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Weathering, Erosion, and Soil

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Presentation on theme: "Weathering, Erosion, and Soil"— Presentation transcript:

1 Weathering, Erosion, and Soil
What type of rock is this, how can you tell?

2 Yosemite Valley, California
Mountains Carved by Glaciers

3 Grand Canyon, Arizona Carved out by the Colorado River

4 Bryce Canyon, Utah Acidic Rainfall has worn away these rocks.
The harder rocks remain standing… but for how long?

5 Weathering The 2 G’s and the 3 W’s
Process by which rocks are broken down due to exposure to processes occurring at the Earth’s surface Caused by Water Waves Wind Gravity Glaciers The 2 G’s and the 3 W’s

6 2 Types of Weathering A. Mechanical Weathering also called Physical weathering Rock is broken down into smaller pieces of the same material (no change in composition) B. Chemical Weathering The breakdown or decomposition of rock that occurs when minerals are changed into different substances (change in composition)

7 Mechanical/Physical Weathering
Frost (Ice) Wedging Process in which water freezes in the cracks of rock and wedges (pushes) it apart because water expands when it freezes. Occurs where there are frequent freezes and thaws.

8 Explain what is happening.

9 Frost/Ice Wedging can cause Potholes to form in pavement

10 Mechanical/Physical Weathering
2. Abrasion The wearing away of rock material by grinding action Usually caused by sediment in Wind, Water, and Glaciers

11 Wind abrasion- sandblasting effect on stationary rocks as seen here in Arches National Park

12 Hydraulic abrasion- water & sediments flowing over boulders as seen here in Ohiopyle State Park, Pennsylvania Notice the rounded river rocks

13 Mechanical/Physical Weathering
3. Plants and Animals Plant roots can split rock Also known as: “Root pry” or “Root action” Animals dig holes ,breaks up rocks

14 Tree growing out of rock, Shenandoah National Park Tree roots also break up sidewalks

15 Mechanical/Physical Weathering
Exfoliation- gradual peeling of layers due to uplift and frost action, typical of granite domes like those in Yosemite N.P.

16 Exfoliation of Igneous rock

17 O2 Chemical Weathering Chemical Weathering
The breakdown or decomposition of rock that occurs when minerals are changed into different substances (change in composition) Involves Water ,water vapor, Acids, and/or Oxygen O2

18 Chemical Weathering Hydrolysis
Carbonic Acid in water dissolves Calcite. This chemical weathering can hollow out underground Caverns Limestone and Dolomite both dissolve because they contain Calcite

19 Acid rain (carbonic acid) weathering the details of statues and tombstones Ex: Marble and Limestone

20 Chemical Weathering Oxidation This is why Mars is the red planet
Oxidation of minerals with iron (magnetite, pyrite) results in the formation of rust or iron oxide. This is why Mars is the red planet Copper turns rocks green

21 Rate of Weathering Surface area Rock composition Climate
How fast a rock weathers depends on 3 factors: Surface area Rock composition Climate

22 Rate of Weathering Surface area
The greater the surface area, the faster the weathering rate There are more surfaces to be weathered

23 Rate of Weathering Rock composition
Some minerals are more resistant than others For example, quartz is more resistant (harder) than calcite Quartz Calcite

24 Rate of Weathering Climate
(long term pattern of moisture and temperature) Weathering rates are faster in warm, wet climates Desert vs. Rainforest

25 Erosion Erosion The removal and transport of weathered materials by natural agents such as Caused by Glaciers Running water Gravity Wind Waves

26 Glaciers Mass of compacted ice and snow that moves under its own weight

27 Glaciers Friction at the base of the glacier is reduced by a thin film of melt water. Glaciers account for about 75% of the fresh water on Earth

28 Glaciers can leave behind large boulders that are known as an erratic

29 Glaciers Glaciers can move lots of sediment that can carve striations (grooves) into rocks These Striations show how glaciers moved

30 Glacial Deposits Drift or Till - all sediment that is deposited by glacial activity Loess: fine powder, pulverized rock, that blankets much of the northern mid-west Moraine: ridge or pile of boulders, gravel, sand, and silt left at the end of a glacier Esker: type of outwash that accumulates in the channels and tunnels of a glacier

31 Glacial Landforms Horne: a pyramid shaped peak where 3 or more cirques meet Cirque Steep-walled bowl-shaped depression

32 Glacial Landforms Trough
U-shaped valley, Glaciers carve U shaped valleys

33 Glacial Landforms Arete Hanging valley
Narrow flat-topped ridge that forms between two parallel troughs or cirques Hanging valley Straight drop-off at the end of a trough

34 Glacial Landforms Moraine: Pile of mixed sediments that have been carried and dropped by the glacier

35 Glacial Landforms Eskers -Mounds of rock from melt tunnels


37 Streams and Rivers Velocity - How fast the water moves
Gradient - The steepness, the slope that a river or stream travels Discharge - The amount of water that moves past a certain point in a river in a given amount of time If there is a steep gradient, high velocity, and a large discharge, then Erosion will be severe! Rivers have energy to move lots of sediment, and even large boulders.

38 River stages affect: Velocity, Gradient, & discharge which cause Erosion


40 Seven Bends of the Shenandoah
River meanders Bends in the river, shows how mature a river is. Is the Shenandoah and old river or a young river?

41 Erosion-Mass Movement
The downward transportation of weathered materials by gravity Massive Landslide

42 Erosion-Mass Movement
Creep Slump Mudflow/Earthflow Landslide/Rockslide

43 Erosion-Mass Movement: A large mass of sediment drops down!

44 Erosion-Mass Movement
Creep Very slow movement of earth material. Caused by repeated freezing and thawing. Sediments are loosened by expanding frost and contracting thaw. Leaning fence posts and telephone poles are a sign of Creep.

45 Fence posts leaning due to creep

46 Erosion-Mass Movement
Slump Slow downward movement of a large mass of soil Occurs when underlying sediments are weakened by heavy rains Characterized by a curved scar in the land surface.

47 Slump can cause road hazards

48 Erosion-Mass Movement
Mudflow/Earthflow Thick pastes of sediments that travel downhill at great speeds Usually occur in dry areas that get a large quantity of rain all at once Leaves a cone shaped deposit

49 Mudflow in the Blue Ridge Mooreman’s Gap near Charlottesville

50 Erosion-Mass Movement
Landslide/Rockslide Fast movement of large blocks of rock Occurs in very steep vertical cliffs Accelerated by ice wedging

51 At the bottom of an old rock slide in N.C. 2011

52 Wave Erosion The crashing of waves on a shoreline combined with storms continually shape the beach. This is a shoreline with erosion.


54 Wind and Waves Wind moves sand dunes at the beach and in the deserts.

55 Wind and Waves Wind can carve out landscapes as it carries sediment

56 Wind and Waves Many storms combine water and wind to cause significant erosion on landforms. Strong winds are capable of moving large amounts of sediment

57 Deposition: The process of dropping or depositing soil and sediments.

58 Soil (dirt) Soil includes loose weathered rock, and organic material in which plant roots can grow

59 Soil Composition Use this pie chart to answer the questions in your notes.

60 Soil Composition What do the arrows mean?

61 Where soil forms Residual soil Transported soil
The parent rock is the bedrock beneath the soil (the soil has not moved) Transported soil Soil forms from parent material left by winds, rivers, glaciers, or soil that was moved from its original location. This soil has been transported by erosion and deposition

62 Factors that affect Soil Composition
Parent material: What bedrock is it from? Time: How long has it had to decompose? Plants and animals: How have roots and animals helped break up the rocks? Were there acid producing mosses that help break down the rocks (chemical weathering)? Topography: What is the shape of the landscape? Climate: Is it warm & wet? Were there glaciers present? Was there acid rain?

63 Soil Profile Cross section of soil layers revealing all soil horizons

64 Soil Horizon A soil layer with physical and chemical properties that are different from adjacent layers O Horizon= organic material (humus) A Horizon = topsoil B Horizon = subsoil C Horizon = partially weathered parent material

65 Idealized Soil Profile
Humus: Dark organic matter in soil that is rich in nutrients.

66 Leaching: The removal of nutrients or toxins in soil as water passes through the layers.

67 Soil Texture The size of soil particles

68 Particle size ranges for sand, silt and clay
 Type of Mineral Particle   Size Range  Sand   millimeters  Silt   millimeters  Clay  less than millimeters Large/ Coarse Medium Small/ Fine

69 erosion EROSION

70 Weathering

71 Deposition

72 Sedimentation to “settle”

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