The desertification of New York City
02.13.2010, 12:00 am
Filed under: Uncategorized

The recent layer of ephemeral stratification in Prospect Park, Brooklyn on 2.09.10 (FOP 2010)

This week New York City will become, as most cities will at some point this winter, coated with a temporary geologic layer. It isn’t a “new” layer, but an ancient one. Its presence results in an odd rearrangement of geologic time.  New York City, a combination of Anthropocene and Pleistocene shaped surfaces (dating from the present to 2.5 million years ago), is being encased this week by a thin stratum made, literally, of the stuff of 8-10 million years ago.

(FOP 2010)

This geologic layer will wash away with spring rains, or dissolve when more snow comes. But for now it’s coating nearly every exterior surface of this city: roads, sidewalks, bikes, cars, shoes and is probably starting to make its way into your apartment.

(FOP 2010)

Most of us know this ephemeral geologic layer as “road salt.”  500,000 tons of it are distributed annually throughout the state of New York (NRC, 1991).

A thick salty coat in Prospect Park, Brooklyn

Salt’s scientific name is sodium chloride (NaCl). It gets rid of ice on sidewalks and roads because it “lowers the freezing point of water. When rock salt is applied properly, small amounts of salt partially melt the ice and form a brine solution. This solution flows under the ice and breaks the bond between the ice and the pavement. This enables the snow plows to remove the ice from the roads.” – from American Rock Salt.

geologic rubble on the streets of Brooklyn

Next time you are walking down the street and feel that crunch beneath your feet, you can know that you are walking on a surface that connects you directly to deep time.

FOP did some detective work this week to track down exactly where New York City’s salty layer comes from. A reasonable guess would have been:  a short distance to the north.  The Finger Lakes region of New York State contains a giant salt reserve.  It extends west to Lake Erie, north to Ontario, Canada, and south through Pennsylvania. Some 550 million years ago, this region of New York State sank below sea level and a shallow, salty sea spread across it. Water collected in lagoons and evaporated, leaving layers of salt hundreds of feet thick.  The I Love Finger Lakes website has an overview of salt mines located in the region.  They include: Cargill Salt, American Rock Salt, Retsof, US Salt.

Apparently, Cargill is “the world’s largest marketer of salt products.” Its mine in Lansing, New York is 40 miles long and has a shaft that dives 2,400 ft. below the bed of the local Cayuga Lake–into salt formations that date to the Permian through Devonian periods (250-400 million years ago). The mine covers a remarkable 18,000 subterranean acres, qualifying it as “the deepest rock-salt mine in North America.” It produces 10,000 tons of salt every day. A local newspaper described the mine as “a dingy, six-mile system of 10-foot-tall corridors and cave-like rooms developed in a salt bed under the lake.”  Cargill extracts nearly 2.5 million tons of rock salt each year. You can read more about the Lansing Mine in this local report.

A drilling machine at the Cargill salt mine in Lansing, N.Y. (Librado Romero/The New York Times)

map of salt reserves in the United States (image the Salt Institute)

FOP contacted a Cargill public relations employee, who told us that the corporation supplies the New York State region, but not New York City. The City requires that enormous quantities of salt be constantly available–something that Cargill couldn’t guarantee. New York City commissioner of Sanitation, John H. Doherty, describes the City’s incredible stock:

“Our 44 salt storage facilities throughout the city have a capacity of 235,000 tons of rock salt and 330,700 gallons of calcium chloride de-icing solution. Prior to the start of any snowfall, our 365 salt spreaders are dispatched to salt arterial highways and bus routes.  Once snow begins to accumulate on city streets and highways, approximately 2,000 plows are mounted on various Sanitation trucks and deployed to clear snow from the city’s more than 6,000 street curb miles — equivalent to plowing from New York to Los Angeles… and back!”

So, the highways of upstate New York are receiving a dramatic 250-400 million year old Permian-Devonian veneer.

But what about the city? If New York City isn’t getting its supply from the upstate reserves, who and where would have enough salt to satisfy the City’s enormous demand?

International Salt does.  It’s a subsidiary of SPL (Sociedad Punta de Lobos) and a member of the K+S Group.  SPL operates at one of the world’s largest open-pit sodium chloride deposits, the Tarapacá Salt Flat, 60 km south of Iquique in the Atacama Desert of Chile. The salt flat measures 45 km by 5 km wide and 60-120 m deep.  Vast salt deposits are exploded from their ancient beds in this, the driest desert in the world (50 times drier than Death Valley).  They are then transported over 4500 miles to New York City. International Salt also supplies Boston, D.C., Philadelphia and Baltimore.

In a recent field trip to the Atacama, Land Arts of the American West explored the landscapes created by this “global redistribution of nitrates from the Atacama Desert”–one that marks “a turning point in the ecological balance of the planet. ” (Atacama Lab: 07)

SPL says their Atacama deposit is, “so pure and plentiful that it is estimated that the world’s salt demand can be met for five thousand years from this one salt deposit alone”.  The Tarapacá Salt Flat began to form 8-10 million years ago, meaning it’s made of the stuff of the Miocene. This ancient mineral, from the driest desert on earth, travels thousands of miles to be dumped on wet urban streets so that it can eat away the ice of bitter urban New England winters.

Atacama Salt Mine, image from the SPL gallery. Watch a video about the Rock Salt Mining in the Atacama here.

image SPL

image SPL

A thoroughly coated clump of organic material (FOP 2010)

American Rock Salt’s website says that salt is the “only rock consumed by people.” Which raises the broader question about where the road salt layer of New York City goes when it dissolves.

In the New York region there has been growing alarm about road salt’s runoff.  It has been finding its way into drinking water and implicated in human consumption of de-icing components added to the salt.  Apparently, run off has been causing elevated sodium and chloride levels in vegetation along roadsides in New York and is mixing with ground water supplies, causing elevated rates of chloride.

“In the New York City watersheds, groundwater is a major contributor to streams. Groundwater discharge accounts for at least 60% of total annual stream flow in the Croton watershed. Chloride concentration in groundwater supplies exhibits a relatively linear relation to road-salt application rate or two-lane road density throughout the year.” – Stormwater

And rock salt isn’t the only thing that runs off after a snow storm:

“Sodium ferrocyanide is added to chloride salts to prevent clumping during storage and application. In water, sodium ferrocyanide can be photolyzed to release approximately 25% cyanide ions (EPA, 1971).”- Stormwater

Read more through the Stormwater (published by the Journal for  Surface Water Quality Professionals) to learn more about these effects.

Sometimes sidewalk salt gets an extra de-icing additive making it a striking blue color (FOP 2010)

The ideal outcome: a snow free sidewalk. Eventually accomplished through the heat of the sun, traveling a mere 93 million miles (FOP 2010)

the road: where salt meets snow (FOP 2010)

after effects of the salt treatment (FOP 2010)

the salt drip, an ephemeral street graffiti viewable in New York City only during winter (FOP 2010)

Supposedly, the salt supplies of the world can meet contemporary human life’s infrastructural demands for thousands of years to come. The Salt Institute claims their supplies are endlessly abundant:

“Salt is the most common and readily available nonmetallic mineral in the world; it is so abundant, accurate estimates of salt reserves are unavailable. In the United States there are an estimated 55 trillion metric tons. Since the world uses 240 million tons of salt a year, U.S. reserves alone could sustain our needs for 100,000 years. And some of that usage is naturally recycled after use. The enormity of the Earth’s underground salt deposits, combined with the saline vastness of the Earth’s oceans makes the supply of salt inexhaustible.”

Salt’s abundance provides a rare instance in which urban planning can actually project its needs into deep futures, confident of having seemingly unlimited amounts of geologic raw materials.  But the ongoing effects of rock salt’s usage are still to be determined.  When the flow of salt from the Atacama to New York City runs out five thousand years from now, will the Atacama Desert have rendered every urban center in North America a salt flat?

For the next few weeks of winter, if you live in New York City, enjoy the temporary desertification made possible by the Miocene and the deeply geologic connection to former worlds offered up by the Atacama’s rock salt stratum.


FOP can’t end a post on salt deposits without mentioning the growing connection between ancient salt beds and the storage of nuclear waste. Our future and former worlds seem destined to collide for deep time:  the only functioning nuclear waste repository in the world, the Waste Isolation Pilot Plant, (located outside Carlsbad, New Mexico) is nested within the salt of the Permian bed of the Salado Formation.

3 Comments so far
Leave a comment

[…] of our region to help provide more of their urgent road and sidewalk clearing needs. However, as this informative blog post reports, this is not the case at all. Find out why NYC imports its salt from Chile instead (and […]

Pingback by All about salt

In Missouri there are several streams listed as impaired due to chloride from salts used as deicers. The Dept. of Transportation here is experimenting with beet juice (alone and mixed with salts)as an alternative deicer to lessen the negative environmental impacts. I don’t know how or why it works, but here’s a Web site that discusses this growing trend:

Comment by MK

[…] sweep it, store it, and use it again next year. This means no contamination of the groundwater and desertification from salt. This also means that many winter walks involve you, your thoughts, and one tiny pebble caught in […]

Pingback by Pebbles « Candy Chang

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