摘要:

AbstractLes variations de diamétre et de longueur de cylindres de roches calcaires poreuses ont été mesurées au cours de cycles de gel‐dégel. Il est apparu ainsi l'existence de variations de dimension de ces roches, fort complexes et non isotropiques. Ces variations résultent essentiellement de la migration d'eau non gelée au sein des échantillons; ces migrations, dirigées vers les pores le plus larges ou vers les faces des échantillons exposées d'abord au front de gel, produisent des contractions là où des dilatations auraient été attendues. Les expériences soulignent toute l'importance du degré d'humidité des échantillons, de la porosité de la roche, de la vitesse de gel et de faibles variations éventuelles des dispositifs expérimentaux utilisés. Ces mesures dilatométriques donnent pour les variations de longueur des échantillons, des indications précieuses sur les tensions que subissent les roches sous l'action du gel et paraissent ětre une méthode d'étud

ISSN:1045-6740    

DOI:10.1002/ppp.3430040102

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractRock glaciers in the Phillips Inlet/Wootton Peninsula area of northwest Ellesmere Island are of the talus‐foot or valley‐side type and all lie below 180 m a.s.l. The rock glaciers are located predominantly below extensive bedrock gullies at the base of steep fiord and U‐shaped valley walls. Two types of rock glacier of talus‐foot type exist in the area. (1)Glacier ice‐cored rock glaciersoccur above marine limit and coincide with projected margins of former glaciers which are demarcated by the use of glacimarine and sea level evidence. Because these rock glaciers are discontinuous and have not been carried down flow line, they probably relate to catastrophic slope failures over stagnant ice. (2)Permafrost‐related rock glacierslie either below marine limit, especially in areas of heavy glacierization by floating glaciers, or in areas of former ice‐dammed lakes. The fine‐grained sediments appear to provide a deformable substrate and/or the perfect medium for the development of substantial interstitial ice. The initiation of all rock glaciers in this environment relates to the palaeogeography of the last glaciation; glacier ice‐cored (glacial) rock glaciers occur at former glacier margins and permafrost‐related (periglacial) rock glaciers occur below the marine limit associated with th

ISSN:1045-6740    

DOI:10.1002/ppp.3430040103

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractFreeze‐thaw activity was studied at two mountain sites in Swedish Lappland, a debris‐mantled slope with small rockwalls at 1200 m altitude and a solifluction slope at 1050 m altitude. During the snow‐free period, there was a low intensity of short‐term frost cycles at the rockwall site, implying that current frost shattering of bedrock is mainly due to the annual freeze cycle. At the solifluction site, during a period with net surficial soil movements of up to 3 cm, short‐term frost cycles were absent below 0.1 m depth in the ground, suggesting a dominance of pure solifluction over frost creep. A considerable variability in near‐ground temperatures implies thatin situmeasurements, rather than meteorological screen data, are essential in assessments of frost action in high mount

ISSN:1045-6740    

DOI:10.1002/ppp.3430040104

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractRecent Russian investigations into cold climate (i.e. cryogenic) weathering are reviewed. Data obtained from both experimental and field studies upon rock breakdown are summarized and values of cryogenic stability and cryogenic contrast are presented for different mineral assemblages and for rocks of different ages. Unconsolidated ice‐rich sediments are emphasize

ISSN:1045-6740    

DOI:10.1002/ppp.3430040105

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe paper describes periglacial structures and landforms developed under Pleistocene coldclimate conditions in western Czechoslovakia. The thickness of Upper Pleistocene permafrost in this territory may have been between 50 and 250 m. Climatically controlled valley asymmetry developed because of different cryogenic processes on opposite valley sides and lateral stream migration (mainly due to thermal erosion). In some cases cryopediment‐like foot‐slopes developed due to down‐wearing of river terraces and/or to the combined effect of down‐wearing and back

ISSN:1045-6740    

DOI:10.1002/ppp.3430040106

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractMassive ice formations found blocking karst cave passages in alpine and permafrost regions are not uncommon, although their origin and age are not readily apparent. With two examples from northern Yukon, we present an approach to elucidate the mode of formation, using stable isotopes, ice fabric and the time of formation by the radiocarbon activity of cryogenic powder found in such ice. These data are supported by14C dates on associated animal and plant remains.Ice formation is sensitive to seasonal air circulation patterns, with condensation from warm humid air flowing inward along the cave roof in summer, and sublimation by cold dry air penetrating along the cave floor in winter. Massive ice blocking the two caves is shown to form by gradual accumulation of floor ice from below, and accretion of hexagonal ice growing down from the cave roof.

ISSN:1045-6740    

DOI:10.1002/ppp.3430040107

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractPollen accumulation rates (PAR) of 48 samples from a permafrost core were calibrated to assess the influence of ice lensing on the calculations. Results show that permafrost formation can radically change PAR values. Accumulation of segregated ice is a major source of error, while the 9% volumetric expansion of pore water upon freezing must also be considered. The basic result of these influences is the exaggeration of sedimentation rates and sample volumes.

ISSN:1045-6740    

DOI:10.1002/ppp.3430040108

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430040109

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY