The warmer weather we've enjoyed over the last several days is causing ice to melt along sections of the Arkansas River. This is leading to an ice jam and flood risk.
The National Weather Service issued an outlook last Friday that ice jams and flooding are possible along the Arkansas River through Thursday, January 30.
Ice jams begin with an extended period of below freezing temperatures along a river - typically but not always in a higher elevation section closer to its origin. The river surface freezes partly or completely.
When temperatures warm rapidly after an extended cold period, ice and snow melt quickly, breaking into large chunks between the size of your refrigerator to the size of your car, or in some cases as big as a large truck! These chunks are then carried downstream by the river.
When these big chunks reach a curve in the river or a narrower section, they can jam. Water upstream of this jam is blocked behind the jam. So as more water piles up behind it, flooding occurs upstream.
Another type of ice jam related flooding can occur when the ice jam breaks apart. As the ice continues to melt and pressure builds, eventually the jam breaks. Then all of the water that's been held behind it gets released all at once. This creates the second type of ice jam flood: the downstream flood.
Ice jams are common during winter warmups along the Arkansas. On January 17th and 18th, 2024, an ice jam in Florence caused upstream flooding in Fremont County. In that case, no major damage was reported. But like any flood, major events do happen and can be very destructive.
Let's talk about where the risk is in general. The Arkansas River begins by traveling alongside the Sawatch Mountains, moving steeply down from Leadville to Salida before winding through the Royal Gorge and Canon City, Pueblo, and east through Lamar. The area of concern for ice jams extends from Salida to Lamar.
This risk goes through Thursday, when temperatures will plunge again.
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