Weathering Definition n Weathering is the gradual breakdown

Weathering

Definition n Weathering- is the gradual breakdown of rock under surface conditions, dissolving it, wearing it away or breaking it into smaller pieces.

2 types- Physical(mechanical) & Chemical n Physical Weathering (mechanical)-is breaking rock by force. ex: hitting, scratching, cracking 1. Frost action (ice wedging)- water seeps through rock, freezes, expands and widens crack 2. Plant action- root hairs seek out cracks and expand by pressure & break through rock 3. Abrasion- rubbing by other rocks 4. Exfoliation- rounded sheets of rock peel off a rock or outcrop (like layers of an onion)

EXFOLIATION

Exfoliation: peeling away of rock layer

b. Frost Action aka (Frost Wedging) n n n 1. This process occurs when water seeps into the cracks in a rock. 2. When water freezes (into ice), it ______ by 9% expands 3. This cycle of freezing and melting causes the rock to split or break apart.

FROST WEDGING

Frost Wedging: this melting and freezing cycle eventually may split rocks

Pot Holes: a common form of frost wedging

PLANT/ANIMAL ACTIVITY

ABRASION OF WIND AND WATER

Formed by wind abrasion (Utah)

Formed by marine abrasion

n Chemical Weathering-is where the rock material is changed into another substance by reacting with a chemical. 1. Oxidation- Oxygen in atmosphere reacts with minerals ex: rusting of a nail 2. Water (hydrolysis)- minerals dissolved in water ex: Halite, Calcite 3. Carbonation- CO 2 in atmosphere dissolves in water- carbonic acid and acid rain

a. Carbonation n carbon dioxide Occurs when ________ in the atmosphere dissolves in the droplets of water that make up a cloud. “carbonic acid” n This mixture forms a weak ______ that dissolves certain rocks and minerals, some limestone marble which include _____, and _______. chalk. Carbonation reaction = (carbon dioxide + water)

Guided Practice n Which minerals will dissolve in the presence of carbonic acid in each of these rocks: a) limestone ANSWERS a) limestone calcite ______ b) marble (hint use your ESRT to look up the mineral composition of each rock) calcite/dolomite b) marble _______

A result of this type of chemical weathering is the formation of caverns or caves! n Using map symbols in your ESRT, describe what type of bedrock this is. limestone _______ • Carbonic acid rain water seeps into the limestone bedrock through cracks. The carbonic acid dissolves the limestone which is carried away by water. • A cave (cavern) forms by this process. Cavern features include: 1. Sink Holes 2. Stalactites (c= ceiling) 3. Stalagmites (g=ground)

Stalactites vs. Stalagmites n Stalactites- an icicle shaped mass of calcite attached to the ceiling of a limestone cavern. n Stalagmite-a cone of calcite rising from the ground of a cavern. n Usually come in vertical

b. Hydrolysis n n The chemical weathering by water reaction of _____ with other substances. very slow process Ex: the rock granite is stable in dry climates, but in moist/wet climates, rainfall dissolves the mineral feldspar in granite. Feldspar becomes a clay mineral (kaolinite) and weakens the bond between the other minerals.

c. Oxidation n A chemical reaction when oxygen ______ from the atmosphere combines with certain minerals in a rock. n Ex: When oxygen combines with iron, iron oxide or ‘rust” forms. n (Iron + oxygen) = iron-oxide (rust) n This chemical change weakens the rock, and the rock begins to crumble. n Oxidation in the presence of water takes on a reddish- yellow brown color.

Rates of weathering will be influenced by. . . n n Surface area exposed - weathering occurs on the surface. More surface exposed, the faster the weathering will occur. Mineral Composition-Some minerals are more resistant than others ex: Quartz = very resistant to weathering

Rate of weathering influenced by: n n Surface area exposed Mineral Composition Climatic Conditions Soil

Climatic Conditions n n Cold and dry climates favor physical weathering warm and moist climates favor chemical weathering n Frost action works best in places where temperatures fluctuate

Egypt New York The stone had stood in the clear dry Egyptian desert air for nearly 3000 years and had undergone little weathering. In a little more than a century in the climate of New York City, pollution and acid rain have heavily pitted its surfaces.

Which type of weathering is being shown? Which example? Which Picture shows the correct order from least shaking Time to most?

Acid Rain- result of sulfur and nitrogen oxides in the air -oxides travel with wind and when it precipitates, - it will be acid rain

Soil n n n End product of weathering Made from rocks, minerals, and organic material (regolith, organic matter) Form layers of different characteristics called horizons

Horizons Layer Description Top Soil Small sediments and organic material, darker in color B Sub Soil Lighter in color, small amounts of organic material C Partly-weathered Bedrock Larger rocks Bedrock Solid Rock Horizon A

Leechingwater carries materials from upper horizons to lower horizons n n Residual soil is located above the rock that it is formed from (parent rock). Transported soil has been moved from another location. Ex: Glaciers Most soil on the Earth's surface is transported.