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This question already has an answer here:

I am evil and wish to destroy a town near a volcano and kill all of its citizens.

The volcano is small - about 15 square kilometers in area. The town is even smaller.

The thing is that I don't live inside the volcano like a bona fide supervillain, but I live near it, a mere 25 metres underground. I'm tired of this glorified basement, so I'm going to fill it with explosives and move out.

My question is this: How strong must this underground explosion be, and where must it and the town be, in order to trigger a pyroclastic flow destroying homes, and ash clouds thick enough to obscure the sun for days?

To be clear, the lair and town can both be any reasonable distance from the volcano and to each other, unless the explosion itself would wreck the town. I presume that the lair would be closer to the volcano than the town.

Edit: Unlike Yellowstone, the volcano is active and it is assumed that less energy is needed to trigger an eruption. I am also specifically asking about the use of an explosive charge. The goal is to avoid giving the townsfolk enough notice to evacuate.

The lair can be deeper underground (e.g., 40m) if truly needed.

I'm not necessarily asking for Vesuvius, but something like Mt. Merapi or Sinabung would be great, as long as the ash plume persists and blocks the sun for a few days.

Mount St. Helens erupted due to an earthquake exposing a hole in the mountain, so surely blowing a hole in a volcano has the potential to have similar effects.

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marked as duplicate by Vincent, L.Dutch, Vylix, sphennings, adaliabooks Nov 19 '17 at 20:35

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ Saint Helen was triggered by a direct impact? How? $\endgroup$ – L.Dutch Nov 18 '17 at 10:03
  • $\begingroup$ Mount St. Helens erupted laterally because of the landslide. The eruption was going to occur one way or another, the landslide (triggered by an earthquake caused by the rising magma) simply caused it to blow out the side due to the sudden decrease in pressure that way instead of forcing its way out and blowing the top, as normal. $\endgroup$ – Keith Morrison Nov 19 '17 at 10:17
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  1. You need the right kind of volcano.
  2. You need an active shallow magma chamber with increasing pressure.
  3. You need the right composition of magma in the chamber.
  4. You need the blow the throat in such a way to trigger the right type of eruption.
  5. You need to ensure the eruption proceeds in such a way to generate a pyroclastic flow of the right size.
  6. You need to ensure the local topography will direct a pyroclastic flow the right way.
  7. At this point you should be wondering if it just wouldn't be easier to blow up the town directly.
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https://www.wired.com/2012/04/could-people-trigger-a-volcanic-eruption-on-purpose/

Armed with this information, if you want to try to get a volcano to erupt, you'll need to do a few things:

Find a volcano that is already showing some signs of magma intruding at shallow depths. This might be high levels of volcanic gases, shallow earthquakes, deformation of the volcano. You want something "primed" to go. Figure out a way to release the lithostatic pressure keeping the "cork" on the volcano so that the bubbles can form. Figure out how to get a lot of water into the volcano quickly ... but not too quickly.

I am hoping this is a fictional scenario. I think you need tool and expertise to determine a lava dome is building pressure beneath you. It would be lucky for you but bad luck generally if this happened to be right under your apartment. Or maybe that is why you put it there?

It occurs to me that fracking techniques or deep earth wastewater disposal could be combined with the explosives to get what you want.

1: Inject under pressure water to a region near but not at the lava dome - maybe an old exhausted area from a previous explosion.

2: Deploy explosives to open conduit from old lava area to new. Hot lava converts water to steam. Explosion ensues, hopefully throwing lava around.

2a should have noted to get rented fracking equipment back before you got step 3 or you will have to pay the deposit.

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Where the flow goes depends on the origin point and topology. It is a kind of aerosol and follows the usual physics, including going where gravity and obstacles let it go. Redirecting the flow by explosions seems like quite a challenge. You might have to blast a canal through a ridge, for example, or create breakwaters with artificial avalances.

Triggering a flow with explosives seems to be a special case of triggering a volcano with explosives. That is generally not possible when you have a few tons at most, in a location that wasn't deliberately chosen next to a volcano that is almost ready to erupt anyway.

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You need a huge internal pressure buildup, not just a way to break open the ground. Think of it like squeezing a zit. The pimple does not blow out if you just open the pore. You have to squeeze.

Like someone above said. You need a primed weapon for you to be able to trigger it.

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Trying to open a volcano before the natural eruption would only help the situation. If you would make a hole into the volcano, you would release all the pressure and heat, it would probably make a lava eruption and cause a huge calamity near the volcano, but no pyroclastic wave. (maybe a nuke would have different results, but then you could use the nuke by itself and just open the volcano to make it seem like a natural disaster for a few days, before somebody would investigate)

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This is not your usual DIY project.

Best bet would be to use a shaped nuclear charge. These focus a large fraction of both the blast and the x-ray/gamma ray energy into a narrow cone. Of course even if the volcano doesn't go off, you probably will have still succeed in your desire to wake up the neighbourhood.

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