Canadian city flooded by ice jam.

Around 15 000 residents of the city of Fort McMurray in northeast Alberta, Canada, have been forced to evacuate after the lower part of the town began to flood on Sunday 26 April 2020. The flooding has been caused by ice jams that have formed on the Athabasca and Clearwater rivers, creating a blockage almost 25 km long, resulting in water piling up behind the obstruction to form a dam lake, which has begun to invade the town.

Flooding in Fort McMurry, Alberta, caused by ice jams on the Athabasca and Clearwater rivers. McMurray Aviation.

Ice jams can be a problem in areas where there is a strong seasonal freeze and thaw cycle. They are generally associated with a rapid spring thaw, which can cause many large chunks of ice to be deposited into a river at the same time. When these ice blocks reach an obstruction on the river, such as a narrow or shallow stretch they can become jammed together, forming a blockage. These blockages cause flooding in two ways; firstly by creating a dam lake behind them, and secondly (and more dangerously) by suddenly giving way, allowing all the water piled up behind them to escape at once, and causing a flash flood downstream. Although generally associated with the spring thaw, ice jams can also occur at the onset of the winter freeze, if an unseasonal warm spell causes a sudden thawing.

An ice jam on the Athabasca River in Alberta, Canada, on 26 April 2020. Vincent McDermott/Fort McMurray Today/Postmedia Network.

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Athabasca River polluted by mine runoff.

Communities along the Athabasca River in west-central Alberta, Canada, have been advised against drawing water from the river five days after the collapse of a wall containing a holding pit that held runoff from the Sherritt International operated Obed Mountain Coal Mine, an open pit mine roughly 30 km to the east of Hinton. Around a billion liters of water contaminated with coal dust, clay and sand were released into two tributaries of the river, on Thursday 31 October 2013. Coal runoff can potentially contain a variety of toxic chemicals, and while tests have not revealed any dangerous compounds in the river, many residents have questioned why they were not informed of the problem immediately, and raised concerns as to how well the Alberta government is policing the mining industry. 

The approximate location of the Obed Mountain Coal Mine. Google Maps.

Sherritt International reopened the Obed Mountain Coal Mine in 2009, having obtained it from previous owners, Luscar, who ran the mine from 1985-2003, when it was closed for economic reasons. At the time there were ambitious proposals to expand the mine, but in 2012 these were scaled back dramatically, apparently due to a drop in the price of coal on international markets, with the majority of the staff being either laid off or transfered to other projects. The mine is currently described by Sherritt as 'economically inactive', with only a skeleton staff employed in maintenance roles. It is unclear what Sherritt's long-term ambitions for the project are.

See also Worker dies at Saskatchewan potash mine, Operations ceased at Padcal Mine following flooding, Acid spill from gold mine adds to Edith River's woes, Copper spill causes pollution alert on the Edith River in the Northern Territory, Australia and River Neath turned orange by mining run-off.

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