Bell Ringer: List and explain the three types of weathering. MID TERM: Monday January 14-17 with makeups on January 18th. You will get a study guide soon and you may use an index card on the midterm. GRADES CLOSE: Friday January 18HOMEWORK: Read pg. 133-142 pg. 133 Key Concepts and vocabulary. Take notes.

Weathering and Soil

Weathering

Mechanical weathering occurs when physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition.

In nature three physical process are especially important causes of weathering: frost wedging, unloading, and biological activity.

Mechanical WeatheringFrost wedging is the mechanical breakup of

rock caused by the expansion of freezing water in cracks and crevices. Ice Heaving.

Sections of rock that are wedged loose may tumble into large piles called talus, which typically form at the base of steep, rocky cliffs.

Examples of Frost Wedging and Ice Heaving

Abrasion Def: the wearing

away of rock material by grinding action

Water, wind and ice are capable of moving rocks.

Sand is a product of abrasion.

ContinueUnloading is the reduced pressure on igneous

rock causes it to expand and allows slabs of outer rock to break off in layers in a process called exfoliation.

Biological the activity of organisms, including plants, burrowing animals, and humans, can also cause mechanical weathering.

Upward Expansion Examples

Chemical Weathering

Chemical weathering is the transformation of rock into one or more new compounds.

Spheroidal causes the corners and edges of rock to be more rounded

Rate of Weathering

Mechanical weathering affects the rate of chemical weathering. By breaking the rocks into smaller pieces,

mechanical weathering accelerates chemical weathering by increasing the surface area.

Two other factors affecting the rate of weathering are rock characteristics and climate.1. Rock characteristics

1. Mineral composition and solubility2. Physical features such as joints

Continued

2. Climate1. Temperature and moisture are the most crucial

factors.2. Chemical weathering is most effective in areas

with high temperatures and abundant moisture.

3. Differential Weathering1. Caused by variations in composition2. Creates unusual and spectacular rock formations

and landforms

Check for Understanding1. Explain the difference between weathering,

erosion, and deposition

2. What powers the rock cycle?

3. What happens to a rock’s mineral composition during mechanical weathering?

4. How does chemical weathering affect the compounds in rock?

5. Why is chemical weathering slow in arid and polar regions?

Soil

Soil is part of the regolith that supports the growth of plants. Regolith is the layer of rock and mineral

fragments that covers most of Earth’s land surface.

Soil has four major components: mineral matter, or broken-down rock; humus, which is the decayed remains of organisms; water; and air.

Q: What’s the difference between soil

and dirt?A: Location,

location, location!

Soil is not DIRT!

Why the different colors?

Hematite: red

Goethite: yellowish brown

Ferrihydrite:reddish brown

Calcite: off white

Quartz:white

Organic matter:black

• Did you know ??????There are more than 20,000

different soil types in the United States

Soil Color Variation

….and each one tastes different

Dr. Greg Pillar, Queens College

SOIL FORMATION!Results from the

continuous weathering (mechanical and chemical) of rocks into smaller and smaller pieces) combined with water, living organisms, air, decaying organic material (humus).

Parent rock is the bedrock from that when weathered rock breaks down and begins the

process of soil formation. Takes 100’s to 1000’s of years to form 10cm of soil.

Extremely important to organisms, decomposition is the source of nutrients and water for all living things

Absorbed by

plants

Plants eaten by animals

Plants and

animals die and decay

Nutrients returned

to soil

Soil composition 80% are rock particles. There are three basic

particle sizes. Sand (0.05mm to 2mm size) - good drainage and aeration,

doesn’t store water well; unsuitable for plants

Silt (0.002mm to 0.05mm size) - good drainage and aeration,

stores water well; suitable for plants

Clay (0.002mm and smaller) - holds water well, doesn’t drain

well, few air spaces; unsuitable for plants

2. Percentage of the 3 particle sizes in the mixture determines soil type and characteristics of soil.

a.Sandy at the beach, red clay in the Piedmont of NC.

b.Loamy soil has equal parts of all 3 particle sizes and is the optimal soil type

Fine Texture - Clay

https://www.soils.org/lessonsDr. Greg Pillar, Queens

College

Course Texture - Sand

https://www.soils.org/lessonsDr. Greg Pillar, Queens

College

Soil Texture Diagram PracticeWhat type of soil has:

1. 20% clay, 40% silt, 40% sand2. 40% clay, 10% silt, 50% sand3. 30% clay, 60% silt, 10% sand

Find the % of each particle at:

4. A5. B6. C

60%clay, 20%silt, 20%sand

30%clay, 40%silt, 30%sand

10%clay, 30%silt, 60%sand

(1) Loam

(2) Sandy clay

(3) Silty clay loam

B

A

C

PROPERTY SAND SILT CLAY

Water holding Low Med-high High

Aeration Good Med PoorNutrient

supplying Poor Med-high High

Pollutant Filtering Low Med High

Why is Soil Texture Important?

SOIL HORIZONS/SOIL PROFILE1. As weathering progresses, distinct soil

layers form. The more time involved the more mature the soil.Takes 1000’s of years to form mature soil.

Observe this SOIL PROFILE through soil

Soil layers are horizons and

assigned letters

O: Organic material (may be absent)A: Topsoil - Organic material & mineral grainsE: Leached zone (may be absent)

B: Subsoil – rich in clay, iron, aluminum

C: Weathered bedrock

R: Bedrock (parent material)

SOIL LAYERS1.O layer- organic material (ex. Dead leaves, twigs)

2.A layer - upper layers/topsoil - dark colored; most fertile- where most organisms exist and composed of humus

3.B layer – subsoil - Mostly clay - 100,000 years to form

4.C layer – partial weather bedrock and extends to parent rock

5.R layer- bed rock

A horizon: organic coatings

B horizon: Iron coatings

C horizon: little coating

Soil Color by Horizon

Fun Fact: It takes 200 to 1,000

years to form an inch of topsoil.

Soil Color – Variation by Geography

Red soils: Southeast US

Dr. Greg Pillar, Queens College

Soil Color – Variation by Geography

Brown/black soils: Midwest

Dr. Greg Pillar, Queens College

http://www.scienceclarified.com

Soil Color – Variation by GeographyWhite (gypsum) sands:

New Mexico

Dr. Greg Pillar, Queens College

Soil Formation

The most important factors in soil formation are parent material, time, climate, organisms, and slope.

1. Parent Material1. Residual soil—parent material is the bedrock2. Transported soil—parent material has been carried

from elsewhere and deposited

2. Time1. Important in all geologic processes2. The longer a soil has been forming, the thicker

it becomes.

Soil Formation

3. Climate-MOST IMPORTANT in soil formation!1. Climate has the greatest effect on soil! Variations in

temperature and precipitation influence the rate, depth, and type of weathering.

2. Climate has an effect on the organisms that live on and in that soil.

4. Organisms1. Organisms influence the soil's physical and

chemical properties.2. Plants are the main source organic matter.3. Microorganisms and animals also contribute organic

material.

Soil OrganismsEx: bacteria, fungi, algae, microscopic

worms, protozoa, plant roots, insects, earthworms, moles, snakes, groundhogs,

etc.

Continued

5. Slope1. Steep slopes often have poorly developed

soils.2. Optimum slope is a flat-to-undulating upland

surface.3. Orientation, or direction the slope is facing,

influences soil formation.1. Soil temperature2. Moisture

15.06.b

ACTIVITIES THAT THREATEN SOIL

REMOVING VEGITATIONOVERGRAZING

SOIL CONTAMINATION

FARMING/AGRICULTURE

• Agricultural: 10% of the worlds best agricultural land damaged due to soil erosion and overuse over last 50 years.

- contour plowing- no-till agriculture (no plowing)- terracing slopes- crop rotation - fallow

PREVENTING SOIL EROSION

Mass Movements and Erosion

Mass movements- the downward transportation of

weathered materials Gravity causes materials to fall, slide, or move at slow

speeds to lower levels

Erosion- the removal and transport of materials by natural agents such

as wind and running water

MASS MOVEMENTSLandslide- movement of

a mass of bedrock or loose soil and rock down the slope of a hill, mountain, or cliffSteep slopesRegions near volcanoes

and in earthquake-prone regions

LANDSLIDESCreep- slow, imperceptible

movement of soil down a slope Causes fence posts, poles and other

objects fixed in soil to lean downhill

Slump- a block of land tilts and moves downhill along a surface that curves into the slope Tends to occur because bottom of

slope can no longer support top of slope

Creep

Slump

Earthflows- the downslope movement of a mass of earth materials that have been saturated with water Slower and less fluid than a

mudflow; velocity affected by amount of water present, the composition of the soil, and steepness of slope

Mudflows- the downslope movement of water that contains large amounts of suspended clay and silt Rapid movement; capable of

moving rocks, boulders, trees, and houses.