In July 1986, the conduit feeding magma to Puu Ōō ruptured, and the eruption abruptly shifted downrift to form the Kūpaianahā vent. With the new vent came a new style of eruption: continuous, quiet effusion from a lava lake replaced the episodic high fountaining. After a few weeks, a roof formed over the main lava outflow channel, which created a lava tube. The lava tube allowed the fluid pahoehoe lava to retain heat and flow long distances. In less than a year, overflow from the lake created a broad and low shield about above Kūpaianahā.