Deformation of Rocks

1. Stress and Strain

Stress is a force applied over an area. One type of stress that we are all used to is a uniform stress, called pressure. A uniform stress is a stress wherein the forces act equally from all directions. In the Earth the pressure due to the weight of overlying rocks is a uniform stress, and is sometimes referred to as confining stress.

If stress is not equal from all directions then we say that the stress is a differential stress. Three kinds of differential stress occur.

· Tensional stress (or extensional stress), which stretches rock;

· Compressional stress, which squeezes rock; and

· Shear stress, which result in slippage and translation.

When rocks deform they are said to strain. A strain is a change in size, shape, or volume of a material.

Continental Drift and Plate Tectonics

Download ebooknya disini

From the time maps of the globe became available, people wondered about the arrangement of the continents and oceans. Hundreds of years later, valid explanations were constructed.

Early Observations

Leonardo da Vinci and Francis Bacon wondered about the possibility of the American and African continents having broken apart, based on their shapes. This thinking continued up into the early 20th century, to a meteorologist named Alfred Wegener.