摘要:

AbstractPeriglacial processes and landforms are described from the Cordillera Neovolcánica of central Mexico. Inactive rock glaciers are related to different late‐glacial and Holocene phases of permafrost conditions. Active discontinuous permafrost occurs abovec. 4600 m ASL and appears to be from the Little Ice Age. The lower limit of late‐glacial rock glaciers is situated 500 and 600 m lower than during the Little Ice

ISSN:1045-6740    

DOI:10.1002/ppp.3430050102

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA gravimetrical study was carried out in the area of the Murtèl‐Corvatsch rock glacier in order to check the applicability of this method in alpine permafrost. The residual anomaly observed after removal of the linear regional trend is up to −1.5 mgal. Cores of borehole 2/1987 through this rock glacier showed a very high ice content in the uppermost 30 m. Borehole geophysical measurements furnished the density distribution with depth at the drill site showing values of less than 1000 kg m−3. According to the core stratigraphy and the density log at the drill site four layers were distinguished: an active layer to 3 m depth; massive ice (3–20 m); an ice‐silt‐sand layer (20–30 m); and a layer with ice‐saturated blocks (30–50 m). The extension of the four distinguished layers is modelled in three dimensions for the entire rock glacier according to the gravity data. The bedrock underneath the creeping permafr

ISSN:1045-6740    

DOI:10.1002/ppp.3430050103

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractGeophysical investigations were undertaken in the Livigno area (Sondrio, northern Italy) during 1991–92 at a number of sites where permafrost had been suggested through the application of other techniques, such as geomorphological studies, measurements of bottom temperature of winter snow cover (BTS), measurement of ground temperature in summertime (STG), and temperature of spring waters. Geoelectrical surveys confirm and characterize these permafrost occurrences. Furthermore, they indicate that, outside the rock glaciers, permafrost is also present in some gelifluction lobes. The permafrost bodies differ with regard to parameters such as resistivity, depth and thickness. Resistivity ranges from 18,000 to 560,000 ωm (ohm metres), depth varies between 8 and 21.1 m, and the active layer is 2 to 4.7 m thick in those bodies that can be considered active on the basis of morphological featur

ISSN:1045-6740    

DOI:10.1002/ppp.3430050104

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractRheological properties of ice and ice/rock‐fragment mixtures relating to rock glaciers are examined. The basic criteria for flow (neglecting sliding components) are discussed with reference to published work. Even if the internal composition of a rock glacier is very variable, ranging from pure ice to an ice/rock mixture, then similar surface velocities are likely to be measured and accounted for by at least two rheological models. Under some circumstances, even when there is ice in excess of the rock debris voids ratio, flow of the frozen material may not be possible. Uncertainty in the ice/debris composition in rock glaciers allows a wide variety of temperature, density, shear strength and creep properties to account for measured velocities. Ice lenses (segregation ice) must interconnect within a surrounding mass of stronger material for substantial deformation to occur. It is suggested that a glacier ice origin can account for the measured surface flow velocities of rock glaciers as long as the ice body is thin, generally<50m. It is usually considered that low flow velocities of rock glaciers are distinctive; however, previous conditions may have shown much greater surface velocities than at present. A test for the origin of rock glaciers is given based upon flow mechanical properties. If a rock glacier had its origin as a glacier then past velocities would have been higher than at present; if as a permafrost body, then there should not have been a major decrease. Evidence is presented to show that the latter may be the case in some instance

ISSN:1045-6740    

DOI:10.1002/ppp.3430050105

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractMacrofabrics of rock glacier debris mantles display significant variation even among similar microtopographic features. Fabrics of longitudinal ridges of La Sal rock glaciers are equally divided between cluster and girdle distributions. In some cases, fabric patterns resemble those of lahars, implying that the flow mechanics of rock glaciers bears some similarity to that of large‐scale debris flows. Shear zones are found at the margins of many longitudinal ridges, and in at least one case these zones separate the rock glacier from a pair of bounding ridges that resemble debris‐flow levees. Other sites display fabric patterns that indicate that the dominant processes are dry creep of the open‐matrix debris mantle. Weak fabrics are found at sites where rockfall inputs occur on a low‐angle surface, or where a debris mantle is undergoing passive transport by a movi

ISSN:1045-6740    

DOI:10.1002/ppp.3430050106

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractExperiments to measure the energy released by the cryogenic weathering of sandstone and shale are described. The energy released by fracturing is thought to be proportional to the importance of new surfaces appearing in the rock at the time of disintegration. The specific surfaces of samples which have been submitted to freezing have been determined by an absorption technique. The energy released by disintegration of sandstone is about −400 Kj/m2of specific surface, and for shale is 700 Kj/m2. These values represent less than 1–2% of the heat flux of the frozen rock and have a negligible effect therefore, on the thermal region of the active la

ISSN:1045-6740    

DOI:10.1002/ppp.3430050107

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430050101

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY