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How much HP does a mountain range have? And I don't mean a mountain, I mean a mountain range. Specifically Kondyor Massif

It's technically a crater, but close enough. Basically I'm homebrewing a dwarven spelljammer space station. I want to know the amount of HP this thing would have, if it was lifted into the air. Not only am I including the mountain range part of it, but I'm also wanting a half-circle of the ground below to be factored in as well. So going from the edges of the mountain to a curving downward into a big half-circle, with a 2.5 mile radius

Kyondor Massif is about 5 miles in diameter as well. We're also assuming this is a perfect circle for simplicities sake.

The reason why I'm asking this, is because in spelljammer objects have a bubble of oxygen around it. The amount of air is equal to its keel length x beam length / 2 + its HP (KxB/2+HP). It's meant for spaceships, but I'm sure a mountain range would fit. I don't know what the HP of a mountain range would be, so I'm asking here.

If you need any more info about this, please ask and I'll clarify.

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  • \$\begingroup\$ What spelljammer rules book are you using? \$\endgroup\$
    – GcL
    Apr 4, 2021 at 1:15
  • \$\begingroup\$ I believe I was using a 5E homebrew spelljammer book now that I look at it. \$\endgroup\$ Apr 4, 2021 at 1:29
  • \$\begingroup\$ @GcL sorry, forgot to @ you \$\endgroup\$ Apr 4, 2021 at 1:36
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    \$\begingroup\$ This question is clear and is easy to answer. I voted to reopen. \$\endgroup\$
    – Akixkisu
    Apr 4, 2021 at 12:37
  • \$\begingroup\$ Related: Hit Points and Damage Thresholds for defensive structures \$\endgroup\$
    – Kirt
    Apr 5, 2021 at 5:55

2 Answers 2

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The object rules tell me that a Medium sized object has 18 hit points if it is "resilient". For very large objects, they should be subdivided into smaller objects and have each section track hit points separately. So a very large stone object can be divided into Medium cubes with 18hp each.

(18hp seems low, for a 5-foot stone cube, but we'll go with it.)

Your object is a sphere with a radius of 2.5 miles (2640 five-foot spaces). The volume of a sphere is 4/3 * pi * r^3, but our sphere is half air, so we'll compute 2/3 * pi * (2640)^3 and get 38 billion 5-foot cubes of stone. Each of them has 18hp, so that's 693 billion hit points for the whole thing. Give or take.

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  • \$\begingroup\$ Is a mountain "range" an object or structure? They are different in the rules albeit very vague. For that matter is a mountain a structure? \$\endgroup\$
    – Slagmoth
    Apr 4, 2021 at 15:47
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    \$\begingroup\$ That number is for reducing the whole mountain range to dust. You probably need considerably less to "destroy" the spaceship. It would probably take a lot less damage to break that mountain range in half for example, an event that doesn't concern a mountain, but that I would consider fatal to a spaceship. \$\endgroup\$
    – nvoigt
    Apr 5, 2021 at 12:15
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A mountain range is not an object, it's a collection of objects.

The DMG has this to say about damaging objects:

For the purpose of these rules, an object is a discrete, inanimate item like a window, door, sword, book, table, chair, or stone; not a building or a vehicle that is composed of many other objects.

Big objects such as castle walls often have extra resilience represented by a damage threshold. An object with a damage threshold has immunity to all damage unless it takes an amount of damage from a single attack or effect equal to or greater than its damage threshold, in which case it takes damage as normal. Any damage that fails to meet or exceed the object's damage threshold is considered superficial and doesn't reduce the object's hit points.

What constitutes an "object" is very much up to the DM's judgement, and a single object could clearly be quite large in the case of a castle wall, but if a castle isn't a single object, then I have a hard time accepting a mountain as a single object, let alone a mountain range. And since it's actually a space station, the analogy to a castle is even stronger.

I would think a space station doesn't have an HP total as such; instead, specific narratively interesting sections would have HP totals (and thresholds, if they're large stone structures) and the rest of the station takes damage or not according to the narrative rather than by tracking hit point damage.

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