Development Characteristics, Causes and Hazard Analysis of Debris Flow in Gansu Province

As one of the four provinces with most serious geological disasters of debris flow in China, Gansu province has developed 6260 debris flow ditches, most of which are concentrated in the east area and few happened in the west of the Yellow River. The debris flow developed seriously in Longnan and Gannan mountain areas, where the terrain elevation is above 1000m, the slope of hillside is more than 30 degrees, the local geological structure is complicated with frequent seismic activities, and there is a wide distribution of loess, mudstone, phyllite, shale and other soft slippery rock mass, that provide the necessary terrain conditions and soil conditions for debris flow. Rainfall, earthquakes and human activities are predisposing factors of debris flow. Over the years, frequent occurrences of debris flow disaster in Gansu have brought serious threat and harm to local people's lives, properties, industrial construction and agricultural production. Having killed about 3715 people, the geological hazard also caused direct economic losses of billions. Among them, the largest debris flow disaster happened in Zhouqu on 8 August 2010 shocked the world, seriously restricted the economic development of Gansu province and disturbed the majority of people's normal life. Therefore, we should plan human activities scientifically and take necessary engineering measures to restrict the occurrence of debris flow hazards and reduce the losses caused by the geological disasters of debris flow.