User blog comment:Unownshipper/Metallurgists Wanted: Rapture's Natural Resources/@comment-3967731-20140810040802/@comment-75.36.139.127-20140812035629

The lava in the tubes (and hole in the seabed it came thru...)- better if it was super hot water with some bioluminescent algae/bacteria in it (or lining the tube) - temp/pressurs probably lowered from what it might be in deep well where water is injected.

Lava hardens with heat loss, and tubes you want to keep flowing is the worst place yo want that.

Also lava would mean an active volcanic site (not just hot water from thermal vent/drill-hole )

Structural failure of the pipes  also could be an issure (basaltic lava melt temp is near partial loss of structure for steel). Corrosion in that heat might be another issue (such tubes just having to be replaced way too often).