January 20, 2022
On February 11, 1981, Bill Clark was transfixed as he watched the erratic behavior of the ice-choked Delaware River, which ran high and acted uncharacteristically. He recalls, “As I watched it, it would move a little bit and stop. And then move a little bit, which was creepy.”
Mr. Clark, who currently serves as the President of the Matamoras-Westfall Historical Society, had lived many years along the river in Matamoras, Pennsylvania. From his town, residents watch the Delaware flowing from left to right, as they look across the water toward Port Jervis, New York. Mr. Clark was rightly concerned in 1981, because a stopped river in mid-winter could only mean that the ice had jammed downstream in a phenomenon called an ice jam, which can dam up water and send it quickly over the banks into riverside communities.
The erratic behavior of the ice-filled river continued throughout the day and into the night, as residents closely monitored conditions. Frank Dale reflected, “The erratic behavior fooled everybody. In the two rivers bordering Port Jervis, the Delaware and the Neversink, observers noted huge ice cakes float downstream, reverse direction and go upstream, then reverse direction again.”
The unpredictability of the Delaware during this flood event is perhaps best seen in the log kept at the command center in Matamoras during the event. Rarely have humans in the crosshairs of a flood encountered such a dramatic turn of events, as wild swings in the water level seemed to change by the minute.
The log reads:
12:45 AM Ice jamming below Tri-States began to raise the river level.
1:25 AM River level was reported going down.
2:15 AM The river was reported rising…
2:40 AM Milford Bridge called, ice there on the move, gauge has dropped 20 points in 20
3:25 AM River coming across the road …
3:30 AM River dropped three feet.
3:40 AM “All Hell Broke Loose!”
Imagine the emotional rollercoaster that residents felt as the river suddenly changed its mind, rising and falling in succession, until, at last, it unleashed its fury, in a sudden, pre-dawn flood. Surely, residents would have felt helpless to stop a flood that was so unpredictable.
When the river was rising during this flood event, water levels increased shockingly fast. In the first hour of noticeable ice jam flooding, the river rose an astonishing 14.5 feet. In Port Jervis, between 1:00 and 3:30 AM on February 12, the river rose 20 feet, according to Mayor E. Arthur Gray in the Times Herald Record.
The tremendous power of this flood came from both the force of the water and the large slabs of ice that flowed over the river banks and into homes and businesses. Fisher recalls, “One Matamoras resident broke into tears several times as he described how ice sections as tall as freight cars and as wide as steamrollers rumbled overland Thursday morning sounding ‘like a jet engine’ revving on a runway.”
By the time the flood waters subsided, the 1981 Ice Jam Flood had devastated multiple communities in the tri-state region. The river level on the U.S. Geological Survey stream gauge at Port Jervis reached its all-time highest level, exceeding the 1904 flood by a foot. Floodwater inundated more than half of residential Matamoras and nearby Westfall, damaging more than 400 homes, and caused 4,000 people to be evacuated in the region. The flood damage reached $14.5 million in 1981 dollars, an amount that converts to $43.39 million in February 2021, according to the U.S. Bureau of Labor.
An ice jam is defined as, “A stationary accumulation of fragmented ice or frazil that restricts flow.” They can form on rivers in cold climates where fragmented river ice gets caught while flowing downstream. Although this phenomenon is sometimes called an ice gorge, in this article I will refer to them as ice jams.
Ice jams tend to form at specific riverine locations. Pinch points, or locations where a river channel narrows, are common areas where they form, as are areas where a river channel splits as it encounters an island. Sharp turns in a river also cause ice jams, because the large blocks of ice get snagged on the riverbank, and eventually other ice blocks, as the ice tries to turn a sharp corner. The greatest danger for ice jam flooding occurs upstream from such locations, as the ice jam dams the water and floods upstream communities.
The Delaware River encounters all three of these factors: a pinch point, islands, and a sharp turn, just downstream from Matamoras and Port Jervis. Within a mile or two of passing these cities, the river takes a 90-degree turn to the right, after passing the New York-New Jersey border. The river then narrows, before encountering two islands, Mashipacong and Thirsty Deer.
The map below depicts the area flooded from the 1981 ice jam flood, shaded in dark grey. Notice how the inundated area is located just upstream (north and northwest) from the 90-degree turn in the river. The map also reveals that the river narrows near this sharp turn. The islands are located just south of this mapped area.
I gained a better appreciation for the drastic change in the river course, after taking a GeoTrek to Point Peter, a scenic overlook on a ridge just north of Port Jervis. From the lookout, I saw the Delaware River consistently flowing to the southeast, then making a sharp turn just after it flowed between Port Jervis and Matamoras. If the ice jammed near this sharp turn, I could clearly see that many buildings are in harm’s way of rising water, upstream from the jam.
Ice jams also form on the upstream side of dams, where river flow is reduced, and the water pools. Slower flow speeds and pooling lead to ice forming earlier in the season and to a greater depth in these areas. During break-up, chunks of ice floating downstream can get caught up on the thicker ice formed upstream of such dams.
While I was traveling around the northeast United States, I took a second GeoTrek to the Albany area of Upstate New York, to investigate this phenomenon. I visited the Vischer Ferry Dam along the Mohawk River, where substantial ice jams sometimes form during river break-up. In this area, ice jams cause 80% of flood events. Although temperatures were running above average during December 2021, and most of the river flowed unrestricted, ice had begun to form in the pool on the upstream side of the dam (see pic below).
In the United States, ice jams are most common from the Northern Plains to New England, including the Great Lakes region, Upstate New York, Pennsylvania and New Jersey. In these regions, winter temperatures are sometimes sufficiently cold to freeze rivers. Although the Pacific Northwest receives severe winter weather at high elevations, milder conditions at lower elevations and near the Pacific Ocean keep rivers from freezing, thereby reducing the threat of ice jams.
Maps of historic ice jam locations confirm these general patterns. For example, the map below depicts ice jam locations from 2016-2019. Although year-to-year variability exists, the general pattern shows the greatest risk of ice jams from the North Central to Northeast states. These maps are made from observations in the Ice Jam Database, maintained by the Ice Engineering Group at the Cold Regions Research and Engineering Laboratory with the U.S. Army Corps of Engineers. The database contains more than 18,000 records from across the United States.
Climatologically, ice jams can form during freeze up in the beginning of winter or during break up, which can occur at the end of winter or during a sudden mid-winter thaw. Break-up ice jams form during “highly unsteady flow conditions,” characterized as a time with rapid snowmelt, heavy rainfall, deteriorating ice conditions and/or increased runoff.
Ice jams more commonly form when weather is persistently cold and/ or snowy, followed by a heavy rainfall or sudden warm up that causes a rapid runoff event into rivers. A U.S. Army Corps of Engineers Study, Ice Jam Flooding on the Missouri River Near Williston, North Dakota, found that colder and/or snowier than average weather conditions preceded the six major ice jams that occurred near Williston, North Dakota, over a 40-year period. The study concluded that these years then observed, “an increase in runoff sufficient to cause breakup came when the ice was still thick and strong.”
Another pattern that increases the risk of ice jams is a persistent drought that reduces water level flows on rivers, accompanied by unusually cold weather that freezes the diminished rivers straight to the bottom. Then a sudden warm-up with heavy rain increases discharge in rivers and breaks up some river ice, while large slabs of ice that were attached to the bottom are brought to the surface.
This pattern occurred during major ice jam events in Port Jervis and Matamoras, such as the ice jam floods of 1875 and 1981. Dale provides the play-by-play conditions that led to the 1875 ice jam in the region. He states, “In 1875 an ice jam threatened the upper valley for most of February and March; low water levels, ironically, caused the full depth of the river to freeze solid. When the rains came they raised up the huge slabs, piled one atop the other, and moved them slowly but inexorably downriver.”
The drought preceding the 1981 ice jam flood was so severe that Pennsylvania Governor Rick Thornburg asked the Small Business Administration (SBA) to declare 50 Pennsylvania counties eligible for low-interest disaster loans to provide relief from the drought . Ironically, this request was submitted three days before the flood struck. The end of this drought and the onset of the ice jam flood are evident in the precipitation records of the Delaware River basin north of Montague, New Jersey, from December, 1980 to February, 1981 (see below). Note the dry conditions in December and January, followed by a wet February.
Table 1. Precipitation from December 1980 – February 1981 for the Delaware River basin north of Montague, NJ. Source: Schaefer and Fish (1982).
Heavy February rain triggered the ice jam disaster, which was then followed by a complex, public dialogue where some people blamed human error, related to mismanagement of the river, lack of action to dislodge the ice, and absence of a flood warning system. One newspaper article reported on this public outcry, under a headline that read, “low water caused the flood,” with photos of a heated, public meeting.
I will discuss mitigation options in the next section, but before we move on, reflect on the context of these complex drought/cold- warm/rain floods. This pattern runs contrary to every other type of inland flooding, in which substantial precipitation, high soil saturation, and elevated river levels lead to increased flood risk. For ice jam floods, just the opposite may occur, as prolonged drought and low river levels set the stage for a higher proportion of the river to freeze in cold weather.
For these floods, the amount of water flowing downriver is unimportant, as the forcing mechanism for the flood is the not the quantity of water, but the ice characteristics that can lead to an efficient ice jam. In the words of Wuebben, “In contrast to open-water flooding, where high water levels directly result from excessive water discharge, ice-affected flooding results from added resistance to flow and blockage of flow and blockage of flow caused by accumulations of ice.”
Ice jam floods impact river communities with damage to buildings from both floodwater and large blocks of ice that flow on the inundation. Many of these communities are historic, as rivers used to provide the major “highways” for transportation, enabling riversides to observe early settlement. Therefore, ice jam floods impact a disproportionate number of historic buildings, such as the Stockade Historic District in Schenectady, New York, which flooded from ice jams on the Mohawk River as recently as 2007 and 2018.
Land-based transportation routes, such as railroads and paved roads, often developed alongside rivers. Ice jams push tremendous amounts of ice onshore, sometimes burying roadways and train tracks under massive blocks of river ice. The 1904 ice jam covered the tracks of the Erie Railroad under huge blocks of ice near Port Jervis; the railroad company hired local men to clear the tracks.
In other locations, ice jam flooding may impact utilities, such as wastewater treatment plants, that are located along rivers. This is a problem in Malone, New York, near the Canadian border. Urban planners should consider ice jams when determining site-selection for such facilities.
Ice jams introduce a complex situation that may cause some confusion in the insurance claims process. Evacuated homeowners may return to find flood damage, as well as evidence that ice pushed through windows, doors, or walls. In the aftermath of such disasters, insurance companies may dispute the primary cause of the damage.
Homeowners insurance may argue that the primary damage is from flooding, and advise residents to submit claims with their flood insurance carrier. Flood insurance may argue that had a large block of ice not crashed through the living room window, flood waters would not have entered the house. Such insurance carriers sometimes dispute such claims in a lengthy litigation process, while the homeowner desperately waits for a settlement.
This type of situation resembles hurricane damage in coastal communities, where insurance companies may dispute the primary cause of damage as wind (including wind-driven rain) or flood (from the ground up). These cases show the importance of ground-based field work during complex natural disasters to document the details of such catastrophes and speed the recovery process.
Ice jam mitigation efforts fall into two categories- actions taken to reduce the impacts of ice jam floods before an event occurs, and actions taken during an ice jam event. Both types of mitigation efforts are important.
Efforts to reduce obstructions on rivers, like bridges, may be helpful for reducing ice jam blockage. Sometimes this means building a bridge higher, to allow elevated ice and water to pass under the structure. In the words of Senator O’ Connell following the 1981 ice jam flood, “I-84 definitely aggravated flooding problems, and the highway ‘Should have been built on stilts’ rather than on landfill.” (The Pike County Dispatch and Port Jervis News).
Removing downstream obstructions may also take the form of reducing the amount of vegetation and tree cover on islands and along riverbanks, to allow water and large blocks of ice to flow faster and not become obstructed. Port Jervis Emergency Management Director Tom Vicchiariello recalled that Port Jervis, Matamoras, and the city of Montague, New Jersey, provided funds to partner with the U.S. Army Corps of Engineers to cut trees and vegetation on Mashipacong Island after the 1981 ice jam. The Army Corps coordinated this work, as they felt it was a long-term action that could be taken to reduce flood risk.
Vicciariello also recalled that the U.S. Army Corps of Engineers took measures to increase the depth of the river channel on the side of the island. Increasing the depth and/or width of river channels allows for more water to flow through these areas, reducing the chance of ice blockage. Deeper water channels may reduce the proportion of the water that will freeze after prolonged cold weather, further reducing ice jam risk.
During an ice jam event, ice breaker ships and tug boats may be deployed to break up jammed ice and keep the river flowing. New York State’s “Reimagine the Canals” initiative deploys both types of vessels to break up ice jams that often form on the Mohawk River, just downstream from Schenectady (DeMola 2020). These vessels are docked at the Vischer Ferry Dam, previously mentioned in this article as a hotspot for ice jam formation.
These ice breaker ships face challenging conditions, however, as they often encounter brash ice, “An accumulation of floating ice made up of fragments not more than 6.56 feet across (small ice cakes), or the wreckage of other forms of ice” (AGU 2022). This accumulation of ice from different sources often refreezes on the river, making it even stronger. The icy conglomeration may contain debris, such as tree branches, that impede the work of ice breaker ships.
Heavy machinery, like cranes, are other resources that local governments may use to break up ice jams. In February, 1982, one year after the massive ice jam that flooded Port Jervis and Matamoras, the Department of Public Works in Orange County, New York, loaded a 10-ton crane to be placed on the Interstate-84 bridge over the Delaware River to break up ice. Fortunately, flood water in that year did not inundate nearby cities, although it's unclear what role the crane may have played in this outcome.
Blasting dynamite has been proposed as a possible solution to breaking up ice jams. This idea was discussed at the public meeting following the 1981 flood at the Matamoras Fire Hall on February 16, 1981. U.S. Geological Survey River Master, Robert Fish, countered, “Blasting would probably not have been effective…when you have five miles of ice, it would probably take a carload of dynamite to even make a dent in it.” He continued, “Blowing any one piece would not move it.”
Unfortunately, If blasting the ice successfully dislodges the jam, the problem is not solved, because the ice could still threaten other communities. In the words of Mr. Vicciariello, this process, “Creates problems for other town downriver.” This is a good reminder that rivers are a twisting highway of water, and when filled with large ice chunks, the threat of ice jams extends for substantial distances.
Perhaps the most high-profile method of breaking up ice jams has come from dropping bombs from airplanes on jammed ice. During a 15-mile ice jam in Alberta, Canada, in April, 2020, Don Scott, the mayor of Wood Buffalo, requested fighter jets to drop bombs on the ice. A pair of fighter jets were dispatched to bomb ice when a 25-mile ice jam formed along the Sukhona River in Russia, in 2016. Courtney provides details to this story, along with an embedded video clip that shows the bombs hitting their target.
The mitigation options listed above, as well as preparations to issue public flood warnings and evacuations, require frequent monitoring of rivers. Such monitoring takes place through remote sensing, field work and water level gauges.
Remote sensing through satellite imagery analysis and air photo interpretation are important tools for ice jam monitoring over broad areas. Such monitoring methods are important because ice can build up for many miles, requiring an aerial viewpoint to assess the scope of the jam. For example, NASA Earth Observatory (2018) provided imagery of ice jams along the Connecticut River, taken from the European Space Agency’s Sentinel-2 satellite.
While remote sensing gives a snapshot of river ice conditions over a large area, ground-based field observations often provide crucial information that cannot be seen from above. Information such as the extent of ice, type of ice, characteristics of ice movement, as well as freeze-up and break-up dates, are all crucial to monitoring and forecasting. The National Weather Service relies on river ice observers to provide such information, as they observe it from riverbanks. For example, the National Weather Service office in Binghamton, New York, publicized their search for river ice observers early during the 2021-2022 winter, to provide information especially for 10 river areas in Pennsylvania and Upstate New York.
Extensive networks of river gauges also provide crucial data on fast-changing water levels around the nation’s rivers. The U.S. Geological Survey’s National Water Information System partners with the National Weather Service’s River Forecast Offices to provide near real-time river level data that could reveal rapid water-level rises upstream from ice jams.
Non-automated water level measurements also serve a purpose in locations that observe frequent ice jam floods. Such gauges or measurement meters calibrate flood levels to the same scale as a community’s elevation certificates, enabling people to connect water levels near a river to inundation impacts in the community. Such gauges and meters also provide invaluable historic data when the mark the level of historic floods in the community. The flood meter at the North Ferry Street Sewage Pump Station in Schenectady, New York, calibrates flood levels for the local community and provides high water marks from floods in the years 1955, 1977 and 1996.
Couture, B., 1982: Emergency actions taken. Article in The Union-Gazette, February 4, 1982, Port Jervis, New York.
Demola, P., 2020: Tugboats, icebreaker to be deployed to break up ice jams along Mohawk. The Daily Gazette, December 15, 2020. Daily newspaper in Schenectady, New York. Link: https://dailygazette.com/2020/12/15/tugboats-icebreaker-to-be-deployed-to-break-up-ice-jams-along-mohawk/.
Fedschun, T., 2020: Ice-jam flooding in Canada forces 15,000 to evacuate, mayor asks for jets to bomb 15-mile jam to loosen it. Fox News online. Published April 29, 2020. Link: https://www.foxnews.com/world/ice-jam-flood-canada-fort-mcmurray-spring-thaw-chucks-ice-water-flooding.
IAHR (1986) River ice jams: A state-of-the-art report. IAHR Section on Ice Research and Engineering, Working Group on River Ice Hydraulics. In Proceedings of the Ninth International Symposium on Ice, Iowa City, August, p. 561–594.
NASA Earth Observatory, 2018: Ice jams on the Connecticut River. Link: https://earthobservatory.nasa.gov/images/91620/ice-jams-on-the-connecticut-river.
National Weather Service, 2021: NWS Binghamton Looking for River Ice Observers This Winter. December, 2021. Link: https://www.weather.gov/bgm/hydrologyRiverIcerecruit.
Pike County Dispatch and Port Jervis News, 1981: The Ice Gorge Flood of Thursday, February 12, 1981. From the pages of the Pike County Dispatch and Port Jervis News. Text by Doug Hay, Photos by Nancy Barletto and Doug Hay, Illustrations by Joe Kreutzfeldt.
Schaefer, F.T., and R.E. Fish, 1982: Report of The River Master of The Delaware River for the Period December 1, 1980- November 30, 1981. U.S. Geological Survey, Open File Report 82-341.
The Times Herald Record, 1981: Lack of Warning Irks Residents. Article in The Times Herald Record, February 13, 1981, page 3. Written by staff members, specific authors unknown.
U.S. Bureau of Labor Statistics, CPI Inflation Calculator: Available online at: https://www.bls.gov/data/inflation_calculator.htm.
Wuebben, J.L., and J.J. Gagnon, Ice Jam Flooding on the Missouri River near Williston, North Dakota. CRREL REPORT 95-19, September, 1995. 25 pp. Cold Regions Research and Engineering Laboratory, U.S. Army Corps of Engineers, Omaha, Nebraska District. Link: https://erdc-library.erdc.dren.mil/jspui/bitstream/11681/9195/1/CRREL-95-19.pdf.
Zufelt, J.E., and W.W. Doe, III, 1986: Upper Delaware River Ice Control – A Case Study. Chapter in a book with unknown host publication title, edited by William L. Ryan and published by ASCE. ISBN (Print): 0872625133.