View is near Crater Rim Drive about 500 m from Halema`uma`u looking south. Lava blocks thrown from Halema`uma`u during a series of steam-driven explosions in 1924 litter the caldera floor, covering deposits of the Keanakako`i Ash Member erupted during much larger explosions that ended in A.D. 1790. The block in lower left is about 0.5 m in diameter.
The explosions from Halema`uma`u occurred after its active lava lake had subsided about 170 m between January and early May 1924. In April, strong earthquakes and ground movements along faults on Kilauea's lower east rift zone, and subsidence at the caldera, were evidence that magma had withdrawn from Halema`uma`u and moved far down the rift zone. Hundreds of explosions between May 6 and 24 were apparently triggered when ground water flowed through the heated rocks beneath the crater. Boulders weighing several tons were thrown as far as 1,000 m from Halema`uma`u. A photographer who ventured too close to the vent between explosions was struck by a rock and killed during a sudden explosion.
The explosions and rock falls more than doubled the size of Halema`uma`u from 430 to 920 m and increased its depth to 410 m!