Rock slope failure in a recently deglaciated permafrost rock wall at Piz Kesch (Eastern Swiss Alps), February 2014          下载免费PDF全文

Marcia Phillips  Andrea Wolter  Rachel Lüthi  Florian Amann  Robert Kenner  Yves Bühler 《地球表面变化过程与地形》2017,42(3):426-438

In February 2014, a rock pillar with a volume of around 150 000  m³ collapsed at Piz Kesch in the Eastern Swiss Alps. A reconstruction of the conditions prior to the event and of the event itself is presented on the basis of different sources of data. The methods applied include photogrammetry, terrestrial laser scanning, structural geological analysis, examination of meteorological data, carbon‐14 (¹⁴C) dating of organic material in permafrost ice from a tension crack and numerical modelling of likely modes of failure. Despite a complete lack of in situ measurements in the rock wall prior to the event and of direct observations during the event, the available data allow the determination of the approximate timing of the event as well as the structural predisposition, the probable mode of failure and the timescale of several millennia involved in the triggering of the failure of the rock pillar. The interdisciplinary analysis of this event contributes towards understanding the complex interaction of processes involved in large rock slope failures currently occurring in warming mountain permafrost regions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

An unusual compound object in Yamato 793408 (H3.2‐an): The missing link between compound chondrules and macrochondrules?     

Jens Barosch  Dominik C. Hezel  Yves Marrocchi  Andrey Gurenko  Christoph Lenting 《Meteoritics & planetary science》2020,55(7):1458-1470

We found a large (~2 mm) compound object in the primitive Yamato 793408 (H3.2‐an) chondrite. It consists mostly of microcrystalline material, similar to chondrule mesostasis, that hosts an intact barred olivine (BO) chondrule. The object contains euhedral pyroxene and large individual olivine grains. Some olivine cores are indicative of refractory forsterites with very low Fe‐ and high Ca, Al‐concentrations, although no ¹⁶O enrichment. The entire object is most likely a new and unique type, as no similar compound object has been described so far. We propose that it represents an intermediate stage between compound chondrules and macrochondrules, and formed from the collision between chondrules at low velocities (below 1 m s^?1) at high temperatures (around 1550 °C). The macrochondrule also trapped and preserved a smaller BO chondrule. This object appears to be the first direct evidence for a genetic link between compound chondrules and macrochondrules. In accordance with previous suggestions and studies, compound chondrules and macrochondrules likely formed by the same mechanism of chondrule collisions, and each represents different formation conditions, such as ambient temperature and collision speed.  相似文献   

Numerical modelling of Cretaceous Pyrenean Rifting: The interaction between mantle exhumation and syn-rift salt tectonics     

Thibault Duretz  Riccardo Asti  Yves Lagabrielle  Jean-Pierre Brun  Anthony Jourdon  Camille Clerc  Benjamin Corre 《Basin Research》2020,32(4):652-667

The preshortening Cretaceous Pyrenean Rift is an outstanding geological laboratory to investigate the effects of a pre-rift salt layer at the sedimentary base on lithospheric rifting. The occurrence of a pre-rift km-scale layer of evaporites and shales promoted the activation of syn-rift salt tectonics from the onset of rifting. The pre- and syn-rift sediments are locally affected by high-temperature metamorphism related to mantle ascent up to shallow depths during rifting. The thermo-mechanical interaction between décollement along the pre-existing salt layer and mantle ascent makes the Cretaceous Pyrenean Rifting drastically different from the type of rifting that shaped most Atlantic-type passive margins where salt deposition is syn-rift and gravity-driven salt tectonics has been postrift. To unravel the dynamic evolution of the Cretaceous Pyrenean Rift, we carried out a set of numerical models of lithosphere-scale extension, calibrated using the available geological constraints. Models are used to investigate the effects of a km-scale pre-rift salt layer, located at the sedimentary cover base, on the dynamics of rifting. Our results highlight the key role of the décollement layer at cover base that can alone explain both salt tectonics deformation style and high-temperature metamorphism of the pre-rift and syn-rift sedimentary cover. On the other hand, in the absence of décollement, our model predicts symmetric necking of the lithosphere devoid of any structure and related thermal regime geologically relevant to the Pyrenean case.  相似文献   

Time splitting and linear stability of the slow part of the barotropic component     

Yves Morel  Remy Baraille  Annick Pichon   《Ocean Modelling》2008,23(3-4):73-81

In this paper, the authors analyse the stability of particular numerical schemes used in oceanic general circulation models to deal with the barotropic momentum advection term. It is shown that, when this term is integrated using time splitting, its stability properties can be drastically reduced in configurations where there exists shallow areas, where velocities become comparable to the propagation speed of external gravity waves. A simple alternative scheme with improved stability is proposed and discussed.  相似文献   

Detailed Study of Three Contiguous Segments of the Mid-Atlantic Ridge,South of the Azores (37° N to 38°30′ N), Using Acoustic Imaging Coupled with Submersible Observations     

Ondréas  Hélène  Fouquet  Yves  Voisset  Michel  Radford-Knoery  Joël 《Marine Geophysical Researches》1997,19(3):231-255

Using a new tool of seafloor characterisation (sonar images from FARA-SIGMA cruise; Needham et al., 1992), coupled with submersible observations (DIVA1 cruise) we compare, at different scales of observation, three contiguous segments of the Mid-Atlantic Ridge, South of the Azores Triple Junction, between 37° N and 38°30 N.The two northernmost segments (38°20 N and Menez-Gwen) show unusual morphological features for the MAR; the rift valley is absent and the present-day magmatism is focused on shallow axial volcanoes. On the third segment (Lucky Strike), the morphology is the one usually found on the MAR. On the Menez-Gwen and 38°20 N segments, volcanic constructional activity can obliterate, during periods of high magmatic supply, the morphology inherited from tectonic activity. The dive results constrain the recent evolution of each segment and show that a temporal variability in volcanic dynamics exists. On the three segments, outcrops of eruptive lavas alternate with large areas of explosive volcanic ejecta. This cycle in volcanic activity is influenced by changes in water depth, both spatially (i.e. between segments) and temporally (i.e. for the same segment through time).Each segment has known a specific history in its accretionary processes with a succession of tectonic and volcanic predominance and changes in its volcanic phases between volcanic ejecta and effusive dynamics.The hydrothermal activity is focused at the central part of each segment and is controlled by the presence of fresh lava and major tectonic features.  相似文献