Graben that drained some of the lava out of 'Alae on Aug. 4, 1969.

Graben that drained some of the lava out of 'Alae on August 4, 1969. Photo taken on September 24, 1969. The graben, more than 10 m (30 ft) wide and locally more than 70 m (230 ft) deep, extended 800 m (2,600 ft) east-northeast from 'Alae. and a trough reached 700 m (2,300 ft) farther. It was an older structure but was reactivated during the draining. A 250-m (820-ft) distance across the area where the graben formed had been previously measured precisely by an electronic distance meter, and remeasurement after the draining showed that the line was 2.7 m (8.8 ft) longer! At 1000 on August 4, rocks along the graben and trough were too hot to touch, and vegetation along the graben was killed (brown bushes and defoliated trees in photo). Later, lava spilled into the graben as 'Alae filled, and in this photo the graben is floored by lava erupted on September 6-7.