14_climate_wind_post - 14: Surface Processes 1-Climate,...

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Unformatted text preview: 14: Surface Processes 1-Climate, Deserts and Wind Why this is important • Earth’s external heat engine is one of two heat engines that power geologic processes. Sand dunes, Namib desert, Namibia. Photo: R. Swart 101/2005/Lecture 1: 1 Climate & Deserts: 1 Why this is important • Winds can transport fine-grained materials far distances. 3 2 Why this is important • Winds are capable of severe soil erosion in arid or semi-arid lands, especially during prolonged droughts. 101/2005/Lecture 1: 4 Climate & Deserts: 4 Why this is important • Fertile soils in the Midwest are deposits of fine silt transported by winds from the edge of ice sheets. 101/2005/Lecture 1: 5 Climate & Deserts: 5 Heat engines Internal heat engine: heat transfer from hot interior to cold exterior results in plate movement, earthquakes, volcanic activity, and mountain-building Heat engines Just like heat from the burning of gas in an automobile engine drives a car, heat from Earth’s two heat engines drives geological processes. 101/2005/Lecture 1: 6 Climate & Deserts: 6 External heat engine • Source of heat: Sun Fig. 1.13 101/2005/Lecture 1: 7 Climate & Deserts: 7 101/2005/Lecture 1: 8 Climate & Deserts: 8 External heat engine External heat engine • Sun’s energy: falls unevenly on Earth’s surface Fig. 20.10 • Sun’s energy: falls unevenly on Earth’s surface Diffuse Concentrated Diffuse Fig. 20.33 101/2005/Lecture 1: 9 101/2005/Lecture 1: 10 Climate & Deserts: 9 Climate & Deserts: 10 External heat engine / iClicker External heat engine Q1. Rising currents of air occur at or near latitude: A. 0° and 30° B. 0° and 60° C. 30° and 60° D. 30° and 90° E. 60° and 90° • Heat transfer --> currents of air, currents water, & ice transfer heat from equator to poles 30° • Effects of heat transfer: currents produce erosion, transportation, deposition Fig. 20.11 101/2005/Lecture 1: 11 Climate & Deserts: 11 60° 0° 30° Fig. 20.11 101/2005/Lecture 1: 12 Climate & Deserts: 12 External heat engine External heat engine • Heat transfer --> currents of air, water, & ice transfer heat from equator to poles • Hydrologic cycle: day-to-day & long-term changes that occur within the hydrosphere driven by external heat engine Fig. 18.10 Plate, p. 552 101/2005/Lecture 1: 13 Climate & Deserts: 13 101/2005/Lecture 1: 14 Climate & Deserts: 14 Review Questions Deserts / iClicker 14-1. A. True / B. False: Moving currents of air and water result because the sun's heat energy falls more intensely at the Earth’s equator. Q2. A desert is a region that is: A. hot B. dry C. hot and dry 14-2. A. True / B. False: Winds are part of the global atmospheric circulation system because the Earth is warmer at the equator than the poles. 14-3. As an air mass rises, it generally experiences ____________. A. an increase in temperature B. a decrease in temperature C. no change in temperature 14-4. In global circulation, air rises at the ____________. A. equator (0°) and poles (90°) B. equator (0°) and polar fronts (60°) C. horse latitudes (30°) and poles (90°) D. horse latitudes (30°) and polar fronts (60°) 14-5. In global circulation, air sinks at the ____________. A. equator (0°) and poles (90°) B. equator (0°) and polar fronts (60°) C. horse latitudes (30°) and poles (90°) D. horse latitudes (30°) and polar fronts (60°) 101/2005/Lecture 1: 15 Climate & Deserts: 15 101/2005/Lecture 1: 16 Climate & Deserts: 16 White Sands National Monument, New Mexico. Photo: P. L. Kresan White Deserts Locations of deserts • Desert: region with <25 cm of rain per year that is too dry to support much vegetation (covers <15% of surface) • ~30°N and 30°S --> descending dry air masses heat up and lose even more moisture Sinking air heats up; soaks up any moisture Focused heating produces rising air; as it cools, its ability to hold moisture decreases, causing rain to fall Fig. 21.4 101/2005/Lecture 1: 17 Climate & Deserts: 17 White Sands National Monument, New Mexico. Photo: P. L. Kresan White Locations of deserts 101/2005/Lecture 1: 18 Climate & Deserts: 18 Locations of deserts • Continental interiors --> little moisture far from oceans • Mountains: rain shadows on down-wind side Fig. 21.5 Death Valley, California. Photo: D. Muench 101/2005/Lecture 1: 19 Climate & Deserts: 19 101/2005/Lecture 1: 20 Climate & Deserts: 20 Locations of deserts • Adjacent to cold ocean currents: cold air holds little moisture Nazca lines Coastal Desert Region, Peru Photos: R.W. Schlische Fig. 21.6 Puerta Inca 101/2005/Lecture 1: 21 101/2005/Lecture 1: 22 Climate & Deserts: 21 Climate & Deserts: 22 Locations of deserts • Polar regions: cold air holds little moisture Macu Piccu Windward side of Andes Mountains Photos: R.W. Schlische 101/2005/Lecture 1: 23 Climate & Deserts: 23 Fig. 21.3 Macu Piccu 101/2005/Lecture 1: 24 Climate & Deserts: 24 Deserts: weathering, erosion Deserts: weathering, erosion Fig. 21.20 Fig. 21.17 Differential weathering: sandstone, limestone, and thickbedded layers form steep slopes in deserts; shale and thin-bedded layers form gentle slopes Mechanical weathering predominates over chemical weathering because of lack of moisture. 101/2005/Lecture 1: 25 Climate & Deserts: 25 101/2005/Lecture 1: 26 Climate & Deserts: 26 Deserts: weathering, erosion Deserts: weathering, erosion • Streams are mostly dry except during flash floods except Fig. 21.20 • Mostly gentle slopes • Thick soil & vegetation cover • Streams flow year-round • Steep and gentle slopes • Little soil & vegetation cover • Streams flow only after T-storms 101/2005/Lecture 1: 27 Climate & Deserts: 27 Plate, p. 671 101/2005/Lecture 1: 28 Climate & Deserts: 28 Deserts: weathering, erosion Deserts: weathering, erosion • Spectacular scenery results from differential weathering and sparse vegetation Fig. 21.20 Most erosion occurs during flash floods (caused by thunderstorms). 101/2005/Lecture 1: 29 Flash flood in Saguaro National Monument, Arizona. Photo: P. Kresan Climate & Deserts: 29 101/2005/Lecture 1: 30 Climate & Deserts: 30 Monument Valley, Arizona. Photo: S. Marshak Review Questions Review Questions 14-6. To qualify as a desert, a region must be ____________. A. hot, with a mean annual temperature greater than 25°C (77°F) B. arid, with less than 15% of the ground surface vegetated C. both hot and arid D. either hot or arid 14-9. Deserts in coastal regions are most likely to be found where the ocean currents are ____________. A. warm B. cold C. headed toward the east D. headed toward the west 14-7. At 30° north latitude, at the northern edge of tropical cell convection in the Northern Hemisphere, ____________. A. cool, dry air sinks and becomes drier as it heats up B. warm, moist air rises, increasing in relative humidity as it rises C. warm, dry air rises, becoming cooler D. cool moist air sinks, providing abundant rainfall 14-8. Desert climate associated with a rain shadow is found ____________. A. on the windward (upwind) side of mountain ranges B. on the leeward (downwind) side of mountain ranges C. in the middle of flat plains D. along continental coastlines 101/2005/Lecture 1: 31 Climate & Deserts: 31 14-10. As compared to humid (temperate) climates, rates of chemical weathering in deserts are ____________. A. much faster B. much slower C. very similar 14-11. A. True / B. False: Spectacular desert scenery is a result of intense chemical weathering and sparse vegetation. 14-12. Deserts are generally found in which of the following areas? A. in belts located around the equator B. on the up-wind sides of mountain ranges C. in polar regions D. adjacent to warm ocean currents 101/2005/Lecture 1: 32 Climate & Deserts: 32 Wind effectiveness Wind effectiveness Extreme daily fluctuations in temperature cause strong winds. • Low moisture causes low soil cohesion. • Sparse vegetation does not bind loose material. Badlands National Park, South Dakota. Owens Lake, CA. Photo: W. Clay Photo: M. Miller 101/2005/Lecture 1: 33 101/2005/Lecture 1: 34 Climate & Deserts: 33 Climate & Deserts: 34 Wind erosion & transport Wind erosion & transport • Fine particles: suspension • Desert pavement: accumulation of coarse particles left behind when finer material is removed by wind transport • Coarser particles: rolling & bouncing (saltation) Fig. 21.10 Fig. 21.11 101/2005/Lecture 1: 35 Climate & Deserts: 35 101/2005/Lecture 1: 36 Climate & Deserts: 36 Wind deposition Wind erosion & transport • Sand dunes: deposit of sand produced when wind loses velocity Desert pavement in Sonoran Desert, AZ. Photos: P.L. Kresan (L) & D. Muench Fig. 21.12 101/2005/Lecture 1: 38 Coastal 101/2005/Lecture 1: 37 Climate & Deserts: 37 Climate & Deserts: 38 dunes at Sandwich Harbor, Namib Desert, Namibia, Africa. Photo: E. T. Nichols Wind deposition / iClicker Wind deposition Sand accumulates around obstacles that locally slow wind velocity Q3. For the dune containing cross bedding shown in side view below, the wind was blowing: A. from right to left B. from left to right C. from right to left and from left to right Cross beds Fig. 21.23 39 101/2005/Lecture 1: 40 Climate & Deserts: 40 Wind deposition Wind deposition • Dunes migrate: downwind • Dunes migrate: downwind • Gentle upwind side: erosion • Gentle upwind side: erosion • Steeper downwind side: deposition • Steeper downwind side: deposition • Cross beds form by: dune migration • Cross beds form by: dune migration Fig. 21.26a Side views 101/2005/Lecture 1: 41 101/2005/Lecture 1: 42 Climate & Deserts: 41 Climate & Deserts: 42 Wind deposition Wind deposition • Loess: thick accumulations of windblown silt and clay. • Most loess derived from deserts & edges of ice sheets • Forms excellent soils Loess deposits in central China. Photo: S.C. Porter 101/2005/Lecture 1: 43 Climate & Deserts: 43 Glacial outwash plain, Alaska. Photo: G.M. Ashley 101/2005/Lecture 1: 44 Climate & Deserts: 44 Wind deposition / iClicker Wind deposition Q4. Which diagram illustrates sediment with the best sorting (uniformity of grain size)? A B C D • Sorting: excellent; coarse material left behind; fine material transported & deposited. E Photos: E. McKee (L) & D. Muench 101/2005/Lecture 1: 45 Climate & Deserts: 45 Review Questions 14-13. Saltation of sand involves ____________. A. grains hopping into the air, traveling a short distance, and returning to the ground B. grains being carried long distances (10’s of kilometers) by strong gusts of wind C. the mixture of sand with salt, which forms from the evaporation of rainwater 14-14. A. True / B. False: Sediments deposited by the wind (e.g., sand dunes) tend to be relatively coarse grained. 14-15. The accumulation of coarse particles left behind when finer-grained material is removed by wind transport is called ___. A. a dune B. a cross bed C. desert pavement 14-16. A. True / B. False: Cross beds are inclined in the up-wind direction. 14-17. A. True / B. False: Wind deposits are very well sorted because the wind is capable of transporting only fine-grained sediments. 14-18. Which of the following statements concerning sand dunes is not correct? A. Dunes migrate downwind. B. Dunes contain cross beds. C. Dunes have steep upwind sides and gentle downwind sides. 101/2005/Lecture 1: 47 Climate & Deserts: 47 101/2005/Lecture 1: 46 Climate & Deserts: 46 ...
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