Another one to watch out for is mud diapirs. In coastal deltas where thousands of feet of infill has occurred over time the interaction between hydrocarbon formation and organic silts can create mud volcanoes.

https://www.researchgate.net/figure/Comparison-of-signatures...

These can be anywhere things that shoot liquid mud out of the ground to areas of very deep low seismic velocities where you could drive a pile thousands of feet to the bottom of hell and barely get any resistance.

Much the same, one should be careful when drilling into mud layers

https://en.wikipedia.org/wiki/Sidoarjo_mud_flow

Also don't accidentally let a lake--and the boats in it--start filling your tunnels through salt.

https://en.wikipedia.org/wiki/Lake_Peigneur

Wow. I knew drilling could cause land to sink. I never imagined it could cause land to rise.

Fascinating, thanks!

This is fascinating, thankyou!