Using a GPS receiver, a scientist surveys an established network of benchmarks across the east rift zone of Kilauea Volcano near Pu`u `O`o (background) during eruptive episode 54 on January 30. On the night of January 29, lava inside Pu`u `O`o drained away, which caused the crater floor to collapse by 150 m! The western rim of Pu`u `O`o (visible in background) also collapsed to form a gap about 150-200 m wide and 75-100 m deep.