0:00:08 > 0:00:11Welcome to Morocco, North Africa,
0:00:11 > 0:00:14and welcome to this - the Sahara Desert.
0:00:14 > 0:00:16The biggest hot desert in the world.
0:00:16 > 0:00:20Deserts get very little rain and are the most barren places
0:00:20 > 0:00:23on the planet, which makes for some of the harshest conditions going.
0:00:23 > 0:00:26But, despite that, millions of people live in the desert.
0:00:26 > 0:00:29Come with us as we as we take a journey into the dunes,
0:00:29 > 0:00:31right to the very heart of the Sahara
0:00:31 > 0:00:35as we find out how to survive in the sandy wilderness.
0:00:39 > 0:00:41'On today's Fierce Earth, we take to the skies
0:00:41 > 0:00:43'to discover how deserts are formed...'
0:00:43 > 0:00:49- Give that a blast! Woo-hoo!- Whoa!
0:00:49 > 0:00:51'Leo is put to the test as he finds out how to escape
0:00:51 > 0:00:53'the deadly grip of quicksand...'
0:00:54 > 0:00:57The more you wriggle, the more you sink in to it.
0:00:59 > 0:01:02'We learn how powerful and destructive sand can be
0:01:02 > 0:01:05'when it gets whipped up by the wind...'
0:01:05 > 0:01:07Today, we're going to try and get right to the heart
0:01:07 > 0:01:09of one of these sandstorms.
0:01:09 > 0:01:13'..and Leah meets the kids who live a roaming life in the desert
0:01:13 > 0:01:17'and finds out how they can survive in this harsh environment.'
0:01:18 > 0:01:21What happens when the ground shakes,
0:01:21 > 0:01:26the seas rise up and the air tears itself apart?
0:01:26 > 0:01:27The Fierce Earth team move in,
0:01:27 > 0:01:30taking on the most powerful forces on the planet.
0:01:49 > 0:01:53Get ready for Fierce Earth: the Earth and how to survive it.
0:01:58 > 0:02:03Deserts make up about one third of the Earth's land surface
0:02:03 > 0:02:07and are defined by the lack of rainfall that they receive.
0:02:07 > 0:02:11Although they are all really dry, deserts aren't all hot.
0:02:11 > 0:02:15The Arctic and Antarctic are covered in snow and ice
0:02:15 > 0:02:19and are the two biggest deserts on Earth.
0:02:19 > 0:02:22But we're heading to the Sahara, the biggest hot desert
0:02:22 > 0:02:25where the lack of water, soaring temperatures
0:02:25 > 0:02:28and ferocious winds that howl across it
0:02:28 > 0:02:32make this one of the most inhospitable places on the planet.
0:02:43 > 0:02:45This is Marrakech.
0:02:45 > 0:02:50Just 400 miles to the north is Europe and the coast of Spain,
0:02:50 > 0:02:54but the reason why we're here in North Africa is 150 miles south
0:02:54 > 0:02:58where the landscape changes to the wilderness that is
0:02:58 > 0:02:59the Sahara Desert.
0:03:02 > 0:03:05To discover why the Sahara and other hot deserts are so barren,
0:03:05 > 0:03:09you have to look a lot further south to the equator.
0:03:09 > 0:03:12The equator is the belt around the middle of the Earth.
0:03:12 > 0:03:14Because of the angle the sun shines,
0:03:14 > 0:03:16it gets the most intense heating.
0:03:17 > 0:03:20So what has that intense heating got to do with
0:03:20 > 0:03:21the formation of the desert?
0:03:24 > 0:03:26Well, to show you, we'll take to the sky.
0:03:30 > 0:03:33And what better way to take to the sky
0:03:33 > 0:03:37than a flight in a hot-air balloon?
0:03:37 > 0:03:38BURNERS ROAR
0:03:41 > 0:03:43- We're flying!- Ooh-hoo-hoo-hoo!
0:03:46 > 0:03:50To get our balloon to fly, our pilot here, Maurice,
0:03:50 > 0:03:52has to give it a blast of hot air.
0:03:52 > 0:03:53BURNERS ROAR
0:03:53 > 0:03:56- Argh!- Whoa!
0:03:56 > 0:03:59With every blast he gives it,
0:03:59 > 0:04:03the balloon fills up and will rise higher and higher.
0:04:03 > 0:04:06- Maurice, give that a blast! - Yes-ah.
0:04:06 > 0:04:10Woo-hoo, ha-ha-ha!
0:04:10 > 0:04:13The burner in this balloon is heating the air
0:04:13 > 0:04:15just like the sun does around the equator.
0:04:17 > 0:04:20The hot air rises, exactly the same as this balloon.
0:04:20 > 0:04:24And that's because hot air is lighter than cold air.
0:04:25 > 0:04:27Down on the ground, it was quite warm,
0:04:27 > 0:04:30but up here, the air is cool.
0:04:30 > 0:04:32Now, as air cools it falls back to the ground
0:04:32 > 0:04:35and any moisture falls back to the ground as rain
0:04:35 > 0:04:37and that's why we have such rich habitats,
0:04:37 > 0:04:40like tropical rainforests near the equator
0:04:40 > 0:04:43because it's that part of the world that gets the most rain.
0:04:43 > 0:04:46Once the air has lost all of the water it contains, it continues
0:04:46 > 0:04:50to move away from the equator, only this time without the rain.
0:04:50 > 0:04:53And little or no rain means deserts form.
0:04:53 > 0:04:56Normally, they receive less than 25cm of rain per year,
0:04:56 > 0:04:58sometimes less than five.
0:04:59 > 0:05:01And that's why all hot deserts -
0:05:01 > 0:05:04some of the biggest being the Sahara, Kalahari,
0:05:04 > 0:05:06and the Great Australian -
0:05:06 > 0:05:08sit either side of the equator.
0:05:10 > 0:05:12Hot deserts also exist
0:05:12 > 0:05:16because of the distance they are from large areas of water,
0:05:16 > 0:05:18like lakes or the sea.
0:05:18 > 0:05:20As we make our way south towards the desert,
0:05:20 > 0:05:24there is another reason why the Sahara gets hardly any rain.
0:05:24 > 0:05:27These are the Atlas Mountains.
0:05:27 > 0:05:30They sit between the Atlantic Ocean and the desert.
0:05:30 > 0:05:34These mountains simply block any water getting to the Sahara.
0:05:39 > 0:05:41On the other side of the Atlas Mountains,
0:05:41 > 0:05:43trees and shrubs start to disappear.
0:05:43 > 0:05:47It's here where it starts to get drier and dustier
0:05:47 > 0:05:49It's here that the Sahara desert starts.
0:05:55 > 0:05:59The Sahara covers an area of 3.5 million square miles -
0:05:59 > 0:06:01that's the size of the United States
0:06:01 > 0:06:05and it covers one third of the giant continent of Africa.
0:06:05 > 0:06:07To the north, you see there's lots of rocks and dirt,
0:06:07 > 0:06:09but in the south,
0:06:09 > 0:06:11there's hundreds and hundreds of miles of sand.
0:06:11 > 0:06:15Sand is formed by the erosion of rocks over thousands,
0:06:15 > 0:06:16even millions of years.
0:06:16 > 0:06:19That builds up to these massive dunes we see around us -
0:06:19 > 0:06:21a giant sand sea.
0:06:22 > 0:06:24Sand dunes form when millions,
0:06:24 > 0:06:26even trillions of small particles of sand
0:06:26 > 0:06:28are blown around by the wind.
0:06:28 > 0:06:33When they come across an obstacle like a rock, or even some vegetation,
0:06:33 > 0:06:34they start to collect.
0:06:34 > 0:06:36And once they collect,
0:06:36 > 0:06:39they get bigger and bigger and bigger.
0:06:39 > 0:06:44Some sand dunes can even get up to 250m in height -
0:06:44 > 0:06:46that's practically a sand mountain.
0:06:46 > 0:06:50Now the sand itself, as you can see, is not stable
0:06:50 > 0:06:53and with the big desert winds,
0:06:53 > 0:06:56that means the sand sea is constantly on the move.
0:06:56 > 0:07:01The desert can get larger and where it moves out onto new land,
0:07:01 > 0:07:03that is when you get desertification.
0:07:08 > 0:07:12To understand how deserts move, I've come to its very edge,
0:07:12 > 0:07:16where the desert is starting to move into the village.
0:07:16 > 0:07:19And just with this light wind that we've got here,
0:07:19 > 0:07:23you can see it's strong enough to move the small particles of sand.
0:07:23 > 0:07:25You can see the sand flying off the sides,
0:07:25 > 0:07:28even making very small dunes on the top.
0:07:28 > 0:07:29But what if I add water?
0:07:29 > 0:07:31Very quickly,
0:07:31 > 0:07:35we've stopped any of those small sand particles from blowing.
0:07:35 > 0:07:38We can do another thing, though -
0:07:38 > 0:07:43we take some vegetation and we have vegetation and water.
0:07:45 > 0:07:49The combination of water and vegetation
0:07:49 > 0:07:52is a very effective way of stopping the desert from moving.
0:07:54 > 0:07:57It's the removal of vegetation by animals grazing
0:07:57 > 0:07:59or people chopping down trees for firewood
0:07:59 > 0:08:02that destabilises the land, causing desertification.
0:08:04 > 0:08:072 billion people are at risk around the world
0:08:07 > 0:08:10as the slow creep of the sand could force people from their homes
0:08:10 > 0:08:12and put a strain on natural resources.
0:08:14 > 0:08:16But there are measures that people can take
0:08:16 > 0:08:18to fight the spread of the sand.
0:08:21 > 0:08:24In situations where there isn't much vegetation,
0:08:24 > 0:08:25the people can lend a hand.
0:08:25 > 0:08:29Here, they've taken palm leaves and created this network of fences
0:08:29 > 0:08:32which acts like a sand trap.
0:08:32 > 0:08:34You can see the buildings just behind me -
0:08:34 > 0:08:37the sand that's trapped here would've migrated all the way over there.
0:08:37 > 0:08:39By putting these in -
0:08:39 > 0:08:41and they put these in all round the country -
0:08:41 > 0:08:45this is how the people can fight against the moving sand seas
0:08:45 > 0:08:47and against desertification.
0:08:48 > 0:08:49Coming up on Fierce Earth -
0:08:49 > 0:08:52Leo ends up in a sticky situation...
0:08:52 > 0:08:53I'm stuck!
0:08:53 > 0:08:55..and Leah meets the kids
0:08:55 > 0:08:58who call the harsh environment of the desert home.
0:09:02 > 0:09:05When the winds blow across the desert,
0:09:05 > 0:09:09it not only moves the sand - it can unleash massive sandstorms.
0:09:09 > 0:09:12Ferocious winds whip up billions of tiny particles
0:09:12 > 0:09:14into a massive wall of nastiness.
0:09:14 > 0:09:15And it's villages like this
0:09:15 > 0:09:18on the very plains on the edge of the desert
0:09:18 > 0:09:20that are in most danger - they've got no escape.
0:09:20 > 0:09:23Today, we are going to try and get to the heart
0:09:23 > 0:09:24of one of these sandstorms.
0:09:25 > 0:09:27Sandstorms can be really dangerous,
0:09:27 > 0:09:30We are taking no chances today
0:09:30 > 0:09:32and are going to follow these basic rules.
0:09:32 > 0:09:34Know the warning signs -
0:09:34 > 0:09:38sandstorms usually happen when the day is at its hottest.
0:09:38 > 0:09:40You can see sandstorms coming from miles away,
0:09:40 > 0:09:43so if you're in a car, try and get out of its way.
0:09:43 > 0:09:48Be prepared - cover your face with a mask, a scarf,
0:09:48 > 0:09:49or even a shirt like this.
0:09:49 > 0:09:53And cover your eyes - you can use sunglasses or goggles.
0:09:53 > 0:09:54You don't want to get sand in those.
0:09:54 > 0:09:57Make sure you have got plenty of water and food -
0:09:57 > 0:09:59sandstorms normally blow over pretty quickly,
0:09:59 > 0:10:01but you don't know how long you could be out there.
0:10:01 > 0:10:03And finally, find shelter -
0:10:03 > 0:10:06get beside a wall, inside a house if you can,
0:10:06 > 0:10:08or even down by the side of your camel.
0:10:09 > 0:10:12We need to put ourselves in the best position
0:10:12 > 0:10:14to get to the heart of a sandstorm,
0:10:14 > 0:10:17so we head out into the middle of the desert
0:10:17 > 0:10:18where there is no shelter
0:10:18 > 0:10:20and the wind should be at its strongest.
0:10:22 > 0:10:24When the wind does start to blow,
0:10:24 > 0:10:27sand and dust is easily lifted into the air.
0:10:27 > 0:10:31As it starts to swirl across the flat desert lands,
0:10:31 > 0:10:33a sandstorm is born.
0:10:35 > 0:10:37Gusts of winds come and go.
0:10:37 > 0:10:39Sandstorms are unpredictable
0:10:39 > 0:10:41and can blow out within a few seconds
0:10:41 > 0:10:44but, sometimes, they can rage for hours
0:10:44 > 0:10:45or even days at a time.
0:10:49 > 0:10:51The weather is so unpredictable,
0:10:51 > 0:10:54you never know when a sandstorm could be on the horizon.
0:10:54 > 0:10:57Unfortunately, it's not very windy today -
0:10:57 > 0:10:58we have seen a few dust devils,
0:10:58 > 0:11:01these little spirals of sand blowing around,
0:11:01 > 0:11:03which are kind of like baby sandstorms,
0:11:03 > 0:11:06but it's just not windy enough for a proper sandstorm.
0:11:08 > 0:11:11Proper sandstorms can cover the desert,
0:11:11 > 0:11:14sometimes hundreds of miles across.
0:11:16 > 0:11:21Some sandstorms are so big, they can even be seen from space.
0:11:23 > 0:11:25Sandstorms do hit this part of the world
0:11:25 > 0:11:27and, when they hit, they hit really hard.
0:11:29 > 0:11:31The air goes thick with sand.
0:11:32 > 0:11:36As sandstorms rage, visibility reaches almost zero
0:11:36 > 0:11:38and it becomes hard to breathe.
0:11:40 > 0:11:43That power of wind and sand can shut down towns and cities
0:11:43 > 0:11:47and then you know you're really in the heart of a true sandstorm.
0:11:56 > 0:11:59Now, you've seen what can happen in a sandstorm.
0:12:01 > 0:12:07But how can tiny little bits of rock and sand cause such damage?
0:12:07 > 0:12:10Well, to find out, I'm going to see a local mechanic.
0:12:14 > 0:12:16Because I reckon they'll have the kit I need
0:12:16 > 0:12:18to make my very own mini sandstorm.
0:12:20 > 0:12:23Every garage has one of these - a compressor.
0:12:23 > 0:12:27This sends pressurised air along this pipe
0:12:27 > 0:12:30and I've attached it to this, which is a sand blasting gun.
0:12:30 > 0:12:33This bag contains dry sand.
0:12:33 > 0:12:35I attach it to the gun
0:12:35 > 0:12:41and let's just see what this does to an old kettle like this.
0:12:48 > 0:12:52As the grains of sand are blasted against the kettle,
0:12:52 > 0:12:55they strip away the surface layer by layer -
0:12:55 > 0:12:57just like sandpaper, but without the paper.
0:12:59 > 0:13:02Wow - just look at that!
0:13:02 > 0:13:06We've taken this old rusty kettle down to bare metal.
0:13:08 > 0:13:09And that is the same destruction
0:13:09 > 0:13:13that, over time, sand can cause to everything in its path.
0:13:15 > 0:13:20So how do people live in a hot and harsh environment of a desert,
0:13:20 > 0:13:22under constant threat of sandstorms?
0:13:22 > 0:13:27Well, they have, for hundreds, even thousands of years,
0:13:27 > 0:13:30but in order to do so, they've had to adapt.
0:13:36 > 0:13:38Everything about this town
0:13:38 > 0:13:42is designed to last in an extreme desert condition.
0:13:42 > 0:13:46The first thing you notice...is there are no windows.
0:13:46 > 0:13:50That's very good when a sandstorm blows through the town.
0:13:52 > 0:13:54The houses are built from desert sand,
0:13:54 > 0:13:57mixed with clay and straw.
0:13:57 > 0:14:00The walls can be up to a metre thick to combat the extreme temperatures.
0:14:02 > 0:14:05It keeps you cool during the day and warm at night.
0:14:08 > 0:14:09It's the middle of the day here
0:14:09 > 0:14:12and the streets of this old town are absolutely deserted.
0:14:12 > 0:14:16That's because living in a desert is hot business -
0:14:16 > 0:14:17you get up at the crack of dawn
0:14:17 > 0:14:20and get all of your work done while the temperature is low.
0:14:20 > 0:14:24When the sun hits the midday, it's too hot to do anything -
0:14:24 > 0:14:27you get inside some shade, you have a siesta.
0:14:27 > 0:14:29There's a little bit of time left at the end of the day
0:14:29 > 0:14:31to get any final chores done,
0:14:31 > 0:14:34but when the sun goes down, the lights go off -
0:14:34 > 0:14:36it's bedtime!
0:14:36 > 0:14:40To live in the hot, dry desert, you need water,
0:14:40 > 0:14:44and this, like any other old town in the desert,
0:14:44 > 0:14:46is built on an oasis.
0:14:48 > 0:14:51An oasis is a permanent source of water in the desert,
0:14:51 > 0:14:54fed by underground springs and rivers.
0:14:54 > 0:14:57There is greenery surrounding the whole of this town.
0:14:57 > 0:15:00Where you find an oasis, you find life.
0:15:05 > 0:15:08When you leave the security of the towns and villages,
0:15:08 > 0:15:11deserts become even more hostile
0:15:11 > 0:15:14and potentially deadly environments for humans to live in.
0:15:14 > 0:15:17Temperatures soar during the day
0:15:17 > 0:15:20and plummet to almost freezing levels at night.
0:15:20 > 0:15:23It's this, combined with the lack of food sources -
0:15:23 > 0:15:24and, more importantly, water -
0:15:24 > 0:15:28that make life in the sandy wilderness tough. Really tough.
0:15:28 > 0:15:33And yet, there are people who have adapted for desert living.
0:15:33 > 0:15:35Dotted across the Sahara desert,
0:15:35 > 0:15:39there are families that make this harsh landscape their home
0:15:39 > 0:15:42and today, I have been invited by the Shaoush family
0:15:42 > 0:15:43to spend the day with them.
0:15:43 > 0:15:44So let's go in.
0:15:46 > 0:15:49The Shaoush family are part of the Berber tribe.
0:15:49 > 0:15:53There are over 20 million Berbers living in North Africa,
0:15:53 > 0:15:55most of whom are nomadic -
0:15:55 > 0:15:57families that travel from place to place
0:15:57 > 0:16:00and never stay in the same spot for very long.
0:16:00 > 0:16:03They set up camp where they can easily get to water,
0:16:03 > 0:16:06living in tents and huts.
0:16:06 > 0:16:09Sahid is seven and shows me around the family's camp.
0:16:11 > 0:16:14This is where Sahid and his family live
0:16:14 > 0:16:16and he is going to give me a little tour.
0:16:16 > 0:16:19So this is maybe the living room where everyone lives?
0:16:19 > 0:16:22- TRANSLATION:- This is my bedroom -
0:16:22 > 0:16:24my mum sleeps there, my sister sleeps there
0:16:24 > 0:16:26and I sleep there.
0:16:26 > 0:16:27It looks quite cosy -
0:16:27 > 0:16:29there are loads of rugs on the floor,
0:16:29 > 0:16:31there's pillows to rest your head.
0:16:31 > 0:16:33It looks like a really good shelter
0:16:33 > 0:16:35because the sand is swirling around right now,
0:16:35 > 0:16:38and under there would be the perfect place
0:16:38 > 0:16:41to shelter from all the sand.
0:16:46 > 0:16:47What's happening here?
0:16:48 > 0:16:50My mum is making fabric.
0:16:50 > 0:16:55So this is goat's hair, camel hair, and she's using this device here
0:16:55 > 0:16:58to knit it all together, effectively,
0:16:58 > 0:17:01for the main tent, which we just saw.
0:17:01 > 0:17:03Sahid, how long have you been at this camp?
0:17:04 > 0:17:06Four months.
0:17:06 > 0:17:09And that's quite typical of nomadic tribes -
0:17:09 > 0:17:11they move on from place to place.
0:17:11 > 0:17:15We travel to find water and food for our animals
0:17:19 > 0:17:21A short walk from their camp
0:17:21 > 0:17:23is the reason they have chosen this spot
0:17:23 > 0:17:25to make their temporary home.
0:17:27 > 0:17:30This is brilliant - in the middle of the desert,
0:17:30 > 0:17:33the family have their very own water supply.
0:17:33 > 0:17:37Their camp is about a minute's walk in that direction.
0:17:37 > 0:17:39That's why they based their camp here,
0:17:39 > 0:17:40they can come here.
0:17:40 > 0:17:42It's not as easy as turning on a tap,
0:17:42 > 0:17:44but it's not half bad -
0:17:44 > 0:17:47whenever they want to cook or make tea,
0:17:47 > 0:17:49they just come here with their bottles,
0:17:49 > 0:17:51fill them up, and there's a short walk back.
0:17:51 > 0:17:52It's brilliant.
0:17:52 > 0:17:56While Sahid helps keep the water supplies topped up,
0:17:56 > 0:17:59his sister Rachid takes the family's goats
0:17:59 > 0:18:01six hours away from the camp.
0:18:03 > 0:18:07Can you tell us why you do this journey?
0:18:07 > 0:18:09- TRANSLATION: - I bring them here to graze.
0:18:09 > 0:18:12These goats are like the family's bank account.
0:18:12 > 0:18:14They sell them at the local market
0:18:14 > 0:18:18so they can buy fruit, vegetables and other essentials.
0:18:18 > 0:18:20The responsibility that I had at about her age
0:18:20 > 0:18:24was walking to the local newsagent and picking up a paper.
0:18:24 > 0:18:28She is in charge of 50 goats in the middle of the Sahara desert
0:18:28 > 0:18:31and to have this as your playground, that's pretty cool.
0:18:31 > 0:18:34The family's camp is not just tents.
0:18:34 > 0:18:37They have built a stone hut as a kitchen
0:18:37 > 0:18:41and Sahid's older sister is cooking the evening meal.
0:18:41 > 0:18:43It's quite a small space
0:18:43 > 0:18:44but you've got everything you need here -
0:18:44 > 0:18:47you've got the vegetables, water,
0:18:47 > 0:18:49and that what we're boiling over here, a bit of water,
0:18:49 > 0:18:52hopefully for some mint tea later on.
0:18:52 > 0:18:54But before dinner,
0:18:54 > 0:18:57there's a goat-related emergency to deal with.
0:18:57 > 0:19:00OK, the goats have got loose, I have no idea how,
0:19:00 > 0:19:04so I'm just trying...to get them back in.
0:19:06 > 0:19:07I promise I didn't open the gate.
0:19:07 > 0:19:09There's another one here.
0:19:09 > 0:19:12Come here...no...come on.
0:19:12 > 0:19:13There we go.
0:19:13 > 0:19:14KID BLEATS
0:19:14 > 0:19:16SHE LAUGHS
0:19:18 > 0:19:20I don't think he likes that.
0:19:33 > 0:19:37I've had a fantastic day with Sahid and his family -
0:19:37 > 0:19:38they've made me feel really welcome.
0:19:38 > 0:19:41They live a simple life here in the desert,
0:19:41 > 0:19:44but it's a tough life and I don't think I could live here.
0:19:44 > 0:19:45I'm too used to my home comforts.
0:19:45 > 0:19:48But it's amazing to think, in a few weeks' time,
0:19:48 > 0:19:52they'll pack all of this up and head off to their new home.
0:20:01 > 0:20:06In this incredibly dry environment, water is the most precious thing
0:20:06 > 0:20:09and I think I've stumbled across loads of it.
0:20:11 > 0:20:14In the desert, all you can see for miles and miles
0:20:14 > 0:20:15are rocks and sand.
0:20:15 > 0:20:18But over there is a huge lake.
0:20:20 > 0:20:23And a lake in the middle of the desert
0:20:23 > 0:20:26is a seriously welcome sight.
0:20:26 > 0:20:28I need to get to it, so I walk...
0:20:29 > 0:20:30..and I walk...
0:20:31 > 0:20:32..and I walk.
0:20:34 > 0:20:37But when the barren landscape and the soaring heat combine,
0:20:37 > 0:20:41they can sometimes hold a nasty trick up their sleeve.
0:20:42 > 0:20:44Ugh - that was annoying.
0:20:44 > 0:20:49As far as my eyes could see, there was a lake in front of me,
0:20:49 > 0:20:51but the closer I thought I got to it,
0:20:51 > 0:20:53the further away it seemed.
0:20:54 > 0:20:56But there is no lake, there is no water.
0:20:56 > 0:20:58This is a mirage.
0:21:04 > 0:21:07Mirages happen when the air near the very hot ground
0:21:07 > 0:21:11becomes much hotter than the air above it.
0:21:11 > 0:21:13The light from the sky is bent back up
0:21:13 > 0:21:17as it passes through cooler and then hotter air.
0:21:17 > 0:21:20So what we see is a reflection of the sky on the ground
0:21:20 > 0:21:22and it looks like water.
0:21:24 > 0:21:28If you find yourself stuck, stranded in this vast desert,
0:21:28 > 0:21:31you will look for that and you'll think it's a lake,
0:21:31 > 0:21:34but it's an optical illusion, a mirage -
0:21:34 > 0:21:36it doesn't actually exist.
0:21:36 > 0:21:37It's really annoying.
0:21:40 > 0:21:42Finding water in the desert is nearly impossible
0:21:42 > 0:21:45because it just doesn't rain for weeks, months
0:21:45 > 0:21:48or even years at a time.
0:21:48 > 0:21:51But when it does rain, it really rains!
0:21:54 > 0:21:58The rain provides much-needed water for the people of the desert
0:21:58 > 0:22:02as rivers and lakes appear almost instantly across the dry sand.
0:22:05 > 0:22:07But the water doesn't stay around for long
0:22:07 > 0:22:09and when it disappears from the surface
0:22:09 > 0:22:11and the rivers and lakes start to dry up,
0:22:11 > 0:22:15it causes another potentially deadly problem.
0:22:15 > 0:22:19Check this out - looks just like any other bit of this vast desert.
0:22:19 > 0:22:22But watch what happens when I poke it with a stick.
0:22:24 > 0:22:25You see that?
0:22:25 > 0:22:27It wobbles like jelly.
0:22:27 > 0:22:29That's because this isn't any ordinary sand -
0:22:29 > 0:22:31this is quicksand.
0:22:31 > 0:22:34Quicksand forms when sand mixes with water.
0:22:34 > 0:22:39It becomes sticky, gloopy, and more importantly, deadly!
0:22:39 > 0:22:42From the surface, you really can't spot it,
0:22:42 > 0:22:44and that's what makes it really dangerous!
0:22:44 > 0:22:47When you stray into quicksand, you sink,
0:22:47 > 0:22:50and getting out is the stuff of nightmares.
0:22:50 > 0:22:51I'm about to take the plunge -
0:22:51 > 0:22:53I'm going to jump into this quicksand.
0:22:53 > 0:22:55The challenge is to see if I can get out.
0:22:55 > 0:22:59OK, Leo, off you go - good luck. I'm here all the way for you.
0:23:01 > 0:23:02Finding quicksand in the desert
0:23:02 > 0:23:05is like finding a needle in a haystack.
0:23:05 > 0:23:08So what do you when you're in the middle of the desert
0:23:08 > 0:23:12and you want Leo waist-deep in quicksand?
0:23:15 > 0:23:18If we can't find quicksand, we'll have to make our own.
0:23:19 > 0:23:21So the boys are doing really good,
0:23:21 > 0:23:25but we still don't know if we're able to recreate quicksand
0:23:25 > 0:23:28in the middle of the Sahara.
0:23:28 > 0:23:31Quicksand forms where rivers or lakes run dry
0:23:31 > 0:23:34or where water oozes up from desert springs.
0:23:36 > 0:23:38The ground is usually so dry
0:23:38 > 0:23:42that a lake or river could go from water to dry sand
0:23:42 > 0:23:43in just a few hours.
0:23:45 > 0:23:47To recreate these conditions,
0:23:47 > 0:23:51we need to fill the hole with water and mix it with sand.
0:23:54 > 0:23:55Quicksand is dangerous.
0:23:55 > 0:23:59We've got a team of people in case Leo gets into serious trouble.
0:23:59 > 0:24:02Do NOT try this at home or on the beach.
0:24:03 > 0:24:06The test will be how quick he'll be able get out.
0:24:06 > 0:24:08If this is above my waist,
0:24:08 > 0:24:10I don't know if I'll be able to get out.
0:24:10 > 0:24:14This heat will just drain any energy that you've got
0:24:14 > 0:24:15and that will be the big problem.
0:24:17 > 0:24:18Leo can now take the plunge.
0:24:20 > 0:24:21Here we go...
0:24:24 > 0:24:25Ugh!
0:24:30 > 0:24:31I'm sinking!
0:24:35 > 0:24:36I'm stuck.
0:24:38 > 0:24:40Leah? Help!
0:24:42 > 0:24:46It doesn't take long before I sink up to my chest.
0:24:46 > 0:24:51The sand has a firm grip as I get pulled deeper...and deeper.
0:24:51 > 0:24:54When sand and water are mixed,
0:24:54 > 0:24:59they make this horrible...sticky, gloopy mess.
0:24:59 > 0:25:03The more you wriggle, the more you sink into it.
0:25:03 > 0:25:06You may think that sinking in over your head
0:25:06 > 0:25:10is what kills you in the quicksand, but it's not -
0:25:10 > 0:25:13it's the sun that gets you out here in the baking hot desert.
0:25:13 > 0:25:17If you were trapped for a long time, you'd die of dehydration.
0:25:20 > 0:25:21There's a camel over there.
0:25:22 > 0:25:24Wonder if they can get me out?
0:25:25 > 0:25:29The camels can't help me in here, so I have to try and relax
0:25:29 > 0:25:32and get myself out of this sticky situation.
0:25:32 > 0:25:34If you ever get stuck in quicksand,
0:25:34 > 0:25:38the trick is don't panic, try not to fight it.
0:25:38 > 0:25:42If you fight it, it's quite scary
0:25:42 > 0:25:44and you feel like you're sinking...ooh.
0:25:44 > 0:25:45But if you just relax,
0:25:45 > 0:25:49it feels a little bit like you're swimming in a giant jelly
0:25:49 > 0:25:50or a blancmange.
0:25:50 > 0:25:54So what you need to do is kind of like swimming -
0:25:54 > 0:25:56spread your weight out.
0:25:56 > 0:26:00The more surface area you've got, the less likely you are to sink,
0:26:00 > 0:26:05so I can almost...lie on top of it.
0:26:05 > 0:26:07Oh...OK...
0:26:07 > 0:26:13And then you can almost push off...the quicksand itself,
0:26:15 > 0:26:16Here we go...
0:26:20 > 0:26:22Ah...yes...!
0:26:32 > 0:26:34HE PANTS
0:26:34 > 0:26:36I made it.
0:26:36 > 0:26:39That is how you escape from quicksand.
0:26:40 > 0:26:43Hey, Leo, well done!
0:26:43 > 0:26:45I would give you a hug, but...
0:26:45 > 0:26:46Please don't.
0:26:47 > 0:26:49It sets around you like concrete.
0:26:49 > 0:26:51Quicksand, best avoided.
0:26:52 > 0:26:54On our Saharan adventure,
0:26:54 > 0:26:58we've discovered what creates dry, hot deserts
0:26:58 > 0:27:02as the hot air from the equator rises and falls back to earth
0:27:02 > 0:27:03with little moisture.
0:27:04 > 0:27:05We got dressed up
0:27:05 > 0:27:09to tackle one of the biggest and most deadly threats of the desert -
0:27:09 > 0:27:10the sandstorm.
0:27:12 > 0:27:14I discovered how a trick in the bright sunlight
0:27:14 > 0:27:18can fool you into seeing things that don't really exist.
0:27:18 > 0:27:23As far as my eyes could see, there was a lake in front of me.
0:27:23 > 0:27:26That lake was really a mirage.
0:27:26 > 0:27:28And I spent the day with a Berber family -
0:27:28 > 0:27:30part of a tribe who have lived in the Sahara
0:27:30 > 0:27:32for thousands of years.
0:27:36 > 0:27:38Next time on Fierce Earth -
0:27:38 > 0:27:41the temperature plummets and the snow just keeps on coming...
0:27:41 > 0:27:43The winds are starting to really pick up here.
0:27:44 > 0:27:48And Leo is chilled to his bones when we create the perfect blizzard.
0:27:48 > 0:27:50It's cold!