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Geography 12: Unit Four

Geography 12: Unit Four. Erosion and Weathering. Announcements. Upcoming tests December 28 Term Paper January 4 th , 2011 (Questions???). Introduction. erosion and weathering are part of the forces of gradation which do battle with tectonic forces

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Geography 12: Unit Four

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  1. Geography 12: Unit Four Erosion and Weathering

  2. Announcements • Upcoming tests December 28 • Term Paper January 4th, 2011 (Questions???)

  3. Introduction • erosion and weathering are part of the forces of gradation which do battle with tectonic forces • Erosion: Denudation by wind, water, or ice, which dislodges, dissolves or removes surface material • Denudation: any process that wears away or rearanges landforms. • Weathering: either disintegrate rock into mineral particles or dissolve them in water. • Tectonic Forces: Strive to build up rock structures

  4. Tectonic Forces • Strive to build up rock structures

  5. Gradational Forces • strive to bring rock structures to a level or a uniform slope; this can be done in two ways--by tearing down (i.e. degradation or erosion) or filling in (i.e. aggradation or deposition)

  6. Erosion • erosion can be divided into two processes: a) the breaking up of rock masses (i.e. weathering )b) the carrying away of the weathered rock fragments (i.e. transportation )

  7. Cycle of Gradation • Deposition is the geological process by which material is added to a landform or land mass • weathering, transportation, and deposition

  8. Physical Weathering • Page 421-422 of Text • When rock is broken and disintegrated without any chemical alteration. • By, breaking up rock, physical weathering produces more surface area on which chemical weathering can operate

  9. Frost Action • When water freezes, its volume expands as much as 9%. This mechanical force is called frost action • Frost: Expanding..... • Thawing: Contracting • Causes rocks to split apart

  10. Plants and Roots • tree roots, for example, growing down into cracks can exert powerful forces- even mosses and lichens can help to split rocks apart • Lichens:Any of many symbiotic organisms, being associations of fungi and algae

  11. Physical Weathering • Dry Weather draws moisture to the surface of rocks • Water evaporates , dissolved minerals in the water grow crystals • The crystals enlarge and exert a force great enough to break up the rock • P.423 • Salt- Crystal growth

  12. Physical Weathering • - in humid climates, running water tends to round off the surface features causing the "skin" of the rock to peel off- this is also an important form of weathering in desert areas where the daily temperature range can be high • Exfoliation

  13. Key Term • Exfoliation Dome: A dome shaped feature of weathering, produced by the response of granite to the overburden removal process. • See page 424 for image

  14. Physical Weathering • is the breakdown of rock into smaller particles due to such factors as freezing and thawing, release of pressure, water absorption, salt crystal formation, landmass uplift, expansion and contraction from the sun or fire, plant root growth, actions of animals, abrasion, or other means that do not directly affect the rock's chemistry.

  15. Chemical Weathering • the decay of rock through actual chemical change in the composition of its minerals- most common in warm and humid climates where both water and heat speedup chemical reactions

  16. Hydration • occurs especially with rocks containing salt minerals- water is absorbed into the internal structure of the rock causing swelling and making it vulnerable to breakdown due to pressure and potential chemical structure changes- a physio-chemical processeg gypsum results from water being added to anhydrite (CaSO4)

  17. Hydration • It converts feldspar, into clay and silica • Feldspar: a group of rock forming minerals which make up 60% of the earths crust • Silica: Sand

  18. Hydrolysis • hydrolysis- occurs especially with granite- causes rock to whiten (erodes slowly)- creates clay • Breaks down minerals in rocks • Hydration: Water combines with minerals in the rock, the hydrolysis process involves water and elements in chemical reactions to produce different compounds

  19. Oxidation • Certain metallic elements combine with oxygen to form oxides. • creates rusty red rock • occurs especially with rock containing iron nitrate • erodes and forms soil • See Page 426: Pictures A and B

  20. Dissolution of Carbonates • occurs with limestone (easiest to erode)- ground water absorbs carbon dioxide to form a slightly acidic solution- destroys joints (joint: line of weakness in a rock) and bedding planes to form karst topography

  21. Karst Topography • Karst: A word from Slovenia which means “Dissolvable rock” • Topography: the surface shape and features themselves • Page 427-431

  22. Karst Topography • Karst is a distinctive topography in which the landscape is largely shaped by the dissolving action of water on carbonate bedrock (usually limestone or marble).

  23. Formation of Karst • For limestone landscape to develop into karst topography there are several conditions: • Limestone formation must contain 80% or more calcium carbonate • Complex patterns of joints are needed for water to form routes to subsurface driainage channels

  24. Formation of Karst • There must be an aerated(containing air) zone between the ground surface and the water table • Vegetation cover is required

  25. Role of Climate • Karst occurs in Arid areas. • Arid: Lacking moisture, especially having insufficient rainfall to support trees or woody plants

  26. Results of Karst Topography • Sinkholes: Nearly circular depression created by the weathering of karst landscapes with subterranean drainage. Also, known as a doline. • Subterranean: underground structures, both natural and man-made. Ex> Cave

  27. Sinkhole

  28. Sinkholes • A complex landscape in which sinkholes is referred to as cockpit karst.

  29. Mass Movement • Any unit movement of a body of material, propelled and controlled by gravity • Also known As Mass Wasting: the downhill of weathered materials resulting from the pull of gravity.

  30. Common forms of mass wasting • Creep • Flows • Slides • Falls • Planet Earth Text Book: 249

  31. Creep • A persistent gradual mass movement of surface soil is called soil creep • Caused by freeze-thaw cycle • See page 439 of Geo Text

  32. Flows • Solifluction: is used to describe a slow downhill flow of water-saturated rock and soil materials • Solifluction common in cold climates • Ground beneath is permanently frozen • Can cause Avalanches

  33. Slides • The simplest form of slide is called a rock slide • Debris Slides: are caused when loose rock and soil in steeply sloping terrain are shaken loose by an earthquake, river or glacial erosion. Such slides move rapidly downhill • A block of soil that makes a rotational slip along a concave surface is known as a slump.

  34. Falls • High Mountains • Frost Shattering • Thumbling • Rubble known as talus or scree • Talus: Bigger rocks • Scree: smaller debris...Basically the same thing

  35. Class Questions • What evidence of weathering have you seen?

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