GEOG 1114 1stEdition Lecture 27 Outline of Last Lecture Landforms Wind erosion Requirement for wind erosion Aeolian Landforms Rock Arches Outline of Current Lecture Deserts Mechanical weathering Desert landforms Desertification Differential Weathering Current Lecture Deserts Specialized environment reflecting the interrelationships between a variety of factors Mechanical weathering Thin soil thin or absent exposing bedrock Abundance of sand allows water to infiltrate transport and shape the sands PPTN can be brief but intense flash floods DESERT STREAMS CHANNELS EPHEMERAL INTERMITTENET STREAM BEDS Wind shifts sands These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Landforms Ergs seas of sand large area covered with and in dune formation from wind Sahara Namibia Arabian deserts Reg Stony desert Erg Sea of sand Reg Surface covered with coarse gravel pebbles or boulders Desertification Expanding of desert conditions due to land degradation and water removal human activity Climate Change Prevalent in Africa Middle East Australia Chile and Peru India Mexico Estimates of 8 100 square miles are decertified each year Affects on human population growth and agricultural Landforms of Differential Weathering Differential Weathering of Sedimentary Rocks Types Shale Mechanically weak easily fragmented into thin flakes Chemically weathers into impermeable clay soils easily cut by stream channels Most erodible of all rock types Evolves into lowlands dissected slopes at the base if high hills or found in valley floor where it s carried away as bed load Sandstone Either weak or strong depending on the type of material Typically hard in semi arid environments Often porous permitting water to soak into it and reduces run off Erodes slowly Frequently forms ledges or cliffs or hills rising above areas of shale of limestone Landforms of Differential Weathering of Sedimentary Rocks Pinnacles columnar Buttes Small surface areas and cliffs that rise above surroundings Mesas Larger flattop landforms associated with horizontal strata resistant sandstone form cap rock Plateaus larger then mesas Cuesta Spanish slope Ridge formed by gently dipping sedimentary rock Have a steep slope where rock is exposed Exposed rock is resistant to erosion Hogback ridges Steeply tilted strata of rock protruding from the surrounding area Name comes from the ridge resembling the high knobby spine between the shoulders of a hog The two strata that compose a hogback are different types of sedimentary rock with differing weathering rates Badlands barren terrain of easily eroded rock eroded by fluvial processes Overland flows from occasional rains develop tiny rills that expand into ravines or gullies Characterized by maze of ravines and gullies lifeless and nearly impassable Mesa scarp terrain Associated with horizontal strata Variable resistance to erosion in strata Plateaus and stripped plains Weathering of Limestone in Semi Arid environments Little water available to dissolve limestone Limestone acts as resistant rock forming cuesta mesas and hogbacks Can also outcrop and be very resistant to erosion
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