Fluvial environments

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  • Fluvial environments
    • Velocity and deposition
      • Streams flow downhill from a source area to a lake or the sea. The gradient down which the stream flows is steeper. The velocity of water in a river is slower near a stream than it is in the centre. Due to friction with the floor and sides.
        • When velocity is reduced, deposition takes place. Reduction in velocity occurs when there is a sudden change in slope and when rivers enter lakes or seas that do not have strong currents.
    • Alluvial fans (breccias, conglomerate)
      • When streams flow onto a flat floor, there is a decrease in gradient and reduction in steam velocity and energy. Sediment is deposited. Breccias - scree fragments. Conglomerate - streams.
    • Channel conglomerates and sandstones
      • Meandering rivers have graded bedding cycles of sediments. Conglomerate is the coarse grain. Sandstone is the medium grained. Mudstone form in the low energy environment of the flood plain.
    • Flood plains of clays and silts - At times of high flow, rivers flood the surrounding flat area to the channel. Clays are deposited may contain fossil plants and fossils with terrestrial origin.


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