Weathering

Weathering The process by which rock materials are broken down by physical or chemical processes 2 types of weathering Mechanical weathering Chemical weathering

Mechanical Weathering The breakdown of rocks into smaller pieces by physical means Mechanical weathering can occur due to: Ice Abrasion Water Wind Gravity Plants Animals

Mechanical Weathering: Ice Frost Action: The freezing and thawing of soil and rock Ice wedging is a type of frost action Water seeps into cracks during warm weather When temperatures drop, the water freezes and expands The ice pushes against the sides of the crack causing the crack to widen

Ice Wedging

Mechanical Weathering: Abrasion Abrasion: the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles

Mechanical Weathering: 3 Forms of Abrasion Water – Rocks in rivers bump and scrape each other as they are carried by the water, causing them to become smooth and rounded Wind – Wind blows sand against rock causing wearing away the rock’s surface Gravity – As rocks fall on one another, they crack, scrape and break into smaller pieces

Water Abrasion

Wind Abrasion

Gravity Abrasion

Mechanical Weathering: Plants & Animals As a plant grows, the force of the expanding root becomes so strong that it can break a rock apart Animals Almost any animal that burrows causes mechanical weathering by mixing and digging through soil and rock particles

Plants

Animals

The Shape of Rocks Weathering takes place on the outer surface of rocks The more surface area that is exposed to weathering, the faster the rock will be worn down Smaller rocks have more surface area and therefore weather more quickly

Chemical Weathering The process by which rocks break down as a result of chemical reactions Chemical weathering can occur due to Water Acid Air

Chemical Weathering: Water Water chemically reacts with the minerals in a rock, causing those minerals to become soft and breakdown

Chemical Weathering: Acid Acid Rain: rain, sleet, or snow that contains abnormally high concentrations of acids Air pollution, from the burning of coal and oil, combines with water in the atmosphere and falls to earth as acid rain The acid in the rain corrodes or chemically destroys the rock Acids in Groundwater Acidic groundwater chemically reacts with rocks in the ground, such as limestone This chemical reaction dissolves the limestone, creating caverns Acids in Living Things Some living things, such as lichens, produce acids that can slowly break down rocks

Acid Rain

Acid Groundwater

Acid Organisms

Chemical Weathering: Air Oxidation: the chemical reaction where iron combines with oxygen in the air to form rust

Rates of Weathering Weathering takes a long time but some rocks with weather faster than other rocks 3 Factors affect the rate of weathering: Makeup of the rock Climate Elevation

Differential Weathering The process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind Devils Tower was once deep inside an active volcano After thousands of years of weathering, the soft outer parts of the volcano have worn away The harder, more resistant rock is all that remains

Differential Weathering

Weathering & Climate Climate is the average weather condition in an area over a long period of time The rate of chemical weathering is faster in warm, humid climates Oxidation happens faster when temperatures are high and water is present

Weathering & Elevation Rocks at higher elevations, like on a mountain, are exposed to more wind, rain, and ice which causes them to weather faster Gravity pulls things, like water and rocks, down faster Water carries rocks down the mountain Rocks fall from the sides of the mountain