Ch 5 (& Ch6 Later) Weathering … Erosion / Deposition
Ch 5 Lesson 1 • 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 …. • 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 • WATER (most) – dissolve substances – move thru spaces – SLOWLY wears down. • 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. • 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 • 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) 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.
Lesson 1 cont. IV) Land shapes caused by Deposition. *Characteristics – flat & low lying. Examples: • By WIND: gradually for deserts of sand. • Where Mt. streams meet Valleys = ALLUVIAL FAN (apron of deposited sediment) • By WATER: happens all the way along any moving water. • By Glaciers: leave ESKERS and MORRAINES -Which are LONG narrow deposits of sediment.
Lesson 2 Water & Wind • Water Erosion Pause for a video on the power of water …
Lesson 2 Cont. • 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 • 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.
3) CREEP • Def: sediments slowly shift down hill. • Common in areas w/ freezing & thawing. • EX) Leaning trees or leaning fence posts.
Lesson 3 cont. IV) Deposition by Mass Wasting • Talus – pile of angular rocks and sediment after rock fall. • 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/alpine_glacial_glossary/glossary.html