0:00:09 > 0:00:15For six months, Yellowstone endures an unrelenting winter.
0:00:19 > 0:00:21An ice world of hunters...
0:00:22 > 0:00:24..and hunted.
0:00:26 > 0:00:31But now footsteps on the slopes of a mountain
0:00:31 > 0:00:33herald a change in the season.
0:00:43 > 0:00:45The sun regains its strength.
0:00:50 > 0:00:52Water flows again.
0:01:01 > 0:01:05The race begins to recover winter's losses...
0:01:05 > 0:01:06to play.
0:01:08 > 0:01:10Learn.
0:01:10 > 0:01:12And breed.
0:01:18 > 0:01:22But the summer ahead will be fleeting and far from easy...
0:01:24 > 0:01:28..in this unpredictable wilderness.
0:01:58 > 0:02:01It's April.
0:02:01 > 0:02:04The land lies exhausted by winter.
0:02:06 > 0:02:09Everything is waiting for the return of the sun's warmth.
0:02:22 > 0:02:24The end of winter comes late
0:02:24 > 0:02:28to the mountainous Northwest of the United States.
0:02:28 > 0:02:32And in particular, it lingers in Yellowstone.
0:02:35 > 0:02:40The heart of Yellowstone is a high, cold plateau 8,000 feet up,
0:02:40 > 0:02:44surrounded by the spires of the Rocky mountains.
0:02:50 > 0:02:53After five months sleeping in those mountains,
0:02:53 > 0:02:55a powerful presence returns.
0:03:00 > 0:03:04This female grizzly bear has awoken early to find food
0:03:04 > 0:03:06for her two-year-old cubs.
0:03:08 > 0:03:12But she may have brought her family here too early.
0:03:17 > 0:03:19The Tetons.
0:03:19 > 0:03:23On the extreme southern edge of the Yellowstone plateau.
0:03:23 > 0:03:27It's where the spring thaw normally begins.
0:03:28 > 0:03:31But this year it's come late.
0:03:37 > 0:03:41Deep snow is still a novelty for her cubs.
0:03:41 > 0:03:43But she is much more focused.
0:03:51 > 0:03:55Led by her nose, she risks her 300 pound bulk
0:03:55 > 0:03:58on the thin ice of a bend in the Snake river.
0:04:04 > 0:04:06It doesn't look promising
0:04:06 > 0:04:10but her cubs follow with only a little hesitation.
0:04:14 > 0:04:16With paws that can knock down an elk,
0:04:16 > 0:04:19she feels delicately in the water.
0:04:25 > 0:04:29A fish frozen beneath the ice by this cold winter.
0:04:39 > 0:04:43One fish won't feed the family but she knows
0:04:43 > 0:04:45there are almost certainly more.
0:04:48 > 0:04:50The cubs must learn to find them.
0:05:28 > 0:05:31A little success for one of the cubs.
0:05:39 > 0:05:44This mother bear's experience gives her family a good chance of survival
0:05:44 > 0:05:46until spring arrives.
0:05:50 > 0:05:55They will return again and again as the thaw releases more fish.
0:06:00 > 0:06:04On the warmer plains and valleys that surround the plateau,
0:06:04 > 0:06:06grazers are on the move.
0:06:06 > 0:06:10They left the high country to avoid the worst of the winter
0:06:10 > 0:06:12and now begin the long journey
0:06:12 > 0:06:15towards the heart of Yellowstone in time for summer.
0:06:18 > 0:06:21These elk are led by experienced adults
0:06:21 > 0:06:24who have made this trip many times before.
0:06:31 > 0:06:34They are followed on their migration
0:06:34 > 0:06:39by the most ancient of American grazers - pronghorn.
0:06:41 > 0:06:45Though predators may follow, none can outpace them.
0:06:45 > 0:06:48Over distance these are the fastest animals in the world,
0:06:48 > 0:06:53taking a long migration in their stride.
0:07:04 > 0:07:08Migrating elk and pronghorn must follow the advancing thaw.
0:07:10 > 0:07:14But higher up in the valleys, one animal is well ahead of them.
0:07:16 > 0:07:19Bison are adapted for cold.
0:07:21 > 0:07:24These herds need to be in Yellowstone early
0:07:24 > 0:07:29to have time to bring up their young in the short summer ahead.
0:07:31 > 0:07:35Calves born during the journey will be tested.
0:08:01 > 0:08:04Clues to why the herds are drawn to the Yellowstone plateau
0:08:04 > 0:08:07lie in its deep and unique history.
0:08:10 > 0:08:14This plateau is the cratered bowl of a huge sleeping volcano
0:08:14 > 0:08:18and molten rock below the surface still pushes the land up
0:08:18 > 0:08:20to the cold of high altitude.
0:08:27 > 0:08:30But it has not been the only force to shape the land.
0:08:33 > 0:08:34Millennia ago,
0:08:34 > 0:08:39the volcano was covered by an ice sheet thousands of feet deep.
0:08:39 > 0:08:43The few glaciers that border Yellowstone are an echo of a time
0:08:43 > 0:08:47when ice scoured and smoothed the entire plateau.
0:08:52 > 0:08:54When these great ice sheets retreated,
0:08:54 > 0:08:57they left pulverised rocks in their wake,
0:08:57 > 0:09:00the foundation for fertile soil
0:09:00 > 0:09:04and some of the richest natural grasslands in America.
0:09:08 > 0:09:12But in May this year, in the heart of Yellowstone,
0:09:12 > 0:09:15that grass is still beneath thick snow.
0:09:24 > 0:09:28Something this ground squirrel was clearly not expecting.
0:09:33 > 0:09:35But as the sun's strength returns,
0:09:35 > 0:09:39spring bulbs start to push through the late snow.
0:09:40 > 0:09:43At last a sign that winter is losing its grip.
0:09:50 > 0:09:55Bluebirds, too delicate to survive deep winter here,
0:09:55 > 0:09:59now return to take advantage of the first hatch of stoneflies
0:09:59 > 0:10:00from a thawing river.
0:10:19 > 0:10:23As six months of snow and ice begins to melt,
0:10:23 > 0:10:26Yellowstone starts to come back to life.
0:10:37 > 0:10:41Cascading snowmelt swells the streams and rivers.
0:10:50 > 0:10:54It's a hazard that the migrating herds must cross.
0:10:58 > 0:11:01Young are barely up to the task.
0:11:30 > 0:11:35The Yellowstone River has increased its flow tenfold.
0:12:23 > 0:12:25In less than two weeks,
0:12:25 > 0:12:29the thaw has brought a remarkable change to the heart of Yellowstone.
0:12:40 > 0:12:44As the migrating herds arrive in the plateau's river valleys,
0:12:44 > 0:12:47the spring is here.
0:13:13 > 0:13:16This is why they have made the journey.
0:13:16 > 0:13:18After the famine of winter...
0:13:21 > 0:13:22..food is everywhere.
0:13:25 > 0:13:30Birds have flown in from as far away as the Arctic and subtropics,
0:13:30 > 0:13:35Canada geese join flocks of white pelicans to breed here.
0:13:52 > 0:13:55A snow-covered wasteland is transformed
0:13:55 > 0:13:58to an American Serengeti.
0:14:12 > 0:14:15But it's a landscape like no other.
0:14:15 > 0:14:18Geysers make Yellowstone famous.
0:14:33 > 0:14:38Yellowstone sits above the molten core of a volcano.
0:14:38 > 0:14:43Underground water becomes super-heated and erupts in the air.
0:14:43 > 0:14:48Strangely, geysers and hot springs can creep around the landscape.
0:14:48 > 0:14:52The curious shapes of Grotto geyser are actually trees -
0:14:52 > 0:14:57entombed and petrified by minerals dissolved in the water.
0:15:01 > 0:15:04Hot water scorches and drowns the roots of trees
0:15:04 > 0:15:06encroaching on the valleys.
0:15:09 > 0:15:14It can keep the forests in check and the rich pastures open.
0:15:14 > 0:15:19Those pastures now produce the new grass needed to make rich milk
0:15:19 > 0:15:22and feed a bison baby boom.
0:15:26 > 0:15:28The few calves born on the migration
0:15:28 > 0:15:32are now joined by hundreds of new youngsters.
0:15:36 > 0:15:38The predators have been waiting for this.
0:15:41 > 0:15:44Coyotes have a voracious reputation here, but on its own,
0:15:44 > 0:15:48this one is certainly no match for a healthy bison and her calf.
0:15:57 > 0:16:00Pronghorn give birth to twins,
0:16:00 > 0:16:04each carefully cleaned to hide their smell from predators.
0:16:15 > 0:16:18While they are with her, they are relatively safe
0:16:18 > 0:16:23and for now the coyote is content with the afterbirth.
0:16:24 > 0:16:28But the mother pronghorn must leave her calves alone while she grazes
0:16:28 > 0:16:33and with legs as wobbly as stilts, their best defence is to lie low.
0:16:44 > 0:16:46She has young of her own to worry about -
0:16:46 > 0:16:50a demanding litter of nine whose arrival has been carefully timed
0:16:50 > 0:16:53to coincide with an abundance of food.
0:17:08 > 0:17:10But they are not top dog here.
0:17:12 > 0:17:17Yellowstone's top predator, the wolf, dominated during the winter,
0:17:17 > 0:17:21but is far less visible in summer.
0:17:22 > 0:17:24They prefer to stay close to well-hidden dens
0:17:24 > 0:17:27to protect their pups from rival packs.
0:17:35 > 0:17:37This pack seem prepared to allow their young
0:17:37 > 0:17:41a brief foray to experience the world beyond their den.
0:17:42 > 0:17:48Even in Yellowstone, it is extremely rare to see wolf pups like this.
0:18:11 > 0:18:16Before long, they are summoned back into the forest by the pack.
0:18:16 > 0:18:20It will be winter before they are regularly seen again.
0:18:27 > 0:18:29As May turns to June...
0:18:29 > 0:18:33Yellowstone sees its nursery season.
0:19:08 > 0:19:12By early June, summer is finally here.
0:19:17 > 0:19:21In the flower meadows, plants turn sunlight into the sugar of nectar -
0:19:21 > 0:19:26just what Yellowstone's smallest migrating bird has been waiting for.
0:19:30 > 0:19:35The Calliope hummingbird has made the journey all the way from Mexico.
0:19:42 > 0:19:46He'll make this flower patch his own
0:19:46 > 0:19:49and he'll fight to defend it.
0:19:49 > 0:19:54He'll even take on a far larger Rufus hummingbird.
0:20:12 > 0:20:14But his high-octane lifestyle
0:20:14 > 0:20:16critically depends on the summer sun.
0:20:17 > 0:20:22And in Yellowstone that's never guaranteed.
0:20:22 > 0:20:26In the mountains surrounding the plateau,
0:20:26 > 0:20:28summer has not yet arrived.
0:20:28 > 0:20:32At this altitude, it is still bitterly cold.
0:20:35 > 0:20:39These mountains barricade Yellowstone in a ring of ice.
0:20:42 > 0:20:44And if the sun is swallowed by cloud,
0:20:44 > 0:20:47the cold can drive down from the mountains,
0:20:47 > 0:20:51bringing with it a punishing echo of winter.
0:20:57 > 0:21:00It can snow in any month in Yellowstone.
0:21:23 > 0:21:26The warm nursery meadows of a few days before
0:21:26 > 0:21:29are now buried by a June blizzard.
0:21:40 > 0:21:44A curtain of snow dulls senses.
0:21:44 > 0:21:48This mother grizzly bear must now be especially careful.
0:21:53 > 0:21:57A male grizzly will often kill cubs if he finds them.
0:22:01 > 0:22:06And though she would rather sit out the storm, she must move.
0:22:15 > 0:22:19Panicky cubs could easily be lost in a blizzard.
0:22:39 > 0:22:42As soon as she feels it is safe,
0:22:42 > 0:22:45she settles to suckle and reassure them.
0:23:03 > 0:23:07Bison can shrug off this sudden change in the weather.
0:23:10 > 0:23:13They are, after all, built to survive a Yellowstone winter.
0:23:17 > 0:23:20But this tiny hummingbird is more vulnerable.
0:23:24 > 0:23:26Flowers damaged by snow will die
0:23:26 > 0:23:30and the nectar the hummingbird needs goes with them.
0:23:33 > 0:23:36Hummingbirds must be resourceful to survive.
0:23:45 > 0:23:50Bark wells dug by a sap sucker, a type of woodpecker,
0:23:50 > 0:23:54quickly fill with sugar-rich sap as soon as the warm weather returns.
0:24:00 > 0:24:04A little pilfering provides this hummingbird with the energy it needs
0:24:04 > 0:24:07until the new flower buds open.
0:24:14 > 0:24:16Summer moves quickly,
0:24:16 > 0:24:21by late June the blizzards of a few weeks before seem a distant memory.
0:24:34 > 0:24:38At last, the summer is well enough established for this hummingbird
0:24:38 > 0:24:41to take the plunge and raise a brood.
0:25:03 > 0:25:06The living is easy.
0:25:13 > 0:25:15But it won't last long.
0:25:19 > 0:25:22At this altitude, the air is so dry that rain evaporates
0:25:22 > 0:25:25before it even hits the ground.
0:25:25 > 0:25:29The water that flows off the plateau is no longer being replaced.
0:25:33 > 0:25:38Already there is drought in forests beyond the meadows.
0:25:42 > 0:25:45Yellowstone has vast ancient lava fields.
0:25:45 > 0:25:50This porous volcanic rock holds onto very little water.
0:25:54 > 0:25:57It is dominated by lodgepole pine,
0:25:57 > 0:26:00a tree that can cope with the arid conditions.
0:26:06 > 0:26:10The forest may be parched but there is still water here
0:26:10 > 0:26:13in lakes formed by ancient glaciers.
0:26:25 > 0:26:29A visiting male otter woos a female on the lake's shore.
0:26:37 > 0:26:39But she seems a little distracted.
0:26:46 > 0:26:49Her two pups are nearby.
0:26:49 > 0:26:52They're about ten weeks old and the time is right
0:26:52 > 0:26:54to lead them from the holt.
0:27:01 > 0:27:04Males are not above stealing food from cubs,
0:27:04 > 0:27:08so she makes it very clear that he is not going to be joining them.
0:27:30 > 0:27:32This female grew up on the lake,
0:27:32 > 0:27:35so she knows where to take the cubs for a very special trip.
0:27:47 > 0:27:50Yellowstone cut-throat trout amassing in the mouth
0:27:50 > 0:27:53of a stream that feeds the lake.
0:27:53 > 0:27:55They are preparing for their annual spawning.
0:28:02 > 0:28:04But the trout must wait.
0:28:04 > 0:28:09The stream is still running fast, too turbulent to lay their eggs.
0:28:13 > 0:28:17It's a nervous time for them, and for good reason.
0:28:28 > 0:28:32This osprey has a brood to feed and will be back.
0:28:49 > 0:28:51Now the otters are here too.
0:28:54 > 0:28:58She chooses her moment to lead the pups upstream.
0:29:05 > 0:29:08Then leaves them to watch and gives them a lesson in hunting.
0:29:35 > 0:29:39A large trout like this, full of eggs, is a trophy catch.
0:29:57 > 0:30:01She chews its tail first to make sure the fish can't get away.
0:30:04 > 0:30:08While the pups are still demanding milk, the mother otter will often
0:30:08 > 0:30:12keep the whole fish for herself.
0:30:12 > 0:30:15Her pups are happy enough with caviar.
0:30:29 > 0:30:32As the flow becomes slow enough to lay eggs,
0:30:32 > 0:30:35there is a brief window of opportunity to spawn
0:30:35 > 0:30:39before the river gets too shallow to swim upstream.
0:30:45 > 0:30:48The female digs a trough with sinuous flicks of her body
0:30:48 > 0:30:53and the attending male fertilises the eggs as they are laid.
0:31:02 > 0:31:03Millions of new lives.
0:31:14 > 0:31:16It's now early July
0:31:16 > 0:31:19and what looks like more snow is actually
0:31:19 > 0:31:22a blizzard of seeds and insects.
0:31:23 > 0:31:27There is more life in the park now than at any other time of the year.
0:31:30 > 0:31:32It's a turning point in the summer.
0:31:36 > 0:31:40Through the coming month, the days will get hotter and drier.
0:31:40 > 0:31:43The plants will grow less vigorously
0:31:43 > 0:31:47and the pace of summer will slow.
0:32:18 > 0:32:20The meadows are not so welcoming now.
0:32:20 > 0:32:23The grass becomes less nourishing
0:32:23 > 0:32:25as it puts its energy into seeds and roots.
0:32:26 > 0:32:31Bison lose the last of their winter coats.
0:32:31 > 0:32:33In the heat,
0:32:33 > 0:32:35tempers fray.
0:32:40 > 0:32:44To escape soaring ground temperatures,
0:32:44 > 0:32:46cowbirds choose a bison's back
0:32:46 > 0:32:49as a cool place to feed and catch the breeze.
0:32:57 > 0:33:01Biting insects now become a draining nuisance.
0:33:07 > 0:33:12A grizzly bear escapes the heat and bugs in the cool waters of a lake.
0:33:40 > 0:33:42As the ground dries,
0:33:42 > 0:33:46bears find little food to eat out on the Yellowstone plateau.
0:33:54 > 0:33:59There is less to graze and digging roots is hard work,
0:33:59 > 0:34:03so they start to head to the cooler mountains beyond.
0:34:28 > 0:34:32In the mountains, glacier lilies that finished flowering
0:34:32 > 0:34:36a month before on the plateau are only just coming into bloom.
0:34:41 > 0:34:47Up here, where spring has only just arrived, bears can find food again.
0:35:01 > 0:35:04As the thaw reaches up into the mountains,
0:35:04 > 0:35:08a part of Yellowstone that few ever see is briefly revealed.
0:35:25 > 0:35:31From its first day above the snow, this pika is obsessed by food.
0:35:34 > 0:35:37It's in a frantic race to restock its winter larder
0:35:37 > 0:35:40before the snow closes in again.
0:35:46 > 0:35:49They're a part of a community of small mammals
0:35:49 > 0:35:52which live life on the edge up here.
0:36:00 > 0:36:03Carefully chosen plants are harvested
0:36:03 > 0:36:09and dried in haystacks before being stored below ground.
0:36:11 > 0:36:14This larder must be over 50 times the pika's bodyweight
0:36:14 > 0:36:16to get it through winter.
0:36:22 > 0:36:24The summer is so short up here
0:36:24 > 0:36:26that few animals can permanently live any higher.
0:36:30 > 0:36:34But higher is exactly where the bears are heading,
0:36:34 > 0:36:39above the tree line towards the barren rocks of the peaks beyond.
0:36:42 > 0:36:46It seems an unlikely journey for an animal led by its stomach.
0:36:51 > 0:36:54Why they do this will only become apparent
0:36:54 > 0:36:57as the summer draws to its close.
0:37:03 > 0:37:08Meanwhile, 2,000 feet below them on the Yellowstone plateau,
0:37:08 > 0:37:11the grasslands are facing drought.
0:37:26 > 0:37:30Bison calves are more independent of their mothers.
0:37:34 > 0:37:39The adults' focus is now set on a ruthless competition to mate.
0:37:41 > 0:37:46A male bids to enter a herd with females in season.
0:37:49 > 0:37:53He uses dust to accentuate all his size and power.
0:38:01 > 0:38:06Another male already established in the herd answers the display.
0:38:10 > 0:38:11And waits.
0:38:19 > 0:38:24The newcomer responds by scent marking and moving even closer.
0:38:39 > 0:38:41This challenge cannot be tolerated.
0:39:20 > 0:39:22The resident male has won.
0:39:22 > 0:39:28Having seen off his rival, next summer's calves will likely be his.
0:39:33 > 0:39:36Victory in the dust of high summer.
0:39:38 > 0:39:44But now there is a larger challenge to the whole of Yellowstone.
0:39:48 > 0:39:51These clouds don't signal rain.
0:39:54 > 0:39:57They are vast smoke plumes.
0:39:57 > 0:40:00Yellowstone is burning.
0:40:03 > 0:40:06Throughout the summer, the dry lodgepole pines
0:40:06 > 0:40:11have become like a tinder box and lightning has struck the match.
0:40:40 > 0:40:43The worst wild fires will burn for weeks.
0:40:52 > 0:40:57In 1988, a third of Yellowstone burnt in a single summer.
0:41:05 > 0:41:07Devastation.
0:41:15 > 0:41:21Animals that depend on these forests will starve this winter.
0:41:27 > 0:41:31But Yellowstone itself has a longer perspective.
0:41:32 > 0:41:35Ashes fertilise the soil
0:41:35 > 0:41:38and fire opens it up to sunlight.
0:41:52 > 0:41:57As the forests regenerate, new life finds opportunity.
0:42:08 > 0:42:13In August, fledgling hummingbirds gorge in fields of fireweed
0:42:13 > 0:42:16that have risen from the forest's ashes.
0:42:23 > 0:42:26For them, the summer is already nearly over.
0:42:29 > 0:42:32They must chase the sun south before winter returns.
0:42:38 > 0:42:41But just as the first of Yellowstone's new generation
0:42:41 > 0:42:46are preparing to leave, its last visitors are arriving.
0:42:50 > 0:42:53Night after night,
0:42:53 > 0:42:56army cutworm moths have been escaping the heat
0:42:56 > 0:42:58of the distant prairie.
0:42:58 > 0:43:02They have been flying in on favourable winds,
0:43:02 > 0:43:05hiding away in rock crevices in the mountains.
0:43:16 > 0:43:20This is why the grizzly bears climb to the barren peaks.
0:43:20 > 0:43:24Two miles up, they begin to search for the moths.
0:43:41 > 0:43:43It's the end of summer
0:43:43 > 0:43:47and the last snow of winter holds on only here.
0:43:47 > 0:43:52It offers a few refreshing mouthfuls for travel-weary cubs.
0:44:05 > 0:44:08Many of these bears learnt about this site from their mothers
0:44:08 > 0:44:12as a part of local bear tradition.
0:44:12 > 0:44:16The family sets to work finding moths, digging into the loose rock.
0:44:30 > 0:44:35Though each moth is very small, a bear that makes a successful strike
0:44:35 > 0:44:39can harvest up to 40,000 in a single day.
0:44:39 > 0:44:43That's 20,000 calories and vital weight gained for winter.
0:44:51 > 0:44:54Having spent all summer avoiding males,
0:44:54 > 0:44:58the mother now finds one much too close for comfort.
0:44:58 > 0:45:03Perhaps he's seeking a mate but he is unwelcome.
0:45:06 > 0:45:09Leaving her cubs, she confronts the male head on.
0:45:39 > 0:45:42As she approaches to see him off again,
0:45:42 > 0:45:44she realises she has been injured.
0:46:05 > 0:46:09A damaged jaw would be a disaster for her and her family.
0:46:11 > 0:46:14Clearly in pain,
0:46:14 > 0:46:18she leads the anxious cubs to high ground away from the male.
0:46:24 > 0:46:27She nurses to calm and reassure them.
0:46:47 > 0:46:51The injury does not seem serious but she decides to lead her family
0:46:51 > 0:46:53back down from the mountain.
0:46:56 > 0:46:59This will be the last time these cubs feed here as a family.
0:46:59 > 0:47:03By next year they will be independent,
0:47:03 > 0:47:05ready to face their world alone.
0:47:13 > 0:47:16Sun has briefly brought warmth to Yellowstone,
0:47:16 > 0:47:21long enough to fuel the raising of new generations.
0:47:38 > 0:47:43But just as summer reveals the full extent of Yellowstone's diversity,
0:47:43 > 0:47:47a curtain of winter ice is set to descend again.
0:47:51 > 0:47:54The days are getting shorter,
0:47:54 > 0:47:56the sun losing its power.
0:47:57 > 0:48:03Now there are just a few short weeks to prepare for winter.
0:48:03 > 0:48:07One final flourish of life in Yellowstone's briefest
0:48:07 > 0:48:09but most glorious season.
0:48:13 > 0:48:14Autumn.
0:48:24 > 0:48:28Bringing Yellowstone's unique natural beauty to the screen
0:48:28 > 0:48:31would have been impossible without the tireless help
0:48:31 > 0:48:35of the local experts that know it like the back of their hand.
0:48:35 > 0:48:37Each has their own story to tell.
0:48:50 > 0:48:54Dancing on the surface of Yellowstone's super volcano
0:48:54 > 0:48:58are more than two thirds of the world's geysers.
0:48:58 > 0:49:02They are what made Yellowstone famous in the first place,
0:49:02 > 0:49:05so for the Yellowstone series, they had to be filmed.
0:49:07 > 0:49:12But the problem is they can be fickle - erupting in their own time.
0:49:14 > 0:49:19Luckily, there is a group of people who spend their time
0:49:19 > 0:49:23trying to predict the unpredictable. They are the geyser gazers.
0:49:24 > 0:49:28'The radio's on, we're about nine minutes in.'
0:49:28 > 0:49:30'Rocket major, 943.'
0:49:30 > 0:49:34My name is Mary Beth Schwarz and I'm a geyser gazer.
0:49:34 > 0:49:37I've been watching geysers for about 47 years.
0:49:37 > 0:49:40It's a whole bunch of different people.
0:49:40 > 0:49:44I don't want to use the word weird but it might fit.
0:49:44 > 0:49:48I spend a lot of my time hiking out to some place that's not too crowded
0:49:48 > 0:49:51and sit down and wait for water to boil.
0:49:51 > 0:49:56I wasn't really aware of the geyser gazers till about eight years ago.
0:49:56 > 0:50:00What my brother says is I fell into bad company.
0:50:00 > 0:50:03I consider it really, really, really good company
0:50:03 > 0:50:09and I discovered there were levels of understanding of geysers
0:50:09 > 0:50:11that I had never appreciated at all.
0:50:11 > 0:50:15Each geyser has its own personality, some of them are playful,
0:50:15 > 0:50:18some of them are forceful, some of them thump,
0:50:18 > 0:50:21you get good splashing noises out of others.
0:50:21 > 0:50:24For the geyser gazers, these are much more than
0:50:24 > 0:50:27just plumes of hot water, squirting from the ground.
0:50:27 > 0:50:31Each geyser not only has its own personality but even its own name.
0:50:31 > 0:50:37I like to see Beehive, I like to see Grand, maybe a Riverside.
0:50:37 > 0:50:41Line erupts to 60, 70 feet
0:50:41 > 0:50:46and you get a roar before it erupts.
0:50:46 > 0:50:48Roooo. Roooo...
0:50:53 > 0:50:57Geyser gazing is not just an obsession with geysers.
0:50:57 > 0:50:59It does have a practical purpose.
0:50:59 > 0:51:03- Nine, two nine. - 'OK, visitor centre copies.'
0:51:03 > 0:51:08They have a network all over Yellowstone, connected by radio,
0:51:08 > 0:51:13and they send all the eruption times to the park's visitor centre.
0:51:13 > 0:51:17This way, there is a permanent record of geyser activity
0:51:17 > 0:51:19and thousands of people can also experience
0:51:19 > 0:51:21the thrill of watching geysers.
0:51:25 > 0:51:28The geyser gazers recognise that each geyser has its own
0:51:28 > 0:51:31idiosyncratic behaviour
0:51:31 > 0:51:34and that helps them predict when it will erupt.
0:51:37 > 0:51:40RADIOS BEEP
0:51:40 > 0:51:44The Castle has not erupted yet, no Castle yet.
0:51:45 > 0:51:50- 'Thank you very much. ' - We're watching it.- Intently.
0:51:50 > 0:51:52Not even teasing us right now.
0:51:52 > 0:51:57Well, that's good, though, you want it to be very quiet
0:51:57 > 0:52:00and it'll maybe do a few practice splashes and then it erupts.
0:52:08 > 0:52:09Whoo! Yahoo!
0:52:09 > 0:52:12'Castle at 0955.'
0:52:15 > 0:52:19That's correct, Castle at 0955.
0:52:19 > 0:52:22Well, you were right, Mary Beth.
0:52:22 > 0:52:24- Yes, yes.- Quiet just before.
0:52:24 > 0:52:28Supposed to be very quiet then it went. It's how it's supposed to do.
0:52:30 > 0:52:35Now let's hope it's a major. That's the next landmark here.
0:52:39 > 0:52:42But with geysers, nothing is certain.
0:52:45 > 0:52:47Oh, come on, come on.
0:52:49 > 0:52:51No, this is very bad.
0:52:53 > 0:52:56- Come on, come on. - It looks like it's finished.
0:52:56 > 0:53:00- I think it's been too long. - It's only a couple of minutes.
0:53:00 > 0:53:05Visitor centre, unless Castle can restart, it appears to be a minor.
0:53:05 > 0:53:09The visitor centre, we copy a minor.
0:53:09 > 0:53:11Very minor.
0:53:12 > 0:53:15I will post the sign as unpredictable.
0:53:20 > 0:53:25That's the way it goes. Sometimes you just can't count on geysers.
0:53:25 > 0:53:30The water that fuels the geysers has to travel from up to five miles
0:53:30 > 0:53:33beneath the surface of the earth, so it's hardly surprising
0:53:33 > 0:53:38that sometimes eruptions are late, or never make it.
0:53:38 > 0:53:42All Mary Beth can do for now is predict that this geyser
0:53:42 > 0:53:43is unpredictable.
0:53:43 > 0:53:48The Castle is unpredictable because it's just had a minor eruption
0:53:48 > 0:53:50and we have to wait for a major.
0:53:52 > 0:53:54The art of predicting geysers
0:53:54 > 0:53:57is about witnessing as many eruptions as you can
0:53:57 > 0:54:01and key to that is spending as much time around geysers as possible.
0:54:04 > 0:54:07Dick Powell is a geyser gazer and retired geologist
0:54:07 > 0:54:11who has even found a whole way of life that allows him to spend
0:54:11 > 0:54:14all of his time near the geysers he loves.
0:54:14 > 0:54:17I'm one of three people trained to do thermal cleaning
0:54:17 > 0:54:19in Yellowstone National Park.
0:54:19 > 0:54:23Most of the stuff that we pick up is with what's called a grabber.
0:54:23 > 0:54:27We also have some more specialised equipment,
0:54:27 > 0:54:32like extension poles with slotted ladles or spoons on them.
0:54:44 > 0:54:47The ground around the geysers is not only very fragile
0:54:47 > 0:54:51but also very dangerous. That's why in most cases he can't step on it.
0:54:53 > 0:54:58Usually we pick up some hats at various features on windy days
0:54:58 > 0:55:01because people don't understand how windy it can be out here,
0:55:01 > 0:55:04and they don't have them secured.
0:55:04 > 0:55:08Obviously this one didn't use his chin strap to save his hat.
0:55:09 > 0:55:13Occasionally he does go off the edge to the boiling pools
0:55:13 > 0:55:16because rocks get thrown in.
0:55:16 > 0:55:19And that's a problem because rocks can block up the throats
0:55:19 > 0:55:21of the geysers and hot springs.
0:55:21 > 0:55:26There's some incidences known where rocks may have been
0:55:26 > 0:55:28a reason a geyser quit erupting.
0:55:32 > 0:55:34As water in underground chambers is heated to
0:55:34 > 0:55:37over 500 degrees Fahrenheit, it explodes
0:55:37 > 0:55:41in a violent eruption of water and steam.
0:55:41 > 0:55:43As soon as the chamber is emptied, it is recharged
0:55:43 > 0:55:45and the process begins again.
0:55:47 > 0:55:50These cycles can be once an hour, or once a decade,
0:55:50 > 0:55:54so you need to put in a lot of time to work them out.
0:55:57 > 0:56:01I have been out here sometimes for six hours or seven hours.
0:56:01 > 0:56:04Early in the summer, when I started watching Sawmill,
0:56:04 > 0:56:09I was out for ten hours, in the sun but it was doing interesting things
0:56:09 > 0:56:12and I hadn't studied it before so,
0:56:12 > 0:56:17I just stayed out and kept drinking water and enjoying it.
0:56:17 > 0:56:21There's Turban, I'll write that down.
0:56:21 > 0:56:25When Grand goes off there are actually three geysers that erupt -
0:56:25 > 0:56:27Grand, Turban and Vent.
0:56:27 > 0:56:34Sometimes you get just one huge series of bursts out of Grand
0:56:34 > 0:56:39but just a couple of days ago, we got four bursts and people were
0:56:39 > 0:56:43standing up, jumping up and down, cheering, it was so exciting.
0:56:50 > 0:56:54It's like watching fireworks all day long every day, it's just that it's
0:56:54 > 0:56:59hot water going up in the air and sparkling in the sunlight.
0:56:59 > 0:57:03It's like handfuls of diamonds, just flying through the sky.
0:57:11 > 0:57:15After a long wait, this is really worthwhile.
0:57:16 > 0:57:19What's going off in the background is Grand geyser.
0:57:19 > 0:57:23It's predictable with a four-hour window,
0:57:23 > 0:57:28that is two hours either side of the calculated time.
0:57:29 > 0:57:32Before I even knew about geyser gazers,
0:57:32 > 0:57:35I'd go out and four hours to wait for this, no, I'm not gonna do that.
0:57:35 > 0:57:41Then I fell in with the geyser gazers and people would say,
0:57:41 > 0:57:46"You really want to stay because it's a really spectacular display."
0:57:46 > 0:57:49And I discovered, hey yeah, they're right.
0:57:49 > 0:57:55It's nice for humans to be able to go to a more natural area than
0:57:55 > 0:57:59where they live and work, and get to see something extraordinary,
0:57:59 > 0:58:03something very different from their everyday life.
0:58:05 > 0:58:11I would like to see Grand erupt an infinite number of times.
0:58:11 > 0:58:16When I am gone, I will be back.
0:58:16 > 0:58:21If there is a beyond, I'll be back to watch the geysers.
0:58:38 > 0:58:41Subtitles by Red Bee Media Ltd
0:58:41 > 0:58:44E-mail subtitling@bbc.co.uk