ISSN:1045-6740    

DOI:10.1002/ppp.3430060102

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractPermafrost regions occupy some 2,150,000 km2or 22.4% of the territory of China. The distribution characteristics are closely related to variations in climatic conditions. The permafrost area has changed since the Late Pleistocene. In north‐eastern China, the southern limit of permafrost extended to latitude 41‐42.N during the coldest stage of the Last Glaciation; in the Holocene Megathermal the southern limit retreated northwards. But the ice‐wedges and permafrost that formed in the Late Pleistocene are still present in the northern part of Mt Da‐Hingganling. The finding of inactive ice‐wedges at Yitulihe indicates a colder climate and an enlargement of permafrost during the Late Holocene. With these climate changes, the lower limit of high‐altitude permafrost in the alpine and plateau regions of western China moved up 800‐1000 m, but most of the high mountains and plateaux still remai

ISSN:1045-6740    

DOI:10.1002/ppp.3430060103

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractActive stony earth circles occur on the less coarse cells of relict sorted nets developed in quartzite debris above 600m ASL on Muckish Mountain, north‐west Ireland. The earth circles are underlain by deformed and truncated podzolic soil horizons that resemble cryoturbations produced by differential frost heave of adjacent sediments. Grain‐size distributions indicate that the soils are frost‐susceptible and possess negative frost‐susceptibility gradients. This infrequent association of coarse quartzite debris and fine‐grained frost‐susceptible matrix probably arises from the weathering of thin inter‐bedded pelites (schists) within the quartzite. Recent activity may have been triggered by climatic deterioration during the Little Ice Age, although present climate on Muckish appears capable of maintaining the surface morphology of the stony earth circles. These features, along with forms described previously, suggest that most if not all upland areas in Ireland above 600‐700m ASL possess climatic conditions favouring frost‐relat

ISSN:1045-6740    

DOI:10.1002/ppp.3430060104

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractBecause of basal melting beneath the massive Antarctic ice sheet, permafrost probably comprises less than 25% of the Southern Circumpolar Region (c. ≥ 50°S latitude). Permafrost is pervasive in ice‐free areas of Antarctica and its offshore islands but is lacking in the sub‐Antarctic islands, except possibly at the higher elevations. Based on limited data, the thickness of permafrost ranges from 100 to 1000m in ice‐free areas of Antarctica. The thickness of the active layer ranges between 50 and 150 cm in the Antarctic islands and maritime East Antarctica and 15 and 50 cm in interior Antarctica. Ground ice is restricted to rock glaciers and ice wedges; the rock glaciers, palsa and thermokarst reported in some areas originate from ice‐cored drift and not permafrost. Active and inactive patterned ground occurs throughout the region. Whereas sorted circles, nets, and stripes are common in the Antarctic islands and in maritime East Antarctica, ice‐ and sand‐wedge polygons are prevalent in ice‐free valleys of Antarctica. Altiplanation terraces may exist in the Antarctic islands and in maritime East Antarctica; however, landforms in interior Antarctica are controlled more by salt weathering than by cryogenic processes. Based‐on the presence of inactive rock glaciers, gelifluction lobes, and large‐scale patterned‐ground features, permafrost was probably present in the sub‐Antarctic islands during the last glaciation. Recommendations are made for f

ISSN:1045-6740    

DOI:10.1002/ppp.3430060105

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractUne douzaine de coins de glace le long de la rivière Porcupine (Yukon) ont été échantillonnés pour identifier leur période de croissance et pour déterminer l'origine de l'eau qui les a formés. Les datations au radiocarbone des sédiments qui les contiennent limitent leur période de croissance aux 4 derniers millénaires. Les isotopes stables montrent une homogénéité entre les centres et les bordures des coins, indiquant une stabilité climatique durant cette période. Le δ18O/δ2H est enrichi par rapport aux précipitations hivernales et se situe au‐dessous de la ligne des eaux météoriques ce qui laisse penser que les fentes de gel sont remplies durant les dernie

ISSN:1045-6740    

DOI:10.1002/ppp.3430060106

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractGravel terrain in the polar desert region of Arctic Canada supports many features such as saturated zones, wetlands, ponds and streams, all of which are associated with local seepage of suprapermafrost groundwater. Gravels have high specific yield and large hydraulic conductivity to facilitate water flow, but a shallow frost table prevents deep percolation so that, given adequate water supply from snowmelt or rainfall, seepage will occur where the topographic surface intersects the water table. Such seepage can be seen on concave slopes to produce local saturated zones. Where seepage is focused, wetlands, ponds and small streams are maintained. Water balance computation for a wetland and a pond shows that seepage from their upslope gravel zones is a major water source. Continual seepage alters the soil, vegetation and moisture characteristics of the site, and the resulting thermal and hydrological feedbacks perpetuate the various features discussed.

ISSN:1045-6740    

DOI:10.1002/ppp.3430060107

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn July 1987 a landslide affected the Val Pola (Central Alps, Italy) causing several casualities and severe damage. The main conditioning and triggering factors for the huge debris avalanche are described and possible mechanisms are suggested. Present‐day high‐mountain periglacial conditions (such as rock glaciers) present in the area highlight the probable role played by the presence of mountain permafrost in triggering the slope instabil

ISSN:1045-6740    

DOI:10.1002/ppp.3430060108

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430060101

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY