Superplume Beneath Continent Is Splitting Africa Apart
Sophisticated chemical analysis of volcanic gases from Kenya have provided the first evidence that a superplume lies beneath East Africa driving active tectonics and slowly separating the Somali plate and the Horn of Africa from the rest of the continent.
An international team of scientists led by Professor Fin Stuart from the University of Glasgow, working in partnership with the Kenya Geothermal Development Company, has discovered surprising results in a new study of gases from the Menengai geothermal field in central Kenya.
The rift valleys of East Africa are some of the largest and most spectacular topographic features on Earth. They extend for 3,500 kilometers through Ethiopia, Kenya, Uganda and Malawi, and host extensive volcanic fields. The rifts are the manifestation of the African tectonic plate being split apart driven by forces in the Earth's interior. However, scientists are uncertain whether the volcanism and rifting is due to shallow processes or whether it is driven by up-welling hot material from Earth's mantle.
As countries along the rift zone are tapping into geothermal energy, scientists get access to new sampling sites. The researchers used gases collected from the Menengai geothermal field (started in 2009 and still in development) in central Kenya to reconstruct the source in Earth's mantle feeding the geothermal activity.
The team notes that the gases are chemically indistinguishable from gases present in volcanic rocks from Hawaiʻi', where volcanism is fueled by a mantle plume. Together with the common chemical 'fingerprint' between different geothermal fields— the researchers compared their results with gas samples coming from the Red Sea to the north and from Malawi to the south — this discovery supports the theory that a single "superplume" is the main source.
'Our research suggests that a giant hot blob of rock from the core-mantle boundary is present beneath East Africa," summarizes Stuart. The plume not only drives the tectonic plates apart, but also pushes up the African continent preventing the rift zone to be flooded by the Red Sea (forming the geologically spectacular landscapes of the Afar Depression).
Map of East Africa showing some of the historically active volcanoes (red triangles) and the Afar ... More Depression (shaded, center).
Seismic surveys indicate the presence of a large anomaly beneath the southern tip of the African continent. Such "Large Low Shear Velocity Provinces" are composed of hot and weak mantle material, and the only other similar anomaly lies beneath the Pacific Plate. They may be the primary source feeding the mantle plume of Hawai'i and the plume beneath Africa, explaining the identical chemical signatures as described by the researchers.
The study,"Neon Isotopes in Geothermal Gases From the Kenya Rift Reveal a Common Deep Mantle Source Beneath East Africa," was published in the journal Geophysical Research Letters.
Additional material and interviews provided by the University of Glasgow.
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The continent of Africa is recognized as the place where humankind originated and evolved over millennia. From famous ancestors like Lucy, the Australopithecus afarensis remains unearthed in Ethiopia in 1974, to the Turkana Boy, a Homo erectus fossil found in Kenya in 1984, archaeological evidence has shown time and again that Africa is the ultimate homeland of not just early hominins, but also modern Homo sapiens, who arose about 300,000 years ago and departed in successive waves to populate much of Earth. Of course, the story of humans in Africa doesn't end with their migration away from the mother continent. After all, many stayed put. But there's a big information gap. Although researchers have plumbed much of humankind's deep past, far less is known about what was happening across much of Africa at the time when permanent settlements were emerging elsewhere starting some 6,000 years ago: in places like Mesopotamia, for example, and later in China and India, as well as Egypt in Africa's northeastern tip. In part, that's because African individuals did not cram together as closely as they did in more well-known cradles of civilization. So it's less likely that modern archaeologists will discover major towns or cities. Another factor is the slave trade that slashed a 400-year wound through African history and led many communities to be abandoned. Longstanding biases about the continent, too, have left the full story of Africa's cultures, trade and urbanism out of many history lessons. That's starting to change. 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I'd like to start with a question you raised in your review: Whose past is East African archaeology about? East Africa is homeland to all of us. I've sometimes joked with Kenyan politicians that any human being entering Kenya should not have to present a passport, because they're actually coming home. I think when many of us think about East Africa, we think about the seminal work of anthropologists Louis and Mary Leakey on human origins, and the discovery of the hominin Lucy. But what do we know about the rise of civilization among modern humans, , in Africa? The human origins question has been settled, but we know precious little about the emergence of civilization in Africa. Most Holocene archaeologists define civilization, in part, in terms of settling down in one place, which happened elsewhere starting around 6,000 years ago. 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There is often a tendency to think of the European Stone Age as the first, the original, the most sophisticated phase of stone working. But you have stone tool technologies in modern-day Ethiopia and Kenya starting 2.8 to 3 million years ago, earlier than it began in Europe. Of course, the European Paleolithic tools were incredibly sophisticated, but the core stone was relatively easy to work; in contrast, African stone is much harder to work than European stone. If you give any modern flintknapper African rock, they immediately recognize how difficult it is. But Africans were using these very tough materials to make extremely sophisticated tools. And what happened when Africans finally started to settle down? In most cases, permanent settlements appear in Africa 3,000 or 4,000 years after they did in places like the Near East. About 8,000 years ago, we begin to see more extensive evidence of settled life in modern-day western Kenya, eastern Uganda and the African Great Lakes region — and I think climate change might have been a reason behind that societal change. Suddenly, around 7,000 to 8,000 years ago you have a dry spell that lasts for about 700 years, and that's when you see the introduction of pastured livestock. So Africans did get there eventually, but we don't see the real emergence of highly complex chiefdoms and societies, with more division of wealth, in much of Africa until about 2,500 years ago. That division of wealth is apparent in differences between households. Some have exotic items from distant places and most others didn't. Just like today, there are things that only elites can acquire. Most likely, they were gifts, given to grease the wheels of business for trade of desirable items. 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But we believe these sites were built and inhabited by Africans, not immigrants from other civilizations, because 96 percent of artifacts such as pottery, metals and beads found in those cities are of local origin. A perfect example of an advanced community, located inland, would be the region of Great Zimbabwe, which was inhabited from about the 11th to 15th centuries CE. It covered about 50,000 square kilometers, including early village settlements and a stone city built later. Great Zimbabwe is an amazing place, but the residential quarters were built out of mud, stone and thatch so they didn't preserve well archaeologically. How did these societies interact with the rest of the world? My work and the work of others shows that before the African slave trade, which reached the continent's interior with slave caravans starting in the 17th century, Africans were trading with other cultures. We've found glass and carnelian beads of Indian origin in every archaeology site in sub-Saharan Africa. Chinese and Indian historians also describe the presence of African mariners in their own towns, so the trade was bidirectional: Africans traded ivory and gold for products such as Chinese porcelain and Indian cloth. Crops were also exchanged. For example, sorghum is a traditional African crop. It's hard to date its origins, but it was being cultivated in Africa from at least the fourth millennium BCE. And it arrives in places like India later. Meanwhile, the banana, first domesticated in southeast Asia, arrived in central Africa more than a thousand years ago. And Africans were trading as equals. Here's one reason I think so: From at least 800 CE, there is clear evidence that people were engaging in the ivory trade, but they traded in mostly cut ivory. This allowed them to weigh it, grade it, and assign value consistent with quality. Cut ivory was also easier to transport from inland to trade partners on the coast. Before the slave trade Africans financed and were in charge of the ivory and other industries. Later, around the 1500s when smaller-scale slave trading began in some regions, that evidence disappears and you begin to see transportation and sale of whole, unprocessed ivory tusks. Similarly, around that time, the evidence of industries such as iron smelting and weaving disappears. The emergence of slavery led to loss of control of their own industries. Work is outsourced, and materials such as cloth are imported. So as people lose skills and become more dependent on external trade, you begin to see a real decline in the political economy of these places. How else did the slave trade impact African civilizations? The 400 years of slavery had a huge, huge effect on this continent. Africans were being invaded both from the Islamic world and, of course, the Western world. Up to that point, communities had settled in comfortable places, such as plains and valleys. There are numerous abandoned settlements with single-household villages, but also remnants of crops such as mangoes, oranges and rice in what is now the Tsavo National Park. These communities provided food to more urban cities along the coasts. But then, suddenly, they all disappeared. From around the 1450s up to the time of the colonial period beginning in the 1870s, we have found little evidence of new, permanent buildings in the interior of Africa — why is nothing being constructed there? In Tsavo, for example, people migrated to uninhabitable but defensible lands, such as hillsides and mountains, for safety. They could not go back to the plains because they were not safe. As these events were happening inland, we also begin to see the abandonment of the coastal towns. They lost their inland food supply. Prior to the slave trade, there were 250 thriving towns in Kenya and Somalia alone. By the time the 400 years of slavery are over, there were, perhaps, less than 10 of those towns still being sustainably inhabited. Slavery and the slave trade led to a loss of knowledge, of power, of memory. This violent gap that history created would open Africa for others to exploit while also conveniently blaming Africans for not being innovative, for not having industries, for not contributing much to global history, even though they did have advanced societies and technologies. Yet despite this, I think we must credit Africans for their resilience. Despite the genocide that they experienced, they're still standing. How has East African archaeology changed over your career? I'm now in my 60s. In my time, there were a handful of African-born archaeologists, probably fewer than five. But today the number of African-born archaeologists, most of whom are our students, has grown. It's rare to see a major paper on East Africa that does not include African authors — though, unfortunately perhaps, the names of those in leadership positions, such as museum directors and department chairs, are often on these publications, which creates the impression that young scientists who do most of the research are not being fully acknowledged. On the other hand, in Europe and the United States, there has been a huge increase in the number of women archaeologists. Obviously, during the colonial period, most of the archaeologists were men, and perhaps they were not much interested in questions of gender dynamics in prehistoric societies. Today most active North American archaeologists working in East Africa are women. This presents a lot of opportunities: For the first time, we have a moment in which women can have a real footprint in the kinds of topics they want to pursue — for example, what role did prehistoric African women play in shaping these societies? 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The Leakeys did a great job in sensitizing East Africans to their long past and their responsibility to care for that history. You can go to any part of Tanzania, Kenya or Ethiopia and find people who are proud of that past, who welcome archaeologists to do all kinds of research. But we are also dealing with population growth. When I was young, Kenya's population was about 8 million, then 15 million, and now it is more than 55 million. There's been similar population explosions in Tanzania, in Uganda, in Rwanda, in Burundi, in Ethiopia. And these people must live somewhere. As in the past many people have migrated. And they move into new areas where they are less emotionally engaged in local histories; they destroy archaeological sites that hold the histories and sacred knowledge of earlier residents. So we have lost a lot of urban sites along the east coast of Africa. I think we archaeologists need to communicate their importance better, and these nations need to manage the heritage sites better. If we can conserve some of these sites, we can make our case for their future study. If we don't, we will fail future generations of young men and women who want to be archaeologists. Stay in the KnowSign up for the Knowable Magazine newsletter today Will East African archaeology be able to continue in the face of such threats, including the loss of those sites and funding woes? Most African governments, with the exception of South Africa and Egypt, do not have dedicated funds for this kind of research. The bulk of funding for archaeology has always come from the United States and Europe. For example, the US National Science Foundation has been one of the engines that funded a lot of archaeology research around the world, but US funding of research has been slashed recently. I think that those moments of change are very important, not only for people in East Africa, but for the rest of us. These funding cuts are very tragic, but this research is very important, and despite threats to supporting research on our origins, I remain optimistic that we'll find a way to continue research of the deep history of humankind in East Africa. This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews. Sign up for the newsletter. Solve the daily Crossword
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