Africa is splitting in two – here is why

Google Earth. Data SIO, NOAA, US Navy, NGA, GEBCO

Lucia Perez Diaz, Royal Holloway

A large crack, stretching several kilometres, made a sudden appearance recently in south-western Kenya. The tear, which continues to grow, caused part of the Nairobi-Narok highway to collapse. Initially, the appearance of the crack was linked to tectonic activity along the East African Rift. But although geologists now think that this feature is most likely an erosional gully, questions remain as to why it has formed in the location that it did and whether its appearance is at all connected to the ongoing East African Rift. For example, the crack could be the result of the erosion of soft soils infilling an old rift-related fault.

The Earth is an ever-changing planet, even though in some respects change might be almost unnoticeable to us. Plate tectonics is a good example of this. But every now and again something dramatic happens and leads to renewed questions about the African continent splitting in two.

The Earth’s lithosphere (formed by the crust and the upper part of the mantle) is broken up into a number of tectonic plates. These plates are not static, but move relative to each other at varying speeds, “gliding” over a viscous asthenosphere. Exactly what mechanism or mechanisms are behind their movement is still debated, but are likely to include convection currents within the asthenosphere and the forces generated at the boundaries between plates.

These forces do not simply move the plates around, they can also cause plates to rupture, forming a rift and potentially leading to the creation of new plate boundaries. The East African Rift system is an example of where this is currently happening.

The East African Rift Valley stretches over 3,000km from the Gulf of Aden in the north towards Zimbabwe in the south, splitting the African plate into two unequal parts: the Somali and Nubian plates. Activity along the eastern branch of the rift valley, running along Ethiopia, Kenya and Tanzania, became evident when the large crack suddenly appeared in south-western Kenya.

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Why does rifting happen?

When the lithosphere is subject to a horizontal extensional force it will stretch, becoming thinner. Eventually, it will rupture, leading to the formation of a rift valley.

Great Rift Valley, Tanzania.
Shutterstock

This process is accompanied by surface manifestations along the rift valley in the form of volcanism and seismic activity. Rifts are the initial stage of a continental break-up and, if successful, can lead to the formation of a new ocean basin. An example of a place on Earth where this has happened is the South Atlantic ocean, which resulted from the break up of South America and Africa around 138m years ago – ever noticed how their coastlines match like pieces of the same puzzle?.

Maps made by Snider-Pellegrini in 1858 showing his idea of how the American and African continents may once have fitted together.
https://en.wikipedia.org/wiki/Antonio_Snider-Pellegrini#/media/File:Antonio_Snider-Pellegrini_Opening_of_the_Atlantic.jpg

Continental rifting requires the existence of extensional forces great enough to break the lithosphere. The East African Rift is described as an active type of rift, in which the source of these stresses lies in the circulation of the underlying mantle. Beneath this rift, the rise of a large mantle plume is doming the lithosphere upwards, causing it to weaken as a result of the increase in temperature, undergo stretching and breaking by faulting.

Mantle plume (left).
Reprinted from Tetrophysics, Vol 513, Oliver Mearle, ‘A simple continental rift classification’ Copyright (2011), with permission from Elsevier.

Evidence for the existence of this hotter-than-normal mantle plume has been found in geophysical data and is often referred to as the “African Superswell”. This superplume is not only a widely-accepted source of the pull-apart forces that are resulting in the formation of the rift valley but has also been used to explain the anomalously high topography of the Southern and Eastern African Plateaus.

Breaking up isn’t easy

Rifts exhibit a very distinctive topography, characterised by a series of fault-bounded depressions surrounded by higher terrain. In the East African system, a series of aligned rift valleys separated from each other by large bounding faults can be clearly seen from space.

Topography of the Rift Valley.
James Wood and Alex Guth, Michigan Technological University. Basemap: Space Shuttle radar topography image by NASA

Not all of these fractures formed at the same time, but followed a sequence starting in the Afar region in northern Ethiopia at around 30m years ago and propagating southwards towards Zimbabwe at a mean rate of between 2.5-5cm a year.

Although most of the time rifting is unnoticeable to us, the formation of new faults, fissures and cracks or renewed movement along old faults as the Nubian and Somali plates continue moving apart can result in earthquakes.

However, in East Africa most of this seismicity is spread over a wide zone across the rift valley and is of relatively small magnitude. Volcanism running alongside is a further surface manifestation of the ongoing process of continental break up and the proximity of the hot molten asthenosphere to the surface.

A timeline in action

The East African Rift is unique in that it allows us to observe different stages of rifting along its length. To the south, where the rift is young, extension rates are low and faulting occurs over a wide area. Volcanism and seismicity are limited.

Towards the Afar region, however, the entire rift valley floor is covered with volcanic rocks. This suggests that, in this area, the lithosphere has thinned almost to the point of complete break up. When this happens, a new ocean will begin forming by the solidification of magma in the space created by the broken-up plates. Eventually, over a period of tens of millions of years, seafloor spreading will progress along the entire length of the rift. The ocean will flood in and, as a result, the African continent will become smaller and there will be a large island in the Indian Ocean composed of parts of Ethiopia and Somalia, including the Horn of Africa.

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Dramatic events, such as sudden motorway-splitting faults can give continental rifting a sense of urgency. However, rifting is a very slow process that, most of the time, goes about splitting Africa without anybody even noticing.

This article was updated and the headline changed on April 7 to reflect ongoing discussion by geologists about the cause of the large crack that appeared on the East Africa Rift and whether its location is related to the African continent split.

Lucia Perez Diaz, Postdoctoral Researcher, Fault Dynamics Research Group, Royal Holloway

This article was originally published on The Conversation. Read the original article.

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Not so fast: why the electric vehicle revolution will bring problems of its own

Electric cars are taking over – but they really as green as they look?
Jack Amick / flickr, CC BY-NC

Martin Brueckner, Murdoch University

After years of being derided as a joke by car manufacturers and the public, interest in electric vehicles has increased sharply as governments around the world move to ban petrol and diesel cars.

We have seen a tremendous rise in availability, especially at the premium end of the market, where Tesla is giving established brands a run for their money. Electric cars are likely to penetrate the rest of the market quickly too. Prices should be on par with conventional cars by 2025.

Electric cars are praised as the answer to questions of green and clean mobility. But the overall sustainability of electric vehicles is far from clear. On closer examination, our entire transport paradigm may need to be rethought.

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Australia’s ‘electric car revolution’ won’t happen automatically

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Compared with combustion engines, electric transport has obvious advantages for emissions and human health. Transport is responsible for around 23% of energy-related carbon dioxide emissions globally. This is expected to double by 2050.

Motor vehicles also put a burden on society, especially in urban environments where they are chiefly responsible for noise and air pollution. Avoiding these issues is why electric vehicles are considered a key technology in cleaning up the transport sector. However, electric cars come with problems of their own.

Dirt in the supply chain

For one, electric vehicles have a concerning supply chain. Cobalt, a key component of the lithium-ion batteries in electric cars, is linked to reports of child labour. The nickel used in those same batteries is toxic to extract from the ground. And there are environmental concerns and land use conflicts connected with lithium mining in countries like Tibet and Bolivia.

The elements used in battery production are finite and in limited supply. This makes it impossible to electrify all of the world’s transport with current battery technology. Meanwhile, there is still no environmentally safe way of recycling lithium-ion batteries.

While electric cars produce no exhaust, there is concern about fine particle emissions. Electric cars are often heavier than conventional cars, and heavier vehicles are often accompanied by higher levels of non-exhaust emissions. The large torque of electric vehicles further adds to the fine dust problem, as it causes greater tyre wear and dispersion of dust particles.

Different motor, same problem

Electric vehicles share many other issues with conventional cars too. Both require roads, parking areas and other infrastructure, which is especially a problem in cities. Roads divide communities and make access to essential services difficult for those without cars.

A shift in people’s reliance on combustion cars to electric cars also does little to address sedentary urban lifestyles, as it perpetuates our lack of physical activity.

Other problems relate to congestion. In Australia, the avoidable social cost of traffic congestion in 2015 was estimated at A$16.5 billion. This is expected to increase by 2% every year until 2030. Given trends in population growth and urbanisation globally and in Australia, electric cars – despite obvious advantages over fossil fuels – are unlikely to solve urban mobility and infrastructure-related problems.

Technology or regulation may solve these technical and environmental headaches. Improvements in recycling, innovation, and the greening of battery factories can go a long way towards reducing the impacts of battery production. Certification schemes, such as the one proposed in Sweden, could help deliver low-impact battery value chains and avoid conflict minerals and human rights violations in the industry.

A new transport paradigm

Yet, while climate change concerns alone seem to warrant a speedy transition towards electric mobility, it may prove to be merely a transition technology. Electric cars will do little for urban mobility and liveability in the years to come. Established car makers such as Porsche are working on new modes of transportation, especially for congested and growing markets such as China.

Nevertheless, their vision is still one of personal vehicles – relying on electric cars coupled with smart traffic guidance systems to avoid urban road congestion. Instead of having fewer cars, as called for by transport experts, car makers continue to promote individualised transport, albeit a greener version.

With a growing population, a paradigm shift in transport may be needed – one that looks to urban design to solve transportation problems.

In Copenhagen, for example, bikes now outnumber cars in the city’s centre, which is primed to be car-free within the next ten years. Many other cities, including Oslo in Norway and Chengdu in China, are also on their way to being free of cars.

Experts are already devising new ways to design cities. They combine efficient public transport, as found in Curitiba, Brazil, with principles of walkability, as seen in Vauben, Germany. They feature mixed-use, mixed-income and transit-oriented developments, as seen in places like Fruitvale Village in Oakland, California.

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These developments don’t just address transport-related environmental problems. They enhance liveability by reclaiming urban space for green developments. They reduce the cost of living by cutting commuting cost and time. They deliver health benefits, thanks to reduced pollution and more active lifestyles. They improve social cohesion, by fostering human interaction in urban streetscapes, and help to reduce crime. And of course, they improve economic performance by reducing the loss of productivity caused by congestion.

Electric cars are a quick-to-deploy technology fix that helps tackle climate change and improve urban air quality – at least to a point. But the sustainability endgame is to eliminate many of our daily travel needs altogether through smart design, while improving the parts of our lives we lost sight of during our decades-long dependence on cars.

Martin Brueckner, Senior Lecturer in Sustainability, Murdoch University

This article was originally published on The Conversation. Read the original article.