Weathering & Erosion

Weathering and Erosion Weathering is the break down of rocks that have been exposed to the atmosphere Once the rocks are broken down, the pieces are transported from one place to another. This process is called erosion Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity. *Most erosion that takes place on Earth is caused by moving water

Types of Weathering   Mechanical weathering – rocks are broken down into smaller pieces without changing their composition (doesn’t change what they’re made of) Chemical weathering - rocks break down as their minerals change in composition (they become different substances)

Types of Mechanical Weathering Ice wedging/frost action water enters small cracks in the rock When it freezes, it expands and forces the crack to open more The process repeats over again until the rock breaks apart

Eventually, the rock splits from repeated frost action!

Types of Mechanical Weathering Wetting and drying breaks up rocks that are made from clay When they are wet they expand, and they shrink as they dry As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!

Types of Mechanical Weathering Exfoliation soil and rock is removed (glaciers or uplifting), exposing rock found deep underground This releases the pressure causing the surface of the rock to expand and eventually crack

Types of Mechanical Weathering Plant Roots The deep roots of trees often break apart rocks Lichen & Moss These low to the ground plants can grow on rocks and eventually break them apart

Types of Chemical Weathering Hydrolysis water (hydro) reacts with minerals such as feldspar and form clay

Types of Chemical Weathering Oxidation oxygen reacts with some minerals, especially those containing iron (magnetite) to form rust (called iron oxide) This occurs faster with water!

Chemical weathering of basalt

Iron Banding in Basalt

Oxidative weathering of mineral deposits (new deposits are white/yellow, weathered deposits are reddish-brown)

Types of Chemical Weathering Carbonic acid carbon dioxide (CO²) dissolves in water to form this acid can cause minerals to dissolve, especially those containing calcite

“Gnarled Rock” – a formation of limestone chemically weathered by acid rain

Factors which affect rates of weathering: Rock’s resistance to weathering (HARDNESS) Amount of surface area Climate: Chemical weathering occurs faster in warm, wet climates Mechanical weathering occurs faster in cold or dry climates

The central area of rock was less resistant to weathering…thus the “arch” was formed!

Surface Area Greater surface area increases the rate of weathering Surface area is the amount of rock surfaces exposed to the atmosphere Weathering creates more surface area

Dry Climate = Mechanical Weathering! Devil’s Marbles, Australia – Mechanical weathering from wind and sand!

Warm Climate = Chemical Weathering Parthenon – Athens, Greece