Page 94 - Fundamentals of Geomorphology

GEOMORPHIC MATERIALS AND PROCESSES 77

b
a
() ()
Sediment gain
Steady
Vertical accretion
state Vertical
accretion
Lateral erosion
100 years 100 years
Vertical High banks
(Lateral erosion = lateral accretion)
erosion less accessible
Sediment loss
d
c
() () Mass movements
or small fluvial events

Colluvium, vertical accretion
100 years 100 years

Flushing

Figure 3.13 Four common patterns of valley sediment storage and flux under natural conditions. (a) Quasi-steady-state
typical of humid regions. (b) Great sediment influx with later amelioration producing vertical accretion of channels and
aggradation of floodplains. (c) Valley trenching (arroyo cutting). (d) High-energy instability seen as episodic gains and
losses in mountain and arid streams.
Source: Adapted from Trimble (1995)

frost and snow processes separately from processes areas where temperatures are sub-zero) to form discrete
associated with flowing ice in glaciers. masses of segregated ice. Segregated ice is common in
sediments dominated by intermediate grain sizes, such
as silt. Coarse sediments, such as gravel, are too per-
Frost and snow processes
meable and very fine-grained sediments, such as clay,
The freezing of water in rock, soil, and sediment gives rise too impermeable and have too high a suction poten-
to several processes – frost shattering, heaving and thrust- tial (the force with which water is held in the soil
ing, and cracking – that are intense in the periglacial body) for segregation to occur. Frost action is cru-
zone. Water in the ground may freeze in situ within cially determined by the occurrence of freeze–thaw
voids, or it may migrate through the voids (towards cycles at the ground surface. Freeze–thaw cycles are