Today’s Objective: Today’s Objective: Be able to explain the difference between mechanical & chemical

WEATHERINGWEATHERING.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 Starter1.Which choice below is not an example of mechanical weathering?A.ExfoliationB.AbrasionC.RustingD.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

HydrolysisFeldspar +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)CARBONATION (causes dissolving)rainwater containing carbon dioxide dissolves

minerals (all rain water is slightly acidic)

Most strongly affected are calcite minerals:

limestone and marble

CARBONATIONCARBONATION

Stalagmites and stalactites

CARBONATION – CARBONATION – SINK HOLESSINK HOLES

-forms caves, caverns,

and sinkholes

CAVES AND SINK HOLES

RUSTING-OXIDATIONRUSTING-OXIDATIONOXIDATION OCCURS when oxygen

combines chemically with iron to form iron oxide

AKA RUST

Rusting

Plant AcidAcids formed by decay of plants can eat away at rocks

Dissolving-ACID RAINsulfuric acid-pollution in air dissolves in

rainwater and eats away at buildings & rocks

Acid RainAcid RainThis 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 WHAT KIND OF CLIMATE SUPPORTS WEATHERING?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 IN BOTH CASES – WATER IS THE PRIMARY INGREDIENT THAT PROMOTES WEATHERINGINGREDIENT 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