showing the front edge of the terminal moraine for the whole US… there’s a hidden boundary worth exploring, for sure.

      1. Any Geology textbook might have maps in their glaciology chapter. I have seen many through the years although I admit I have a Minor in Geology which means MUCH reading. If you get lucky there will be several maps representing the last few terminal moraines of the most recent glaciations. Here in Iowa we can easily find both the Nebraskan and Kansan Terminals. Each one advanced and ended at different places along their South border. I find it thrilling when driving up and down the hills whether it is just 20 miles South of Waterloo, just North of Des Moines, or just past Tama on the other side of the Iowa River. As a last thought, look up specific state’s Geology and you may get luckier with more detailed maps.
        Enjoy,
        Dan

      2. Supposedly these was no glaciation in southwestern New York around the Salamanca area southward as the terminus was around that area. But even the most detailed lidar maps that show the finest ground striation show nothing in particular. In fact the hills and valleys of Pennsylvania south of there look the same on the lidar maps as the hills and valleys of the southern tier of New York which supposedly WERE glaciated. All the flat bottom valleys of both look the same as well. No long ago they changed where the southern terminus was from just north of Binghampton

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