Erosional Landforms – Landform and their Evolution

There are numerous types of landforms; we’ll be starting with the erosional because they make up the majority of “land.” Erosional landforms include headlands, bays, caves, arches, stacks, stumps and wave-cut platforms. There are also depositional landforms such as beaches, spits and bars. Normally when we think about landforms we think about their shape and size.

1. Valleys

• Valleys start as small and narrow rills; the rills will gradually develop into long and wide gullies;
• A gorge is a deep valley with very steep to straight sides and a canyon is characterised by steep step-like side slopes and may be as deep as a gorge. A gorge is almost equal in width at its top as well as its bottom. In contrast, a canyonis wider at its top than at its bottom. In fact, a canyon is a variant of gorge.
• Valley types depend upon the type and structure of rocks in which they form. For example, canyons commonly form in horizontal bedded sedimentary rocks and gorges form in hard rocks

2. Potholes and Plunge Pools

• Over the rocky beds of hill-streams more or less circular depressions called potholes form because of stream erosion aided by the abrasion of rock fragments.
• A series of such depressions eventually join and the stream valley gets deepened. At the foot of waterfalls also, large potholes, quite deep and wide, form because of the sheer impact of water and rotation of boulders. Such large and deep holes at the base of waterfalls are called plunge pools.

3. Incised or Entrenched Meanders

• In streams that flow rapidly over steep gradients, normally erosion is concentrated on the bottom of the stream channel.
• Also, in the case of steep gradient streams, lateral erosion on the sides of the valleys is not much when compared to the streams flowing on low and gentle slopes.
• Because of active lateral erosion, streams flowing over gentle slopes, develop sinuous or meandering courses.
• It is common to find meandering courses over floodplains and delta plains where stream gradients are very gentle.

4. River Terraces

• River terraces are surfaces marking old valley floor or floodplain levels.
• They may be bedrock surfaces without any alluvial cover or alluvial terraces consisting of stream deposits.