Ch 5 (& Ch 6 Later) Weathering … Erosion / Deposition.
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Transcript of Ch 5 (& Ch 6 Later) Weathering … Erosion / Deposition.
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