“We don’t survive the desert, we live here” - Pima Indian
Deserts: where & why Earth’s dry regions: 30% of all land 2 climate types of dry regions: ◦ desert (arid) ◦ steppe (semi-arid, surrounds deserts) Question:How much rain do deserts get every year? ◦ Sahara Desert receives as little as 2mm and as much as 100mm of precipitation per year
Climate Graphs – Semi-arid and AridWhat do you notice about the minimum and maximum temperatures?What do you notice about the amount of precipitation?
Deserts: where & why What causes deserts? Global distribution of ◦ air pressure ◦ wind Relationship between ◦ rainfall ◦ evaporation
Deserts: where & why Low-latitude deserts ◦ Tropic of Cancer ◦ Tropic of Capricorn In contrast…. ◦ Equator: hot air rises to 15-20 km low pressure belt
Evaporation > Precipitation Playa: ephemeral (not existing all year long) lake beds that consist of salt and mud flats Spotted Lake, just outside of Osoyoos, BC
Wind erosion + deposition Wind erosion: Important in arid environments Example…Sand dune shape depends on: ◦ Flat or hilly? ◦ How much sand? ◦ Winds steady or intermittent? ◦ Wind direction constant? ◦ Vegetation present?
Wind Deposition Loess from Aeolian (or Eolian) transportation: ◦ Deposit of wind- blown silt and clay in angular grains and weakly cemented by calcite ◦ Develop rich, fertile soils
Water Erosion Wadi: a dried up river bed that only has water during rainy season Town of WadiTiwi, Oman
Water Erosion Hoodoos (or fairy chimneys): column of soft sedimentary rock often with resistant layer of “cap” rock on top Water flows through badlands causing further erosion to theBryce Canyon National Park, Utah spires
Water ErosionFairy chimneys that people still live inside in Cappadocia,Turkey
Water Erosion Antelope Slot Canyons, Page, AZ Flash floods from localized thunderstorms carry sediments that abrade and polish the sandstone
Water ErosionMesa: a flat-topped “table” formed bydifferential erosion of softer rockunderneath a layer of “cap” rock
Water Erosion Butte: a smaller version of a mesa
Water Erosion Pedestal rock: softer rock erodes quicker than resistant “cap” rock
Water DepositionAlluvial Fan: deposition of sediments as rivers or flashfloods leave mountain ranges and spread into thevalley
Water Deposition Bajada: several adjacent alluvial fans that have merged together
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