If ground water hadn't come in contact with a source of magmatic heat, a phreatic eruption wouldn't have occurred. If erosional processes didn't occur, there would be more fossils. The geothermal gradient is low in subduction zones. The continental crust base is dry. Granite is not easily soluble.
Rivers meet obstacles such as resistant rock outcrops or fault lines.
Volcanic magma is highly silicic. Regional metamorphism takes place. There aren't many fossils. Striped magnetic anomalies are detectable. They don't flow in the same direction over their entire length.