105_15-deserts_part_1 - Deserts and Wind Action What’s...

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Unformatted text preview: Deserts and Wind Action What’s the grading plan? Exams Exams (best 3 of 4 @ 100 pts each) Quizzes Quizzes (10 @ 10 pts each) Comprehensive Comprehensive final (100 pts) Total Total points +Bonus +Bonus points (25 pts) 300 pts 100 pts 100 pts 500 pts 25 pts Chapter 15 *Remember that Moodle gradebook includes all grades, including dropped exam! How many points do I need for an A? Final Final grade: The determination of the final grade is The based on the following scale: 450 450 - 500 = A 400 400 - 449 = B 350 350 - 399 = C 300 300 - 349 = D below below 300 = F >90% >80% >70% >60% <60% What about the final? •Comprehensive •Mandatory •Study guide *Remember that Moodle gradebook includes all grades, including dropped exam! Desert Distribution Most Most deserts are located where air currents sink towards the Earth and retain their moisture. Best Best known deserts are located at 30° N 30° & S of the Equator Desert Distribution 1 Desert Distribution Not Not all deserts form near 30° latitudes 30° RainRain-shadow deserts – air crossing a mountain range rises, cools and drops its moisture. Desert Characteristics Dry Dry – less than 25 cm/year rainfall – rare cloudbursts and flash floods Hot Hot – mostly hot, but very cold winter nights – cold climate deserts in the polar regions Desert Characteristics Vegetation Vegetation – may be very sparse . . . – . . . or specialized to need little water Desert vegetation Desert Characteristics Rocky Rocky or sandy 2 Desert Characteristics Lack throughLack through-flowing streams – Most streams are intermittent – Drainage runs towards interior landlocked basins instead of to the sea Desert Landforms Plateaus Plateaus – Broad, flat topped areas elevated above the surrounding land and bounded by cliffs – Formed by flat layers of rock highly resistant to weathering Limited Limited rainfall occurs in violent storms – High volume of rain in a short time – High runoff causes flash floods flash – Sparse vegetation can’t hold sediment, causing mudflows Desert Landforms Mesas Mesas – Broad, flat-topped hill bounded by cliffs. flat– Small remnants of plateaus Desert Landforms plateau mesa butte Buttes Buttes – Narrow hill of resistant rock – Flat topped, steep sided – Formed by continued erosion of mesas Desert Landforms mesa plateau 3 Desert Landforms Playa Playa lakes – shallow, temporary lakes playa lake evaporates – and salt pans – salts left on desert floor after Vamos a jugar por la playa! -The Pixies Desert Landforms alluvial fans – and bajadas Alluvial fan Bajada: several combined alluvial fans Pediment: Nevada Desert Landforms pediments - erosional bedrock surfaces along a mountain front - covered by thin layer of debris - gently sloping surface 4 Work of Wind deserts deserts coastal coastal dunes near near glaciated areas anywhere anywhere where vegetation does not stabilize surface sediments Work of Wind MOST MOST TRANSPORT IN DESERTS IS BY RUNNING WATER !!! Desert Desert rainstorms are infrequent but can cause flash floods. Wind Transport bed bed load – saltation and creep Wind Transport suspended suspended load – silt and clay dust dust storms long long distance transport glacial glacial loess 5 Wind Erosion Abrasion Abrasion – sand-blasting sandVentifacts: sandVentifacts: sand-blasted stones with flat surfaces Wind Erosion Deflation Deflation – blowing away of loose sand creates creates depressions (blowouts) Depression caused by wind Desert pavement Wind Erosion Deflation Deflation – blowing away of loose sand may may leave surface layer of pebbles (desert pavement) 6 ...
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This note was uploaded on 05/18/2011 for the course GEOL 105 taught by Professor Jack during the Spring '08 term at University of Louisiana at Lafayette.

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