SERENE MUSIC NZ ` the largest land mass above sea level of a vast continent that broke away from Gondwanaland. 23 million years after the landscape emerged from the ocean depths, it's still as diverse as it is unique. Remote corners of this world have seldom been seen. Isolated and rugged, unique plants and creatures have evolved that are found nowhere else on earth. KEA CHIRRUPS Since the arrival of human life, this wilderness and many species have been under threat, some lost forever. But today almost a third of this dynamic country is being protected. 14 national parks have been established to preserve this diverse landscape and the multitude of life that live here. Gus Roxburgh is an environmental specialist and adventure guide who's heading out to explore the country's wilderness and discover the often unseen backcountry world of these national parks. 125 years after the first national park was created, he wants to capture a sense of what these ever-evolving conservation parks have become through the people who work, play and preserve the wilderness that is our national parks. And I think you'll find it's quite possibly the best backyard in the world. INTRIGUING MUSIC In the heart of the Southern Alps of the South Island stands a dynamic alpine paradise. A vast mountainous range dominated by NZ's tallest peaks and largest glaciers. The lure of reaching the pinnacles of this world draws men and women from around the planet. Mountaineering legends like Sir Edmund Hillary cut their climbing teeth on the treacherous faces and ridges that abound. Aoraki Mt Cook was formally declared a national park in 1953. This 700km2 estate contains 140 peaks taller than 2000m and more than 70 of the country's largest glaciers. All life is dwarfed by the sheer scale of the landscape. There is virtually no flat land in the entire park, and a third of it is permanently covered in ice and snow. INTRIGUING MUSIC GLIDER HUMS To get a really good look at Aoraki Mt Cook, the place to do it is up here in the air, and I couldn't have picked a better guy than the man in the hot seat up there. Gavin Wills is a trained geologist, climber and pioneering heli-ski guide in this park. These days, he prefers to explore its wonders from the air. Gavin, what's going on? These mountains look incredibly rugged compared to others around the country. Yeah, the mountains here are really steep, and it's because it's one of the youngest mountain ranges in the world. There's been very rapid uplift here in the last 6 million years. There's been very rapid uplift here in the last 6 million years. Whoo! These alps are one of the most rapidly rising mountain ranges in the world. FOREBODING MUSIC The tallest section is being pushed up at around 10mm a year ` about the same speed as your fingernails grow. At that rate, this section should be over 20km high by now ` three times taller than the Himalayas. But these mountains, which form a divide between the West and East Coasts, are also being worn down by the elements just as fast as they're growing. Temperature shifts from freezing to thawing, along with high rain, create rapid rates of weathering and erosion, creating one of the steepest and most unstable landscapes in NZ. So unpredictable that, in 1991, a huge section of the peak collapsed. FOREBODING MUSIC It sent 14 million m3 of rock careering down the mountain, lowering its height by 10m. FOREBODING MUSIC Whoo! SERENE MUSIC It's definitely a unique experience soaring over the top of our tallest mountain. And this perspective shows off its unusual shape. The top isn't a single peak. It's actually elongated and narrow like a knife blade and aptly called the Summit Ridge. Technically, Aoraki Mt Cook has three summits ` the High, Middle and Low Peaks, spread along the 1.5km length of the Summit Ridge, also known as NZ's highest mile. So, we're right on the main divide here, Gavin? That's right. Between the west and the east. SERENE MUSIC From up here, you can clearly see the dramatic effect the Southern Alps have on the weather. Out to the west, there's a sea of cloud as the latest storm that's crossed the Tasman slams into the rocky wall of the main divide. Most of the water those clouds were carrying is now falling as heavy rain on the West Coast, while over here, on the other side of the Alps, it's a classic blue-sky day. You know, I guess it's that westerly that makes this place so good for gliding too? Yeah, the west wind that comes across the mountains sets up giant atmospheric lee waves on the eastern side of the mountains, just like water going over a weir or over rocks in a river. And, uh, these waves enable glider pilots to go to 30,000ft, 40,000ft and to make very long flights. Very pure, isn't it? Just using that terrain and the` and the weather. Yep. It's the sport of kings, really. SERENE MUSIC BOTH CHUCKLE Whoo! (CHUCKLES) CHUCKLES: Oh my God. Just amazing. GLIDER WHOOSHES ENIGMATIC MUSIC The genesis of this mighty terrain is steeped in legend. For Maori, the Southern Alps are the edge of a mighty waka or canoe. Four sons of Raki, the Sky Father, descended to Earth, exploring the oceans above the ancient submerged continent, Zealandia. The eldest, Aoraki, was preparing the incantation that would return the canoe to the heavens when it struck a hidden reef and became stranded. The four brothers climbed into the tilted western edge of the waka and waited for a rescue that never came. The canoe turned to stone, becoming the South Island. Its petrified crew became the four highest mountains in the Southern Alps, with Chief Aoraki becoming the tallest of all. To this day, the Alps are known to Maori as Ka Tiritiri o te Moana ` The Frothing Waters of the Ocean. MEN PANT The challenge of climbing into these restless alps and conquering its peaks draws adventure seekers from around the world. First time coming here in '88, you know, I got down here on a bus and I fell in love with it. An-And` And the reason: it has everything here. From the top-notch skiing, steep ice, alpine ice, water ice to, uh, vertical rock. Some of the best rock climbing. This all trains me up for the Himalayas; for the greater mountain ranges. Marty Schmidt was born in California and has summited many of the highest and most dangerous peaks in the world. Check it out. Check it out. Isn't this gorgeous? Now, we're pretty safe here because you can see it's` it's solid cubes of ice. That is stunning, isn't it? That is stunning, isn't it? It is stunning. This is the blue ice. Spectacular. BOTH PANT Since moving here in the '80s, Marty has become a Kiwi citizen. Fallen in love with not only the country but one mountain in particular. There she is ` Aoraki Mt Cook. There she is ` Aoraki Mt Cook. Beautiful, mate. Marty has summited Aoraki 25 times, but it's never a climb to be taken lightly. FOREBODING MUSIC This national park has claimed the lives of over 230 people over the past 120 years. From the mountain base, the climb to the summit involves negotiating glaciers, rock faces and a 20-hour leg to the summit that sees climbers battling countless vertical ice faces. If you're ever to consider conquering this mountain, ice climbing is the number-one skill. All right. Steep water-ice climbing is all about front-pointing and learning how to swing the tools. Get those hooks in. Feel it. Feel it. It's really a feeling. Yeah, it's a real thock, isn't it? Yeah, it's a real thock, isn't it? It's a thock. I-It's` It's a beautiful` You know it's good. After a while, when you get experience, you know what's not good, and that's crucial. And then you're 20% in your arms, 80% in your legs. And, remember, you can work off those wrists. You can work off the bones and not the muscles of your arms, OK? Good placement. Beautiful. Sometimes you have to clear the bad ice. Remember ` you got to clear the bad ice to get to good ice. < That's it. You're doing it. I'm right behind you. (PANTS) So get that one. Clear the ice. solid. Keep your feet apart. So you're trying to form a V with your` with your legs > and a V with your` with your arms, so it turns it into an X. Yo-Your` Your placement with your both hands and your both feet turns into X. So, Marty, back in the day, the guides didn't have all this gear, did they? They were cutting steps? Exactly. So they basically would have to take these big axes and literally cut steps. Put a foot down, cut a little hip placement before standing up on their feet, balance perfect, and then chop another step for their left foot. and then chop another step for their left foot. That's how they climbed these peaks. Hobnail boots; cutting steps the whole way. Hobnail boots; cutting steps the whole way. Awesome. Exactly. Phenomenal. Phenomenal. When crampons developed in Europe, revolutionised everything. Yeah. Aoraki Mt Cook was first conquered by three young locals ` Tom Fyfe, George Graham and John Clarke. They reached the top of the mountain's High Peak via the North Ridge on Christmas Day 1894. But it would take another 50 years before a team of climbers tackled the treacherous South Ridge. A young Kiwi climber named Edmund Hillary and three others ascended Mt Cook up this route in 1948 ` a climb that served as perfect training for Hillary's challenge on Mt Everest five years later. In recognition of this incredible feat, the South Ridge of Aoraki Mt Cook was officially renamed The Hillary Ridge. She's a bit steep around here, mate. She's a bit steep around here, mate. She's vertical. Here we go. MARTY: Watch out for ice. You're right there on that, uh, bulge. So get your high steps up and around the bulge and stand up. There you go. That's a good one. Good. Trust your feet. 80% in your legs. Here we go. Heading on up. Get that... Get that breath going again. Yep. Not easy. This is vertical ice now. (GASPS) (GASPS) It's OK. This is a really good test right now. Trust it. Trust it. OK. So try and get... Yeah, it's OK. I hear you. There you go. Two more placements and we're gonna be on top. I'll be right here, watching your heels. Don't lift those heels. Here we go. Take your time. Right there. Right there. Beat that. Right there. Beat that. There you go. Amazing. Harder than it looks. Harder than it looks. It is. That's it. Awesome, Gus! Your first big ice! Awesome, Gus! Your first big ice! (CHUCKLES) Not the prettiest, but, uh, we got there. Not the prettiest, but, uh, we got there. We got there, mate. > But this is a mountain that is ever evolving. Lives will continue to be lost by those brave enough to negotiate the massive shelves of ice that hang from sheer cliffs as they seek to conquer its summit. MAJESTIC MUSIC 23 mountain peaks higher than 3000m tall exist in NZ. Aoraki Mt Cook National Park is home to 22. For climbers serious about mountaineering in NZ, this is where they come. The king of the peaks ` the park's ultimate challenge and namesake ` is mighty Aoraki Mt Cook. Well, sometimes you're just sitting up here, watching it, and your eyes just keep getting drawn to it. And yo-you, sort of, stop and listen to the quiet, and it... it sounds like the mountain's breathing. Yeah, just sort of` it's like it's alive. Elke Braun-Elwert has a deep family connection with this area and a love of this mountain since she was a young girl. Well, Elke, you were, I understand, the youngest person to climb Aoraki back in the day? Yes, I was 14 ` uh, very nearly 15 ` and it had been something I wanted to climb for a while. I guess you could say climbing is in my blood. Elke's father, Gottlieb Braun-Elwert, was a nuclear physicist who emigrated from Germany in the late 1970s and made these mountains the new family home. Elke and her sister grew up skiing and climbing almost as soon as they could walk. It was almost inevitable she'd grow up to be a mountain guide. Were you scared on that at 14? Going up there? Were you scared on that at 14? Going up there? Um, the only time I... guess I really felt fear or felt scared was at the very top. Back then, you couldn't stand on the summit. It was not long after the top had fallen off. So I just remember being on all four points. So hands and feet. You have to look down where you're putting your feet, of course. Yeah, sort of looking straight down between my legs, straight down the east face. Ooh! (CHUCKLES) Th-That was` I was, like, 'Yep, yep. This` This is enough. Let's go down now.' (CHUCKLES) There's a long tradition of female climbers who have conquered the mountain. The most legendary is Sydney-born Freda Du Faur, who in 1910 became the first woman to summit Aoraki. MAJESTIC MUSIC Three years later, this remarkable mountaineer was part of the expedition which made the first grand traverse of all three peaks along the lethal and unstable mile of the Summit Ridge. Still considered one of the most dangerous mountaineering feats in NZ, and Freda Du Faur did it in hobnail boots and a skirt. HELICOPTER WHIRS Today, a climb to the peaks can be made via a stopover at a high-altitude hut. This hut on the Bull Ridge, directly below Aoraki's towering Caroline Face, was established by Elke's father, Gottlieb, 28 years ago. It lives on as a legacy after he passed away guiding former Prime Minister Helen Clark on a climbing trip in 2008. Caroline Hut is the only private mountain hut in the national park and is used by hiking groups guided by Alpine Recreation, Elke's family business. Well, the good news is I've got a room tonight with probably the most spectacular view you could ever imagine. But the bad news is I've got to dig it out first. How deep are we here? How deep are we here? Oh, a couple of metres to go to the door. So we've got a bit of work to do? So we've got a bit of work to do? Yeah, we do. Elke had a desk job as a computer modeller, but in 2009, couldn't resist the lure of the mountain and returned to work full-time for the family guiding business. Oh, I think that will just about do it, Gus. Yeah. Moment of truth, huh? See if the keas have moved in over the winter. Moment of truth, huh? See if the keas have moved in over the winter. Oh, no, shouldn't be a problem. A bit stuck. Here we go. Welcome to Caroline Hut. (SIGHS) Welcome to Caroline Hut. (SIGHS) Oh, beautiful. Look at that. Luxury! Yeah. > Today is a big day as Elke, friends and family prepare Caroline Hut for the beginning of a new summer season. After the hut is dug out, a whole summer's worth of food and supplies must be brought in and stored with the efficiency of a military operation. As well as choppering in supplies, some of last season's leftovers must be choppered out. Oh! Oh! They get flown to the sewerage ponds. That all those Moro bars, is it? That all those Moro bars, is it? That's right. That all those Moro bars, is it? That's right. From last summer? Gonna get these out and, uh, once we've got them out, the helicopter's coming back in. < The pooh gets a flight. Hopefully, it doesn't fall off because it would leave a nasty smear in this nice, pristine white wilderness that we've got here. Here we go. > Here we go. > BARREL SCRAPES AGAINST ICE Until recently, the huts around the mountain simply dumped their sewage down the nearest crevasse. But now strict new regulations mean disposing of human waste is taken very seriously here. REFLECTIVE MUSIC And, with the hut stocked for the season, there's only one thing left for it ` to sit back and savour the fact that I am almost 2km above sea level, with some of the most stunning alpine views in the country. And, of course, a warm, cosy hut and a few bottles of plonk. Remember that? That dunny that hung out, and you looked down there and`? We were going to go there, but it was too windy. So we just hung the shovel out at the door, and it just got... (MAKES WHOOSHING SOUND) SERENE MUSIC MUSIC CONTINUES The first rays of dawn strike the most dramatic and dangerous face of Aoraki first. Now there are many climbing routes up the mountain, but the climb above the hut is so unstable and dangerous, it wasn't conquered until 1970. Its name is the Caroline Face. FOREBODING MUSIC Even looking at it sends a shiver down your spine ` two vertical kilometres of ice, snow and rock. The shelves of ice hanging off the sheer cliff are actually small glaciers, and as the sun hits the face, it warms up the ice and makes it highly unstable. I can't even imagine how you would go about climbing this. After four climbers died attempting it in the 1960s, the Caroline Face was finally conquered in 1970 by two legendary long-haired climbers ` John Glasgow and Peter Gough. They described it as 'a triumph for the hippies'. And you've got to admire those hippies. The Caroline Face is the most dangerous climb I've ever seen. SNOW RUMBLES SNOW RUMBLES Holy shit! It might look small from here, but I reckon that avalanche is at least 100m across. And of all the dangers mountaineers face, it's avalanches that kill the most in NZ. SNOW CRUNCHES MAJESTIC MUSIC Aoraki Mt Cook National Park is a Mecca for mountain climbers from around the world. This is a high-altitude wilderness that can take a life in a second. To safely explore these peaks, climbers need to be able to read the mountain and know how to survive the dangers of the alpine zone. SNOW CRUNCHES The biggest threat to climbers is an avalanche. SNOW CRUNCHES So, Dave, what is it that makes this Aoraki Mt Cook area so prone to avalanches? Uh, it's pretty much the... the massive amount of snowfall that we have in this zone. It's` It's probably th-the highest snowfall zone in the country. I'm tagging along on a training exercise with a couple of avalanche experts ` Dave McKinley, a mountain guide and search-and-rescue legend, and Simba, his 7-year-old avalanche dog. The amount of snow coming out of the sky, the wind, the wind direction. The Southern Alps are prone to avalanches because of their steepness and the changeable weather. They can strike in an instant, and if you get completely buried, you don't have much of a survival window. Even though it's almost T-shirt weather up here, that doesn't mean there's no danger. There's been plenty of avalanches lately, and we're looking for a fresh one as a location for Simba's training. < Looks like a pretty big slide. < Looks like a pretty big slide. Yeah, this looks like a really good one to play with the dog. Could this bury a person? This could bury your car. There's an avalanche risk all year around in Aoraki Mt Cook National Park. Most of the snow falls in winter, but the most dangerous time of year is spring, when late snowfalls are exposed to warmer temperatures. Whole mountainsides can soon become highly unstable. It's a good, long slide. Even if you were climbing and walking out down this valley, uh, you'd be in danger from these things coming down up here. Pretty much. You'd think where we're standing, you're in the flat, you're in the safe. Th-That would be the logic, but obviously, you're not safe at all. Not at all. That's a lot of snow. I wouldn't want to be underneath that. < So, what's the plan here today, Dave? Oh, we're setting up a training exercise here. We've got the dog hidden away. She's not cheating. OK. OK. So we've got a dog. We've got a hole. We need some dog bait. I guess that would be me, wouldn't it? Yeah, I had a feeling you might have something up your sleeve. You all right there, mate? You all right there, mate? Yep. If this was an actual avalanche, I'd be crushed from the sheer weight of the snow and struggling for air. Every minute would be a matter of life and death. While I get buried alive, Simba is on standby, waiting for Dave to signal it is time to start searching. Oh. Hey. > Wait, Simba. Wait. Show! She's a 7-year-old black Lab-spaniel cross who was found as a puppy by Dave's wife. Dave took her on as a rescue dog, and three years of intensive training, plus a few years in the field,... Wait. Show! ...has turned her into one of only 10 fully operational avalanche dogs in the country. I've actually had three good friends that have died in avalanches, and being down here, I mean, it's` it's just horrible thinking about that, and it makes you realise how quickly a beautiful day in the mountains can just go from being fantastic to a nightmare. Like all dogs, Simba's nose is packed with scent receptors, and her sense of smell is around 1000 times more powerful than a human. This super sense can make the difference between life and death for someone under an avalanche. DOG BARKS DOG BARKS Oh, that's Simba. Here's rescue. Where is he? Show! Where is he? Show! DOG BARKS A well-trained avalanche dog is equivalent to 20 people on foot and can search an avalanche debris field like this eight times faster. Whoo-hoo! Whoo-hoo! < There she is. Go, Simba. Whoo-hoo! < There she is. Go, Simba. Where is he? Where is he? The trick is to use the right tone of voice and make it fun. Whoo-hoo! Whoo-hee! Whoo-hoo! Whoo-hee! Hey, Simba. Oh, am I glad to see you. Not the place you want to spend too long, is it? By too long, I'm talking 15, 18 minutes. That's about all you got in there. Nice work. Thanks, mate. Nice work. Thanks, mate. Come on out. Nice work. Thanks, mate. Come on out. (GRUNTS, SIGHS) Eh? Good girl, eh? Oh,... (SIGHS) she was quick, huh? Oh,... (SIGHS) she was quick, huh? Yeah. Oh,... (SIGHS) she was quick, huh? Yeah. Jeez, mate, that was amazing. FOREBODING MUSIC Avalanches can be the most spectacular danger to climbers, but the rapidly changing weather can be deadly for anyone venturing into this park. Conditions can transform from pristine to horrendous in a couple of hours. Distinctive clouds called hogsbacks forming over the Alps mean conditions are about to get nasty. Still enjoying the last rays of the sun here, but look up to the left there. The cloud is just pouring over the main divide, and that means one thing ` the dreaded nor'west storm is coming in. URGENT MUSIC Winds of over 230km/h have been recorded at the airfield, and over half a metre of rain has fallen in a single day at Mt Cook Village. Higher up, above the freezing level, this moisture falls as snow, and that half metre of rain in the village could mean as much as 5m of snow on the high peaks. This just shows you how quickly the weather can change around here, and if it's blowing this hard down in the village, you don't want to be near the high peaks. This is the sort of fast-moving nor'west storm that skiers and climbers dread getting caught out in. The high winds and blizzards caught many climbers unaware in the days before modern weather forecasts. Over 230 people have lost their lives in the park. This place has a great history of mountaineering. In fact, climbers were coming here long before it was even a park, and just like the climbers' graveyards in European alpine towns like Chamonix and Zermatt, this monument serves as a memorial for those climbers who never made it back from the hills. And climbers often add to these memorials with a personal gesture of respect for the fallen and the mountains. REFLECTIVE MUSIC By day, the Aoraki Mt Cook National Park landscape is stunning. By night, a whole other world emerges. The effect of the main divide blocking bad weather from the west is that the eastern side of the mountains has more clear nights than almost anywhere in the country. This means the park and the vast MacKenzie Basin are some of the best places in the world to go stargazing. Over 4000km2 of atmosphere above Mt John Observatory near Tekapo was designated a unique International Dark Sky Reserve ` the world's largest conservation park in the sky. The point about featuring a dark-sky park is to get the people who have not seen a-a dark sky to come out and have a look at one, and they then find that` that it is quite a spectacular thing. REFLECTIVE MUSIC Alan Gilmore is one of those lucky people who gets paid to do his hobby. He's been interested in the night sky since he was a small boy, and now he is head astronomer at Mt John and a driving force behind the sky park. Alan, this dark-sky reserve is a different kind of conservation, isn't it? Conserving dark spaces? There's been, I think, um, an awakening of interest fairly simultaneously in several parts of the world because people have realised that we are losing the night sky. The biggest threat to the night sky is light pollution from towns and their street lights. Several communities in the area, including Mt Cook Village, now have laws in place to protect the sky park. Street lights must be shielded and filtered, and all unnecessary lights must be turned off by 11pm. Locals are more than happy about the restrictions, as international visitors now travel here especially to gaze at the stars ` a new kind of travel called astro-tourism. SERENE MUSIC Most of them have just simply never seen a night sky. They've` They've lived in cities where you're lucky to see half a dozen stars in the sky, and they step off` out of the bus an-and, there, suddenly, they've got a sky with thousands of stars, the Milky Way. They are, quite literally, blown away. This phenomenal night-sky reserve is the grandest in the world, suspended above the tallest peaks in the country, in a national park also dominated by our biggest glaciers. 40% of this park is covered by these frozen rivers of ice. The largest glacier in the park, and in all of NZ, is the Tasman. It flows from high in the main divide, past the eastern edge of Aoraki Mt Cook, and 29km to the plains. 4km wide and over 600m thick, it's a massive conveyor belt of ancient snow and ice, slowly flowing down from the mountains. The Tasman Glacier covers an area of 100km2 ` large and flat enough for a very unique form of transport. PLANE ENGINE HUMS PLANE ENGINE DRONES In the 1950s, World War II fighter pilot and pioneer tourism developer Harry Wigley decided he wanted to land on top of Tasman Glacier. The problem was no ski-plane in the world could take off from grass and land on snow. So Wigley invented a new kind of landing gear using a Formica table and Kiwi ingenuity. He invented a system that could raise and lower wooden skis, activated by leaning out the window and cranking a handle while coming in to land. On the 22nd of September 1955, Wigley took off from the grass airstrip of Mt Cook Village and successfully landed on the Tasman Glacier. One of his first passengers was a young climber named Edmund Hillary. Sir Harry Wigley's pioneering ski-planes now allow tens of thousands of people a year to explore the Tasman Glacier. The Tasman's not only the longest glacier in the country, but at 10 K's, it's by far the longest ski run. SERENE MUSIC The Tasman Glacier may not hold that title for much longer. The frozen river of ice is undergoing dramatic changes and shrinking at an alarming rate. We tend to think of places like the Southern Alps as immortal landscapes that never change, but in Aoraki Mt Cook National Park, the opposite is true ` this alpine wonderland is, in fact, incredibly fragile and faces many threats, both natural and man-made. Glaciers have been described as the canaries in a coal mine for climate change, and almost half of this park is covered in them. Out of all the national parks in NZ, this is the one that will be most affected by a changing climate, and there is already spectacular evidence that things are changing fast. The Tasman Glacier, NZ's largest, is currently 29km long, but it's shrinking every day. Glaciers evolve through cycles, often over thousands of years. The Tasman has been retreating in size for the past two decades with no sign of expanding. This could be part of the normal glaciation cycle or an indicator that human activity is fast-tracking the demise of these icy phenomena. This is a perfect place to get a handle on the whole Tasman Glacier. It starts all the way up around the corner there, where I was skiing, sweeps down under the Minarets there, then comes all the way down here behind me. Now, when my mother first tried skiing as a young girl in the early '50s, they skied on the Ball Glacier, which is down here, beneath me. And, in those days, the Tasman Glacier was white ice all the way down to here. Since then, the glacier has retreated by several kilometres and got a hell of a lot thinner as well. It's still down there, but what's left of the ice is now covered in rocky debris from the moraine walls. But down here is the feature that's really changing quickly on the Tasman Glacier. You can just make it out behind me ` the Tasman Glacier Lake. Looking at the lake, you'd think it's been part of the landscape for a long time, but it's actually a real newcomer. What began as a sinkhole at the end of the glacier grew into a pond, which grew into a small lake, and it's been rapidly expanding ever since. REFLECTIVE MUSIC Just a few decades after it appeared, the lake is now 5km long and growing by hundreds of metres a year as it eats away at the ice of the Tasman Glacier. Mid-1970s, a sinkhole started to then expand. A couple of warm summers and the` the rest, they say, is history. Denis Callesen has lived and worked in the park for years. He's been watching the Tasman Lake expand since it was a puddle. So, Denis, this is the terminal face here. Well, it's hard to get a sense of scale cos, I mean, it's so amazing and massive around here. < But how big is the ice on that terminal face? Well, the lake at this point, is 1.2km wide. So that's nearly a kilometre wide there. OK. OK. The dark line at the water is the thermal notch. That's where the waves lap and undermine the glacier, which then causes the` the calving from above` above the water surface. Because huge chunks of ice are constantly falling off, it's too dangerous to get within 800m of the terminal face of the Tasman Glacier. Once they calve off, the icebergs get blown down the far end of the 5km lake and form one of the most surreal landscapes in NZ. ENIGMATIC MUSIC And, down this end, you can get a lot closer to the action. Check this out. So that ice is 300 years old. So, around about the time that Abel Tasman was discovering NZ, that fell in a snowstorm at the head of the Tasman Glacier, 20km away from us. That is beautiful, isn't it? The larger chunks of ice floating in the lake are just as beautiful but a lot more dangerous. The lake water is a few degrees warmer than the ice and gradually eats away at the bottom of the icebergs until they either fall to bits or spectacularly roll over. FOREBODING MUSIC Denis, this berg here looks like the biggest one. That, uh, came off on the day of the second Christchurch earthquake. Really? That calved off at the` at the front? Really? That calved off at the` at the front? It was a major calving. It was around about 50 million tons, or 50 million m2 of ice, calved in one event, over in about 30 seconds. Amazing. So what happens when you get 50 million tons of ice crashing in here? You get a tsunami. You get a tsunami. Was anyone on the lake? There was two boats from Glacier Explorers out on the lake at the time, and in the middle of the lake, about 2km from where the calving occurred, the wave was 3m high. Luckily, in the middle of the lake, the tsunami hadn't broken yet and was just a giant swell. So the boats just turned into` into the wave and rode it out very easily. But, yeah, trip of a lifetime, that one. The Tasman Glacier Lake is now one of the national park's most popular attractions. Every year, thousands of people can experience this unique and rapidly changing landscape. It's amazingly beautiful, but the fact remains this lake is destroying NZ's largest glacier at a dramatic rate and changing the national park radically. I mean, I guess the million dollar question is, is it climate change? Is it as simple as that? It's a whole range of processes. You've got increased precipitation. As the lake gets larger, the waves get larger. The thermal notches get larger quicker. So it's all feeding on each other? So it's all feeding on each other? It is. So whilst global warming might have started the process, it's now become irreversible, and it's taken on a life of its own. So the process is still speeding up, and who knows how long that's going to keep speeding up for. How big do the scientists think this lake could grow? How big do the scientists think this lake could grow? Uh, it's 5km long now. It will reach a point of equilibrium when it's about 15km long, and that will happen some time, I would expect, in the next 30 years. So that` that beautiful, long ski run is gonna get a bit shorter? It's gotten a lot shorter in the last, uh, certainly, three decades, and yeah, it will get a lot shorter quite quickly now. There's no denying the Tasman Glacier will continue to retreat during our generation, but I can't help but wonder what irreversible impact our global-changing climate will have here. And, I guess, this is a landscape that is always evolving. But this is quite simply an incredible snapshot of Aoraki Mt Cook today, and it reveals one thing ` this is one of the most dramatic and dynamic landscapes in the country. Aoraki Mt Cook National Park. Continually thrust skyward and worn down by incredible natural forces. It's an unstable, unpredictable and ever-evolving landscape. This conservation sanctuary stands tall and proud amongst its peers. Its sheer alpine scale and the heroic history of those who have challenged its heights will ensure it remains an enduring icon. Captions by John Ling. Edited by Jessica Boell. www.tvnz.co.nz/access-services Captions were made possible with funding from NZ On Air. Copyright TVNZ Access Services 2013