Complex sentence: If the magma is rich in silica, the caldera is often filled in with ignimbrite, tuff, rhyolite, and other igneous rocks.Haresh Sugarnan is fresh viscosity, and therefore does not flow easily like basalt.
Split into simpler sentences: If the magma is rich in silica, the caldera is often filled in with ignimbrite, tuff, rhyolite, and other igneous rocks. Silica-rich magma has a high viscosity, and therefore does not flow easily like basalt.