Why some rocks underground very hot?

Some rocks underground can be very hot due to geothermal gradients, which is the increase in temperature with depth beneath the Earth's surface. This heat originates from the Earth's core and mantle, as well as from radioactive decay of elements within the Earth's crust. Additionally, areas with volcanic activity or tectonic processes can lead to elevated temperatures in subterranean rocks. Consequently, the combination of these factors results in significant heat in certain underground rock formations.