the sahara

Question 1

what are ergs?

Answer 1

seas of sand, making up around 20% of the sahara. mostly in the northern sahara. a dune field

Question 2

what are regs?

Answer 2

stony desert plains, making up around 70% of the desert

Question 3

what are hamadas?

Answer 3

elevated rocky plateaus

Question 4

describe physical weathering and the sahara

Answer 4

breaks rocks intomsmaller debris. debris forms sediment grains.
weathering, erosion, transportatio, deposition, lithification

Question 5

describe transport and the sahara

Answer 5

once eroded, sediment grains may be transported by water, ice and wind
grains become smaller and rounded during transport

Question 6

how can you descibe sediment grains?

Answer 6

roundness - angular, subangular, subrounded, rounded, well rounded
grain size - the Wentworth Scale

Question 7

describe the classifications in the wentworth scale

Answer 7

gravel - sediment more than 2mm in diameter
> conglomerate = rounded pebbles
> breccia = angualr pebbles
sand - sediment 63 micros to 2 mm
slit - 4 to 63 micros, form siltstones
clays - less than 4 micros, forms claystones

Question 8

descibe saharan sand

Answer 8

fine to medium sand grains
very well sorted
colourless to reddish brown (iron)
texture = frosted
rounded grains
high sphericity
windblown in a hot arid environment

Question 9

what are aeolian landforms?

Answer 9

ripples that form with ridge crests and right angles to the prevailing wind
dunes tend to form either as free dunes (enlarged ripples or as impended dunes

Question 10

what are sand dunes and what are the different types of dunes?

Answer 10

windblown accumulation of sand
brachan, star, transverse, parabolic and longitudinal

Question 11

what is desert pavement?

Answer 11

a deflation mechanism, forming a hamada

Question 12

describe the mechanism of desert pavement

Answer 12

air is less dense than water, so a very strong wind is required to transport sand sized grains. usually coarser grains are left behind.

Question 13

describe porosity

Answer 13

water can be stored in 2 places in a layer of rock
1. pore space - the space between induvidual sediment particles that can fill with water ans store it
2. fractures/ cracks - water stores in cracks
different rock types have different porosity
can be expressed as a number
porosity = volume of voids/ total volume

Question 14

descibe permeability

Answer 14

how easily a fluid can pass through a material
low = hard for a fluid to move through
connections between pore spaces and fractures help to increase permeability
mud and clays help to decrease permeability as the gaps between them are very small
a well sorted sediment has a higher permeability

Question 15

what is an aquifer?

Answer 15

a geological unit of rock or sediment that can store and transmit water

Question 16

what is a confining layer?

Answer 16

a geological unit that does not allow water to move through it quickly

Question 17

what are the 3 different types of aquifers?

Answer 17

1. unconfined aquifer - above the water table, pore spaces are filled with water (saturated zone)
2. confined aquifer - has a confining layer e.g. clay which prevents the movement of water. has a recharge are where water enters the aquifer
3. perched aquifer - above the water table, has springs connecting

Question 18

describe the water table

Answer 18

loosely follows the topography, generally as a subdued image of the surface. Is close to the ground in valleys, where rivers and streams often form
can change over time e.g. between the beginning and end of the rainy season

Question 19

how does water move?

Answer 19

from points of high pressure to points of low pressure
in a typical aquifer, groundwater moves 5 - 30 cm a day

Question 20

describe groundwater abstraction

Answer 20

during pumping, a cone of depression is formed around the well, lowering the water table
where abstraction id greater than the recharge of water, groundwater id depleted

Question 21

what are some probelms of groundwater abstraction?

Answer 21

• wells can stop being functional
• reduced surface water supplies
• land subsidence - surface of the land is lowered
• water quality (saline intrusion) - saltwater invading freshwater aquifers