[ruytlm]

Your conclusion of ~3L of gasoline is right, but it looks like you dropped a few zeroes on the way there - your example of 1x1x1m sunk 10km below the surface would be sitting beneath 10,000,000kg of mass, not 10,000kg.

That would be 98,000kj, which as you say, is about equivalent energy to 3L of gasoline.

[janc_]

And for reference: a ultra-tiny tactical nuclear bomb would still be >1 GJ.