In 50 Million Years, How Will The Red Sea Change?
Standing next to a lava lake at the elevation of a massive volcano, Christopher Moore, a Ph.D. candidate at the Schoolhouse of Earth and Environment at the University of Leeds in the U.k., could come across the crimson brume of lava flows a few kilometers away. This might seem like a rare sight, only at Ethiopia's Erta Ale, information technology's business as usual.
Are such behaviors the showtime signs of a tectonic transition? This question is part of what Moore has been studying at Erta Ale. The unabridged Distant region in eastern Africa finds itself in the centre of changes that could split the continent, forming a new ocean basin. The magmatism at Erta Ale might be offer signs of this switch by mimicking the characteristics of a mid-ocean ridge.
However, at that place isn't agreement about how shut the Afar region is to this tectonic transition. The geophysical characteristics of magma storage at Erta Ale could point to the region's conversion to an incipient oceanic spreading heart, merely the petrology of the erupting lava might be telling us that we aren't there yet.
What we will be able to run into continuing on top of Erta Ale will change dramatically in 5 million, 50 million, or 100 million years. The question is whether Erta Ale and the Distant region volition become a new ocean, or whether ongoing tectonic collisions to Africa's n and east will forbid this transition from occurring.
The Circuitous Tectonics of Eastern Africa
Few places on Globe remind people of the surface of the Moon more than the Distant region. Pressed against the Red Sea, this dry and desolate section of eastern Africa is covered in lava formed from the rifting of the continent.
The Distant region is domicile to a triple junction at the boundaries of three tectonic plates: the Nubian, Somali, and Arabian. They all encounter near Djibouti and Eritrea, forming a massive Y on the Earth's surface. The Great Rift Valley opens to the south, reaching over vi,000 kilometers into the heart of Africa. The Red Sea Rift extends to the northwest until information technology meets the Sinai Peninsula. To the e stretches the Aden Ridge, an oceanic spreading ridge. All of these boundaries are spreading at rates of up to 1.5 centimeters per yr.
This tectonic complication means that Africa is a continent tearing itself apart. For 30 million years, part of eastern Africa, known equally the Somali plate, has been peeling away from the rest of the continent. This has created the Bully Rift Valley, which starts in Ethiopia and Eritrea and splits around the Republic of kenya Dome until recombining in the Malawi Rift. On a map, you can trace the rifting continent past looking at the chain of lakes like Tanganyika and Nyasa (Malawi) that line the lesser of the Great Rift Valley.
At the same fourth dimension, the Arabian plate has been moving abroad from Africa as the Carmine Sea Rift opens at a rate of around a centimeter per year. Someday the Arabian plate will stop moving as it collides with the Eurasian plate in what is now Iran, closing the Persian Gulf and becoming part of Eurasia.
The Distant region'south tectonic complication has created some of the largest volcanoes on Earth. This volcanism is bimodal, significant eruptions prevarication on the ends of the compositional spectrum. Vast lava flows of basalt intermingle with massive explosive eruptions of lava more silica rich. These volcanoes line the Great Rift Valley.
To the north, massive basaltic shield volcanoes like Erta Ale lie near the Red Sea. Traveling s, you encounter Ethiopia's massive Corbetti Caldera, one of the most potentially dangerous volcanoes on the planet. Farther into Africa, you lot find oddities similar the carbonatite-spewing Ol Doinyo Lengai in Tanzania to the east and the Democratic Republic of the congo's massive twin volcanoes of Nyamuragira and Nyiragongo to the west. All of these volcanoes reveal the active rifting beneath eastern Africa.
What Drives a Continent to Split?
Why is this surface area such a hub for rifting and spreading? One explanation is that the Distant plume has been heating the region from below. This mantle plume prompted the African continent to begin to ascent and split up, creating rift valleys. Much like how the North Atlantic Ocean opened fourscore million years agone, there appears to be a close connection betwixt a large mantle plume and the creation of new continental rifts and, eventually, two passive (continental) margins separated by seafloor spreading at ocean ridges.
Extensional (divergent), collisional, and transform boundaries have been recognized for decades. How i boundary turns into another is less well understood.
Geologists have long been able to identify dissimilar tectonic settings and plate boundaries. Extensional (divergent), collisional, and transform boundaries have been recognized for decades. How ane boundary turns into another is less well understood. When does subduction start at a passive margin? What happens when a spreading center gets sucked into a subduction zone? When does the rifting of a continent finally create a new ocean basin? These questions are difficult to answer because we have express modern examples of these transitional phases of tectonics.
How can we recognize the signal at which a rifting continent becomes a new ocean basin? All continental rifts are not the same, and some rifts fail, never producing truthful oceanic spreading. The Midcontinent Rift, for instance, was the site of an try to split North America nigh 1.i billion years ago, but it failed. The mere observation of continental rifting does not mean that we are heading toward a new ocean.
The Afar region, at the nexus of tectonic plate boundaries, may be in the process of undergoing the transition from continental rift to oceanic spreading ridge. Ane way to arroyo the question of this transition is to examine the region'due south crust. Instead of the 35-kilometer thickness that is typical for continental crust, the crust nether Afar might be less than 20 kilometers thick. This includes layers of volcanic basalt that accept spilled out over the area for millions of years.
Erta Ale: Afar's Monster Volcano
Another way to approach the question of the possible transition from continental rift to oceanic spreading in Afar is to await at the region's volcanoes. Erta Ale, in northwestern Ethiopia, is one of the almost agile volcanoes on Globe. The massive shield volcano stretches 50 kilometers beyond, is almost 100 kilometers long, and rises 600 meters from the Danakil Depression.
Past most accounts, Erta Ale has been erupting constantly for over fifty years, producing lava flows that stretch far down its slopes. It is also a member of a very sectional guild of volcanoes that are dwelling to active lava lakes. In fact, simply 2 volcanoes in the past quarter century have hosted multiple lava lakes simultaneously: Erta Ale and Kīlauea. Equally of March 2020, at that place is ane active lava lake in the superlative caldera of Erta Ale, and it is potentially one of the longest-lived lava lakes in the world, first observed in 1906.
Erta Ale is not the easiest identify at which to conduct fieldwork. Earlier 2010, the trek to the summit was long and chancy. Today the peak area virtually the lava lake is accessible by a tarmac highway. This has meant that tourists tin can easily visit the lava lake, only not without risks from both the volcano and exterior violence. In 2012 and 2017, tourists visiting Erta Ale were killed past gunmen, sending chills down the spines of many who visit the volcano regularly.
Analyzing Magma Storage
By pure coincidence, Erta Ale erupted six months into Christopher Moore's Ph.D. research on magma storage in the East African Rift. "Science changes very quickly, so you lot follow the exciting things," said Moore.
The eruption prompted a question amongst volcanologists: Is Erta Ale more like a rift volcano or an emergent mid-sea ridge volcano? Moore and his collaborators have been attempting to answer just that question to sympathise how magma is stored under Erta Ale. In his 2019 paper in Geochemistry, Geophysics, Geosystems, Moore laid out data showing that Erta Ale shares characteristics of a fast spreading mid-ocean ridge like the East Pacific Rise (EPR). Magma is stored in shallow bodies just underneath the EPR, a characteristic typical for mid-ocean ridges. If the Afar region is an incipient oceanic spreading heart, how would magma storage at Erta Ale compare?
Moore and his collaborators used Lookout man-1 synthetic aperture radar data to unravel how Erta Ale physically changed during the course of an eruption that began in January 2017. Using the Sentinel-i data, Moore modeled the deformation at Erta Ale equally shallow intrusions under the volcano's meridian and under the site of a scissure eruption on its southwestern slopes.
"The contraction that we run across [at the summit] combined with opening of the new dike [on the slopes]…was pretty much symmetrical," said Moore. This meant that magma was moving from the meridian to the fissure and responding rapidly to changes in the shallow magmatic system nether the volcano.
Across this deformation, Moore and his collaborators were able to use the level of the lava lake at Erta Ale's summit as a gauge for the pressure state in the magmatic system nether the volcano. During periods prior to the fissure eruption, the level of the lava lake remained relatively constant according to Sentinel-i data besides every bit to observations from tourists and scientists visiting the volcano. However, once the January 2017 eruption event started, the lava lake level dropped precipitously. This meant the level was very sensitive to the pressure state of the magma stored nether the volcano, dropping as pressure level was released during the new fissure eruption. The new eruption down the slopes of the volcano prompted the summit lava lake to drain rapidly.
On the basis of both the lava lake levels and the geophysical models, Moore and his colleagues call back that there are stacks of shallow magma bodies nether Erta Ale, all within kilometers of the surface. Thus, Erta Ale is much like the EPR, where shallow magma bodies lurk beneath the mid-ocean ridge.
Is Information technology or Isn't It?
Does this mean that Erta Ale is in that transition phase from a rift volcano to a mid-ocean ridge? Tyrone Rooney of the Department of Globe and Environmental Science at Michigan State University in Eastward Lansing argues that information technology might be more complicated than that.
"If information technology looks like a duck and quacks like a duck, is information technology a duck? Possibly not," said Rooney. There is no agreed-upon definition for what constitutes a transition from one tectonic setting to another in this situation. Rooney has studied the Eastward African Rift for years and recently published a study in Lithos that tackles the evolution of magmatism in the expanse.
Rooney agrees that the Afar region is clearly in the advanced stages of continental rifting just doesn't know whether the rifting is a directly precursor to oceanic spreading. The sources of melting under the Afar region acquired by the Afar feather look to be different than one might expect at a newly forming mid-ocean ridge.
And fifty-fifty though the crust is sparse in the Distant region, information technology is non clear whether the lithospheric pall under the crust has thinned as well. On tiptop of that, the rifting in the region of Erta Ale is propagating due north every bit opposed to southward, equally would be expected if the Red Sea Rift were driving the extension. Even so, the Afar region still might exist the closest electric current relative nosotros have to a new oceanic spreading heart.
What Is the Transition?
Although the processes going on at Erta Ale and at a mid-body of water ridge look like, they might exist controlled by different tectonic processes.
Right now, Moore agrees that Erta Ale is nevertheless in a transitional phase. The question becomes what the Afar region will expect like in five million years. He said the transition to an oceanic spreading center will exist recognizable when the region develops the typically dumbo, 7-kilometer-thick igneous oceanic crust. The presence of shallow magma bodies under the active parts of the rift will be another inkling. A farther sign will exist the evolution of telltale "magnetic stripes" on both sides of the boundary, as lava erupts and captures the state of Earth's magnetic field. In all cases, the switch to an oceanic spreading center volition be gradual.
So far, information technology seems that Erta Ale is showing at least one of those signs: shallow magma storage. Still, as Rooney has pointed out, we haven't seen any evolution of true oceanic crust in the Distant region. All the petrologic testify and so far still points to the Afar plumage as the source of the basalt erupting at Erta Ale. To him, this means that although the processes going on at Erta Ale and at a mid-ocean ridge look like, they might be controlled by dissimilar tectonic processes.
Africa'due south Time to come
The future of tectonics in the Distant region is unclear. It is far from agreed upon when, if always, the region will become an oceanic spreading center or whether an ocean basin volition form between the Somali and Nubian plates and how spreading in the Red Sea and the Gulf of Aden volition progress. In one model, Christopher Scotese's "future world" tectonic map suggests that 50 million years from now, the Red Sea and the Gulf of Aden will be gone as the Somali and Nubian plates slam into Arabia, suturing today's three plates together.
The eruption at Erta Ale continues today. Moore's research has shown that the volcano'south magmatic plumbing is a close continental analogue to the mid-bounding main ridge magmatism in the Due east Pacific Rise. The question remains whether that similarity is a sign of things to come.
—Erik Klemetti (@eruptionsblog), Science Writer and Acquaintance Professor of Geosciences, Denison University, Granville, Ohio
Citation:
Klemetti, Eastward. (2020), Are we seeing a new ocean starting to form in Africa?, Eos, 101, https://doi.org/10.1029/2020EO143740. Published on 08 May 2020.
Text © 2020. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Whatever reuse without limited permission from the copyright owner is prohibited.
Source: https://eos.org/articles/are-we-seeing-a-new-ocean-starting-to-form-in-africa
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