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Weathering and ErosionWeathering and Erosion Earth’s subsystems or “cycles”Earth’s subsystems or “cycles”

1. Weathering and Erosion

2. Surface water systems (rivers)

3. Groundwater systems

4. Groundwater in-class activity (grade)

Outline for next couple weeks Weathering(breakdown of rock)

Mechanical: physical breakdown (disintegration) of rocks and minerals

Chemical: chemical alteration (decomposition) of rocks and minerals

ErosionThe physical removal and transport of material by

agents such as water, wind, and ice.

Mass Wasting(special case of erosion)

Downslope movement of rock, regolith, and soil under the direct influence of gravity. Does not require medium such as water or wind - just gravity-driven.

Weathering is the disintegration or decomposition of a rock

Weathering is the disintegration or decomposition of a rock

Erosion is the removal and transport of the decomposed rock that results from

weathering

Erosion is the removal and transport of the decomposed rock that results from

weathering

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Weathering comes in two varieties:Weathering comes in two varieties:

Mechanical (physical) weathering

Chemical weathering

Acid mine drainage

H.Rae online blog: weathered cobbles, Eel River, Mendocino, CA Mechanical weatheringMechanical weathering

Freeze/Thaw (frost wedging) - water expands by 9% when it freezes

Unloading-related expansion - pressure release; exfoliation

Thermal expansion – temperature-related expansion and contraction of minerals creates stress in rocks

Biological activity - tree roots and micro-organisms

Mechanical abrasion - grain-to-grain contact during transport

Freeze/Thaw (frost wedging) - water expands by 9% when it freezes

Unloading-related expansion - pressure release; exfoliation

Thermal expansion – temperature-related expansion and contraction of minerals creates stress in rocks

Biological activity - tree roots and micro-organisms

Mechanical abrasion - grain-to-grain contact during transport

Frost wedging and joint-controlled weathering

Frost wedging and joint-controlled weathering

Unloading-related expansion - pressure release; exfoliation

Biological Activity(example: roots)

Biological Activity(example: roots)

Weathering comes in two varieties:Weathering comes in two varieties:

Mechanical (physical) weathering

Chemical weathering

Acid mine drainage

H.Rae online blog: weathered cobbles, Eel River, Mendocino, CA

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Feldspar weathers to clay

(not all silicates weather to clay)

Mafic rocks weather to iron oxide

Carbonate rocks totally removed

Chemical weathering processes

hydration

oxidation

dissolution

Hydrolysis – Oxidation – Dissolution

can chemically alter to form a completely new mineral

can chemically alter to form a completely new mineral

hydrolysis

oxidation

The minerals can actually dissolve . . .The minerals can actually dissolve . . .

Calcite is especially proneto dissolution

Mafic (Fe & Mg-rich) minerals are more susceptible to chemical weathering than are

felsic (Si-rich) minerals

Mafic (Fe & Mg-rich) minerals are more susceptible to chemical weathering than are

felsic (Si-rich) minerals

Quartz is resistant to chemical weathering, forming sand, but all other common silicate minerals break down chemically to form clay

minerals, the stuff of mud

Quartz is resistant to chemical weathering, forming sand, but all other common silicate minerals break down chemically to form clay

minerals, the stuff of mud

Because chemical reactions can occur only on rocks exposed to water, joints are

particularly important in accelerating this process

Because chemical reactions can occur only on rocks exposed to water, joints are

particularly important in accelerating this process

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Weathering(breakdown of rock)

Mechanical: physical breakdown (disintegration) of rocks and minerals

Chemical: chemical alteration (decomposition) of rocks and minerals

ErosionThe physical removal of material by agents such as

water, wind, and ice.

Mass Wasting(special case of erosion)

Downslope movement of rock, regolith, and soil under the direct influence of gravity. Does not require medium such as water or wind - just gravity-driven.

Water erosionWater erosion

Wind erosionWind

erosion

Glacial erosionGlacial erosion Clicker Question #1A flash flood removed the material

from underneath this road. This is an example of:

Clicker Question #1A flash flood removed the material

from underneath this road. This is an example of:

A. Mechanical weathering

B. Chemical weathering

C. Erosion

A. Mechanical weathering

B. Chemical weathering

C. Erosion

Jamestown, CO during 2013 flood

Clicker Question #2The dark rock in the center of the photo is a remnant of what the entire rock once was.

The red/white material surrounding it is much softer than the original rock. This

surrounding material represents:

Clicker Question #2The dark rock in the center of the photo is a remnant of what the entire rock once was.

The red/white material surrounding it is much softer than the original rock. This

surrounding material represents:

A. Mechanical Weathering

B. Chemical Weathering

C. Erosion

A. Mechanical Weathering

B. Chemical Weathering

C. Erosion

Weathering(breakdown of rock)

Mechanical: physical breakdown (disintegration) of rocks and minerals

Chemical: chemical alteration (decomposition) of rocks and minerals

ErosionThe physical removal of material by agents such as

water, wind, and ice.

Mass Wasting(special case of erosion)

Downslope movement of rock, regolith, and soil under the direct influence of gravity. Does not require medium such as water or wind - just gravity-driven.

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Rockfall in Zion

National Park

Can be rapid(meters/sec)

I-70, Western Colorado, May 2003

Figure 6.AFigure 6.A

Face of “Old Man in the Mountain”,New Hampshire, fell off in 2003 Slides

movement of material along a planar failure surfaces

Slides movement of material

along a planar failure surfaces

Rockslide along I-40 in Pigeon River Gorge, NC, July 1997

Slides movement of

material along a planar failure surfaces

Slides movement of

material along a planar failure surfaces

Slides on Fountain Formation Sandstone, Boulder, CO, during 2013 floods

Bedding plane

Weathered shale forms rubble at base

of cliff

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Angle of Repose

Weathered shale forms rubble at base

of cliff

Mass Movement Depends on Nature of Material

Angle of Repose:the maximum angle at which a pile of unconsolidated particles

can rest

Factors affecting mass movement

Steepness of slopeSlope composition WaterVegetationTriggers (floods, earthquakes, etc.)

Which house is more likely to slide into the valley?

Which house is more likely to slide into the valley?

a. The blue one on the left b. The pink one on the rightc. Equal chance d. Neither willd. Don’t know

Why?a. Because it is close to the valley bottomb. Because the bedding planes make sliding easierc. the hill it sits on is steeperd. b and c e. Because it is pink

Identify features in this landscape that represent 1) Erosion (what medium?)2) Mass wasting3) Chemical weathering

https://www.youtube.com/watch?v=eL06PWjOFxo

Mudslide in Boulder Canyon Sep 2013

Next time: Surface Water