Valley Asymmetry Research Articles

Eco‐geomorphic implications of hillslope aspect: Inferences from analysis of landscape morphology in central New Mexico

We investigate the influence of hillslope aspect on landscape morphology in central New Mexico, where differences in soils, vegetation, and landforms are observed between mesic north‐facing and xeric south‐facing slopes. Slope–area and curvature–area relations, derived from a Digital Elevation Model (DEM), are used to characterize the opposing hillslope morphologies. In all geologies and elevation ranges studied, topographic data reveal significantly steeper slopes in north‐facing aspects, and shallower slopes in south‐facing aspects. North‐facing slope curvatures are also greater than south‐facing curvatures. Using a conceptual slope‐area model, we suggest that for a given drainage area, steeper north‐facing slopes imply lower soil erodibility. We argue that this interpretation, consistent with recent views of ecosystem control on semiarid erosion rates, shows the influence hillslope aspect on topography and its associated vegetation communities. Observed valley asymmetry in the region reinforces this concept and suggests a long‐term legacy of aspect‐modulated ecogeomorphic processes.

Valley asymmetry and glacial versus nonglacial erosion in the Bitterroot Range, Montana, USA

Theories that propose feedbacks among climate, tectonics, and surface processes commonly assume that erosion is enhanced by glacial activity. Indeed, studies have shown that glaciers appear to limit the elevation of mountain ranges; however, comparisons between rates of glacial and nonglacial erosion are difficult to make. Ideally, such comparisons must hold precipitation and lithology constant, while only varying the erosional regime. Located in a climatic transition zone during the Pleistocene, the east-west–trending valleys of the Bitterroot Range present an opportunity for a quantitative analysis of glacial and nonglacial erosion because the north-facing sides of the valleys were glaciated, whereas the south-facing slopes were not. The different erosional regimes operating on either side of the valleys created strongly asymmetric ridges. Ridgelines separating the east-west–trending valleys have been pushed southward by glacial headwall retreat such that ridge-to-valley distances are ∼50% greater on the north-facing slopes than on the south-facing slopes. In addition, mean hillslope angles are 6° lower on the glaciated slopes than on the unglaciated slopes, and calculations of geophysical relief suggest that, on average, glaciers have removed nearly twice as much rock as nonglacial processes. Finally, we conclude that, although rates of vertical incision by glacial processes in the Bitterroot Range were more rapid than nonglacial processes, the dominant geomorphological impact of glaciers was lateral erosion by headwall retreat.

Neotectonics and channel evolution of the Lower Ivinhema River: A right-bank tributary of the upper Paraná River, Brazil

The Ivinhema River, an important right-bank tributary of the upper Paraná River, cuts a series of terraces, geomorphic surfaces, floodplains and associate features. Through terrace mapping, sediment composition, absolute ( 14C, TL) dating and morphostructural analysis, this paper presents the composed longitudinal profile and the structural analysis of the lower course of the Ivinhema River. The tectonic model of the study area constitutes a sequence of NW tilting fault-blocks formed from antithetic faults that control channel sinuosity, longitudinal profile, floodplain distribution and valley asymmetry. The area began to be structured during the Paleocene with formation of the oligomict conglomerate, probably under an arid climate. Another tectonic reactivation in the Mio-Pliocene boundary defined the divides of the Upper Paraná and Paraguay River basins, with formation of the polymict conglomerate. An active depositional phase taken place at the Tertiary–Quaternary limit produced the massive reddish clayey sand sediments very common in the area. During the Late Pelistocene (42.5 ± 1.7 and 31.1 ± 1.7 ka BP), the Paraná and Ivinhema rivers constructed a sedimentary sequence of gravelly sand deposits in a braided channel environment. At the beginning of the Holocene a new tectonic pulse, lifted up a group of blocks parallel to the Paraná River valley, developed a series of antithetic faults. Tectonic intensity associated with the pluvial stage (Hypsithermal phase between 8 and 6 ka) changed the channel pattern of the river from braided to meandering. Channel evolution during the Late Pleistocene and Holocene was also influenced by climatic changes.

A study of valley-side slope asymmetry based on the application of GIS analysis: Alexander Island, Antarctica

Geographic Information System (GIS) data from southern Alexander Island were used to evaluate valley asymmetry from an area where ground observations had suggested that south facing slopes were steeper than north facing. Using digital elevation modelling (DEM), data were collected from 2° and 10° arcs centred on the four cardinal directions in order to determine average slope angles for a whole nunatak area (Mars Oasis). It was found that south facing slopes were significantly steeper (34°) than the north facing (28°); east and west facing slopes were each 31°. Bedrock in this area is (approximately) horizontally bedded and so valley asymmetry is considered to be due to aspect-influenced periglacial weathering processes.

Block and debris deposits in the high drakensberg, lesotho, southern africa: implications for high altitude slope processes

Past evaluation of high altitude slope development in Lesotho, southern Africa, is largely based on hypothetical or macro‐scale geomorphic approaches. Consequently, the information pertaining to high altitude southern African Quaternary slope environments has remained rather rudimentary. The present study describes the morphology and discusses the likely palaeogeomorphic processes of blockstreams and debris deposits on the Popple Peak and Njesuthi‐Mafadi south‐facing‐slopes in the Drakensberg. The geomorphic evidence provides much needed information to help improve the understanding of south‐facing slope processes during past colder periods. A model for high altitude Drakensberg south facing slopes is presented and used to challenge and expand on recent models and ideas on southern African valley asymmetry. It is found that solifluction and debris flows/avalanches were operative on south‐facing slopes during past cold periods and thereby contributed to past slope development at some high altitude sites in Lesotho. However, the geomorphological observations do not support the valley asymmetry hypothesis and it is suggested that greater caution be exercised in valley‐form interpretations, particularly where geomorphological ground‐truthing has been absent.

Drainage and valley asymmetry in the Tertiary Hills of Lower Bavaria, Germany

Valley asymmetry with steeper west-facing valley sides is a common feature in the Tertiary Hills of Lower Bavaria. Several previous studies have attributed these forms to microclimatic differences under periglacial conditions during the Pleistocene glacials. However, little attention has been given to the pattern of drainage networks in this area as a means of explaining valley asymmetry. Drainage networks show asymmetry both in length and number of tributaries on either side of the main stream. Drainage asymmetry is very likely primarily the reason of a drainage development in competitive situations. Four possible causes have been identified: (1) the position of an initial channel in relation to its adjacent parallel or subparallel drainage lines, (2) different rates of headward erosion of tributaries on either side of an inter-stream divide, (3) drainage development oblique to an initial terrain slope and (4) tilting of a landsurface and the resulting preferential headward erosion of consequent running streams. Thus, asymmetric drainage development causes differences in slope dimensions and an imbalance in run-off and sediment yield on opposite valley sides leading to the development of asymmetric valleys.

Pleistocene periglacial structures and landforms in Western Czechoslovakia

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‐wearing.

Some Aspects of Valley Asymmetry in the High Drakensberg

Abstract Considering the extent of geocryological activity in southern Africa, valley asymmetry, like many other aspects of periglacial geomorphology, is little understood. This study, based primarily on analysis of 1:50 000 maps, provides evidence for south-facing slopes having steeper gradients than north-facing slopes in the high Drakensberg region of southern Africa. The fact that periglacial features are active today at high altitudes provides evidence for the hypothesis that this asymmetry could, at least partially, have resulted from former periglacial processes during the cooler climate of the Pleistocene.

A 3‐d model of quaternary terrace development, simulations of terrace stratigraphy and valley asymmetry: A case study for the allier terraces (limagne, France)

AbstractThe combined effects of climate and tectonism on general terrace stratigraphy and valley asymmetry during the last half million years in the Allier system (France) are simulated by a 3‐D conceptual model (LIMTER). This model allows the formulation and evaluation of long term terrace formation scenarios for the Allier system. Simulation results suggest that terrace stratigraphy in the study area is mainly the result of internal dynamics and climatic change. Local tectonism contributed to the development of unpaired terraces while the general regional uplift played a dominant role in determining terrace formation and preservation in general.

Valley asymmetry: Evidence for periglacial activity in the central North Sea

AbstractPresent‐day open valleys with distinct asymmetric profiles have been studied from the central North Sea. The bulk of the valleys exhibit steep north‐facing and shallow south‐facing slopes. This asymmetry is ascribed to preferential slumping of the south‐facing slope under periglacial climatic conditions. Exceptions to the regional asymmetric trend are probably the result of more localized factors such as fluvial and microclimatic processes and the effects of local geology. The recognition of this type of within‐valley asymmetry associated with slumping in buried valleys within the Quaternary sequence may be indicative of former periglacial activity.

Slope profile variability in first‐order drainage basins

AbstractIf the three‐dimensional form of a hillslope is regarded as an infinite population of two‐dimensional slope profiles, values for attributes of the form of the hillslope can be determined by sampling and estimating the means of the attributes of the population of slope profiles. Twelve attributes are examined in seven first‐order drainage basins located on the South Downs in East Sussex to determine necessary sample sizes. Results show that if spatial randomness is assumed the size of sample required varies considerably from one attribute to another but is commonly very large. Of four alternatives to spatial randomness that are tested, consideration of both hillslope plan form and valley asymmetry are shown not to lead to reduction in sample size. However, results do suggest that maximum slope, percentage of profile length in the range 5° to < 10°, and mean angular difference between adjacent slope segments may all be dependent upon distance of the slope profile down valley. Furthermore, initial tests of the effect of spatial autocorrelation suggest that for some attributes consideration needs to be given to this factor when determining sampling strategies.

Morphometrical characteristics of valley asymmetry in some North Moravian regions

The authors deals with morphometrical data on asymmetric valleys in the eastern part of the Nízký Jeseník - Highland (357 asymmetric segments - 8211 data), the northern part of the Moravian Gate (284 segments - 6532 data), and in the hilly land of Hlučín (968 asymmetric segments of the valleys - 27186 numerical data). Among others, the author shows the dependence between the index of asymmetry and the valley size. Correlation coefficients and those of regression lines have been established on Hewlett-Packard 9825A computer.

Valley development and Quaternary tectonics in the Hlučínská pahorkatina (hilly land)

The author describes delis, dry valleys, river valleys, cryopediments as well as valley asymmetry in the area consisting of Pleistocene deposits. Special attention is devoted to the role of Quaternary tectonics in valley development. Hlučínská pahorkatina (hilly land) is situated in the region near the Czechoslovak-Polish frontier (North-West from Ostrava, North Moravia, Czechoslovakia).

Systematic valley asymmetry in the central California Coast Ranges

Asymmetry of east-west-trending valleys is a prominent landscape feature in the Salinas Valley and Gabilan Mesa area of the central California Coast Ranges. North-facing side slopes in these valleys are significantly steeper, less dissected and more heavily vegetated than south-facing side slopes. This systematic asymmetry persists throughout terrains of widely varying lithology, structural style, and tectonic history, and it is most strongly developed in areas that are underlain by horizontal to very gently dipping semiconsolidated sedimentary rocks. Asymmetric distribution of fill terraces and beheaded streams and close correlation between valley side-slope angle and valley gradient demonstrate that preferential lateral stream erosion has played a dominant role in the development of this valley asymmetry. For most of the valleys studied, this preferential lateral erosion is not related to tectonic movement; it is caused mainly by the asymmetric operation of slope-wasting processes arising from microclimatic differences on opposing valley side slopes.

Origins of Valley Asymmetry at Sarah Canyon, California

Origins of Valley Asymmetry at Sarah Canyon, California

Geomorphic Methods in Oil and Gas Prospecting

The structural-geomorphic technique advocated for use in oil and gas prospecting is based on the influence of geologic structure on the development and appearance of surface relief. Structural-geomorphic analysis is most effective in areas where inherited surface forms predominate; it is more difficult to apply in areas with a young, dynamic surface relief. The morphometric school in structural analysis focuses on map measurements of drainage patterns, valley asymmetry, stream orders and slopes. The genetic school emphasizes study of the origin and age of surface forms. Another geomorphic method in oil and gas prospecting is the paleogeomorphic technique, based on the prediction of the occurrence of hydrocarbons in stratigraphic and lithologic traps associated with the regional pinch-out of permeable rocks. Structural-geomorphic maps showing types of surface relief and their relationship to geological structure are an important aid in oil and gas prospecting.

The degradation of Lias clay slopes in an area of the east Midlands

Summary This paper presents a survey of slopes in an area of Rutland and Northamptonshire where the valley sides are formed of Upper Lias Clay capped by the Inferior Oolite. The observations support the pattern of degradation observed for natural slopes of London Clay. The slopes are considered in their regional context, from which it is seen that the steeper areas (where slides are most likely to occur) are encountered just beneath the Inferior Oolite and at valley heads. Valley asymmetry is also found, southern slopes being generally the steeper. Attention is drawn to agricultural activities which may partly or completely conceal the presence of landslides.

Geomorphological Development of the Area of Bělá nad Radbuzou

Geomorphological Development of the Area of Bělá nad Radbuzou

A Preliminary Study of Valley Asymmetry in the Ogotoruk Creek Area, Northwestern Alaska

Reports on the pattern and origin of asymmetry in this area, investigated in 1959 and 1960 in connection with Project Chariot studies. Observations from field traverses and interpretation of topographic maps and vertical aerial photographs indicate a high preponderance of steeper north-facing valley sides. This development seems best explained by a sequence of processes initiated by a greater morphologic activity on the warmer south-facing slopes. Effects of snowbanks should also be considered.

INTRAVALLEY VARIATION IN SLOPE ANGLES RELATED TO MICROCLIMATE AND EROSIONAL ENVIRONMENT

East- or west-trending stream valleys that have erosional slopes have been reported to be (1) asymmetrical with the north-facing slopes steeper, (2) asymmetrical with the south-facing slopes steeper, and (3) symmetrical, with both sides of equal mean slope angle. A series of measurements of angles of erosional slopes, taken in three east-trending, low-gradient valleys in the Laramie Range, Wyoming, shows that north-facing slopes there tend to be 4.4° steeper than opposed south-facing slopes; slope angle is further affected by nearness to the channel. In valleys that have channel gradients greater than 6° and greatly differing vegetation density across the valley, measurements of slope angles definitely show valley symmetry. The interpretation given is that unless the channel has been maintained against the base of the north-facing slope by greater slope wash from the south-facing slope, vegetation differences and resulting rates of slope erosion alone do not produce asymmetric valleys. Valley asymmetry that results from a variety of basic causes can be attributed to a single mechanism, asymmetric lateral corrosion by the stream. Difference in frost action on north-and south-facing valley sides is rejected as a cause of valley asymmetry in the areas studied because (1) the asymmetry is opposite that reported in tundra regions elsewhere, and (2) the degree of asymmetry in two widely separated areas does not reflect differences in the degree of frost activity in the two areas.