Vertical deformation in the Main Ethiopian Rift: levelling results in its northern part, 1995–2004
Published:January 01, 2006
Laike M. Asfaw, Henok Beyene, Amde Mkonnen, Tadesse Oli, 2006. "Vertical deformation in the Main Ethiopian Rift: levelling results in its northern part, 1995–2004", The Afar Volcanic Province within the East African Rift System, G. Yirgu, C. J. Ebinger, P. K. H. Maguire
Download citation file:
A levelling line consisting of 43 benchmarks was established between the towns of Wolenchiti and Metehara in the northern part of the Main Ethiopian Rift in July 1995 by the Geophysical Observatory of Addis Ababa University and the Ethiopian Mapping Authority. The measurement was repeated in November 2003 on 30 of the surviving benchmarks. In both epochs of measurement, the standard accuracy attained is ± 4 mm √K corresponding to a first order levelling, where K is the inter-benchmark distance in kilometres. The line crosses the northern and southern parts of the Nazret (Boset—Kone) and Sabure (Fantale—Dofen) magmatic segments respectively where 80% of rift deformation is believed to be localized. In eight years, interval height differences ranging from +3 mm to −22 mm are found along the line with the maximum subsidence rate of 2.8 mm a−1 corresponding to the Kone-Gariboldi volcanic complex in the northern part of the Nazret magmatic segment. On the other hand, at the eastern end of the line, despite the existence of large fissures and an expanding lake in the vicinity suggesting possible significant subsidence, on the contrary relatively small vertical deformation is found. The strong subsidence measured at the Kone-Gariboldi volcanic complex is interpreted to be due to remnant processes of subsidence at these volcanic centres following withdrawal of magma in the recent past. Regarding the eastern end of the line where Lake Beseka is located, the result is particularly important in verifying that the rapid expansion of the lake associated with elevation increase of 40 cm a−1 could not be attributed to tectonic subsidence or uplift in the region.
Figures & Tables
The Afar Volcanic Province within the East African Rift System
The seismically and volcanically active East African Rift System is an ideal laboratory for continental break-up processes: it encompasses all stages of rift development. Its northernmost sectors within the Afar volcanic province include failed rifts, nascent seafloor spreading, and youthful passive continental margins associated with one or more mantle plumes. A number of models have been proposed to explain the success and failure of continental rift zones, but there remains no consensus on how strain localizes to achieve rupture of 125–250 km thick plates, or on the interaction between the plates and asthenospheric processes. This collection of papers provides new structural, stratigraphic, geochemical and geophysical data and numerical models needed to resolve fundamental questions concerning continental break-up and mantle plume processes. It focuses on how mantle melt intrudes and is distributed through the plate, and how this magma intrusion process controls along-axis segmentation and facilitates break-up.