The Sciences

# Can You Walk on Lava? Falling into Lava Revisited

By Erik KlemettiJan 12, 2012 1:29 PM

The response to my post about what might happen, contrary to Hollywood's vision, if you fell into lava was, to say the least, amazing. Thanks for everyone who has read the original so far. I have gotten a lot of comments about that post, so I'm trying to respond to some of them (sorry if I didn't pick yours) to tackle some of the current questions and criticisms for my analysis -- the idea that you aren't to likely to quickly sink into the lava lake, but rather burn yourself to a crisp like a hush puppy in hot oil (well, a hush puppy in molten iron). So, enjoy this followup and see what I suggest as some of the best ways to navigate a lava flow.

Paul: In another stupid disaster movie, sweaty survivors cross over a pond of lava on a horizontal fire truck ladder. In reality, the radiant heat would cause clothes and skin to burst into flame within seconds, even at a distance (incident infrared radiation would be the same at 20 ft as at 1 ft.). And the aluminum ladder would sag very quickly.

Me: That is one of the many aspects of

Volcano

that bother me -- you know, other than a scoria cone erupting from the La Brea tar pits. I think to most people, the heat from a lava flow is the same as the heat from your oven. However, most ovens get to 525°F / 273°C on broil, so the average basaltic lava flow as shown in Volcano would be about four to five times hotter.

Cory: Consider, a body (of a certain weight) falling from a substantial height into a pool of lava that is of a certain variable viscosity—differing at different depths, AND flowing with underlying current. A body might then penetrate the surface to some necessary extent, and be pulled under by strong currents of high-viscosity molten rock flowing below. True, a body is not necessarily ‘sinking’ as is more familiar to us in our ‘normal experience’ (considering only the relative densities of a ‘still’ fluid and an object), however, the hapless Gollum (or, some other body) may, nevertheless, be observed ‘sinking’ into the lava after striking the surface.

Me: Cory has an interesting point -- if there were active currents in the lava flow (see below), you could get “pulled in” as if you fell into a flowing river. However, the viscosity and density differences would still not allow you to sink. It would be like a stick on a stream -- even when caught in the current, the stick wants to float rather than get entrained.

Bob: Sadly - you've got something else wrong. At those temperatures, you wouldn't burst into flames. Considering the human body is made up of 80% water, the portions of your body that come in contact with the lava would generate huge amounts of steam, which would likely have sufficient pressure to blow you up off of the surface (at those temps the transformation of water to steam will expand by a volumetric factor in the thousands almost instantly).

I work in the metals industry, and the fear of steam explosions is a constant. At our facility, well before things like OSHA were around to keep everyone safe, an individual fell into a furnace three feet deep, full of molten aluminum (roughly 760°C). He was blown back out of the furnace, and actually died from the impact of that as opposed to anything else.Me: I think the key limitation here is how that steam would escape -- remember, all that water is conveniently kept in a sack of skin, so first you’d have to get that steam out of that sack. I think I’ll leave it at that. However, Bob's story does seem to lend credence to the idea that the steam could pop you right back off the lava.

Paul: But isn't that assuming he just sort of walks off the edge and it's right under him? After watching the video of the film on YouTube, I count that he falls for seven seconds. While I don't know offhand if that would allow for him to reach terminal velocity, would not the velocity of his fall, in effect, ADD something to his weight (at least in terms of downward acceleration) for the purposes of penetrating the viscosity resistance of the lava below? Assuming that Middle Earth has a similar gravity to the Earth, the downward acceleration of 9.81 m/s, at 7 seconds, would result in Gollum hitting the lava with a velocity of 68.67 m/s - surely that would affect how he hits the lava (or would it still be magma, as it is still technically in the earth and not on the surface)?

Marc: I realize this entire post is satirical, but if I were to jump into lava and land on my feet, my entire weight would be applied over about 1/2 sq ft. My density wouldn't be at issue, but instead the pressure I'm applying to the lava would. Granted I might not sink, but I might end up without the lower part of my legs.

Me: This is one thing I didn’t fully tackle in the original. However, think about jumping into the water from a diving board. You penetrate the surface but are usually forced back to it by your buoyancy relative to water. Water is much less viscous than lava, so it would be much easier to penetrate the surface and sink in by some depth, so if you fell the same way into lava, you wouldn’t penetrate nearly as deep. However, it would take much longer to rise back (likely longer than it would take to burn you to embers) due to that increased viscosity of lava as well.

Boris: I picked a huge chunk of dense, cold lava from the surface - it weighed a good 20 kilos - and threw it through the skylight onto the bright golden-yellow lava surface, where it impacted without creating the least bit of a dent, but rather burst into numerous pieces. If I had thrown a human being instead of that large rock, probably that unfortunate person would have burst into flame and largely evaporated before touching the lava surface. You get an idea about the heat in such environments when standing on the rim of a skylight over a lava tube - if you stand on the wrong (downwind) side, you will soon feel how your eyelashes, eyebrows and hair are seared by the heat.

In contrast, at Kilauea there are documented cases of people sinking into small pahoehoe lava flows. One of them was familiar with Etna's more viscous lavas and believed he could likewise step onto a Hawaiian lava flow, which resulted in him breaking through the crust covering the lava, and his trousers catching fire. That was very painful, and an even worse incident happened to an American volcanologist in 1985, who somehow came to SIT on an active pahoehoe lobe and slowly his legs began to sink into it, while he frantically tried to push the incandescent lava from his legs with his NAKED HANDS. So, no doubt, you can sink into a Hawaiian (tholeiitic basaltic) lava flow, and since the lavas of Erta-Ale and Nyiragongo are very similar (the latter volcanoes are still more fluid), I guess you would easily sink into those lavas, too. Unless, of course, these lavas occur in the form of lava lakes, where you'd presumably evaporate practically in the same instant you step on the lava surface.

Ed K: I think the alkalic lava at Nyiragongo probably behaves more like the stereotypical Hollywood lava.

Me: Boris has another good, first-hand account of throwing something in lava -- if a rock doesn’t penetrate the surface of a flow, then the likelihood of a person to do so, even if they fell from a great height, seems unlikely. The story from Hawai’i, however, does show you can slowly sink into a lava flow -- and, as Boris and Ed point out, certain lava types, such as the alkaline basalts of Erta’Ale, might make sinking easier because of their lower viscosity. Alkaline basalts are called that because they contain, proportionally, more sodium and potassium (alkaline elements) than other lavas. This extra Na and K breaks up the bonds between silicon and oxygen, lowering the viscosity of the magma. If you really wanted to have the best chance of sinking to your fate in lava, try to super-odd carbonitite lavas of Oldoinyo Lengai in Tanzania.

JayS: So, with the right shoes, you could run over lava?

Me: I thought about this some and, in theory, I would say the answer is “yes”. You’d need something like snow shoes, except instead of a mesh you have a sole of some heat resistant material. You don’t want to use anything that will transfer heat, so maybe the best bet would be asbestos – probably at least 25 cm thick. You’d want the soles to be big so they can block some of the radiant heat from the lava and you’d need to wear a heat-resistant suit (see right) as well. And you’d need to walk reeeeal slowly because falling down is not an option. The biggest issue would be that as you walk, you will sink a little into the lava and the viscosity of the lava means you will “go with the flow.” Most molten lava at the surface has some flow to it, even in a lava lake, as the hot lava churns, so the closest equivalent to this might be trying to walk across moving ice. Except you stick to the ice. And you’ll burn to a crisp if you lose your balance. So, possible “maybe” but I wouldn’t want to be on the Japanese gameshow that makes you try this out.

Claude G: Two [of them] got serious burns in Iceland and New Zealand as the crust broke under their feet on a geothermal field. The other two got much more serious burns on Lengai and Kilauea (Boris knows one of them) when a lava tube broke under the weight of their bodies. Contrary to what many people think, it would be a great mistake to walk on a lava field on Kilauea wearing fireproof boots. As long as you can bear the heat, it means lava is strong enough for you to walk on it. If your shoes start taking fire, just move away!

Me: More evidence that walking on lava might be feasible, but not recommended. I imagine more people have accidentally ended up in thin lava flows and live to tell the tale. Oddly, I don't know if I've ever seen anything about someone falling into a lava lake and dying -- at least with anyone around to tell the tale.

RP Bird: Here is Gollum's death from Return: "...and then with a shriek he fell. Out of the depths came his last wail Precious, and he was gone."

Me: I can handle the questions of magma, but my Tolkien knowledge isn’t as sharp.

Greeble: I have personally walked on VERY slow moving lava at Kileua in nothing more than tennis shoes! I only did it for about 15-20 seconds, and it damaged the shoes, but I didn't sink in the least bit. A local did it first, and then I had to try it as well. As the local said, "Dude, it's rock. It's just really HOT rock. Would you sink into a bucket of gravel?"

Me: It sounds like here you were walking on A’a lava instead of pahoehoe, which is what is normally pictured in Hollywood films. A’a is cooler and slower moving, almost like a pile of hot rubble moving like a tractor-tread. That should be a lot easier to walk across than the less viscous pahoehoe lava.

214Jim: If the lava is outgassing, the gasses dispersed therein would make its density considerably lower, allowing a body to sink below the lava's surface. E.g., a ship attempting to sail through subsurface gas vent of sufficient size would promptly sink as though someone had yanked the rug from under it. (Yes, this has happened in the offshore oil industry.) But it's possible that the intense heat would cause a falling body to reach combustion temperature before it even reached the lava.

Me: This is an interesting idea -- the viscosity of a magma will go down with increased volatile (mostly water vapor and carbon dioxide) content. It might not work exactly like methane bubbles in the ocean causing boats to sink as high bubble content in a lava might lead to an explosive eruption, but theoretically, volatiles could help you more readily sink.

Jan S: Does that also mean that Dante's Peak riding a truck over the lava is actually closer to reality than Gollum? Or is the truck's density (it's mostly steel after all) too high to not get stuck?

Me: This one is tricky -- the scene in Dante’s Peak where our hero Pierce Brosnan (right) guns a pickup truck over a lava flow (successfully -- and they even rescue the dog!) is very different than Gollum’s fate. First off, the lava flow in the scene from Dante’s Peak is thinner. Also, Pierce has the advantage that he’s not the one burning, so he can use the progressive ablation of the tires on the truck to his advantage. However, one thing that has always bothered me: Why didn’t the gas tank explode? It should have heated so rapidly when the bottom of the truck over the lava that you would think that the flashpoint for gas should have been passed, so Pierce and co. would have blown up before they could ever save Rover … but this may be a quandary for another day.

Simon Smith: In the Top Gear episode, tire temperature was maintained with water spray except when he stopped. All four tires caught fire after which he got rolling again...tires were extinguished but didn't fail.

Me: This might be one way to keep things from getting too hot -- a constant spray of water to keep things cool. I have to admit, I haven’t seen this on Top Gear, but I imagine the water helps in both keeping the tires intact and from the gas tank from exploding. Problem might be the amount of water you might need to keep things cool.

Aruisdante: You would likely sublimate well before you died of asphyxiation if you flat out fell into lava. While your lungs would almost undoubtedly be irrevocably charred from the hot air above the lava (assuming relatively static air conditions over the lava), it takes about 80 seconds for the average human to fall unconscious from lack of oxygen, and I highly doubt your body will last that long.

Me: This is another aspect I didn’t really tackle -- what happens on the way down or, in other words, is it the lava that will kill you when all is said and done.

Frank: Wouldn't the temperature just roast your body or would you pop like a tick with your now boiling blood? Hairs would certainly be the first to go, bones last?

NZMCA: It didn't quite say beyond the obvious (that one bobs on top of lava) what really happens when you fall into it. Do you combust? Do you burn slow, writhing in agony as your flesh is seared? Come to think of it, the One Ring behaved correctly, floating gently on top and melting away like a truffle on top of a grill...

Me: I think your actual demise might vary -- not to be too gruesome, but might a 150-pound marathon run see a different fate than a 400-lb sumo wrestler (see above)? Summary: The long and short here is that you might be able to make it across lava if you have the right equipment -- maybe a 4x4 truck with a 10-cm layer of asbestos across the bottom and a 1000-liter tank of water constantly spraying your vulcanized rubber tires. Then again, I have trouble envisioning a situation where you might need to employ this, except, of course, in the next big disaster movie where lava flows spread across London. I’ll be taking bids from agents/studios for that script (tentatively titled either London Bridge is Melting Down or Mount Python Frying Circus.)

Images: 1) USGS/HVO. 2) Schizoform/Flickr. 3) Interpretive Arson/Flickr. 4) Modified from Flickr images by pandrcutts, cruccone and coolinsights.

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