Thus a flow was unable to materialize. Rhyolitic lava flows are much more viscous and thus form larger, more steep-sided features. A dome is a viscous dacitic to rhyolitic lava flow that was too viscous to move very far. Shield volcano a volcano with very gentle slopes composed almost entirely of very fluid basaltic magma. Pyroclastic is a general term for rocks and deposits generated by explosive eruptions.
Pumice is a rock composed of little more than the sides of tiny bubbles.
It can be less dense than water. Pyroclast is a general term for a fragment of of rock ejected during an explosive eruption. Pumice is an example of a pyroclast. Tephra is a deposit of pyroclasts, that have not yet turned into a rock. Pumice is coarse tephra, ash is fine-grained tephra.