Lava spattering from the west vent in West Gap Pit of Pu`u `O`o sails over a hornito on the rim of the pit, now filled with lava. Several flows spilled from the pit down the northwest flank of Pu`u `O`o, adding yet more lava to the west shield. The hornito and West Gap Pit were present before this most recent activity.

Within minutes of erupting on the crater floor of Pu`u `O`o, lava drains back into the East Pond Vent and causes vigorous lava spattering as high as 10 m. The flow and drainback lasted only a few minutes. Such activity is probably caused by rising bubbles of gas that lift lava to the surface. The crust breaks, allowing gas to escape vigorously and drive brief spattering or a low fountain. When most of the gas has been lost, lava drains back into the vent. This activity is called gas pistoning. For full sequence of images, see September 2003 archive.