Jagged danger: Ice floes, jams show a different force of nature at work
They look like giant slabs of white concrete with razor sharp edges. Such ice floes and jams are huge floating masses that can be dangerous to life and property.
They all involve ice, but they're not the same. Find out what makes ice floes, ice jams and ice shoves different.
The large chunks of jagged, floating ice look threatening -- and they are. Ice floes and ice jams have the potential to cause significant damage and unexpected flooding along rivers in cold climates by blocking the channels.
While ice floes and jams are usually not a problem from year to 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.
These dangers can also occur early in the winter when a thaw follows a siege of cold weather with sustained temperatures below 32 degrees F.
Ice jammed the Winooski River and caused it to flood downtown Montpelier, Vermont, 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.
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.
A derailed Conrail freight train sits trapped by ice on tracks south of Harrisburg, Pennsylvania, on 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 can develop.
Ice jams may slow the motion of the river to the point where water levels rise significantly farther upstream.
Other formations, called ice shoves, are massive chunks of ice that are pushed onto land by currents and even strong winds that stack on top of each other forming huge piles of ice.
An ice jam rose up along the Kankakee River and encroached on waterfront property on Feb. 28, 2014, in Wilmington, Illinois. (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 can also lead to flash flooding downstream.
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