By Helen Briggs
BBC News science reporter
An international team is monitoring two million years of rock history
The largest tear in the Earth's crust seen in decades, if not centuries, could carve out a new ocean in Africa, according to satellite data.
Geologists say a crack that opened up last year may eventually reach the Red Sea, isolating much of Ethiopia and Eritrea from the rest of Africa.
The 60km-long rift was initially sparked by an earthquake in September.
Follow-up observations reported in the journal Nature suggest the split is growing at an unprecedented rate.
It betrays events deep beneath the ground, where some of the tectonic plates that form Africa are gradually moving apart from the Arabian plate, causing the crust to stretch and thin.
As rifts appear, molten rock bubbles up from beneath the surface, hardening to form a new strip of ocean floor.
Dr Tim Wright from the University of Oxford, UK, said if the ripping of the crust continued, the horn of Africa would eventually split off from the rest of the continent, in about a million years.
"We think if these processes continue, a new ocean will eventually form," he told the BBC News website. "It will connect to the Red Sea and the ocean will flow in."
Dr Wright is a member of a team from the UK and Ethiopia that has been monitoring the creation of the new ocean basin; a rare event on dry land.
They used sensitive seismic instruments, field measurements and satellite images from the European Space Agency's Envisat spacecraft to study what is happening beneath the ground.
"We've been able to work up all the satellite data and get a very precise map," said Dr Wright.
"It's the biggest rifting episode at least since the 1970s and possibly in hundreds of years.
"It's the first time we've been able to use satellite images to investigate the fundamental processes behind rifting."
The shift in the Earth's plates is generally a very slow process occurring over millions of years - but every now and again earthquakes and volcanic eruptions herald sudden break-ups.
One such event took place in September last year, opening up a 60km-long (37 mile) stretch of a fault-line that runs from Ethiopia to the southern edge of the Red Sea.
"It's amazing," said Cindy Ebinger, from Royal Holloway, University of London.
"It's the first large event we have seen like this in a rift zone since the advent of some of the space-based techniques we're now using.
"These techniques give us a resolution and a detail to see what's really going on and how the Earth processes work."
Scientists have calculated that 2.5 cubic km (0.6 cubic mile) of magma has flowed up through the crack in the Earth's crust.
It is enough to fill London's Wembley stadium 2,000 times or smother the area within the capital's M25 orbital motorway with molten rock to a depth of 1m (1 yard).