Chapter 8 Part 2 Weathering, Soils and Weathering, Soils and Mass Movement GRB Pages

Types of Chemical Weathering #1 HydrolysisHydrolysis –water (hydro) reacts with minerals such as feldspar and hornblende to form clay.

Lichen & Moss –These low to the ground plants can grow on rocks and eventually break them apart by the acids that they secrete! Types of Chemical Weathering - #2

Types of Chemical Weathering - #3 OxidationOxidation –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!

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

Types of Chemical Weathering - #4 Carbonic acidCarbonic 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

Pitted limestone from rainfall

Rates of Weathering

Factors that 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! This is differential weathering.

Devil’s Tower, Wyoming - An igneous intrusion surrounded by less resistant sedimentary rock layers. Erosion has exposed this monolith! This is differential weathering You may recognize it if you’ve ever seen “Close Encounters of the Third Kind”

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!

Wet Climate = Chemical Weathering! Water runoff seeps into the soil at the base of granite rock faces. Over time, water and permanently moist soil conditions act together to chemically weather away granite minerals such as feldspar and mica!

Cold Climate = Mechanical Weathering

Warm Climate = Chemical Weathering Parthenon – Athens, Greece