Bumpass Hell is Lassen’s largest hydrothermal area and features fumaroles, hot springs, and mudpots. Devils Kitchen is located about 2 miles south of Lassen Peak. From the Warner Valley Trailhead it is a 4.2 mile round trip to Devils Kitchen. A 1983 USGS inventory of the thermal area included about 75 hot springs and fumaroles. (
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The highest temperature of water generally is close to the boiling temperature at the altitude of the particular spring or fumarole The intensity of Lassen’s hydrothermal features varies both seasonally and from year to year. In spring, when cool ground water from snowmelt is abundant, the fumaroles and pools have lower temperatures, and the mud in mudpots is more fluid. In late summer and in drought years, the features become drier and hotter because there is less mixing with shallow, cool ground water.
For more background on Lassen hydrothermal system check out the USGS Fact Sheet “Hot Water in Lassen Volcanic National Park -- Fumaroles, Steaming Ground, and Boiling Mudpots”. (
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Signs along the boardwalk in Bumpass Hell:
One Furnace, One System -- N 40°27.443' W 121°30.140'
Molten rock -- magma -- lies miles below your feet. The magma that is chambered there is the same that fed the eruptions of Lassen Peak and other dacite-dome volcanoes like Bumpass Mountain. The magma
superheats a reservoir of groundwater deep within the Earth. Steam, as hot as 464°F (240°C), rises and condenses into water again, mixing with percolating groundwater nearer the surface. The mixture produces sulfate water that escapes through park hydrothermal features at temperatures about 200°F (93°C).
Bumpass Hell is the largest “escape valve” for the underground boiler or hydrothermal system and is the main upward vent. Lesser upward flow emits at Sulphur Works, Devils Kitchen, Boiling Springs Lake, and Little Hot Springs Valley. One furnace, one system.
Sulfur Link -- N 40°27.449' W 121°30.136'
The lava rock that once filled this area has been eaten away and altered into clay by sulfuric acid. The acid can be linked to a high temperature form of sulfur (sulfur dioxide) released from the magma body that fires Bumpass Hell. The rotten-egg smell that fills the air can also be linked to sulfur. It is hydrogen sulfide gas a forerunner to the formation of sulfur -- yellow, pyramid-shaped crystals that form on the ground here.
The white and orange-yellowish ground crusts are also sulfur relatives, called sulfates. Sulfate-rich water evaporates at the surface, leaving the colorful sulfates behind. The sulfates build up in ground crusts and change colors, depending on how wet or dry the crusts are.
Big Boiler -- [N 40°27.461' W 121°30.123']
Big Boiler is the hottest fumarole -- within a non-erupting volcano -- in the world. The steam temperatures measured here reach as high as 322°F (161°C). That’s mighty hot. But for perspective, flowing lava can reach 2,000°F (1,093°C) and the core of the Earth weighs in at a mere 12,000°F (6,648°C).
Getting Bigger. Constant churning action and heat eat away at surrounding clay banks, enlarging Big Boiler’s size. Compare the historic photograph shown below to the present-day scene. Big Boiler has collapsed a huge portion of the surrounding clay crust since this photograph was taken in 1915. Just a few years ago Big Boiler engulfed a portion of the boardwalk that once extended out from here.
Mudpot Metamorphosis -- [N 40°27.439' W 121°30.095']
A mudpot is the intermediate phase between a fumarole (steam vent) and a boiling spring. It has less water than a boiling spring, but more than a fumarole. In wet years a mudpot can become saturated allowing the sediment to thin and settle, forming a boiling spring. Whereas, during drier years, a mudpot can dry up, harden, and emit steam -- as a fumarole.
All of the surface material around you is in a constant state of change. The bubbling and thumping mud here was once solid lava rock. Heat, water, gases, and time have altered the rock to clay. The actions of hydrothermal features, in concert with volcanoes, glaciers, and running water, have shaped the landscape of Lassen Volcanic National Park.
Boiling Pool -- [N 40°27.429' W 121°30.079']
Bumpass Hell occupies the old eroded vent of a dormant dome volcano -- Bumpass Mountain. More than 75 fumaroles, hot springs, and mudpots composed this 16-acre hydrothermal area. Hot spring water, far hotter than the boiling point, surges into and fills Boiling Pool. At the surface, the acid-sulfate water cools to the boiling point, and, amazingly, bacteria live in the boiling water.
The temperatures of each of the pools may vary. Which is all relative, of course, when “slightly cooler” means 150°F (66°C) instead of 200°F (93°C)!
Pool “Fool” of Gold -- [N 40°27.436' W 121°30.045']
Do you see black scum on the surface of this pool? It’s pyrite. The frothy mass contains tiny pyrite crystals, an iron-sulfide mineral that is perhaps better known as “Fools Gold.” Iron leaches from rocks deep below and combines with sulfur as it rises through the hydrothermal system, arriving at the surface as pyrite.
The stream emptying into East Pyrite Pool only slightly tempers the heat of this boiling pool. The upflow of Bumpass Hell’s superheated steam is like a stove burner always on high. Still, plant life finds favorable conditions to grow near the pool’s edge. Bog-laurel and mountain heather are two common plants tat grow in moist soils.