Arid Landforms : Arid Landforms Basic Concepts : Basic Concepts I. Most deserts exhibit highly angular landscapes.
mechanical weathering dominates
angular particles of weathered rock; bedrock outcrops
little soil or vegetation to soften landscape
II. Softer, more rounded landscapes appear where deposition is predominant.
III. Desert rainfall is infrequent, intense, and unreliable.
intense flash flooding, intense erosion
ephemeral streams Slide 5: Death Valley, July 15, 1999 Slide 6: Las Vegas Flash Flood Types of Deserts : Types of Deserts Erg - sea of sand
largest are in Sahara and Arabian Deserts, sand covers about 20% of world’s deserts
sand probably formed during more humid climate Slide 8: Death Valley, California Types of Deserts : Types of Deserts Reg - desert “pavement” of pebbles and stones
all small materials and sand removed by wind
may be very thin coating of stones Slide 10: A gibber plain in Australia Desert pavement Slide 11: Hamada - bedrock predominates Slide 12: Desert varnish - oxidation of iron and manganese, useful for dating desert surfaces DESERT FLUVIAL PROCESSES/LANDFORMS : DESERT FLUVIAL PROCESSES/LANDFORMS Fluvial Erosion - rare, intense flash floods.
steep slopes; steep-walled canyons; washes, wadis, arroyos, canyons.
fluvial systems decrease in discharge downstream
Fluvial Transportation - large amounts of rock and sand moved short distances.
Fluvial Deposition – where water slows on flat playas material is deposited and sorted by size.
rock debris in piedmont region Slide 14: Arroyo Slide 15: Virga Slide 16: Joshua Tree N.P. Slide 17: Slot Canyon Slide 18: The Narrows, Zion N.P., Utah AEOLIAN (WIND) PROCESSES/LANDFORMS : AEOLIAN (WIND) PROCESSES/LANDFORMS Aeolian Erosion - much less effective than fluvial
deflation - the movement of small particles
abrasion - polishes and etches exposed surfaces
Aeolian Transportation - moves nothing bigger than sand
dust storms - can extend thousands of feet up
sand storms - only very near the surface
Aeolian Deposition - dunes form and shift where winds and terrain combine to slow the winds or block the movement of dunes. Slide 21: Dust Storm, Senegal Sand Storm AEOLIAN (WIND) PROCESSES/LANDFORMS : AEOLIAN (WIND) PROCESSES/LANDFORMS Types of Dunes : Types of Dunes BARCHAN TRANSVERSE DUNES SEIFS Types of Dunes : Types of Dunes Barchans - migrating crescent dune with horns pointing downwind; form where strong winds blow in a consistent direction. Move fast. Common in central Asia and Sahara. Can reach hundreds of feet in height. Slide 25: Transverse Dunes - parallel waves of crescent dunes perpendicular to wind direction; migrate downwind. Found in areas with large supply of sand. Slide 26: Seifs - multiple very long narrow, parallel dunes. May be caused in areas with at least two dominant wind directions. Can be tens of miles long. Common outside of U.S. Slide 27: Namib Desert Star Dunes BASIN AND RANGE TOPOGRAPHY : BASIN AND RANGE TOPOGRAPHY Slide 29: Piedmont - gently sloping land that extends out from base of mountains.
Pediment - sloping bedrock at base that develops. Slide 30: Badwater, Death Valley, CA Slide 32: Playas Mesa and Scarp Topography : Mesa and Scarp Topography Slide 34: Differential Erosion Slide 38: Uluru (Ayer’s Rock), Australia Slide 39: Inselberg - “island mountains” rise abruptly out of desert landscapes
Bornhardt - highly resistant rock landform; a type of inselberg. Kata Tjuta (The Olgas), Australia Slide 40: Bornhardt, Arches National Park, Utah Slide 41: Delicate Arch, Arches National Park, Utah