While we looked, the plume changed colour from dirty white to a dark grey.
"There must have been some kind of collapse down below," said Bob Fewell, our guide from Hawaii Forest and Trail. "That's put a lot more rock and ash into the mixture."
If that sight was a little nerve-racking, the museum's display of photos and charred timbers showing damage from when the new vent first burst into life in March last year was downright scary. Among other things, the eruption shattered the platform from which visitors like us used to view the crater and worshippers of Pele left their offerings of flowers, fruit and, apparently, bottles of gin.
"It's lucky it happened at three in the morning," said Bob laconically, "or someone might have been hurt." Indeed.
Instead, the main victims of the latest outburst have been the plants found in the Hawaii Volcanoes National Park - of which Kilauea forms the centrepiece - many of which have been devastated by acid rain caused by the outpouring of sulphur. As an example, Bob showed us a field of bamboo orchids, normally producing masses of beautiful purple blossoms, whose leaves had been scorched brown. "Usually there would be hundreds of flowers. Now there's only this one ... no," he pointed, "two."
But impressive though all this activity was, even more impressive is the geothermal activity that you can't actually see. Not far below the mouth of the new vent - "maybe only 200-300ft down," according to Bob - molten rock from the core of the planet is boiling to the surface.
A video in the observatory shows that at night the lava glows up through the vent, lighting up the wider crater, giving an eerie picture of the forces lying just below the surface.
But instead of erupting at Kilauea, as it has often before, this time the lava has forced its way to another vent, Pu'u O'o, and from there is pouring via a lava tube into the sea.
Needless to say you can't watch the lava's progress but you certainly can get a feel for what is going on below.
A row of seismographs in the museum record tremors from the various volcanic hot spots around the island - including the taller volcanic peaks of Maunu Kea and Maunu Loa - with wavy lines recording the constant small tremors, and a worrying number of black blotches registering bigger movements.
Exploring the park, you regularly come across plumes of steam caused by rainwater seeping through the earth, coming into contact with the lava and seething back out again.
From time to time the lush tropical forest that covers most of the national park is interrupted by fields of relatively recent lava. Here we found bizarre sculptures in stone, one looking like a seal playing with a giant ball, amazing patterns in the surface of the lava, of which the strangest was the evocatively named entrail lava, lots of small caves, and some mysterious brown pipes through the stone, which turned out to have been formed when tree trunks were consumed by the molten rock.
At a couple of places Bob scrabbled through the volcanic debris and came up with teardrops of stone known locally as Pele's tears, in honour of the goddess, formed when droplets of erupting lava fall back to Earth. And in the museum is a display of the extraordinarily hairlike silica threads, created in similar fashion, known as Pele's hair.
There are also several huge vents from past eruptions, of which probably the most scary is the Devil's Throat, a pit crater about 50m wide and at least 50m deep, which burst forth in 1912 and still appears as though it could erupt at any minute.
It looks so dangerous that a few years ago officials used it to dispose of confiscated marijuana ... until they discovered that some desperate potheads were rappelling down the crumbling lava walls to rescue the stuff. You can even explore a lava tube from earlier eruptions, a 120m stretch of the Thurston Lava Tube having been developed as a walkway, with stairs and lights allowing visitors to stroll through a rock tunnel 10-12m in diameter where molten rock once flowed. If you're feeling really adventurous there's a further 330m length of the tube you can scramble through by torchlight.
As we strolled through I couldn't help thinking that just a couple of kilometres away molten rock was pouring through another tube just like this on its way to the sea.
But, amazingly, everywhere life was springing forth. Even on the most recent lakes of stone, plants are starting to establish themselves. The older lava flows support healthy tropical forests. Birdlife is obviously flourishing. And at one point Bob screeched our vehicle to a halt to excitedly point out a large beautifully marked goose, stepping delicately across the rock.
"That," he said, "is a nene, the Hawaiian national bird, and it's very rare. At one point I think there were only 35 of them left though the numbers have recovered since. We very rarely see them."
Pulling out his camera, he added, "You know you've struck something special when the guide starts taking photos."
CHECKLIST
Getting there: Air New Zealand flies direct to Honolulu up to three times per week. Long-term airfares in Pacific Economy class are available from $1500 per person return plus airport and government costs.
Where to stay: Shipman House in Hilo is a charming luxury bed and breakfast in a historic mansion and a great basis for exploring the volcanic attractions. See hilo-hawaii.com/.
What to do: Hawaii Forest and Trail's volcanic tours are on the web at hawaii-forest.com. You can find out about Hawaii Volcanoes National Park at nps.gov. There's a webcam on the rim of the Halema'uma'u crater, from which the glow of the lava can be seen at night.
Further information: For general information about visiting Hawaii see discoverhawaii.co.nz.
Jim Eagles visited Hawaii as guest of Air New Zealand and Hawaii Tourism Oceania.
