WEATHERING AND MASS MOVEMENTS 1. Introduction 2. Physical/mechanical weathering 3. Chemical weathering 4. Mass movement processes
Mean annual temperature ( C) Hot Cold TEMP. -10 0 10 20 Strong chemical weathering Moderate physical Moderate chemical weathering with frost action Moderate chemical weathering 200 150 100 50 Annual rainfall (cm) Very slight weathering Wet RAINFALL Dry
Pressure-release joints (exfoliation) on Half Dome, Yosemite, CA
Pressure-release joints, Half Dome, Yosemite, CA
Freeze-thaw weathering on Long s Peak, CO: note talus slope at the foot of the Diamond
Another view of the talus slope below the Diamond, Long s Peak, CO
Felsenmeer: the Boulder Field on Long s Peak
Cliff Palace, Mesa Verde, Colorado
Cliff dwellings, southern Utah.
Salt weathering in Grand Gulch, southern Utah.
Root wedging: plants and physical weathering
Main processes of chemical weathering 1. Carbonation and solution 2. Oxidation 3. Hydrolysis
Carbonation: the effects of mild carbonic acid H 2 O + CO 2 H 2 CO 3 Mild carbonic acid H 2 CO 3 + CaCO 3 Ca(HCO 3 ) 2 Calcite (a key mineral in limestone) Calcium bicarbonate (soluble)
Cavern features. Source: Christopherson, 2012, p. 385.
Limestone features, Marengo Caves, Indiana. Source: Christopherson, 2012, p. 385.
Sinkhole- Florida karst. Source: NASA, Geomorphology from Space.
Sinkhole- Florida karst. Source: NASA, Geomorphology from Space.
Satellite image of the karst region of southern Montenegro. Source: NASA, Geomorphology from Space.
Oxidation Oxygen combines with metallic elements in minerals to produce a change in the crystal structure of the minerals, and a mechanically weaker rock.
A house with multi-coloured bricks is analogous to a rock made up of many different minerals
Chemical weathering attacks the weakest minerals, thus weakening the rock as a whole.
Oxidation of iron minerals in sandstone, Red Rock Canyon, Nevada. Source: Christopherson, 2006, p.412.
Hydrolysis Water combines chemically with minerals to form new compounds and minerals.
Example of hydrolysis: breakdown of potassium feldspar to form kaolinite 2 K Al Si 3 O 8 + 2 H 2 O Potassium feldspar water Al 2 Si 2 O 5 (OH) 4 + K 2 O + 4 SiO 2 Kaolinite (an important clay mineral) Soluble potassium oxide Silicic acid
The GOLDICH system: rank order of mineral susceptibility to weathering Dark-coloured minerals Olivine Augite Hornblende Biotite mica Light-coloured minerals Calcic plagioclase Sodic plagioclase Orthoclase Muscovite mica Quartz Least resistant Most resistant
The GOLDICH system: rank order of mineral susceptibility to weathering Dark-coloured minerals Olivine Augite Light-coloured minerals Calcic plagioclase Least resistant Hornblende Minerals in granite shown in green Biotite mica Sodic plagioclase Orthoclase Muscovite mica Quartz Most resistant
The first stages of weathering in granite
Wet River Mudflow Earthflow Classification of mass movements based on speed and moisture content. Landslide Solifluction Dry Slide Fast Rockslide Talus creep SPEED Seasonal soil creep Slow Heave
Rate of mass movement Water content
Effects of soil creep. Source: Clowes and Comfort, 1982.
DRIVING FORCE vs. RESISTING FORCE (shear stress) (shear strength)
Angle of repose for materials of different grain sizes and shapes. Source: Press and Siever, 1988. Fine sand ~40 ~35 Coarse sand Angular pebbles ~45
The effects of water on unconsolidated materials. Source: Press and Siever, 1988. Air in pore spaces. Water held at grain contacts by capillary tension. Water-filled pore spaces pushing grains apart.
Santaquin
Mudflow in Santaquin, UT, 2002. Source: US Forest Service/Utah Geological Survey.
Mudflow in Santaquin, UT, 2002. Source: US Forest Service/Utah Geological Survey.
Bingham Canyon copper mine, west of Salt Lake City, UT. Source: Christopherson, 2012, p. 393.
Satellite image of Bingham Canyon copper mine.