The Great African Rift at the crossroads of time - ^1st day

Inauguration and presentation

• Collège de France, Arnaud Roffignon, Directeur général des services : welcome address
• CNRS, representatives of theInstitute of Ecology & Environment (Agathe Euzen, Deputy Director of the Institute), theInstitute of Human & Social Sciences (Stéphane Bourdin, Deputy Scientific Director of Hommes et milieux : évolution, interactions and Mondes anciens et médiévaux), theInstitute of Earth & Universe (Stéphane Guillot, Deputy Scientific Director of Solid Earth) and the Mission pour les Initiatives Transverses et Interdisciplinaires (Martina Knoop, Director).
• Organizers: Jean-Renaud Boisserie, Sandrine Prat and Christel Tiberi : presentation of the symposium and the book " Le Grand Rift, à la confluence des temps ".

Scientific introduction

A scientific adventure through time

Authors : Christel Tiberi (CNRS), Stéphanie Gautier-Raux (Université de Monptellier), Tony Rey (Université Paul-Valéry-Montpellier 3)

Abstract : Conducting research within the Rift means observing and working on different time and space scales : from seconds to millions of years, from nanometers to hundreds of kilometers. It also means adapting to contrasting topography (from -155 m to 6000 m), evolving cultures and societies, anticipating the imponderable but accepting the unforeseen. Research in the Rift means taking the time to exchange ideas and collaborate with others, and benefiting from the complementary nature of scientific approaches and cultures, in order to approach and understand this multifaceted territory.

The time spiral

Authors : Cédric Gaucherel (INRAE), Olivier Dauteuil (CNRS), Marc Jolivet (CNRS)

Abstract : Processes take time. The processes studied by scientists, the mechanisms responsible for tangible change, take place over a wide range of times, at often very different scales, and according to contrasting dynamics. Despite this diversity, is it possible to identify constants that would help us understand the physico-chemical, bio-ecological and socio-economic processes they underpin ? The Greeks had already mentioned the differences between processes based on linear, cyclical or event-driven time. These are easily illustrated in the African Rift, whether in terms of geological forces, the evolution of living organisms or the arrival of humans. Perhaps we could unify these different representations of temporal processes in the form of a spiral, which has the advantage of combining all three types of time. To this end, we will show that it is possible to capture this temporal spiral for the dynamics of the Rift using a new kind of formal model (known as possibilistic).

Turkana : a workshop to study social ecosystems

Author : Sandrine Prat (CNRS), Jean-Renaud Boisserie (CNRS).

Abstract : The Turkana Depression, at the junction of the Ethiopian and Kenyan portions of the Great Rift, is occupied by Lake Turkana, a semi-arid lowland zone subject to very high evaporation rates. It is renowned for its paleontological wealth, particularly in terms of ancient human remains (more than half of all remains on the African continent), and is a benchmark for the study of the relationship between biological evolution and environmental change. However, this region and its mainly pastoral populations have long been overlooked by development policies. More recently, they have been confronted with strategies for exploiting resources such as water, land and oil. The heritage angle enables us to develop an interdisciplinary scientific approach to past and present changes in this region, a mix of international and local tensions, environmental challenges and conservationist imperatives.

Evolutionism and the evolution of societies : dynamics of pastoral populations in the East African Great Rift

Author : Jean-Baptiste Eczet (EHESS)

Abstract : Societies based on pastoralism and its corollaries, nomadism and transhumance, are not easily understood by observers from largely agricultural cultures and hosted by state political forms, i.e. by most social scientists in the northern hemisphere. We will see that these societies force us to revise our conceptions of " modes of subsistence " (and the hunting-gathering/pastoralism/agriculture tripartition), of relationships with animals (beyond the dichotomy " material conditions " versus " symbolism ") and of political forms (or how statelessness and democracy come together).

Deep rift dynamics and their consequences

Authors : Raphaël Pik (CNRS), Nicolas Bellahsen (Sorbonne University), Pierre Sepulchre (CNRS), Laurent Husson (CNRS), Jean-Renaud Boisserie (CNRS), Sandrine Prat (CNRS), Christel Tiberi (CNRS)

Abstract : The East African Rift is rooted in a region of the globe where lithospheric plate movements and vertical movements of the underlying mantle have governed its evolution for tens of millions of years, creating the typical relief of " rift valley " and high plateaus, as well as producing the magmas that have poured onto the surface. This geological context, with its topographical, volcanic and hydrological specificities, has influenced the regional climate and constrained the development of the biological populations that have colonized it. This is particularly and probably the case for the evolution and migrations of hominins, even if such forcings are still poorly understood.

Living with volcanoes : risks, opportunities, adaptations

Authors : Stéphanie Defossez (Université Paul-Valéry-Montpellier 3), Miangaly Rakoto (Université Paul-Valéry-Montpellier 3).

Abstract : The Ol Doinyo Lengai volcano in northern Tanzania poses a major risk to the surrounding population, mainly Maasai communities with their traditional pastoral way of life. But the relationship between these communities and the volcano, and more generally their use of the land, reveals uses and perceptions that are not exclusively based on the volcano's dangers. The semi-nomadic way of life, ancestral traditions and local knowledge all play a part in the adaptive capacities developed by these communities to live with the volcano.

" Hot springs " and " geothermal resources ". What socio-techniques for pastoral societies in the Kenyan Rift ?

Authors : Benoit Hazard (CNRS), Yves Géraud (Université de Lorraine), Christine Adongo (EHESS)

Abstract : From the earliest colonial explorations to the recent definition of geothermal energy as a renewable energy source, Kenya has established itself as a leading producer of geothermal energy. Contributing to a vision of growth, this energy benefits from the mechanisms of the carbon market, and is often presented as a solution adapted to the fight against climate change. Yet the manufactured landscapes of geothermal energy were not human and ecological "voids" at the time of colonial expansion, which forms the historical context of geothermal energy's emergence. This presentation explores the antagonisms between national development, global discourses and the place of local societies in the development of geothermal resources in the Kenyan rift. It invites us to explore the scales and socio-techniques of energy (" mega-system " versus " Low Tech ") in an " economy of need " rather than of resources.

Diving in the Okavango Delta

Authors : Olivier Dauteuil (CNRS), Marc Jolivet (CNRS), L. Gaudaré (Université de Rennes 1)

Abstract : The Okavango Delta in northern Botswana lies at the southwestern end of the East African Rift. This immense wetland is a sensitive ecosystem with remarkable biodiversity. Every year, a flood of 11 billion tonnes of water inundates the entire system, controlling the development of vegetation, the migration of fauna and the transport of matter. The current functioning of the Delta is therefore the result of a precarious balance between climate, tectonics, the biosphere and human activities. Our work shows that this singularity could rapidly evolve with a natural detour of water towards the Zambezi River, but also by the upstream capture of water linked to the development of economic activities in Angola and Namibia.

Program