Vegetation-Erosion Dynamics - River Dynamics and Integrated River Management - page 51

sediment are not confined to areas which experience or formerly experienced a periglacial climate and
prior glaciation, but also occur in vegetated upland environments (Garcia-Ruiz et al., 2001; Curry and
Black, 2002). Usually shattering erosion is found in high mountains with elevations of 1200-4000 m (Saas
and Krautblatter, 2007; Matsuoka, 2008). But it is also found in south Wales at 650-770 m (Harris and
Prick, 2000). The lithology of the weathering rocks are limestone, dolostone, marls, and sandstone (Curry
and Black, 2002; Turner and Makhlouf, 2002; Saas and Krautblatter, 2007). Only a few data have been
obtained about the rate of shattering erosion because it is very slow. Thirteen years of observations in the
southeastern Swiss Alps found that shattering erosion occurred at an average rate about 0.1 mm/yr with
significant spatial and inner-annual variations (Matsuoka, 2008). The freeze-thaw cycle is the main agent
for shattering erosion. A five-year study in the Japanese Alps revealed that the shattering rate of rocks
was much higher in the freeze-thaw period from October to next May than in the frost-free period from
June to September (Matsuoka, 1990).
Shattering erosion in high mountains, especially the particle movement on slopes, has caused some
problems to highways. Some studies have been done on the movement of grains on the slopes and
protection of the highways from the deposition of grains. The deposits are called stratified scree deposits
or alpine scree slopes in some literature (Hetu et al., 1995). Chinese researchers studied the structure of
grain deposit fans, repose angles, and stability of the fan (Wang et al., 2007a, 2007b and 2007c). This
research focused on the velocity distribution of grain flow on the slope and the pressure exerted on the
protection walls of highways by the deposit fan. Other researchers studied the critical initiation of slump
of grain deposits on slope (Chang et al., 2006).
(a) (b)
Fig. 2.2 (a) Freezing and thawing of rocks resulted in rock erosion on a 47,00 m high mountain at Luhuo on the
Qinghai-Tibet Plateau; (b) Eroded sediment resulting from freezing and thawing deposits at the toe of the Rocky
Mountains in Canada
Wind erosion is the result of sand movement by the wind. There are two main effects. First, wind
causes small particles to be lifted, and, therefore, moved to another region. Second, these suspended
particles may impact on solid objects causing erosion by abrasion. Wind erosion generally occurs in areas
with little or no vegetation, often in the areas where there is insufficient rainfall to support vegetation.
Sand dunes in deserts are the most common example of wind erosion. Wind erosion of bare lands has
intensified desertification by depriving the ground of good top soil. Wind erosion is referred to as eulian
erosion, the name being a reference to Aeolus, the Greek god of the winds encountered in Homer's Odyssey .