Rocksand

Weathering

Chapter 8.1

Weathering- the breaking of rock into smaller fragments• Mechanical weathering – breaks rock

apart without changing the chemical

composition

Examples:

Rocks colliding with other rocks in rivers

Tree roots lifting rock

Ice wedging caused by freezing and thawing

• Chemical weathering – reaction of air,

water and/or other substances with the

minerals in rock

The composition of therock is changed

Water is the main cause of chemical weathering

• It dissolves away some minerals leaving a different composition behind

• Compounds in air combine with water and react with minerals upon contact

• Some metals react with oxygen and water(oxidation)

Acids cause chemical weathering

• Water and carbon dioxide form

carbonic acids which dissolve

calcite and create caves

• Plant roots and decaying plants create acids that

dissolve minerals making rock weak

Climate effects the speed of weathering

- Chemical weathering is most rapid in warm, moist areas.

- Mechanical weathering is most rapid where freezing and thawing occur.

Chemical or Mechanical?

Colonies of lichens growing on the surface of rocks.

Chemical

Chemical or Mechanical?

The wedging of tree roots along natural joints in granite outcrops

Mechanical

Chemical or Mechanical?

Solution of limestone by acidic groundwater

Chemical

Chemical or Mechanical?

The oxidation of minerals which contain iron

Chemical

Chemical or Mechanical?

Animal burrows dug in rock which let in water and air

Mechanical

Chemical or Mechanical?

Repeated freezing and thawing of water cracks rock or joints

Mechanical

Chemical or Mechanical?

The action of water, salt and air on car fenders and panels

Chemical or Mechanical?

The action of water, salt and air on car fenders and panels

Chemical

Chemical or Mechanical?

The sun fading paint on houses and cars

Chemical

Chemical or Mechanical?

Formation of potholes in streets during severe winters

Mechanical

Chemical or Mechanical?

Lifted sections of sidewalk along tree-lined streets

Mechanical

How Soil Forms

Section 8.2

Soil Profile

Soil – a mixture of weathered rock and organic matter- can take hundreds of years to form- varies in thickness

Humus – decaying plants and animals that mix with weathered rock

Soil Profile - shows the layers of soil and weathered rock

O-HorizonLitter layer- leaves

A-HorizonTop Soil – dark colored, sediment, decayed material, insects, worms

B-HorizonLighter color, little or no humus, contains minerals from leaching

C-HorizonSome material leached from B-horizon, partly weathered rock, no humus

Solid rock below soil profile