Chapter 15.1, Problem 1BYL

To determine

The ways of formation of joints.

Answer to Problem 1BYL

Joints can be developed in rocks at depths that may be then raised to the land surface. Certain joints might develop because of the expansion on cooling or due to the pressure released when the upliftment of rocks to the surface takes place. Exfoliation, in which the Earth is shaped and carved by erosion, can also cause formation of joints.

Explanation of Solution

The fractures or very thin cracks that developed in rocks with no considerable displacement are defined as joints. Joints aid in splitting the rocks into smaller fragments and also allow the penetration of water and roots into the rock and thus stimulate weathering.

Most of the joints might develop in rocks at depth and might be uplifted to the land surface later. The estimation of the physical and chemical weathering rates at the surface is possible through the study of alignment and spacing of pre-existent faults and joints. Joints that are more closely spaced can enhance faster weathering.

The expansion of rocks in response to cooling or the release of pressure owing to upliftment to the surface might result in the development of some joints. It may be hard to distinguish such expansion joints from the pre-existent joints that are formed as a part of other processes.

When erosion shapes the Earth, the resulting topography would cause stresses, which are built up due to the unloading of weight from the overlying rocks. Through unloading, expansion joints might develop that mimic landscapes and peel off fine sheets of rock; this process is entitled as exfoliation. These exfoliated landscapes also exhibit several joints.

Jointing may be exhibited on the landscape in several forms such as exfoliation joints, columnar joints, curved faces of rocks, natural stair steps, and dome-shaped landscapes.