Slope failures and erosion rates on a glacierized high‐mountain face under climatic changes     

Luzia Fischer  Christian Huggel  Andreas Kääb  Wilfried Haeberli 《地球表面变化过程与地形》2013,38(8):836-846

In this study, rapid topographic changes and increased erosion rates caused by massive slope failures in a glacierized and permafrost‐affected high‐mountain face were investigated with respect to the current climatic change. The study was conducted at one of the highest periglacial rock faces in the European Alps, the east face of Monte Rosa, Italy. Pronounced changes in ice cover and repeated rock and ice avalanche events have been documented in this rock wall since around 1990. The performed multi‐temporal comparison of high‐resolution digital terrain models (DTMs) complemented by detailed analyses of repeat photography represents a unique assessment of topographic changes and slope failures over half a century and reveals a total volume loss in bedrock and steep glaciers in the central part of the face of around 25 × 10⁶ m³ between 1988 and 2007. The high rock and ice avalanche activity translates into an increase in erosion rates of about one order of magnitude during recent decades. The study indicates that changes in atmospheric temperatures and connected changes in ice cover can induce slope destabilization in high‐mountain faces. Analyses of temperature data show that the start of the intense mass movement activity coincided with increased mean annual temperatures in the region around 1990. However, once triggered, mass movement activity seems to be able to proceed in a self‐reinforcing cycle, whereby single mass movement events might be strongly influenced by short‐term extreme temperature events. The investigations suggest a strong stability coupling between steep glaciers and underlying bedrock, as most bedrock instabilities are located in areas where surface ice has disappeared recently and the failure zones are frequently spatially correlated and often develop from lower altitudes progressively upwards. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

An evaluation of the effect of degassing on the oxidation state of hydrous andesite and dacite magmas: a comparison of pre- and post-eruptive Fe2+ concentrations     

Stephen M. Crabtree  Rebecca A. Lange 《Contributions to Mineralogy and Petrology》2012,163(2):209-224

The bulk (post-eruptive) wt% FeO concentration in each of 11 phenocryst-poor (<5%) andesite and dacite (60–69 wt% SiO₂) lavas from different monogenetic vents in the Mexican arc has been measured by titration, in duplicate. The results match, within analytical error, the wt% FeO content of the magmas during phenocryst growth (pre-euptive), which were calculated on the basis of oxygen fugacity and temperature results from Fe–Ti two-oxide oxygen barometry. The average deviation between the pre- and post-eruptive FeO concentrations is ±0.15 wt%. Application of the plagioclase-liquid hygrometer shows that at the time of phenocryst growth, these 11 magmas contained from ~3–8 wt% H₂O, which was extensively degassed upon eruption. There is no evidence that degassing of ≤8 wt% H₂O changed the oxidation state of these magmas. Calculations of pre-eruptive and post-eruptive oxygen fugacity values relative to the Ni-NiO buffer (in terms of log₁₀ units) for the 11 samples span a similar range; pre-eruptive ∆NNO = −0.9 to +0.7 and post-eruptive ∆NNO = −0.4 to +0.8. The data further show that extensive groundmass (closed-system) crystallization had no affect on bulk Fe³⁺/Fe²⁺ ratios. Finally, there is no systematic variation in the range of pre-eruptive Fe³⁺/Fe^T values of the samples as a function of SiO₂ concentration (i.e., differentiation). Therefore, the results of this study indicate that the elevated Fe³⁺/Fe^T ratios of arc andesites and dacites, compared with magmas erupted in other tectonic settings, cannot be attributed to the effects of (1) degassing of H₂O, (2) closed-system crystallization, and/or (3) differentiation effects, but instead must be inherited from their parental source rocks (i.e., mantle-derived arc basalts).  相似文献   

Photometry of Galaxies in the Field of the Galaxy Cluster aBELL 1781     

K. Fritze  M. Lange  G. M. Richter  D. Stoll 《Astronomische Nachrichten》1978,299(2):61-68

A method for determing the brightness and diameter of galaxies in a large field on Schmidt plates by automatic scanning with a microphotometer is described and applied to the ABELL cluster A 1781. The accuracy of this method is tested. The overall errors (r.m.s.) of brightness and diameter are 0.16 mag and 0″.44. The cluster A 1781 has been prooved to be a very poor cluster of about 10 members up to m_B ≈ 19^m.5.  相似文献