Today’s Objective: WEATHERING Today’s Objective: Be able to explain the difference between mechanical & chemical WEATHERING. Science Starter: Read the Article on POTHOLES! Mark the text-this paper is science starter for next few days! In margin write a 1-2 sentence explanation about how water creates potholes! Glue CHART for notes on right 48, VOCAB on LEFT 48

Science Starter 1.Which choice below is not an example of mechanical weathering? A.Exfoliation B.Abrasion C.Rusting D.Ice Wedging 2. What type of weathering is shown in the picture? Mechanical or chemical, and why? ** Rate yourself on how well you know weathering (1 to 4) Take Weathering Walk sheet out; get Grand Canyon Reading and questions from front table!

WEATHERING Definition: The physical and chemical processes that break down rocks

What is Mechanical Weathering? Rocks physically broken apart into sediment (but composition does NOT change) Increases surface area (lots of crushed broken pieces)

MECHANICAL WEATHERING MOST IMPORTANT IN OUR CLIMATE FROST ACTION / ICE WEDGING ALTERNATE FREEZE AND THAW Water expands when frozen, breaking apart rock

ROCKS ARE CRACKED BY WATER FREEZING

EXAMPLES: POT HOLES, Cracks in walkways, roads

Frost action also called Ice Wedging

MECHANICAL WEATHERING - ABRASION Wearing down rocks by friction of water or wind WATERWIND

Abrasion

Pressure Release & Exfoliation -Earth’s forces push down on rocks, so when it’s unearthed pressure off rock causes it to expand & crack EXFOLIATION –layers of rock gradually break off like layers of an onion being peeled

EXFOLIATION

MECHANICAL WEATHERING – PLANT ROOT ACTION PLANT ROOTS UPLIFT AND SPLIT/ BREAK ROCK

Plant Root Growth

ANIMALS Animals that burrow in ground can cause weathering

GRAVITY Falling of rocks causes breaking

What is Chemical Weathering? Breakdown of rocks by chemical reactions that change the composition of rocks

Hydrolysis Feldspar +Water = Clay Feldspar A Clay Cliff OCCURS WHEN Water combines with minerals – most often in granite (mica and feldspars) to form CLAY

CARBONATION (causes dissolving) rainwater containing carbon dioxide dissolves minerals (all rain water is slightly acidic) Most strongly affected are calcite minerals: limestone and marble

CARBONATION Stalagmites and stalactites

CARBONATION – SINK HOLES -forms caves, caverns, and sinkholes

CAVES AND SINK HOLES

RUSTING-OXIDATION OXIDATION OCCURS when oxygen combines chemically with iron to form iron oxide AKA RUST

Rusting

Plant Acid Acids formed by decay of plants can eat away at rocks

Dissolving-ACID RAIN sulfuric acid-pollution in air dissolves in rainwater and eats away at buildings & rocks

Acid Rain This is a monument called Cleopatra’s Needle. It was carved in Egypt around 1450B.C. The sides are carved with hieroglyphs, the writing of ancient Egypt. It stood in the dry, hot Egyptian desert for over 3000 years. During that time, the hieroglyphs remained distinct.

Weathering In 1800, the monument was moved to New York City. Almost immediately, the hieroglyphs began to fade. In only a few years in the wet and variable climate of New York, the Egyptian writing became indistinct!

Cleopatra’s Needle was carved from granite, a hard tough, crystalline rock. Although it is tough, granite is changed by the atmosphere. Some of the minerals that make up granite change to clay. Chips and flakes of minerals break away from the granite surface.

WHAT KIND OF CLIMATE SUPPORTS WEATHERING? COLD →→→→→→→→→→ HOT HIGH PPT ↑ LOW PPT

CLIMATE CONTROLS WEATHERING PHYSICAL WEATHERING: COLD AND MOIST ALTERNATE FREEZE / THAW CHEMICAL WEATHERING: WARM AND MOIST (just like a chemical reaction) IN BOTH CASES – WATER IS THE PRIMARY INGREDIENT THAT PROMOTES WEATHERING

THE END PRODUCTS OF WEATHERING CALLED SEDIMENTS OR SOIL SOIL: a combination of sediment, rock minerals, and humus (organic material from biologic activity)

WEATHERING SUMMARY PHYSICAL WEATHERING – INCREASES SURFACE AREA - COLD/HUMID CLIMATE CHEMICAL WEATHERING – WARM/HUMID CLIMATE IN BOTH CASES, WATER IS THE PRIMARY INGREDIENT