Rockslides into valleys may dam streams uplift of the land gives streams new energy glaciers grow and carve valleys into different profiles, or divert streams to a new locales and volcanoes grow and change the landscape altogether. Any change in the base level will propagate up the stream in some manner to affect its flow. A rockslide damming the a river makes a new, temporary base level for the upper part of the stream. Naturally the stream deposits all the debris it carries in the lake that forms. Eventually the stream spills over the top of the dam and, falling rapidly down the face, begins to erode it away.
All lakes are temporary interruptions in a stream's course.
We must enjoy them while we can. This site is a cooperative endeavor of the US Geological Survey Western Earth Surface Processes Team and the National Park Service .