The lava pond resides deep within the vent cavity in Halemaumau, at a depth of about 180 m (200 yards). Photograph taken from the former Halemaumau Overlook on June 20. (Photo courtesy of HVO)

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

If you have visited the HVO Web site recently, you may have noticed that the Halemaumau Overlook Webcam has shown exceptional views of the lava pond within the Halemaumau vent cavity.

The lava surface is about 60 m (65 yards) wide and consists of large crustal plates broken by long, thin incandescent cracks. At spots along the pond margin, small spattering sources emit gas and throw lava up to 20 m (22 yards) above the pond.

Lava upwells at the north margin of the pond, then sinks back into the conduit at the south margin.

Since early February of this year, we have enjoyed a period of remarkable stability in the Halemaumau vent, with the lava pond continuously visible now for almost five months.

This stability is unusual when we consider that, for most of the ongoing summit eruption (which began in March 2008), lava pond behavior in the vent has been highly variable.

Our first view of lava was in September 2008, almost six months after the eruption started. Lava was probably present deep in the vent before September but was out of view due to thick fume.

For the rest of 2008, lava was seen only a few brief times and was usually too deep in the conduit to be visible (in part because the vent opening was smaller early in the eruption).

The lava pond returned in February 2009 for a few days and in March 2009 for a similarly brief period. In the intervening periods, only small holes, emitting gas, could be seen on the floor of the vent cavity, because the lava had retreated to deeper levels in the conduit.

One of the longest periods of sustained lava viewing followed in June 2009, when a lava pond was present for about a month. The pond alternated between periods of vigorous roiling and more placid, crusted movement. This phase was terminated by a large vent collapse that buried the floor of the vent cavity on June 30, 2009.

For the rest of 2009, lava was only occasionally visible. For instance, the lava pond appeared for a few days in early October and in late December. Although these periods were brief, they often displayed spectacular cycles of rising and falling of the lava surface. Again, when the pond was absent, there were simply small degassing holes and pits on the floor of the vent cavity.

The current phase of lava pond activity began Feb. 11 this year, when a large collapse occurred at the bottom of the vent cavity. This may have widened the upper conduit and enlarged the pond, so that the pond has not been able to completely crust over, thereby providing a consistently open lava surface.

The continuous views have already provided improved insights into the dynamics of the vent, aided by the excellent high-resolution Webcam at the Halemaumau Overlook that provides views around the clock.

For instance, we confirmed our initial suspicion that a particular kind of seismic signal (called a very-long-period event) can be triggered by rock falls into the pond. Also, we’ve observed that these rock falls can trigger violent spattering and gas release in the pond, which may explain the handful of explosions that occurred in the vent in 2008.

Unfortunately, it is impossible to say how long this phase of continuous lava pond activity will last. But we can speculate as to how it could end, when we consider earlier activity. The previous phase of prolonged lava pond activity, in June 2009, ended with a large collapse of the vent cavity.

Considering that much of the vent cavity is still severely overhung, another large collapse could occur, burying the pond beneath a pile of rubble again for some period of time. Ultimately, though, Pele will decide how long this lava pond show will last.