Volcanic activities have a profound influence on the earth's landforms. Solid, liquid or gaseous materials may find their way to the surface from some deep-seated reservoir beneath. Molten magma is mobile rock that forces its way into the planes of weakness of the crust to escape quietly or explosively to the surface. The resultant landforms depend on the strength and fluidity of the magma, the types of cracks, faults and joints that it penetrates, and the manner in which it escapes to the surface. Magma while thrusting its way up to the surface may cool and solidify within the crust as plutonic rocks resulting in intrusive landforms. Magma that reach the surface and solidify, form extrusive landforms. Rocks formed by either plutonic or volcanic activity are called igneous rocks.