Chapter 8

1. Chapter 8 Weathering, Soils and Mass Movement BFRB Pages 157 - 161

2. Weathering and Erosion • Weathering - Def. - 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 callederosion. • Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity. • VIF - Most erosion that takes place on Earth is caused by moving water

3. What is W.E.D.? • Weathering - the breakdown of rock into smaller pieces due to physical or chemical changes. • Once the rocks are broken down, the pieces are small enough to be transported from one place to another. This process is calledErosion. • Since the weathered rocks have been moved, eventually they are going to have to be dropped. This process is called Deposition.

4. Remember the Rock Cycle Diagram? Page 6 of the “Handy Dandy” ESRT’s…

5. Chemical weathering– rocks break down as their minerals change in chemical composition (they become different substances). Physical weathering– rocks are broken down into smaller pieces without changing their chemical composition (what they’re made of). AKA - mechanical weathering 2 Types of Weathering

6. Agents of Physical Weathering

7. Types of Physical Weathering • #1 - Frost action (aka Ice Wedging) • water enters small cracks in the rock. • when water freezes, it expands and forces the crack to open more. • the ice melts back into liquid water and fills the crack again. • the process repeats over and over again until the rock breaks apart.

9. Mt. Brewster – looks solid, right?

10. Close up shows jagged rocks from FROST wedging!

11. This boulder has been split apart by frost action!!!

12. Types of Physical Weathering • #2 - Abrasion • It is the physical wearing down of rocks as they rub or bounce against each other. This process is most common in windy areas, under glaciers, or in stream channels. • It can also happen during rock slides (gravity)

13. Rocks that have undergone different kinds of abrasion look very differently! Rock weathered by a rockfall Rock weathered by a stream

14. Types of Physical Weathering • #3 Plant RootsThe roots of trees often wedge in between cracks in rocks and force apart rocks even further as they grow!

17. Types of Physical Weathering • #4 Animals Animals (worms, groundhogs, rabbits, etc.) burrow into the ground exposing more rock surfaces to the agents of weathering.

18. Types of Physical Weathering • #5 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)!

24. Types of Physical Weathering • # 6 - 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 and flake off.

25. Horizontal Exfoliation

26. Horizontal Exfoliation

27. Vertical Exfoliation

28. Agents of Chemical Weathering

29. Agents of Chemical Weathering • #1 - Hydrolysis • water (hydro) reacts with minerals such as feldspar and hornblende to form clay which weakens the rock and breaks it apart.. Link to visualization

31. Agents of Chemical Weathering • #2 - Plant Acids - Lichen & Moss • These plants live and grow on rocks and eventually break them apart by the weak acids that they secrete! Lichen – light green/looks like bread mold Moss – dark green

33. Agents of Chemical Weathering • #3 - Oxidation • oxygen reacts with some minerals, especially those containing iron to form rust (called iron oxide). • The rusty spots weaken the rock and it breaks apart. • Water is not needed for oxidation to occur, but it does speed up the process!

35. Chemical weathering of basalt - an iron rich (mafic) igneous rock! You see, it all comes together!!!

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

38. Agents of Chemical Weathering • #4 - Acids in water • Carbon dioxide, nitrogen dioxide, and sulfur dioxide dissolve in water and create carbonic acid, nitric acid, and sulfuric acid. • This acidic water can cause rocks to dissolve, especially those containing calcite like limestone and marble! • Acids may be found in ground water (forms caves) or in rain water (acid rain).

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

40. Pitted limestone from rainfall

42. Carbonic acid in groundwater causes caves to form. When the acidic groundwater comes in contact with limestone, the limestone dissolves and caves and caverns are formed. Howe Caverns in NY and Carlsbad Caverns in NM are examples of these beautiful geologic formations

43. Stalactites Stalagmites Carlsbad Caverns – New Mexico

46. Rates of Weathering

47. 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

48. The central area of rock was less resistant to weathering…thus the “arch” was formed! This is differential weathering.

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