4.1 The quantity, area and distribution of alluvial fans
There are many sizes of alluvial fans in LRB, and the distribution of
quantity and area is uniformed. The formation and development of
alluvial fans base the catchment characteristics, tectonics and climate
(Sarp, 2015). The size of alluvial fans is major determined by the
characteristics of catchment (Mather et al., 2016). Typically, the
larger alluvial fans have larger and gender catchment with greater
possibility to accumulate to sediment flows. Moreover, the catchments of
smaller alluvial fans are smaller and steeper, which the ability of
storing slope deposits is limited (Mather et al., 2016). And this
regulation needs to be verified in LRB. As above, the sediment flow is a
direct factor for alluvial fan. The mountain including many catchments
of alluvial fan is covered by ice and glaciers throughout the year in
the west of LRB. Especially, the area of ice and glaciers of Damshung is
largest in LRB with 535.95 km2 in 2010 (Xu, 2013), so
the water (meltwater) carrying sediment is enough. The ice or glaciers
in LRB except Daumshung are shortage because the majority of elevation
of those regions is not more than 4000m (Wei et al., 2012). Therefore,
the size of alluvial fans in the west is more than other regions in LRB.
Furthermore, the exist of ice or glaciers should be an important factor
for the sizes of alluvial fans.
Meanwhile, the size and uniformed distribution of alluvial fans may be
caused by tectonic activity. The topographic uplift of Damshung area is
earlier than other area in LRB ((Wang et al., 2017), which induce a
difference of accommodation space of alluvial fan and fan catchment due
to tectonic force (Sarp, 2015). The size, distribution, formation and
development of alluvial fan should be studied in next step.