Volcano Watch | USGS Hawaiian Volcano Observatory

The steady stream of lava cascading down the slopes above Kalapana village died out shortly after March 5 this year, when the spectacular Kamoamoa fissure eruption began. That fissure eruption lasted four days and was followed by a pause in activity on the east rift zone that persisted for 17 days. On March 26, lava returned to Pu`u `O`o crater, which has been the main vent area for much of the 28-year-long eruption.

For the last month, the activity in Pu`u `O`o has remained relatively stable, with a small lava lake on the crater floor. Lava rises at one end of the lake, slowly migrates to the opposing side, and sinks. Occasionally, the lava level rises a small amount, but it has, overall, stayed deep below the crater rim. With lava confined to the crater in relatively unremarkable fashion, it begs the question, What’s next for Pu`u `O`o?

The answer will likely have important ramifications. If lava were to exit Pu`u `O`o on its east side, flows could return to the Kalapana area and again threaten houses (three occupied houses have been destroyed over the past year). If lava exits on the west side, flows will remain in the National Park and may be more accessible for visitors.

Let’s look at some recent examples of these two scenarios. In January 1997, an intrusion and fissure eruption occurred much like that in March of this year. The floor of Pu`u `O`o crater collapsed as magma drained back into the conduit—again, like the recent episode. There was a pause of 23 days, after which Pu`u `O`o slowly refilled with lava. Eventually, lava began pouring out from vents on the west flank of Pu`u `O`o.

These flows traveled south and eventually reached the sea, establishing the first of several lava tubes that carried lava away from Pu`u `O`o for the next 10 years. The flows expanded the west margin of the flow field, consuming more of the Chain of Craters Road. Since the flows were often just a short walk from the end of the road, lava-viewing was exceptional and because they flowed in the Park, there was no hazard to Kalapana residences.

In late June 2007, another intrusion and brief eruption occurred, and the floor of Pu`u `O`o collapsed as magma once again drained back into the conduit. This was followed by a pause of 10 days, after which lava started to refill Pu`u `O`o crater. On July 21, 2007, fissures opened on the east flank of Pu`u `O`o, and flows focused on the Fissure D vent. Flows were directed northeast for the first four months after which a vent wall collapse diverted them to the south.

The Fissure D vent (also called the TEB vent) remained active for three-and-a-half years and sent flows down the east side of the flow field. These flows destroyed several occupied houses and buried a significant amount of private property in Kalapana Gardens and Royal Gardens subdivisions. Because the flows were on state and private property, access to them was severely restricted, making lava viewing more limited.

The two examples above show the very different consequences for flows exiting Pu`u `O`o from the east versus the west sides. But in both cases, flows traveled south towards the ocean. There is a third possibility that flows could exit Pu`u `O`o and travel north of the rift zone. In this case, the flows could slowly migrate northeast toward communities north of Pahoa. This possibility, however, is much less likely, as Pu`u `O`o prefers to send its flows down the much steeper slopes to the south.

Right now, it’s impossible to tell whether lava will leave Pu`u `O`o on the east or the west side. As Pu`u `O`o’s magma reservoir continues to pressurize over the coming weeks, we may begin to see more changes on the surface that could provide an indicator.

While it is too soon to tell what course the eruption will take in the coming weeks, HVO will continue to keep a close eye on Pu`u `O`o and watch for Pele’s next move.