Scientists rush in where fools fear to tread
As they note, this happens in Iceland at Grímsvötn.
When I were a lad, I used to work for Vatnamælingar, the Department of Hydrology at the National Energy Authority. Summer job; but it was fun, we covered almost the whole country, spend 12 days up in the mountains, 2 days in town, while the Sun and weather lasted. 100 hour work weeks, with overtime and per diem. Outdoor work, occasional use of explosives, large drills (I still have the boots) etc and so forth.
And, sampling rivers from ice melts on volcanoes, to look for spikes in dissolved sulfates etc, as possible predictors for eruptions. And especially jökulhlaup. Including Skeiðará which drains Grímsvötn and the rivers which drain Katla volcano.
The thing was, you can smell the sulphur.
And once the sampling rig is deployed it takes 10-20 minutes to retract it (it was built into the truck). Now you could just cut it, except at Katla the bridge was a girder bridge, and you had to actually retract the whole gear, couldn't cut the arm, cutting the "fish" off the wire wouldn't help. And every time I was hanging on the outside of the bridge guiding the "fish" down into the river, the smell got noticably stronger... and stronger... and stronger.
Oh, and it takes ~ 30 minutes for the flood crest to reach the bridge once it starts.
So, one summer we spend several weeks on the north coast, and for weekend leaves we flew back, leaving the gear up north.
So one time I asked how we would get to Skeiðará if there was an eruption? Since clearly we'd want to be there ASAP to start measurements.
I was rather surprised when my boss said, quite seriously, that he'd fly up north and stay with the equipment and I could stay in town, you'd have to be an idiot to actually go there during a real eruption. Very disillusioning.
Then, in 1996, and again 1998, there was a medium eruption, and there, on the web, were me old mates, with the trucks. Measuring.
The time to run is when Bárð&arbunga erupts, explosively.
Now that's a volcano.
OoEr, When I Were a Lad... actually here is a good set of photos from a German who did a short loop around the southwest, that kinda stuff...
Now, wtf did they switch to Nissan trucks. Yuck.