摘要:

AbstractLes formes cryergiques identifiées en Aquitaine montrent que cette région de France a vraisemblablement été affectée par le développement d'un pergélisol. Celui‐ci se serait manifesté au cours de deux épisodes climatiques distincts: l'un daterait de la partie supérieure du dernier Pléniglaciaire (Dryas ancien); l'autre, plus hypothétique, se situerait dans la deuxième moitié de l'avant dernier Glaciaire. Le type de ces pergélisols ne peut être défini avec une totale certitude. Par rapport à l'actuel, la baisse de température moyenne annuelle de l'air peut être est

ISSN:1045-6740    

DOI:10.1002/ppp.3430040302

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe surficial movement of debris was monitored on a talus cone in the Venezuelan Andes for about a decade. The talus surface was classified into three textures (blocks, pebbles, sand). Painted stones were placed along four transects perpendicular to the slope; many markers (≈︁ 36%) were lost, mostly in pebble and sand areas, owing to burial. Mean stone movement decreased downslope, being much lower on the talus base (33.8 cm) than on the lines above (157.9, 239.9 and 107.8 cm). Tracers on blocks shifted a shorter distance (36.9 cm) than those on either pebbles (152.3 cm) or sand (225.1 cm). A regression showed that annual movement rates on 46 plots were inversely correlated with mean particle size (r=−0.878). An ANOVA indicated that the difference in rates between textures was more significant than that found between slope positions. Markers below outcrops also moved less than those on open talus. A line painted on the rockwall at the talus apex showed alternate periods of debris erosion and accretion, with an overall drop of 22.2 mm of the talus surface during a period of 11.5 years. Rates of debris movement vary substantially between talus textures because these are affected by different transport processes. Mean rates of debris movement remained essentially erratic during the study period, showing no consistent trends through

ISSN:1045-6740    

DOI:10.1002/ppp.3430040303

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThermokarst involutions form primarily by loading, buoyancy and water‐escape during the degradation of ice‐rich permafrost. In the Summer Island area of the Pleistocene Mackenzie Delta, they are formed mainly by loading and buoyancy, and occur within a Late Wisconsinan‐Early Holocene thaw layer. Involutions formed by water‐escape (fluidization) occur within slump‐floor deposits.To form thermokarst involutions, ice‐rich permafrost must thaw, drainage conditions must be poor and sediments must vary in texture or composition. In addition, the sediments should be susceptible to fluidization, liquefaction or hydroplastic deformation. Thermokarst involutions formed by loading and buoyancy require a reverse density gradient; those formed by fluidization require open‐system groundwater conditions or associated water‐saturated sediments susceptible

ISSN:1045-6740    

DOI:10.1002/ppp.3430040304

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe morphology and site characteristics of talus‐foot debris accumulations in the Aghla Mountains, Ireland, suggest that these landforms are fossil protalus ramparts and talus‐derived rock glaciers. The ramparts are linear or arcuate ridges or benches located within 45 m of the talus foot. The rock glaciers comprise several transverse ridges and depressions, interpreted as flow structures, and extend further from the talus foot than the ramparts. At least one rock glacier developed from a rampart. The ramparts indicate the former existence of perennia snowbeds and the rock glaciers are considered to result from the deformation and creep of interstitial ice (permafrost). There is no clear evidence of large scale‐slope failures or glacier ice having influenced debris accumulation. The landforms are probably of Nahanagan Stadial age (c. 11‐10 ka BP) and testify to the susceptibility of well‐jointed quartzite cliffs and talus to significant modification under the severe climatic regime of th

ISSN:1045-6740    

DOI:10.1002/ppp.3430040305

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractRock moisture content was determined for rock samples on different aspects of rock outcrops on Livingston Island during a summer season. As a result of the dominant rainbearing northerly winds the southern aspect usually has rock moisture levels lower than the northern. The southern aspect, however, experiences high rock moisture levels during periods of snowmelt; snow accumulates on the southern, lee‐side of the rock outcrops. Wetting and drying events are more frequent on the northern exposure, although not as common as at a site open through the full 360°, while the southern aspect tends to experience continuous, low moisture levels with infrequent dry events. Contrary to earlier suggestions, freeze–thaw weathering does not appear to be a major factor during the summer. Although rock moisture levels are conducive to freeze–thaw, rock temperatures rarely go below 0°C. Rather, it appears that weathering due to wetting and drying may be more common on the northern aspects than was previously thought while chemical weathering is active on southerly aspects. Rock moisture levels may support rock damage due to segregation ice during the winter freeze when the rate of freezing is slowed by the overlying snow cover.Contrairement a ce qui a été suggéré précédemment, l'altération par gel‐dégel ne semble pas ětre, l'été, un facteur de désagrégation principal. Quoique les niveaux d'humidité soient favorables aux actions de gel‐dégel, les températures des roches y descendent rarement sous 0°C. Au contraire, il apparaǐt que l'altération due aux alternances sèchage / humidification doit ětre plus fréquente sur les versants exposés au nord, tandis que l'altération chimique serait surtout active sur les versants exposés au sud. Les niveaux d'humidité des roches peuvent engendrer une désagrégation due à la formation de glace de ségrégation pendant l'hiver parce que la vitesse de g

ISSN:1045-6740    

DOI:10.1002/ppp.3430040306

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe landscape of the Tuktoyaktuk Peninsula coastal plain, Northwest Territories, has been strongly affected by thermokarst processes. Along thermokarst lakes developed in glacio‐fluvial sands lake‐shore dunes are common. Their formation seems related to complete or partial lake drainage. During the Holocene the rise of relative sea level has induced the submergence of the coastal plain that extended offshore of the present‐day coastal lowlands. Today coastal retreat rates in excess of 1 m/yr result in thermokarst lakes breaching and landward migration of spits and barrier‐islands. A unique type of coastal dune has been observed along two coastal sections. Late Holocene lake‐shore dunes are eroded alongshore and capped by modern coastal dunes. These coastal dunes developed in a thermokarst environment are indicators of lake drainage probably induced by late Holocene sea l

ISSN:1045-6740    

DOI:10.1002/ppp.3430040307

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430040308

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430040309

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430040301

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY