EAGLE

EAGLE  2001 - 2003

The Ethiopian – Afar Geoscientific Lithospheric Experiment

Summary

EAGLE is a major British initiative to investigate how the African continent is splitting along the Ethiopian Rift in the Horn of Africa.  The project involves the Universities of Leicester, Leeds and Royal Holloway working with the University of Addis Abeba and Ethiopian government groups.  The work will involve recording seismic “echoes” from controlled explosions and natural earthquakes, to provide an image of the top 100km or so of the Earth; the results will provide the 3-D picture of a continental rift system immediately prior to the formation of an ocean basin, a missing snapshot in the study of continental break-up.

The Ethiopian Rift

Ethiopia lies where the southern Red Sea and the Gulf of Aden – which are slowly widening to become oceans - meet with one of the major geological features on the surface of the Earth, the East African Rift Valley.  This extends from the Zambesi valley in the south through Malawi, Tanzania, Congo, Uganda and Kenya into the Main Ethiopian Rift Valley before emerging into the furnace-hot region of Afar at the junction with the Red Sea and Gulf of Aden.  The Rift Valley has formed as a result of the brittle African continental ‘plate’ responding to stretching forces that are driven by very slow creep of rocks hundreds of kilometres deep in the Earth.  In time the African plate will split apart along the line of the Rift Valley and form a new ocean.  Here we have one of the very few places on Earth where we can study the active processes of volcanism and stretching of the continental plate immediately before flooding by a newly formed ocean.

Why should we study the Rift?

Our aim is to understand one of the fundamental processes occurring on our Earth, namely the break-up of continents.  But there are also immediate economic, environmental and cultural objectives.   We hope to identify possible geothermal fields in the Rift.  Oil and geothermal exploration geologists also need to know about the embryonic stages of continental break-up to work out how to discover and exploit reserves along other continental margins where plates have successfully rifted, e.g. the oilfields offshore west Africa.  The Rift is environmentally hazardous and our studies will help in both earthquake and volcanic risk assessment.  The region of Afar is an area closely linked to the development of Man.  Anthropologists, archaeologists and geographers, in their studies of early Man and his interaction with the environment, need to know about the active processes of rifting; the type of faulting; the amount and timing of crustal subsidence and uplift; the distribution of volcanic centres and their associated volcanic rocks.

EAGLE

EAGLE is an international project and will involve more than 20 scientists in a series of seismic projects in the Ethiopian Rift Valley and the south-western corner of Afar over a period of more than a year.  Two large deployments of seismic recording instruments will take place between October 2001 and January 2003.   In the first deployment 180 instruments including seismometers, data loggers, batteries, solar panels and GPS receivers will be distributed over a 250x250km² area covering the rift and centred on the Nazret ‘volcanic segment’ to the south-east of Addis Abeba.  This segment lies within a new zone of active crustal deformation marked by aligned chains of volcanoes, vents, faults and a 60km long ‘dyke’ zone comprising vertical intrusions of magma from deep magma reservoirs.  The instruments will record seismic waves from global and local earthquakes.  These waves will have travelled up beneath the rift and will provide an image of the Earth’s crust and mantle to depths of a few hundred kilometres, illuminating the hot mantle zone and pockets of molten rock that are believed to underlie this region. The local earthquakes will provide direct evidence of active faulting and deformation within the rift.

In January 2003, some 20 scientists will be involved in the second major experiment, deploying 400 seismic instruments on a 400km long profile from the Blue Nile in the Ethiopian Highlands to the north of Addis Abeba, across the Rift and the Nazret volcanic segment, and up and over the south-eastern flank of the Rift.  The project will require the use of many all-terrain vehicles, drilling rigs, equipment trucks, infield communication systems and other supply systems.  Eight borehole shots will be fired on this profile, the resulting seismic data being interpreted in terms of a very high resolution image to depths of about 50km.  This image will show the amount by which the crust has been stretched, the distribution of sediments  and volcanic rocks within the Rift, and the location of the source for the Nazret volcanic segment beneath the Rift.

In Closing –

The project is one of the largest seismic projects ever undertaken by a group of UK universities.  It will link with projects undertaken by US and European scientists.  It will involve young scientists at the outset of their careers and will forge strong links with Ethiopian colleagues.  The results will be of importance to all Earth Scientists and will be published in the international scientific journals and popular literature.  It is an Earth Science project for the beginning of the 3^rd millennium!

Professor Peter Maguire (University of Leicester)

Dr. Cindy Ebinger, Dr. Mary Fowler, (Royal Holloway, University of London)

Dr. Graham Stuart, Dr. Mike Kendall (University of Leeds)