Rejuvenation: What is it, what are its causes and its resulting landforms?
Rejuvenation occurs when the base level that the river is flowing down to is lowered. Rejuvenation may result from causes which are dynamic, eustatic or isostatic in nature. All of these cause the river to undergo a sudden increase in vertical erosion as the river gains gravitational potential energy.
Dynamic rejuvenation often occurs because of the uplift of a land mass. This can be caused by the removal of glaciers or tectonic plate movement in the form of severe earthquakes. The land mass is raised up, so the river has to cut down through the rising land mass to again reach the base (sea) level. It is know as “dynamic” rejuvenation because the base level is constantly changing in relation to the river.
Eustatic rejuvenation is caused by a decrease in the base (sea) level which the river is attempting to reach. Much like the above dynamic rejuvenation, this causes the river to cut down into the land to reach the new base level.
Static rejuvenation is caused by a number of things. Either: a decrease in the rivers load, an increase in run off because of increase rainfall or an increase in steam volume through the addition of new tributaries.
All causes of rejuvenation result in a knick point in the graded profile, where the river suddenly undergoes an increase in vertical erosion to quickly meet the new base level as it gains GPE. This is illustrated in the picture below.
Rejuvenated rivers usually have complex landforms as the older graded profiles of the river are somewhat preserved. Parts of floodplains may remain intact as terraces along the down cutting river channel. Meandering streams and rivers that have been rejuvenated often become entrenched, creating a very steep “V” shaped valley.
A good example or rejuvenation is the river Nile, which was rejuvenated when the Mediterranean sea dried up about 10,000,000 years ago. During this period, its base level...