Lennart Strömquist

Slope Erosion Due to Extreme Rainfall in the Scandinavian Mountains

AbstractHeavy rainstorms in summer and autumn trigger landslides and debris flow in arctic mountains. However, the recurrence intervals are long. Some cases from Scandinavia are described. They wer...

Transport, sorting and deposition processes of Alpine debris slope deposits in the Polish Tatra Mountains

This study is an inventory of different types of talus slopes found in the Polish Tatra mountains close to Zakopane. Several active and inactive types were found; rockfall talus, alluvial talus and complex slopes formed by different processes. The slope deposits are described in relation to the altitudinal zonation of climates and the active processes. The paper finally presents an hypothesis, based on our findings, for the Postglacial slope deposition in this part of the Tatra Mts. Aims and background This study aims to analyse the morphogenetic evolution of slope deposits in terms of transport, sorting and deposition. The development of slope deposits in relation to climatic variation and altitudinal zonation of climates is also discussed. Field studies were made within two areas in the Polish Tatra Mountains, where the spatial distribution of forms was mapped by air-photo interpretation (Fig 1). The field observations, which include measurements of particle form, size and orientation as well as slope morphometry, were made close to the experimental sites used by Kotarba and others (cf Kotarba et al. 1979 and Kotarba 1981) for studies of the present slope activity in the area. The study areas The Tatra mountains constitute the highest and northernmost high mountain group of the Carpathians. Field studies were made close to Lake Morskie Oko (Fig 2) and in the Hala G4sienicowa area (Fig 3). A total of eleven different slopes were studied in detail. The rocks of the study areas can be described as granitoids belonging to the Paleozoic core of the mountain range (Table 1). The relief in the field areas is about 1300-2000 Geografiska annaler * 66 A (1984) 4 Fig. 1. The study area in Southern Poland. metres and is characterized by very steep mountain slopes below peaks and ridges reaching an altitude of about 2300-2500 metres. While different types of slope deposits cover the lowest parts of the slopes, the valley floors are characterized by glacial drift or glacifluvial deposits. The general climate of the area is summarized in Table 2. The altitudinal zonation of climates have been made by Hess (1965). He divides the mountain range into six distinct altitudinal zones such as temperate-warm s 2200 m of altitude. According to Klimaszewski (1971), the most intense present day frost weathering occurs in the interval between 1700 and 2050 metres above sea-level, hence the highest peaks are excluded having too cold a climate with a lower freeze-thaw intensity compared with the lower zone (cf also Kotarba and Starkel 1972).

Overbank Sedimentation Rates of Fine Grained Sediments. A Study of the Recent Deposition in the Lower River Fyrisån

ABSTRACTRecent overbank deposition of fine grained sediments along Swedish rivers is a rare process. Favourable conditions for overbank deposition exist, however, near the base level of low gradient rivers on the central Swedish plains. Lack of sedimentation data has inspired us to make this study which aims to estimate the present sedimentation rate and to test a field method to observe the spatial variation in deposition, by using simple sediment traps. The study area lies within the River Fyrisan drainage basin, previously investigated in several studies of fluvial geomorphology and sedimentology. The suspended sediment transport was calculated from actual discharge figures and from concentration figures obtained by water sampling and by using a “Surface Scatter Turbidimeter”. The total sedimentation in the deposition area was estimated in three ways, i.e. from actual figures on sediment transport, by a sedimentation formula and by using the results from the sediment traps. The surface deposition rates...

Gelifluction and surface wash, their importance and interaction on a periglacial slope

Studies of soil loss and sediment transport in periglacial areas often concentrate on either mass wasting or fluvial transport. Few studies discuss the interaction between the various processes in this environment. This study was made on a gelifluction slope in an alpine valley (Karkevagge) in Swedish Lappland, and is an attempt to describe the interaction between gelifluction and surface wash and the transfer from mass wasting to fluvial transport. Gerlach sediment traps were used to collect material transported by surface wash. The saturated overland flow, responsible for the bulk of erosion by water, is activated during the snowmelt. Compared with the actual transport in gelifluction on the same slope, the amount of material transported by surface wash is however diminutive. The results indicate that there is a little transfer of sediments along the entire slope profile as more material seems to be relocated within the gelifluction system then transported away. The slope can be divided in several subsystems acting more or less individually, connected only by catastrophic events such as avalaches and mudflows transporting material to the base of the slope. The actual transfer from gelifluction to fluvial transport is caused either by surface erosion in rills eroding the collapsing gelifluction lobes or by subsurface erosion. Introduction and purpose Studies of soil loss and sediment transport in periglacial areas often focus on either mass movements or fluvial transport. Few studies discuss the interaction between the various processes in this environment. The denudation balance (cf. Jahn 1954), its spatial variability and time scale as well as the flux of sediments through the different systems (cascading systems) is still little understood (cf. Chorley and Kennedy 1971, Caine 1971, 1979) although the magnitude and frequency of the various processes have been discussed by several workers (cf. Rapp 1960, Rapp and Stromquist 1976, 1979). The time lag between sediment production (through mass wasting) and peaks of fluvial sediment transport has also been observed (cf. Froelich and Sugar 1976 or in this area by Rehn, Stoertz and Stromquist 1982) but few observations have been made of the processes involved in the actual transformation of transport from mass wasting to fluvial transport. The aim of this paper is therefore to describe and discuss the interaction between one of the mass wasting processes (gelifluction) and fluvial transport as a first step in describing the sediment production from various kinds of periglacial slopes and their contribution to the fluvial system. The studies have been made in Karkevagge valley, an high alpine valley within the Scandinavian mountain range. Previous investigations there have focused on mass wasting processes and their quantification (Rapp 1960, Rapp and Stromquist 1976, 1979). A current research programme (by J. Rehn) aims to quantify the ionic mass balance and the fluvial transport from the valley (cf. preliminary results in Rehn et al. 1982 and in Stromquist and Rehn 1980). The good access to background data from the other projects makes the Karkevagge valley a good site also for the more detailed experiments and process studies. The approach of this study is, however, qualitative rather than quantitative because of the short study period (1980-1982), but nevertheless the results will inform about the processes involved, their possible rates and relations to other hillslope processes.

Integrated landscape analyses of change of miombo woodland in Tanzania and its implication for environment and human livelihood

Abstract. Landscapes bear witness to past and present natural and societal processes influencing the environment and human livelihoods. By analysing landscape change at different spatial scales over time the effects on the environment and human livelihoods of various external and internal driving forces of change can be studied. This paper presents such an analysis of miombo woodland surrounding the Mkata plains in central Tanzania. The rich natural landscape diversity of the study area in combination with its historical and political development makes it an ideal observation ground for this kind of study. The paper focuses on long‐term physical and biological changes, mainly based on satellite information but also on field studies and a review of documents and literature. The miombo woodlands are highly dynamic semi‐arid ecosystems found on a number of nutrient‐poor soil groups. Most of the woodlands are related to an old, low‐relief geomorphology of erosion surfaces with relatively deep and leached soils, or to a lesser extent also on escarpments and steep Inselberg slopes with poor soils. Each period in the past has cast its footprints on the landscape development and its potential for a sustainable future use. On a regional level there has been a continual decrease in forest area over time. Expansion of agriculture around planned villages, implemented during the 1970s, in some cases equals the loss of forest area (Mikumi‐Ulaya), whilst in other areas (Kitulangalo), the pre‐independence loss of woodland was small; the agricultural area was almost the same during the period 1975–1999, despite the fact that forests have been lost at an almost constant rate over the same period. Illegal logging and charcoal production are likely causes because of the proximity to the main highway running through the area. Contrasting to the general regional pattern are the conditions in a traditional village (Ihombwe), with low immigration of people and a maintained knowledge of the resource potential of the forest with regards to edible plants and animals. In this area the local community has control of the forest resources in a Forest Reserve, within which the woody vegetation has increased in spite of an expansion of agriculture on other types of village land. The mapping procedure has shown that factors such as access to transport and lack of local control have caused greater deforestation of certain areas than during the colonial period. Planned villages have furthermore continued to expand over forest areas well after their implementation, rapidly increasing the landscape fragmentation. One possible way to maintain landscape and biodiversity values is by the sustainable use of traditional resources, based on local knowledge of their management as illustrated by the little change observed in the traditionally used area.

Environmental impact assessment of natural disasters, a case study of the recent lake Babati floods in northern Tanzania

Babati town was one of several areas in Tanzania that was flooded during the heavy rains in 1990. Lake Babati, situated to the south of the town, is a shallow fresh water lake rapidly responding to climatic fluctuations. The lake surged on April 6, 1990. The flood created a new outlet of the lake through the town centre. Street gutters were transformed into gullies and several buildings were destroyed. Analyses of climatic data, aerial photography and old records indicate that the floodings commenced in 1964 after a relatively long dry spell when the lake was reduced to about 1/4 of its present size. Subsequent floods occurred in 1979 and 1990 and can all be related to the building up of ground and surface water resources in the catchment after periods of increased rainfall amounts. The recent land use changes are discussed in relation to the natural causes of the floods.

Fluvioglacial Landforms and Ice Margin Characteristics: An example from the Torneträsk area in northern Sweden

Fluvioglacial landforms and ice margin characteristics: An example from the Tornetrask area in northern Sweden.