Dr Chris and Dr Xand return to Store Glacier in Greenland with a team of top experts and explorers to find out more about glaciers and icebergs.
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BOTH: We are Dr Chris and Dr Xand van Tulleken.
-And we're tracking down the most awesome...
BOTH: And epic things in the universe!
Come with us and discover unbelievable things...
that will blow your mind!
Blow Your Mind will be bringing you loads of top experts
and scientists to help you find out more about some amazing stuff
from the Arctic to elephants, spaceships to sharks,
and this week, it's all about ice. Yes, frozen water.
So, hold on to your brains.
Cos here's what's coming up!
We'll find out exactly what makes a glacier move,
find the plughole deep inside a blue lake,
and watch some super speed-bergs on the move.
So, Chris, you've kept me waiting all day to find out more
about what you and the scientists
got up to on the Store Glacier in Greenland.
You're not going to keep me waiting any longer, are you?
Xand, would I do that to you?
Yes, you probably would, actually.
It was absolutely incredible to see the new iceberg forming,
and you said the glacier you were on
was the size of 4,000 football pitches
and yet it's actually moving
the length of two double-decker buses every day.
So what I want to know is, how? How does it move?
It's so huge, you'd think it would be difficult to move at all.
Well, it is moving and we showed how the experts discovered
that it is moving very fast.
There are different theories about how it moves, so check this out.
Today's team of intrepid explorers and scientists are...
Chris Packham, wildlife and nature expert.
Dr Helen Czerski, physicist and oceanographer.
Andy Torbet, extreme explorer and glacial diver.
Doug Allan, polar cameraman and glacial diver.
Jason Box and Michelle Koppes, glaciologists and ice experts.
The team headed to the centre of the glacier
to carry out experiments to prove Helen's theory
about how the glacier moves.
Something is helping it along.
The icebergs form mostly in the summer,
so the glacier is flowing fastest in the summer.
And we think there are some clues to why that happens right up ahead.
This is what is known as a blue lake.
It's a lake that's formed 15km into the glacier
and it's a sensational, beautiful area of water
more than a kilometre wide.
There were half a dozen of these blue lakes on Store Glacier
and they appeared in the spring when some of the ice melts
and the water begins to form pools which become blue lakes.
There is a theory that eventually the water from the blue lake
drains to the bottom of the glacier,
causing it to slide along the bedrock.
So what we're really trying to do is try to figure out,
where does this water go
and is it contributing to more calving
at the terminus of the glacier?
So what's happening from here all the way to the end.
So what Michelle was saying was that the water in this lake
might drain to the front of the glacier,
causing calving events or icebergs to break off.
The team wanted to find out how much water was in the lake
before it drained.
The danger of doing an experiment at a blue lake
is that no-one knew when it might crack open and empty.
Ice expert Jason Box has been studying this blue lake
and his results show it should have drained already.
So this lake's now two days past the average time when it would drain.
It could go at any moment.
The team set up a time-lapse camera
to see what happened on the surface of the lake
and a depth sensor to record how much water melts into it daily.
The depth sensor had to be attached to something heavy,
as it needed to be positioned ten metres down, deep in the lake.
And expert glacial diver, Andy Torbet,
had to dive down with it to put it in place.
I've never dived anywhere like this.
And certainly nowhere where, at any point during the dive,
the water can all just drain under your feet.
I think we can kit up and get in fairly quickly.
Do the job, put in the sensors where necessary and we'll get out
and everything will be fine.
Famous last words.
Um, why is he laughing?
He's about to go into a blue lake
that at any time could empty like a giant bathtub
with him getting flushed down the plughole!
I know. It's bonkers.
But that's the kind of guy you need on an expedition like this.
Someone fearless, like me.
Actually, he is really incredibly safety conscious
and he's made sure everything is being done as safely as possible.
I'm glad to hear it.
Now, how are these blue lakes
supposed to help the glacier move towards the sea?
Well, this is how it works.
Now, imagine these ice cubes are a glacier
weighing billions and billions of tonnes.
Not like that!
Now, they're stuck on the bedrock, but if I pour water on it
so it flows under the glacier...
-Like the water draining from the blue lake?
Watch what happens.
Oh, there we go. It's moving.
And now they slip down the dish and move easily into the sea.
What an amazing demonstration. It was just like being there!
Believe me, it wasn't.
Diving into a blue lake is really dangerous
because the water could drain at any time.
If that happened when Andy and Doug were in there,
they would have been sucked right down with it.
Three, two, one... Jump.
You should never, ever dive into any icy water.
Only experts with experienced safety teams
should ever attempt anything like this.
It's absolutely beautiful down here. All these shades of...
I'm going to...
..try and place this...sensor here.
When the ice melts, the water level in the lake rises
and this device will tell the team exactly by how much.
To push further out...
..into the middle.
Let's have a bit of an explore
and see if you can find where this plughole is, eh?
Despite the dangers,
Andy couldn't help himself from exploring to find the plughole.
Chris, that does look really amazing, but really,
this thing could go at any time and he's swimming merrily further down.
-Is he mad?
-Far from it, Xand.
He's an explorer, like me, and his instinct is to find things out.
Remember, there's a full safety team above him
and, of course, cameraman Doug is down there too.
Wow, I mean, what Doug is doing is really impressive.
He's swimming around too and he's having to operate a massive camera.
The thing is, I just can't get the sound
of a massive toilet flushing out of my head.
I'd hate to see these guys getting washed away.
-Imagine how worrying it was at the time.
There's a big...big cave here going straight down.
-Andy's found the lake's giant plughole...
-Let's go have a look.
..and decided to go down it.
It's pretty dark in here.
It's definitely getting narrower.
This was incredibly dangerous as he could have got stuck.
It's getting too tight.
It's getting way too tight.
I'm still...nowhere near the bottom.
40 minutes on the dive now. 41, now.
It's cold and they'll be using air quickly,
so they'll be out very soon, whatever they're doing.
Andy couldn't get further into the plughole and, thankfully,
decided to come out.
But the extreme cold started to cause a much more urgent problem.
HE BREATHES HEAVILY I need to surface.
I think this air hose is freezing up.
Ice was blocking Andy's air supply, making it harder for him to breathe.
It was time to get him out.
In this sort of environment,
you can only do so much about trying to fix your kit under water.
There comes a point where you just need to sack it and go home.
In one piece.
Absolutely. But what a successful dive.
Not only did Andy position the sensor deep in the glacier,
he also located the entrance to the plughole.
So, with all the equipment set up,
the team decided to head back to base camp for a few days.
That is mind-blowing.
I can't believe that something, or somewhere actually,
can be so, so beautiful and so scary at the same time.
I mean, at any point, that lake could have drained
and sucked the divers through its massive plughole,
never to be seen again.
You're right. It's terrifyingly beautiful.
But the question is, did the sensor do its job?
And do they get the results for their water depth test?
Do you want to find out?
Of course I want to find out! That's why I'm here.
-And that's why we're watching.
-All right. Well, watch, then.
The team didn't know what they'd find
when they headed back a few days later.
The entire lake could have drained and disappeared,
taking all their equipment with it.
The lake is quite definitely still there. It hasn't drained.
And it... The lake's got bigger so it looks as though it's been rising.
-It's filled up.
-Helen was right.
The lake had risen so much
that the time-lapse camera they left behind
was almost underwater.
This meant that Andy had to get back in the lake,
just to get to the equipment.
And Helen was really worried about him.
I just want him out of the water as quickly as possible.
I'm finding, like...
Finding it a bit stressful watching him.
I know he's good, and I know he's a good swimmer,
and he knows what he's doing in the water, but...
..this water is not a human habitat.
Cup of tea, I think.
Andy's bravery paid off
and the footage from the time-lapse camera was amazing.
I love the way that you can see the little bits blown by the wind.
Because they're speeded up,
they're just zooming across the field of view.
Yeah, we call those speed-bergs.
See that one? Nee-ow...
But it's the results from the depth sensor
that they'd left deep in the lake
that gave them an accurate measurement
of how much the water level has risen.
It looks like it filled on... You can see on this axis, it's...
Let's call that, like, 18 to 25.
-Yeah. That's impressive.
-That's a lot of water.
The results show that in one part of the lake,
the water had risen by seven metres, which is loads.
About as high as a three-storey building.
The scientists calculated that this lake
held over five million cubic metres of water,
which is a mind-blowing amount.
To give you an idea,
that's roughly the same as 2,000 Olympic swimming pools.
The team had come to the blue lake
to find out if it held enough water to move a glacier.
These results showed that the combined amount of water
from all the blue lakes on Store
would definitely be enough to move it towards the sea,
where it creates icebergs.
That was amazing stuff. So now, we know how an iceberg is made.
Gravity is pulling the glacier down towards the sea anyway,
but the lakes on the glacier's surface
are draining to the bottom of the glacier,
which helps it slide along faster.
And when it gets to the sea, chunks break off to form icebergs.
Science made simple.
Simple? Are you kidding?
That expedition and those experiments took for ever to plan.
The amazing results took a lot of blood, sweat and tears
and the team faced a lot of danger in very difficult conditions.
-Anyway, that is our journey over for today, Xand.
-I hate this moment.
It's all so exciting. I want to find out more, more, more about icebergs.
Well, there is plenty more, more, more to see.
So join us next, next, next time
when we will bring you much, much, much
more brilliant stuff that will...
BOTH: Blow, blow, blow your mind.
Doctors Chris and Xand van Tulleken return to Store Glacier in Greenland with a team of top experts and explorers to find out more about glaciers and icebergs. In this episode they find out exactly what makes a glacier slide towards the sea. Diver Andy Torbet dives to the bottom of a blue lake in search of a giant plug hole that could drain the lake at any time and they see amazing time-lapse pictures of the lake which reveal the existence of speedbergs.