Geomorphology - Desert Dune Processes

Front 1

Cards by adac - please rate and favorite.

Sourced mainly from Thomas D. S. G., 2011, Arid Zone Geomorphology: Process, Form and Change in Drylands - Chapter 19 (written by Nick Lancaster).

I recommend studying my cards in order, at least for the first few tries.

Back 1

My cards are designed so you describe the subject, rather than naming something after seeing the description. My method will better prepare you for short answer and essay questions.

Front 2

Name as many types of dunes as you can think of.
(We will focus mainly on two types)

Back 2

Two types we will focus on:
- Crescentic
- Linear

Others:
- Star
- Parabolic
- Zibars and sand sheets
(Refer to text books for more information on these)

Front 3

Dune type: Crescentic dunes

- Wind regime (direction)
- Describe their morphology

Back 3

- Unidirectional wind regime
- Crests aligned normal to the direction of sand transport. Typically elliptical in shape with a concave lee face and horns extending downwind.

Front 4

Isolated crescentic dunes form under what conditions? What is another name for these dunes?

Back 4

Isolated crescentic dunes form in undersaturated sand transport conditions (sand supply low relative to wind capacity to transport sand).

Also known as barchans.

Front 5

How do crescentic mega dunes form?

Back 5

Mega dunes form from the super-imposition of smaller crescentic dunes on their stoss slopes (windward slopes).

Front 6

Name the broad varieties of linear dunes.

Back 6

Simple, compound and complex.
The latter two occur as mega dunes.

Front 7

Identify two simple linear dune types.

Back 7

- Sinuous; relatively short dunes (aka seif dunes)
- Longer, straight, vegetated dunes (common in Australia)

Front 8

Describe compound linear dunes.

Back 8

Consist of several narrow, closely spaced, seif-like ridges on the crest of broad linear plinths which are spaced as much as 2.5km apart.

Front 9

Describe complex linear dunes

Back 9

Comprised of relatively straight, continuous, linear ridges on which other dunes super impose.

Front 10

What wind regime do linear dunes form in?
(Currently a debatable issue)

Back 10

Generally accepted to be bidirectional wind regimes with the two modes separated by 90 degrees or more.

Front 11

How do linear dunes extend in relation to wind?

Eg. Perpendicular? Parallel? Downwind? Upwind?

Back 11

Tend to extend downwind but may also migrate laterally since sand transport by bimodal winds is rarely equal.

Some linear dunes form parallel to the dominant wind direction - this occurs mainly where vegetation partially stabilizes the sand or topographic obstacles anchor the sand in place.

Front 12

Controls of dune morphology.

Name the main determinant of dune morphology.
What are some subordinate controls?

Back 12

Dominant control: Directional variability of wind regime.
Subordinate controls: Wind speed, grain size and vegetation.