# Determining maximum cave depth

I am planning on making this planet of caves, and it has cave systems that dwarf Earth's. It's got carbon-based life, a chemical composition rich in copper, a good amount of water, and less gravity than Earth. Example living beings include creatures that roll around to go fast, worms that tunnel through solid rock, and chemoautotrophs that don't need the sun to gather energy and support an environment.

The surface gravity of the planet is 0.8 g, or 7.85 N/kg. We need multiple types of rock, with strong, lightweight rock to remain stable even after weaker variants of rock are eroded away to make the caves. As with sufficient support, a cave that's just a few dozen meters from the surface can be indefinitely long, I'd like to know in particular how deep below the surface a natural cave can be on that planet, without collapsing from pressure.

For reference, caves on Earth cannot be more than 3000 m, or 9843 ft, beneath the surface. That's an estimation. But here's a fact before you go: The deepest known cave on Earth is Krubera Cave, which is about 2200 m deep.

• the main reason for the limit on earth is the rock gets too hot and soft o support its own weight. you need a colder planet at least internally.
– John
Commented Apr 4 at 1:16

For reference, caves on Earth cannot be more than 3000 m, or 9843 ft, beneath the surface. That's an estimation. But here's a fact before you go: The deepest known cave on Earth is Krubera Cave, which is about 2200 m deep.

Taking your reference for good, and considering that the load bearing capacity of materials doesn't depend on the gravity and that the load can be considered to increase linearly with depth, you just need to solve the following proportion to determine the maximum depth of your cave:

$$D_{Earth}:g_{Earth}=D_{Tyson}:g_{Tyson}$$

$$D_{Tyson}=D_{Earth}g_{Earth}\over g_{Tyson}=D_{Earth}/0.8$$

• You named the planet after me. Awwww. The planet is actually called Oblaetis (got that from RNG), but that means that its caves can get 4.8 km, or 2.98 miles, deep. Commented Dec 4, 2020 at 14:45
• @TysonDennis, 3/0.8=3.75
– L.Dutch
Commented Dec 4, 2020 at 14:53
• Oops, my bad. You’re right. But the caves would get 4.8 km deep if we were talking about a gravity of .625 g, or 6.13 N/kg. I had a brain fart. 3.75 km is equivalent to 2.34 mi. Commented Dec 4, 2020 at 15:03