Many natural phenomena that occur on the Earth's surface due to processes occurring in the upper mantle of the Earth. Some of them is Deep Heat Flow. Heat flows constantly from its sources within the Earth to the surface. The Earth's internal heat was originally generated during its accretion, due to gravitational binding energy, and since then additional heat has continued to be generated by the radioactive decay of elements such as uranium, thorium, and potassium. The geothermal gradient is the rate of increase in temperature per unit depth in the Earth. This geothermal energy is transferred to Earth's surface by diffusion and by convection movement of magma (molten rock) and deep-lying circulating water.