CHAPTER 12: Weathering, Soil, and Erosion

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CHAPTER 12 Weathering, Soil, and Erosion
Breaking down rocks since the beginning of time!
I heard Oprah was herewhere is she??
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WEATHERING
Weathering is simply the breakup of rock due to
various Earth processes.
2 TYPES
MECHANICAL Rocks are split and broken into
smaller pieces of the same material. The
composition of the rock is NOT changed! Also
called PHYSICAL weathering.
CHEMICAL Rocks are broken down b/c their
minerals are changed into different substances.
Keep him away!!!
Ill find you!!!
The two types of weathering work together to
break down rocks!
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MECHANICAL WEATHERING
Lets take a look at a few examples of mechanical
weathering.
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Mechanical weatheringa closer look
Ice wedging Water seeps into cracks in the
rock. When this water freezes it expands,
breaking the rock apart. Water is pretty strong,
eh?
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Mechanical weatheringa closer look
Tiny root hairs make their way into the cracks in
rock. When the roots growBAM!the rock splits.
Ever seen grass growing through a sidewalk???
Same thing!
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Mechanical weatheringa closer look
Abrasion by wind and watercool stuff here!
Think about it this waywind and water carry
small particles of sand and rock. When the sand
and rock rub up against other rocks, the rocks
are gradually worn away. This type of mechanical
weathering is called abrasion.
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Chemical Weatheringa closer look
Remember Chemical weathering changes the
composition of the rock!
Lets check out how carbonic acid and acid rain
affects rocks. What the heck is carbonic acid?
So the result is
Ok, so stay with me heretheres carbon dioxide
in the atmosphere, right? When raindrops fall
through the atmosphere, sometimes carbon dioxide
becomes dissolved in those raindrops! When
carbonic acid seeps into the ground, it slowly
dissolves the rock below AMAZING!
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Chemical Weatheringa closer look
CAVES!!!
Sothis carbonic acid has a BIG impact on
calcite. Remember Limestone is made up
primarily of calcite. When the limestone rock is
worn away, it leaves caves behind. This is
chemical weathering!
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Chemical Weatheringa closer look
This same process can cause sinkholes at the
surfacewatch out!
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Chemical Weatheringa closer look
Oxidation Weathering by oxygen. Oxygen??? But
we breathe that!
Yes, believe it or not, oxygen can cause chemical
weathering. When oxygen interacts with certain
rocks that contain high amounts of iron, the rock
is worn down and rust forms. Rust is also known
as hematite.
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What affects how fast rocks weather?
Well look at three different variables

• Surface exposure of rock
• Type of rock (composition)
• Climate the rock lives in

More surface area faster rate of weathering.

• Cold and/or dry climates favor mechanical
  weathering.
• Warm and wet climates favor chemical weathering.
  
• Frost action works best in areas where the
  temperature fluctuates wildly.

Different types of rocks weather at different
rates because they are made up of different
minerals.