How to survive an avalanche

How do avalanches happen and how do you face one? We speak to a survivor...
10 December 2019
Presented by Chris Smith, Phil Sansom
Production by Amalia Thomas, Phil Sansom.


An avalanche.


This week we’re exploring a terrifying force of nature: avalanches. Why do they happen? How do you avoid them? And if you encounter one, how could you survive it? We speak to Lawrence Jones, who 20 years ago was caught in an avalanche - and lived to tell the tale. Plus, in the news: measles cases triple, we ask whether physicists have really discovered a new fundamental force, and the scientifically-proven solution to hangovers (sort of) - we’ve tested the recipe...

In this episode

A stomach displaying a measles rash.

01:01 - Measles cases triple in a year

Plus, Samoa declares a curfew and a mass vaccination campaign...

Measles cases triple in a year
Freya Jephcott, University of Cambridge

Cases of measles virus have tripled since last year, new figures from the Word Health Organisation reveal. In 2018, numbers were already significantly higher, with nearly 150,000 people dying of the infection and an estimated 10 million infected. The United States has reported its highest number of cases in 25 years, and four countries in Europe - including the UK - lost their measles elimination status following long-term outbreaks of the disease. This week, in the grip of a massive outbreak, the Pacific island of Samoa declared a curfew and a mass vaccination campaign to try to stop it. So why is this happening, what will be the consequences, and what can be done to stop it? Chris Smith asked Freya Jephcott, who studies disease outbreaks at the University of Cambridge…

Freya - Well, I guess the short answer is that vaccination coverage has dropped, but then when we try and understand why vaccination coverage is dropping, we have to look at, sort of, individual countries and take it region by region.

Chris - Why is measles such a scourge?

Freya - Measles is incredibly infectious. I think people somewhat underestimate quite how infectious it is. So if say none of us were vaccinated, and someone with measles was walking around, that one person would be expected to infect maybe 16 to 18 other people.

Chris - How would that compare with say flu? Because that's infectious too.

Freya - Well, I think a really good point of comparison is maybe Ebola because that's also in the news at the moment. Ebola is typically, you could expect a case to maybe infect one or two other people.

Chris - So yes, it is the king of infectious viruses then?

Freya - Very much so.

Chris - And so the point is that once it gets a toe hold, it really goes to town quickly. It spreads like wildfire.

Freya - It's incredible. I think that Samoa makes a really good case for this. So just since October they had 4,500 cases and we're talking about a country with only 200,000 people.

Chris - And it's not trivial once you catch measles, is it? Because the death toll, I mentioned there in the introduction 150,000 people that we know about in 2017/18. Each year we're seeing these big numbers. That's probably the tip of the iceberg though, isn't it?

Freya - Absolutely. I think this is one of the things underlying low vaccination rates, especially in North America and Europe, is that we've largely forgotten quite how dangerous it can be.

Chris - And when people talk about vaccines, how does this actually work to curtail the spread of these things and why are we getting low uptake of vaccines?

Freya - So the measles vaccine does two things for us. It protects us on an individual level, so we can't get sick, but when we have 95% of the population protected, or ideally even more, then it can't spread through populations either. Which is great because not everybody can receive the measles vaccination, like babies under one for instance. So this protects them too.

Chris - And this is the concept of herd immunity, isn't it? The idea that you've got protection from being part of that herd where the vast majority of them cannot propagate measles?

Freya - Yeah absolutely, and I think in this day and age with sort of international travel and such, you've got to understand that the community we're trying to protect is much larger than just our local village town or country.

Chris - So Samoa have had a sort of lockdown, they've had a curfew, why will that work? Or will it indeed work? Because at the same time they've also started a mass vaccination campaign, because their vaccine rates are only about 30%. So now they've tripled them to about 90%, so they're close to the magic number that you're highlighting, but not quite there.

Freya - Unfortunately, Samoa was in the situation where they had a reactive measles vaccination, which is where, sort of, the cat's already out of the bag and you're doing everything you can to sort of limit the damage. So essentially they told everybody to stay home, to try and stop people who are potentially un-vaccinated mixing with infected people. Before that they had actually locked down the schools and stopped children going to any public places.

Chris - What's the lesson that we can learn from this and what might be therefore the next steps in trying to deal with the fact that we're just seeing this enormous escalation in numbers around the world?

Freya - Obviously the answer is getting vaccination rates above 95% across the world, but I think for North America, Europe, the Pacific islands, we've got to look at public health education and science communication. I think they're really the answers to getting rates back up.

Chris - Because you've helped to investigate and control Ebola outbreaks as well in your career, haven't you? And there must be some parallels here? Because one of the things that emerged when we had the huge outbreak in West Africa of Ebola in the last five years, five years ago, 2014 wasn't it? The people said that there was so much misinformation floating around that the local population didn't know the right thing to do, not to catch Ebola.

Freya - Ebola is slightly different in that it is such an unusual situation. Ebola outbreaks are really quite rare, that when they happen - and these large, quite strange responses, people in sort of spacesuits running around - it's quite a terrifying and novel experience for people. So then everything you're doing is kind of weird, intimidating and unfamiliar. I think maybe we have less of an excuse on the measles vaccination front. And again, we're aware that this is an effective, readily available way of protecting ourselves against this.

Chris - So don't take risks?

Freya - Yeah.

Cartoon schematic of an atom

06:04 - Fifth fundamental force

A Hungarian team claim to have found a new fundamental particle and force - but many are skeptical...

Fifth fundamental force
Ben Allanach, University of Cambridge

There's some news going around recently about the discovery of a supposed “fifth fundamental force” in physics. This comes from the Atomki Institute in Hungary, where a team of scientists claim to have found evidence for a new fundamental particle that they’re calling X17. They first detected this as a blip on their instruments back in 2015, and now they claim to have repeated it. If it’s true it completely disrupts the current models of physics, which don’t have much room for a brand new particle. But lots of people are skeptical, as no independent team has yet replicated the finding. To get an independent perspective, Phil Sansom went to visit physicist Ben Allanach…

Ben - The scientists are claiming to have discovered a new particle which hasn't been found before.

Phil - That seems like quite a big deal.

Ben - That would be a huge deal if it were true.

Phil - How do they claim to have discovered this?

Ben - Okay, so they are doing nuclear collisions, you know, the hard dense centres of atoms, and they're bombarding them with protons and making heavier nuclei in excited states. These nuclear excitations can lose energy by giving out particles of light. And if the energy is high enough, the particle of light will then turn into an electron-positron pair. So by analysing the angular separation, they can tell something about what's going on.

Phil - How are they actually detecting this stuff? Because you can't put on a pair of zooming glasses and go, oh, there goes an electron.

Ben - No, that's right. They've got fancy kit to measure the electron going through it. There are basically detectors arranged around the point of collision. Positrons and electrons go through the material and leave charge deposits, and so then you read out that with electronics and you can tell where it's gone and so on. If you've got the theory right, you should be able to tell how often they come out with a particularly wide angle. And they're finding that rather large angles, 120 degrees, there are far too many of them coming out and that's consistent, they say, with the production of a new particle which is decaying into the electron and positron,

Phil - What's the name of this new particle and what does it do?

Ben - Well they've called it X17, mysteriously. "X" because they don't really know what it is, and 17 because it weighs 17 million electron volts worth of energy. What does it do? We don't know.

Phil - Why are people relating it to a, quote unquote, fifth force? What's that all about?

Ben - Actually particles and forces are kind of different sides of the same coin. When you go deep into the quantum theory, you find that forces are given by the exchange of many quantum particles. Best example probably is the electromagnetic force. You're aware of magnets repelling each other, if you put the North pole to the North pole, but really what's happening is the magnets are exchanging particles. The particle, the photon, is producing the force. So many, many exchanges, many times a second. In the same way this X17 is a particle, but exchanging it a lot would produce a force.

Phil - What would that force do?

Ben - It would give you a force between electrons and nuclei. That's all we know. It could do other things as well, but seeing as it's only been observed in interactions with nuclei and with electrons and positrons, that's all we know about its supposed effects.

Phil - What do you think? Is this the real deal or is this a little bit overhyped?

Ben - I'm sceptical for three reasons. Firstly, why haven't other experiments seen this? This isn't a particularly heavy particle. It should have been observed in other collider experiments. The other thing that makes me feel a bit nervous is that the same authors, or at least a large subset of them, have made three other discoveries of supposedly new forces in the past 20 years or so, and they're all incompatible with each other. Thirdly, there's an issue with the calibration data. So I looked at the scientific paper that they wrote today and the calibration of the angular separations is not as good quality as you'd want. So it's not a killer or anything, but it just makes you a bit suspicious that maybe there's something a bit off in the calibration that's affecting their results.

Phil - It sounds like this is almost a boy who cried wolf type situation, potentially.

Ben - Well, you never know. I mean you know, at some point they could be right. That's why good science is to check these claims with a different experimental setup, and you know different number of people with a different methodology, and then you'll know for sure, hopefully.

Phil - Well if it's not a new particle, then what is it exactly?

Ben - Well, it could be some problem with the experiment. I mean, these are difficult experiments to interpret sometimes, and you need to calibrate very precisely. Tiny uncertainties and errors in the wrong direction can lead you to the wrong conclusion sometimes. So it could be something like that if they are unlucky.

Phil - And if it is a new particle and you had first shot on naming it, what would you call it?

Ben - The heaven 17.

The Earth sinking in water.

12:31 - Climate change - behind the headlines

Are we really on the road towards a carbon-neutral future, and what’s it going to take to get there?

Climate change - behind the headlines
Eric Wolff, University of Cambridge; Eliot Whittington, Cambridge Institute for Sustainability Leadership

This week the UN’s Annual Climate Change Conference - COP 25 - has been taking place in Madrid. The conference’s aim is to take the next crucial steps in implementing the global carbon-cutting proposals agreed 4 years ago in Paris. But are we really on the road towards a carbon-neutral future, and if not, what’s it going to take to get there? Chris Smith sat down with to untangle the headlines with climate experts Eric Woolf and Eliot Whittington...

Eric - My name is Eric Wolff, I'm a professor in the department of Earth Sciences in Cambridge.

Eliot - My name is Eliot Whittington. I lead the work for the Cambridge Institute for Sustainability Leadership around engagement between policy and business, which has a strong focus on climate change.

Chris - We heard a few years ago people saying, look, we're in trouble. If we carry on the way we're going, we will have irreversible climate change and everyone said, this is ghastly. We must do something about this. Governments all around the world signed up and said, yep, we're right behind this. We're going to accept these targets. We're going to make a difference. I'm not seeing much action.

Eliot - We haven't seen action that is coherent with the scale of the problem, but we have definitely seen action. Before the Paris agreement people were sort of saying, we're on track for four and a half degrees. After the Paris agreement, if the agreement is implemented fully, went down to about three and a half degrees. We are bending the curve. Practical things like the number of coal fired power stations in Europe, the US, China, are far less than people predicted were going to be. So action is taking place. What we really need to do is vastly accelerate it.

Chris - What will be the consequences if we do carry on, on the present trajectory, what do models predict?

Eric - If we carry on, on literally the present trajectory. In other words, if people don't even meet the commitments that are made in Paris, then we'll end up with a global warming of about four degrees. If they meet the Paris commitments, it's more like three degrees.

Chris - By when?

Eric - By 2100, and if people go and meet the Paris agreement, then 2 degrees, maybe 1.5 degrees. The difference between those numbers is a lot. So at four degrees, the Arctic sea ice is definitely gone. The whole of the Greenland ice sheet, which contains six metres of sea level roughly, is certainly vulnerable and part of the West Antarctic ice sheet as well. So then potentially, with that four degrees, we're talking about committing ourselves to sea level rises of 5 to 10 metres. Well, there are Island nations that have been talking a lot this week, whose average height above sea level is two metres.

Chris - If one considers the impact it'll have on the average person's lifestyle in order to achieve the kinds of reduction in emissions that we're striving for, can you put that into practical terms for me Eliot, in terms of what would I have to give up in order to do my bit?

Eliot - A net zero economy could be a much more pleasant place to live than our current economy. Better designed towns, cleaner air, better diets. There are more and more people who are thinking about their diet and they're thinking about their health. They're thinking about animal welfare, other concerns and so we are shifting. We are realising that actually our current diet is probably a bit too much sugar, a bit too much processed stuff and a bit too much meat, and it's good to reduce that. We just carry on that trend and we will be on a good track. It is not the case that we should see a net zero economy as inherently hair shirted and punitive. How we travel and how we eat are the things that will change most, but we can still travel places maybe not quite as quickly or quite as far all the time.

Chris - You optimistic, Eric?

Eric - I'm reasonably optimistic in the sense that I can now see how it can be done. I'm a little less optimistic because obviously there are some countries that just aren't engaging with the process properly at the moment.

Chris - Like?

Eric - We can't deny that the United States is saying that it's going to pull out of the UN climate agreement. That's a worry that there's a country that for at least the next few years is not going to engage with the process because we don't have a few years. We can't afford to wait 10 years and then stop the process because otherwise we won't make it.

Listen to a longer version of the interview on the In Short podcast episode "Climate change: what does net zero look like?"

A cartoon brain outweighing a cartoon heart on a balance scale.

16:24 - Think about sex, change your mind

How does the possibility of sex influence how we present ourselves to others?

Think about sex, change your mind
Helen Keyes, Anglia Ruskin University

Could the possibility of sex influence how we present ourselves to others? A paper recently published by Gurit Birnbaum and her colleagues in the Journal of Experimental Social Psychology suggests that - surprise surprise - yes we do! Anglia Ruskin University psychologist Helen Keyes, who wasn’t involved in the study, took Katie Haylor through the findings...

Helen - They were trying to find out whether we would change our own behaviour when we feel that we're around a potential sexual partner. First of all, what they looked at was whether showing people videos of people making out would make them more agreeable or give more ground in an argument with another person. So first of all, they divided participants into groups where one half would have seen videos of people making out, and the other half would have seen just control videos over a couple engaged in a conversation. And after this, heterosexual participants were paired with a stranger of the opposite sex and they were asked to role play a disagreement or an argument. People who had seen the sexual imagery or people who are sexually primed, reported giving more ground in that argument, and this was true for both men and women. Then they wanted to look at what happens when we're more subliminally primed. So this is quite interesting. Participants had to fill out quite a long dating questionnaire about themselves. Then half of these participants were subliminally shown sexual images of semi-naked men and women, and half of the participants were subliminally shown images of nature. And by subliminal, I mean these images were flashed up for less than 30 milliseconds. So participants weren't aware that this is happening.

Katie - Were they watching some... like, watching a film or something whilst these images were just flashing up?

Helen - They were doing a really innocent task of choosing between like Thai food and Italian food. Little did they know that they were seeing some saucy images. Following this, each person was shown another person's dating profile - an imaginary profile that the experimenters had manipulated. Then, the participant went to make their own dating profile, and what they found was those who had been subliminally shown sexual images, conformed much more. They brought their responses much more in line with the dating profile they'd just read. So, if they had initially been opposed to cuddling, they now, kind of, moved a little bit closer to cuddling on the cuddling scale. They conformed more if they'd been sexually primed, but not if they hadn't been sexually primed. And then finally they wanted to know about explicit untruths or lies we might tell about ourselves. So they looked at how we report how many sexual partners we've previously had. Interestingly, they asked people to either anonymously report this or report it in an online chat with a potential partner, who they thought, somebody they thought was a potential partner. And they found that for both men and women, people revised downwards the number of sexual partners they reported having if they were in the online chat compared to an anonymous forum. That's not surprising, but interestingly this was only for people who had watched sexually explicit material. So again, people who had been sexually primed had their sexual system activated, they reported downwards, both men and women, the number of partners they had. And this is just conforming again to what you would imagine the other person wants to hear.

Katie - What do you make of this?

Helen - I think it isn't surprising. I think it's largely harmless and quite a nice positive thing to think that we might accommodate other people, or we might engage in relationships with new people in a way that we think is going to establish that relationship, or encourage that bond between people. So it's actually quite a nice finding, but it also might tell us that maybe when we begin a relationship with somebody, or we are exploring that possibility with somebody, they may be presenting themselves in a way that they believe is conforming to what we would like of them, and to just bear that in mind when were are establishing that relationship.

Katie - Or indeed you might behave slightly differently to the way that you would truly feel about something?

Helen - Absolutely, and you'd hear people saying sometimes, Oh you know, you've really changed around this new person, and it's nice to have a study to say, well that's not that surprising and I'm engaging in really pro-social behavior here.

A hungover man collapsed face down on a table cradling a bottle.

20:33 - The perfect hangover cure

Scientists have tested all sorts of food in the lab to see which breaks down booze the best...

The perfect hangover cure
Alex Thom, University of Cambridge

Now that the office party season’s in full swing, here’s some crucial research results: chemists in Mumbai have been searching out the perfect hangover cure. They’ve tested all sorts of fruits, foods and vegetables in the lab to see which ones help break down the nasty by-products of booze. And while it might not actually represent what goes on inside your body, they did come out with quite an interesting concoction. Phil Sansom went to get the opinion of a - slightly hungover - scientific onlooker: theoretical chemist Alex Thom…

Alex - So they found that various fruits and vegetables actually changed the way alcohol is degraded in the body.

Phil - Are we talking about treating a hangover?

Alex - Basically? Yes. I mean it's the products when you drink alcohol and it ceases to be alcohol and it turns into some nasty things, and then eventually turns into fat.

Phil - Okay. Explain how they investigated this.

Alex - Okay. So they didn't actually use any live subjects. They got some of the enzymes that are used in alcohol degradation called dehydrogenases. One that turns alcohol into acetaldehyde and that works fairly slowly, and a second one that takes acetaldehyde and takes it to acetate. And it's the rate of the two fighting against each other which keeps a steady state of this acetaldehyde, which gives you the hangover. If you make acetaldehyde faster than you get rid of it, you get a build up, and so they did separate tests on these two enzymes with all manner of different fruit juices and vegetable juices.

Phil - What fruit juices and vegetable juices?

Alex - So they went down to the local market in Mumbai and picked up basically everything they could find from pineapple, papaya, carrots, coffee, spices, coconut milk and coconut water.

Phil - Sounds like a horrible hangover concoction if you mix it all together.

Alex - They did them separately, but then they tried to work out what would be the best combination, and they had a panel who decided whether or not this concoction they were going to make was pleasant. The panel universally said that anything involving vegetables wasn't a very nice drink.

Phil - That makes a lot of sense to me. How good is this science? Is this actually testing whether these things are good hangover cure?

Alex - Probably not, because they're doing this in vitro, in glassware, rather than in the liver. All manner of other things are probably going on in the body, so take this with a pinch of salt as to actually whether it does the same thing in the body is in the test tube.

Phil - What was the weirdest thing that they tried, in your opinion?

Alex - So they tried cheese as a hangover cure.

Phil - Cheese?

Alex - Cheese, yes, and it actually appears to be a hangover cure. What was an interesting one I found was that coffee, which they tried, actually has the opposite effect on hangovers. That it causes your hangover to get longer.

Phil - That's mind-blowing. I always drink coffee when I'm feeling any sort of headache.

Alex - Same here. So I've deliberately avoided a coffee this morning.

Phil - Have you got a hangover this morning for the sake of science, can I ask?

Alex - I'll say I had a relatively late night at a friend's birthday. So, I wouldn't say I'm entirely fresh this morning.

Phil - Right. Well this is the ultimate test because you're in the perfect state. Now, did the scientists find what they think is the perfect hangover cure?

Alex - They found their best combination that would get rid of the acid aldehyde quickly, and it was a combination of pear, sweet lime and coconut water. So we've got three different liquids here. So there's some pear juice, freshly squeezed, some lime juice, freshly squeezed, and a little bottle of coconut water and we're going to mix them together. I have a little cocktail shaker here just for science, and let's. So it involved a bit more pear juice. A third of the same quantity of lime juice is probably about that much.

Phil - It doesn't look too appetising yet.

Alex - Yes, it's got a slightly murky brown colour. And the same amount of coconut water.

Phil - Well, it's still murky brown. All right. Bottoms up.

Alex - Bottoms up. Actually, it's quite nice. The lime really gives it a zing and it's certainly waking me up at the moment. I could just drink this for breakfast, actually.

A row of double and triple A batteries.

25:12 - Mailbox - do dead batteries bounce?

Adrian asks: why would a used battery bounce on its end more than a full one? Phil Sansom explains...

Mailbox - do dead batteries bounce?

This is the part of the show where we read out some of your correspondence. Adrian has written into our Facebook page to ask: “why would a used battery, double or triple A, bounce on its end more than a full battery? Phil Sansom explains...

Phil - I actually thought this was a really interesting question. In fact, I didn't expect it to be true. Sometimes people say that you can tell a flat battery from good one because the flat ones bounce, but I actually thought it was just a rumour. It turns out though, that scientists from Princeton did a study testing this by dropping batteries down tubes, and the flatter ones do indeed bounce higher, at least up to the point where they're half drained. To find out why they dissected the batteries and saw that at the negative end, which starts out containing a zinc gel. It slowly turns into a ceramic as the battery drains and the zinc oxidises. That ceramic gives it the extra bounciness, so the dead batteries bounce story is half true. The key thing is they might still have half their charge left.

Chris - I think I'll stick with a multimeter though, if that's all right. Probably a bit more reliable, isn't it? And quieter.

Phil - I think so.

Chris - Thank you very much Phil. Well, when you're not dropping your batteries, why not drop us a line to or tweet @nakedscientists, if you've got something you want mentioned here on the mailbox.

An avalanche.

27:00 - Caught in an avalanche - I was terrified

20 years ago, Lawrence Jones was caught in an avalanche - and barely lived to tell the tale...

Caught in an avalanche - I was terrified
Lawrence Jones

20 years ago, Lawrence Jones was caught in an avalanche - and barely lived to tell the tale...

Lawrence - I was with a group of friends and we were in a resort called Alpe-d'Huez, which is in the French Alps. It's got a mountain called Pic Blanc. It's known for having the longest black run in the world, and it's a fierce mountain, it's a fierce black run. I opened the shutters the next morning, and it was cloud, and I came downstairs pretending to have all that bravado. "Aw, really looking forward today, chaps", you know. But I actually was terrified.

But they said, "oh, don't worry, we'll just head up to the mountain rescue hut and see what they have to say about it." And even though the lifts were closed, they managed to talk the lifties into opening both lifts. And off we went.

Off we were going up to the top and sure enough, all the signs for every single run: closed. Everything's saying fermé, fermé. And we traversed across the very top of this ridge, where there were lots of signs that essentially in French were reading "only idiots go past this point." And it was amazing. There was no two ways about it. And when we stopped, I said, “this is the most amazing experience I've ever had.” I said, “I will never ski on piste ever again, this is so good.”

We went one at a time. I think I was the second to last, so I was the penultimate person. And there was a moment where Danny overtook me, and as he went past me, he dug me in the ribs, messing around, and I fell off my snowboard, I was going very slowly at this point anyway. And so I unclipped the bindings and I stood up, and I waved, and I saw all the boys over in the distance waving and waving and waving. What now I understand was: they were frantically waving. And I just thought they were being enthusiastic, and so I enthusiastically waved back. And I didn't hear anything. To this day I don't remember anything.

The next thing I realised was I was suddenly enveloped in this force of nature, where I was being pushed, and pulled, and dragged, and I tumbled down the mountain; and I'm being sucked under the snow, and suddenly I'm above it, and then I'm under it. The whole mountain just picked me up, and the whole mountain went down together.

A snowy mountainside in Zermatt, Switzerland.

29:57 - The recipe for avalanche risk

Mountain guide Mark Diggins and avalanche professor Jim McElwaine discuss a survival story...

The recipe for avalanche risk
Mark Diggins, Scottish Avalanche Information Service; Jim McElwaine, University of Durham

Joining Chris Smith and Phil Sansom are Mark Diggins, co-ordinator of the Scottish Avalanche Information Service, and Jim McElwaine, a professor of geohazards at Durham University. They’re going to help unpack what happened to avalanche survivor Lawrence. Chris asked Mark, who's in charge of producing the avalanche hazard forecast for part of Scotland, why there might have been a high avalanche risk on that day...

Mark - There are five typical problems. Wind; the wind destroys grains and makes a compact small grain layer. There is something called a persistent weak layer, where you have a layer of grains or crystals underneath the surface, and you actually have no idea that they may exist, but what's happening is they may be developing, getting weaker and weaker. And then the next is a new snow, of course. If you get lots of new snow, logically that's going to load a slope and slide away, and then wet snow, which is obvious, a warming or rain, which will make the snow turn into a sort of slurry. And then gliding snow, which is spring effect where you get big cracks and slowly the snow is creeping down the mountainside. And then finally what we have, and other countries have, is a problem which is a cornice, which overhangs a slope and if it collapses, that can produce a big trigger. But the two key ones are the wind slab, and the persistent weak layer underneath the surface. Which it sounds from Lawrence's case that this may well have been one of the culprits.

Phil - Jim, does that jibe with your research into avalanches? Do you look at the same sort of factors?

Jim - Yeah, exactly. I mean it's precisely how Mark described it. I'm the sort of, more theoretical end of it, but it's all these factors. If the load from gravity in the snow pack exceeds the weakest layer, then the avalanche will occur.

Chris - And Mark, the factors that you described, those are things that you know, you can tell without having to actually potentially go onto the slope. You could potentially observe those from a distance. Can you actually, if you go and look at a patch of snow, tell: "Hey, that's a big avalanche risk?"

Mark - One can, if one is aware of what you need to do when you're going into into the mountains. And that's the real challenge for recreationists, people going skiing or climbing, is the boundary between having a fantastic time in sunshine, and having some terrible event occur is unseen. And so what you really need to know is what's gone on. So you need to know the history of the snowpack. You can't just turn up and expect to know the complete picture. You need to have some understanding of what's gone on before in the days before.

Close-up view of fresh snow.

32:36 - What triggers an avalanche?

What caused the avalanche that caught Lawrence Jones?

What triggers an avalanche?
Lawrence Jones; Jim McElwaine, University of Durham; Mark Diggins, Scottish Avalanche Information Service

Returning to the story of Lawrence Jones, who twenty years ago was caught in an avalanche - here's what happened next...

Lawrence - Two Swedish guys who'd followed us up, taken a higher traverse than us, and as they stopped, those two triggered the thing off. They just saw this thing obviously crack at the top and then just gather momentum, gather and gather and gather and gather, and then just hit me like a thunderbolt.

As a younger man I played a lot of rugby, and there are moments - not very often - but there's a moment every now and again where you get caught up in a scrum or a ruck of some sort, where you are literally lifted off the ground and there's nothing you can do about it. And you may as well just stop fighting. And you realise, I'll save my energy 'til I'm unpeeled and I can get back out again. It was like that, but a thousand times more. I was sucked underneath all the snow and then the lights were out. And the thing I remember most about that is the eeriness, this terrifying silence.

Professor of geohazards Jim McElwaine and avalanche forecaster Mark Diggins join Chris Smith and Phil Sansom. Jim explains what it means when an avalanche is triggered...

Jim - Like Mike was saying, it was most likely it was a slab avalanche. So you've got hard, rigid snow and it's on top of a weak layer, and if you put extra loading on it, it can cause the weak layer to fail. And then the fracture can propagate extremely quickly. So this is what the trigger was, most likely; these Swedish people, they overstressed the weak layer and started it.

Chris - And Mark, would you concur with that? It's basically putting more mass on the slope above where the group of skiers involved with Lawrence were?

Mark - It may not be as clear as that. So it could be that when Lawrence went off his snowboard and was on his feet, he may have penetrated the snow. So if you imagine when you're traveling along a snow slope, you have a globe of effect underneath your feet. And if that globe coincides with a weak layer you'll get a collapse underneath that weak layer. That then can propagate, and it can propagate great distances, and that's relative to the density of the surface layer: so if it's harder, it'll propagate great distances; if it's not so hard, it won't travel as far. But it could well be that Lawrence, by coming off a snowboard, he could have initially weakened the slope. And then the final straw, if you like, was another pair of skiers on that slope could have made it release again.

Producer Amalia Thomas has an experiment to demonstrate, so if you’ve got your baking tray, flour, cornflour and salt, it’s time to follow along...

Amalia - So I put my baking tray flat on the table and on it I spread, as evenly as I can, course salt. On top of the salt, I put the cornflour; again, another thin layer of cornflour. So now I put the plain flour on top of the yellow cornflour. And I'm going to slowly tilt it until all my ingredients avalanche.

So this experiment is interesting for a couple of reasons: first of all because the combination of salt and flour avalanches at the same angle - between 35 and 38 degrees - as snow does in real mountains. And secondly, the way that the avalanche of salt and flour happened resembles the way snow avalanches break off the side of a mountain as well.

Jim explains how these layers of salt and flour and cornflour relate to the layers of snow mentioned earlier...

Jim - Well what you've got here is two sets of particles with different properties. So the salt particles are large and they're behaving like what we would call a dry granular medium. So that's like dry grains of sand. The only force between them is friction, there's no cohesion, so they're quite weakly bonded and they can easily move. Whereas the flour is much smaller so you get electrostatic effects and effects from the humidity that makes the particles stick together, so they have a lot more strength. You have this mixture of the different flowers, I think the cornflour makes it even stronger. So you've got a lot of strength in this slab-like layer on top of this weak layer. And then as you increase the slope angle, this simulates increasing the load - so this could be like a skier moving over the top or a fresh snow falling on top - and then the weak layer fails when the force of gravity down the slope overcomes the friction in between the salt particles.

Chris - Can the same science be used to explain any other natural phenomena? Or is this purely something related to avalanches?

Jim - Well that failure mechanism is purely related to avalanches, but they're very much like all sorts of other natural disasters: geophysical flows, like pyroclastic flows, debris flows, rockslides. And we use the same mathematical models really for all of these different types of events.

Chris - So do you have effectively a computer simulation that you can plug in all of the parameters of, say, snowfall, or an environment, and work out what the likely risks are and what the likely outcomes will be if things went wrong?

Jim - Well that's the aim of the work that I do, but we're not there yet. And I would say at the moment our models are not that predictive. So we can fix parameters to agree with past events, but we can't really say what's going to happen in the future.

Chris - Easy question to ask, impossible to answer: well why is it going wrong?

Jim - Well part of the problem is until recently there's been very little really good data about how these things flow and what's going on. Because normally you have a big powder cloud on top, so you couldn't really see what was going on. But now we have all sorts of great data, a lot of it from Switzerland where we artificially trigger avalanches. So this can really give us insight as to what is happening and help us develop better models.

Chris - Can you actually put things into the snow so that when an avalanche does happen, they're carried along and you can monitor what happens?

Jim - That's a great idea. And the avalanche people in Austria are working very hard on that. The big problem is then how to collect these things afterwards and get the data back out of them. Because the radio waves and things don't travel very well through solid snow, so you can't really get the data out easily while the avalanche is happening. And it's how to find these things afterwards is the tricky problem at the moment.

A snow shovel half-buried in snow.

38:53 - Buried in snow - search and rescue

Lawrence Jones is stuck beneath ten feet of snow. How can his friends find him in time?

Buried in snow - search and rescue
Lawrence Jones; Mark Diggins, Scottish Avalanche Information Service; Jim McElwaine, University of Durham

Returning briefly to the story of Lawrence Jones, who had just been dragged away by an avalanche and buried in snow...

Lawrence - I think I was something like eight or ten feet down, about twelve minutes or something like that. So quite a long time. I was upside down as well, so when they found me I was in the position of John Travolta, Staying Alive, you know that dance movie he does with his one arm in the air, almost like Superman pointing downwards. Which again wasn't very helpful when they're trying to dig me out and the first thing they do is find my boots. When you're in there you have no idea which way is up or down. So even if you had the ability to try and dig yourself out you wouldn't know which way to go.

Mark Diggins explains to Chris Smith the procedure for the people searching for Lawrence...

Mark - Well firstly I think Lawrence is very lucky to have survived, because statistics show that after ten minutes you've got a 10% chance of survival. So he is very lucky to have survived that depth and for that length of time. It's absolutely critical then that the people on the surface have equipment that enables them to find somebody that's buried. So everybody carries these transceivers, and they both transmit and receive a signal. So when you're skiing around, they were transmitting; but then if someone gets buried, those people on the surface will have to turn the machines to 'receive' so they can find somebody. So they will take you to an area of probably about a metre square or so on the surface. But of course if someone is buried deeply, then on the surface the signal might be the same in a larger area. So then what you really need is an avalanche probe. And these are three metres, so you push those into the snow, and they're actually quite sensitive so you can tell when you've got something that's yielding. And then as soon as you find somebody, you leave the probe in, and then you have to dig down. And the digging down is also extremely tiring because you're talking about a weight of 600 kilos per cubic metre. It's an enormous amount of weight that you have to move very quickly.

Phil - Jim, I want to ask you: I've also heard you can get these backpacks with airbags in, for if you're free skiing for example, that you can activate in the event of an avalanche. Why would that help at all?

Jim - They have several effects, one of which is just to shield you from impacts, which can often do an awful lot of damage. But their main effect is through something called segregation, so they help you end up on the top of the snow. So that means you're less likely to be damaged, you're more likely to be able to breathe, and you're more likely to be seen. Now why is it that they help you stay on the top of the snow? Well it's the same reason that if you have a box of cereal and you shake it around, then the larger lumps of cereal end up on the top; and this is through an effect called kinetic sieving. If you have large particle with lots of small particles moving around it, they can fall through the gaps in between, and they effectively force the large particle up to the top. And in an avalanche, if you put an air bag on, you are acting like a very large particle in amongst these smaller snow grains or blocks of snow, so you've got a very much higher chance of ending up on the top of the snow.

Phil - Does that difference then between your normal size, as a human shape, versus with a big swollen airbag; is that enough increased size to actually bring you way up in the avalanche?

Jim - Yeah. A friend of mine actually did that for their PhD. They put a load of dummies on a slope, half with airbags and half without, and then they blasted the slope. And all of the dummies with the airbags had some part of them on the surface that was visible, whereas I think half of the dummies that didn't have airbags ended up buried deep down in the snow.

Chris - Sounds like a good opportunity to ask you Mark: do you actually detonate avalanches? Because I know in some ski resorts they do do that in order to reduce the risk.

Mark - Yeah. So in many avalanche services, they control the avalanche situation by... if they leave the snow to build up, then you get huge avalanches that may come down and be totally, really destructive. So they have a process whereby they control them. So they will fire charges into start zones so they release avalanches bit by bit, so you don't get a whole mass coming down but you get smaller avalanches coming down.

Chris - And Jim, why would a charge like a shockwave from sound trigger an avalanche?

Jim - So it's surprisingly difficult to actually trigger avalanches with explosives. Normally you want the explosion actually to go off in the air, to fire a shockwave into the surface; and it really can trigger them for the same reason that skiers do, it's just additional loading over an area. But it can take quite a lot of explosives.

Chris - Because I think I've heard it; and also I've seen on James Bond, so it must be true, when the baddie fires a gun and unfortunately that shock is enough to dislodge an avalanche. Is that possible or is that artistic license because it's James Bond?

Jim - That's artistic license. The energy in sound waves is so low that they're never going to trigger an avalanche.

Chris - Jim, I'm disappointed.

Jim - It's a disappointing answer. But the science is the science.

Chris - And just returning to you, Mark: when a person's actually buried... because Lawrence alluded to the fact you don't know what direction's up or what direction's down, but also you've got this enormous amount of weight bearing down on you, you must effectively just be locked in position. You're completely at the mercy of the snow and anyone who comes to dig you out, presumably?

Mark - Yes, you are totally locked in. You cannot move a millimetre. So if you're twisted or in a really awkward position, you're held in that super awkward position. And also as you're breathing, then you slowly encase the snow in front of your face with ice, and so that starts to inhibit your ability to breathe. So it's a bit of a grim prospect.

A yellow helicopter in flight above a mountainous region.

44:40 - Emergency medicine for an avalanche survivor

An avalanche survivor needs crucial kit to be rescued - but also needs emergency medical treatment...

Emergency medicine for an avalanche survivor
Lawrence Jones; Mark Diggins, Scottish Avalanche Information Service; Jim McElwaine, University of Durham

When we last left Lawrence Jones he had been trapped for twelve minutes, upside-down and buried deep in a snowdrift. And luckily, his companions had brought some of the crucial kit...

Lawrence: The transducers played an important part in everything and obviously locating me. Mine obviously was left on and the guide Stephan, he kept his on and I think you flip it to another mode, which is to search for the one that is lost and, and everybody else has to switch theirs off. And then what they do is they get a very, very long pole, almost like a tent pole, one of these modern tentpoles that's quite bendy, and they'll go around prodding, looking for me. Well two things that I brought on that trip that I would never go anywhere off piste ever again, one was a heart surgeon and the other one was a casualty doctor. They were digging with snowboards and their hands and the two doctors were giving out the instructions exactly what was going to happen, what everyone was to do when they were to find me because obviously I was completely unconscious and needed to be resuscitated.

The helicopter came and picked us up and when it did arrive and they came out with the stretcher and had the worst headache you could ever imagine, and Danny was explaining to me, it's because my brain will have expanded with a lack of oxygen and would have been touching the outskirts of my skull.

Phil Sansom asks Chris Smith whether this is true...

Phil: Chris, based on your medical knowledge, is that true?

Chris: Yeah, the brain has the highest metabolic rate of pretty much any tissue in your body. And as soon as you start to deprive it of oxygen, either because you're not breathing in enough oxygen, or because your circulatory system stops, then the brain cells become more excited than they should do. And as a result, they swell and they swell because they take on water out of the bloodstream for various reasons. And that swelling - because the skull is a closed space, if your finger swells, your finger swells into the air of the room. If your brain swells, there's nowhere for it to go because it's enclosed within your skull. So you do end up with a higher intracranial pressure, at least for a short while. And that's probably why Lawrence had a bad headache. Apart from the fact he'd also been probably hit by 600 tons of snow, which probably didn't help.

Phil: That might do it. Is that something that the paramedics need to treat, or is that just a side effect?

Chris: Well we alluded to with Mark just now the fact that when you are deprived of oxygen, then this is a serious threat to your health because people will have brain damage because of the lack of oxygen reaching the brain. If this goes on for a period of a significant period of time. But lowering the temperature can help as we mentioned. And equally, if people are resuscitated promptly and you can restore a circulation, then actually usually the outcome can be pretty good. But it does rely on you being found quickly and resuscitated effectively and quickly. And obviously there's a chance that that's not going to happen. And so that's why, as Mark and Jim was saying, the outcome often is dismal for people because they get buried and it takes a long while to find them.

Phil: It is an incredible story from Lawrence. It sounds like he's very lucky. Mark have you ever dealt with a case like this?

Mark: Yes, unfortunately it was not a good outcome because the victims were buried to quite a significant depth and it was a longer period of time of extraction. But in terms of hearing of people that have been resuscitated after being buried for 10 minutes or so, then they were revived, it concurs with what was just said now is that they actually had a really significant rash on their forehead, which was a sign that obviously the brain had been swelling through lack of oxygen. It's very hard to always talk about the grim aspects of going into the mountains and hopefully we try and talk about the positive things as well.

Phil: And Jim, any thoughts further on what we heard from Lawrence?

Jim: Well, it sounds like he was skiing in a group of all guys. So the safest way to avoid avalanches to ski with a lot of women because they have almost no accidents.

Phil: You're joking!

Jim: No, absolutely. Well the most dangerous group is a group of all guys with one or two women. There's a lot of emphasis now on safety and group safety while other than on the physics and it's a question of communication and how decisions are made and it's like Lawrence says, he was feeling scared but felt he should go anyway because of his friends and they were probably all feeling the same and the guys were not wanting to discuss their concerns and their worries about the avalanche safety by the sounds of it and that's a classic pattern of why these things occur.


A caribou in a snowy forest.

48:59 - Avalanches and the ecosystem

Avalanches are hugely destructive - but some ecosystems might actually rely on them...

Avalanches and the ecosystem
Christian Rixen, Institute for Snow and Avalanche Research

Avalanches are giant forces of nature with enormous destructive power; they kill plenty of people, around a hundred every year in the Alps alone. But with that destruction seems to come new creation, because research from Swiss scientists shows that whole ecosystems may in fact rely on avalanches. Christian Rixen told Amalia Thomas how he compared biodiversity outside versus inside an avalanche zone...

Christian - In our plant study we found, in the darker forest next to the avalanche tracks, about 10 different plant species; and in the central zone, with the highest disturbance of the avalanche tracks - with a frequency of an avalanche every year - we had around 30 plant species.

Amalia - That's three times the number of plant species in a place where avalanches occur regularly. But how can there be higher biodiversity where an avalanche has been? You would think that they wipe out the ground as well as plants and animals in their path.

Christian - The effect is not that disastrous that all the soil would be cleared. It's simply that the continued disturbance by avalanches keeps out the competitive taller plants like trees and also taller shrubs. So from a tree perspective an avalanche is clearly a disaster. However, for the smaller, less competitive plants, there's more space, more room, more light to grow. And that results in more species, higher biodiversity in avalanche tracks.

Amalia - So where the avalanche has happened around once a year, only the taller plants are uprooted without really disturbing the soil, allowing a wider variety of shorter plants to flourish instead.

Christian - So the plants that grow in avalanche tracks are very different ones. You also have some high alpine specialists, which would normally only grow at high elevation, because with the snow you can also have seeds and parts of plants going downhill, and then possibly growing and germinating at low elevation. Again, simply because there's space.

Amalia - And a wider variety of plants means more healthy and varied diets for animals that live in these ecosystems. Several species of animals, including bears and deer, think that those delicious plant salads in the tracks are worth the risk of getting caught in an avalanche.

Christian - Where you have a lot of plants growing, that is also interesting for food for animals. So for example in the Rocky Mountains, mountain caribou feed in avalanche tracks and not only in summer but also in winter. So when the snow goes downhill you have clear patches of grass and the animals need to find food, so they go to these grassy patches where they can eat. So that's a good thing for them in winter. However, that also comes at a certain risk. So while feeding in the avalanche, there could be a new avalanche starting and taking the caribou down. And 10-15% of mountain caribou feeding in these avalanche tracks might in the end become victims of avalanches themselves.

Amalia - But what is bad news for the herbivores like the caribou may be good news for other animals.

Christian - For example, the elusive and rare wolverine, a predator - or a scavenger - actually spends a lot of time in avalanche tracks searching for carcasses. And probably much of the food in winter for the wolverine comes from animals in avalanche tracks. So that is obviously a disaster for the individual caribou, but for the ecosystem, it is a very important process and an important natural disturbance.

A skier stands on a frosty ski slope.

53:19 - Reflecting back - stop and think

Twenty years after Lawrence Jones survived an avalanche, he still goes skiing with his family every year...

Reflecting back - stop and think
Lawrence Jones

Twenty years after Lawrence Jones survived an avalanche, he still goes skiing with his family every year. Here he is one more time reflecting on what the experience has taught him...

Lawrence - It does scare me with the ease that people go off-piste and the casual way it's approached. We as human beings, we like to plan things, don't we? And we'll say, "well we'll do this on this day, and this day on that day." That's probably not the best way of doing it. And when not to go is a really, really important thing to consider. People should stop and think, and take a responsible look at their own ability, and don't feel that you need to do anything under peer pressure.

Listen to the full version of the story on the In Short podcast episode "Avalanche survivor: Lawrence's story".


54:21 - QotW: Do hairs grow grey or turn grey?

Do hairs grow out grey, or do hairs that had colour eventually turn grey?

QotW: Do hairs grow grey or turn grey?

Katie Haylor finds out for listener Elizabeth why, when it comes to colour, it’s a question of 'hair today, gone tomorrow', with hair expert Desmond Tobin from University College Dublin...

Katie - Interesting question. Forum user Halc said that his grandmother's hair turned white in a week when her oldest son was killed in WWII, and user Evan_au said that genetic factors (eg age) and environmental factors (eg stress) affect the colour and darkness of the colour, and determine when the colour turns off, and how quickly the colour turns off in a given hair follicle. 

To get to the root of the question, we spoke to hair expert Desmond Tobin, director of the Charles Institute for Dermatology at University College Dublin.

Desmond - Hair greying is associated with the aging process and is characterised by growth of hair lacking colouration within the hair follicle - a little ring of stem cells embedded in your skin that makes the hair. Under normal conditions, the colour-making cells in the hair follicle actively produce and transfer their natural hair dye, melanin, to keratin-producing cells that make up the bulk of the hair strand during this growth part of the life cycle. The result? Fully coloured hair - be it blonde, brown, black or red.

presenter - But, as some of us may well have experienced, hair doesn’t stay colourful for ever! Why?

Desmond - After between 5 and 8 rounds of the hair follicle life cycle (which each last up to 5 years), parts of hairs’ colouration machinery slow down, which results in either not as much colouration (so grey hair) or no colouration (white hair). And it's not just age, there is now good scientific evidence that psychosocial stress can affect many aspects of hair growth, including hair graying.   

So Elizabeth, as you look at hair, you’ll see it either as “regrowing” or growing in a different colour to the others on the head, even from the same hair follicle. You might see, for instance, a black hair tip becoming grey-ish in the middle, even to white at the scalp.

Having said that, it is much easier to spot the fully white hairs against a dark background, and we do not know the ratio of fully white versus gradual greying hairs on the average scalp.


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