1. Arid Landforms: Fluvial and Eolian Processes in Arid Zones

2. Global Distribution of Arid/Desert and Semi-arid/Steppe Regions

3. Types of 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

4. Namib Desert, Namibia

5. Death Valley N.P., California

6. Hamada – Bedrock predominates

7. Death Valley N.P., California

8. Desert varnish – oxidation of iron and manganese, useful for dating desert surfaces

9. 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

10. Joshua Tree N.P., California

12. Las Vegas Flash Flood

13. Wash
Arroyo

14. The Nile River meanders through the Sahara
A braided stream near Chinle, Arizona

15. 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

16. Slot Canyon

17. The Narrows, Zion N.P., Utah

20. Differential Erosion

21. MESA AND SCARP TOPOGRAPHY

23. Pediments and Inselbergs
– eroded bedrock and resistant knobs

24. Uluru (Ayers Rock), Australia
Inselberg - “island mountains”
rise abruptly out of desert landscapes
Inselberg - “island mountains” rise abruptly out of desert landscapes
Uluru (Ayers Rock), Australia

25. Bornhardt
highly resistant rock landform; a type of inselberg.
Kata Tjuta (The Olgas), Australia

26. A Bornhardt in Arches National Park, Utah

27. 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

28. Alluvial fans  Bajada  Piedmont Alluvial Plain
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)

29. Piedmont – gently sloping land that extends out from the base of
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).

30. Badwater, Death Valley, CA

31. Death Valley N.P., California
Bajadas
Death Valley N.P., California

32. BASIN AND RANGE TOPOGRAPHY

33. Playas

34. 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

35. Wind Transportation Mechanisms

36. Dust Storm, Senegal
Sand Storm

37. 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

38. Desert pavements: Also known as: “gibber” in Australia
“reg” in North Africa

39. Wind Erosion Features:
An Yardang in the Kharga
Depression, Egypt
Wind Erosion Features:
Ventifacts,
Yardangs,
Pedestal Rocks
A sand-blasted
rock, or Ventifact,
on Mars
Pedestal Rocks
(Rock Mushrooms)
in Utah’s Goblin Valley S.P.

40. EOLIAN (WIND) DEPOSTION FEATURES
Active/Shifting/Migrating
Dunes

41. LONGITUDINAL DUNES (SEIFS)
Types of Dunes
BARCHAN
TRANSVERSE DUNES
LONGITUDINAL DUNES (SEIFS)

42. 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.

43. Transverse Dunes - parallel waves of crescent dunes perpendicular to wind direction; migrate downwind. Found in areas with large supply of sand.

44. Seifs – multiple, very long, narrow, parallel dunes
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.

45. Other Types of Dunes
Star Dunes

46. Stabilized Dunes – when plants establish themselves in a dune area

47. 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

48. Major Loess Regions of the World (Most loess deposits are peripheral to deserts and recently glaciated areas)

49. Finally,
Combined effects of
Weathering, Mass Wasting + Fluvial and Eolian processes!
Delicate Arch, Arches National Park, Utah