The region of the Earth's interior where heat increases to the point that rocks begin to melt is called the asthenosphere. The asthenosphere is located beneath the lithosphere, which is the rigid outermost layer of the Earth, and extends down to the Earth's mantle. The asthenosphere is partially molten, and the movement of this molten material is responsible for plate tectonics and other geological processes. The temperature in the asthenosphere can reach up to 1,600 degrees Celsius, and the pressure is extremely high. These conditions cause the rocks in the asthenosphere to melt and form magma, which can eventually rise to the surface and erupt as lava.