Maybe even a lava tube that runs to deep into the ground?

It would probably be better to add this to the 1.11.2 TODO list instead, and backport later if necessary..

hmm.. i still using 1.7.10

We are only developing for 1.10/1.11 now. 1.7.10 is retired and no new features will be backported before 1.10.

to bedrock....

to bedrock....

Could maybe even add a config option for the depth of the tube.

yes yes.. good option..
but for me it will be alwas bedrock, i using vulcanoes for building deep structures :)

Added for 1.10.2 in 33a56e9 and 02c113a

mc-1.11.2 label? you are working on 1.11.2? we're waiting for it eagerly :)