摘要:

AbstractActive and inactive periglacial landforms are described for a small, south‐facing mountain catchment at Giant's Castle, 3140–3300 m A.S.L. Natal Drakensberg, South Africa. Micro‐patterned ground is found at the water divide and indicates marginal present‐day frost activity with soil frost penetration to a depth of 0.1–0.2 m. Downslope, thin stone‐banked sheets migrate over larger, inactive, stone‐banked lobe complexes. Block fields, suggested to be of a gelifluction origin, occupy the central part of the valley and gelifluction sheets cover the lower valley slopes. All are inactive. The range of inactive periglacial slope deposits suggests the presence of severe seasonal fros

ISSN:1045-6740    

DOI:10.1002/ppp.3430050302

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractObservations of permafrost temperatures in shallow drill holes in northern Alaska near the Beaufort Sea coast show that these temperatures have cycled during the decade from 1983 to 1993. The two sites nearest the coast indicate a period of about 10 years and an amplitude at the permafrost surface of about 2°C. The two sites farthest from the coast have similar periods but reduced amplitudes of about 0.6°C. Changes in air temperatures, snowfall, length of sea ice season, solar effects, and other factors could, in principle, produce the observed temperature changes. Barrow air temperatures have a periodicity of 10.1 years but currently lead the sunspot cycle. Snowfall also shows evidence for a periodicity near 10 years. Near Prudhoe Bay, the length of the sea ice season increased about one week from 1979 to 1986 which could have caused a decrease in coastal air temperatures. The sunspot cycle (10–11 year period) leads temperatures at the 30 m depth by two to three years which is about the expected lead. During the descending part of the last solar cycle, satellite measurements of the solar total irradiance showed a decrease of about 3W m−2, which is about four times the calculated mean energy flux at the permafrost table (0.6 to 0.7 W m−2) required to produce the observed temperature

ISSN:1045-6740    

DOI:10.1002/ppp.3430050303

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe growth of protalus ramparts is self‐limiting, as progressive thickening of a firn field will increase basal shear stress, encouraging creep of ice and basal sliding, and thus cause the transformation of stationary firn into a small glacier with consequent destruction or modification of the rampart. Modelling of the threshold conditions under which significant movement of the firn field begins indicates that the maximum distance between the rampart crest and the talus foot upslope cannot exceed c. 30–70 m, the limiting value being dependent on the gradient of the firn field. This finding implies that ridges or ramps of debris lying at greater distances from the talus foot cannot be [true] protalus ramparts formed by debris descending an essentially stationary firn field, and hence that many landforms previously described as protalus ramparts have been misinterpreted. Modelling of the limiting conditions for gravitational transport of debris suggests that clasts may continue to reach the front of a steep incipient glacier even after ice movement has been initiated, at least until the toe of the ice reaches a position 85–125 m from the talus foot. This implies the possible existence of [protalus moraines]whose form is influenced by moving ice, yet which continue to receive a supply of debris by direct gravitational transport across the ice su

ISSN:1045-6740    

DOI:10.1002/ppp.3430050304

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractDes coupes réalisées dans un cǒne de flots de débris alpin ont mis en évidence une stratification, dont la physionomie varie en fonction de la distance à l'apex du cǒne. Dans les fadès proximaux, la stratification est discontinue et constituée par des lentilles de cailloutis ouvert dans un diamiction. L'origine des cailloutis est discutée à la lumière des figures sédimentaires observées dans un flot récent. La partie distale du cǒne est caractérisée par l'interstratification de lobes, de colluvions et de paléosols. Stratification, fabriques et microstructures sont significativement différentes de celles produites par la solifluxion et peuvent constituer des figures diagnostiques pour reconnaǐtre

ISSN:1045-6740    

DOI:10.1002/ppp.3430050305

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractTalus foot ridges interpreted as protalus ramparts have been identified along 17 out of 42 km of the Niagara Escarpment within the Niagara Peninsula. They are distinguished from various types of slope form (rotational slumps, debris slides, quarries, dumps, moraines, raised shorelines and bedrock ledges) by their regular linear nature and their restriction to slopes facing between north‐east and north‐west. Morphologies range from a simple terrace with a flat top and a steep rocky outer slope, to compound ridges with closed depressions between. Maximum widths from rampart crest to main talus foot average 25 metres. Ramparts are characteristically extremely bouldery and include angular blocks of Thorold and Grimsby Sandstones weathered from the Escarpment slope, Ironde‐quoit Limestone and Lockport Dolomite blocks with metre dimensions transported to the outer slopes of the ramparts from the upper edge of the Escarpment, and clay from the weathering of Escarpment shales and from Wisconsinan diamictons. Associated firn field dimensions probably fluctuated dramatically in size during the year, and the palaeoclimatic implication is that there existed substantial late‐lying to perennial firn fields following local deglaciation at 12.5 ka BP. Independent confirmation of an early postglacial tundra climate is provided by the basal portions of pollen stratigraphies obtained nearby. The latest period when the firn fields might have existed is during the Younger Dryas chronozone (11 ka to 10.0 ka BP) when regional climatic cooling may have allowed the re‐establishment of a tundra‐like climate, especially in areas with severe mi

ISSN:1045-6740    

DOI:10.1002/ppp.3430050306

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSamples of silty clay were kept under constant boundary temperature conditions of +1°C (top) and −1°C (bottom) in a series of cold room laboratory experiments. Water migration and ice enrichment near the permafrost table were observed in all samples. Cryogenic layering was observed in soil layers with boundary temperature conditions of −0.5 to −1.0°C. These results confirm earlier observations which explain the occurrence of an ice‐rich layer near the permafrost table, and they may be used to explain the influence of snow cover on isotopic composition of near‐surface ground w

ISSN:1045-6740    

DOI:10.1002/ppp.3430050307

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe general and specific effects of predicted climate change on groundwater systems in permafrost regions are summarized. Besides a general decrease in the thickness and areal distribution of permafrost, a large unfrozen near‐surface aquifer with perennial groundwater flow might develop. Recharge and discharge would become more active and increased groundwater discharge would affect the baseflow of many rivers and the chemistry of their water

ISSN:1045-6740    

DOI:10.1002/ppp.3430050308

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430050309

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430050301

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY