Unit 2 Rocks: Note 4 Weathering

Definitions

1. Weathering: processes that break up and corrode solid rock, transforming it into sedimentary rock

2. Erosion: the removal and transport of Earth’s surface materials by moving water, air, or ice

3. Weathering & Carbon Cycles: natural processes and the regulation of greenhouse gas, temperature

   1. solid rock broken down contains C, release C once weathered

      • plant consumption in soil

      • into the atmosphere as a gas

   2. Globally warm- the more plant growth, the more precipitation

      • increases the rate of rainfall

      • increase of CO2 removal by weathering

      • reduction of initial warming

Mechanical Weathering: Jointing, Wedging, Organism Activity, Abrasion

Definition: breaks down rock into smaller pieces, this does not effect the composition of minerals or chemicals found in the rock

1. Jointing/Exfoliation: natural cracks due to temperature/pressure change

   1. Joints: are sets of cracks that are parallel, shows how/direction the pressure moved through the rock

   2. Thermal expansion: increase of heat expands the outer layer as the rock is cooling and causes it to contract

      • need heat and cool

      • after forest fires, when magma passes by, the sun

2. Columnar Jointing: molten rock of a volcano starts to cool, the inside it hotter than the outside causes the outside to crack. They are vertical along the outside of a volcano, from the top each ridge has a hexagonal cap

3. Wedging: expansion in joints

   1. Frost Wedging: ice causing expansion in joints, when water is put under pressure it exerts stress outwards. The the water at the top freezes first.

   2. Root Wedging: roots causing expansion in joints, when roots grow into the joints of a rock

   3. Salt Wedging: growth and expansion of salt crystals in pores and joints

4. Organism Activity: when organisms create and intensify rock breakage

5. Abrasion: when rock pieces collide as they are being transported, causing weathering

Chemical Weathering: Hydrolysis, Dissolution, Oxidation, Hydration

Definition: the breakage of rock into smaller pieces through a change in their chemical makeup, which creates more surface area which leads to more weathering

• change in minerals, and chemical reaction

• chemical changes to minerals that are unstable at Earth’s surface

1. Hydrolysis: a reaction between a mineral and water

   1. H+ ions are added to the mineral and a chemical equivalent amount of cations are released into the solution

   2. usually leaves pores behind in rocks

2. Dissolution: mineral breaks down completely into ions by dissolving into a fluid

   1. Acid water, usually leaves large holes in rock

3. Oxidation: reaction between a mineral and O2

   1. Iron minerals react with O2 to become iron oxide and iron hydroxide minerals, turning orange

   2. Associated with a color change, Iron to orange, copper to green

4. Hydration: absorption of water into a structure

   1. Clay, with the addition/subtraction of H2O