Fragmentation has been proposed as an important dynamical process in the propagation of rock avalanches. The occurrence of an intense block fragmentation inside a rock avalanche traveling on smooth inclined terrain followed by a flat region (a geometry common to many landslides) is first studied numerically by means of a discrete element 2-D code in which blocks are subjected to mutual collisions and impact with the terrain. This numerical model confirms that the locations where fragmentation is more likely to occur are those in correspondence of abrupt slope changes. We thus analyze this geometry of impact in two cases: low- and high-impact energy. In the first case, where recent experimental data are available, a kinematic analysis shows that the energy released at impact causes high velocities of the smallest fragments, a highly probable scenario in rock avalanche dynamics. When the impact is so energetic to disintegrate the landslide, we find that explosive fragmentation at the slope break provides an extra horizontal boost to a rock avalanche via a peculiar mechanism coupling the geometry of the slope path to the dynamics of the rock avalanche. As a consequence, a net momentum gain (boost) results along the horizontal direction due to the terrain asymmetry. However, under normal field conditions, only when the slope angle is greater than 70° and fragmentation produces clasts of fairly uniform size, the momentum and runout distance are significantly enhanced. Allowing for a spectrum of fragment sizes and velocities, we find a relationship between the degree of fragmentation and the magnitude of the extra boost. Key Points Excessive runout of granular flows on steep slopes Impact energy effect on rock fragmentation Topographic and geometric effects on fragmentation and mobility

DE BLASIO, F., Crosta, G. (2015). Fragmentation and boosting of rock falls and rock avalanches. GEOPHYSICAL RESEARCH LETTERS, 42(20), 8463-8470 [10.1002/2015GL064723].

Fragmentation and boosting of rock falls and rock avalanches

DE BLASIO, FABIO VITTORIO
;
CROSTA, GIOVANNI
2015

Abstract

Fragmentation has been proposed as an important dynamical process in the propagation of rock avalanches. The occurrence of an intense block fragmentation inside a rock avalanche traveling on smooth inclined terrain followed by a flat region (a geometry common to many landslides) is first studied numerically by means of a discrete element 2-D code in which blocks are subjected to mutual collisions and impact with the terrain. This numerical model confirms that the locations where fragmentation is more likely to occur are those in correspondence of abrupt slope changes. We thus analyze this geometry of impact in two cases: low- and high-impact energy. In the first case, where recent experimental data are available, a kinematic analysis shows that the energy released at impact causes high velocities of the smallest fragments, a highly probable scenario in rock avalanche dynamics. When the impact is so energetic to disintegrate the landslide, we find that explosive fragmentation at the slope break provides an extra horizontal boost to a rock avalanche via a peculiar mechanism coupling the geometry of the slope path to the dynamics of the rock avalanche. As a consequence, a net momentum gain (boost) results along the horizontal direction due to the terrain asymmetry. However, under normal field conditions, only when the slope angle is greater than 70° and fragmentation produces clasts of fairly uniform size, the momentum and runout distance are significantly enhanced. Allowing for a spectrum of fragment sizes and velocities, we find a relationship between the degree of fragmentation and the magnitude of the extra boost. Key Points Excessive runout of granular flows on steep slopes Impact energy effect on rock fragmentation Topographic and geometric effects on fragmentation and mobility
Articolo in rivista - Articolo scientifico
boosting; fragmentation; modeling; rock avalanche; rock fall; runout; Earth and Planetary Sciences (all); Geophysics
English
2015
42
20
8463
8470
none
DE BLASIO, F., Crosta, G. (2015). Fragmentation and boosting of rock falls and rock avalanches. GEOPHYSICAL RESEARCH LETTERS, 42(20), 8463-8470 [10.1002/2015GL064723].
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/109013
Citazioni
  • Scopus 52
  • ???jsp.display-item.citation.isi??? 42
Social impact