Lecture 20

Question 1

Air and water

Answer 1

Both are fluids and flow in similar ways.
Wind process are similar to running water.
Wind flows due to air pressure differences (instead of water running downhill from gravity. Near ground, air is slowed by friction.

Question 2

Sediment transport

Answer 2

SEE CHART.

Question 3

Suspension

Answer 3

Sediment stay above surface while traveling (dust).

Question 4

Saltation

Answer 4

Sediment bounces while traveling (smaller sand).

Question 5

Creep

Answer 5

Sediment rolls and slide on surfaces (larger sand).

Think; creeps along ground.

Question 6

Sorting

Answer 6

Different size sediment travels in different ways, so a mix of sizes may get divided by size after deposition.

Question 7

Factors affecting wind erosion

Answer 7

Wind speed.
Vegetation; slows wind near surface, absorbs wind energy.
Soil conditions; grain size, cohesion.

Question 8

Ralph Bagnold

Answer 8

Taught us almost everything we know about Aeolian geomorphology and a lot about sediment transport.
Explored North Africa in army and later researched and experimented sand dunes.

Question 9

Ripples

Answer 9

Small ridges of wind blown sand.

Question 10

Dunes

Answer 10

Hills of wind blown sand.

Question 11

Sand seas

Answer 11

Regional accumulations of windblown sand.

Question 12

Backslope

Answer 12

Upwind side of dune.

Wind compresses and speeds up, also carrying sand.

Question 13

Crest

Answer 13

Highest point of dune.

Question 14

Slipface

Answer 14

Downwind side of dune.

Wind slows down and deposits sand, therefore building up.

Question 15

Angle of repose

Answer 15

Loose material can be stacked only to a certain angle, then it comes unstable and falls.
Sand; 34°, angle of slipface.

Question 16

Transverse dunes

Answer 16

Crest is perpendicular to wind direction; one main wind direction.
Barchan: small amount of sand, crescent shape (horns point downwards).
Transverse ridge: lots of sand, straight crest.
Barchaniod ridge: moderate amount of sand, wavy ridge.

Question 17

Linear (longitudinal) dunes

Answer 17

Two main wind directions from similar directions. Crest parallel to average direction.

Question 18

Star dunes

Answer 18

Complex wind pattern. Peak with radiating arms.

Question 19

Reversing dunes

Answer 19

Wind from opposite directions, like transverse ridge.

Question 20

Parabolic dunes

Answer 20

Stabilized, but part becomes unstable. Grows to U shape with horns pointing upwind.

Question 21

Blowout

Answer 21

Depression formed by erosion following vegetation removal.

Question 22

Loess

Answer 22

Thick deposit of windblown dust.

Most come from glaciated areas, some deserts.