Deserts Winds Fluvial and Eolian Processes in Arid
- Slides: 51
Deserts & Winds: Fluvial and Eolian Processes in Arid Zones
Why Do Deserts Exist?
Desert – any spot on Earth that receives less than 25 cm (10 in) rain per year Semi-desert – 25 -50 cm (10 -20 in)
Global Distribution of Arid/Desert and Semi-arid/Steppe Regions
Types of Deserts Subtropical High, Rain-shadow, Coastal, and Interior deserts. Erg – Sea of Sand • Largest are in Sahara and Arabian Deserts • Sand covers about 20% of world’s deserts • Vegetation is rare • Sand probably formed during more humid climate
Namib Desert, Namibia
Death Valley N. P. , California
Hamada – Bedrock predominates
Death Valley N. P. , California
Desert varnish – oxidation of iron and manganese, useful for dating desert surfaces
Arid Landscapes: Basic Concepts I. Most deserts exhibit highly angular landscapes. • mechanical weathering dominates • angular particles of weathered rock; bedrock outcrops with wind erosion • little soil or vegetation to soften landscape II. Softer, more rounded landscapes appear where deposition is predominant. • dunes • alluvial fans III. Desert rainfall is infrequent, intense, and unreliable. • intense flash flooding, intense erosion • ephemeral streams
Joshua Tree N. P. , California
Las Vegas Flash Flood
Wash Arroyo
The Nile River meanders through the Sahara A braided stream near Chinle, Arizona
FLUVIAL LANDFORMS IN ARID REGIONS Fluvial Erosion – sporadic nature of desert runoff (rare, intense flash floods), and lack of vegetation to protect surface materials causes rapid erosion. • Ephemeral stream channels – washes or arroyos (orwadis in the Middle East, and barrancas in Latin America) • Even streams originating in humid regions cannot maintain sufficient discharge and eventually disappear • Steep slopes – steep-walled canyons Mesas and Buttes
Slot Canyon
The Narrows, Zion N. P. , Utah
Differential Erosion
MESA AND SCARP TOPOGRAPHY
Pediments and Inselbergs – eroded bedrock and resistant knobs
Inselberg - “island mountains” rise abruptly out of desert landscapes Uluru (Ayers Rock), Australia
Bornhardt highly resistant rock landform; a type of inselberg. Kata Tjuta (The Olgas), Australia
A Bornhardt in Arches National Park, Utah
The Badlands of South Dakota – Impermeable clays and lack of soil cover produced rapid runoff, and a dense network of barren ridges dissected by a maze of steep, dry gullies and ravines – Badlands topography. Fluvial Transportation – large amounts of rock and sand moved short distances during sporadic flows
Fluvial Deposition – alluvium deposits at the base of mountains or in closed basins – does as much to level the land as does erosion – differentiated from coarse to fine • Alluvial fans Bajada Piedmont Alluvial Plain • Rock debris in piedmont region Debris flow fans • Desert basins of interior drainage – Bolsons Playas Also playa lakes, clay pans, salinas, salt flats (or salt-crust playas )
Piedmont – gently sloping land that extends out from the base of mountains, composed of a series of alluvial fans – (depositional). Pediment – sloping bedrock at base that develops due to gradual retreat of the adjoining mountain slope – (erosional).
Badwater, Death Valley, CA
Bajadas Death Valley N. P. , California
BASIN AND RANGE TOPOGRAPHY
Playas
EOLIAN (WIND) PROCESSES AND LANDFORMS Eolian Erosion - much less effective than fluvial • deflation – picking up and moving small particles of rocks; helps produce deflation hollows and desert pavements • abrasion – like sandblasting effect; polishes and etches exposed surfaces; produces ventifacts and yardangs Eolian Transportation - moves nothing bigger than coarse sand • duststorms - can extend thousands of feet up • sand storms - only very near the surface Eolian Deposition - dunes form and shift where winds and terrain slow the winds or block movement of dunes; loess deposits – wind-deposited silt ← dust storms
Wind Transportation Mechanisms
Dust Storm, Senegal Sand Storm
EOLIAN (WIND) EROSION FEATURES “Desert pavement” of pebbles and stones – result of deflation • all small materials and sand removed by wind • very thin coating of stones
Desert pavements: Also known as: “gibber” in Australia “reg” in North Africa
Wind Erosion Features: An Yardang in the Kharga Depression, Egypt Ventifacts, Yardangs, Pedestal Rocks A sand-blasted rock, or Ventifact, on Mars Pedestal Rocks (Rock Mushrooms) in Utah’s Goblin Valley S. P.
EOLIAN (WIND) DEPOSTION FEATURES Active/Shifting/Migrating Dunes
Types of Dunes BARCHAN TRANSVERSE DUNES LONGITUDINAL DUNES (SEIFS)
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.
Transverse Dunes - parallel waves of crescent dunes perpendicular to wind direction; migrate downwind. Found in areas with large supply of sand.
Seifs – multiple, very long, narrow, parallel dunes. They occur in areas with at least two dominant wind directions. Can be tens of miles long. More common outside the U. S.
Other Types of Dunes Star Dunes
Stabilized Dunes – when plants establish themselves in a dune area
Loess Deposits: Wind-deposited silt, transported by dust storms; vary in thickness from few inches to over 300 feet Gully eroded thick loess in Northern China Unstable loess bluffs in Vicksburg, Mississippi
Major Loess Regions of the World (Most loess deposits are peripheral to deserts and recently glaciated areas)
Finally, Combined effects of Weathering, Mass Wasting + Fluvial and Eolian processes! Delicate Arch, Arches National Park, Utah
- How are ox bow lakes formed
- Global winds and local winds worksheet answers
- Trade winds blow from the
- Westerlies
- Local winds are caused by
- Wind belts
- Morphological analysis of landforms
- Chapter 21 harsh and arid lands
- Concurrent processes are processes that
- Modelado fluvial
- Modelado fluvial
- Modelado fluvial
- Alluvial vs fluvial
- Fluvial process
- What is a fluvial process
- Vale fluvial
- Procesos fluviotorrenciales
- Pez teleosteo fluvial
- Fluvial landforms
- Applied fluvial geomorphology
- Curs calificare marinar fluvial
- Ollem
- Transport routier caractéristiques
- Mapa fluvial de colombia
- Perfil transversal
- Middle course of a river
- Modelado torrencial
- Erosão fluvial
- Curiosidades de las torres de quart
- Iklim humid
- Iklim af
- Hot semi arid grassland
- Temperate grassland climate graph
- Arid region with sparse to almost noneexistent vegetation
- Climograph of savanna
- Arid landforms
- R madarid
- Chapter 7 glaciers deserts and wind
- How are deserts formed
- How were deserts formed
- Biome desert location
- Food deserts in minnesota
- 5 types of deserts
- Wind action in desert
- What causes deserts
- Characteristics of deserts
- Ancient chinas geography
- Fertile
- Mohabbi desert
- Rain shadow deserts
- Great wall of california
- What are deserts