Evolution of Landforms: 3 Stages | Landforms | Geology

Davis had divided the evolution of landforms into three distinct stages: 1. Youthful Stage 2. Mature Stage 3. Old Stage.

1. Youthful Stage:

By this time, if rainfall occurs, the rain water will start flowing along the natural slope towards the sea in the form of alls, gullies, streams and ultimately rivers.

As a consequence, erosion is in. This is the youthful stage of the Davis’ cycle.

At this stage:

(a) The vertical erosion of the streams is most significant,

(b) The streams follow the natural slope,

(c) The river valleys are deep and steep-sided,

(d) Mountain summits are high and rugged,

(e) Streams divides are broad and irregular.

As the process of erosion continues, towards the end of the youthful stage, the depth of the river goes on decreasing and erosion increases towards the top of the mountain. At this stage, the river gets affected by the structure of the rock.

The river cannot vertically cut the land below the sea level. Over the land, the level (assumed to be extension of sea level) below which the river cannot perform any vertical erosion is called base level. For the water of the river to keep running, it is necessary that the river has to remain above the base level.

However, continued erosion brings the rivers to such a stage where erosional activities stop completely and the sediments are carried away along with the flow of water. This stage of the river is known as graded stage.

2. Mature Stage:

Through continued erosional activities of the river, the land surface begins to be levelled down. As soon as the lowering of the relief of the uplifted area starts, the landform is said to have attained mature stage.

Maturity is marked by:

(a) Wide river valleys

(b) River capture, meandering, ox-bow lakes and formation of flood-plains

(c) Horizontal erosion becomes more dominant and intensity of vertical erosion decreases

(d) The rivers get closer to graded condition

(e) The whole area is covered with sediments

(f) The mountain slopes become very gentle

(g) Stream divides get smaller and gentler.

3. Old Stage:

At this stage, the rivers flow in a zig-zag way through their floodplains. The landform attains such a low relief and gentle slope that it becomes almost an undulating plain known as peneplain. The whole area is covered with tremendous amount of sediments and the slope of the area becomes very gentle.

However, the hard and resistant rocks in the water-divides are seen to have scattered over the area. These eroded and low relics of landforms are called Monadnocks.

The old stage is marked by:

(a) Gentle undulating plain

(b) Very low inter-stream divides

(c) Meandering courses of river

(d) Thick layers of sediments and erosional remnants scattered over the water-divides.

After attaining the old stage, the area over which the rivers flow may be raised again by the endogenetic forces. It is known as rejuvenation of the landform.