On September 14, 2005,
there was an earthquake in a remote part of Afar, a region in northern Ethiopia.
It wasn’t very strong, but it was the firstof many.
Over the next 12 days, there were over a hundred more quakes,
most of them also relatively small. Then,
接着 9月26日 附近的达巴布火山喷发
on September 26, a nearby volcano called Dabbahu erupted.
This was its first eruption in recorded history,
and it came from a flat part of the
volcano a few kilometers from the summit.
The eruption didn’t do too much harm—no
people were seriously hurt, and at most it
killed a couple hundred goats and camels.
But it opened up a gigantic crack in the earth,
which grew to 60 kilometers long and as much
as eight meters wide—in only ten days.
And as you can probably imagine,
this caught the attention of geologists around the world.
It turns out that as dramatic as it was, the crack
was just one of the latest symptoms of an ongoing seismic shake-up
in Africa that’s eventually going rip the continent in two,
leading to the creation of a brand-new ocean.
Right now, eastern Africa is going through a process called rifting,
where the tectonic plates that make up the Earth’s
crust and upper mantle pull apart from each other.
A giant plume of magma rising from deep inside the mantle
is forcing the African and Arabian plates away from one another,
forming a rupture in the Earth’s surface.
The result is the Great Rift Valley,
which stretches more than 3000 kilometers through the eastern part of the continent.
Scientists have been studying the Great Rift Valley since around the
turn of the 20th century, when an English geologist named
John Gregory encountered it for the first time.
Even though the theory of plate tectonics wouldn’t
be fully accepted for another 50 years or so,
he realized how important it might be.
The valley is a system of several fractures that
began forming at different times, and it ’
s home to lots of seismic activity.
The pressure from tons of magma bubbling up is what
leads to earthquakes and volcanic eruptions like what happened in 2005.
For a study published in 2018,
scientists installed two seismic networks in Ethiopia and Eritrea.
And these networks of seismographs recorded almost 5,000 earthquakes
of at least magnitude 2.0 in two years.
All that activity has spawned other volcanoes, too—one, called Nyamuragira,
erupted fifteen times between 1894 and 1979.
What’s happening in eastern Africa is actually more
common at the bottom of the ocean, where magma
bubbling up into tectonic rifts forms features called seafloor ridges
and helps drive the movement of continental plates.
But the activity in Africa is giving geologists
a chance to study the process up close—no submarines needed.
As it turns out, what happened in 2005
was that a huge length of the rift cracked
open all at once, beginning with the volcanic
eruption and spreading in both directions from there.
This was a bit of a surprise to scientists, who
previously thought that such cracks—on the ocean floor as well as
on land—only broke open a little bit at a time. Eventually,
the Horn of Africa is going
to split off from the rest of the
continental plate and go its own way.
Large areas of the Great Rift valley are below sea level,
cut off from the ocean only by a
small piece of higher land in Eritrea.
So when the split finally happens, seawater is going to
come flooding into the rift, turning the Horn of Africa
into an island and creating a new ocean.
Odds are none of us will actually get to see the new ocean.
The process has been happening slowly for about 30 million years,
and the rift is only widening at an
average rate of a couple of centimeters a year. So,
it will probably be tens of millions of years
before traveling from Sudan to Somalia requires a boat.
But in the meantime, we get to watch our planet
reshape itself, giving us a teaser
for what the world would look like long after we’re gone.
Thanks for watching this episode of SciShow,
and a special thanks to our President of Space, Matthew Brant! Thanks,
Matthew, for your support!
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