Point out the effects of joints on weathering

Joints are small scale fractures that result when a rock shows brittle failure under the tensional/shearing stress. Rock cleavage consists of fractures along closely spaced parallel surfaces and is due to preferred orientation of platy minerals closely spaced parallel surfaces and is due to a preferred orientation of platy minerals such as mica, muscovite etc. Degree of cleavage depends upon the mineralogy of deforming rocks and on the magnitude  of applied stress. It influences weathering as it allows water to penetrate along the fractures, which are planes of mechanical weaknesses. Tensional stresses tend to produce joints that are open and provide zones of ready water movement. Shearing stresses tend to result in joints that are tightly closed and much less permeable. The openness of joints may be called 'thickness'.

 Two other geometrical characteristics affect the response of jointed rocks:-

1)joint spacing expressed as average distance between the joints. The closer the spacing the more rapid is the rock mass reduction by weathering due to large area of potential water-contact surface per unit volume of rock.

2)joint continuity, where this is well developed. Permeability is enhanced, mechanical strength is reduced and susceptibility to weathering is increased.