Alistair McNaught; Peter Symonds College 2001 The rock cycle describes the perpetual recycling of minerals by * weathering and erosion processes on the

Alistair McNaught; Peter Symonds College 2001

The rock cycle describes the perpetual recycling of minerals by

* weathering and erosion processes on the surface

* transport and deposition processes involving water, ice, waves or wind

* rock creation and transformation involving crustal and tectonic processes

* Landscape creation

Weathering and erosion

Transport and deposition

Rock creation

Rock transformation

Landscape creation

Landscape creation

Weathering & erosion

Transport & deposition

Rock creation Rock transformation


Landscape creation




Chemical weathering:

Water penetrates rocks

The presence of water results in

• solution weathering (soluble minerals dissolve)

• carbonation (CO2 enriched water dissolves limestone)

• hydrolysis (feldspars degrade to clays)

• hydration - salts swell on water uptake

Physical weathering:

•Water in rocks freeze - expanding joints

•Extremes of heating cause thermal weathering

•Release of pressure as surface layers wear away

Rocks

Erosion is distinguished from weathering because erosion involves removal of material whereas weathering involves only rotting of material.

Erosion therefore implies transport of weathered material


Landscape creation




Transport takes place by:

Ice - glaciers wear down highland areas

Water - rivers and streams move material to the oceans from the land

Wind - particularly in areas of low rainfall

Deposition takes place in:

•the ocean

•inland lakes

•river floodplains

•inland basins (eg rift valleys)

Deposition of eroded sediment sets the scene for the creation of new rocks (sedimentary rocks) from the rotted, weathered and eroded remains of the old rocks.


Landscape creation




Ocean

The first stage of rock creation is burial - sediment is buried by later layers of sediment being deposited.

The pressure of overlying sediment squeezes the water out of the sediment - this is dewatering and compaction.

Finally, cementation takes place as minerals dissolved in the in the sediments precipitate out and cement together adjacent grains of sediment. At this stage the rock is forming and lithification has taken place


Landscape creation




Sedimentary rock

Metamorphicrock

Sedimentary rocks laid down in the ocean become increasingly buried by younger sediments. As they gradually subside into the crust they experience increasing heat and pressure. This changes the structure and composition of their minerals to create Metamorphic rocks.

Pressure

Heat

Metamorphic rocks can also be created dynamically by crustal plate movements.Intense heating and pressure at plate collisions eventually melts the rock. Molten rock (magma) rises through the crust. Some solidifies underground to form intrusive igneous rocks. Others rise to the surface erupting as extrusive igneous rocks - for example, lavas.

Intrusive igneous rocks

Extrusive igneous rocks

Regional

meta

morp

hism


Landscape creation




Extrusive igneous rocks create distinct volcanic landscapes like those of central America.

After many millions of years of erosion the underlying intrusive igneous rocks may be revealed, creating a distinctive granite landscape like Dartmoor in SW.England

The plate collisions - resulting in large scale regional metamorphism underground - are expressed on the surface as large scale fold mountain ranges such as the Himalayas.

As soon as new rocks are exposed on the surface by either uplift (fold mountains) or eruption (volcanoes), weathering and erosion start the whole cycle again.

The Rock Cycle is powered by two energy sources -

1) geothermal heat (to drive plate tectonics)

2) solar energy (to drive climate and therefore weathering and erosion systems)


Weathering and erosion

Transport and deposition

Rock creation

Rock transformation

Landscape creation

Documents

Alistair McNaught; Peter Symonds College 2001 The rock cycle describes the perpetual recycling of minerals by * weathering and erosion processes on the