Physical weathering

Chemical weathering

HideShow resource information
  • Created by: Thea
  • Created on: 12-06-10 14:45

Physical weathering

This leads to the break-up of rock without any change in minerals that form the rock.

In cold climates the most widespread type is frost shattering or freeze-thaw. The volume of water expands when it freezes, so each time water freezes and expands within a crack or joint in the rock more pressure is put on the surrounding rock and the crack widens.

The more often the tempereature fluctuates above and below freezing point during the year, the more effective the frost shattering is at breaking off pieces of rock.

The sharp-edged (or angular) pieces of rock that are broken off form scree, which can be seen below rock outcrops in all upland areas.

Some of the largest scree slopes in the UK are on the side of Westwater in the Lake District.

1 of 3

Chemical weathering

This happens when the minerals of which the rock is composed are changed, keading to the disintergration of the rock.

Granite is one type of rock that is vulnerable to chemical weathering. Feldspar, one of the minerals that make up granite, is converted into clay minerals such as kaolin (china clay).

The distinctive landforms both above and below the ground areas of Carboniferous limestone owe their origins to limestone solution.

This type of chemical weathering is also called carbonation because the dissolivng of the limestone changes calcium carbonate into bicarbonate.


CaCo3 + H2O + CO2 --> Ca(HCO3)2

Calcum carbonate + Water add Carbon dioxide (carbonic acid) --> Calcium bicarbonate

2 of 3

Weathering- grykes, caverns, stalactites, stalagmi

Limestone is little affected by pure water, but rain water is slightly acidic and contains some carbon dioxide in the atmosphere combine to form carbonic acid, in which calcium carbonate (of which limestone is made) slowly dissolves. Limestone is changed into calcuium bicarbonate, which is removed.The limestone is very vulnerable to attack from chemical weathering because of its many lines of weakness, both horizontal (bedding planes) and vertical (joints). The joints visible between the surface blocks of the limestone pavement can be widened by limestone solution to form grykes.

Surface streams disappear underground down joints widened by limestone solution. Underground streams follow the lines of joints and bedding planes. Fresh supplies of acidic water continue the work of solution until a labyrinth of caves is dissolved out of the limestone. Loosened blocks of rock fall from the roofs which have been weakened by solution, turning caves into caverns. There is a slow seepage of water charged with lime into the roofs and walls of caves. Lime (calcium carbonate) is deposited when water evaporates or loses its carbon dioxide. The chemical formula is reversed. The lime builds up to form stalactites, stalagmites and pillars within caves and caverns.

3 of 3


No comments have yet been made

Similar Geography resources:

See all Geography resources »See all Rock landscapes and processes resources »