Essential Questions. What is erosion? What is mass wasting?

Transcription

1 Erosion

2 Essential Questions What is erosion? What is mass wasting?

3 What is Erosion?

4 Erosion The transportation of sediment from one area to another Caused mainly by running water but also caused by glaciers, waves, and wind

5 Erosion features in a river valley Meanders Oxbow Lakes Levees

6 Erosion by Water

7 Meander is a bend in a sinuous watercourse is formed when the moving water in a river erodes the outer banks and widens its valley a stream of any volume may assume a meandering course, alternatively eroding sediments from the outside of a bend and depositing them on the inside the result is a snaking pattern as the stream meanders back and forth across its down-valley axis

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9 Oxbow Lake is a U-shaped U body of water formed when a wide meander from the main stem of a river is cut off to create a lake

10 Levee is a natural or artificial slope or wall to regulate water levels it is usually earthen and often parallel to the course of a river or the coast when a river floods over its banks, the water spreads out, slows down, and deposits its load of sediment over time, the river's banks are built up above the level of the rest of the floodplain

11 Erosion features of an alpine Cirques Horns Tarns Aretes Cols U-shaped valleys Hanging valleys landscape

12 Erosion by Glaciers

13 Cirques is an amphitheatre-like valley head, formed at the head of a valley glacier by erosion.. The concave amphitheatre shape is open on the downhill side corresponding to the flatter area of the stage, while the cupped seating section is generally steep cliff-like like slopes down which ice and glaciated debris combine and converge from the three or more higher sides.

14 The floor of the cirque ends up bowl shaped as it is the complex convergence zone of combining ice flows from multiple directions and their accompanying rock burdens, hence experiences somewhat greater erosion forces, and is most often scooped out somewhat below the level of cirque's low-side outlet (stage) and its down slope (backstage) valley

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16 Horns Sharp peak that remains after cirques have cut back into a mountain on several sides (fig in text)

17 Tarns a mountain lake or pool formed in a cirque excavated by a glacier Bedrock depressions were infilled by lakes Eg.. Lake Louise in Banff

18 Aretes Frost wedging cuts back the side walls of a valley Sharp ridges called aretes separate adjacent valleys that were carved from glaciers Figure in text

19 Cols A route through a mountain range, or it may go over a ridge Also called a gap or pass

20 U-shaped valleys Glacial troughs have steep bedrock walls and a fairly flat floor Glaciers receded and previously deposited sediment collapses along the steep valley walls End up with a smooth profile in a U shape Found in areas with high elevation and high latitudes Figure

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22 Hanging valleys Different rates of erosion of two valleys Floors of the entering valleys erode at a slower rate than the main valley This means the valleys will have differing depths

23 Gros Morne Hanging Valley

24 Mass Wasting Movement in which bedrock, rock debris, or soil moves down a slope in a mass, because of the pull of gravity Includes movement so slow that you may not notice (creep) as well as landslides (rapid movement)

25 Types of Movement Flow: moving as a fluid Slide: mass is intact, moving along a surface Fall: materials free-falls falls or bounces off a cliff

26 Types of slip Translational: descending mass moves parallel to the slope of the surface Rotational (slump) : movement along a curved surface

27 Water and Mass Wasting When debris is saturated with water, it will be heavier and more likely to move downwards (gravity) Water will also force grains of debris apart But a small amount of water can prevent it as surface tension will cause the grains to adhere to one another (ie( think of building a sand castle with wet versus dry sand)

28 Erosion by Wind Wind can only erode fine sediment such as sand, silt, and clay The faster the wind, the more erosion The desert has stronger winds than humid regions due to temperature fluctuations. This compounded with the lack of vegetation increases erosion in the area

29 During the 1930s, a dust bowl occurred in the Prairies due to a lack of rain and poor soil conservation Wind erosion is worse when soil is disturbed by animals or vehicles Dust storms were so strong that the sun was blacked out, fertile soil was blown away, and rivers and streams were full of dust

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31 Deflation is the term used to describe the removal of clay, silt, and sand particles from the land by wind A blowout is a depression on the land surface caused by wind erosion The public will walk through the sand, increasing erosion and destroying any natural recolonisation, or make their way around the obstruction and so widen the area of impact.

32 Erosion by Waves Coastal erosion can be a big problem in Nova Scotia Rocky shorelines have minor retreat Where the coast has loose sand, gravel, and mud, erosion rates can be up to 12 meters per year! The average is less than one meter per year

33 Can slow the rate of erosion by placement of gravel or large rocks Erosion also a problem along Great Lakes Sand and silt along Scarborough Bluffs (near Toronto) were eroding 1+ meters or more Arctic coasts also have erosion Shore ice protects it from waves, but if there is little sea ice, the shoreline will erode

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35 Soluble rock such as limestone will dissolve when waves hit them Granite can crack from the pressure of the waves hitting the rocks Wave erosion can cause sea cliffs An irregular shore will be straightened over time by erosion (coastal straightening)