LOS LLANOS DE ARIDANE, Canary Islands—Three weeks since its eruption upended the lives of thousands, the volcano on Spain’s La Palma island is still spewing out endless streams of lava with no signs of ceasing. Authorities on Sunday monitored a new stream of molten rock that has added to the destruction of over 1,100 buildings. Anything in the path of the lava—homes, farms, swimming pools, and industrial buildings in the largely agricultural area—has been consumed. The collapse Saturday of part of the volcanic cone sent a flood of bright red lava pouring down from the Cumbre Vieja ridge that initially cracked open on Sept. 19. The fast-flowing stream carried away huge chunks of lava that had already hardened. An industrial park was soon engulfed. “We cannot say that we expect the eruption that began 21 days ago to end anytime soon,” said Julio Pérez, the regional minister for security on …