摘要:

ABSTRACTThis paper applies a variety of relative-age dating techniques on rock glaciers of the La Sal Mountains, Utah to interpret the area's Holocene paleoclimates. Relative ages of rock glaciers and talus of the La Sal Mountains, Utah, were determined using several techniques: lichenometry, Schmidt-hammer rebound value, clast roundness, clast surface roughness, and weathering rind thickness. The techniques were compared against one another and evaluated as to their effectiveness. Lichenometry can be used to differentiate among depositional episodes of the past 2–3000 yrs, but lichens are sometimes adversely affected by environmental factors such as prolonged snowcover, which can periodically reduce or eliminate thalli. Rock hardness, as measured by the Schmidt hammer, and roundness did not prove to be particularly useful in differentiating sites. Weathering rind development is less subject to variations in rate, and its measurement is less subjective than most of the other methods. Weathering rinds were therefore used in conjunction with lichenometry to establish a Holocene paleoclimatic chronology. The combination of methods permits some potential disadvantages of lichenometry to be exploited to advantage and used for paleoenvironmental interpretation.Data support a threefold sequence of deposition during the late Holocene. Weathering rind data indicate deposition in early Holocene-late Pleistocene as well, but precise relative-dating of this older material is beyond the resolving abilities of these techniques. Our conclusions are in general agreement with radiometrically-based Holocene chronologies of the Colorado Front Range.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880448

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTPico de Orizaba (5,700 m), on the eastern edge of the Transmexican Volcanic Belt, is an active volcano whose most recent eruption took place in 1687. Its summit is now covered by an ice cap from which several glaciers form. As on other mountains of central Mexico, the glaciers of Pico de Orizaba have retreated considerably during the past century and, in particular, during the last decades. This study focuses on the recent evolution of Jamapa Glacier, on the northern part of the mountain. It analyzes the geomorphologic processes in relation to the rapid retreat of the glacier snout and the intense periglacial activity on the valley sidewalls. The paper presents data on the thermic regime of ice cover deposits and their contrast with that of the glacier. At the end, it summarizes a model of the geomorphic evolution of the area below a retreating glacier.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880449

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTEarlier reports, maps, aerial photographs, and tree-ring dates for moraines are used to investigate and compare the oscillations of the land-based San Quintin Glacier and the calving, tidewater San Rafael Glacier in Southern Chile. The findings show that these two very different outlet glaciers of the North Patagonian Icefield (NPI) have displayed similar trends of ice front retreat and advance since the end of‘The Little Ice Age’. The similarities imply that these glaciers are chiefly controlled by common climatic factors. A review of the literature suggests that some of the earlier reported positions of the San Rafael Glacier may be in error, but all authors agree on the beginning of the recessional trend in the late nineteenth century. The retreat of the San Rafael Glacier stopped in 1991 and by 1993 the San Quintin glacier was advancing over vegetated ground. This study mapped the San Quintin Glacier moraines and dated them by dendrochronology. Twelve years were added to tree-ring counts for colonization and growth to core height. Dendrochronology is also used to provide minimum rates of ice surface downwasting. Investigation of records from the nearest weather station suggests that precipitation could be the main control of ice front oscillations, with a response time of 20 years. A comparison of records from other weather stations to the north and south shows that these glaciers lie in a highly sensitive area between two climatic regimes, with precipitation and temperature, at present, weakly reflecting northern rather than southern Patagonian weather patterns.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880450

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTThirty-four dye tracing experiments conducted from a moulin (m3Cf), located 1.5 km from the snout of the Haut Glacier d'Arolla, Switzerland, during the summers of 1989–1991 reveal two distinct drainage paths between the moulin and the glacier snout. In July, drainage appears to be predominantly via a hydraulically efficient channelised drainage system which results in dye breakthrough curves with velocities of>0.3 m s-1and dispersivities of<10 m. In August, drainage is via a more hydraulically inefficient distributed system which results either in velocities of10 m or in zero dye recovery. One injection conducted in mid July 1991 produced a double peaked breakthrough curve, indicating simultaneous drainage through both systems. The observed behaviour is opposite to that displayed by injections made at over 50 other moulins on the glacier, in which channelised flow replaces flow through a distributed system as the melt season progresses. It can be explained if moulin m3Cf intersects an englacial conduit which conveys water rapidly to a major subglacial channel in July when the distributed system is poorly developed and water pressures are high, but which is abandoned later in the year when increased glacier bed separation has expanded the drainage capacity of the distributed system. Dilution and retardation of dye within this enlarged distributed system can account for the frequency of zero recoveries from the August dye injections.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880451

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTRelict sorted patterned ground (sorted circles and polygons) is a characteristic periglacial feature of Rostu in northernmost Sweden. In an attempt to assess the age of the formation and the time of activity, the distribution and relationship to glacial morphology were analysed with detailed cross-sections in the fine-grained centres.Relict sorted patterned ground located on narrow, well- drained plateaus between glaciofluvial channels with truncated sorted circles and large boulders on top of the fine-grained centres suggest a pre-Late Weichselian age. This is further supported by the fact that relict sorted circles occur in a relatively older, superimposed, marginal channel system but rarely in a younger system.Cross-sections in relict sorted circles revealed multiple soil injections, interstratified with organic horizons. This stratigraphy was interpreted to be a result of several phases of reactivation with diapiric soil injections from below, increasing the height of the fine-grained centre up to a metre. The main mechanism of the soil injections is suggested to be translocation of silt and clay, causing an increased frost susceptibility at deeper layers and differential frost heave. Radiocarbon datings suggest a minimum circle age of 5 200 BP.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880452

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTThe relationships between aggregate stability dynamics and soil temperature and moisture were studied at three sites in Israel under Mediterranean and arid climatic conditions. Soil moisture and temperature were monitored and aggregate stability was measured during a two year period. The data were analysed in terms of the effect of soil temperaure and moisture on bonding and breakdown agents and mechanisms such as clay and organic matter content, microbial activity and polysaccharide release, and freeze/thaw cycles.The conclusions were: 1. Aggregate stability decreases with increasing aridity. This trend reflects the influence of soil properties that have evolved over long period of time. 2. Soil temperature and moisture exert a strong control on aggregate stability dynamics in the seasonal scale under both Mediterranean and arid climatic conditions.The applicability of the conclusions to different environments was examined in the central Cordillera. While the general relationships with temperature and moisture could not be applied, the effect of agricultural activity on aggregate stability could be explained.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880453

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTThe specific geomorphological problem addressed in this paper is which thermal conditions determined moraine formation in west Greenland during Holocene deglaciation. Ice sheet modelling and geothermal research are used to delineate boundary conditions for landform formation and thereby improve and evaluate geomorphological hypotheses concerning moraine formation. Marginal thermal conditions are reconstructed from modelled basal temperature and estimates of Mean Annual ground Surface Temperature (MAST) contemporaneous to moraine formation. In mountainous areas with an altitude above 800 m, ice marginal morphology will be characterized by landforms typical for cold conditions owing to the combination of relatively thin ice throughout Holocene deglaciation and pronounced negative MAST values in the proglacial area. Low lying areas (0–250 m), with a sufficient areal extension in the direction of ice flow, have relatively thick ice throughout Holocene deglaciation. The combination of basal temperatures at the pressure melting point with positive MAST values in the proglacial area is postulated to produce deposits related to temperate beds and margins.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880454

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor