VisionIAS - Video Classroom Lecture

Geography Optional Class 01

SLOPE DEVELOPMENT (5:30 PM)

It is defined as the angular inclination of terrain between hilltops and valley bottoms.
The cause of formation can be endogenetic as well as exogenetic as well as exogenetic.
Genetic classification of slopes:
Exogenetic slopes are mostly created by outside forces.
They are broadly categorized as:
Aggradational slope and degradation slopes.
Slope elements:
Distinctive sediments of slope profile are called slope elements.
i) Summital convexity:
It is found on hilltop.
Most of the summital convexity develops because of denudational processes dominated by weathering, soil creep, or rainwash.
If the convex element dominates the hillslope profile it is called the vaxing slope.
ii) Free face:
It is the wall-like slope of bare rocks.
It is devoid of any debris.
It is also called the slope of deprivation because of the immediate downslope transport of materials.
When the free face is subjected to back-wasting it results in parallel retreat.
iii) Rectilinear elements:
The straight of the linear segment is between the free face and the lower concavity.
Rock debris accumulates in the segment and is called debris slope.
Basal concavity is the lowermost segment.
The slope angle decreases as this segment increases in length.
It is also called a lower wash slope.
If the slope is dominant segment is called the waning slope.

SLOPE DECLINE THEORY BY DAVIS (6:16 PM)

Youth stage:
Mainly in newly uplifted landscapes where slopes are steep and convex.
Rivers cut sharply into the terrain forming deep valleys and high-relief.
Convex upper part is produced by soil creep.
Mature stage:
Lateral erosion becomes dominant.
The slope begins to reduce in steepness.
Progressive decline in slope angle, valleys widen, hills become rounded and there is a reduction in height.
Old stage:
Slopes decline further and they become flatter and nearly level.
Hills are reduced to low-rolling surfaces, a condition which Davis called peneplain.

SLOPE REPLACEMENT THEORY BY PENCK (6:40 PM)

He proposed that slopes instead of declining progressively retreat parallel to themselves.
As erosion works on the face of the slope the entire slope moves backward maintaining its steepness.
Penck considered mass movement as the primary process responsible for slope formation.
Slope profiles:
i) The upper part of the slope is called the convex section.
ii) Middle section with straight gradient.
iii) Concave lower section where material from above accumulates.
As the steep slope retreats, it maintains its gradient and gives rise to a basal slope of the lesser gradient.
Over a period of time, new units of gentler gradient will be formed at the foot of the slope which gradually undergoes upslope migration.
The overall result will be the development of basal concavity as the steep slope undergoes parallel retreat through back wasting.

SLOPE DEVELOPMENT THEORY BY WOOD (6:55 PM)

It starts with a steep side cliff which is known as a free face.
Denudation of the free face generates debris which starts collecting near the base in the form of talus or scree.
Gradually talus stands upward and the free face is proportionately reduced.
Over a period of time, the entire slope is covered by talus forming a constant slope forming a constant slope.
The constant slope and its debris cover are affected by rainwash and the particles gradually move down and the free face is completely pushed back developing into a gradual concave shape.

PARALLEL RETREAT THEORY BY KING (7:33 PM)

Parallel retreat theory by King was proposed as a part of the theory of landscape evolution in dry and arid areas.
As a result of vertical down-cutting in the youth stage steep development.
The steep slope also called a scarp tends to move away parallel from the river.
The gradient of the slope remains constant but the road is retreating away, a process known as parallel retreat.
Due to this, the pediment between the river and the slope gets extended in length.
Finally, at the end of the cycle, a multi-concave landscape is formed.
The extensive flat surface that was finally formed is known as a peneplain.
Significance of studying hillslope:
i) Water management:
Hill slopes influence water runoff, infiltration, ground groundwater recharge which it affects the river basins, and the drainage system even along the plain areas.
It is crucial for water security.
It is also helpful for flood control.
ii) Disaster management
The analysis of slope stability helps us in assessing erosion, weathering, mass wasting, and the types of movements to which we can assess landslide risk which is essential for disaster preparedness.
iii) Vegetation and biodiversity:
Different types of hillslopes provide different conditions for the growth of natural vegetation resulting in unique habitats.
Understanding them helps in better ecosystem conservation.
iv) Agriculture and soil health:
The slope study helps us understand the nature of soil and soil formation rates supporting agriculture.
For example, terrace farming, and contour bunding at the steep side slope.
v) Human settlements:
Hill slope study, the nature of the slope, nature of the rock surface help us in better planning human settlements, road constructions, tunnels, etc. in a sustainable manner.
The slope study enables us to better plan human settlements and economic activities that include tourism etc depending on the climatic conditions of the slope.
The hillslope processes help us in understanding the degradation of the mountain slope, mountain soils, and its vegetation which help in carbon sequestration and are contributing to awards climate change.
The glacial regions experience changes in the slope due to faster glacier erosion due to the retreat of glaciers.

TOPIC OF THE NEXT CLASS: Remaining topics of the geomorphology