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    Ice floes, jams can pose major dangers during winter and spring

    By Alex Sosnowski, AccuWeather senior meteorologist

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    Ice floes and ice jams have the potential to cause significant flooding and damage along rivers in cold winter climate areas.

    While ice floes and jams are usually not a problem every year for a particular location, they are most common during the late winter and early spring, when the strengthening rays of the sun create runoff and rises on the streams.

    However, these dangers can also occur early in the winter when a thaw follows a siege of cold weather with sustained temperatures below 32 F.

    Static Ice Jam Vermont 1992

    Ice jammed the Winooski River and caused it to flood downtown Montpelier, Vt., in March 1992. (AP Photo/Toby Talbot)


    Prolonged cold weather causes ice to form in still water areas of streams and rivers.

    Depending on the severity of the cold conditions, the surface of these waterways may freeze over completely, while water flows rapidly beneath the surface.

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    Fluctuations in the level of the river cause the ice sheet to heave or sag.

    Since water has tremendous force, a change in water level by a mere couple of inches may be enough to cause the ice sheets to break up and begin moving downstream as an ice floe.

    Static Susquehanna River ice floe 1996

    A derailed Conrail freight train sits trapped by ice on tracks south of Harrisburg, Pa., Sunday Jan. 21, 1996. The freight train was headed to Pittsburgh from Baltimore when rising waters and ice on the Susquehanna river derailed several cars. (AP Photo/Tim Shaffer)


    Most often, it is the heaving produced from a significant thaw accompanied by heavy rain that results in major ice floes.

    As these blocks of ice move downstream and become lodged against each other near bridges, the confluences of streams, between narrow passages and around bends in the river, an ice jam may develop.

    Ice jams may slow the motion of the river to the point where water levels rise significantly farther upstream.

    Static Ice Jam Kankakee River Feb. 2014 AP

    An ice jam rose up along the Kankakee River and encroached on waterfront property on Friday, Feb. 28, 2014, in Wilmington, Ill. (AP Photo/Charles Rex Arbogast)


    In addition to raising the risk of flooding along the immediate banks of the river, damage to adjacent bridges, levees and property may occur. The ice can act like a giant slab of concrete with razor sharp edges.

    A rapid breakup of a major ice jam may also lead to flash flooding downstream.

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