Hydrogeological potential of major fractures in Eritrea

Neogene rifting and associated uplift on the western flank of the Red Sea r elate to a variety of steep to vertical faults and fracture zones. These in clude reactivation of north-northwest-south-southeast Precambrian shear zon es, normal faults roughly parallel to those earlier structures and prominen t east-southeast-west-northwest fractures. Where exposed, some of the last features prove to be products of large-scale dilatation and contain fills u p to 25 m wide of clastic sediments and highly altered basaltic and felsic dykes. These dilatations may have considerable potential for groundwater pr oduction, especially as their trend takes them from areas of high elevation with regionally the highest precipitation to lowland semi-arid areas. The lowlands of interior Eritrea have abundant fertile soils that were derived by erosion of Tertiary sediments and volcanic rocks from the uplifting Erit rean Highlands. Geophysical profiling across several of these structures in both lowland and highland terrains reveals conductive features believed to relate to saturated zones in these fractures. Drilling of some has proved sustainably high well yields. Although dilatational fractures are potential ly useful in supplying water, zones of deep weathering in their highland ca tchment may add soluble compounds that reduce the quality of supplies. (C) 2001 Elsevier Science Limited. All rights reserved.