Geology 12

Presents

• Outline:

– Chp 14 Mass Wasting (Landslides)

– Chp 15 Running Water

– Chp 16 Groundwater

– Chp 17 Glaciers and Glaciation

– Chp 18 Wind and Deserts

Chp 18 Wind Sediments

• Erosion by: (because no protective vegetation)

• 1. Abrasion: sandblasting of rocks by sand (mainly quartz)– Ventifact = sandblasted boulder

• 2. Deflation: removal of loose particles by wind– Desert pavement = mosaic of rocks remaining

after deflation

blowout

Desert Pavement

• Suspension: carries silt and clay (think of dust storm)

• Saltation (bouncing): carries sand

• Deposits– Sediments are well sorted by size (like

rivers)• Low energy: clay-silt loess• Med-high energy: sand dunes

– Sediment grains are well rounded, but slight pitting due to impacts

– Mainly quartz • (b/c Ford tough)

• Dunes = large asymmetrical ripples– sand

windward leeward

Dune migration

saltationSlide/roll

Cross bedding

•Much larger and steeper than stream ripples

WIND

• a) barchan dune

• b) parabolic dune

• c) longnitudinal dune

• d) transverse dune

WIND

depression

Barchan

Parabolic

Longnitudinal

Transverse

Star

• 2. Loess = silt and clay– Blown from glacial outwash plains, deserts,

and floodplains to areas where they have been stabilized by vegetation

– From rich top soils of the Ukraine to Germany, China and the northern plains of U.S.

Shanghai loess deposits

Loess deposits

Loess deposits

Loess deposits

Review of Depositional Environments

1. Streams

• strata/beds,

• low angle, smaller, asymmetrical ripples

• Cross beddinga) Near source: semi-sorted and semi-rounded

b) For 95% of streams: sorted and rounded

2. Beaches and wave action

• Sorted and rounded

(mainly sand)

• Strata/beds: low angle, smaller asymmetrical and symmetrical ripples

3. Tidal Pools

• Sorted, fine grained (fine sand to clay)

• Smaller symmetrical ripples or mudcracks

4. Wind: very well sorted and very rounded• Strata/beds: high angle, large (up to 200m)• Asymmetrical ripples & cross-bedding

5. Lakes/Ocean

• Very fine grained (clay -> shale),

• Except graded bedding due to turbidity currents

6. Ice:

• Unsorted and concoidal, & striated (scratched)

Continental rise/end of flood

Shallow angle, small = river

Steep, large = wind

Tidal pool, dry lakeShallow angle, small = river

Steep, large = wind

• Do WS 18.1

• Do Unit 4 Review WS

• Next Unit 5 Planetology (Chp 20)