摘要:

ABSTRACTIn February 1970, a heavy rainstorm triggered off more than 1000 landslides in the Mgeta Valley in the western Uluguru mountains, Tanzania. The area, originally forested, is densely populated and under intensive land use, mainly annual cropping. The slides are described by Temple and Rapp (1972), who studied the geomorphological and economic effects of the catastrophe. This is a follow up study of that report. Continued erosion in the areas affected by the landslides, topsoil development and recolonisation of vegetation in the landslide scars and land reclamation by the local farmers have been investigated on fourteen landslides during the period 1970 to 1977.Sheet, rill and gully erosion on the bare surface of the landslide scars and retrogressive slumping of the slide edges have been of such a magnitude that the amounts of material eroded from the slide in some cases are as much as that removed in the initial landslide. Gullies up to 4 m deep and areas of slumps up to 150 m2have been measured.The surface soil layer of the landslides, which has been analysed for organic carbon content, bulk density, pH, texture, and plant available and reserve phosphorus and potassium contents, shows weak development during the period. Organic carbon content has increased from 0.16% to 0.44%, compared to 1.8% in the topsoil of the surrounding areas. The clay content has decreased from 13% to 8%, compared to 15% in the corresponding topsoil, due to the high erosion rate. Available potassium content has increased. The other parameters show very weak or no change during the period.Recolonisation of vegetation has been investigated in 2×2 m sample plots on the slide scars. The vegetation shows a clear succession from annual herbs to perennial grasses, though the total average cover is still small—appr. 25%—after seven years. Recolonisation has mainly occurred through seed germination. Vegetative growth from“floes”and slide edges seems to have played an unimportant role. Only species found in the neighbourhood, i.e. weeds and species from grazing land, have been found in the slides. Water availability has most likely been the major factor restricting vegetation establishment, since the coarse textured soils of the landslides readily dry out.Setting aside the affected areas for grazing, planting trees, and terracing the recultivated slides are conservation measures used by the farmers. But these measures have been haphazard and generally not effective.

ISSN:0435-3676    

DOI:10.1080/04353676.1978.11879967

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

ABSTRACTAn examination is attempted of the premise of correlation between the inferred relative ages of landsurfaces and the properties of their soil mantle. Trends in particle-size distribution and adsorption complex and soil reaction values of 38 soil profiles distributed over four surfaces, have been examined. The results are interpreted as demonstrating that properties of soils are related to the rate and nature of current geomorphic and pedogenic processes and that bevelled surfaces do not always represent unmodified ancient planation.

ISSN:0435-3676    

DOI:10.1080/04353676.1978.11879968

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

ABSTRACTField mapping of slope, cover, and soil characteristics in seventeen 2.59 km2(1 mi2) units was carried out in the Bow River Basin, Alberta. A total of 153 surface soil samples from selected sites were collected and tested for erodibility in the laboratory, using the Edmonton-pattern rainfall simulator. Testing results were extrapolated to unsampled but similar sites. Weighted mean erodibility for each unit was then plotted against mean elevation. Erodibility was found to decrease with increasing elevation from the prairies. It reaches a minimum at 1350 m but then rises to a maximum at 1900 m. This observed pattern was explained in terms of regional variations in climate and topography. The quantitative erodibility data obtained were found to be useful in evaluating sediment sources related to sheet erosion.

ISSN:0435-3676    

DOI:10.1080/04353676.1978.11879969

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

ABSTRACTA large debris flow was witnessed in Reshūn Gol in the Pakistan Hindu Kush on 13th August, 1975. Observation of the debris flow and its effects contributes to the growing body of data concerned with extreme geomorphic events in high mountains. Moreover, the observations presented in this paper are of a process which is very important in the northwestern Himalayas. Karakoram and Pamir. The Reshūn debris flow was initiated by a landslide which was triggered by rainfall. The debris flow behaved in much the same way as other debris flows, and displayed high competence by carrying a large number of boulders with long axes between 1 and 2 m. The flow had an estimated maximum surface velocity of 3 m sec-1, and lasted for about 65 minutes. The debris flow moved a large quantity of sediment, and it is estimated that the volume of sediment was of the order of 105m3. It seems that a debris flow of the same approximate magnitude has not occurred in the last 30 years, but debris flows of lesser magnitude have an estimated return period of less than 10 years. The debris flow left deposits of boulders and finer sediment in embayments along the sides of the stream, thinly veneered the banks of the stream, and deposited lobes on the apex of Reshūn Fan.

ISSN:0435-3676    

DOI:10.1080/04353676.1978.11879970

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

ABSTRACTCurrent interrelationships between surface morphology and forest vegetation are studied in a small Post-glacial re-entrant valley in the Niagara Escarpment of Southern Ontario. Relationships are examined between valley morphology, location and type of mass wasting features, forest associations and the nature of revegetation after the occurrence of localized“catastrophic”earth surface movements. The results indicate that there are no common trends discernible in the way in which vegetation re-establishes itself on these latter features although there are some general species association/surface morphology relationships identifiable throughout the valley. The local movements appear to have the effect of opening up the prevailing vegetation community to species not normally encountered in the valley. However, when this apparently random series of events is placed within the context of the time and the dynamics of both morphological and vegetational systems it is possible to construct a model of interrelationships which may have wider, more general applications.

ISSN:0435-3676    

DOI:10.1080/04353676.1978.11879971

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

ABSTRACTDebris slopes are examined from within a series of small valleys on the Mio-Pliocene Hamada du Guir. It is shown that slopes below approximately east northeast and west southwest-facing cliffs are steeper than those of different orientations. This can be related to enhanced weathering on these slopes, which experience diurnal cycles of moisture retention coupled with rapid heating and cooling. It is suggested, however, that the variations in angle are, like the slopes themselves, essentially relict from an earlier period of moister climate, when similar differences in weathering must also have held. At present differential weathering is maintaining the differences in slope angle, but the debris slopes are undergoing gradual destruction through periodic gullying.

ISSN:0435-3676    

DOI:10.1080/04353676.1978.11879972

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

ABSTRACTA reconnaissance study suggests that on alpine slopes in the Colorado Front Range which have both a soil and winter snowcover, pocket gophers (Thomomys talpoides) may be the dominant geomorphic agent. Well vegetated sites occupied by gophers appear to experience soil disturbance amounts an order of magnitude greater than nearby nivation hollows in colluvium, and three orders of magnitude greater than estimates for the general tundra surface. Preliminary evidence suggests a strong correlation between degenerated gopher tunnel systems and the appearance of small scale terracettes which are widespread in the region.

ISSN:0435-3676    

DOI:10.1080/04353676.1978.11879973

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

ABSTRACTObservation of raised beaches, erratics and glacial striae made by the Stockholm University Svalbard expeditions—Nordaustlandet, Kong Karls Land. Hopen, Edgeöya, Barentsöya, Björnöya and Spitsbergen—have shown that large parts of the Barents Sea shelf were once covered by an inland ice sheet. Other earlier observations even led to the suggestion that the ice front once stood at a position far to the north of Nordaustlandet. No nunataks are believed to have existed during the maximum extent of the ice sheet. This was confirmed in 1966 from observations of glacially sculptured rock surfaces on the summits of the peninsulas in the northern part of Nordaustlandet.In Nordaustlandet the late ice movement was in accordance with the topography, and the ice front retreated towards the position of the present ice caps. This retreat was controlled by the orientation of the fiords and the valleys. Beacause of the width and the depth of the fiord the ice broke up faster in Nordenskiöldbukta and in the northern part of Rijpfjorden than in the area west of the fiord. After the deglaciation of Nordenskiöldbukta ice moved from the southwest on Laponiahalvöya towards the ice free fiord. In the shallower Brennevinsfjorden there was not such a rapid break-up of the ice sheet. East of Nordenskiöldbukta and Rijpfjorden there is evidence of ice movement from Prins Oscars Land towards the fiord only in the southernmost part of the peninsula.The area between Vestfonna and Austfonna became ice free by a retreat of the ice front in a southeasterly direction; i.e., towards Austfonna. Only in the immediate vicinity of Vestfonna are there indications of an ice movement from westerly directions.

ISSN:0435-3676    

DOI:10.1080/04353676.1978.11879974

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

ABSTRACTShore displacement along the coast of Kenya has been studied by means of levelling of raised beaches, terraces, caves, stacks and cliffs. The results indicate a rather complicated pattern. Within the area of investigation no particular trend indicating an uneven shore-displacement in north-south direction has been found. So far, only one locality gives an indication about the age of the raised beaches.

ISSN:0435-3676    

DOI:10.1080/04353676.1978.11879975

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor