SLOPE FORM AND ASSOCIATIONS WITH GROUND BOULDER COVER IN ARID ENVIRONMENTS, NORTHEAST JORDAN

Many studies of slope form and sediment transfer dynamics use either b ounded field plots or laboratory physical hardware models to study ass ociations between morphology and process. Results are presented here o f a study which examines spatial variations in slope form, changing gr ound surface boulder cover between sites and at different points along slope profiles and evidence for the movement of fine-grained sediment s which underlie the boulder cover. The study site is located in north east Jordan, an arid landscape, characterised by a late Tertiary to ea rly Quaternary basalt plateau, spreading across the foot-slopes of the Druz Mountains. Basalt age ranges from approximately 8.9 Ma to recent scoracious deposits from local eruptive centres, which are no more th an 100,000 years old. The study considers whole slope profiles rather than a representative section of a slope and accounts for form differe nces by quantifying slope shape using a length:height integral. Slope form differs with basalt age, gradually changing from concave to conve x shapes. The boulder cover can be used to examine the mobility and re distribution of underlying fine-grained sediment by establishing the d egree of clast burial at points along slope profiles. Twenty-five slop e profiles were surveyed and five plots, distributed between crest and toe, located at similar points on thirteen. The axial dimensions of b oulders within each plot were recorded. Sorting and the preferential m ovement of smaller clasts is a characteristic of the steepest part of slopes, while mean clast size increases downslope for older basalts an d decreases downslope for younger basalts. The degree of wadi network evolution and the development of sediment pans, known as Qa and Marab, varies with flow age. Links can be established between the age and ph ysical nature of individual lava flows, differences in slope form and their spatial distribution. Associations also exist between changes in boulder dimensions, basalt type and the extent of clast burial betwee n topographic highs and lows. (C) 1998 Published by Elsevier Science B .V. All rights reserved.