This is a basic question and explains the feature of earth’s landforms. Introduction should in general explain about the relief and landforms which are the geomorphological process and polycyclic is one of the features of such landforms.
Next, in the main body explain the formation of polycyclic relief and its features. Bring examples of such relief and conclude.
In geography, the relief of a place is the difference between the highest and lowest elevations in an area. Landforms are generally created by complex geomorphological process, often involving a number of geographical cycles.
- We may notice, in a single landscape, a number of features representing different ages or stages, thus indicating a variety of incomplete geographical cycles which were interrupted (also called accidents) for various reasons.
- A landform created by a number of geographical cycles occurring one after the other in order, leaving their distinct marks on the landscape, is called a polycyclic landform.
- Many landforms show the influence of several of the processes like weathering, erosion, sediment deposition. They are known as landforms polygenetic.
- Processes acting on landforms can also change over time, and a single landscape can undergo several cycles of development. This type of landscape development is polycyclic.
- There are various reasons for the formations of these reliefs.
- Dynamic reasons involving uplift or subsidence of land resulting in a change in base level. Such changes are mostly localised.
- Eustatic reasons implying a worldwide change in sea level due to diastrophism or glaciation.
- Static reasons, e.g. a reduction in river load or an increase in volume (due to precipitation or deforestation) may alter the rate of erosion.
- Climatic reasons, such as aridity, glaciation etc.
Examples of polycyclic reliefs:
- Older alluvium terraces, for instance, Bhangar terraces in north Indian plains.
- Existence of synclinal ridges and anticlinal valleys in successive cycles.
- Rejuvenated landforms.
- Scraped erosional surface of different ages. Examples—Appalachians and Western Ghats.
- Fault Line scarp due to differential erosion.
- Pleomorphic landforms which are those formed under conditions which do not exist now. These landforms include relict landforms (those based on earlier ones, e.g. drainage systems of north Sahara in Africa), buried landforms, e.g., those formed by continental glaciers in USA, exhumed landforms (initially buried but now resurrected).