Aplunge pool (orplunge basin orwaterfall lake) is a deep depression in a stream bed at the base of awaterfall orshut-in. It is created by theerosional forces of cascading water on the rocks at the formation's base where the water impacts.[1] The term may refer to the water occupying the depression, or the depression itself.[2]
Plunge pools are formed by the natural force of falling water, such as at awaterfall or cascade; they also result from man-made structures such as somespillway designs.[3] Plunge pools are often very deep, generally related to the height of the fall, the volume of water, the resistance of the rock below the pool and other factors.[4] The impacting and swirling water, sometimes carrying rocks within it,abrades the riverbed into a basin, which often features rough and irregular sides. Plunge pools can remain long after the waterfall has ceased flow or the stream has been diverted. Several examples of former plunge pools exist atDry Falls in theChanneled Scablands of easternWashington.[5] They can also be found underwater in areas that were formerly above sea level, for example,Perth Canyon off the coast ofWestern Australia.
Plunge pools arefluvial features oferosion which occur in theyouthful stage of river development, characterized by steepergradients and faster water flows. Where softer or fractured rock has been eroded back to aknickpoint, water continues to bombard its base. Because this rock is often less resistant than overlying strata, the water from the higher elevation continues eroding downward until an equilibrium is achieved.
A somewhat similar bowl-shaped feature developed by flowing water, as opposed to falling water, is known as ascour hole. These occur both naturally and as a result ofbridge building.
| Large-scale features | |
|---|---|
| Alluvial rivers | |
| Bedrock river | |
| Bedforms | |
| Regional processes | |
| Mechanics | |
