A flyby revealed that Barvinn would be consumed by lava, and the overland route would be cut before anyone can use it. The railroad would likely manage to stay open almost to the end, however.

The lava was following ground contours and flowing much like a river, and flying parallel allowed them to estimate the rate of advance. They determined that Barvinn had two hours before the flow reached it.

There was still some doubt as to whether Salbarii was in imminent danger or would need to be evacuated in the longer term. Will realised that the only way to determine this was to get more data.

“So what you’re saying WIll is that Grim and I have to hop off, drill in more sensors, and hopefully not be burned alive?” said Taeva with a certain edge to her voice.

“It should be perfectly safe” said Will reasonably, “It’s not as though we’ll be doing this on the most active parts.”

Against their better judgements, they agreed to go along with Will’s plan. Fortunately the locations they used were currently quite undisturbed, and with the help of rebreathers they had planted half a dozen additional sensors within an hour or so. The additional data from the new sensors started to contribute to the larger picture.

" Well" said Will, " The flow rate has dropped because a plug has built up in the mountain somewhere. Now, sometimes this is a good thing as it can block the route to the surface and thus cause the eruption to end."

“I feel there’s a But coming” said Max.

“Um, yes” continued Will, “In cases like this where there is a lot of pressure underneath, a plug of this sort tends to be short-lived. When it breaks, it will be like a dam bursting; the lava flow will massively increase and a chink of the mountain may be quite literally blasted off.”

“And that’s bad is it?”

“According to the sensors and the model, Mount Salbarii is under rapidly increasing stress. Within a few minutes the plug is going to fail and a massive eruption will take place. Worse, a huge cloud of super-hot ash and gas will be ejected from the mountain and will hurtle out across the coastal plain. The town of Barvinn will be destroyed and anyone in it will die.”

“On a positive note the town of Salbarii will probably not be too badly affected, though a lot of ash is going to fall on it. In the long term the town may end up being abandoned.”

“I’m sure they’ll all be really pleased at that Will” said Grim sarcastically.

“Don’t shoot the messenger” snapped Will, reddening.