A crack that opened up in Kenya’s Rift Valley, damaging a section of the Narok-Nairobi highway, is still growing… pic.twitter.com/T5YocDauYj
— BBC (@BBC) March 26, 2018
Dynamic topography and the African super-plume : Why is Africa rifting?
by J. Michael Kendall & Carolina Lithgow-Bertelloni / 6 July 2016
“…We consider the stresses induced by mantle flow, crustal structure and topography in two types of models: one in which flow is exclusively driven by the subducting slabs and one in which it is derived from a shear wave tomographic model. The latter predicts much larger stresses and a more realistic dynamic topography.
It is therefore clear that the mantle structure beneath Africa plays a key part in providing the radial and horizontal tractions, dynamic topography and gravitational potential energy necessary for rifting. Nevertheless, the total available stress (c. 100 MPa) is much less than that needed to break thick, cold continental lithosphere.
Instead, we appeal to a model of magma-assisted rifting along pre-existing weaknesses, where the strain is localized in a narrow axial region and the strength of the plate is reduced significantly. Mounting geological and geophysical observations support such a model. Rifts play an important part in shaping our planet, breaking continents apart and eventually leading to the formation of ocean basins. The topography they generate affects our climate and gives rise locally to fertile regions, which have had an important role in human evolution (Bailey et al. 2000; King & Bailey 2006).
The East African Rift (EAR) is the best example of a continental rift currently active on Earth; it captures the early stages of rift development in southern Africa through to incipient oceanic spreading in Afar. This rift environment hosted the earliest hominoid evolution and is the site of numerous natural resources, including freshwater, minerals containing the rare earth elements and precious metals…
…To overcome the plate force paradox, melt can be invoked as a mechanism that weakens plates and localizes the accommodation of strain to magmatic segments (e.g. Buck 2004). There is now abundant evidence for focused melt distribution throughout the uppermost mantle and crust in the EAR (e.g. Keir et al. 2011; Desissa et al. 2013; Hammond et al. 2013; Stork et al. 2013; Hammond & Kendall 2016). Based on laboratory experiments and seismic observations, Holtzman & Kendall (2010) argued for melt partitioning and strain localization as a mechanism that lubricates plate boundaries and facilitates rifting in both continental and oceanic settings….
…Africa, as a continent, sits anomalously high in elevation. Whereas most cratons have an average elevation of a few hundred metres, large portions of Africa stand more than 1 km above sea-level (Lithgow-Bertelloni & Silver 1998). It is difficult to explain this topography by isostatic compensation due to thickness and density variations, given the known crustal and lithospheric structure of Africa. Instead, it is now commonly accepted that mantle flow driven by density anomalies in the mantle acts to dynamically support the excess elevation in Africa (Lithgow-Bertelloni & Silver 1998) and may even explain the uplift of the western margin of the Arabian craton (Daradich et al. 2003).
Africa is underlain by a large low shear velocity province (LLSVP) (Fig. 3), which is one of two large (degree-two in spherical harmonics) features of planet Earth that extend upwards from the core–mantle boundary (the other lies beneath the south-central Pacific Ocean). These are sometimes called ‘super-plumes’ and are thought to be long-lived thermo-chemical anomalies that may spawn smaller plumes and may even be associated with the location of diamond formation (Torsvik et al. 2010).
#WATCH The incredible sinkhole that opened up on a Bay of Plenty farm is the biggest @gnsscience volcanologist @Eruptn has ever seen. It's revealed 60,000 year old soil and is threatening road access. @zacflemng reports. https://t.co/z0bJVbG00k
— Checkpoint (@CheckpointRNZ) May 2, 2018
The ‘super-swells’ seen in the South Pacific (McNutt 1998) and African (Nyblade & Robinson 1994) regions are attributed to these anomalously buoyant regions of the mantle. We note that most studies of the dynamic topography of these features are interpreted in terms of thermal effects. The effects of compositional differences is a challenge as there is still no consensus about the chemical nature (if any) of these anomalies; see Davies et al. (2015) for a discussion of LLSVPs…
…Magnetotelluric experiments provide complementary geophysical methods to image the presence of melt. Whaler & Hautot (2006) showed evidence of crustal melt beneath magmatic segments of the Main Ethiopian Rift and even in the lower crust beneath the flank of the Ethiopian plateau. There appears to be large volumes of melt beneath parts of Afar that extend well into the mantle (Desissa et al. 2013).
There is some discrepancy between the estimated melt volumes from magnetotelluric and seismic methods, but the effect of melt composition may explain some of this (Pommier & Garnero 2014). Linking seismic and electrical images of melt and their anisotropy is an ongoing challenge.
Cumulatively, these observations suggest that strain is localized along narrow zones and that melt is localized on the marginal lithosphere–asthenosphere boundary (see Holtzman & Kendall 2010 for a more extensive discussion)…”
Africa is splitting in two
by Lucia Perez Diaz / April 7, 2018
“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.
“Dynamic topography (in km) of Africa over the past 105 Ma (Conrad & Gurnis 2003).”
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.
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 by Snider-Pellegrini in 1858 showing how continents may once have fitted together.”
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“
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.
“Topography of the Rift Valley James Wood and Alex Guth, Michigan Technological University. Basemap: Space Shuttle radar topography image by NASA“
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.
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.
So this will happen in the next 50M yrs. Can't wait pic.twitter.com/g2uogxK9or
— Nel (@KimNelson_) March 20, 2018
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.
“Spherical small Earth models of a Jurassic to present-day increasing radius Earth. Each small Earth model demonstrates that the seafloor crustal plate assemblage coincides fully with seafloor spreading and geological data and accords with derived ancient Earth radii (Maxlow 1995).”
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. 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.”
Mantle plumes emitted from the core-mantle boundary region to reach the Earth’s crust.”
by Charles Choi / February 12, 2013
“Volcanoes are often found near the borders of tectonic plates. Mysteriously, however, volcanoes sometimes erupt in the middle of these plates instead. The culprits behind these outbursts might be giant pillars of hot molten rock known as mantle plumes, jets of magma rising up from near the Earth’s core to penetrate overlying material like a blowtorch.
Still, decades after mantle plumes were first proposed, controversy remains as to whether or not they exist. The concept of mantle plumes began in 1963 with the enigma of the Hawaiian volcanoes, which dwell more than 2,000 miles (3,200 km) from the nearest plate boundary. Scientists think that as the Pacific plate slid over a “hot spot,” a line of volcanoes blossomed.
In 1971, geophysicist W. Jason Morgan proposed that hot spots resulted from plumes of magma originating in the lower mantle near the Earth’s core at depths of more than 1,550 miles (2,500 km). Researchers think these mantle plumes are shaped like mushrooms: narrow streams of molten rock topped with bulbous heads that buoyantly bob upward, like blobs in a lava lamp.
The potential importance of mantle plumes may go well beyond explaining volcanism within plates. For example, the mantle plume that may lie under Réunion Island in the Indian Ocean has apparently burned a track of volcanic activity that reaches about 3,400 miles (5,500 km) northward to the Deccan Plateau region of what is now India. Catastrophic volcanism there 65 million years ago gushed lava across 580,000 square miles (1.5 million km2), more than twice the area of Texas, potentially hastening the end of the age of dinosaurs.
However, it remains hotly debated whether mantle plumes exist. For example, Massachusetts Institute of Technology seismologist Qin Cao and her colleagues used seismic waves to image activity beneath Hawaii; instead of finding a narrow mantle plume, they discovered that a giant thermal anomaly about 500–1,250 miles (800–2,000 km) wide located far west of the islands is apparently what feeds its volcanoes.
The seismologists suggest Hawaiian volcanoes are fueled by a vast pool of hot matter on top of the lower mantle, not at its bottom near Earth’s core by a deep mantle plume. Some researchers suggest hot spots may form in ways besides mantle plumes, such as spreading or cracking within tectonic plates, or “superplumes” that reach up from near the core to the near the base of the upper mantle, where they then give rise to smaller plumes that rise to the surface.
To help see if mantle plumes are real, a French-German experiment known as RHUM-RUM (Réunion Hotspot and Upper Mantle-Réunions Unterer Mantel) is seeking to image the area beneath Réunion down to the bottom of the mantle. In 2012, the investigators deployed nearly 60 seismometers on the floor of the Indian Ocean over a vast area of about 1.5 million square miles (4 million km2). Another 30 instruments will be installed on land to assist, making this project the largest campaign ever to map a mantle plume.”
“…Mentioned for the interested reader is the book Environment of Violence Ref 11 and its successor Expanding Geospheres Ref 12. Author C. Warren Hunt, in association with Lorence G. Collins and E. A. Skobelin, a leading Russian geologist, promotes new insights consistent with carbide-hydride systematics.
Hunt’s general concern is the heat-induced chemical reaction and expansion potential of inorganic matter. As a field engineer he staunchly opposes the drift theory and enhances an expansion concept which parallels S. Warren Carey‘s.
Vladimir N. Larin‘s revolutionary idea of hydrogen systematics came so close to Hunt`s own ideas that Hunt translated his Hydridic Earth Ref 13. The book, according to a reviewer, promotes to geologists and geophysicists the riches of a Russian scientific literature that will greatly enlarge the scope of Western thinking.
Another author sympathetic to the concept of catastrophic events is Derek Ager. Periodic upheaval is his theme. This stratigraphicus extraordinaire is, in The New Catastrophism Ref 14, confused by the inadequacy of geological record.
His experience tells him that the stones are constantly lying to us. Perhaps the stones tell the truth if regarded from a different angle. A particularly interesting possibility for the Earth’s expansion potential is Dr. Hugh Owen’s plasma core.
A first approach with this thesis to a renown magazine ended with a refusal and the words “interesting, but here it is returned… and best wishes”. In other words, “try to sell it”. Two months later, Spectrum Ref 9 ran a treatment of Dr. Hugh Owen’s Atlas of Continental Displacement: 200 Million Years to the Present Ref 10 published in 1983.
While at the British Museum (Natural History) Owen found, after painstaking research, that “a reduced curvature of the Earth would give a better fitting of the separated continents if they were brought together”, the same conclusion garnered here.
At the same time, Owen also introduced an ingenious idea: “Are the pressure and heat in the interior of the Earth enough to maintain a plasma core? They probably are, and the solid nickel-iron core of the textbooks may be a myth”.
According to the transmission of seismic waves through the Earth’s core and the composition of meteorites, it had previously been thought that the inner core was solid, composed of nickel, iron and probably sulphur. The outer core was assumed to be molten.
Owen explains that “the behaviour of waves passing through a plasma core would be similar to that in a solid iron-sulphur core”. He suggests that if the inner core is plasma there is a potential for expansion when the core changes from a plasma into an atomic state.
The Earth’s outer core may be molten because it has already changed into its atomic state. (This author adds that an explosion potential would also be present if the gravity envelope had been broken by an impact catastrophe. Mercury, Mars and the Moon appear too low in mass to sustain plasma cores much after their formation. On the other hand, Venus is almost as massive as the Earth and may still have a plasma core. Information about its surface so far indicates a highly mobile crust.
Owen points out that a plasma core provides a better explanation for the behaviour of the mantle which surrounds the Earth’s outer core. The mantle lies directly beneath the crust and its convection currents are responsible for the creation of new crust and continental movement. Furthermore, the Earth’s magnetic field can be generated as effectively by a plasma core as by one of nickel-iron. Owen emphasised that, “as far as the Earth’s interior is concerned, these are only ideas”.
An understanding of these matters is not yet clear. Such knowledge is necessary to fully understand the how of expulsion and expansion. According to Owen though, the development of the Earth’s crust is “however, something that can be tested critically. The field data fit an expanded Earth model; they do not fit a constant modern dimension Earth model”. Both Owen and S. Warren Carey propose a global expansion of millions of years.
A tremendous disturbance of a gravity-condensed plasma core, such as a break in its envelope by a celestial body impact, could have produced the same effect in a much shorter period of time. A subsequent renewal of the planet’s equilibrium would, as a result, produce an expanded Earth and not an expanding Earth. Continual expansion would jeopardise all of the consolidated measuring axioms.”
After researching the continental shelves, the portions of the land masses below water, at the depth line of 1094 yards (1000 metres), Dr. Hugh Owen concluded that, even over a long time, little erosion or deformation had occurred at that depth. Had the continents drifted, erosion would be expected at these points. When he also concluded that the continents fit better on a smaller planet curvature, it is reasonable to assume that he considered this lack of erosion on all sides of the continents.
A bird’s eye view of a smaller planet with the continents reconnected would show spaces between the coasts. The continental shelves, which extend beyond the coastlines, would slope down to meet each other. Thus, here are the actual seams between continents. Eroded very little, they make a good fit. (On the model the continents fit quite closely because there are no continental shelves.)
Owen’s conclusions are assets for the live expansion model. After an impact catastrophe and an expansion process, it is expected that the coagulation and solidification of the side-thrust upheaval of the original Earth would have deformed the continental contours around the Pacific Basin. Owen’s studies indicate that they did not further erode or deform. If the model is taken at face value, the reader might first wonder “Where would all the water be on the smaller Earth?”
If our current-sized planet were levelled, eliminating mountain heights and sea floor depths, it would be under 7,500 feet of water, according to The Almanac for Farmers and City Folk Ref 17, its source being Omni magazine. The water would cover the original, smaller Earth by more than 12,000 feet. The same source states that if the planet’s current amount of water evaporated, the oceans’ salt content would yield a 500-foot thick blanket on the Earth. On the smaller planet, the layer would be more than 800 feet deep.
Given the information, it is possible to deduce that there was, at a certain time in this planet’s history, a sudden influx of salt water, concurrent with the onset of the expansion (the impact of a celestial body causing the expulsion of the Moon). No habitation would be possible. However, the excessive amount of salt could have supported the survival of the planet itself, after the impact of celestial matter.
As the water evaporated, the remaining salt subdued magma evictions at weak points in the Earth’s crust. Finally, the salt was vacuum-sucked into caverns where expansion ruptured the crust, forming the rock salt bulk we now exploit. As the anonymous Dutch writer came so close to the fundamentals of expansion with his model-induced thesis, it is worthwhile to take another look at his impact hypothesis.”
1. See the National Geographic Society’s Atlas of the World, 1981, pages 22-23. The pictures show the perimeters of these two large continents as they are assumed to appear at different stages of development through to the current form.
2. Graves, W. Editor, Atlas of the World, Revised 6th Edition, National Geographic Society, Washington D.C., 1992
3. Carey, S.W., The Expanding Earth, Elsevier Scientific Publishing Company, Amsterdam, 1976. Unfortunately now out of print.
4. Whiston, W., A New Theory of the Earth, reprinted by Arno Press, New York Times Company, New York, 1978.
5. Carey, S.W., Theories of the Earth and Universe: A History of Dogma in the Earth Sciences, Stanford University Press, Stanford, 1988, p. vii.
6. Miller, R., Continents in Collision, Ed. T.A. Lewis, Time-Life Books, Alexandria, Virginia, 1983.
7. Miller, R., Continents in Collision, Ed. T.A. Lewis, Time-Life Books, Alexandria, Virginia, 1983, p.76.
8. 1985, Spectrum, British Science News, v. 193, coverpage.
9. 1985, Spectrum, British Science News, v. 193.
10. Owen, H.G., Atlas of Continental Displacement: 200 Million Years to the Present, Cambridge University Press, Cambridge, 1983.
11. Hunt, C.W., Environment of Violence, Polar Publishing, Calgary, Alberta, Canada, 1989.
12. Collins, L.G., Hunt, C.W., and Skobelin, E.A., Expanding Geospheres, Ed. C.W. Hunt, Polar Publishing, Calgary, Alberta, Canada, 1992.
13. Larin, V.N., Hydridic Earth, Ed. C.W. Hunt, Polar Publishing, Calgary, Alberta, Canada, 1993.
14. Ager, D., The New Catastrophism, Cambridge University Press, Cambridge, 1993.
15. Lyell, C., Principles of Geology, 1830-33, reprinted by Lubricht and Cramer, Forestburgh, New York, 1970.
16. Gould, S.J., 1989, An Asteroid to Die For: Discover, v. 10, 10, p. 60-65.
17. The Almanac for Farmers and City Folk, Ed. L. McFadden, Greentree Publishing, Inc., Las Vegas, Nevada, 1995, p. 163.
18. Anonymous, The Moon Problem: Solved, Luctor et Emergo, Amsterdam, 1928.
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