摘要:

AbstractOn a sélectionné dans les Alpes deux talus d'éboulis présentant un matériel de faible cohésion sur le profil desquels on a fait des mesures de pente et de granulométrie selon un pas régulier. Sur l'un d'eux, on a relevé et localisé les apports reçus de la corniche pendant 10 ans et mesuré le déplacement des fragments pendant 2 ans. Le traitement statistique de ces données et les résultats obtenus convergent vers un modèle biphasé de ce type d'accumulation: le segment proximal fonctionne en accumulation‐transit, le segment distal en accumulation pure. Le passage d'une phase à l'autre se réalise par un point de rupture dynamique bien repérable sur le profil. Ce modèle remet en question les précédents, notamment ceux qui ont été conçus à

ISSN:1045-6740    

DOI:10.1002/ppp.3430020302

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractChanges of mean annual ground temperature at the depth of zero annual amplitude (tan) with elevation is well known for regions of high latitude and alpine permafrost. However, this phenomenon is not sufficiently studied in the intracontinental regions of Siberia. The authors analyse the altitudinal zonality of mean annual ground temperatures (tan) in the Udokan Ridge, Northern Trans‐Baikal. Measurements were obtained from 321 boreholes situated on different relief elements with altitudes ranging from 830 m a.s.l. to 2170 m a.s.l. A mean integral temperature (t*an), as well as the range oftanvariations, was determined for every 200 m altitudinal interval. The results of large‐scale geocryological mapping were used to determinet*an, which allowed one to consider the spatial distribution of landscape types characteristic of certaintanvalues. It is established that with increasing altitude,t*anvalues uniformly decrease with a gradient of ‐0.3 °C/100 m. The difference intanbetween ‘cold’ and ‘warm’ landscapes changes from 2°C to 5°C for the altit

ISSN:1045-6740    

DOI:10.1002/ppp.3430020303

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractObservations of wind action were made in the late winter, spring and summer at three lowland sites located on Banks Island (1977‐79), Melville Island (1986‐87) and Ellesmere Island (1989‐90). Erosion pin measurements in north‐central Banks Island showed minimal activity on interfluves and the highest rates at a blowout site in an unvegetated sand plain. The timing of aeolian activity during the year depended on the site characteristics. Where the snow cover was incomplete in winter, either because a rugged microtopography resulted in terrain elements protruding above the surface of the snow or because sublimation of snow exposed the ground surface, aeolian transport could occur year‐round. In areas with a flatter microtopography, summer transport took place but deflation was negligible over the winter and niveo‐aeolian deposition was confined to the autumn and spring when the snow cover was patchy. Windblown sediment became spatially concentrated by denivation at some sites and was deposited on slopes as fans or layers up to 8 cm thick. In the years this occurred, the rate of deposition was greater than sediment removal by wash or other processes and, at least in the short term, the form of the slope

ISSN:1045-6740    

DOI:10.1002/ppp.3430020304

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractSand‐filled, wedge‐shaped structures beneath a thin layer of aeolian sand penetrate a pre‐Illinoian till and gravel in northeastern Nebraska. Interpreted to be relic thermal contraction crack wedges, they provide the first definite evidence in this State of the former presence of permafrost. The wedges are 5‐7 m apart, 1.8‐2.8 m deep and 0.6‐0.9 m across at the top, taper downward to a crack and intersect to form polygons. They are filled with medium sand that contains mostly rounded and frosted grains. Vertical fabric is present in each wedge. Ventifacts lie along the top of the till, which is covered by 0.3‐0.4 m of interlaminated medium and fine sand that grades upward into 1.0 m of Peoria Loess.These sand wedges formed in thermal contraction cracks, in dry, windswept areas 25‐50 km south of the Late Wisconsinan ice margin, where snow cover was minimal, so that blown sand fell into the open cracks. They probably required mean annual temperatures of —6 °C to —8 °C or lower, along with strong winds and rapid drops in temperature. Yardang‐like topography, beyond the limit of Wisconsinan till across central South Dakota and northeastern Nebraska, is further evidence of exceptionally strong winds parallel to the ice margin during the Late Wisconsinan glacial maximu

ISSN:1045-6740    

DOI:10.1002/ppp.3430020305

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractLes naleds sont fréquents dans le nord du Yukon, surtout dans le lit des rivières qui entaillent les monts British et Richardson. Presque tous se situent dans le voisinage de massifs calcaires et de failles. Leur épaisseur atteint plusieurs mètres et leur surface peut couvrir des kilomètres carrés. Le plus grand, celui de la rivière Firth, atteint 28 km2. Les eaux et les dépéts de calcite de quatre naleds, ceux de Timber Creek, Fish Hole Creek, Babbage River et Salmon Fork River ont fait l'objet d'analyses isotopiques é18O, é13C et é2H. Les résultats indiquent que l'origine des eaux est locale et que leur gel par la base est un processus assez lent, ce qui permet à la calcite de pr°Cipiter en équilibre á une température proche de 0 °C. Une comparaison entre la superficie du naled de la rivière Firth au cours de l'été et les valeurs de rayonnement solaire enregistrées à Inuvik, montr

ISSN:1045-6740    

DOI:10.1002/ppp.3430020306

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPloughing blocks (boulders) consist of three elements, namely, a rock fragment, a mound and an elongate depression. The movement of a block downslope leads to the formation of a pressure mound ahead of the block, while in its rear there is a furrow. In the Tien Shan mountains the size of the largest ploughing block is ≈11 m3, the height of the largest mound is about 1.0 m and the most elongated furrow is ≈37 m long.Seasonally frozen ground below the blocks or in their immediate vicinity gives rise to their movement. Seasonal freezing is the key factor that dictates a high ice content and ground moisture beneath the block which causes the gliding downslope. The block movement velocity is not regular and reaches its maximum in the second half of spring. Velocity varies also from year to year: in certain years it is nil and sometimes it is high as 7‐10 cm a

ISSN:1045-6740    

DOI:10.1002/ppp.3430020307

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe aim of this note is to identify the beginnings of growth of two pingos located in Sarqaq Dalen, west‐central Greenland. One is located at the toe of an alluvial fan, and seems to be active; the other is on a river bed, and already collapsed. Marine sand covers the pingos and indicates that the Holocene transgression predates their growth. The pingos are located approximately 2 km from the present coastline. Pollen analysis of the overlying sediments of the two pingos leads to the following conclusions: (1) although the study area had already emerged from the sea at Post Fjord stage (7800 years BP), it was submerged again sometime between 7000‐5000 years BP; (2) one pingo started its growth approximately 4500 years BP; (3) the other pingo started its growth approximately 6000‐5500 yea

ISSN:1045-6740    

DOI:10.1002/ppp.3430020308

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPermafrost field investigations in the Gu Lian Mining area of Great Xi'an Ridge (in Chinese: DA HINGAN LING) was undertaken in the second year following a forest fire. It was found that after the fire air temperature, ground temperature, evaporation (measured by pan) and wind velocity increased but humidity, ground ice and water content decreased. These changes led to an increase in seasonal thaw depths. These results illustrate that the permafrost environment is changed greatly by forest fire.

ISSN:1045-6740    

DOI:10.1002/ppp.3430020309

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe Mayo District, Yukon Territory, lies in the widespread discontinuous permafrost zone. Permafrost thicknesses of up to 40 m have been measured in valleys, and of 135 m at higher elevations. Many observations of ground ice have been made by placer miners, but generally these are unrecorded. Recently, over 200 shallow geotechnical boreholes have been drilled in the area in association with municipal or highway construction. Ground ice is usually encountered at undisturbed sites within 4 m of the surface. In the main valleys at elevations below 1100 m a.s.l. coarse, clastic, outwash materials, sand dunes and slopes with southerly aspect are usually frost‐free. Stripping of vegetation for construction or placer mining leads to permafrost degradation, but permafrost can re‐establish as vegetation regenerates. Ground temperatures at Mayo and Keno Hill indicate a geothermal flux of over 0.1 W

ISSN:1045-6740    

DOI:10.1002/ppp.3430020310

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430020301

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY