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
(largest)
CLAY
(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 Weathering
A) 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 …
I)
Lesson
1
Reshaping Processes
Weathering
*Breaking down!
*Agents:
-water
-wind
-ice
Erosion
Deposition
*PICKING UP & moving *PUTTING Down
*Factors affect rate
or “settling”
-weather
*ENERGY slows or
-climate
stops & pieces
-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) Structure
2) Elevation
3) 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 rock
2) 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.
3st stages of stream development
• 1 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 TYPES
a) 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) Horn
2) Arete
3) Cirque
4) U shaped valley
5) Hanging valley
(you look up definitions)
Glacier Feature Pictures
• http://www.uwsp.edu/geo/faculty/Lemke/alpi
ne_glacial_glossary/glossary.html