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Chapter 4: Weathering, Erosion and Landscapes

Chapter 4: Weathering, Erosion and Landscapes. Why do Rocks Weather?. When rocks are exposed to different environments, they begin to break down.

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Chapter 4: Weathering, Erosion and Landscapes

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  1. Chapter 4: Weathering, Erosion and Landscapes

  2. Why do Rocks Weather? • When rocks are exposed to different environments, they begin to break down. • Physical weathering is when the size and/or shape of the rock changes due to forces upon it. For example: tree roots, frost action/ice wedging, abrasion, • Chemical weathering is when a chemical change results in different rock or mineral composition. For example: rusting/oxidation of iron or feldspar turns to clay. • Chemical weathering is fastest in warm, moist climates!

  3. How do Soils Form? • Soil is produced by weathering of rocks and biological activity. • Eventually, there will be several different soil horizons. The top layer will be the “top soil” – the one with the most organic (humus) material. • Protecting the soil is important! Decrease erosion, keep plants in place. Be careful about over-using road salts and other poisonous materials.

  4. How are Weathered Materials Transported? • Broken rocks (sediments) are moved by forces of erosion. These forces include gravity, water, wind and ice. • Gravity: mass movement/mass wasting –materials slide down due to gravity alone. Rocks are all jumbled, broken and angular. • Water: running water is our most important form of erosion in moist areas – like NY! Materials are carried by rolling along the river bed, suspension in the water, dissolved in solution or flotation.

  5. More about water erosion… • Stream velocity: The faster water flows, the larger particles it can carry. See p. 6 in the ESRTs. • When a stream meanders, the faster water is on the OUTSIDE curve. The slower water is the inside. • The fastest water flow is just below the surface in a straight part of a river.

  6. Wind erosion… • Smaller particles only. • Wind erosion picks up loose materials – where it is dry and there isn’t much plant cover.

  7. Erosion by ice…. • Glaciers are powerful enough to move ALL materials! • Moving large boulders over lower bedrock can leave scratches (striations). • U-shaped valleys are left by glaciers. • Unsorted, unconsolidated sediments are left when a glacier suddenly melts. • If meltwater runs over the sediments, they may become sorted.

  8. Characteristic Changes Caused by Agents of Erosion: • Gravity: angular – not enough time to smooth down. Piles at the bottom of hills. • Running water: smooth and round – especially when the water carries the rock along the bottom (abrading the rock) for a long time. • Wind: ventifacts are triangular…may have pits from being sand-blasted. Only small particles can be moved! May form sand dunes. • Glaciers: striations, unsorted, loose. May have LARGE boulders alone in a field.

  9. What is Deposition? • Sediments will eventually stop moving. • Deposits can show characteristics that give clues to how they were moved to their new location: • Gravity: angular, unsorted talus piles. • Water: smooth, rounded. May form deltas (if particles are small, like silt or clay!) • Wind: small, piles, sand dunes that move with the wind. • Ice (glaciers): unsorted, unconsolidated, scratched..

  10. Sorting of Sediments: • Horizontal and vertical sorting happens when the erosional force slows or sediments fall down through water. • No sorting with gravity and moving ice. • Sorting will occur with running water and wind….and with meltwater off of glaciers. • The LARGEST, ROUNDEST and DENSEST will be deposited first.

  11. New York and Ice Ages: • As recently as 20,000 years ago we were covered in ice. (see the ESRTs pages 8 and 9) • See p. 94 and 95 in the review bk. For maps. • Some features: U-valleys, polished bedrock, grooves or striations (from sediments dragged by the ice), drumlins moraines, kettles.

  12. Oceans and Coastal Processes: • Ocean info can be found in the ESRTs. • Also, illustrations are on p.98 and 99 in the review book! • Saving our shorelines from erosion is extremely important see p. 98-100 in the review book for examples!

  13. What is a Landscape? • Topographic relief (plain, plateau or mountains) defines a landscape. • See p. 2 in the ESRTs for the Landscape Regions of New York. • Climate plays a role in landscape development. The arid areas have steeper slopes and sharper angles because there is little weathering and very little soil development! Therefore, there is very little plant growth.

  14. Geologic Factors and Landscapes: • Resistance to weathering determines whether a rock will be easily worn down or not. The resistant rock is NOT worn down as much and will therefore stick up more. It will stick out at the sides of cliffs (escarpments) or be at the tops of mountains. • Softer rocks are more easily worn away and become the bottoms of valleys.

  15. Landscape = Drainage Patterns: • The way the land slopes and the presence of low spots determines where the rivers and their tributaries will flow. • Figure 4-7 on p. 104 in the review book shows some of these patterns. • See the landscapes of NY map on p. 2 in the ESRTs and compare it to the Bedrock map on p. 3 in the ESRTs.

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