6.1 Gravity Erosion: Natural Hazard and Soil Erosion
77
rotational landslides with sliding masses composed of two different packages of strata
(Li et al. 2015). Another field investigation of 13 loess landslides in Yan’an area of
the Loess Plateau showed that the infiltration depth of rainfall in integrated loess
mass is generally limited to 3.0 m underground, and rainfall infiltration inducing
loess landslide can be divided into three modes (Tang et al. 2015). Through the field
investigation and statistical analysis based on the 52 loess avalanches in the Baota
district of Yan’an, Qiu et al. (2015) found power law correlations between avalanche
volume and avalanche area. The other field investigations also showed although
the avalanche in Tuban was small in size, the death toll and financial losses were
shocking (Xu et al. 2015a). All these studies focused on location, type and modes of
the landslide and disaster losses. A commonly used method to estimate the sediment
yield of existing landslides is to calculate the change in surface elevation over time
based on digital elevation models (Tsai et al. 2012). Nevertheless, few papers have
examined the role of soil erosion caused by landslides, especially those in small size.
For years, the authors of this study have carried out field investigations and statistical analyses of landslides on the Loess Plateau of China. The objectives of this
study are to analyze hazards and soil erosion caused by the loess landslides and then
to determine how to control the hazards that occur so widely in the rural areas of the
Loess Plateau.
6.2 Characteristics of the Loess Plateau
The Loess Plateau is located in the upper and middle reaches of the Yellow River,
covering a total area of 624,000 km
2 , and over 60% of the land is subjected to serious
soil and water loss. It is mostly located in arid or semiarid regions, featuring lots of
dry air, little cloud and abundant sunlight. The average annual precipitation on the
Loess Plateau is only 350–550 mm, decreasing gradually from the southeast to the
northwest, and most of the precipitation is concentrated in the rainy season from
June to September (Xu et al. 2004). Usually, a single rainstorm, most of which is
in the form of short but very intense rainfalls, can account for more than 60%, even
90%, of the total precipitation in the year, and causing the greatest amount of soil
loss (Zhou et al. 2000). The rain often lasts 30–120 min, which will result in a 10–
40 min hyperconcentrated flow with an average concentration of 200–300 kg/m
3 and
a maximum suspended concentration of 1000 kg/m
3 (Wang and Jiao 1996).
The most crucial area is the Loess Mesa Ravine Region and the Loess Hill Ravine
Region, which cover altogether 30% of the total area. As one of the most severe
areas of soil and water losses in the world, the average erosion rate can be as high as
5000–10,000 t/(km
2 a), and sometimes even up to 20,000–30,000 t/(km
2 a) (Meng
1996). In the area, landslides frequently occur that are induced by the rainstorm,
slope excavation, freeze-thaw and earthquake, because the undulating terrain is very
steep, the vegetation is so sparse, and especially because the loess is collapsible and
in vertical joints.
77
rotational landslides with sliding masses composed of two different packages of strata
(Li et al. 2015). Another field investigation of 13 loess landslides in Yan’an area of
the Loess Plateau showed that the infiltration depth of rainfall in integrated loess
mass is generally limited to 3.0 m underground, and rainfall infiltration inducing
loess landslide can be divided into three modes (Tang et al. 2015). Through the field
investigation and statistical analysis based on the 52 loess avalanches in the Baota
district of Yan’an, Qiu et al. (2015) found power law correlations between avalanche
volume and avalanche area. The other field investigations also showed although
the avalanche in Tuban was small in size, the death toll and financial losses were
shocking (Xu et al. 2015a). All these studies focused on location, type and modes of
the landslide and disaster losses. A commonly used method to estimate the sediment
yield of existing landslides is to calculate the change in surface elevation over time
based on digital elevation models (Tsai et al. 2012). Nevertheless, few papers have
examined the role of soil erosion caused by landslides, especially those in small size.
For years, the authors of this study have carried out field investigations and statistical analyses of landslides on the Loess Plateau of China. The objectives of this
study are to analyze hazards and soil erosion caused by the loess landslides and then
to determine how to control the hazards that occur so widely in the rural areas of the
Loess Plateau.
6.2 Characteristics of the Loess Plateau
The Loess Plateau is located in the upper and middle reaches of the Yellow River,
covering a total area of 624,000 km
2 , and over 60% of the land is subjected to serious
soil and water loss. It is mostly located in arid or semiarid regions, featuring lots of
dry air, little cloud and abundant sunlight. The average annual precipitation on the
Loess Plateau is only 350–550 mm, decreasing gradually from the southeast to the
northwest, and most of the precipitation is concentrated in the rainy season from
June to September (Xu et al. 2004). Usually, a single rainstorm, most of which is
in the form of short but very intense rainfalls, can account for more than 60%, even
90%, of the total precipitation in the year, and causing the greatest amount of soil
loss (Zhou et al. 2000). The rain often lasts 30–120 min, which will result in a 10–
40 min hyperconcentrated flow with an average concentration of 200–300 kg/m
3 and
a maximum suspended concentration of 1000 kg/m
3 (Wang and Jiao 1996).
The most crucial area is the Loess Mesa Ravine Region and the Loess Hill Ravine
Region, which cover altogether 30% of the total area. As one of the most severe
areas of soil and water losses in the world, the average erosion rate can be as high as
5000–10,000 t/(km
2 a), and sometimes even up to 20,000–30,000 t/(km
2 a) (Meng
1996). In the area, landslides frequently occur that are induced by the rainstorm,
slope excavation, freeze-thaw and earthquake, because the undulating terrain is very
steep, the vegetation is so sparse, and especially because the loess is collapsible and
in vertical joints.