Hydrothermal Areas

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Learn where and how to find hydrothermal or "hot water" areas at Lassen Volcanic National Park.


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.

Top: A waist-deep hole remains where an individual broke through a thin crust at Sulphur Works after stepping around the barrier. Bottom: The badly burned foot of a visitor who traveled off-trail in Devils Kitchen hydrothermal area.
Top: A thigh-deep hole where a person broke through a thin crust at Sulphur Works after stepping around the barrier. Bottom: The badly burned foot of a visitor who traveled off-trail in Devils Kitchen hydrothermal area.

NPS Photo

Hydrothermal Area Danger

Hydrothermal or hot water areas are intriguing and spark our curiosity about the wonders of our natural world. You may feel tempted to explore thermal features up close by walking beyond established trails and walkways. However, a venture to satisfy curiosity may land you in the hospital with severe burns. It is dangerous and unlawful to travel off-trail or enter waters in hydrothermal areas.

Improve your safety in hydrothermal areas:

  • Stay on trails or boardwalks. Ground in these areas may look solid, but may actually be a thick crust hiding pools of acidic, boiling water or mud.
  • Note that footprints are not evidence that ground is solid (only evidence someone took unnecessary risk).
  • Do not touch or enter hydrothermal water. Even if it is not hot enough to burn you, prolonged exposure to sulfuric acid in the water and gases can cause damage to your skin and lungs.
  • Set a good example! If you see someone attempting to walk in a closed area, remind them of the risk they are taking or inform park staff.
  • Keep close watch on young children—do not let them roam about freely.

Visitors Have Been Burned While 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 airlifted to a regional burn unit after stepping off the sidewalk at Sulphur Works. The ground appeared solid, but she easily broke through the one-inch crust, exposing her foot and ankle to boiling acidic water and mud.


Where to Find Them

Bumpass Hell

The largest hydrothermal area in the park is accessible by trail only in the summer and fall (approximately June through October). The 3-mile, round-trip Bumpass Hell Trail begins from the parking area on the park highway (7 miles from the Southwest Entrance). A boardwalk provides up-close access to some of the hydrothermal features in the 16-acre basin.

Little Hot Springs Valley

Located at the bottom of a steep valley, steam vents can be viewed via the park road with binoculars. There is no trail in this area.

Pilot Pinnacle

There is no trail or parking area for this feature which includes steam vents, boiling pools and mudpots. One part of this area is visible from the park road; "Fart Gulch" is a chalk-colored hillside on the north side of the road near Little Hot Springs Valley. The sulfur smells makes this area easily identifiable.

Sulphur Works

The park's most easily accessed hydrothermal area features boiling mudpots and steam vents viewable via a sidewalk. A parking area with sidewalk access to the features is located one mile north of the Southwest Entrance. Learn more about visiting Sulphur Works in summer/fall or spring/winter.

Devils Kitchen

This moderate hiking trail in the Warner Valley area leads visitors to this bubbling cauldron. Explore steam vents, mudpots, and boiling pools on a short loop.

Boiling Springs Lake

Accessed from the Warner Valley trailhead, this short hike leads to a bubbling lake with a temperature of the lake around 125 degrees. Mudpots and steam vents line part of the shore and drainage creeks. Be careful to stay on clearly marked trails in this area as the ground around the lake is unstable; travel in these areas may result in severe injury.

Terminal Geyser

Access this gigantic steam vent from the Warner Valley trailhead. Although not a true geyser, this spurting steam located in the middle of a creek, provides a spectacular show!

Cold Boiling Lake

Enjoy a short hike from the Kings Creek Picnic Area to this quaint lake where "cold boiling" bubbles rise like soda water.


Explore with 360-Degree Photos

Last updated: April 7, 2024

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