Structural analysis of the early stages of catastrophic stratovolcano flank-collapse using analogue models |
| |
| Authors: | S Daniel Andrade Benjamin van Wyk de Vries |
| |
| Institution: | 1. CNRS, IRD, Laboratoire Magmas et Volcans, OPGC—Université Blaise Pascal, UMR 6524, 5 rue Kessler, 63000, Clermont-Ferrand, France
2. Instituto Geofísico, Escuela Politécnica Nacional, A.P. 17-2759, Quito, Ecuador
|
| |
| Abstract: | Many major volcanic flank collapses involve the failure of low-angle strata in or under the edifice. Such failures produce
voluminous, destructive debris avalanches that are a major volcanic hazard. At Socompa, Las Isletas-Mombacho and Parinacota
volcanoes, field studies have shown that during catastrophic flank collapse a significant segment of their substrata was detached
and expelled from beneath the volcanic edifice and formed a mobile basal layer on which the sliding flanks were transported.
Previous studies have proposed that gravitational flank spreading was likely involved in the onset of sudden substrata failure.
The early stages of this particular type of flank collapse can be modelled under laboratory conditions using analogue models.
This allows us to study the development of structures accommodating early deformation of the sliding flank during catastrophic
collapse. In the experiments, the detached substratum segment (low-viscosity basal layer) was modelled with a silicone layer,
and the overlying stratovolcano with a layered sand cone. The first structure developed in the models is a graben rooted in
the low-viscosity basal layer. This graben forms the limits of the future avalanche-amphitheatre and divides the sliding flank
into a ‘toreva’ domain (upper sliding flank) and a ‘hummock’ domain (lower sliding flank). These domains display distinctive
structural patterns and kinetic behaviour. Normal faults develop in the toreva domain and inside the graben, while the hummock
domain is characterised by transtensional structures. The hummock domain also over-thrusts the lower amphitheatre sides, which
allows subsequent sideways avalanche spreading. Measurements show that horizontal speeds of the hummock domain are always
higher than that of the toreva domain during model collapse. The main role played by the low-viscosity basal layer during
this type of collapse is to control the size, shape and structural complexity of the sliding flank; it also transmits mass
and momentum from the toreva to the hummock domain. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
