The eruptions at Uzu-san were among the first to be recorded by modern means (and work here significantly advanced science in early detection). Here you can see video footage of eruptions in action, and before and after photos that clearly show new land masses forming.
The museum, a short walk west from the Tōya-ko Onsen bus terminal, is part of the Tōya-ko Visitor Centre, which also has excellent (and free!) information on the local topography and indigenous flora and fauna.