Presentation on theme: "Wearing Down Earth’s Surface"— Presentation transcript:
1Wearing Down Earth’s Surface Unit CChapter 6 Lesson 2C14 – C19
2ObjectivesIdentify destructive forces as processes that wear down Earth’s land features.Identify weathering as a destructive force.Recognize that weathering can be either mechanical or chemicalDefine erosion as the carrying away of weathered rock by water, wind, and glaciers.
3Main IdeaDestructive forces, such as weathering and erosion, wear down Earth’s surface features.
4VocabularyErosion – (noun), destructive force in which pieces of rock are moved by water, wind, or moving ice.Sediment – (noun), small pieces of rockWeathering – (noun), destructive force that breaks down rocks into smaller pieces
5Weathering A destructive force that breaks down rocks. Two types: MechanicalChemical
6Mechanical Weathering The breaking of larger rock into smaller rock called sedimentIce – water goes into cracks of rocks, freezes, and breaks rock apart.Moving air & Water – causes weakening of rock and it will crumbleLiving things – plant roots and burrowing animals
7Mechanical Weathering - No change in the rock,it just gets smaller!
8Chemical Weathering Rocks change into other materials Water is the main factor causing chemical weathering.Water dissolves minerals that make up certain rockWater dissolves certain chemicals from the air & soil to form a weak acid – which dissolves minerals
9Often there is acombination ofdifferent types ofweathering at work.
10Cave Formation Underground hollow areas created by weathering Weak acids seep into the groundAcid dissolves minerals in rockOver time, holes produced in the rockAt first full of water, but eventually water drains
11Limestone Many caves are made from limestone The minerals in limestone is easily dissolved by weak acid
12Describe three ways that mechanical weathering may occur? Water in the cracks of rocks, freezes, and busts rock into smaller piecesWind or rushing water hitting rocks causes them to weaken and crumble.Plant roots breaks apart rock.
13Why do many caverns form in limestone? The minerals in limestone are easily dissolved by acids.
14ErosionThe carrying away of sediments by moving water, wind, or moving iceCommon agent of erosion: Water moving down a river
15River Valley Formation Begins as a shallow stream at higher elevationStream grows and carries sediment awayIn time, the river cuts a V-shaped valley
16Frozen Water Glaciers formed the rolling plains and the Great Lakes. Glaciers move down stream toward the sea.Move large amounts of rock & soil.They form hallows in the land they erode. When they melt they form lakes.
17Ocean waves & CurrentsCrashing waves break down rock along coastlines.Sediments are dragged back and forth, slowly turning into sand.Wind & Waves erode the land.Sea caves may join to form a sea arch.Erosion may continue until arch falls creating a sea stack.
19Weathering vs. Erosion Weathering Process that breaks down rock into smaller pieces called sedimentErosionThe carrying away of sediments by moving water, wind, or moving ice
20Slow and Fast Changes Chemical weathering = takes thousands of years But, after a cave is formed, the weight my be to great causing a sudden collapse which forms a sinkhole.
21Sinkholes Form very suddenly Land above weathered rock sinks into a hole.
22Landslides Occur suddenly due to erosion Large movements of land that tumble down a steep slope.Mudslides, rock falls, & avalanches
23Causes of landslides Gravity is the main cause Erosion from rivers, rain, glaciers, or ocean waterThese steepen the slope and loosen sedimentA disturbance, such as an earthquake, can shake the rocks loose.Volcanoes can cause landslides also.
24How are a sinkhole and a landslide alike? How are they different? Occur quicklyResult of weathering & erosionGravity pulls sediment downwardDIFFERENTSinkhole is formed when rock above a cave falls into the caveIn a landslide, rocks and soil tumble down a hill.
25What are the four forces that can combine to cause a landslide? Erosion loosens sediments making a steep slopeRain causes sediments to become heavy with waterEarthquakes shake the sediments looseGravity carries the sediments downhill
26Turn to page C19 to answer the Review questions.
36List three causes of mechanical weathering. IceWindMoving waterPlant & animal activity
37Describe how chemical weathering can take place below Earth’s surface. Water seeps into deep cracks and dissolves minerals in rock.Acid rain seeps into cracks in rock and dissolves below the surface.
38Wind, running water, and glaciers lead to erosion Wind, running water, and glaciers lead to erosion. Which one moves sediments most quickly? Which moves sediments most slowly? Which is capable of moving the heaviest sediments?Fast-flowing water & high speed winds can carry small sediments quickly.Glaciers move most slowly, but are capable of carrying large amounts of sediment with them.