Explore the Hydrothermal Areas

mud pot at Bumpass Hell
This mud pot can be seen from the Bumpass Hell boardwalk.

NPS Photo

The remarkable hydrothermal features in Lassen Volcanic National Park include roaring fumaroles (steam and volcanic-gas vents), thumping mud pots, boiling pools, and steaming ground. Water from rain and snow that falls on the highlands of the park feed the hydrothermal system. Once deep underground, the water is heated by a body of hot or molten rock beneath Lassen Peak. Rising hot water boils to form boiling pools and mud pots. Super-heated steam reaches the surface through fractures in the earth to form fumaroles such as those found at Bumpass Hell and Sulphur Works. These features are related to active volcanism and are indications of the ongoing potential for further eruptions from the Lassen "volcanic center."
 
Hole in ground at Sulphur Works where a visitor stepped off-trail and broke through.
A visitor stepped on thin ground hiding boiling water and mud at Sulphur Works

NPS Photo

Hydrothermal Area Danger
For your safety, stay on established trails and boardwalks. Ground in hydrothermal areas can look solid but may actually be a thin crust hiding pools of acidic boiling water or mud. Traveling off-trail in these areas may result in severe injury.

Visitors Have Been Injured When Traveling Off-Trail.

  • A visitor was severely burned in the summer of 2010 after he traveled off-trail in the Devils Kitchen hydrothermal area. He stated that "It feels like I put my leg in a flame."
  • On May 5, 2012, a visitor was air-lifted to a regional burn unit after stepping off the sidewalk at Sulphur Works. The ground appeared solid, but she easily broke through a one-inch crust, exposing her foot and ankle to boiling acidic water and mud.
 
 

Contact the Park

Mailing Address:

PO Box 100
Mineral, CA 96063

Phone:

(530) 595-4480
Park information

Contact Us