Orogenesis and erosion

Changing the earths reliefEvolution of the landscapeTodays topic: the earths relief and how it changes. Does anyone know what the term relief in the context of earth sciences means? -shape of earth surfaceCan anyone name me any components that make up the relief of a landscape? River, lake mountain, valley, plainHow do these components influence us humans our way of living, or our behaviour?Tourism in mountains or near water, Quebec, Montreal on St. Laurence river as means of transportation, agriculture in flat regions not in mountainTodays topic changing earths relief Have been talking about plate tectonics. What happens at convergent plate boundaries? Demonstrate with two tows pushed against each other folding and uprising, mountain formationWhere in the world? All high mountain chains in the world: Andes, Rocky mountains, Europe: Alps, Pyrennees, Himalaya, Ural 1Changing the earths relief: mountain formationRelief = shape of the earth surfaceFormation of mountains = Orogenesis through convergent tectonic plate movements mountain: - steep slopes - at least 600m highMountains in the making: Himalaya, Rocky mountains, Alps

Talk about effects of relief on human activity tourism in laurentians (ask whether anyone goes skiing check with Millie whether anyone is likely to be able to afford)agriculture in prairies, milk production in mountain regionsrelief has influenced where people have settled often along rivers because used to be important means of transportation, Montreal Qc on St. Laurence river.Is mount royal a mountain? not 600m high (233m) -> ONLY A HILL 2

LaurentiansRocky MountainsWhy are they different??Have Laurentians always looked the way they look today? Are mountains here to stay forever without changing once they are formed?Clue montreal streets, did they look this way before the winter? Laurentians used to look like rocky mountain what happened?Rocky mountains younger mountains, Laurentians have been worn down How does this happen? 3Montreal streets :

After the winter: worn downWearing of mountains similar to wearing of our streets process is called weathering4

LaurentiansRocky MountainsLaurentians a lot older have been worn down!Why are they different??Laurentians used to look like rocky mountains what happened?Rocky mountains younger mountains, Laurentians have been worn downHow does this happen?First thing that must happen: rock must somehow be broken down, called weathering 5WeatheringGradual destruction of rock on the earth surface.

http://www.youtube.com/watch?v=z2nwiba0N0Y

For the next little while will be talking about what causes rock to break down. What are the mechanisms causing weathering? Anyone any idea? watch clip and ask again whether anyone has an idea how rock might get destroyed

6Mechanical weatheringThe power of water:

Rock is fragmented, but not changed in its compositionSee the little cracks I here what happens when it rains what happens when rain freezes in there?But how did the first little crack get there in the first place? Heating and cooling not evenly, when rock is heated it expands, when it cools again it contracts sometimes not evenly, tension in rock -> cracks Explain and define mechanical weathering

7Mechanical weathering Fragmentation of rock through: - Variations in temperature andpressure- water example: freeze thaw cycle of water-wind Composition of rock does not change

Demo: limestone with acid, show egg in vinegar -> transition to chemical weathering.When we talk about mechanical weathering the rock is broken down into smaller pieces, but its still the same kind of rock afterwards and this is different in another kind of weathering, which is called chemical weathering.We saw what vinegar, which is an acid can do to an eggshell. Where do we encounter acid something acidic in nature? (especially nowadays?) which is composed of a carbonate mineral. 8Minerals in rock are dissolved and changed.

Chemical weathering

Stalagmites rise from floor. CaCO3 from limestone (sedimentary rock) dissolves in water and then re-crystallizes.Chemical weathering of marble through acid rainHowever, chemical weathering also without acid rain but a lot slower9Chemical WeatheringDissolving and changing minerals in rocks Composition of rock changes.Through: - washing out of certain minerals enhanced through acid rain

Biological WeatheringLiving organisms destroy rock.Talked about mechanical weathering which means that rock is broken into pieces and about chemical weathering, where the rock material is changing. There is another kind of weathering which is called biological weathering. What could be the characteristic of biological weathering be?11Biological weatheringPlant roots can break rocks Living organisms release acids changes and weakens the rock

Practice: what kind of weathering?

1. Mechanical 2. Chemical 3. Mechanical + Chemical 123Think pair shareAnother example if you think of an old car what do you see on its outside? -> rustWhat kind of weathering would that be?13

Talked about weathering of rock but something else happens to transform mountains like the rocky mountains into mountains like the Laurentidestransportation of material. Weathering + Transportation is called EROSIONHow could material be transported away / removed? 14

Water erosionWater the most common force that causes erosion15Glacial erosion

Wind erosion

Ever walked along peoples front lawns and noticed that at the very front the lawn does not grow very well when the slope of the lawn is kind of steep?Why soil is eroded 17Erosion of soil

Soil Erosion rates on farmed land between 17 and 40 tons per ha and year average natural soil production only 1 ton per ha and year !!!Soil is being washed away; where will it ultimately end up? -> in the oceanCan it then still be used? -> noWhy is the soil on these pictures being washed away? Does this always happen on every piece of land? plant roots protect soil keep it in place. In the last 200 years 30% of farm land in US abandoned because of erosion (land has become unfertile for agriculture)

18Journeys end: Deposition

Material that is being removed from mountains needs to be deposited somewhere -> in streams, lakes and ultimately oceans. What is the remarkable feature of this river ending? Wide smooth and flat eroded material deposited here. 19

The three stages of ErosionErosion1.) Weathering2.) Transport: water, wind, ice3.) Deposition: in lake, stream,oceanChanging the earths relief: Erosion Erosion is the gradual wearing away (destruction and /or removal) of land surface material, for example rock or soil.Three step process:Weathering of rock (destruction of rock)Transportation of soil and rock debris (through water, wind, glaciers).Deposition of material at another location

Erosion is the process by which the surface of the earth gradually gets worn down -> results in flattening of landforms

21View from the mountain:

View from mount royal landscape pretty flat why?1.)glaciers2.) champlain sea22

Montral

MontralAfter glacier retreated champlain sea eroded soil from great lake area deposited here flat Landscape, deep soils in the area of St. Laurence river. Good for agriculture here.24Effects of erosionHole on Sherbrooke May 2012Caused by hole in water collecting pipeWhat happened?

homeworkWorksheet to be collected next classTo create marks26Categories of Weathering / ErosionMechanical Weathering Composition of rock does not changeThrough: - Variations in temperature and pressure example: freeze thaw cycle of water - Wind and waterChemical Weathering Composition of rock changes Through: - washing out of certain minerals enhanced through acid rain Biological WeatheringLiving organisms release acids change + weaken the rockPlant roots can break rocks. Midway summary Slide too busy, simplify chemical composition of rock -> rephrase27