Ch 5 (& Ch 6 Later)

Weathering … Erosion / Deposition

Ch 5 Lesson 1

I) Weathering: breaking down!!*Mechanical processes*Chemical processes*Change objects on Earth’s surface *Over … TIME

Lesson 1 Cont.

II) What do processes do to Rocks & Rock Surfaces?

* BREAK*WEAR * Abrade (scrape away)*Chemically alter

(makes rock easier to break down over time.)

Lesson 1 Cont.

III) Results (1000’s and 1000’s of years) of the break down of rock SOIL.

Sediment Size …SAND SILT CLAY(largest)

(smallest)

Lesson 1 Cont.IV) Rate of weathering depends on ….

1) Surface area of rock surface.2) Environment

*Slow in cold, dry places **Faster in wet areas or areas w/ lots of freezing

and thawing. 3) Type of Rock

*If rock has minerals low on hardness scale – will weather quicker.

Lesson 1 Cont.V) Mechanical Weathering – Physical processes

that break down ROCK. (Composition does not changed.)

4 types ….1) Ice Wedging (most effective)

*Water enters cracks (pores, any space) *Temp drops = freezing*Water expands when freezes = widens the

cracks.*Process repeats = rocks breaking.

Lesson 1 Cont.• 4 Types Cont. 2) Abrasion – grinding away by friction or impact.Ex) Stream carries loose fragments downstream –

fragments hit each other & other rocks – eventually makes smaller & smaller pieces.Ex) Others:

- Glaciers (as they move)- Wind (picks up small bits – hit against rock as moves)- Waves (picks up small bits – hit against rock as moves)

Lesson 1 Cont.• 4 types … cont.3) Plants

*Grow into / thru cracks in rock*Roots absorb chemicals from rock*Makes rock weaker*Continues to grow until rock breaks

4) Animals – burrowing into soil*Causes holes that water enters.*Causes rocks to break as they dig, etc.

Lesson 1 Cont.

VI) Chemical WeatheringA) Changes the material that is part of the rock. *Composition, of smaller pieces, is altered – actually different from original rock. B) HOW: 3 ways ….

3 ways

1) WATER (most) – dissolve substances – move thru spaces – SLOWLY wears down.

2) Acids – enters rain thru pollutants, volcanoes, burning coal, etc.

(Acid Rain – more damage than reg. rain.)3) Oxidation – oxygen combines with other elements *Metallic minerals ….. RUST!!! *Not evenly – happens on the outside of the rock first.

Ch 5 Lesson 2: Soil Formation

• Rocks breaking down eventually make SOIL.I) Soil is a mixture of

*weathered rock*rock fragments*decayed organic matter*water In pores (small spaces between pieces).

*air

Lesson 2 Cont.

II) Organic Matter*Def: once living things like …

leaves, dead insects animal “potty”

*Decomposes – end result is the dark colored organic matter in soil. (Humus) Good “stuff” for growing plants!

Lesson 2 Cont.III) What affects soil formation: (6)

1) Parent Material – original rock or sediment that starts forming the soil.2) Climate affects speed.

Ex) freezing / thawing /wet … 3) Topography

– shape & steepness of land.- How water moves or soaks in.

*Flat – water soaks in well – more dark material*Steep – water runs away – not as good.

Lesson 2 Cont.

4) Biota *Def: all organisms that live in a region.*More: speeds up soil formation process.5) Time – soil formation is a SLOW & CONSTANT

process. Soil 1000 yr. old is considered “young” soil.

Lesson 2 cont. 6) How deep the LAYERS (horizons) A Horizon: top *Part we see.

*Part w/ plant growth*Darker = organic matter

B Horizon: Middle*Water picks of clay particles from A and deposits them in B along w/ other material.

C Horizon: Bottom*Weathered parent material (rocks / sediment)

Lesson 2 cont.

• Why do we care about soil formation? ? • SUPPORTS life (comes from rocks )

• Done w/ Ch 5 … whew!• Start reviewing!

Ch 6 already Erosion / Deposition

• Remember … Earth’s Surface –CONSTANTLY SHAPING & RESHAPING–COMBINATION OF:• Constructive Processes – like lava

from volcanoes.•Destructive Processes – like

hurricanes, weathering …

Lesson 1 I) Reshaping Processes

Weathering Erosion Deposition*Breaking down! *PICKING UP & moving *PUTTING Down *Agents: *Factors affect rate or “settling”-water -weather *ENERGY slows or -wind -climate stops & pieces -ice -topography get dropped.

-type of rock *Rounding -well rounded = more erosion-poorly rounded = less erosion *Sorting – sorts by size

Lesson 1 cont.

II) Interpreting Landforms A) Characteristics of Landforms

(what to look for) 3 things!!1) Structure2) Elevation3) Rock exposure

B) Those (1-3) tell us whether Constructive or Destructive made the landform

Lesson 1 cont.

III) Landforms created by Erosion (destructive)*Look for tall, jagged structures w/ cuts in rock layers.*Examples: P. 182

1) See: exposed layers of rock2) See: unusual shapes 3) See: U shaped valleys (from glaciers) 4) See unique shapes like sea cliffs, caves, sea arches.

Pictures

Lesson 1 cont. IV) Land shapes caused by Deposition.*Characteristics – flat & low lying.Examples:1) By WIND: gradually for deserts of sand.2) Where Mt. streams meet Valleys = ALLUVIAL

FAN (apron of deposited sediment)3) By WATER: happens all the way along any

moving water.4) By Glaciers: leave ESKERS and MORRAINES

-Which are LONG narrow deposits of sediment.

Lesson 2 Water & Wind

I) Water Erosion

Pause for a video on the power of water …

Lesson 2 Cont.

A) Streams – how much erosion depends on ENERGY of stream.

*Tell a YOUNG stream by … straighter, faster moving*Tell an OLDER stream by … CURVEY

MEANDER – Large C shaped curves in stream.

3 stages of stream development• 1st stage: YOUNG

– Rapid water movement– Moves downhill– Carves out V shaped valleys

• 2nd stage: MATURE– Reached gentle slopes– Slows– Erodes the sides more than its bottom = starts making curves.

• 3rd stage: OLD– Slows even more– More erosion on the outside of bends (curves) = water moves

faster– More deposition on the inside of bends = water moves slower

Lesson 2 cont.

B) Coasts – waves crash onto shore OR currents running parallel will move weathered material.

C) Ground water – underground water creates CAVES.

D) HUMANS – we can increase erosion by building, plowing etc. WHY?

Lesson 2 Cont.

II) Wind

• Wind Erosion – causes ABRASION • Wind Deposition

– Dune: pile of windblown sand- Loess: crumble-y deposit of silt & clay

Lesson 3 Mass Wasting & Glaciers

I) Mass Wasting – downhill movement of LARGE mass of rock or soil because of GRAVITY.

**REMEMBER – gravity always wins!**

Lesson 3 Cont.II) 3 Types of Mass Wasting

1) Landslides – RAPID movement 2 kinds …

a) Rock Fall or Rock Slide Chunks of rock or sections of rock fall down a steep area b) Mudslide*area of thick layers of loose sediment*heavy rains*thick & pasty* once it loses energy – it deposits all it is carrying.

Video / pictures

• video of rockslide Tenn 2009• 2007 Afganistan mud slide

• Why do we care about these things? • KNOW WHERE AND WHAT YOU ARE BUILDING ON

OR BY!!!!• Gravity ALWAYS will WIN.

2) Slump

– DEF: material moves down along a curved surface– Looks like: curved scar – HOW happens:• Base can’t support rock & sediment.• Water moves to base & weakens area.• Strong layer on top of a weak layer.• It slips.

Example of Slump

3) CREEP

• Def: sediments slowly shift down hill.

• Common in areas w/ freezing & thawing.

• EX) Leaning trees or leaning fence posts.

CREEP

Lesson 3 cont. IV) Deposition by Mass Wasting 1) Talus – pile of angular rocks and sediment after

rock fall.2) Glaciers

*Large mass of ice*Moves SLOWLY across land *Picks up rock / sediment as it moves & deposits them. *Deposits are called:

TILL Moraine Outwash

(You can copy definition out of book.)

Lesson 3 Cont.

2) Glaciers cont. – 2 TYPESa) Alpine

*most common*in mountains*moves downhill

b) Ice Sheets *covers HUGE areas of land (more common during

the “Ice Age”) *moves outward.

Lesson 3 Cont. 2) Glaciers cont*WEATHER AND ERODE AS THEY MOVE*SCRATCHES IN ROCKS = STRIATIONS*LAND SHAPES CAUSED BY Glacier erosion

1) Horn2) Arete3) Cirque4) U shaped valley5) Hanging valley

(you look up definitions)

Glacier Feature Pictures

• http://www.uwsp.edu/geo/faculty/Lemke/alpine_glacial_glossary/glossary.html