Transcript 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 WATER WIND 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 OCCURS WHEN Water combines with minerals – most often in granite (mica and feldspars) to form CLAY Feldspar A Clay Cliff 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? HIGH PPT ↑ ↑ ↑ ↑ ↑ ↑ ↑ LOW PPT COLD →→→→→→→→→→ HOT 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