processes and products in hot desert environments

Question 1

wadis

Answer 1

river channels in hot desert regions in which a flow may occur very occasionally

Question 2

what gives wadis very high energy and what does this allow them to do?

Answer 2

their source is in the mountains so they have a steep gradient
intense rainfall
they can transport coarse grained fragments

Question 3

how is energy lost quickly in wadis?

Answer 3

rain stops

water sinks into porous rock of channel

Question 4

what is the sorting of wadis?

Answer 4

poorly sorted as deposition is rapid

Question 5

what is the grain shape of wadis?

Answer 5

sub rounded if transported on several occasions

angular if briefly transported e.g. during a flash flood

Question 6

how do alluvial fan arkose form?

Answer 6

coarse grained sediments deposited near to the mountains become breccias but in the middle part, a fan arkose is formed by sand-sized material, deposited in arid conditions

Question 7

what percentage of feldspar do alluvial fan arkose contain and what is its source?

Answer 7

25% feldspar which shows little sign of weathering, usual source is granitic rock upstream

Question 8

what do high energy winds and attrition do to Aeolian sandstones?

Answer 8

very well sorted
very well rounded
have high sphericity
frosted due to the frequent collisions between grains

Question 9

why are Aeolian sandstones composed entirely of quartz?

Answer 9

other minerals present in the source rock have been removed by mechanical and chemical weathering
quartz remains as its unreactive and hard

Question 10

what are the sedimentary structures formed by Aeolian sandstones?

Answer 10

Show large scale cross bedding because they are deposited in large dunes. Dunes may be crescent shaped barchans dunes or straight seif dunes with crests transverse to the prevailing wind

Question 11

what are the grains coated in and what type of cement do they have? (Aeolian sandstones)

Answer 11

coated in oxidised iron minerals

silica cement

Question 12

evaporites

Answer 12

sedimentary rocks resulting from the evaporation of saline water

Question 13

playa lakes

Answer 13

temporary lakes formed by storm run-off in deserts having inland drainage

Question 14

why do playa lakes tend not to flow all the way to the sea?

Answer 14

hot climate, infrequent rainfall, high rates of evaporation and infiltration

Question 15

what sedimentary structures form in playa lakes?

Answer 15

fine grained sediment is deposited form suspension to form mudstones. these may contain desiccation cracks, ripple marks and salt pseudomorphs, as well as lenses of evaporates, usually gypsum

Question 16

what is the order of precipitation in a playa lake?

Answer 16

1st: calcite
gypsum
anhydrite
halite
k minerals e.g. sylvite

Question 17

what ions are transported by streams into playa lakes and where do they come from.

Answer 17

ions of calcium, sodium and potassium

products of weathering of rock upstream