Placeholder Image

Subtitles section Play video

  • It's a bit funny to be

  • at a conference dedicated to things not seen,

  • and present my proposal to build

  • a 6,000-kilometer-long wall

  • across the entire African continent.

  • About the size of the Great Wall of China,

  • this would hardly be an invisible structure.

  • And yet it's made from parts that are invisible, or near-invisible, to the naked eye:

  • bacteria and grains of sand.

  • Now, as architects we're trained to solve problems.

  • But I don't really believe in architectural problems;

  • I only believe in opportunities.

  • Which is why I'll show you a threat,

  • and an architectural response.

  • The threat is desertification.

  • My response is a sandstone wall

  • made from bacteria and solidified sand,

  • stretching across the desert.

  • Now, sand is a magical material

  • of beautiful contradictions.

  • It is simple and complex.

  • It is peaceful and violent.

  • It is always the same, never the same,

  • endlessly fascinating.

  • One billion grains of sand

  • come into existence in the world each second.

  • That's a cyclical process.

  • As rocks and mountains die,

  • grains of sand are born.

  • Some of those grains may then cement naturally into sandstone.

  • And as the sandstone weathers, new grains break free.

  • Some of those grains may then accumulate

  • on a massive scale,

  • into a sand dune.

  • In a way, the static, stone mountain

  • becomes a moving mountain of sand.

  • But, moving mountains can be dangerous. Let me try and explain why.

  • Dry areas cover more than one third of the Earth's land surfaces.

  • Some are already deserts;

  • others are being seriously degraded by the sand.

  • Just south of the Sahara we find the Sahel.

  • The name means "edge of the desert."

  • And this is the region most closely associated with desertification.

  • It was here in the late '60s and early '70s

  • that major droughts brought three million people

  • to become dependent upon emergency food aid,

  • with about up to 250,000 dying.

  • This is a catastrophe waiting to happen again.

  • And it's one that gets very little attention.

  • In our accelerated media culture,

  • desertification is simply too slow

  • to reach the headlines.

  • It's nothing like a tsunami or a Katrina:

  • too few crying children and smashed up houses.

  • And yet desertification

  • is a major threat on all continents,

  • affecting some 110 countries

  • and about 70 percent of the world's agricultural drylands.

  • It seriously threatens the livelihoods

  • of millions of people,

  • and especially in Africa and China.

  • And it is largely an issue that we've created for ourselves

  • through unsustainable use of scarce resources.

  • So, we get climate change.

  • We get droughts,

  • increased desertification,

  • crashing food systems, water scarcity,

  • famine, forced migration,

  • political instability, warfare, crisis.

  • That's a potential scenario

  • if we fail to take this seriously.

  • But, how far away is it?

  • I went to Sokoto in northern Nigeria

  • to try and find out how far away it is.

  • The dunes here move southward at a pace of around 600 meters a year.

  • That's the Sahara eating up almost [two meters] a day of the arable land,

  • physically pushing people away from their homes.

  • Here I am -- I'm the second person on the left --

  • (Laughter)

  • with the elders in Gidan-Kara,

  • a tiny village outside of Sokoto.

  • They had to move this village in 1987

  • as a huge dune threatened to swallow it.

  • So, they moved the entire village, hut by hut.

  • This is where the village used to be.

  • It took us about 10 minutes to climb up to the top of that dune,

  • which goes to show why they had to move to a safer location.

  • That's the kind of forced migration

  • that desertification can lead to.

  • If you happen to live close to the desert border,

  • you can pretty much calculate how long it will be

  • before you have to carry your kids away,

  • and abandon your home and your life as you know it.

  • Now, sand dunes cover only about one fifth of our deserts.

  • And still, those extreme environments are very good places

  • if we want to stop the shifting sands.

  • Four years ago, 23 African countries

  • came together to create the Great Green Wall Sahara.

  • A fantastic project, the initial plan

  • called for a shelter belt of trees to be planted

  • right across the African continent,

  • from Mauritania in the west, all the way to Djibouti in the east.

  • If you want to stop a sand dune from moving,

  • what you need to make sure to do is to stop the grains

  • from avalanching over its crest.

  • And a good way of doing that, the most efficient way,

  • is to use some kind of sand catcher.

  • Trees or cacti are good for this.

  • But, one of the problems with planting trees is that

  • the people in these regions are so poor

  • that they chop them down for firewood.

  • Now there is an alternative to just planting trees

  • and hoping that they won't get chopped down.

  • This sandstone wall that I'm proposing essentially does three things.

  • It adds roughness to the dune's surface,

  • to the texture of the dune's surface, binding the grains.

  • It provides a physical support structure for the trees,

  • and it creates physical spaces,

  • habitable spaces inside of the sand dunes.

  • If people live inside of the green barrier

  • they can help support the trees, protect them from humans,

  • and from some of the forces of nature.

  • Inside of the dunes we find shade.

  • We can start harvesting condensation,

  • and start greening the desert from within.

  • Sand dunes are almost like ready-made buildings in a way.

  • All we need to do is solidify the parts that we need to be solid,

  • and then excavate the sand,

  • and we have our architecture.

  • We can either excavate it by hand

  • or we can have the wind excavate it for us.

  • So, the wind carries the sand onto the site

  • and then it carries the redundant sand away from the structure for us.

  • But, by now, you're probably asking,

  • how am I planning to solidify a sand dune?

  • How do we glue those grains of sand together?

  • And the answer is, perhaps, that you use these guys,

  • Bacillus pasteurii,

  • a micro-organism that is readily available in wetlands

  • and marshes, and does precisely that.

  • It takes a pile of loose sand

  • and it creates sandstone out of it.

  • These images from the American Society for Microbiology show us the process.

  • What happens is, you pour Bacillus pasteurii onto a pile of sand,

  • and it starts filling up the voids in between the grains.

  • A chemical process produces calcite,

  • which is a kind of natural cement

  • that binds the grains together.

  • The whole cementation process takes about 24 hours.

  • I learned about this from a professor at U.C. Davis called Jason DeJong.

  • He managed to do it in a mere 1,400 minutes.

  • Here I am, playing the part of the mad scientist,

  • working with the bugs at UCL in London,

  • trying to solidify them.

  • So, how much would this cost?

  • I'm not an economist, very much not,

  • but I did, quite literally, a back of the envelope calculation --

  • (Laughter)

  • -- and it seems that for a cubic meter of concrete

  • we would have to pay in the region of 90 dollars.

  • And, after an initial cost of 60 bucks to buy the bacteria,

  • which you'll never have to pay again,

  • one cubic meter of bacterial sand

  • would be about 11 dollars.

  • How do we construct something like this?

  • Well, I'll quickly show you two options.

  • The first is to create a kind of balloon structure,

  • fill it with bacteria, then allow the sand to wash over the balloon,

  • pop the balloon, as it were, disseminating the bacteria into the sand and solidifying it.

  • Then, a few years afterwards,

  • using permacultural strategies,

  • we green that part of the desert.

  • The second alternative would be to use injection piles.

  • So, we pushed the piles down through the dune,

  • and we create an initial bacterial surface.

  • We then pull the piles up through the dune

  • and we're able to create almost any conceivable shape inside of the sand

  • with the sand acting as a mold as we go up.

  • So, we have a way of turning sand into sandstone,

  • and then creating these habitable spaces inside of the desert dunes.

  • But, what should they look like?

  • Well, I was inspired, for my architectural form, by tafoni,

  • which look a little bit like this, this is a model representation of it.

  • These are cavernous rock structures that I found on the site in Sokoto.

  • And I realized that if I scaled them up, they would provide me

  • with good spatial qualities,

  • for ventilation, for thermal comfort, and for other things.

  • Now, part of the formal control over this structure

  • would be lost to nature, obviously,

  • as the bacteria do their work.

  • And I think this creates a kind of boundless beauty actually.

  • I think there is really something in that articulation

  • that is quite nice.

  • We see the result, the traces, if you like,

  • of the Bacillus pasteurii being harnessed to sculpt the desert

  • into these habitable environments.

  • Some people believe that

  • this would spread uncontrollably,

  • and that the bacteria would kill everything in its way.

  • That's not true at all.

  • It's a natural process. It goes on in nature today,

  • and the bacteria die as soon as we stop feeding them.

  • So, there it is --

  • architectural anti-desertification structures

  • made from the desert itself.

  • Sand-stopping devices, made from sand.

  • The world is likely to lose one third of its arable land

  • by the end of the century.

  • In a period of unprecedented population growth

  • and increased food demands, this could prove disastrous.

  • And quite frankly, we're putting our heads in the sand.

  • If nothing else, I would like for this scheme to initiate a discussion.

  • But, if I had something like a TED wish,

  • it would be to actually get it built,

  • to start building this habitable wall,

  • this very, very long, but very narrow city in the desert,

  • built into the dunescape itself.

  • It's not only something that supports trees,

  • but something that connects people and countries together.

  • I would like to conclude by showing you an animation of the structure,

  • and leave you with a sentence by Jorge Luis Borges.

  • Borges said that "nothing is built on stone,

  • everything is built on sand,

  • but we must build as if the sand were stone."

  • Now, there are many details left to explore in this scheme --

  • political, practical, ethical, financial.

  • My design, as it takes you down the rabbit hole,

  • is fraught with many challenges

  • and difficulties in the real world.

  • But, it's a beginning, it's a vision.

  • As Borges would have it, it's the sand.

  • And I think now is really the time

  • to turn it into stone. Thank you.

  • (Applause)

It's a bit funny to be

Subtitles and vocabulary

Operation of videos Adjust the video here to display the subtitles

B1 US TED sand dune sandstone desert bacteria

【TED】Magnus Larsson: Turning dunes into architecture (Magnus Larsson: Turning dunes into architecture)

  • 96 6
    Zenn posted on 2017/06/18
Video vocabulary