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This guest post was contributed by a scientist, student or a professional in the Earth, planetary or space sciences. The EGU blogs welcome guest contributions, so if you've got a great idea for a post or fancy trying your hand at science communication, please contact the blog editor or the EGU Communications Officer to pitch your idea.

NH10 Multi-Hazards: The Latest EGU Natural Hazards Sub-Division

NH10 Multi-Hazards: The Latest EGU Natural Hazards Sub-Division

Earlier this year, the EGU Natural Hazards Division approved the addition of a new sub-division focused on the theme of ‘multi-hazards’. The Science Officers representing this sub-division, Joel Gill (British Geological Survey) and Marleen de Ruiter (IVM-VU Amsterdam), reflect on why this sub-division is necessary and how you can get involved.

Many regions are affected by multiple natural hazards, with hazards and/or their impacts not always occurring independently. The Sendai Framework for Disaster Risk Reduction, therefore, advocates for ‘multi-hazard’ approaches to disaster risk assessment and reduction. The UN defines ‘multi-hazard’ as follows: 

“Multi-hazard means (1) the selection of multiple major hazards that the country faces, and (2) the specific contexts where hazardous events may occur simultaneously, cascadingly or cumulatively over time, and taking into account the potential interrelated effects” (UNDRR Terminology, 2017).

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Alpine rock instability events and mountain permafrost

Alpine rock instability events and mountain permafrost
Rockfalls, rock slides and rock avalanches in high mountains

The terms rockfall, rock avalanche and rockslide are often used interchangeably. Different authors have proposed definitions based on volume thresholds, but the establishment of fixed boundaries can be tricky. Rockfall can be defined as the detachment of a mass of rock from a steep rock-wall, along discontinuities and/or through rock bridge breakage, and its free or bounding downslope movement under the influence of gravity[1,2]. Usually, we use this term when the volume is limited, and there is little dynamic interaction between rock fragments, which interact mainly with the substrate. Rockslides involve a larger volume (up to 100,000 m3) and the blocks often break in smaller fragments as they travel down the slope. In both rockfall and rockslide, the blocks move downslope mainly by falling, bouncing and rolling. On the other hand, rock avalanches involve the disintegration of rock fragments to form a downslope rapidly flowing, granular mass demonstrating exceptionally high mobility[3]. The size of these rock failures can vary from single boulders to several million cubic meters (e.g. the catastrophic failures of Triolet, 1717, and Randa, 1991).

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