ISSN:1045-6740    

DOI:10.1002/ppp.3430020102

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430020103

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractActive periglacial features are described for the Natal Drakensberg, a mountain region in southern Africa reaching up to 3482 m a.s.l. Surficial diurnal freezing is evident by features associated with needle ice activity, while thufa and micropatterned ground indicate more severe frost penetration. Solifluction phenomena are noted but have been insufficiently described as yet. Local environmental factors, such as aspect, moisture, topography, soil depth and texture, appear important in the regional distribution of periglacial features.An altitudinal zonation of periglacial activity is tentatively linked to climatic thresholds but is inhibited by the influence of other environmental factors and a lack of climatic data. A marginal periglacial environment appears to prevail in the Drakensberg.

ISSN:1045-6740    

DOI:10.1002/ppp.3430020104

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractExtensive Pleistocene debris deposits occur in the Western Cape Mountains, South Africa. Although a cryogenic origin for the clasts is generally accepted, there is still discussion about the conditions under which debris transport and deposition took place. In the Waaihoek Mountains solifluction features occur at 1800m a.s.l. Present‐day periglacial activity results from surficial soil frost action and snowfalls in the cold season. To assess the significance of freeze‐thaw action on soil movement rates, continuous and periodic measurements are being made of climatic parameters and soil movement at several experimental sites, including a snowpatch site, at 1850m a.s.l. in the Waaihoek Mounta

ISSN:1045-6740    

DOI:10.1002/ppp.3430020105

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe cirque‐like hollows of the Lesotho high Plateau and its South African extension are a class of erosional landform attributed to processes active during Pleistocene cold phases. The hypothesis that these hollows are the product of glaciation is examined by a morphological analysis based on 12 parameters from a population of 628 hollows. Eight parameters were derived from map analysis. The survey extends over 156000 km2between latitudes 28º30′ S and 30º00′ S. The data were considered by latitudinal belts subdivided into the Escarpment region and the Interior.Most hollows are 800‐1000 m wide, almost circular and relatively shallow. Hollow distribution is related to plateau residuals on Drakensberg Formation basalt. Hollow frequency and density are greatest adjacent to the Great Escarpment between latitudes 29º S and 30º S and diminish westwards towards the Interior.Indices of Flatness, as a means of differentiation between cirques of glacial and nival origin, were computed. Only 27% fall unequivocally into the glacial size class; a further 29% are intermediate in depth. The correlation of hollow frequency, density and morphological variability with areas of high present‐day precipitation and high altitudes support the hypothesis. The strong northern orientation and strong preference for hollows on the leeside of ridges aligned NW‐SE and E‐W is attributed to snow‐bearing southerly and southwesterly winds. This also supports the hypothesis. The conclusion is reached that weak cirque glaciation occurred on the high plateau at least once dur

ISSN:1045-6740    

DOI:10.1002/ppp.3430020106

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe morphology and sedimentology of slope deposits exposed in a road cutting at Sonskyn are examined. The deposits have a lobate morphology and extend outwards from the lower reaches of a basin hollow at an altitude of approximately 2000 m a.s.l. The general stratigraphy shows an upward sequence from shattered bedrock and isolated pockets of colluvium, through stratified angular sediments which in turn are truncated by a series of channelized bouldery deposits.The concentration of colluvium towards the base of the sequence, together with the subjacent shattered bedrock, suggest cold‐climatic conditions, a scarcity of vegetation cover and slopewash processes. The transition up‐sequence to more clastic stratified sediments is indicative of freeze‐thaw cycles accompanied by slopewash during the melting phases. This has been attributed to the seasonal ablation of a snow patch. The overlying channelized bouldery deposits are attributed to solifluction processes related to the final dissolution of the snow patch.Palaeolithic artefacts found within the stratified sediments were used in southern Africa between 140000 and 40000 yearsBP. This indicates that the slope deposits at Sonskyn were laid down within the last 140000

ISSN:1045-6740    

DOI:10.1002/ppp.3430020107

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe processes responsible for the formation of fans and river terraces is deduced from sedimentological evidence. The older fans are a result of solifluction and may have formed between 24000 and ± 12000 yearsBP. A younger fan is predominantly composed of colluvium and accumulated in at least three phases, the most recent of which post‐dates ± 2440 yearsBP. The lower of the two solifluction fans has been partially reworked by fluvial action: some of the eroded debris has been redeposited and now forms a river terr

ISSN:1045-6740    

DOI:10.1002/ppp.3430020108

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA survey of cryoplanation surfaces in the Andean mountain range near latitude 35º south, and longitude 70º west shows cryoplanation surfaces are present on plutonic, volcanic, sedimentary and metamorphic rocks. Gypsum mountains above the lower limit of permafrost do not show cryoplanation. Most cryoplanation terraces are in areas with mean annual air temperature below −1ºC, (i.e. above the lowest limit of sporadic permafrost at 2800 m). The largest cryoplanation surfaces are observed on sedimentary rocks and located in areas where mean annual air temperatures are near 0ºC. Possibly, these surfaces are inactive under the present climate and were formed in a colder, past cryogenic episode.The largest cryoplanation surfaces are formed in sedimentary rocks, followed by volcanic, metamorphic and intrusive rocks. Gypsum rocks of low frost susceptibility (non‐porous) do not produce cryoplanation terraces. Cryoplanation is thought to be the result of frost shattering, frost heave and gelifluction of frost‐susceptible (porous) rocks in a climate with numerous freeze‐

ISSN:1045-6740    

DOI:10.1002/ppp.3430020109

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractDuring various expeditions to the High Andes of Argentina at latitudes 30º and 33º south, extensive geomorphological investigations have been carried out. The subtropical semiarid climate is characterized by intense global radiation with peaks of more than 1400 W/m2and daily sums of>39 MJ/m2. The daily amplitudes of the soil temperatures (≤25 cm depth) correlate with incoming radiation. Diurnal ranges of soil surface temperature (1 cm) usually exceed 45ºC, with maximum values of 55ºC at 4150 m a.s.l. Active rock glaciers exist above 4000 m a.s.l. and the thickness of the active layer varies from 1.4 to 2.5 m between 4000 and 4700 m a.s.l. Periglacial features (rock glaciers, thermokarst, gelifluction, etc.) are widespread. They are used as edaphic indicators for the lower limit of discontinuous permafrost, which is thought to be at an elevation of 4000 ± 200 m

ISSN:1045-6740    

DOI:10.1002/ppp.3430020110

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe stratigraphy of cryogenic and glacigenic episodes recorded in Central Andes at latitude 33º south is compared with the magnetostratigraphy of five (I‐V) main Patagonian glaciations. Most of the Central Andes cold episodes are relatively dated. A much older event (≈ 2.3 × 106yearsBP) is needed to explain the oldest and largest Central Andes glaciation, the sediments of which are tectonically deformed. This is the beginning of climatic change in the Central Andes. Ice‐wedge casts in till formed 3.5 × 106yearsBPin southern Patagonia are related to an even older cold

ISSN:1045-6740    

DOI:10.1002/ppp.3430020111

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY