Linked from
The 19 pages that link to Lava tube, each with the reason it gives.
Lava flowBroader topic: Tubes insulate lava and can carry it far beyond the exposed flow front.
LavaBroader topic: Tubes can carry lava far beyond the visible source and remain as caves.
HallasanBroader topic: Hallasan’s eruptions produced lava tubes across Jeju’s volcanic slopes.
Lava fieldBroader topic: Tubes can carry lava far beyond a field’s visible vents.