We get our first glimpse of the volcano from where the road begins a steep, corkscrewing descent from the backbone of Tanna Island. It's a small cinder cone, at 361m, hardly distinct from a mountainous spur that juts into the sea on the far side of the valley. The lush vegetation before us gives way in the middle distance to an ash plain that extends to its foot and, as we watch, a white puff of smoke issues from the peak. A muffled boom, not unlike a thunderclap, carries to us.
It may not dominate the landscape, but Yasur won't be ignored.
After another 10 minutes of rattling over bone-shaking corrugations and potholes, we cross the surreal moonscape of Yasur's zone of devastation - black dunes of ash, interspersed with dull red scoria hummocks, marking ancient lava flows. As we skirt the foot of the volcano, our guide James clearly relishes this rare chance to open the throttle on the Landcruiser and we coast over the black plain. Yasur's cone looms ahead of us, fuming silently.
James Cook sighted Yasur from the sea in 1774, and compared its constant light show to that of Stromboli, a little island off Sicily's north coast that is known as "the lighthouse of the Mediterranean" because it has been in a state of constant, low-level eruption since ancient times. Yasur's style of eruption - regular explosions that toss glowing material into the air - is termed "Strombolian" for the same reason. Because they put on such a reliable show, pleasing and aweing crowds (mostly) without killing them, both Stromboli and Yasur have become attractions for the more adventurous breed of tourist.
But whereas the lookout over Stromboli's active vents is reached only by an arduous, four-hour climb, the road up Yasur takes you to a carpark that's a five-minute easy stroll from the crater rim. That's why it is known as the world's most accessible active volcano. It's the major drawcard on an island that is rapidly becoming the jewel in Vanuatu's tourism crown.
Vanuatu - and Tanna - have lately featured on New Zealand television with the series Meet the Natives, in which a group from a Tanna tribe - who consider Prince Philip to be a deity - visit Great Britain. And TV3 news recently ran footage of Yasur. Once we're on the crater rim, the laconic James becomes noticeably more animated. "This way, this way," he waves. "Best spot this way."
We can see a well-worn path to a spur where there are perhaps a dozen people overlooking the crater. But James is taking us in the opposite direction, and we scramble around after him. We sidle around to a point almost directly opposite the main gaggle of tourists and reach his favoured vantage just as the sun finds a gap in the clouds and gilds the sulphurous vapour rising from the volcano. The warmth it briefly bestows is welcome: we've brought rain-jackets and trousers in case of showers, but still feel the cool breeze.
Below us, perhaps 400m, there are two furiously smoking vents. The volcano snorts like some great, agitated beast, the sound amplified by the sheer, fuming walls of the crater.
We've only been watching for a few minutes when there's a loud bang, and gouts of glowing lava hurtle into the air. They seem to hang there for an impossible length of time before dropping lazily back to earth with heavy, muffled thuds, festooning the crater with incandescent fragments that slowly fade. A couple of seconds after the explosion, a gust of warm air dashes grit into our faces.
The sun has dropped below the horizon and as the light ebbs, it's showtime. Each majestic burst of lava glows a fierce red, and is followed immediately by the sparkle of camera flashes across the crater.
"These are good holes," chuckles James, gesturing at the two explosive vents. "That one over there," he points to a third, glowing sullenly beyond them, "that one kills people."
He laughs his guttural, kava- and tobacco-modulated laugh.
We hardly need reminding that Yasur kills people. It's done for three people in the past few years - two tourists and a guide.
Soon enough, the volumes of grit getting in our eyes - and, we fear, our cameras - prompts us to move to the main vantage. The view here is not quite so good, but it's far more comfortable. And the view is plenty good enough. Italy's Stromboli is world-renowned for the close encounter it offers with an active volcano, but the relaxed guiding regime on Tanna lets you get far more intimate with Yasur than they'd ever dare allow on Stromboli. Somehow, the prudent spectator feels more like edging away than getting closer. But not everyone who comes here is so cautious. Just below us, at the foot of a steep ash slope, there's another broad ledge to which you might feel tempted to descend if you were daredevil - or foolhardy - enough. That, James tells us, is where a Japanese tourist and his reluctant guide were killed a couple of years ago.
Sure enough, just after we decide we're ready to go, Yasur indulges in a bit of chest-thumping, as if to underscore for us the danger that all volcanic tourists flirt with.
First, there's an explosion that sends material flying at an oblique angle, straight towards the spot where we'd been standing half an hour before. Then a larger-than-usual explosion dumps fulminating blobs the size of a grand piano all over the ledge where the fatalities occurred, probably no more than 50m from where we stand. And finally, as we leave, the biggest explosion of the night throws lava so high into the air so that we can see it over the crater rim, even though we're nearly back down at the carpark.
Vanuatu offers plenty that's out of the ordinary, but Yasur is something else: a sight that everyone should see once in their lifetime - and feel grateful to have got away with it.
Air Vanuatu flies to Port Vila twice a week, and daily between Vila and Tanna. Most accommodation providers run tours to Mt Yasur, and fees for permission to climb are included in the price. We stayed at Tanna Evergreen Resort, owned by the son of Yasur's first volcano guide. Access to the volcano is by four-wheel-drive, and a short walk.
What to take: Tour operators provide wind-breaking and waterproof clothing and torches. Wear sturdy walking shoes and take warm clothes regardless of the time of year. Take a camera.
When to go: Yasur can be visited year-round, but is inaccessible in heavy rain (due to a river crossing on the road) and when in a more vigorous state of eruption than normal. Tour operators will advise.
* John McCrystal travelled to Vanuatu with assistance from Air Vanuatu, and Tanna Evergreen Resort.