GEOL 1425 1ST Edition Lecture 23 Outline of Last Lecture I. About winds and deserts,II. Winds as a flow of air,III. Winds as a transport agent,IV. Wind as an agent of erosionOutline of Current Lecture I. Wind as an agent of deposition,II. Types of dunes,III. Where deserts are found,IV. Desertification Current Lecture—Winds and Deserts 2I. Wind as an agent of depositiona. Large area of interest—wind as an agent of deposition creating forms in desert-type lands as wind transport.b. Sand dunes can be very high. To make these there must be a ready supply of sandc. Quarts tend to not weather down and are late forming crystals in igneous rocks. This means many beaches are made from quartz. Beaches and coastlines have lots of sand and wind leading to possibility of deposits d. Ex—Namic (sp?) desert off south coast of Africa—close to coast, dry, on-shore winds are strong and frequently keep sand dunes (or surface layers of dune) in motione. There can be stabilized dunes through vegetation—roots are set down and it provides a wind barrier. There are changes of stabilization in dune areas depending on climate shiftsf. Ripples in dunes change constantly, a fast processII. Types of dunes: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.a. Barchans- leeward behind windward side. Form in fields with unidirectional flow of airb. Blowout dunes- opposite direction of wind from barchans. c. Transverse dunes- cut across the normal wind direction, lack of vegetation, and often behind beaches where there are strong breezes. d. Linear dunes- orientation is almost parallel to wind direction. Can go on for a while. Moderate sand supply with winds always in same general directione. Dropping of sand, thick sequences of sand deposits in specific conditions—we have loess deposits in US and China. III. Where deserts are found:a. Great desert belts—most at 30 degrees N and 30 degrees S, right between prevailing westerlies and tradewinds! But some deserts exist between 30 and 50 degrees both N and S, and in polar regionsIV. Desertificationa. The creation of extensive extending deserts outwards across once what were aridareas. Climate change can lead to different change in rainfall patterns—can go on for long or short periods of time. b. In desert areas there may not all be quarts sand. There may be feldspar sand as wellc. The color or deserts--Red coatings on things from present iron oxides
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