underground, cooling to form giant vertical sheets called dikes. As it rises, the
moving magma causes the ground to
tremble in an earthquake drumroll. For
the past couple of years scientists have
listened to the landscape’s clamor, trying to discover what Afar has to say about
the death of continents.
New findings reveal that the dikes
stack up against each other — fresh ones
pushing their way into places where the
rock is least stressed, crackling with
seismicity as the magma arrives. Other
discoveries include the first-ever glimpse
at how magma flows from storage reservoirs into such dikes along an intricate
system of volcanic plumbing. For the
first time, researchers have seen some
of the planet’s most common geologic
activity transpire nearly in real time, and
on land where they can watch.
To its list of superlatives — hottest,
lowest, least hospitable — Afar can now
add the title of best-studied birth of
an ocean.
A violent story
A single earthquake, of magnitude 4. 5,
first alerted scientists to the tale unfolding in Afar. At Addis Ababa University in
Ethiopia, in September 2005, seismologist Atalay Ayele saw the sign of an Afar
quake pop up on his monitors. Then
more quakes appeared, bigger ones, and
then yet more. Something unusual, he
realized, was going on.
“It was a surprise,” Ayele says. “We
didn’t know at the beginning how big it
was going to be. We just recorded all the
quakes as we normally do.”
Ayele called Cynthia Ebinger, a geo-
physicist then at Royal Holloway College
at the University of London, who arrived
within days with extra seismometers to
monitor the quaking ground. Ebinger in
turn asked Wright to check for satellite
imagery that, by bouncing radar waves
off the ground and measuring their
return, can reveal how much the ground
is shifting, and where. If a big eruption
As Afar is pulled and jostled from below,
fissures form across the landscape.
Some areas are already below sea level.
Red Sea rift
Gulf of Aden rift
Erta Ale volcano
Dabbahu rift segment
Dabbahu volcano
M ain Ethiopian rift
Addis Ababa
were going on just under the surface,
she reasoned, the satellites should have
captured it.
“I kept bugging him and bugging him,”
remembers Ebinger, now at the University of Rochester in New York. And then
one day Wright called with striking news.
Because the Afar quakes hadn’t got-
ten much bigger than magnitude 5. 5,
Wright says, “we didn’t expect to see
very much. But when we downloaded the
data what we saw was astounding — the
biggest signal we’d ever seen in terms of
ground deformation. At that point it was
immediately clear that something really
unusual had happened.”
Whereas the ground might move a
few centimeters during most volcanic
eruptions or earthquakes, places in Afar
had moved eight meters in just 10 days, a
world record. By the time Ayele and col-
leagues arrived in the region to check
what had happened, fresh fissures and
steep cliff faces yawned across the land-
scape, created by the massively shifting
ground. Brand-new lava glistened in the
desert sun.
All this geological action traces to the
fact that Afar sits at the intersection of
three segments of Earth’s crust that are
pulling apart, or rifting.
Like pieces in a moving jigsaw puzzle,
the planet’s tectonic plates constantly
elbow against one another, carrying
continents great distances and allowing
new oceans to be born and die. In large
part, this plate jostling is driven by fresh
magma that wells up from seams that
run along the centers of oceans, like the
underwater mountain chain that splits
the Atlantic Ocean in two. Molten rock
erupts onto the seafloor there, then cools
and rifts away from the ridge on either
side in a process known as seafloor
spreading. Geologists can take a peek at
this in Iceland, where the Atlantic’s mid-
ocean ridge surfaces above the waves.
