蜜芽传媒

The Rakaia valley in New Zealand has a sediment layer 100m deep. In the upper profile, the bed is wide with more sediment than water. Around 15,000 years ago after the ice age, the river was deeper than present due to meltwater from glaciers. Sediment from landslides and scree filled the river, raising its level. The present river flows on this raised bed in braided channels, resembling the mudflats normally associated with a river mouth.