Lava. Picture by Flickr Hrafnhildur Árnadóttir under license https://creativecommons.org/licenses/by/2.0/legalcode
This is a general public service announcement, because it’s everywhere. The most glaring examples are Star Wars: Revenge of the Sith, Star Trek: Into Darkness, The Lord of the Rings: The Return of the King (movie version), and Dante’s Peak. Volcanoes don’t work that way, and rather than seeming ‘awesome’, in actuality it’s just kind of dumb.
It’s possible that you can handwave the science in Star Wars, because on the whole it’s a lot more light science fiction than hard science fiction, and you can use ‘oh, the Force’ as an excuse. Note that if you want to write a light SF anything, it works better if you show or tell the audience about it and don’t just attempt to explain it later when people ask questions. In general, you want to address questions in your novel or other story, not when people write in or post about it online or ask you on the street or in a conference. (Though oddly enough, science does suggest that the type of planet shown in this movie does actually exist. I just wouldn’t recommend fighting very close to the lava flows on such a planet. In fact, considering that you’re trusting your innate powers not to run out and let you be burned alive or choke on ash, I’d get a spacesuit and only rely on the Force if the spacesuit got torn or otherwise broken.) The other examples…don’t quite have the same excuse.
Some of it, of course, depends on the type of lava. Different types of lava flows actually exist, mostly differentiated by temperature (from about 1100oF-2200oF or 593-1204oC), composition (which type of rock melted into lava) and speed of cooling. The hottest is about five times the maximum temperature you’d use for your oven. Fortunately, like slow-moving zombies, lava flows are generally slow enough to outrun (but you don’t want to be caught in their path, either). It’s been a while since I’ve watched Dante’s Peak, so I don’t remember if anyone died by being submerged in lava, but the way people die as shown by Hollywood isn’t scientifically correct (surprisingly), and here are a few links to tell you why (with varying amounts of math). Gollum died in this unrealistic way. I also wouldn’t want to stay too close to the lava flows coming from Mount Doom, or any real-life equivalents for too long, even if you can get close and be relatively safe. It is one of the draws to places like Hawaii, so they have a description of how to stay safe when viewing lava flows.
In general, lava flows slowly enough (along the lines of molasses speed, depending on viscosity) that it’s easy to outrun or in some cases outwalk, but there are a number of other dangers that accompany volcanic explosions and/or lava flows. Hollywood disaster movies are notorious for bad science (only matched by Syfy disaster movie silliness). At least Dante’s Peak did a decent job depicting the various volcanic steps and some of the dangers, but the ‘driving over lava’ scene was still a terrible idea. While they did show the tires melting eventually, the tires would melt a whole lot faster than eventually. Rubber in your tires would melt at 180oC, or 356oF. It would probably melt instantly on contact with the lava given the temperature range of lava given above, which would make driving across the lava flow very, very difficult. Steel or iron would be more like 1093-1649 oC or 2000-3000 oF, so some of it melting wouldn’t be out of the question. They did also accurately show the truck catching on fire—the ignition point (when it would catch on fire) of steel is 1500 oF, or 816 oC, so metal catching on fire when in contact with lava would be accurate enough. However, I’m not sure you could drive on the rims especially if you needed traction to get over the lava, much less at a quick ‘let’s not get buried alive by lava’ pace.
For a real-life comparison, a man ran over lava and ruined his shoes (possibly also rubber!). It should be noted that he was going quick (i.e. his shoes had less contact than the tires, because the tires are in constant contact with the ground, even if it is different parts of the tire) and didn’t run over a long length of ground. There’s also the obvious—that heat is not limited to just touch (think about standing looking into an oven when it’s open trying to decide whether your food’s done). What about the clothing? Different fabrics have a much lower ignition temperature than rubber or metal (humans have an ignition temperature of 1400oF or 760oC, while depending on the material your clothes are made out of 730-1200 oF or 390-650 oC). The exact temperature of the air is probably not a high enough temperature for autoignition, given that in real life you can stand nearby lava without your clothes auto-igniting. Of course, the point is moot if the outside of the truck is on fire (which it was), since cars are not airtight (unlike what was shown in the movie) and can’t keep out things like pesky flames, which would spread, particularly over things like leather seats and clothing which given a spreading flame and a lower ignition point would catch on fire more quickly. Neither running over lava nor driving on lava are recommended at home. Listen to any calls for evacuation, and if at any point you run into lava coming down, go around (off-road if necessary)!
Also, lava is hardly the only problem you would face with a volcano. The amount of pressure that builds up in a volcano means that the volcano occasionally flings ‘lava bombs’, which could easily kill. As Pompeii taught us, there’s no outrunning a pyroclastic flow (and being buried alive in ash and pumice doesn’t help either). Explosive eruptions, unlike lava flows, cannot necessarily be outrun. Changes to the global temperature due to ash blocking out the sunlight can cause secondary issues like starvation, and if the lava melts other things (like snow), this can cause problems like lahars or mud flows (basically, a flash flood). Areas near rivers or the sea are probably the most dangerous, other than active, all-red lava. Lava benches (where lava meets water) can collapse unexpectedly, or cause explosions. Steam can form and burn you, acid rain can fall, heavy fog can prevent you from seeing other dangers, and sulfur dioxide and other dangerous gases can damage your lungs or suffocate you. (Gases are not only a danger near bodies of water but everywhere lava is, though the danger is highest near bodies of water and through an eruption or the weak point in the crust where the lava comes out.) Still, falling is dangerous, since volcanic glass or igneous rock is sometimes very sharp (and may not always be fully dried), and just like visits to sand dunes, heat exhaustion is a definite danger.
Along the same lines as the Dante’s Peak example, one of the (multiple) issues in Star Trek: Into Darkness (specifically the volcano scene) were related to unexpected logical issues. Visually, they did well, and they’d both recognized that heat was a problem and fixed that problem (though neither the script nor Scotty realized they had solved it). Specifically, they did some of their research, but didn’t look at everything. An actual geologist points out that the actual problem that would’ve been encountered would have been the volcanic ash messing with instruments. The device to freeze the lava could potentially be a force field rather than ‘cold fusion’, given that a type of force field already exists in canon (deflector shields)—and if so, there’s an interesting thread on stackexchange speculating on how lava and force fields would theoretically work. They also messed up the idea of volcanic pressure—the more pressure you build up in the volcano, the worse it’ll be when it finally does explode (that’s part of why supervolcanoes are terrifying).
What other media have you seen that depicts volcanoes and lava, and are the dangers depicted realistic?