Introduction
The first purpose of this site is to acquaint the casual scholar with the four Pleistocene glaciations in Eastern North America and their present traces in one of the world's best known public spaces. It is quite remarkable to see evidences of the last ice age in an urban setting. It serves as a reminder that human influence is still very new and small in comparison.
The second purpose of this blog is to demonstrate how relevant glaciology is. When I told my friends that I was taking a glaciology class, the response was one of general boredom. I reasoned that this was because they felt removed from glaciers in both geography and space. However, it is hard to argue this after taking a closer look at the park.
Photo: Cornell Manecan
The Pleistocene was a geologic period of multiple glaciations and interglacials that occurred between 2.5 million and 11,700 years ago. In North America, four major glaciations within this period are commonly recognized, from oldest to most recent:
The Nebraskan
The Kansan
The Illionian
The Wisconsin
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Source: http://earthguide.ucsd.edu, Professor Molfgang Berger
Photo: public domain
The multiple glaciation theory was popularized by Albrecht Penck (German) and Eduard Bruckner (Austrian) in the beginning of the 20th century. They named four glacial divisions: the Gunz, Midel, Piss, and Wurm, which correlate with the aforementioned North American glacial periods.
Source: Jurgen Ehlers and Philip Gibbard, Extent and Chronology of Glaciations
Quaternary Science Reviews
Multiple glaciations and interglacial periods mean that there are more than one direction for glacial features and deposits across North America
The ice flowed in these general directions
Nebraskan: NW to SE
Source:
John Sanders and Charles Merguerian, Classification of Pleistocene deposits, New York City and Vicinity
The evidence of glaciations from different directions is also supported by the glacial sediments associated with the two flow directions.
Glacial sediment and till deposited from NNW to SSE by ice is reddish brown, a result of abrasion of hematite rich rocks
Glacial sediment and till deposited from NNE to SSW is yellow, brown, and grayish, indicating grinding of metamorphic rocks
Source: John Sanders, Charles Merguerian, Levine, Jessica, Carter, Paul
Pleistocene Multi-Glacier Hypothesis supported by newly Exposed Glacial Sediments, South Twin Island, the Bronx, New York
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| Photo: 123RF stock photo |
The four glacial advances are named for the areas which show the best and most compelling evidences of the glaciations were originally found in North America. In Europe, as referenced below, the advances were given different regional names.
Each glacial resurgence altered and reshaped previous glacial deposits and debris. It is quite possible that other advances occurred, but the proof for them has been eliminated by more recent glacial events. For this reason, in the area of the northeast to be examined, most of the indications of the Pleistocene are from the youngest Wisconsin.
Source: Geology and Geography of the New York Bight, Phil Stoffer and Paula Messina CUNY Earth, Science, and Environmental Science Ph.D. Program.
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| Visualization of multiple glaciations. Source: arcserver2.iagt.org |
We owe much of theory of an ice age to a Swiss naturalist, geologist, and jack of all 19th century sciences, Jean Louis Agassiz. He proposed that a "great glaciation" had occurred in Europe, and had led to the extinction of regional megafauna. Agassiz also noted that ice in his native Switzerland had gouged out bedrock and deposited debris down-slope. Like many scientists and thinkers of the past, he wasn't entirely correct, but he was on the right track.
Source: http://earthguide.ucsd.edu, Professor Molfgang Berger
Photo: public domain
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| Penck (r) Bruckner (l) Photo: public domain, http://www.quaternary.stratigraphy.org.uk/about/climatostrat.html |
The multiple glaciation theory was popularized by Albrecht Penck (German) and Eduard Bruckner (Austrian) in the beginning of the 20th century. They named four glacial divisions: the Gunz, Midel, Piss, and Wurm, which correlate with the aforementioned North American glacial periods.
Source: Jurgen Ehlers and Philip Gibbard, Extent and Chronology of Glaciations
Quaternary Science Reviews
The Glacial and Interglacial Periods
Multiple glaciations and interglacial periods mean that there are more than one direction for glacial features and deposits across North America
The ice flowed in these general directions
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| Photo: 123RF stock photo |
Nebraskan: NW to SE
Kansan: NNE to SSW
Illionian: NW to SE
Wisconsinan: NNE to SSW
Illionian: NW to SE
Wisconsinan: NNE to SSW
Source:
The evidence of glaciations from different directions is also supported by the glacial sediments associated with the two flow directions.
Glacial sediment and till deposited from NNW to SSE by ice is reddish brown, a result of abrasion of hematite rich rocks
Glacial sediment and till deposited from NNE to SSW is yellow, brown, and grayish, indicating grinding of metamorphic rocks
Source: John Sanders, Charles Merguerian, Levine, Jessica, Carter, Paul
Pleistocene Multi-Glacier Hypothesis supported by newly Exposed Glacial Sediments, South Twin Island, the Bronx, New York
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| Photo: Transpassive, text added This Youtube video posted by drgvettoretti shows the general advances and recessions of the Pleistocene in North America.
The Geology of Central Park
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Geologic Map of New York
Source: amnh.org
The park's bedrock is comprised of mainly of Fordham gneiss, Manhattan schist, Inwood marble, and the Hartland formation
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Underlying geology is important to understanding the impact that glaciers have on topography.
For example, rocks which are easily eroded, especially by water, are poor candidates for groove or striation preservation. Homogeneous rocks like sandstone, granite, and limestone uphold evidence of glacial activity quite well. Thickness and silica content also improve the preservation potential of gouges and grooves. (L.P. Gratacap, Geology of the City of New York)
Gneiss and schist fall in the middle of the range of preservation potential. According to early American mineralogist Louis Pope Gratacap, "the grooves, scratches, and striae over the gneisses and mica-schists of Manhattan Island undergo blurring".
(L.P. Gratacap, Geology of the City of New York)
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The park's bedrock is comprised of mainly of Fordham gneiss, Manhattan schist, Inwood marble, and the Hartland formation
_______________________________________________________________________________
Underlying geology is important to understanding the impact that glaciers have on topography.
For example, rocks which are easily eroded, especially by water, are poor candidates for groove or striation preservation. Homogeneous rocks like sandstone, granite, and limestone uphold evidence of glacial activity quite well. Thickness and silica content also improve the preservation potential of gouges and grooves. (L.P. Gratacap, Geology of the City of New York)
Gneiss and schist fall in the middle of the range of preservation potential. According to early American mineralogist Louis Pope Gratacap, "the grooves, scratches, and striae over the gneisses and mica-schists of Manhattan Island undergo blurring".
(L.P. Gratacap, Geology of the City of New York)
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Oskar
With the spirit that glaciology is fun and worthy of being shared with both the erudite and laypersons, I introduce Oskar:
He measures 11 inches from tail to tusk and is 6 inches tall. I wrapped him in a tape measure to indicate his use as a "scale". He served as a lovely companion on my trip to photograph the glacial leftovers of central park. As such, the photos I took with him are property of Kristen Srnecz.
Glacial Striations
The layout of the photos is a south to north progression within the park.
Striations are caused by the abrasion of rocks within glacial ice, being dragged along the glacier's base under immense pressure.
Photos: Kristen Srnecz
Source: Sanders, John E., and Merguerian, Charles, 1998, Classification of Pleistocene deposits, New York City and vicinity
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Erratics
In the same vicinity as Umpire rock, there is a very good example of an erratic, a boulder moved by glacial ice and deposited hundreds of miles away as the ice melted in place. The mineral composition of erratics do not match with surrounding bedrock.
This erratic is from the Canadian shield, hundreds of miles north of New York City. It looks like it was just placed on top of the flat schist.
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Multiple Striae
These photos show striations in two directions, direct evidence of multiple glaciations. Glacial abrasion from more than one advance impacted the bedrock.
Photos:
Kristen Srnecz
Belvedere Castle and More Striations
And the northernmost site I went to was Belvedere Castle, around 79th street. According to the official Central Park website, the castle architect Calvert Vaux (and co-designer of Central Park) wanted to give the impression that the castle was rising up from the bedrock below. To achieve this, bottom material of the castle is made of the same schist as the Vista Rock, on which it sits.
Vista Rock shows glacial striations.
Source:
Central Park was designed by landscape architects Frederick Law Olmsted and Calvert Vaux.
They also collaborated on the design of Morningside Park in Manhattan and Propect Park in Brooklyn.
Belevedere Castle provides tourists beautiful
views of the Great Lawn and Turtle Pond
Belevedere Castle currently houses the Central Park weather station.
The observatory also houses
nature exhibits for visitors,
including bird watching materials for use throughout the park.
Vista Rock, the schist outcrop beneath the castle, is the second highest outcrop in the park: 130 feet above sea level
Source: http://www.nycgovparks.org/parks/centralpark/highlights/11956
Photos: Kristen Srnecz
Above: Belevedere Castle and striae on the schist on which it sits.
Below: Me, explaining striations and grooves
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| Must. Photograph. More. Rocks. |
The Bigger Picture of the Last Ice Age
YouTube video. From the Discovery Channel series "Making of a Continent"
http://www.youtube.com/watch?v=7NdpiUxD2U8&playnext=1&list=PL922D398A6E3B0CAD&feature=results_video
A USGS map which shows the impact of the Pleistocene over the greater New York area
A USGS map which shows the impact of the Pleistocene over the greater New York area
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| Source: USGS |
Which brings us to Long Island, the peninsula jutting out into the Atlantic. Long Island is actually a combination of two terminal moraines from the Illonioan and Wisconsin periods.
Harbor Hill to the North, Ronkonkoma to the South
Source: Geoarchaeology of Landscapes in the Glaciated Northeast,
David Cremeens and John Hart
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Works Cited
"American Museum of Natural History." AMNH. 07 Nov. 2012 <http://www.amnh.org/>.
Burger, Wolfgang. "Discovery of the Ice Age." Discovery of the Ice Age. 10 Nov. 2012 <http://earthguide.ucsd.edu/virtualmuseum/climatechange2/02_2.shtml>.
Cremeens, David L., and John P. Hart, eds. Geoarchaeology of landscapes in the glaciated Northeast: Proceedings of a symposium held at the New York Natural History Conference VI. Albany, NY: University of the State of New York, State Education Dept., 2003.
Ehlers, J. "Extent and chronology of glaciations." Quaternary Science Reviews 22 (2003): 1561-568.
"GEOLOGY AND GEOGRAPHY OF THE NEW YORK BIGHT." GEOLOGY AND GEOGRAPHY OF THE NEW YORK BIGHT. 10 Nov. 2012 <http://www.geo.hunter.cuny.edu/bight/coast.html>.
Gratacap, L. P. Geology of the city of New York. New York: H. Holt and Co., 1909. Republished by Forgotten Books, 2012
Merguerian, Charles, John E. Sanders, Jessica Levine, and Paul M. Carter. "Pleistocene Multi-Glacier Hypothesis supported by newly Exposed Glacial Sediments, South Twin Island, the Bronx, New York." (1997). July-Aug. 2010. <http://hdl.handle.net/1951/48069>.
"New York City Department of Parks & Recreation." New York City Department of Parks & Recreation. 07 Nov. 2012 <http://www.nycgovparks.org/>.
Sanders, John E., and Charles Merguerian. "CLASSIFICATION OF PLEISTOCENE DEPOSITS, NEW YORK CITY AND VICINITY--FULLER (1914) REVIVED AND REVISED." (2010).
Picture/ Video Credits
Photos not cited are property of Kristen Srnecz
arcserver2.iagt.org
http://www.quaternary.stratigraphy.org.uk/about/climatostrat.html
Transpassive stock photos
123RF photos
USGS
You tube links are property of their respective posters
http://www.youtube.com/watch?feature=player_detailpage&v=USIAcXfv39k
http://www.youtube.com/watch?v=7NdpiUxD2U8&playnext=1&list=PL922D398A6E3B0CAD&feature=results_video
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