Lex could survive a lot. His body had literally blown up and had then come back together. So being in the center of a volcanic eruption, for him, would be no problem. That was not the same for Jack.
Now Jack, for a fairy, was strong. Heck, even for a mortal, he was strong. He was far superior to most Nascent realm cultivators, even if he never used his fairy dust, or his most lethal weapon, his puns. But was he strong enough to survive being in the center of a volcanic eruption? It was questionable, since survival didn't necessarily mean remaining in top condition.
A volcano in hell, though? Well, he would have to find out.
The eruption wasn't instantaneous. There was a buildup, however brief. Jack was studying the cage Tinker was in when an earthquake struck. By now, there had been a few earthquakes, but none of them were this bad. As if that was not enough, a deep rumbling began all around them.