Geological-environmental hazard chain: phenomena, process, and principle

Numerous contaminated rock and soil slopes are widely distributed around the world. When these slopes become destabilized and slide, they not only cause loss of life and property damage but also severely contaminate the surrounding soil and water environments. A novel hazard chain characterized by both geological hazards and environmental pollution can be defined, profoundly impacting the human-social-ecological system. Based on extensive historical events, this paper introduces the concept of the geological-environmental hazard chain, clarifies its components, and explores its evolutionary processes, zonal and stratification characteristics, and structure. It analyzes the types of hazard chains, hazard formation modes, and control factors, revealing their amplification and overlapping effects, and ultimately synthesizes the principles of coupling with concomitance. The research indicates that: (1) The geological-environmental hazard chain consists of eight major elements: Potential instability sources and potential pollution sources, primary geological hazards and proximal environmental pollution, secondary geological hazards and regional environmental pollution, as well as elements at risk and pollution receptors. This chain is the result of the coupling between geological and environmental hazard chains. (2) Horizontally, the evolution process can be summarized into four zones: slope failure-polluted source release (I), flow cascades-migration and dispersion (II), damming and sedimentation-retention and precipitation (III), and flood propagation-watershed pollution (IV). Vertically, the evolution can be categorized into three layers: surface water-soil pollution, vadose zone pollution, and saturated zone pollution. Each zone and layer has distinct hazard and pollution characteristics, together forming a spatial network structure of the hazard chain. (3) The types of hazard chains can be divided into two main categories and four subcategories: Surface sedimentation-type (I-II-III) and watershed pollution-type (I-II-IV, I-III-IV, I-II-III-IV), each with corresponding hazard formation modes. Internal factors primarily control the type of hazard, while external factors govern the chain combination pattern. This combined action determines the specific hazard type and pattern of chain combination, both of which collectively affect the occurrence and evolution of the hazard chain. (4) The amplification and overlapping effects within the geological-environmental hazard chain are categorized into three types: Geological hazard chain effects, environmental hazard chain effects, and inter-chain effects. The hazard chain adheres to the principle of coupling with concomitance: The entire process of geological hazards and subsequent environmental pollution is dominated by amplification effects such as increased hazard and pollution intensity or expanded impact range. It is also influenced by overlapping effects, including repeated hazards and the overlap of pollution plumes. Geological and environmental hazard chains are sequentially connected over time and interlinked in space, driven by consistent forces. This principle can be expressed in a matrix format, allowing for the scientific quantification of amplification and overlapping effects through iterative calculations to address specific geological-environmental hazard chain issues. From the perspective of hazard chains, this study provides fundamental research ideas and theoretical basis for the issues of coupling and concomitance of geological hazards and secondary environmental pollution, and offers guidance for hazard prevention and pollution control measures concerning major safety and environmental risks in China.