Freeze-thaw
water goes into cracks, expands 10%, widens crack. stress from expansion is
greater than rock resistance. repeats, results in disintegration and scree
production. no. cycles rather than intensity of frost is the main feature. not active
in winters with constant frost. shape and size of produced particles is controlled by
rock nature
scree: angular rock fragments. falls from cliffs, falls down galleys and deposited as
fan/cone shapes. prominent feature of many mountain slopes
Heating and cooling (thermal fracture)
large temp ranges in deserts results in expanding and cooling then disintegration.
granular disintegration: process produced in deserts. rates of expansion and
contraction vary between: different mineral, crystal axes and sizes. different
coloured minerals absorb/emit heat at different rates. pale colour (granite): reflect
more heat than dark colour (basalt). complex stresses set up in rocks, results in
disintegration, produces mineral grains and great sand seas/ergs.
block disintegration: produces rock fragments. results in features of stony deserts
known as reg. scree slopes at cliff foot and boulder fields are produced.
Salt crystal growth
happens when salt solutions in pores/joints of rock crystallises. crystals expand
then force rocks apart. effective in 27-degree places as temp fluctuates so
produces 300% expansion rates
Pressure release (dilatation)
(unloading). affects areas where ground surface is lowered by erosion. removes
weight from previously buried deep rocks. e.g. granite pluton, formed at immense
pressure, several km below earth surface.
removal of weight leads to upper parts expansion of granite & allows cracks to
occur parallel to ground surface, pseudo-bedding planes. similar process –
horizontal pressure released by rock falls, allows vertical crack growth, further rock
fall. significant after glaciation. can be caused by quarrying.