1. Stuff as it relates to deserts featuring:
The Great basin

2. Deserts and Kinds of Deserts
Deserts compose 1/3 of the Earth’s surface and are characterized by little rainfall, little vegetation, and limited populations of people. Running water, tectonic forces, and wind effects are clearly apparent in shaping these distinct landscapes.
Type
Characteristic Location
Examples
Polar
Region of cold, dry, descending air with little precipitation
Ice-free dry valleys of Antarctica
Subtropical
A belt of dry, descending air at degrees N/S latitude
Sahara, Arabian, Kalahari, Australia’s Great Sandy and Simpson
Mid-Latitude
Deep within continental interior remote from the influence of an ocean
Gobi, Takla Makan, Turkestan
Coastal
Coastal areas in mid latitudes with cold, upwelling ocean current chills the shore
Atacama and Namib
Rain-shadow
Leeward of a mountain barrier that traps moist ocean air
Mojave, Great Basin

3. Deserts of the World
The yellow= sub-tropical, light blue = cold winter, and dark blue represents coastal deserts.

4. Geologic Processes in Deserts
Weathering: Greatly reduced because lack of moisture and scarcity of organic acids from decaying plants
Chemical weathering does happen, produces clays and iron-silicate oxidation reactions giving a rust-color appearance to some desert landscapes
Water: Ephemeral streams (aka: wash, arroyo, wadi, donga, or mullah)
Rainfall is rare so when showers come runoff in the form of floods happen.
Arrive and subside quickly and erosion usually great
Usually no tributaries, water table very far beneath the surface

5. Deserts and Wind Erosion
Deflation: the lifting and removal of loose material
Blowouts: shallow depressions as a result of deflation
Desert Pavement: portion of a desert that consists of closely packed coarse particles (only about 1-2 stones thick)
Control on wind erosion because underneath this layer are significant portions of silt and sand
May be formed in some deserts as wind deflates the finer sediment to expose the coarser particles that make up the pavement OR…
The coarse particles were initially present on the surface and as the wind blows, finer sediments accumulate, settle, and sift down with the aide of water

6. Deserts and wind erosion continues…
Venitfacts: wind shaped stones
As wind erodes by abrasion (like in glaciers and streams) sand can cut and polish exposed rock surfaces
Side exposed to the prevailing wind is abraded, if wind is not consistent, will have abrasions on many sides
Sand doesn’t travel more than a meter above surface
Yardangs: streamlined, wind-sculpted landform that is oriented parallel to the prevailing wind
generally small features about 5-10 meters high, but Peru and Iran have examples meters in height
Deserts and wind erosion continues…

7. Wind Deposits Dunes: which we all know about Loess (Silt)
Surface of some deserts mantled with deposits of windblown silt
Primary sources are from deserts and glacial outwash
Largest deposits occur in western and northern China blown from the desert basins of central Asia, gives the Yellow River its name
The loess in the U.S.= indirect product of glaciation.
As ice sheets retreated, sediments choked the river valleys. As strong winds swept through, the finer sediment was carried and deposited on the eastern sides of these valleys.

8. Other desert features
Alluvial fans: fan-shaped deposits where a stream flattens and fans out.
Often formed on margins of sedimentary basins (found in basin and range province of North America)
Playas: lakebeds formed during more humid times which have long been dry
Alvord Lake in the Great Basin is an example
Desert varnish: dark coating on rocks in arid environments
Rocks no longer subject to precipitation, fracturing or wind abrasion
Primarily composed of clay, Fe, and manganese particles
The racing rock mystery: In Death Valley boulders journey through the desert
Wind and water= slick clay surface for the boulders to race on
bacteria with filaments growing on surface of rock could create a slick surface
The direction of the rocks are moving uphill!
It’s a wilderness area so no radio transmitters allowed…

9. The Great Basin Desert
Largest desert in the U.S. about 190,000 square miles
Bordered by the Sierra Nevada range to the west and the Rockies to the east
The Columbia Plateau borders the northern extension and the Sonoran and Mojave deserts border it in the south

10. Geology of the Great Basin IN ORegon
17-15 mya significant volcanic activity near OR/WA border= lava flows that covered most of present day OR
The Columbia River basalt, the result of the lava flows, is the formation beneath much of the Great Basin in southeastern Oregon
15-2 mya, volcanic activity began again as the crust began to crack= creation of basin and range type landscape.
The last ice age and the melting of the ice sheets filled these basins with water= Pluvial lakes which have since dried up and become remnants or playas (Harney lake, Goose Lake, Lake Abert, Summer Lake, Malheur Lake)

11. Alvord Desert playa Can either be wet or dry depending on the season
Largest playa in Oregon: 6 miles wide and 11 miles long
Many many moons ago a lake 200 feet deep covered the Alvord desert and into Nevada
Old shoreline formed terraces at the edge of the valley
Underneath are the same lava flows that make up the Steens Mountains

12. Steens Mountains
During the Ice Ages glaciers formed in the major stream channels
Cut U-shaped gorges: Kiger, Little Blizten, Big Indian, and Wildhorse
Famous notch on east side of Kiger is a result of a glacier eroding through the ridge top
Internal pressures forced the Steens upward
30 mile long fault-block mountain range
Rugged east face that rises one vertical mile above the Alvord Desert
Largest fault-block mountain in the northern Great Basin

13. The End
Welwitschia mirabilis : sole species in its family. Found in arid desert region of Namibia.
Grows 8-15 cm/yr
2 strap-like leaves that get frayed in the wind
About 200 km inland: fog could be source of precipitation
Oldest possibly years old and leaves can get 6.2 meters long