Morphological activity of ice on the bed of the Tana River of Finnmark, Norway, during the Spring flood is concentrated into a short period of time when water stage is changing rapidly. Ice affects the bed in four ways. 1) Actual contact of the ice with the bed gouges grooves if the ice is still moving or flattens the micro-relief of the surface if the velocity is low. 2) Grounded blocks in a strong flow generate separation eddies which cause local depositional and erosional irregularity. 3) Blocks of ice melting on a subaerially exposed sediment surface disturb the surface as they collapse. 4) Depressions are thought to be due to the melting of buried ice blocks. probably frozen to the sediment surface. The preservation potential of these structures is low but they might, in exceptional circumstances, be found in fluviatile sandstones.

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