Thermal energy is deposited inside the Earth and serves as the "origin" for volcanic activity. Volcanoes not only erupt on land but also are quite active at the bottom of the ocean. Due to sea water pressure volcanoes located in deep sea locations do not erupt fiercely. Instead, they extravasate lava or emit iron or copper compounds like smoke along with hot water. Volcanoes are the field sites where the thermal energy of inner Earth is emitted.