landforms of mid- and low-latitude deserts Flashcards
types of mechanical weathering
insolation, exfoliation, salt, freeze-thaw
types of chemical weathering
hydration, oxidation, solution
Insolation weathering
high temp ranges (from 80C at day to under freezing at night) cause expansion and contracting rocks causing disintegration
exfoliation or onion skin
as weathering occurs pressure is released from rocks at depth, cracks form parallel to rock surface, capillary action brings salts to surface, salts deposited in cracks and enhanced chemical weathering peel rock from surface
salt weathering
water in joints evaporates leaving salts, crystals grow making pressure
freeze-thaw weathering
heat loss at night makes water in joints freeze and expand, causes gradual rock break up
hydration weathering
absorption of minimal moisture causes rocks to swell and makes them vulnerable
oxidation weathering
oxygen in water reacts with minerals, making them expand, weakening rocks
solution weathering
some minerals dissolve in slightly acidic water and causes rock disintegration
biological weathering
sparse veg in deserts limits this, however trees and shrub root systems can widen joints and dislodge small particles
debris flow (mass movement)
large amount of rock fragments, mud and soil move downslope at speed after heavy rain where veg is sparse
rockfalls and rock slides (mass movement)
resistant rock rests on weaker rock, undercutting at base of slope can be destabilising
aeolian transport processes
creep, saltation (confined under 2m above surface) and suspension
aeolian erosion processes
deflation: removal of fine particles, corrasion: wind blown sand against rocks, attrition: particles carried by wind become smaller and rounder hitting each other
aeolian deposition
as wind energy declines, deposition occurs forming sand seas or ergs in the sahara
wadis
steep sides, wide bottomed, gorge-like valleys, formed by fluvial erosion, rarely filled with water, sediment build up on valley floor, either always dry or ephemeral streams that are fast and result of intense storms
canyons
narrow river valleys with near vertical sides, caused by fluvial erosion, vertical erosion mostly since solid rock walls allow little sideways movement of river channels
zeugen
collective term for pedestal rocks, rock pillars and yardangs. Undercutting where less resistant rock lies under more resistant rock. Created by sand grains in aeolian erosion and moisture in weathering
pedestal rocks
mushroom shaped rocks within zeugen group
yardangs
streamlined parallel ridges of rock, aligned in prevailing wind direction, within zeugen group
ventifacts
rocks on desert surface shaped by abrasion of wind blown sand
desert pavements
fine material is removed and coarse material and pebbles left behind
dune formation
adequate sand supply, strong and frequent wind, and an obstacle to trap the sand. sand accumulates on peak and small avalanche occurs on slip face
barchan dunes
two horns facing downwind, where wind is predominant in one direction, horns move faster than main body, move at 30m/yr, eddying maintains steep slopes on leeward
transverse dunes
form similar to barchans but are right angle to wind have steep and less steep sides, often in ergs and can be huge
linear or seif dunes
straight or slightly curved, can be 100km long, long steep slip faces on alternate sides, parallel to prevailing wind direction
star dunes
slip faces on three or more arms, form where wind is multidirectional, tend to build upwards and can be tallest dunes in the world
alluvial fans and bajadas
where rivers leave steep sided valleys and enter adjacent lowlands, reduction in gradient causes sudden energy loss and so deposition happens. Many alluvial fans in a row makes a bajada
