Document Type

Thesis

Abstract

Bieta Giyorgis is a subcircular igneous plug rising 250 m above the surrounding Axumite plain, northwest of the city of Axum in northern Ethiopia. The mountain is distinguished by a horseshoe-shaped plateau 200 m above the plain and which surrounds a 50 m high Central summit. The basement rock of Bieta Giyorgis is metasomatized syenite, known as the Bieta Giyorgis syenite. Syenite on the Ona Nagast plain of the plateau is capped by the Dungr formation, a sedimentary sequence of conglomeratic sandstones and massive to laminated siltstones. These units have been subjected to normal faulting. All units are covered by humanrelated debris known as geomista, as well as colluvial deposits which covers slopes and spreads onto the plain. An ancient cistern, no longer in use, has been excavated into the Dungr formation of the Ona Nagast plain and is supported by an aquifer. The Bieta Giyorgis syenite creates an impermeable boundary to bind the aquifer beneath the Ona Nagast plain and along two uplifted fault zones. The Dungr formation is the largest permeable unit of the aquifer and is supported by the permeable colluvium and geomista deposits. Erosion related to natural processes and human activity has subsequently truncated the aquifer supporting the cistern. However, based on investigations of the geology and hydrology of the Bieta Giyorgis, reclamation of the cistern would restore a reliable and more healthful source of water for the subsistence farmers inhabiting Bieta Giyorgis.

Date Awarded

2002

Department

Geology

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