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Geology 12 Presents Sedimentary Rocks Weathering and Erosion.

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Presentation on theme: "Geology 12 Presents Sedimentary Rocks Weathering and Erosion."— Presentation transcript:


2 Geology 12 Presents

3 Sedimentary Rocks Weathering and Erosion

4 Weathering: the physical breakdown (disintegration) and chemical alteration (decomposition) of minerals and rocks at of near the Earth’s surface Erosion: removal of weathered material (by water, wind, or ice)

5 3 Types of Weathering: 1. Physical/Mechanical Weathering: –Physical forces break rocks into smaller pieces without changing chemistry –4 kinds a)Frost action/ice wedging: water seeps into cracks, freezes, expands (9%) and pushes rock apart. Most effective in areas where temperature fluctuates above & below 0’C animation link

6 Joints = rock fractures cliff Talus = debris accumulation Ice wedging

7 3 Types of Weathering  1. Physical (Mechanical) Weathering: –a) Ice Frost Wedging

8 Ice Frost Wedging

9 Talus = fallen rock debris

10 Talus cone

11 b) pressure release: many minerals/rocks are formed under immense pressure. When they are uplifted and exposed through erosion, the pressure is greatly reduced. The rock expands forming layer of fractures (joints) Sheet joints

12 Exfoliation: slabs of rock break along sheet joints and fall off Popping/rock bursts: sudden pressure relief in deep mines rock explodes like a grenade injuring/killing miners before after Exfoliation dome

13  B) Pressure Release



16 Exfoliation Dome: Chief

17 c) Thermal expansion & contraction: rock is a poor heat conductor; in deserts where the temperatures rise and fall 30’C/day, the outside of the rock heats- expands and cools-contracts animation animation daynight + dark minerals get hotter than white minerals

18 C) Thermal Expansion and Contraction

19 d) Salt crystal growth: salts in rock crevices grow. Expand prying the rock apart like ice wedging. Road salt in roads & bridges, inside of concrete foundation.

20 D) Salt Crystal Growth


22 2. Biological Weathering = activities of organisms a) animals: burrow, tramp, bring materials to surface for more weathering, help transmit gases and water to depths, etc. Animation Animation b) plants: roots wedge rocks apart Animation

23 2. Biological Weathering  A) Animals:Moles

24 2. Biological Weathering  A) Animals:ants

25 2. Biological Weathering  A) Animals:clams

26  B:Plants:root wedging



29 Lichens

30 B) Plants Root Wedging



33 3. Chemical Weathering: chemical alteration of rock/parent material 3 kinds a) Solution: a solid dissolves (halite, calcite) and is usually helped by CO 2 in water which forms carbonic acid (also in plant roots) Results in hard water, caves & karst topography (sink holes).

34 3. Chemical Weathering  A) Solution




38 Sinkhole

39 b) oxidation: reacts with oxygen to form oxides (rust). Ferromagnesians (olivine, pyroxene amphibole & biotite) combine with O 2 for form hematite or limonite. Hi sulfur/sulfide coal acid rain/runoff Iron sulfides (pyrite FeS 2 ) sulphuric acid + iron oxide

40  B) Oxidation

41 Chevy: like a rock all right!

42 c) Hydrolysis: cations (metals) in minerals are replaced by H+ from water Ex: Potassium (K) Fs + water clay + K + silica Ex: Plagioclase Fs + water clay + (Na, Ca) + silica

43  C) Hydrolysis

44 Kaolinite clay

45 Terminology: Differential Weathering: rocks that weather at different rates produce uneven surfaces Resistant cap rock plateau Mesa/butte Hodo/ pinnacle rock

46 Differential Weathering Hard Caprock


48 Spheroidal Weathering: reactangular rocks weather into roundish rocks because corners are attacked on 3 sides, edges on 2 sides, but flat planes on 1 side Result: rounded (& smaller) rocks

49 Spheroidal Weathering

50 Resistance to Weathering poor good


52 Higher temperature minerals weather most easily (olivine, calcium-rich plagioclase) Lower temperature minerals weather least (quartz)

53 That’s all folks!  Do Ws 5.1 + look at Unit 1 Review WS + look at Unit 1 Review WS

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