Desert LandscapesDominated by Wind

“We don’t survive the desert, we live here” - Pima Indian

Deserts: where & whyEarth’s dry regions: 30% of all land2 climate types of dry regions:

◦desert (arid)◦steppe (semi-arid, surrounds deserts)

Question: How much rain do deserts get every year?◦Sahara Desert receives as little as 2mm and as

much as 100mm of precipitation per year

Climate Graphs – Semi-arid and Arid

What do you notice about the minimum and maximum temperatures?What do you notice about the amount of precipitation?

Deserts: where & whyWhat causes deserts?Global distribution of

◦ air pressure◦ wind

Relationship between◦ rainfall◦ evaporation

Deserts: where & whyLow-latitude deserts

◦Tropic of Cancer◦Tropic of Capricorn

In contrast….◦ Equator:

hot air rises to 15-20 km low pressure belt

Deserts: where & why

Deserts: where & why

Deserts: where & why

Deserts: where & why

Deserts: where & whyMiddle-latitude deserts (ie. 45°N)

◦exist in rain shadows.

Deserts: where & whyMiddle-latitude deserts

The Great BasinBasin (valley)

and Range (mountains) topography◦ mountainous

desert landscape◦ Nevada, Arizona,

California, Utah◦ Death Valley,

Mojave Desert, Great Salt Lake

Great Salt Lake, Utah

Evaporation > PrecipitationPlaya: ephemeral (not existing all

year long) lake beds that consist of salt and mud flats

Spotted Lake, just outside of Osoyoos, BC

Wind erosion + depositionWind erosion: Important in arid

environmentsExample…Sand dune shape

depends on:◦Flat or hilly?◦How much sand?◦Winds steady or intermittent?◦Wind direction constant?◦Vegetation present?

Wind erosionDesert pavement

Wind erosionDeflation: the process of wind

removing silt and sand-sized particles

Wind erosion + depositionErgs: seas of dunes

Wind erosion + depositionHow sand dunes are formed…

Wind erosion + depositionSand dune formation

Singing Sand Dune Phenomenon

Fog in the Namib Desert???

Wind erosionVentifacts: rocks abraded, pitted,

polished by windblown sand

Wind DepositionLoess from

Aeolian (or Eolian) transportation: ◦ Deposit of wind-

blown silt and clay in angular grains and weakly cemented by calcite

◦ Develop rich, fertile soils

Water ErosionWadi: a dried up river bed that

only has water during rainy season

Town of Wadi Tiwi, Oman

Water ErosionFlash flood retaining basin in Las Vegas, NevadaWhy does the water runoff so quickly?

Water Erosion

Water ErosionHoodoos (or fairy

chimneys): column of soft sedimentary rock often with resistant layer of “cap” rock on top

Water flows through badlands causing further erosion to the spires

Bryce Canyon National Park, Utah

Water ErosionFairy chimneys that people still live inside in Cappadocia, Turkey

Water ErosionAntelope Slot

Canyons, Page, AZ

Flash floods from localized thunderstorms carry sediments that abrade and polish the sandstone

Water Erosion

Mesa: a flat-topped “table” formed by differential erosion of softer rock underneath a layer of “cap” rock

Water ErosionButte: a smaller version of a mesa

Water ErosionPedestal rock:

softer rock erodes quicker than resistant “cap” rock

Water DepositionAlluvial Fan: deposition of sediments as rivers or flash floods leave mountain ranges and spread into the valley

Water DepositionBajada: several adjacent alluvial

fans that have merged together

Living in the Desert