Cold snap causes Narva River ice jam fields to form
The Narva River has burst its banks and risen to a record high following the recent cold snap.
This has led to the phenomenon of ice-jam fields (see gallery).
These are most extensive at Kuningaküla, around halfway along the length of the river, which runs from Lake Peipus (Peipsi järv) downstream to Narva Jõesuu and the Baltic. However, those going to view the ice formations should keep in mind that the river forms the eastern border with the Russian Federation, in addition to the hazard posed by ice on a flowing body of water.
The river has risen by three meters this month compared with summer levels, a record high since measurements began in their current format, 15 years ago.
Jana Põldnurk, head of the climate department at the Estonian Environment Agency (Keskkonnaagentuur), said the sudden cold snap, when December's mild conditions were replaced in the new year with temperatures well below zero day and night, was the cause. The river's topography is also a factor.
"Half a kilometer downstream from Kuningaküla is the Omuti Rapids. At that point, the river becomes shallow and the current is very fast. The river is not covered by ice there, and with strong sub-zero temperatures, the fast flow causes the water to cool," Põldnurk said.
A comparable situation happened around New Year on Tallinn's Lake Ülemiste, she added; in that case, the result was a large portion of the capital's population being without running water for several hours.
"Ice 'needles' form in the water — the recent freezing of the water in Tallinn happened according to exactly the same logic. These ice needles then stick together and slush forms in the river. Upstream, where the river is covered by ice, the current can push the ice floes loose. These in turn stick together, and a very solid ice mass with large chunks of ice forms in the river," Põldnurk explained.
In the case of the Narva River, time should resolve the matter as it freezes over more evenly in the continued cold weather, and in fact, the level has started to recede already.
Ice jams happen when drifting ice in a river becomes obstructed, typically at bends, shallow areas, or bridge piers. This blockage slows the flow of water, causing water levels upstream to rise (known as backwater). As a result, ice jams are a major winter flood risk. Additionally, when the jam breaks, the water held back can flood areas downstream, depending on the circumstances. Ice jam floods are often more unpredictable and can occur more quickly than open-water floods.
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Editor: Andrew Whyte, Marko Tooming
