A view of the summit lava lake at dusk. The lava lake is contained within a crater informally called the “Overlook” crater, and this crater is set within the larger HalemaÊ»umaÊ»u Crater. The lava lake is about 50 m (160 ft) below the rim of the Overlook crater. In the southeast portion of the lake, a persistent spattering source ejects spatter more than halfway up the Overlook crater walls. Photo courtesy of USGS/HVO

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

Six years is a blink of an eye in geologic time, but it can fly by for people, too. In a way, it doesn’t seem very long ago that the summit eruption began, with a small explosion that threw blocks around the Halema‘uma‘u Crater rim. On the other hand, so much has happened at the new vent that it is getting harder to remember what it was like when Kīlauea Caldera was open to traffic, and Halema‘uma‘u was quiet.

The summit eruption began on March 19, 2008, following several months of increasing seismic tremor and gas emissions. A new crater, about 35 m wide, formed that day on the wall of Halema‘uma‘u Crater. We informally call the new crater the “Overlook” crater, as it formed directly below the closed visitor overlook. Over the next two years, the Overlook crater enlarged dramatically due to frequent collapses of the overhanging crater walls. A handful of small explosions threw blocks and fresh spatter around the Halema‘uma‘u Crater rim. Lava was sporadically observed in the new crater during 2008 and 2009, but was very deep – about 200 m below the floor of Halema‘uma‘u Crater.

The eruption changed in February 2010, when a more persistent lava lake appeared in the crater and slowly rose to higher levels. The lake disappeared only once, when it drained for a week during the Kamoamoa eruption in March 2011.

The lake today is quite large, about 200 m (660 ft) long by 160 m (525 ft) wide, making it one of the largest lava lakes on Earth. The lava level has been fairly shallow over the past year, about 30-60 m (100-200 ft) below the floor of Halema‘uma‘u. Normally, lava upwells at the north margin of the lake and quietly migrates towards the south margin, where it sinks back into the magmatic system. A persistent spattering source is often present in the southeast portion of the lake, throwing spatter up to 20 m (65 ft). The gas plume is normally carried towards the southwest in the tradewinds, but can drift towards other parts of the island when winds shift.

By closely monitoring the eruption, we have learned a number of interesting things. For instance, geophysical data indicate that the lake has a very low density, close to that of water, due to abundant gas bubbles in the lava. We also know that the lava level fluctuates nearly perfectly in tune with the pressure of the summit magma chamber, meaning that the lava lake acts as a kind of liquid pressure gauge. Moreover, a number of indicators measured over the past few years – including lava level, gas emissions, and lava chemistry – reaffirm that an efficient magmatic connection exists between the summit and east rift zone vent at Pu‘u ‘Ō‘ō.

The eruption has also been a draw for National Park visitors, who can view the strong glow from Jaggar Museum. For residents of the Big Island, the glow is another reminder of how close we all live to volcanic activity.

But as much as the eruption has enhanced scientific understanding, or boosted tourism, this is little consolation for those adversely affected by the persistent vog. The primary hazard of this eruption has been the long-term elevated gas emissions that are carried downwind into residential and agricultural areas. Vog is a respiratory irritant and can aggravate existing respiratory problems, like asthma. Farming and ranching, particularly in the Ka‘ū district, have been hit hard. The increased amount of sulfur dioxide can cause chemical burning of cultivated plants and faster corrosion of metal fencing that is essential for ranching.

When will the eruption end? There are no signs of any imminent change in the eruption, and recent activity has been remarkably steady. We have to look at Halema‘uma‘u’s history to gain longer-term insight into the future. There was lava lake activity at the summit from at least 1823 to 1924 – over a hundred years – with most of it focused around Halema‘uma‘u. This history shows that Halema‘uma‘u has the potential for eruptive activity lasting decades. Now entering its seventh year, the current eruption may turn out to be a repeat performance of Halema‘uma‘u’s sustained lava lake.

More details on the summit eruption can be found online in a new fact sheet (http://pubs.usgs.gov/fs/2013/3116/).

KÄ«lauea Caldera from HVO (2/27/14-3/13/14)

Halemaʻumaʻu Overlook Vent from HVO (2/27/14-3/13/14)