How does the Earth's crust grow at divergent plate boundaries? A unique opportunity in Afar, Ethiopia.

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment

Abstract

The African continent is slowly splitting apart along the East African rift valley, a 3000 km-long series of deep basins and flanking mountain ranges. This process may eventually lead to the formation of a new ocean, but on a time scale of millions of years. In the remote Afar depression in northern Ethiopia, Earth's outermost shell, usually a relatively rigid, 150 km-thick plate, has been stretched, thinned and heated to the point of rupture, to the extent that a new ocean is about to form. Below the surface, upwelling rocks from Earth's mantle below are partially melting, rising, and cooling. Here, we have the unprecedented opportunity to witness the process of plate rupture and upwelling of molten rock (magma). Normally, this process occurs within shallow seas, or along the established seafloor spreading centres deep under the oceans; in Afar, though, we can actually walk across the region as it happens. Satellite observations of the earth show that tectonic plates move apart, on average, very slowly: usually at a few centimetres per year, or about the rate of fingernail growth. Very occasionally, however, sudden large movements occur, often with devastating consequences. In September 2005, a series of fissures opened along a 60 km section of the Afar depression, as the plate responded catastrophically to forces pulling it apart. Over about a week, the rift pulled apart by 8 metres, and dropped down by up to 1 metre. As told by local people, a series of earthquakes signalled the rise of molten rock to the surface on September 26, and ash darkened the air locally for 3 days. At the same time, satellites tracking the region showed that the surface above nearby volcanoes subsided by as much as 3 metres, as magma was injected along the fissure below the surface. The rapidity and immense length of rupture are not unexpected, but have never before been measured directly. The Afar depression is so hot and dry that almost no vegetation obscures the rocks exposed on its top surface; this also means that we can use satellites to image them and to measure the way that the Earth's surface changes as faults move, and as pressurised molten rock moves up and along the length of fissures within the rift valley. In the nine months since the first major earthquakes, more dramatic surface changes have continued to take place, and earthquakes continue to stir the earth. We are proposing a major set of experiments that will bring together experts on Earth deformation, and on magma sources, movement and eruption to this unique natural laboratory. Over the next five years, a team of UK, Ethiopian and US scientists will collaborate to find answers to fundamental questions of plate tectonics: . How do the different layers of the plate stretch apart? . Where does molten rock form and rise to form new oceanic crust? . How does the molten rock move up to the surface? Satellites will image the earth from above, and sensors will record sound waves from distant and near earthquakes and natural magnetic signals to image the thickness of the rock layers the plate comprises, and discover where the magma is located prior to eruption. We will also collect and analyse the composition of rocks from young volcanoes in the same region. The Earth history deduced from compositional variations in space and time will give us clues as to when and how often similar sorts of events happened in the past / and may happen again in the future.

Publications

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Daniels K (2014) Thermal models of dyke intrusion during development of continent-ocean transition in Earth and Planetary Science Letters

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Daniels K (2012) The shapes of dikes: Evidence for the influence of cooling and inelastic deformation in Geological Society of America Bulletin

 
Description We continue to publish papers that arise from work conducted in the grant. See list of new publications in the publications section

Previous entries:
The main work of the Afar consortium is now finished, but we are still producing key publications from the project. Some highlights of the achievements in 2012 are:



1. The successful running of an international conference in Addis Ababa in January 2012 on the theme Magmatic Rifting and Active volcanism. This conference attracted more than 200 scientists from all over the world to a 3-day meeting. Many of the scientists had never been to Ethiopia before, and were also able to take part in associated field trips.



2. The successful acquisition of a second LiDAR survey of the Dabbahu segment of the Afar rift. By comparing the results with the previous survey, we have been able to reveal deformation that occurred between the two surveys and map the lava extruded in this time period.



3. We published three high profile papers in Nature Geoscience. These were (i) a detailed review and comparison of geophysical observations from Iceland and Afar, the two portions of mid-ocean ridge that are exposed above sea level (Wright et al); (ii) a study of the deformation preceding, during and following an eruption in 2008 on the Erta Ale segment of the rift, which showed that the magmatic plumbing system there was very shallow, analogous to those found on fast-spreading mid-ocean ridges (Pagli et al); (iii) a seismic receiver function study that suggests, controversially, a strong temperature anomaly does not exist under Afar today (Rychert et al) .



4. A paper in Bulletin of Volcanology that uses seismicity, petrology and geodesy together to constrain the magmatic plumbing system beneath Dabbahu volcano, suggesting that it must be configured in a series of stacked sills (Field et al, 2012a), and a second study of Dabbahu that details its magmatic history for the first time (Field et al, 2012b).



5. An integrated study of the November 2010 eruption of Erta Ale, using satellite, field and petrological data (Field et al, 2012c).



6. A geodetic and study of the Dallol region that shows a previously-unknown dyke intrusion occurred in 2004 (Nobile et al).



Several other key papers are published or in press for 2013.
Exploitation Route In addition to hazards, the work in Afar is a dramatic demonstration of plate tectonics in action. We have created materials for schools that can be viewed on our website. The results of the consortium have implications for understanding of hazards at magmatic rifts, particularly those in Ethiopia and Iceland. We helped establish a geohazards forum in Ethiopia that brought together key stakeholders from government, academia, and the geological survey to discuss a strategy for the mitigation of volcanic and earthquake hazard in Ethiopia.
Sectors Creative Economy,Education,Environment

URL http://see.leeds.ac.uk/afar
 
Description Our results have been used to influence the policy in Ethiopia on Natural Hazards. We convened a full meeting of all the key stakeholders in hazards in January 2012, which was the first time they had all been a room together. This opened up an ongoing locally-led dialogue on volcanic and tectonic hazards.
First Year Of Impact 2012
Sector Environment,Government, Democracy and Justice
Impact Types Societal

 
Description Collaboration with USGS 
Organisation US Geological Survey
Country United States 
Sector Public 
PI Contribution Use of Ar-geochronology lab and expertise of Andy Calvert
Start Year 2009
 
Description Blog post: volcano degassing 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Blog posts to explain the background context to the journal articles on Afar published by David Ferguson and colleagues in 2013. The main post, called 'Sea floor spreading, on land' is the most well read post on the blog site, volcanicdegassing.wordpress.com. It accounts for over 10% of all of the specified page views on the site, and has been read over 1000 times; it has been widely recommended as a resource to school students of physical geography and geology, based on comments posted on social media.

This short blog post explains how our work helps to contribute to a better understanding of how volcanic rifts form. The post received over 300 page views in the first week with an audience from around the world, and is now the best-read page on the websi
Year(s) Of Engagement Activity 2013,2014,2015,2016
URL http://volcanicdegassing.wordpress.com