Cordula Robinson

Tertiary-Quaternary faulting and uplift in the northern Oman Hajar Mountains

Field mapping and remote sensing investigations reveal two new major fault sets cutting through Tertiary rocks, Quaternary terraces and a several-hundred-year-old irrigation canal system in the Hajar Mountains of northern Oman. They extend for tens of kilometres, forming fracture intensification zones several hundred metres wide. WNW- to NW-oriented faults run parallel to the mountain fronts in the plains adjoining the central Hajar range then obliquely crosscut the mountains in the north. Motion along these faults explains how Quaternary marine terraces became elevated 190 m above sea level. A second fault set strikes north to NNE. The associated juvenile topography suggests that they also accommodate recent uplift, subsidiary to the WNW-striking faults, with minor strike-slip and differential movement between various segments of the Hajar Mountains. Both fault systems, and the amount of Quaternary uplift (between 100 and 500 m), are similar to those in other active and ancient forebulge environments. Using the fracture patterns observed, it is proposed here that the Hajar range lies on the active forebulge of a collision zone between the NE margins of the Arabian plate, the Zagros fold belt and the Makran accretionary prism, which resulted in the recent uplift.

Radar topography data reveal drainage relics in the eastern Sahara

The Shuttle Radar Topographic Mission (SRTM) elevation data reveal segments of inactive drainage channel systems in the eastern Sahara. Four sites are investigated and their drainage networks are delineated and compared with processed Synthetic Aperture Radar (SAR) and Enhanced Thematic Mapper Plus (ETM+) images. These include parts of the drainage lines that lead to the Kufra Oasis in Libya; the eastern Gilf Kebir drainage system that straddles the border region between Egypt and Sudan; the lower reach of Wadi Howar, the extinct western Nile tributary in Sudan; and a reversed flow channel of Wadi Kubbaniya northwest of Aswan in Egypt. These features are delineated using SRTM data and a Geographic Information System (GIS) hydrologic routine. The results show that the SRTM signals penetrate the desert‐sandy surfaces and map ancient drainage systems in the same way as SAR. The study also demonstrates that SRTM data can be used to confirm or modify pathways of channel courses mapped from radar images alone. Because of this capability, it is also recommended that SRTM data be used in place of GTOPO30 elevation data in hydrologic modelling of sand‐covered deserts.

Radar Images and Geoarchaeology of the Eastern Sahara

The first Shuttle Imaging Radar (SIR-A) instrument was flown in earth orbit in November 1981. Data were obtained pertaining to a flat, sand-covered region in the eastern Sahara of North Africa. These data revealed courses of three channels or dry river courses varying in width from 8 to 20 km. This revelation increased interest in the geomorphology of desert regions and implications thereof to the geoarchaeology of prehistoric environments, particularly in southwestern Egypt.

Understanding the Distribution of Groundwater Resources using Synthetic Aperture Radar Data over Southwest Egypt

Two NSF-funded studies (OISE-0417704; OISE-0513379) carried out by the author over SW Egypt (between 20-24.5degN and 25-32degE, in the East Oweinat and Tushka regions, respectively) used C-band Radarsat-1 SAR images and topographic data to understand groundwater distributions in the local aquifers that underlie the study areas. In these studies, areas with enhanced groundwater represent the best locations for groundwater development in order to address the water and food pressures that exist in the regions. In the East Oweinat area, small-scale agricultural development is already underway, while in Tushka there are plans for development in the near future. Radar waves are uniquely able to image beneath the desert sand in the eastern Sahara to reveal groundwater-related near-surface features, that is, the courses of ancient rivers and streams and faults and fractures. The depth of near-surface imaging for the datasets used is on the order of half a meter. The distribution of groundwater-recharge near-surface features was analyzed and the variation in groundwater storage was appraised. Three new areas have been identified as promising sites for agricultural development.

SIR-C analysis of desert sabkha

Sabkhas are systems which play hydrogeologic roles in desert or coastal environments. Active sabkhas are topographically flat areas of excessive saline evaporation characterized by rough surface residual evaporite deposits and a shallow water table (0.5-1 m). SAR is ideally suited to sabkha study due to its dependence on surface roughness and surface and sub-surface dielectrics. Three active sabkhas in the Middle East and North America imaged by SIR-C are selected for this study. Backscatter values from sabkha areas and the surrounding desert environment show high backscatter values at L-band and C-band compared to the surrounding desert environment. For two sabkhas, SAR backscatter is average 5-6 dB higher. Future work involves SAR-derived sabkha classification and development of a backscatter model.