Hawaiian Volcano 


Mauna Loa


Other Volcanoes

Volcanic Hazards


The episode 55 eruption has occurred chiefly at three sites in the Pu`u `O`o area. A fourth vent appeared on Monday, May 12. The accompanying figure may be useful to those who wish a better understanding of the Pu`u `O`o cone and adjacent vents. Topographic contours on this figure are imprecise, especially on the cone's west flank, where a large pit has grown through repeated subsidence whenever magma drains away beneath the cone. Our intent is merely to depict the setting. Bold lines on the figure show the outline of main crater and the west-side pit (now an elongate gash). The active vents are shown as large dots.

Vent 1
The crater floor of Pu`u `O`o became active again on February 24, 1997, the starting date of the episode. A crater-filling pond appeared, and successive flows kept resurfacing it until the pond was within 60 m of the crater rim. Activity diminished, the pond crusted over to form a new floor, and a small spatter cone was built up on the crater floor. This spatter cone is intermittently active.

Vent 2
A spatter cone formed on the southwest flank of Pu`u `O`o on March 28. This cone was positioned at the site of a previous vent that built the episode 51 shield. We originally referred to this new cone as the "51 vent site" while we waited to see if it became long lived. By mid-April the vent clearly was a major player. Needing a better name, we now call it the "55 spatter cone" to indicate its origin and its episode number. This vent has been robust.

Vent 3
Another vent began issuing lava from the south side of Pu`u `O`o on April 18, 1997. This vent was in roughly the same position as the vent that built the episode 53 shield, so thus went briefly by the name "53 vent site." We now call it the "uplift vent." It, too, is robust. This vent formed when lava flows were deformed against the flank of Pu`u `O`o. New lava then began to issue from this site, feeding a near-constant stream of lava onto the flowfield. The mechanism of deformation for the third site remains unclear but may be explained by a small, shallow intrusion. At issue is whether the site is connected at depth to the magma supply beneath Pu`u `O`o, or whether it is a rootless feature fed via shallow connection to the spatter-cone vent on the southwest flank.

Vent 4
On May 12 at 1245 hrs, a new vent was observed at the base of Pu`u `O`o between the 55 spatter cone and the uplift vent. All other vents were inactive at this time. The May 12 vent was feeding a channeled flow that had advanced 1.5 km southward, according to a recent report on May 13.

HomeVolcano WatchProductsPhoto GalleryPress Releases
How Hawaiian Volcanoes Work

The URL of this page is
Updated: 31 March 1998
This page was created on April 18, 1997, and modified on May 13, 1997.