EES 1030 Lecture 19Outline of Current Lecture I. Distribution of arid landII. Key QuestionsIII. Dry Climate ZoneIV. Types of DesertsV. Desert FloodsVI. Desert RiversVII. Interior Drainage SystemVIII.Early Landscape EvolutionIX. Late Landscape EvolutionX. Wind in the desertXI. Wind TransportXII. Wind ErosionXIII.Sand DunesXIV. Changing Wind DirectionXV. Lithified DunesXVI.Deserts as Climate IndicatorsCurrent Lecture- Distribution of arid landThese 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.o Dry regions (deserts and steppes) cover 30% of Earth’s land surface (roughly 42 million square kilometers).- Key Questionso 1. What is a “dry” climate? o 2. Where are deserts located? o 3. Why do deserts form where they do? o 4. How does erosion occur in desert landscapes? - Dry Climate Zoneo Climatologists define “dry climate” as one in which annual precipitation is less than water loss by evamporationo Desert: Arid, driest of the dry climate zoneso Steppe: Semi-arid, marginal zone borders arid deserts.- Types of Desertso Hot & Dryo Semiarido Coastalo Cold- Desert Floodso Precipitation rare in deserts, usually very heavy raino Sparse vegetation and poorly integrated drainage systems contribute to unhindered runof- Desert Riverso Most permanent rivers crossing deserts originate outside desert often in mountainso Combination of infiltration and evaporation rapidly deplete streams- Interior Drainage Systemo Most arid regions lack permanent tributary systems, with interior drainage and discontinuous, intermittent streams that do not flow to ocean- Early Landscape Evolutiono In arid regions, landscape evolution often driven by block faulting and tectonic uplift of mountainso Running water erodes during and following orogenesiso Alluvial fans form at canyon mouthso Playa lakes (ephemeral lakes) form in flat central area of undrained desert basins- Late Landscape Evolutiono Over tie, ongoing erosion lowers the mountains and fills basins with sedimento Alluvial fans coalescue to form a bajada: an apron of sediment along a mountain fronto Eroded mountains may form inselbergs: isolated mountain remnants- Wind in the Deserto Although most desert erosion results from running water, wind also works to erode, transport, and deposit sedimentso Key Diferences between running water and moving airo Wind is less capable than water of picking up and transporting coarse particleso Wind is not confined to channels and can spread sediment over a large area- Wind Transporto Suspended Load: fine particles transported within the airo Saltation: transport of particles through series of bounceso Bedload: particles moved along the ground surfaceo As wind velocity increases, it can transport larger sedimentary particles by saltation and suspensiono Wind transportation can result in dust and sand stormso In a sandstorm, about 20-25% of sand is moved by saltation- Wind Erosiono Deflation: Wind lifts fine, loses sediment from desert floor, leaves behind larger grainso Wind erodes by abrasion friction and impact of particles on rock surfaceso Physical weathering: limited in vertical extento Wind produces distinctive depositional landforms in desertso Loess forms where windblown silt accumulates, blown in from deserts or glacial outwash deposits- Sand Duneso Dune: hill or ridge of wind-deposited sando Dunes form where wind speed slowso Dune shape reflects multiple factorso Most dunes have an asymmetrical profile, with a steep leeward slope and a gently inclined windward sideo Initially, bed load accumulates in wind shadowo Sand moves up windward slope by saltation accumulating at the cresto When leeward side of dune becomes steeper than angle of repose of sand, crest collapses down slip faceo Sand deposited on slip face forms layers slanted in direction of wind: cross bedso Saltation and deposition results in slow migration of dune in direction of wind- Changing wind directiono Changes in the prevailing wind direction are recorded by changes in layers of cross beds- Lithified Duneso Dunes can be lithified, buried under layers of sediment and turned to sandstone:cross bedding is often prominent- Deserts as Climate Indicatorso Dunes and cross bedding in sandstones indicate an arid paleoclimate at time of deposition- Types of Duneso Longitudinalo Barchan o Transverseo