Planet Earth - Afar Valley

19 December 2010

Interview with

David Ferguson, University of Oxford

Kat -   Now it's been subzero this week in the UK, so we're taking you to one of the hottest places on Earth, the Afar depression and that's a region of the Sahara Desert on the Ethiopian border.  But it also contains a series of rifts that are slowly ripping the African continent apart to form a new ocean, and that's what makes it a dream destination for geologists like Oxford University's Dr. David Ferguson who explained to Sue Nelson the Afar Depression's appeal.

David -   Well Afar is a geologically fascinating place because it's one of the few places on the Earth's surface where we can see the continental crust - and that's the rocky outer shell of the Earth that we live on - we can see it being ripped apart by the movement of tectonic plates, and hot afar Depressionmagma from the Earth's mantle, which is the region below the crust, wells up to fill the gap and creates a new ocean basin.

Sue -   How long have geologists known about this particular region?

David -   The first geologists to visit Afar were probably there during the 1960s and the 1970s, and it was recognised at this point that it was an exceptional place to understand how plate tectonics work, and firstly, due to the independence war in Ethiopia, we haven't really been able to visit the area for decades.  So it's only in the last 10 years or so that scientists have been able to get back into Afar and been able to study, in detail, the processes that are going on there.

Sue -   Before we go into the processes themselves, you've brought a couple of rocks here.  Describe to me and to us, what the surface of this rocky remote place looks like.

David -   So in this bag, we have a piece of the basaltic lava, it's one of the most common rocks on Earth actually and this is one of the newest rocks on Earth.  This is just approaching its first birthday.  This piece of the Earth's surface was underground a year ago.

Sue -   It's almost like a hard, black grey piece of sponge, very porous.

David -   Yes, so it's full of holes, so these are all the gas bubbles that escaped.  It's quite spiky because it flowed across the surface and it's still young enough to preserve all these spiky bits.  And if you look carefully, you can see it's full of shiny crystals, large, white, kind of glassy looking crystals.

Sue -   Oh yes.

David -   These grew underground in a magma chamber where this lava was stored before it erupted.  We have another piece of rock here which is very different.  There's no bubbles in this and this is a piece of volcanic glass.

Sue -   Very shiny.

David -   It's incredibly shiny.

Sue -   Almost looks like black marble.

David -   Yes, it's very heavy and it's composed almost just entirely of glass.

Sue -   Let me just feel a bit.  It's like the size of a bag of sugar, this bit.  And actually, feels pretty much, probably a bit heavier than a bag of sugar as well.

David -   Yeah, the difference between these two really is their chemistry and this magma was so viscous that the crystals that we see in this lava weren't able to grow and so, it just solidified into just a chunk of glass really.

Erta Ale VolcanoSue -   Now this great big rift, you say it's an ocean forming rift.  Does that mean in the foreseeable future that the area, this part of Ethiopia that you're looking at, will be covered in sea, in hundreds of thousands of years time?

David -   Yes, the crust that forms Ethiopia is being slowly stretched apart, at about 20 millimetres a year for instance.  However, right now in Afar that process within the last five years have speeded up dramatically and it's moved approximately a metre a year, or two metres a year even, within the last five years.  We think this probably goes in stops and starts and so, at the average speeds of maybe 20 millimetres a year, if this continues for 10 million years for instance, then we'd probably see a new ocean basin in Afar.

Sue -   How normal is this for geologist to actually see this taking place?

David -   It's incredible.  It's pretty much a once in a lifetime opportunity.  Tectonic plates move very slowly and it's not common that we get a chance to witness a furious stage of activity.  There was one other well-documented phase which was in Iceland in the 1970s, but apart from that, this is a very rare occurrence. But we think in this part of Afar, it probably happens every 400-500 years.

Sue -   So how often do you get to go out there because I know from reading, you kept a blog at one stage, that you had this hot date with a volcano.  So how likely are you to go out there or do you go out there as soon as you hear that there's activity?  Is it being like a fireman on-call or the geologist equivalent of a fireman?

David -   Yeah, a little bit.  We're volcanologists on-call and we go out for two reasons.  We go out to collect rock samples and from older lava flows to perform experiments on.  But yes, as you say, when we hear there's an eruption, we try and get out there as quick as we can because we want to collect samples, and we want to actually witness these eruptions in progress if we can to learn a little bit about it.  We're always ready to drop everything and run out if we get the opportunity.

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