0:00:02 > 0:00:04No matter how well we think we know our planet,
0:00:04 > 0:00:07the natural world still has the ability to surprise us,
0:00:07 > 0:00:10to shock us and maybe sometimes even to scare us
0:00:10 > 0:00:14with its extraordinary events and bizarre behaviour.
0:00:14 > 0:00:18And new technology means that nature's weirdest phenomena
0:00:18 > 0:00:21are being caught ever more readily on camera.
0:00:21 > 0:00:24So we're going to bring you the strangest stories
0:00:24 > 0:00:26our world has to offer...
0:00:28 > 0:00:32..from an island where the locals are awash with crabs...
0:00:32 > 0:00:36to the residents overwhelmed by a deafening plague of insects.
0:00:36 > 0:00:39Argh! There's one on me!
0:00:39 > 0:00:40SHE SCREAMS
0:00:40 > 0:00:44With the help of scientists, experts and eyewitnesses,
0:00:44 > 0:00:49we're going to try and unravel exactly what on earth is going on.
0:01:10 > 0:01:14Nature often has the power to amaze us,
0:01:14 > 0:01:18but sometimes it can feel that it's gone just a bit too far,
0:01:18 > 0:01:21stopping us in our tracks with events that are impossible
0:01:21 > 0:01:24to ignore, and we start with animal invasions
0:01:24 > 0:01:30so shocking that they disrupt, disturb and suspend normal life,
0:01:30 > 0:01:35from the elk running riot to the crabs on an unstoppable mission.
0:01:36 > 0:01:40But we start in America, in Nashville, Tennessee,
0:01:40 > 0:01:45where every spring the air softly buzzes with the sound of insects.
0:01:45 > 0:01:51But in 2011, this gentle chorus turned into a deafening roar.
0:01:51 > 0:01:54LOUD CHORUS OF CHIRRUPING
0:01:54 > 0:01:56- Yes, ma'am, they are loud!- Oh!
0:01:57 > 0:01:59MAN LAUGHS
0:01:59 > 0:02:04Peaking at over 100 decibels, the noise was as loud as a rock concert,
0:02:04 > 0:02:07one that went on nonstop for five weeks.
0:02:08 > 0:02:11But the cause of the racket soon became clear.
0:02:11 > 0:02:13CHIRRUPING CONTINUES
0:02:13 > 0:02:17The town was under siege from a plague of insects.
0:02:19 > 0:02:22The locals were under attack from all directions.
0:02:22 > 0:02:24STRIMMER BUZZES
0:02:24 > 0:02:29And anyone using a power tool outside was being completely mobbed.
0:02:30 > 0:02:32SCREAMING
0:02:32 > 0:02:36Residents like John G Brittle Jr
0:02:36 > 0:02:39got out their video cameras to record the invasion.
0:02:39 > 0:02:41If you think you got bugs...
0:02:41 > 0:02:42let me tell you something.
0:02:42 > 0:02:45You ain't got bugs like these.
0:02:45 > 0:02:48We got 'em...in the millions.
0:02:49 > 0:02:53And the insects in question were cicadas, a completely harmless
0:02:53 > 0:02:56but very vocal relation to the aphid.
0:02:56 > 0:03:01It's noisy. There's just this din all the time, a hum.
0:03:01 > 0:03:03'It can be pretty scary.
0:03:03 > 0:03:06'They're literally flying around and you're batting them away
0:03:06 > 0:03:08'and trying to get them out of your hair.
0:03:08 > 0:03:10'I have friends who didn't leave their houses.'
0:03:10 > 0:03:12WOMAN SCREAMS
0:03:12 > 0:03:15'There are people who don't like bugs.'
0:03:15 > 0:03:17I quite like bugs, yeah.
0:03:17 > 0:03:19Oh, Amy! Oh, whoa!
0:03:19 > 0:03:22INDISTINCT
0:03:22 > 0:03:26The invasion started on a warm spring evening in May.
0:03:28 > 0:03:30All over town, wave after wave
0:03:30 > 0:03:32of cicadas crawled their way
0:03:32 > 0:03:34out of the earth.
0:03:34 > 0:03:38In just five days, almost ten million of them
0:03:38 > 0:03:40had formed a ghostly, red-eyed army.
0:03:47 > 0:03:51One by one, they moulted out of their old skins...
0:03:53 > 0:03:55..which remained clinging eerily to the trees.
0:04:00 > 0:04:04Their arrival brought the town to a standstill.
0:04:09 > 0:04:10SHE SCREAMS
0:04:12 > 0:04:16So what had caused this plague of almost biblical proportions?
0:04:19 > 0:04:23Dr Gene Kritsky has been studying these astonishing swarms.
0:04:25 > 0:04:28The first few that come out and transform into the adults
0:04:28 > 0:04:31usually get eaten by birds and squirrels and raccoons, but
0:04:31 > 0:04:36eventually, the predators become so tired of eating them, they just stop.
0:04:37 > 0:04:40To use an illustration, if you were to go outside and see
0:04:40 > 0:04:44the place being riddled with hundreds of chocolate candies,
0:04:44 > 0:04:47you might eat as many as you can, but eventually you get
0:04:47 > 0:04:50kind of tired of it, and that's what happens to the predators.
0:04:50 > 0:04:53And that allows the second wave, as they continue to emerge,
0:04:53 > 0:04:57to have enough for individuals around to survive to reproduce.
0:04:57 > 0:05:02Now, these incredibly high numbers of insects are weird enough,
0:05:02 > 0:05:05but there was also something truly extraordinary going on -
0:05:05 > 0:05:10these invasions were happening as regular as clockwork every 13 years.
0:05:15 > 0:05:20What could possibly cause this bizarre 13-year pattern?
0:05:20 > 0:05:23Scientists discovered that these weren't the usual annual cicadas
0:05:23 > 0:05:25that Tennessee was used to.
0:05:26 > 0:05:28This was a totally different species,
0:05:28 > 0:05:31known as a periodical cicada -
0:05:32 > 0:05:37an insect that only emerges in plague-like numbers every 13 years.
0:05:39 > 0:05:42Clearly, the number 13 must be pretty important,
0:05:42 > 0:05:45but what's interesting is that it's a prime number -
0:05:45 > 0:05:49it can only be divided by itself or one.
0:05:49 > 0:05:52Now, if parasites or predators have a different type of annual
0:05:52 > 0:05:55cycle - say two, three or four years -
0:05:55 > 0:05:59their peak emergence will never coincide with that of the cicadas.
0:05:59 > 0:06:03Therefore, the cicadas will have a greater chance of survival -
0:06:03 > 0:06:06proving that for at least some species,
0:06:06 > 0:06:08the number 13 is far from unlucky.
0:06:10 > 0:06:14But it seems like a weird life, waiting underground
0:06:14 > 0:06:16for so many years.
0:06:16 > 0:06:19So what exactly is going on down there?
0:06:20 > 0:06:24So what I'm looking for right now are cicada nymphs, immatures
0:06:24 > 0:06:26that will be inside these little clusters of dirt,
0:06:26 > 0:06:28and they're not sleeping -
0:06:28 > 0:06:31they're actually digging along a tree root, feeding, growing,
0:06:31 > 0:06:34moulting and getting ready for their emergence.
0:06:34 > 0:06:37They only emerge from the ground to transform into the adult
0:06:37 > 0:06:42and sing, mate, lay eggs and die.
0:06:42 > 0:06:44Oh! What have we got here?
0:06:46 > 0:06:48We have a cicada.
0:06:48 > 0:06:49There you see it.
0:06:49 > 0:06:50It just fell onto my hand.
0:06:50 > 0:06:52That is an eight-year-old
0:06:52 > 0:06:56cicada nymph, seeing light that it wasn't expecting to see,
0:06:56 > 0:07:00and it digs with rather enlarged forelegs,
0:07:00 > 0:07:03which it's using right now to crawl on my hand.
0:07:05 > 0:07:09Finally, in their 13th year, they're ready to crawl up into the light.
0:07:11 > 0:07:15The mission - to find a mate and breed.
0:07:15 > 0:07:19But to do this, it needs an important last-minute addition -
0:07:19 > 0:07:21wings.
0:07:24 > 0:07:27But cicadas of the opposite sex weren't the only things
0:07:27 > 0:07:29getting their attention.
0:07:29 > 0:07:30BUZZING
0:07:30 > 0:07:33Remember the power-tool users getting mobbed by cicadas?
0:07:33 > 0:07:35What on earth could be the attraction?
0:07:38 > 0:07:40Argh! There's one on me!
0:07:40 > 0:07:43STRIMMER BUZZES
0:07:43 > 0:07:44SCREAM
0:07:44 > 0:07:47Well, the answer might be linked to the reason that they
0:07:47 > 0:07:50invaded the town in the first place.
0:07:50 > 0:07:53Males gather in trees in large numbers -
0:07:53 > 0:07:54we call them chorusing centres.
0:07:54 > 0:07:57It's almost like a periodical cicada singles bar.
0:07:57 > 0:08:01Here, they all try to outsing each other, hoping to win
0:08:01 > 0:08:03the affections of the females.
0:08:05 > 0:08:08But vibrating at much the same frequency as the males'
0:08:08 > 0:08:11deafening love song is your average power tool.
0:08:11 > 0:08:12BUZZING
0:08:12 > 0:08:15It's this that explains the fatal attraction.
0:08:35 > 0:08:39And for a lot of people, the affection goes both ways.
0:08:39 > 0:08:42The residents of Tennessee and all the other places
0:08:42 > 0:08:45they visit have taken cicadas to their hearts,
0:08:45 > 0:08:47celebrating their arrival.
0:08:48 > 0:08:52# The cicadas are invading our state of Tennessee
0:08:52 > 0:08:54# Hatching and chillaxing on everything they see... #
0:08:54 > 0:08:56# The cicadas
0:08:56 > 0:08:59# Why can't you leave us all alone?
0:08:59 > 0:09:02# Vacate to Vegas
0:09:02 > 0:09:05# And say farewell to this time zone
0:09:05 > 0:09:07# Oh, cicadas
0:09:07 > 0:09:09# Why don't you... #
0:09:09 > 0:09:12But, actually, it's not just 13-year cicadas.
0:09:12 > 0:09:16In other parts of the United States, there's another type of cicada
0:09:16 > 0:09:18which emerges every 17 years.
0:09:18 > 0:09:22And, amazingly, that's another prime number, so clearly the same
0:09:22 > 0:09:26survival strategy is working for this species, too.
0:09:26 > 0:09:29Now, whether you love or loathe cicadas, there is
0:09:29 > 0:09:32one date you should put in your diary.
0:09:32 > 0:09:34Every 221 years,
0:09:34 > 0:09:38all of these animals will emerge at the same time.
0:09:38 > 0:09:40There's just one bit of bad news -
0:09:40 > 0:09:44I'm afraid that the next time this is going to happen in Tennessee...
0:09:44 > 0:09:46is in 2076.
0:09:48 > 0:09:51But if Tennessee thought it was struggling to cope
0:09:51 > 0:09:55with its plagues of insects, that's nothing compared to what
0:09:55 > 0:09:59one town have to put up with from another amorous animal.
0:10:00 > 0:10:01Estes Park, Colorado.
0:10:05 > 0:10:09Nestled amongst the stunning scenery of the Rocky Mountain National Park.
0:10:12 > 0:10:16A peaceful wilderness retreat where nature lovers and wildlife
0:10:16 > 0:10:21can live cheek by jowl in harmonious equilibrium.
0:10:22 > 0:10:26Until the autumn, when everything changes.
0:10:26 > 0:10:28ELK BELLOWS
0:10:28 > 0:10:31This is going to get hairy.
0:10:31 > 0:10:32Uh-oh! No! No!
0:10:35 > 0:10:41The elk in Estes Park suddenly flip, attacking anything that moves
0:10:41 > 0:10:45and becoming a danger to the local residents and themselves.
0:10:46 > 0:10:47It's going to get him.
0:10:50 > 0:10:51Watch, watch, watch.
0:10:51 > 0:10:53CRASH!
0:10:56 > 0:10:59Back up, people! Back up!
0:11:07 > 0:11:12Wildlife consultant Chris Rowe knows all about the elk of Estes.
0:11:12 > 0:11:16In the town you essentially have two different populations living there.
0:11:16 > 0:11:20You've got the population of people and you've got the population of elk.
0:11:20 > 0:11:24For most of the year it's a pretty peaceful coexistence.
0:11:24 > 0:11:27There's only a couple of times during the year where all of a sudden
0:11:27 > 0:11:28we have conflict.
0:11:28 > 0:11:31PEOPLE SHOUT OUT
0:11:31 > 0:11:32So what's going on?
0:11:32 > 0:11:36What could suddenly snap this harmonious coexistence?
0:11:37 > 0:11:39ELK BELLOW
0:11:39 > 0:11:43Well, just like the red deer we have in Britain, elk have one
0:11:43 > 0:11:46period each year when they get a bit more hot and bothered.
0:11:49 > 0:11:53During the rut the males' bodies are pumped with testosterone.
0:11:53 > 0:11:56They spend every bit of energy defending their patch
0:11:56 > 0:11:59and attracting a harem of females.
0:12:00 > 0:12:03As we move into the month of September,
0:12:03 > 0:12:07that testosterone level ramps up and their aggression and their
0:12:07 > 0:12:12intensity level on protecting those cows REALLY, really ramps up.
0:12:12 > 0:12:15They're not afraid to lock antlers and get physical.
0:12:17 > 0:12:21Given the fact that Estes sits right smack-dab in the middle
0:12:21 > 0:12:25of some of the most perfect habitat, all this occurs right in town,
0:12:25 > 0:12:28in and around the houses, in and around the vehicles,
0:12:28 > 0:12:30right in the middle of the street a lot of times.
0:12:33 > 0:12:36The males are so driven that they don't
0:12:36 > 0:12:39differentiate between threats to their dominance.
0:12:39 > 0:12:41Anything that moves is fair game.
0:12:45 > 0:12:49One of the newspaper people got a picture of a young bull attacking
0:12:49 > 0:12:55Samson, who's a big bronze statue that's about 12ft tall at least.
0:12:55 > 0:13:00With these human-habituated elk right around people in Estes,
0:13:00 > 0:13:02there's not really a usual day.
0:13:02 > 0:13:06I've taken a bicycle off of an elk, garbage-can lids,
0:13:06 > 0:13:08every kind of fencing material you can imagine.
0:13:10 > 0:13:12So, for two months a year,
0:13:12 > 0:13:16the normally peaceful Estes Park fills with chaos and disruption.
0:13:18 > 0:13:20Enormous, rampant deer are one thing,
0:13:20 > 0:13:22but when it comes to disruption,
0:13:22 > 0:13:28sometimes it's the little things that pack the biggest punch.
0:13:28 > 0:13:31Our trail of extraordinary animal invasions now leads us
0:13:31 > 0:13:34to Christmas Island in the Indian Ocean.
0:13:34 > 0:13:39The island looks like the perfect tropical paradise.
0:13:39 > 0:13:44# How'd you like to spend Christmas
0:13:44 > 0:13:48# On Christmas Island? #
0:13:48 > 0:13:51These are a species called Christmas Island crabs
0:13:51 > 0:13:54and they're on their annual migration from their home
0:13:54 > 0:13:56in the rainforest to the water's edge.
0:13:59 > 0:14:02They may be land crabs but they still need to lay
0:14:02 > 0:14:04their eggs in the sea.
0:14:04 > 0:14:06THUNDER CLAPS
0:14:07 > 0:14:11So, once a year, the arrival of the monsoon rains prompts
0:14:11 > 0:14:14the crabs to emerge from all over the forest.
0:14:16 > 0:14:19Crab expert Dr Simon Webster has been
0:14:19 > 0:14:22studying this perfectly timed march to the water's edge.
0:14:24 > 0:14:27They're tiny animals, they're only 20cm across,
0:14:27 > 0:14:30and they can travel 300 metres an hour.
0:14:30 > 0:14:34They may travel anywhere between 9-15km, which is
0:14:34 > 0:14:35an enormous distance for a crab.
0:14:35 > 0:14:38It's the equivalent of a marathon distance.
0:14:39 > 0:14:45They must migrate, mate and spawn within one lunar cycle,
0:14:45 > 0:14:48so within 28 days they must complete everything.
0:14:50 > 0:14:52As they emerge from the rainforest,
0:14:52 > 0:14:54they instinctively know which way to go.
0:14:57 > 0:15:01It's the same well-trodden path that their ancestors have been
0:15:01 > 0:15:03taking for generations.
0:15:08 > 0:15:11It's a route that takes them straight through the village
0:15:11 > 0:15:16and headlong into the everyday lives of the long-suffering humans here.
0:15:18 > 0:15:21Roads are carpeted with red
0:15:21 > 0:15:25and millions upon millions of those crabs come out of the rainforest,
0:15:25 > 0:15:29cross roads, go through people's houses down to the sea.
0:15:29 > 0:15:32It is one of the most spectacular animal migrations on Earth.
0:15:32 > 0:15:34These crabs are very good climbers.
0:15:34 > 0:15:38They can climb up the corner of a room quite easily.
0:15:38 > 0:15:40CAT MEOWS
0:15:40 > 0:15:44And they will go through any doorway, wardrobe...
0:15:44 > 0:15:48They will end up in drawers, in sinks, anywhere.
0:15:50 > 0:15:53Having run the gauntlet of all of the human obstacles,
0:15:53 > 0:15:56the crabs arrive at the beach exhausted.
0:15:57 > 0:16:00But there's only time for a quick dip to refresh their parched
0:16:00 > 0:16:04bodies before their thoughts turn quickly to mating
0:16:04 > 0:16:06and releasing their eggs into the sea.
0:16:09 > 0:16:12Once they're set adrift, the crab larvae are completely
0:16:12 > 0:16:14dependent on the movements of the tides.
0:16:16 > 0:16:18And it's a dangerous world.
0:16:19 > 0:16:23Most years these babies end up as fish food, or get swept out and
0:16:23 > 0:16:29lost in deep waters, but once, maybe twice a decade, they get lucky.
0:16:29 > 0:16:33The tide brings vast numbers of tiny crabs back to the shore to
0:16:33 > 0:16:35begin their march into the forest.
0:16:39 > 0:16:41The small crabs, when they emerge, are just a few
0:16:41 > 0:16:47millimetres across - about half the size of a small fingernail.
0:16:47 > 0:16:51They're almost transparent, you can see the organs within them.
0:16:51 > 0:16:53They are very, very delicate.
0:16:53 > 0:16:57They have the same sort of texture as a pea.
0:16:57 > 0:17:00So they're very easy to crush.
0:17:00 > 0:17:04The islanders take great care not to kill any animals at all.
0:17:04 > 0:17:07There are underpasses on the roads, roads are closed,
0:17:07 > 0:17:10there are even a couple of crab bridges.
0:17:10 > 0:17:15It's hard to imagine how something so fragile can survive the journey.
0:17:17 > 0:17:21But having completed this amazing migration back to the shore,
0:17:21 > 0:17:24what happens next is actually a bit of a mystery.
0:17:24 > 0:17:27You see, just a month after the first tiny crabs
0:17:27 > 0:17:31arrive on the beach, they all disappear back into the rainforest,
0:17:31 > 0:17:35millions and millions of them, all going their own separate ways
0:17:35 > 0:17:37and living in isolation.
0:17:38 > 0:17:42What all these stories show is when it comes to reproduction,
0:17:42 > 0:17:45nature is a force to be reckoned with.
0:17:45 > 0:17:48Whether it's a plague of insects looking for love...
0:17:49 > 0:17:53..a mob of amorous elk scaring off the competition,
0:17:53 > 0:17:57or an invasion of crabs caused by a race to mate,
0:17:57 > 0:18:01when we get in the way of nature's need to breed,
0:18:01 > 0:18:04it can stop us in our tracks.
0:18:07 > 0:18:08In this next section,
0:18:08 > 0:18:12we move from the devastating power of biological onslaughts...
0:18:14 > 0:18:16..to atmospheric ones
0:18:16 > 0:18:18and to some of the most spectacular meteorological
0:18:18 > 0:18:20mysteries on the planet...
0:18:22 > 0:18:23..from apocalyptic clouds...
0:18:23 > 0:18:26That is one crazy-looking storm.
0:18:28 > 0:18:30..to lightning that's lost its storm.
0:18:34 > 0:18:37And for that story, we travel to Iceland.
0:18:39 > 0:18:41April, 2010.
0:18:41 > 0:18:45A volcano that had been dormant for 200 years suddenly erupted.
0:18:49 > 0:18:52This is as close as we dare go to this huge plume.
0:18:54 > 0:18:58As lava oozed out down the mountain, huge plumes of ash
0:18:58 > 0:19:02were sent skywards, reaching heights of over 10km.
0:19:03 > 0:19:06It's when the ash cloud started spreading out across
0:19:06 > 0:19:10Northern Europe that the eruption really hit the headlines.
0:19:11 > 0:19:14UK airspace is closed for the first time.
0:19:14 > 0:19:16All flights have been grounded amid safety fears
0:19:16 > 0:19:19as a cloud of volcanic ash drifts over Britain.
0:19:20 > 0:19:23And with all eyes trained on that ash cloud,
0:19:23 > 0:19:27people started to notice freak flashes of light.
0:19:27 > 0:19:29Whoa! Look at the lightning up there.
0:19:33 > 0:19:35There wasn't a storm cloud in sight,
0:19:35 > 0:19:39but bolts of lightning were coming in thick and fast.
0:19:43 > 0:19:47So why on earth was a volcano alive with lightning?
0:19:51 > 0:19:54Well, it turns out this strange spectacle isn't as rare as
0:19:54 > 0:19:55you might think.
0:19:56 > 0:19:59First spotted way back in 79 AD,
0:19:59 > 0:20:03it's been making the occasional mystifying appearance ever since.
0:20:05 > 0:20:07But to work out what causes it,
0:20:07 > 0:20:10first we need to get to grips with lightning.
0:20:10 > 0:20:11Oh!
0:20:11 > 0:20:18THUNDER CRASHES AND LIGHTNING STRIKES
0:20:18 > 0:20:21Not easy when even Graham Anderson,
0:20:21 > 0:20:23one of the top brains at the Met Office,
0:20:23 > 0:20:25admits it's a tricky subject.
0:20:25 > 0:20:27The way that lightning is generated in normal thunderstorms
0:20:27 > 0:20:30isn't completely understood.
0:20:30 > 0:20:33Lightning from volcanic eruptions is even rarer
0:20:33 > 0:20:37and even more treacherous if you want to get in and try and study it.
0:20:37 > 0:20:41Most lightning is created within shower clouds and thunderclouds.
0:20:41 > 0:20:44Those clouds are created when the atmosphere is said to be unstable.
0:20:46 > 0:20:48In these stormy conditions,
0:20:48 > 0:20:51moisture in the air is drawn high up into the clouds.
0:20:51 > 0:20:54Here, it reaches temperatures so cold
0:20:54 > 0:20:57that the water droplets turn to ice.
0:20:57 > 0:21:00And this is where the physics gets weird,
0:21:00 > 0:21:04because to get lightning, which has a temperature hotter than
0:21:04 > 0:21:09the surface of the sun, you actually need large quantities of ice.
0:21:10 > 0:21:14Those ice particles are bouncing and rubbing off each other and over time,
0:21:14 > 0:21:18this leads to a generation of charge that spreads out within the cloud.
0:21:18 > 0:21:20When the charge within the cloud becomes big enough,
0:21:20 > 0:21:22it can lead to a spark.
0:21:23 > 0:21:25And that is what you see as lightning,
0:21:25 > 0:21:28all of that charge rushing in a very narrow channel.
0:21:31 > 0:21:33The lightning within a volcanic ash plume
0:21:33 > 0:21:37is generated from moisture emitted from the volcano,
0:21:37 > 0:21:42rising up into the atmosphere and condensing into water droplets,
0:21:42 > 0:21:46that then carry upwards and freeze, creating ice particles.
0:21:46 > 0:21:48You need a particularly vigorous eruption,
0:21:48 > 0:21:52one that's going to really throw out a lot of heat and energy
0:21:52 > 0:21:54and pump a lot of moisture into the upper atmosphere,
0:21:54 > 0:21:56several kilometres into the air,
0:21:56 > 0:22:00so that it reaches those cold levels of the atmosphere.
0:22:00 > 0:22:02Not all volcanoes will have enough energy
0:22:02 > 0:22:04to get water high enough to freeze,
0:22:04 > 0:22:09which is what makes volcanic lightning so unpredictable.
0:22:09 > 0:22:11But as long as you have ice,
0:22:11 > 0:22:15you have your key ingredient for lightning.
0:22:15 > 0:22:18That process of generating lightning in the same way
0:22:18 > 0:22:22as a thunderstorm can work within a volcanic ash plume.
0:22:22 > 0:22:26Regions of charge within the plume will lead to a spark,
0:22:26 > 0:22:29which is the lightning strike that you can see.
0:22:30 > 0:22:32- RADIO:- This is catastrophic.
0:22:32 > 0:22:34Wow, look at the lightning there.
0:22:38 > 0:22:40Dramatic stuff!
0:22:40 > 0:22:43But did you know that what we perceive as a single
0:22:43 > 0:22:48bolt of lightning could be composed of up to as many as 25
0:22:48 > 0:22:50super-fast subflashes
0:22:50 > 0:22:54and they are so quick that we still see it as a single bolt?
0:22:55 > 0:22:59And they're not only fast, they're also incredibly intense
0:22:59 > 0:23:01and incredibly bright,
0:23:01 > 0:23:05so much so that they burn an image onto our eyes
0:23:05 > 0:23:07that lasts for several seconds
0:23:07 > 0:23:11despite the fact that their combined duration is less
0:23:11 > 0:23:14than 100 millionth of one second.
0:23:16 > 0:23:19But weather doesn't always have to be loud and flashy
0:23:19 > 0:23:22to have us stopped in our tracks.
0:23:22 > 0:23:26Sometimes, even a silky sky presents us
0:23:26 > 0:23:31with events that are more science fiction than science.
0:23:31 > 0:23:34In Burketown, Australia, every September,
0:23:34 > 0:23:37residents wake up to these incredible scenes.
0:23:39 > 0:23:46This amazing cloud formation here in Burketown. Wow!
0:23:46 > 0:23:50Row after row of long, tube-like clouds,
0:23:50 > 0:23:52stretching from horizon to horizon.
0:23:54 > 0:23:58The phenomenon has been dubbed the Morning Glory by the locals.
0:24:00 > 0:24:04And every year, as spring arrives, so do the clouds.
0:24:08 > 0:24:11So, what brings this Morning Glory to Burketown?
0:24:13 > 0:24:17Gavin Pretor-Pinney, a dedicated cloud spotter,
0:24:17 > 0:24:20has spent a lifetime staring skywards.
0:24:20 > 0:24:25The clouds are expressions on the face of the atmosphere
0:24:25 > 0:24:31and they can be read, like the expressions on the face of a person.
0:24:31 > 0:24:34They reveal the moods of the atmosphere.
0:24:35 > 0:24:39When it arrives, this cloud looks very dramatic.
0:24:39 > 0:24:44The sky is clear, you see this tube rolling along towards you
0:24:44 > 0:24:49and as it passes over, momentarily, the sky becomes overcast,
0:24:49 > 0:24:54and then as it moves on, and you're left in its wake,
0:24:54 > 0:24:55the sky clears again.
0:24:55 > 0:25:00With that movement, you get the rushing winds as it approaches,
0:25:00 > 0:25:03and then once it's over you, the wind momentarily drops
0:25:03 > 0:25:05and as it passes on, the wind picks up again.
0:25:05 > 0:25:08So it's quite an experience
0:25:08 > 0:25:12when one of these Morning Glory clouds passes over.
0:25:12 > 0:25:15OK, if clouds are trying to tell us something about our skies,
0:25:15 > 0:25:18what on earth is the Morning Glory saying to us?
0:25:18 > 0:25:22The peninsula gets heated up by the sun during the day.
0:25:22 > 0:25:24The sea breezes come in, both sides collide
0:25:24 > 0:25:28and set off this wave which travels through the night,
0:25:28 > 0:25:33arriving at Burketown, and within that wave of air,
0:25:33 > 0:25:35a roll of cloud can form.
0:25:38 > 0:25:42And although no other place puts on quite such a spectacular
0:25:42 > 0:25:47show as Burketown, you do get the odd show-stopping single roll cloud
0:25:47 > 0:25:49appearing in other coastal areas.
0:25:49 > 0:25:53Oh, what is it? It's right above us.
0:25:53 > 0:25:58And these aren't the only clouds that have had us mystified.
0:25:58 > 0:26:00Across the globe, people have rushed out
0:26:00 > 0:26:03to record their own seemingly inexplicable skies.
0:26:05 > 0:26:10It's a very strange-looking cloud formation.
0:26:10 > 0:26:12But when it comes to causing alarm,
0:26:12 > 0:26:16few clouds can compete with a cumulonimbus.
0:26:16 > 0:26:20It looks a little bit like an atom bomb cloud, a mushroom cloud.
0:26:21 > 0:26:24It can reach 10, 12 miles up into the sky.
0:26:25 > 0:26:29The cumulonimbus is known as the King of Clouds.
0:26:29 > 0:26:32This is because of its size
0:26:32 > 0:26:37and because of the sort of weather it produces.
0:26:37 > 0:26:40This is the extreme end of our weather.
0:26:42 > 0:26:47We're so used to seeing these different cloud forms above us,
0:26:47 > 0:26:52they're so omnipresent, clouds, and yet the chaotic movements
0:26:52 > 0:26:56of the atmosphere make them really rather difficult
0:26:56 > 0:26:58sometimes to understand.
0:27:01 > 0:27:05As a child, I also had a fascination with those atomic bomb clouds,
0:27:05 > 0:27:08although, I must confess, in a rather dark way.
0:27:08 > 0:27:13But what I didn't realise then was that clouds are heavy, very heavy.
0:27:13 > 0:27:16Take the average fluffy cumulus cloud.
0:27:16 > 0:27:19Using the volume, the air density and the concentration of water
0:27:19 > 0:27:25droplets, we can calculate that it might weigh a million tonnes.
0:27:25 > 0:27:29That's the same as 200,000 African bull elephants,
0:27:29 > 0:27:35or 6,200 blue whales, all just hovering above our heads.
0:27:37 > 0:27:40These weird weather events show us that the natural world
0:27:40 > 0:27:44still has the power to surprise and keep us guessing,
0:27:44 > 0:27:48whether it's bolts of light fired down through the ash,
0:27:48 > 0:27:52or clouds that make us feel like we're under siege from above.
0:27:57 > 0:27:59What all of these stories seem to tell us
0:27:59 > 0:28:04is that sometimes you can't ignore the full force of nature.
0:28:04 > 0:28:07So, whether we're just trying to live alongside it,
0:28:07 > 0:28:12or perhaps even contain it, it's bound to throw up a few surprises,
0:28:12 > 0:28:17curious and baffling events that are sure to have us sitting up
0:28:17 > 0:28:18and staring in amazement.
0:28:20 > 0:28:23Next time on Nature's Weirdest Events:
0:28:23 > 0:28:25There's the mystery of oozing sea slime.
0:28:28 > 0:28:30Bizarre body snatchers.
0:28:32 > 0:28:34And a butterfly blizzard.
0:28:34 > 0:28:37Do you see that, guys? Wow!