Magma also contains gases, which expand as the magma rises. Lava domes are formed by the extrusion of viscous felsic magma. Igneous rock is formed through the cooling and solidification of magma or lava. Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They may be formed by upwelling of volcanic magma or extrusion of lava. Glass can form naturally from volcanic magma. Phreatomagmatic eruptions are eruptions that arise from interactions between water and magma. They are formed by the cooling of molten magma on the earth's surface. Explosive eruptions are characterized by gas-driven explosions that propels magma and tephra. Strombolian eruptions are driven by the bursting of gas bubbles within the magma. Intrusive rock forms within Earth's crust from the crystallization of magma. It forms from solidification of a magma ocean. This implied that there was a rising column of fresh magma beneath the volcano. Embedded in the granite are xenoliths or pieces of foreign rocks entrained in the magma. The difference is the result of the lower viscosity of the magma that forms scoria.