Valley development through erosional processes typically tends to create symmetrical valleys. Over time, water cuts through the substrate to create valleys, gorges, and canyons for which the sides are the valley are evenly sloped. However, there are anomalies to this process. Asymmetrical valleys have been well-documented even in areas of uniform substrate or little tectonic uplift. One proposed explanation for the asymmetry of these valleys is differential insolation. This may lead to different microclimates from one slope to another which alter the rate and extent of erosion. Since the differences in received insolation vary with latitude (especially in streams that flow along an east/west axis), it follows that the degree of asymmetry should also vary with latitude if differential insolation is a primary driving factor in the development of these valleys. To evaluate if insolation plays a role in the development of asymmetrical valleys, this study examines variability in asymmetry across 447 valleys in nine study areas located at different latitudes. The degree of asymmetry for each valley was measured by using 30 meter resolution digital elevation models (DEMs) to determine the slope angle of each side of the valley. Asymmetry was measured by computing a ratio of the average slope angle for each side of the valley (larger value divided by smaller). If the resulting value is one, the valley is deemed symmetrical. As the value increases, the degree of asymmetry increases. This investigation found that contrary to expectations, valleys at lower latitudes tend to have a higher degree of asymmetry than those at higher latitudes, which suggests that differential insolation does not play a major role in the development of these valleys. Instead, this study found that high altitudes and low latitudes are more frequently associated with a higher degree of asymmetry. These unexpected findings open the door to new avenues of investigation into the causes of asymmetrical valley development.

Abstract The main goal of this study is to examine mechanisms controlling valley asymmetry development at two locations with distinctly differing environmental parameters and to develop a model for the two locations. As a secondary aim the knowledge gained from the main goal is thought to help understand the very uncertain glacial past of the high Drakensberg as it can be compared to the much accepted glacial history of Abisko. Parameters studied were slope angle, landforms, vegetation cover, block abundance, available moisture, bedrock characteristics, temperature and soil moisture. Some parameters were not studied in the field due to time issues; these were instead gathered by literature study. These parameters were structural weakness, soil depth and glaciation. Results show that the environmental differences noted between each sites north and south facing slope are clear. The side facing the equator is at both locations less steep, warmer and has more diverse vegetation. Temperature development with elevation was statistically analyzed and showed no correlation or not statistically significant correlation on all slopes. The expectation the south facing side of the Sani Pass transect showed where a statistically significant decline in temperature with elevation. The main conclusion drawn is that valley asymmetry development at both locations is controlled by the increased intensity of denudational processes on the side facing the equator as a result of the larger input of radiative energy there. It is also suggested that internal feedback mechanisms are related to the hastening of asymmetric development. The main constraint of the study is that not large enough data sets were gathered and that some important parameters like soil depth could not be included in the study. More research is needed in the field of vegetation’s role in interacting with physical processes on mountain slopes. The role of vegetation as an enhancer or retarder of geomorphic processes is not sufficiently understood. / Sammanfattning Denna studies huvuduppgift var att undersöka de mekanismer som kontrollerar uppkomsten av dalgångsasymmetri vid två områden som innehar vitt skilda naturliga förutsättningar och att skapa en modell för platserna. Informationen som ges från huvuduppgiften tros kunna hjälpa förstå den osäkra glaciala historien för Sani Pass eftersom den då direkt kan jämföras med Abiskos väldokumenterade historia. Undersökta parametrar vid båda platserna är sluttningsvinkel, landformer, vegetation, blockmängd, vattenmängd, berggrundskaraktär, temperatur och markfukt. Vissa parametrar kunde inte mätas i fält och fick därför hämtas från facklitteratur. Exempel på sådana parametrar är svagheter i berggrunden, jorddjup och glacial historia. Resultaten visar att det finns tydliga skillnader mellan nord och sydsluttningarna vid båda platser. Den sida som vetter mot ekvatorn har lägre sluttningsvinkel, är varmare och har mer varierande vegetation. Temperaturutveckling vid ökande höjd över havet undersöktes statistiskt där resultaten inte påvisade någon signifikant korrelation mellan ökande höjd och lägre temperatur vid alla områden utom en. Denna plats, Sani Pass nordliga sluttning, påvisades en statistiskt signifikant sänkning av temperaturen med stigande elevation. Den huvudsakliga slutsatsen som utgår från studien är den att utvecklingen av dalgångsassymetri vid båda platserna är kontrollerad av den ökade intensiteten av de nedslitande processerna på den sida som vetter mot ekvatorn. Detta sker på grund av den större mängd solenergi som denna sida mottar. Interna feedback processer verkar även vara kopplade till skapandet av dalgångsasymmetri. Den största motgången i denna studie är att inte nog med data har samlats samt att vissa viktiga parametrar som jorddjup inte kunnat studeras. Mer forskning behövs inom vegetations roll i interaktionen med fysiska processer på bergssluttningar. Om vegetation intensifierar eller motverkar dessa geomorfiska processer är inte tillräckligt förstått.