Jakarta –
For several days in September 2005, amidst a series of volcanic eruptions and hundreds of earthquakes, the land in northeastern Ethiopia ripped open. For millions of years, molten rock bubbles have seeped beneath the Earth in the Afar Depression. Over time, it came to the surface, split the ground and created a rift nearly 64 km long and up to 7 meters wide.
“We’ve never seen anything like it. This kind of thing happens regularly on the ocean floor, but this is the first known example of it happening on land,” said Cynthia Ebinger, a geologist at Tulane University.
The Dabbahu Fissure, as the fissure is known in 2005, is not the first geological event to rock Afar, a remote region filled with geysers, gas vents, hot springs, volcanoes and the world’s only lava lake.
Being a ‘mecca’ for Earth scientists, the Afar Triple Junction is located in the Y-shaped cradle of the Arabian, Nubian and Somali plates. At about the same rate as the growth of a human fingernail, these plates are moving apart, while processes beneath them generate the extreme heat and energy that causes the unique geophysical features known in the region.
Of these features, today the Dabbahu Rift comes to the fore. Scientists suspect that it was along this rift that the first continental split since Pangea would have occurred and that within a few million years or so, Africa might span the two continents.
Geological miracle
One of the world’s greatest geological wonders, the north-southeast East African Rift System (EARS) is actually a network of rifts and valleys caused by fracturing of the Earth’s crust. The EARS was formed approximately 25 million years ago and consists of two branches: the Eastern Rift Valley which extends from Jordan to the coast of Mozambique, and the Western Rift Valley which stretches from Uganda to Mozambique, containing several lakes.
But of all the land masses squeezed into the EARS, the Afar Depression is the most extreme, with the highest magma production rates and the most active volcanoes in the region. Over time, plumes of mantle magma have formed beneath the Afar Depression, pushing hot rocks to the surface like plumes of oil rising in a lava lamp. Eventually, the extreme pressure caused magma to be pushed into the gaps between the rocks, opening the Dabbahu Fissure in 2005.
The pressure is so intense that the plates are 8 meters apart, achieving the equivalent of 400 years of separation in just a few days, according to Ebinger. It was an amount so large that one of the scientists who used satellite data to measure the new rift believes this pressure is record-breaking.
The Birth of the Ocean
Within weeks of the events of 2005, Ebinger was on a plane bound for Ethiopia. He is working with scientists from around the world to get geophysical instruments on land as quickly as possible. The team noticed that the plates underlying the region were moving much faster than normal, due to the volume of magma beneath the surface.
Ebinger said that over the next five years, there were 13 similar but less severe events from the 2005 rifting. Now, the plate’s movement has slowed back to its normal pace.
Going forward, Ebinger predicts there will be more dramatic moves of this kind, perhaps once every 50 or 100 years. As the ground splits, the Afar Depression will sink deeper and deeper, a process known as seafloor spreading. “If we fast-forward by about 500,000 years, the Afar Depression could fall below sea level and be flooded with water,” he said.
The new sea may not completely split the continent in two. “The degree of separation decreases as we head south. So it could just be a wedge of seawater coming in,” Ebinger said.
Make scientists curious
Not all continental rifts turn into oceans, and there is still a chance that the East Africa Rift will fail. In fact, scientists have discovered areas of molten rock extending across the Earth’s crust tens of kilometers from the rift, a discovery that goes against conventional geological wisdom, which holds that all of the rift activity usually occurs in the rift itself.
The Dabbahu Fissure could lead to North America’s Midcontinental Rift (MCR), a rainbow-shaped seam that cracked open more than a billion years ago. The rift, which stretched from modern Detroit to central Kansas, produced more than 240,000 cubic miles of volcanic rock over 30 million years before suddenly, mysteriously, stopping spreading. There are many theories as to why, but the MRC remains the deepest crevice ever discovered that did not become an ocean. Perhaps Dabbahu Pass will follow in his footsteps.
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(rns/asj)
2023-06-29 22:45:38
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