Located next to the park road just north of Norris on the Norris-Mammoth section of the Grand Loop Road, Roaring Mountain is a large, acidic thermal area (solfatara) that contains many steam vents (fumaroles) which make noises ranging from a nearly inaudible whisper to a roar that can be heard miles away. In the late 1800s and early 1900s, the number, size, and power of the fumaroles was much greater than today.