Rocks are worn away by many different processes every day. Depending on the location, the processes may vary because they are affected by climate, rock types, relief and slope angle. These processes we call ‘External Forces’ lower the land through denudation, and also builds up the land by deposition.

Denudation: the lowering of the surface of the earth by forces of weathering, erosion and mass wasting. Simply put, denudation is the processes that wear away the land. It includes all natural agencies such as sun, rain, frost, wind, river, sea, ice, temperature change and even plants and animals. This set of major processes is responsible for the creation of Earth’s varied landscapes such as river canals etc.

Weathering: the destruction of solid rock without it being moved (in situ- in that place) by physical, chemical and biological means. Rocks are being disintegrated or decomposed due to weather and atmospheric conditions. The particles or sediments are not taken anywhere. Only in some cases, due to gravity the particles might move for example they might slip down a slope or hill. As the rocks begin the break down, they form a layer of unconsolidated rocks on the earth’s surface called the regolith.

Mass wasting or mass movement follows weathering. It is the downhill movement of soil and rock due to gravity. Most rocks are held together by a structure of solid minerals. When the rocks are weathered, the structure is weakened and becomes a mixture of clay minerals, larger soil and sand particles, and small fragments of rock. When the loose rock accumulates or gathers on slopes it is subjected to the force of gravity and will eventually move down to the bottom of the slope. This only happens when too much debris is gathered on the slope.

Erosion: the removal of soil, sediment or rock from the landscape. Weathered material can be removed by running water, the wind, in cold climates by glaciers. In the Caribbean, water is the chief agent of erosion. The land may be eroded or removed by transporting agents such as rain action, rivers and streams and by the sea. The material that has been eroded is then later deposited in another location for example at the base of a slope or in the sea.

Types of Weathering

Weathering is the term that describes all the processes that break down rocks in the environment near the earth's surface.  When you look at a mountain range and see piles of loose boulders and debris from landslides, it is weathering that has loosened them from the solid rock of the mountain.  When you dig in a garden or a farmer plants a field, the soil you dig is the natural product of slow, gradual weathering of rocks.  There are three different sorts of weathering:

·         Physical (or mechanical) Weathering
       Physical weathering breaks up the rock, but does not change the mineral composition. The
       rock particles are not softened and do not change their colour.

·         Chemical Weathering
       Chemical weathering alters the minerals that make up the rocks. It may produce changes in 
       colour and texture. The rocks rot as a result of reaction between the air and water in the
       soil.

·         Biotic (or biological) Weathering
       Plants and animals may sometimes help to break down rocks, particularly in the rocks are
       already unconsolidated or soft. Biotic weathering includes physical and chemical
       weathering. 

Physical Weathering Processes

Frost Shattering

    Frost shattering or freeze thaw process is an important and wide spread type of weathering in temperate climates. However, it is less common in the Caribbean due to the regions’ tropical latitude. Frost action is possible but rear, it mostly occurs in the very high mountains in the Greater Antilles. When it rains, or from dew, or from melting ice and frost, exposed rocks with cracks, pores and crevices caused by earth movements, chemical change or other weathering processes collect water. When the temperature drops below zero, the water in the cracks or pores freeze and expand with great force. The spaces in the rocks widen and the rock eventually breaks up. This is process continues until the rock reaches a pebble size or crumbles totally.  

Temperature Changes

    Rocks are heated during the day and cooled at nights, the outside of the rock therefore expands and contracts repeatedly. As this happens, the outer layer of the rock becomes weak and eventually peels off or detaches like onion layers. This process is known as exfoliation (shedding skin) or onion-skin weathering.

    Temperature changes also have another effect on rocks. Rocks such as granite are made up of different minerals. The minerals in the rocks expands and contracts at different rates. This causes the minerals to become separate and the rock to disintegrate- this process is called granular disintegration. Limestone is made up of only one mineral and therefore not affected by granular disintegration.  

Pressure Release

    Some rocks such as igneous intrusion (granite) are buried deep underground, overtime the upper layers are eroded. The overlying layer exerts great pressure on the rocks below. When upper layer is eroded, the rocks below gradually expand creating cracks or joints throughout the layers.  This weakens the rocks and makes it vulnerable to other forms of weathering. The weathering processes may widen the cracks and joints in the rocks until the layers break away. Land forms such as the Pitons in St. Lucia and Sugar Loaf Mountain in Rio de Janeiro were formed by this process.