Post on 05-Jan-2016
description
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