A geothermal spring, or more commonly known as a hot spring, is a natural spring that’s heated by geothermal heat, which is heat from the Earth’s interior.
When water in volcanic areas comes into contact with rocks that’s heated by magma, naturally it will get warm and rise back up to the Earth’s surface again, forming a pool. In active volcanic zones, sometimes this water may even get extremely hot – like the ones at Yellowstone National Park in the United States – so it is best to keep your distance from these kinds of hot springs.