Physical and Chemical Weathering

“Weathering” Vocabulary chemical weathering permeable physical weathering sediment ice wedging limestone abrasion uprooting oxidation acid precipitation carbonation

Weathering Physical Weathering Chemical Weathering Plant Growth Animal Actions Release of Pressure Freezing and Thawing Abrasion Chemical Weathering Water Oxygen Carbon Dioxide Living Organisms Acid Rain

Weathering and It’s Effects Weathering breaks rocks into smaller pieces, such as sand, silt, and clay. These smaller, loose pieces are called sediment. Sand, Silt and clay are used to describe specific sizes of sediment. Sand is bigger than silt which is bigger than clay

Weathering and It’s Effects Weathering wears down mountains to hills. The sediments from the top of the mountain are broken down by gravity, water, and ice.

Physical Weathering Temperature can also have an effect on the mechanical weathering process. When it is extremely warm things expand and when it is cold they contract. In the desert, rocks go thru these extreme temperature changes daily. This shapes the rocks and canyons .

Frost Wedging When water enters cracks in rocks and freezes, it expands, causing the cracks to enlarge and the rock to break apart. This process is part of mechanical weathering. This process is very similar to that of an ice cube tray. If you’ve noticed, in order to remove an ice cube from a tray you need to bend the tray; almost break it, if not the ice will not come out because of how much it has expanded!

Chemical Weathering A chemical change is one that takes place at the where a substance is changed into a completely NEW substance never being able to return to its original composition. In chemical weathering, a similar process takes place. Rocks can react with natural acids, plant acids, and oxygen to break down their minerals and form completely NEW minerals and sometimes even making the minerals weaker.

Chemical Weathering Chemical weathering includes the effect of weathering on molecules and atoms. As with all chemistry, the greater the surface area of an object, the more chemical reactions can take place. Moisture and heat must be present for this to occur.

Natural Acids Natural acids such as Carbonic Acid (Carbon Dioxide + water) react with minerals such as calcite. This is the main mineral that makes up limestone. Over many thousands of years, carbonic acid has weathered so much limestone that caves have formed. Chemical weathering also occurs when naturally formed acids come in contact with other rocks.

Plant Acids Some roots and decaying plants give off acids that also dissolve minerals in rock. When these minerals dissolve, the rock is weakened.

Oxygen There are certain rocks that when exposed to oxygen and water TOGETHER create a chemical reaction. This chemical reaction is referred to as oxidation. One common example of this type of weathering is the alteration of the iron-bearing mineral magnetite to a rustlike material called limonite. Oxidation of minerals gives some rock layers a red color. This also makes the rocks softer. Think of how easy a rusty piece of metal breaks!

How does climate affect it all? In cold climates, where freezing and thawing are frequent, mechanical weathering rapidly breaks down rock through the process of ice wedging. Rock type also can affect the rate of weathering in a particular climate. In wet/hot climates, for example, marble weathers more rapidly than granite creating a chemical weathering effect.

Compare and Contrast How do chemical and mechanical weathering differ? Chemical Weathering Physical Weathering How do chemical and mechanical weathering differ? How does climate affect chemical and mechanical weathering?

Review Which of the following does not describe a size of sediment? A. Clay B. Sand C. Silt D. Soil What weak acid is formed when water reacts with carbon dioxide gas in the air or soil? Carbonic Acid Hydro-Carbonic Nitric sulfuric

Lab!! Sum it up! “Weathering” Let’s put all of our knowledge to test in this interactive virtual lab. Please take out a sheet of paper and title it Mechanical/Chemical Weathering Lab Mechanical/Chemical Weathering Virtual Lab