Penk's Cycle of Erosion

Penck's Cycle of Erosion:

           German scientist Walther Penck analysed the morphological system for the description of landscape development. According to him, landforms of a given region are related to tectonic activity. Thus the landforms are a result of the ratio between exogenetic forces and endogenetic forces. His theory of landform development is time independent. He used the term 'Primarumph'   to represent the initial landform.

            Unlike Davis, Penck used the term 'phase' to represent his model of erosion, which are as follow-

Phase 1 (Aufstensteigende Entwickelung):

               It is waxing (accelerated) phase of landform development. In this phase, initially the land surface rises slowly but after sometime, upliftment is accelerated because of this upliftment, flow velocity, kinetic energy of the stream increases and it results in accelerated rate of valley depending. Both the water divide and valley floor of the river is increasing in altitude. The rate of upliftment always exceeds the rate of erosion.

              In this phase, V shaped Valleys are formed by vertical erosion.

Phase 2 (Gleichformige Entwickelung):. 

              It is the phase of constant development. It is further divided into three sub- phases-

Phase A: 

             There is accelerated uplift. Rate of upliftment is till less than rate of erosion. Altitudes of both, water divide and valley floor increases but at a slower rate. There is uniform rate of valley deepening and lowering of water divide. The valley sides are characterized by straight slopes.

Phase B:

            Relief neither increases nor decreases as rate of upliftment is equal to rate of erosion.

Phase C:

          Upliftment of land stop completely. Relief starts declining due to continued rate of erosion. Altitude of water divide and valley floor declines continuously.

        Phase 2 is  characterized by constant landforms development and parallel retreat of river valleys. Parallel retreat creates vertical steep valleys.

Phase 3 (Absteigende Entwickelung):

            This is the waning phase of development. Here landscapes are dominated by lateral erosion and velley widening and reduction in rate of valley deepening.

               Water divide is continuously eroded and lowered in altitude. Gravity slope (Boschungen) and wash slope (Haldenhang) are formed. At the intersect of Boschungen and Haldenhang, sharp breaks in slopes are produced. In further, Haldenhang continues to expand at the cost of Boschungen and Boschungen is reduced to conical residual hills called Inselbergs. Eventually Inselbergs are also eroded and a series of concave Haldenhangs or wash slopes are formed, which are known as Endrumph.