Theories of Landform Development – UGC NET Geography – Detailed Notes

• Davisian Geomorphic Cycle (Cycle of Erosion) (William Morris Davis): Views landscape evolution as a time-dependent process through stages (youth, maturity, old age) ending in a flat peneplain, driven by uplift and denudation.
• Penck’s Slope Replacement (Walther Penck): Argued that slope retreat (parallel or replacement) depends on the balance between tectonic uplift and erosion rates, forming stair-like slopes (Piedmonttreppen).
• Dynamic Equilibrium Theory (J.T. Hack): Proposes that landscapes reach a steady state where processes and resistance balance, remaining stable unless energy input changes.
• Pediplanation Cycle (L.C. King): Focuses on the parallel retreat of slopes to form pediplains, contrasting with Davis’s peneplains. 

Davisian Theory

The most popular theory of landform development was given by American geomorphologist William Morris Davis. His concept of geographical cycle (or

commonly known as cycle of erosion) provided a genetic classification and systematic description of landforms.

According to Davis, geographical cycle is a period of time during which an uplifted landmass undergoes its transformation by the process of land sculpture ending into low featureless plain or peneplain (which Davis called peneplane), Davis’s theory was the outcome of a set of theories and models presented by him during the 1880s and 1890s.

He propounded the model of ‘complete cycle of river life’ in his essay on The Rivers and Valleys of Pennsylvania (1889), and that of ‘geographical cycle’ (1899) and ‘slope evolution’. He, under the concept of ‘complete cycle of river life’, postulated the cycle concept of progressive development of erosional stream valleys, and through the ‘geographical cycle described the sequential development of landforms through time.

However, Prof. Savindra Singh says that the general theory of landform development of Davis is not the ‘geographical cycle as many of the geomorphologists believe. Davis’s theory may be expressed as: “There are sequential changes in landforms through time (passing through youth, mature and old stages) and these sequential changes are directed towards well defined end product development of peneplain”.

Penck’s Theory

According to German geomorphologist Walther Penck, the characteristics of landforms of a given region are related to the tectonic activity of that region. Contrary to the Davisian concept that “landscape is a function of structure, process and time (stage)”, Penck put forward his view that geomorphic forms are an expression of the phase and rate of uplift in relation to the rate of degradation, where it is assumed that interaction between the two factors, uplift and degradation, is continuous. According to Penck’s view the landforms observed at any given site give expression to the relation between the two factors of uplift and degradation that has been or is in effect, and not to a stage in a progressive sequence.

The main premises of Penckian model of landscape development are the following:

• The morphological characteristics of any region of the earth’s surface is the result of competition between crustal movement and denudation processes.
• On the basis of morphological characteristics tectonic movements can be explained and their causal factors ascertained.
• Development of landscape is not time-dependent.
• The shape of the hillslope depends on the relative rates of valley incision by rivers and removal of debris from the hill -slope.
• Three crustal states are witnessed:
• 1. state of crustal stability with no active displacement;
  2. state of initial domed uplift in a limited area followed by widespread unlift; and
  3. state of extensive crustal upliftment.
• Upliftment and erosion are always coexistent.
• Three states of adjustment between crustal movement and valley deepening are observed:
• 1. if for a longer time crustal upliftment remains constant, the vertical erosion by the river is such that there is balance between the rate of upliftment and erosion;
  2. if the rate of uplift is more than the rate of valley deepening, then the channel gradient continues to increase till the rate of valley deepening matches with the rate of upliftment and the state of equilibrium is attained when both become equal; and
  3. if the rate of valley deepening is more than the rate of crustal uplifment, then the channel gradient is lowered to such an extent that the rates of upliftment and erosion become equal and the state of equilibrium is attained.

However, it must be noted that there was certain misunderstanding in the interpretation of Penck’s work as it was published in obscure German language.

Penck’a morphological system was severely criticised in the United States in the same way the ‘geographical cycle’ was criticised in Germany. Penck’s concepts of parallel retreat of slope and continued crustal movements were subjected to severe criticism by many geomorphologists and geologists.

However, despite lack of support for Penck’s concept of long continued upliftment and tectonic speculations, his concepts of slope development and weathering processes are of immense geomorphological significance.