Mechanical and Chemical Weathering Mechanical and Chemical

What Caused This? http://commons.wikimedia.org/wiki/File:Toad_Rock_-_geograph.org.uk_-_767454.jpg http://en.wikipedia.org/wiki/File:KharazaArch.jpg

What is Weathering? First step to forming soil and sedimentary rock Breakdown of rock into smaller pieces The smaller pieces do not move to a new location until erosion carries them away. Many types of weathering

What is Mechanical Weathering? Breakdown of rock into smaller pieces without any change in the chemical composition of its minerals Sometimes called “physical” weathering Rock is torn apart by physical force, rather than by chemical breakdown. Smaller pieces do not move to a new location until erosion carries them away.

Mechanical - Ice Wedging Water fills joints of rocks and freezes. Water expands 10% when it freezes, pushing rock apart. Repeated freeze and thaw cycles over the years causes rock to break along joint. http://upload.wikimedia.org/wikipedia/commons/9/90/Permafrost_pattern.jpg

Mechanical - Exfoliation Exfoliation or unloading -Rock breaks off into sheets along joints which are parallel to the surface. -Caused by expansion of rock due to uplift and removal of surface material that originally buried the rock http://commons.wikimedia.org/wiki/File:Exfoliation_and_mass_movement.jpg

Mechanical - Thermal Thermal Expansion Repeated daily heating and cooling of rock Heat causes expansion; cooling causes contraction. Different minerals expand and contract at different rates causing the rock to split. http://commons.wikimedia.org/wiki/File:Penmaen_Dewi-St_David%27s_Head_-_geograph.org.uk_-_1097950.jpg

Mechanical - Biotic Biotic – means life Weathering caused by living organisms Plant roots act as a wedge and widen cracks. Other causes of biotic weathering: burrowing animals microscopic plants animals algae fungi http://commons.wikimedia.org/wiki/File:Wedge_Rock_Turkey_Run_SP,_IN.jpg

What is Chemical Weathering? Chemical reactions break down the bonds holding the rocks together, causing them to fall apart. Chemical weathering occurs in all types of rock. Rock reacts with water, gases. and solutions.

Chemical - Oxidation Oxidation - oxygen combines with other elements in rocks to form new types of rock New substances due to oxidation: rock softer than original easier for other forces to break rock apart “rusting” of the rock color change in the rock http://commons.wikimedia.org/wiki/File:Sandsteinformation_in_garden_of_the_gods.jpg

Chemical - Carbonation Carbonation – Carbon dioxide (CO2) is dissolved in water making carbonic acid ACIDS Weak acid is formed when CO2 in the air mixes with rain. Acid is too weak to harm plants and animals but slowly causes feldspars and limestone to decompose. http://commons.wikimedia.org/wiki/File:Betonrot_Hippodroom.JPG