The agents – running water (river), glaciers, wind, sea waves and groundwater, – do the work of erosion, transportation and deposition. Because of these agents, the earth’s surface keeps undergoing changes and new landforms are formed. 

(i) Running water (river):

• The river beds, as well as the banks of a river, are eroded due to the speedy flowing stream of water. The load that a river carries also erodes the banks and the bed of the river. 
• The rocks, stones, sand, etc. collide with one another and break into fragments 
• Different landforms like gorge, V-shaped valley, pothole and waterfall are formed due to the erosional work of a river.

(ii) Glaciers:

• As a glacier is nothing but a solid mass of ice, its velocity is very low. Nevertheless, the mass of water in the solid form is quite high. Therefore, glaciers cause a considerable amount of erosion.
• The glaciers erode the ice-clad base of the mountain slopes and the snow-clad sides of the mountains to a large extent. 
• The Cirque, Arete and horn, U-Shaped valley and hanging valley are the landforms formed by the erosional work of a glacier.

(iii) Wind:

• The wind carries sand and pebbles. 
• When they strike and scratch the rocks, the elevated and basal parts of the rocks get eroded. 
• Due to the erosional processes of the wind, deflation hollows, mushroom rocks and yardangs3 are formed.

(iv) Sea waves:

• The basal portions of the headlands get severely eroded due to the continuous attack of sea waves. This leads to the erosion of the rocks on a large scale. 
• Rocky coasts are formed where the headlands get severely eroded. 
• Landforms such as sea cliffs, sea caves, wavecut platforms, sea arches and sea stacks are formed due to the erosional work of sea waves.

(v) Groundwater:

• Soluble minerals in the rocks dissolve in water and they move along with the ground water. This process is called erosion by ground water. 
• The work of ground water is predominant in the region where rock like limestone is found on a large scale. 
• Limestone dissolves in carbonic acid. Carbonic acid is formed due to the presence of carbon? dioxide in ground water. This acid dissolves carbonates like limestone. Thus, chemical weathering takes place. 
• The landforms like sinkholes and caves are the result of the erosional work of groundwater.