The Largest Hydrothermal Area in the Park
Bumpass Hell trail – Lassen Volcanic National Park
Bumpass Hell is the largest hydrothermal area in the park and marks the principal area of upflow of steam and discharge from the Lassen hydrothermal system. The temperature of high-velocity steam jetting from Big Boiler, the largest fumarole in the park, has been measured as high as 322°F (161°C), making it one of the hottest fumaroles in the world. The steam heated waters are typically acidic and are not safe, even for bathing.