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Landslides on the Loess Plateau of China: a Latest Statistics Together with a Close Look

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Landslides on the Loess Plateau of China: a Latest Statistics Together with a Close Look Landslides on the Loess Plateau of China: a latest statistics together with a close look Xiang-Zhou Xu, Wen-Zhao Guo, Ya- Kun Liu, Jian-Zhong Ma, Wen-Long Wang, Hong-Wu Zhang & Hang Gao Natural Hazards Journal of the International Society for the Prevention and Mitigation of Natural Hazards ISSN 0921-030X Volume 86 Number 3 Nat Hazards (2017) 86:1393-1403 DOI 10.1007/s11069-016-2738-6 1 23 Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media Dordrecht. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Nat Hazards (2017) 86:1393–1403 DOI 10.1007/s11069-016-2738-6 SHORT COMMUNICATION Landslides on the Loess Plateau of China: a latest statistics together with a close look 1,2 2 2 Xiang-Zhou Xu • Wen-Zhao Guo • Ya-Kun Liu • 1 1 3 Jian-Zhong Ma • Wen-Long Wang • Hong-Wu Zhang • Hang Gao2 Received: 16 December 2016 / Accepted: 26 December 2016 / Published online: 3 January 2017 Ó Springer Science+Business Media Dordrecht 2017 Abstract Landslide plays an important role in landscape evolution, delivers huge amounts of sediment to rivers and seriously affects the structure and function of ecosystems and society. Here, a statistical analysis together with a field investigation was carried out on the Loess Plateau of China to address the challenges. The study tracks landslide-related deaths and collects knowledge about this natural hazard. Since the 1980s, 53 fatal landslides have occurred, causing 717 deaths. As the most important trigger, rainfall induced 40% of the catastrophic landslides, while other factors, i.e., human activities, freeze–thaw and earth- quake, accounted for 36, 23 and 1%, respectively. Furthermore, landslide frequency and death toll related to human activities were increasing as time went on. Landslide also plays an important role in sediment delivery, especially in areas with steep terrain. Sediment discharge from landslides accounts for a considerable proportion of the total soil loss in the upper and middle reaches of the Yellow River. In some catchments of the Loess Plateau, landslides contributed over 50% of the total sediment discharge. The result shows that landslide is a widespread geologic hazard in the rural area of the Loess Plateau, China. Keywords Geological hazards Á Landslides Á Soil yield Á Triggering mechanism & Xiang-Zhou Xu [email protected] 1 State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest Agriculture and Forestry University, Chinese Academy of Sciences and Ministry of Water Resources, Yangling 712100, Shaanxi, China 2 School of Hydraulic Engineering, Dalian University of Technology, Dalian 116024, China 3 State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China 123 Author's personal copy 1394 Nat Hazards (2017) 86:1393–1403 1 Introduction A landslide is the downslope movement of soil, rock and organic materials under the effects of gravity and also the landform that results from such movement (Highland and Bobrowsky 2008). Serious landslides occur in nearly all areas of the world, and they could cause serious natural hazards and major ecological and environmental issues such as soil erosion on steep slopes, billions of dollars of damage and many casualties (Zhang et al. 2014; Keefer and Larsen 2007). In the period from 2004 to 2010, there were 2620 fatal landslides worldwide, resulting in 32,322 deaths (Qiu 2014). For instance, a landslide in the southern Philippines led to 122 deaths and 1328 missing (Stone 2006). Landslides are also especially prevalent in the rural area of the Loess Plateau of China. According to investigations and statistics, landslides have resulted in approximately 1000 fatalities per year over the past 20 years in China (Runqiu 2009), and one-third of them occurred on the Loess Plateau (Zhuang and Peng 2014). For example, catastrophic landslides on the Loess Plateau occurred on March 7, 1983, in Dongxiang County, September 17, 2011, in Xi’an City and August 12, 2015, in Shanyang County, resulting in 237, 32 and 65 casualties, respectively (Runqiu 2009; CGEIS 2016). 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 km2 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% 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. Occurrence of landslide is controlled both by a series of internal factors, e.g., geolog- ical, geomorphological, soil property and hydro-geological and external factors, including seismicity, heavy rainfall, human activities and freeze–thaw (Zhuang and Peng 2014; Conforti et al. 2015). Most landslides occur during or just after storms. In China, 50% of large-scale landslides with volume greater than two million m3 that occurred in the past three decades were induced by direct rainfalls (Runqiu 2009). In addition, adverse destabilization from human activities has been another major contributory factor to trig- gering landslides since the 1980s in China. With the development of the Chinese economy, residential areas on the Loess Plateau are rapidly expanding along steep slope terraces and adverse destabilization from human activities, i.e., no protection practices after slope cutting, is the major cause of landslide incidents (Xu et al. 2015b). 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, freeze–thawing 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 (Runqiu 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. 123 Author's personal copy Nat Hazards (2017) 86:1393–1403 1395 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 land- slides (Xu et al. 2015a). 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 indicates that the main type of landslide was deep-seated rotational landslides with sliding masses composed of two different packages of strata (Li et al. 2015). Another field investigation of 13 loess land- slides in Yan’an area of the Loess Plateau shows that the infiltration depth of rainfall in integrated loess mass was generally limited to 3.0 m underground, and rainfall infiltration inducing loess landslide could 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 the power law correlation between avalanche volume and avalanche area. The other field investigations also show although the ava- lanche in Tuban was small in size, the death toll and financial losses were shocking (Xu et al. 2015b). All these studies focused on location, type and casualty loss of the landslide. 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. 2 Method and materials The Loess Plateau is located in the upper and middle reaches of the Yellow River (Fig. 1), covering a total area of 624,000 km2. Most of the area is an arid or semiarid region with dry air, few clouds and abundant illumination, but it is short of moisture.
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