NH
Natural Hazards

Archives / 2019 / April

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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InSAR Norway: the big eye on Norwegian unstable rock slopes

InSAR Norway: the big eye on Norwegian unstable rock slopes

Marie Keiding is a researcher in the Geohazard and Earth Observation team at the Geological Survey of Norway. Together with her colleague, John Dehls, who is leading the project, she works to develop and operate the new mapping service called InSAR Norway.

Before we start, let’s briefly describe what is InSAR. First, the Synthetic Aperture Radar (SAR) is a day and night operational imaging system that can be operated from satellite aircraft or ground and has high capabilities of penetrating clouds because it uses microwaves. Its ‘interferometric configuration’, Interferometric SAR or InSAR, uses two or more SAR images to generate maps of surface deformation or digital elevation models. This is made by calculating differences in the phase of the waves returning to the sensor, as a function of the satellite position and time of acquisition.

Measurements of phase variations are possible only in those pixels of the image where the signal maintains a sufficient coherence between different acquisitions. For this reason, InSAR techniques are particularly suitable to monitor relatively small deformations, in the order of millimetres to centimetres.

Hi Marie, can you tell what is InSAR Norway?

InSAR Norway is the first free and open, nationwide, [Read More]

#EGU19 program is ready! Are you ready for it?

#EGU19 program is ready! Are you ready for it?

#EGU19 program is ready! Are you ready for it?

 

The next EGU’s General Assembly is taking place in one week! We bet you already started planning your program for the week, that Natural Hazard (NH) sessions are included, and, especially if you are an Early Career Scientist (ECS), you have found many sessions and courses targeting your specific needs and interests.

 

What fits more to your interests: Attend talks and posters, learn and improve skills, or take an active role in a serious game? Or maybe a mix of all of them? To get to the point, the Natural hazards Early Career scientist Team (NhET) is organizing 3 sessions and 4 short courses during the General Assembly that you can find in the NH division program. Let’s have a look at them! And remember that the conference last until Friday, and that we have interesting activities to convince you remaining at the conference until the very last minute!

 

Before presenting the program, we would like to invite all ECS to become an active part of NhET and help us organising these activities also in the future. If you have ideas for new sessions or short courses to be proposed at next year’s conference or if you want to help us in the ones already proposed this year, please contact us!

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