When we got to the lodge the night before, the host asks us "so you are aware of the eruptions right?" Unfortunately, we were unaware that Mt Tongariro had erupted twice in the last six months, the second time being 3 weeks before we got there. Because of this, we were not allowed to hike the whole crossing. After having done the section we were allowed to hike (and after reading this article from National Geographic), I actually can't believe we were allowed up there! We were basically on Mt. Tongariro and the article states that scientists predicted another eruption within the few weeks following the last one.
Anyway, we're home and in one piece so obviously no eruption happened while we were hiking. We were allowed to hike out and back, basically to the viewpoint of the Emerald Pools and Blue Lake, making our out-and-back hike a similar distance to the point-to-point crossing (19.4km). We would have loved to hike to the top of either Mt. Ngauruhoe (Mount Doom from LotR) or Mt. Tongariro, but the fog/clouds were so thick this day we knew we wouldn't have seen anything up there anyway.