Geological processes transform rocks through external agents like water, ice, wind and living things. Weathering alters and breaks down rocks physically, chemically or biologically. Physical weathering causes disintegration without composition changes, through freezing/thawing or thermal stress. Chemical weathering forms more stable minerals through oxidation, carbonation, dissolution or hydrolysis. Transportation moves eroded material by water, wind or glaciers in different ways depending on particle size and transport speed. Sedimentation deposits materials in basins, then diagenesis forms sedimentary rocks through compaction and cementation between grains.

1. UNIT 7. GEOLOGICAL PROCESSES
Geological processes are the transformation of rocks by external geological agents: water, ice,
the atmosphere, wind and living beings.
1) WEATHERING:
Is the process of alteration and fragmentation of rocks by the action of the atmosphere, water
and living things. Weathering can be physical, chemical or biological:
a) Physical Weathering: is the disintegration of rocks into smaller fragments without
changing its mineral composition:
- Cryofracturing: when water accumulated in cracks in the rock freezes, and its
volume expands creating pressure against the walls of the crack which
fractures the rock.
- Thermal stress weathering: as a result of the strong contrast between the
temperatures during the day and at night, rocks continuously contract and
expand, causing them to fracture.
b) Chemical Weathering: it occurs when minerals in rocks are changed into other
minerals which are more stable under the conditions of the surface. The most
frequent transformations are:
- Oxidation: when minerals contain iron. The most common result is ferrous
oxide, which gives a red colour to rocks.
- Carbonation: when atmospheric CO2 combines with water, producing a weak
acid which dissolves limestone rocks.
- Dissolution: it happens to soluble rocks.
- Hydrolysis: when water reacts with silicate minerals, dissolving them.

2. c) Biological Weathering: it is caused by living beings, and can be physical or
chemical.
2) TRANSPORTATION:
Is the transporting of eroded material. Depending of the transporting agent, there can be
different processes:
a) The particles transported by the water in rivers and oceans move in different ways:
dissolved, floating on the surface, suspended or even jumping, rolling and dragged
along the river.
The type of transport depends on the size and the weight of the materials and on
the speed of the water.
b) The particles carried by the wind may be transported by traction (particles are
carried without losing contact with the Earth’s surface), saltation, and by
suspension (when small, light particles remain in the air without touching the
ground for a long time).
c) Rock material eroded by a glacier may be transported at the base of the glacier, or
within the glacier.

3. 3) SEDIMENTATION AND FORMATION OF SEDIMENTARY ROCKS:
Sediments are deposited when the agent transporting loses energy, in areas called
Sedimentary Basins. Sedimentary rocks are formed from these materials through a process
called Diagenesis, which consist of two stages:
1. Compaction: sediments volume is reduced as the result of the pressure exercised
by the weight of sedimentary layers. It closes any gaps in the sediment, and the
water they contain is expelled.
2. Cementation: is the precipitation of natural cements, such as calcium carbonate,
among the grains of the sediment. These salts were dissolved in the water that
circulates through the holes in the sediment.