摘要:

ABSTRACTThe characteristics and instability of recently exposed valley-side moraines are described. The presence of an ice-core, largely of glacial origin, is a major contributing factor in their instability by encouraging mass wasting on the moraine proximal slopes. An inventory of the spatial distribution and magnitude of mass wasting events over two field seasons indicates that the most unstable slopes are those closest to the glacier and, presumably, most recently deglaciated. The temporal distribution of mass wasting events indicates that they are triggered by the accumulation of rain water and/or water from ablation at the ice-core surface.

ISSN:0435-3676    

DOI:10.1080/04353676.1991.11880337

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

ABSTRACTOn 10 November 1976, a 1.5 km×0.5 km rockslide deposit on the surface of an unnamed outlet glacier of Mýrdalsjökull ice cap, southern Iceland, was observed from an aircraft. Deposits from two different rockslides, including the larger one observed on 10 November 1976, were visible on a 10 September 1978 aerial photograph of the unnamed outlet glacier. An analysis of vertical and oblique aerial photographs, Landsat images, and seismological records was used to establish the time of occurrence of the larger rockslide to a 30-day period between 9 September 1972 and 9 October 1972. The trigger mechanisms for the rockslide activity appear to have been heavy precipitation prior to the event and the decrease of buttressing mass at the base of the valley wall resulting from recession of the glacier (decrease in width and thickness). The recession led to instability of highly altered hyaloclastite bedrock, talus, and morainal materials on an oversteepened slope. An earthquake as a trigger mechanism was considered to be unlikely from a thorough review of seismic records. Measurements of the downglacier movement of the larger rockslide deposit give an average speed of the glacier as 30±3 m a-1between September/October 1972 and 10 September 1978. From measurements of aerial photographs taken on 10 September 1978 and 4 September 1984, the average speed of the glacier increased to 45 m a-1during this 6-year interval. Although the terminus of the unnamed outlet glacier had not yet begun to advance in 1986, it had undergone thickening since 1978.

ISSN:0435-3676    

DOI:10.1080/04353676.1991.11880338

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

ABSTRACTA growth curve forRhizocarponlichens has been constructed for a valley in the Polish High Tatra Mountains. Monuments and buildings of known age have been, used as measurement sites for the lichen sizes. The lichen growth could be described by the equation: Ld= 0,44 A—4, where Ld- lichen diameter in mm, A-lichen age in years. As an application, this curve has been used for dating of debris flow deposits. These datings show that most of the investigated debris flows were triggered during the later part of the Little Ice Age, due to alluviation. During the last hundred years, only a few debris flows have occurred.

ISSN:0435-3676    

DOI:10.1080/04353676.1991.11880339

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

ABSTRACTThe ancient shoremarks of the Járlåsa esker have been levelled. The most common shoremarks of the Járlåsa esker are small boulder fields (Sw.“stentorg”), but shore terraces with beach scarps also occur. The latter are not so well developed as on e.g the adjacent Heby esker but have nevertheless been included as data for the stratification of the shorelines, or rather the strata of shoremarks. A stratification attempt has been made. This identifies a number of strata in the altitude interval between c. 60 and 70 m a.s.1. This result is in good agreement with studies from the Heby esker, situated at c. 20 km W of the Járlåsa esker.

ISSN:0435-3676    

DOI:10.1080/04353676.1991.11880340

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

ABSTRACTThis paper discusses a technique for mapping the area coverage of sea ice regardless of a cloud cover. Data from the AVHRR sensor of the NOAA-9 satellite were recorded on 22 May 1988. The study area is situated in the Arctic from Greenland to Norway including the islands of Svalbard. One of the thermal channels of the NOAA AVHRR sensor is used for the cloud inventory, but it is not suitable for separation of ice and open water due to similar brightness temperatures. The visible and near infrared channels of NOAA AVHRR are, on the other hand, suitable for ice and water separation. Problems arise when the ice margin disappears under a cloud cover. The visible and near infrared channels are highly correlated in the Arctic, mainly due to lack of vegetated surfaces. By extracting the small portion of uncorrelated features in these two channels, the extent of the ice cover is revealed even under the clouds. It is possible to estimate and map the extent of sea ice, cloud types and areas where ice and cloud overlap.

ISSN:0435-3676    

DOI:10.1080/04353676.1991.11880341

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

ABSTRACTA subarctic population of Picea abies ssp. obovata in northern Sweden was retrospectively analyzed dendroecologically: tree-ring chronology (A.D. 1773–1989) and age structure. Additionally, recent canopy change and ground temperatures were assessed. Tree-ring width correlated best with the mean temperature of June, when thawing of the seasonal ground frost beneath the crowns normally takes place. Hypothetically, steeply declining radial growth since the 1950s or even earlier preconditioned substantial canopy dieback in 1987, triggered by extreme meteorological conditions associated with exceptionally late thawing and the evolution of new local permafrost. The tree-ring response to this episode had at least four equivalents, all between the 1780s and 1870s, which may indicate severe ground frost conditions. Structural features of the ground microrelief and of the spruce stand further point to previous permafrost episodes, which possibly rendered establishment of a forest stand impossible. It is hypothesized that the natural forest history is influenced by historical ground frost variations and that the northern range limit of spruce in Sweden is partially controlled by severe ground freezing, late thawing and edaphic conditions.

ISSN:0435-3676    

DOI:10.1080/04353676.1991.11880342

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

ABSTRACTThe Central Pacific coast of Mexico can be classified into four zones, each showing different rainfall patterns. As a result of tropical cyclone influence in the Pacific coast, the level of rainfall probability differs between zones. Such influence is revealed in the total annual rainfall, in the seasonality and in the monthly rainfall pattern.

ISSN:0435-3676    

DOI:10.1080/04353676.1991.11880343

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor