NCERT Solutions For Class 11 Geography Chapter 16 Geomorphic Processes

(i) (d) Erosion

(ii) (b) Clay

(i) The earth's crust is dynamic and ever-changing. All changes take place under the influence of certain forces working continuously within the earth as well as over the surface of the earth. The forces working over the earth's surface are known as exogenic forces, while those working within the earth are called endogenic forces. The exogenic forces cause degradation of relief of elevations and aggradations of basins on the earth's surface. The phenomenon of wearing down of relief variations of the surface of the earth by exogenic forces is known as gradation. Endogenic forces working inside the earth bring about the variations in the surface relief. It may be sudden forces like earthquakes, volcanoes, etc., in general, the endogenic forces are mainly land hurtling forces and exogenic forces are mainly land wearing forces.

(ii) Exogenic forces act on the surface of the earth. All exogenic forces such as weathering and denudation derive their energy from the sun. Sunlight causes air to move, water to evaporate, and ocean waves to rise. These moving fluids like water, wind and waves, etc., attack the solid surface, eroding it, carrying the broken pieces far away, and depositing them to fill low places in the landscape. Weathering is a process of the breaking of rocks by static agents of weather. In this process, the rocks are disintegrated by physical forces and decomposed by chemical action. Agents of physical weathering such as insulation, frost, etc., wholly depend upon energy derived from the sun. The agents of denudation like a river, glacier, wind, sea waves, etc., also derive their energy from the sun.

(iii) Weathering is the action of elements of weather and climate over earth materials. Physical and chemical weathering processes are not independent of each other, rather work of agents of physical and chemical weathering are interdependent. Chemical weathering is brought about by oxidation, carbonation, hydration and solution. The agents of physical weathering, like unloading and expansion, temperature changes and expansion, freezing, thawing and frost weathering, and salt weathering, easily break these decayed and decomposed rocks. Chemical weathering depends upon the work of physical weathering because physical weathering prepares the ground for agents of chemical weathering to work. For example, agents of physical weathering like the variation in temperature, freezing, thawing and frost wedging, salt weathering, etc., break the rocks and agents of chemical weathering can easily work on them.

(i) Weathering processes are responsible for breaking down the rocks into smaller fragments. Biomes and biodiversity is a result of forests and forests depend upon the depth of weathering mantles.

(ii) Mass movements transfer the mass of rock debris down the slopes under the direct influence of gravity. These include creep, flow, slide, and fall.

(iii) Weathering, mass movements, erosion and transportation as well as deposition are the main mobile and mighty exogamic geomorphic agents. All these agents bring geomorphic changes on the surface of the earth.