76
6 A Close Look of the Gravity Erosion …
12, 2015 in Shanyang County, resulting in 237, 32 and 65 casualties, respectively
(CGEIS 2016; Huang 2009). In addition to the loss of human life and property directly
due to landslides, the corresponding sedimentation is another significant issue that
deserves attention (Tsai et al. 2012). For example, in the headwaters of the 2150 km
2
Waipaoa River catchment, an area well known for its severe erosion in New Zealand,
gullies contributed 59% of the total sediment load. The amount of slumps, shallow
riparian landslides and earthflows accounted for 34, 6 and 1% of the total sediment
load, respectively (Marden et al. 2014). On the Loess Plateau of China, landslide
plays a more important role in yielding sediment in the small watershed. Hence, how
to prevent or mitigate disasters triggered by landslides is an urgent problem.
The Occurrence of landslide is controlled both by a series of internal factors,
e.g., geological, geomorphological, soil property and hydro-geological and external factors, including seismicity, heavy rainfall, human activities and freeze-thaw
(Conforti et al. 2015; Zhuang and Peng 2014). Most landslides occur during or just
after storms. In China, 50% of large-scale landslides with volume greater than two
million m
3 that occurred in the past three decades were induced directly by rainfalls (Huang 2009). In addition, adverse destabilization from human activities has
been another major contributory factor in triggering landslides since the 1980s in
China. With the development of the Chinese economy, residential areas on the Loess
Plateau being rapidly expanding along steep slope terraces and adverse destabilization from human activities; i.e., no protection practice after slope cutting, is the major
cause of landslide incidents (Xu et al. 2015a). The steep-cut slopes encourage the
concentration of shear stress at the foot of the slope and tension stress at the top,
leading to the formation of cracks in the inner slope (Zhuang and Peng 2014), which
results in the instability of the side slopes. Moreover, seismic activities make the
slopes unstable and more vulnerable to failures. In 2008, the Wenchuan earthquake
in China triggered a vast number of landslides (Parker et al. 2011). Finally, freezethawing is an influential factor in triggering landslides. In Northwest China, thawing
of the frozen layer in spring is responsible for triggering some landslides in the loess
region. For instance, a landslide in Dongxiang County killed 237 people (Huang
2009). However, the different combinations of these geo-environmental factors lead
to differences in mechanisms of landslide destruction. Evaluating the behaviors and
triggers of landslides has significant implications for understanding their kinematic
mechanisms and evolution.
Field investigation and statistical analysis are among the most important tools
for recognizing and evaluating the landslides. Field investigations can provide a
basis for better understanding and illustrating the spatial distributions and hazards
related to landslides (Xu et al. 2015b). In recent years, field investigations were
always immediately performed after major landslides in China, such as the landslides
in Wenchuan County triggered by the earthquake in 2008 (Yang et al. 2015) and
landslides in Guanling County triggered by rainfall in 2010 (Xing et al. 2014). The
results of these investigations provided useful information for landslide mitigation
and detailed landslide inventory compilation. A field observation in the Guanzhong
area of the Loess Plateau indicated that the main type of landslide was deep-seated
6 A Close Look of the Gravity Erosion …
12, 2015 in Shanyang County, resulting in 237, 32 and 65 casualties, respectively
(CGEIS 2016; Huang 2009). In addition to the loss of human life and property directly
due to landslides, the corresponding sedimentation is another significant issue that
deserves attention (Tsai et al. 2012). For example, in the headwaters of the 2150 km
2
Waipaoa River catchment, an area well known for its severe erosion in New Zealand,
gullies contributed 59% of the total sediment load. The amount of slumps, shallow
riparian landslides and earthflows accounted for 34, 6 and 1% of the total sediment
load, respectively (Marden et al. 2014). On the Loess Plateau of China, landslide
plays a more important role in yielding sediment in the small watershed. Hence, how
to prevent or mitigate disasters triggered by landslides is an urgent problem.
The Occurrence of landslide is controlled both by a series of internal factors,
e.g., geological, geomorphological, soil property and hydro-geological and external factors, including seismicity, heavy rainfall, human activities and freeze-thaw
(Conforti et al. 2015; Zhuang and Peng 2014). Most landslides occur during or just
after storms. In China, 50% of large-scale landslides with volume greater than two
million m
3 that occurred in the past three decades were induced directly by rainfalls (Huang 2009). In addition, adverse destabilization from human activities has
been another major contributory factor in triggering landslides since the 1980s in
China. With the development of the Chinese economy, residential areas on the Loess
Plateau being rapidly expanding along steep slope terraces and adverse destabilization from human activities; i.e., no protection practice after slope cutting, is the major
cause of landslide incidents (Xu et al. 2015a). The steep-cut slopes encourage the
concentration of shear stress at the foot of the slope and tension stress at the top,
leading to the formation of cracks in the inner slope (Zhuang and Peng 2014), which
results in the instability of the side slopes. Moreover, seismic activities make the
slopes unstable and more vulnerable to failures. In 2008, the Wenchuan earthquake
in China triggered a vast number of landslides (Parker et al. 2011). Finally, freezethawing is an influential factor in triggering landslides. In Northwest China, thawing
of the frozen layer in spring is responsible for triggering some landslides in the loess
region. For instance, a landslide in Dongxiang County killed 237 people (Huang
2009). However, the different combinations of these geo-environmental factors lead
to differences in mechanisms of landslide destruction. Evaluating the behaviors and
triggers of landslides has significant implications for understanding their kinematic
mechanisms and evolution.
Field investigation and statistical analysis are among the most important tools
for recognizing and evaluating the landslides. Field investigations can provide a
basis for better understanding and illustrating the spatial distributions and hazards
related to landslides (Xu et al. 2015b). In recent years, field investigations were
always immediately performed after major landslides in China, such as the landslides
in Wenchuan County triggered by the earthquake in 2008 (Yang et al. 2015) and
landslides in Guanling County triggered by rainfall in 2010 (Xing et al. 2014). The
results of these investigations provided useful information for landslide mitigation
and detailed landslide inventory compilation. A field observation in the Guanzhong
area of the Loess Plateau indicated that the main type of landslide was deep-seated