They are! Europa and Ganymede have cryo eruptions! Europa from geysers and cryovolcanoes for Ganymede, but more evidence is needed for Ganymede. There are missi

They are! Europa and Ganymede have cryo eruptions! Europa from geysers and cryovolcanoes for Ganymede, but more evidence is needed for Ganymede. There are missions planned to fly through the plumes of these worlds. https://en.wikipedia.org/wiki/Europa_(moon)#Plumes https://en.wikipedia.org/wiki/Europa_(moon)#Plumes https://www.lpi.usra.edu/meetings/LPSC98/pdf/1666.pdf https://www.lpi.usra.edu/meetings/LPSC98/pdf/1666.pdf Io is close enough to Jupiter, that thanks to the inverse square law, the forces it experiences cause substantial heating that then results in hot, classical volcanism.