When you reach the end of the Bumpass Hell trail at Lassen Volcanic National Park (just a short walk after you get a glimpse of the hydrothermal activity at Bumpass Hell), you reach the Bumpass Hell boardwalk. Just to the right of the boardwalk, you’ll also see Bumpass Hell creek where all the water that is part of the hydrothermal activity drains out of Bumpass Hell:
The Bumpass Pass boardwalk allows you to get a much better view of all the different types of hydrothermal activity taking place and it has a nice variety of information signs to explain exactly what hydrothermal activities are going on:
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 a 464 degrees Fahrenheit (240 degrees Celsius), rises and condenses into water again, mixing with the percolating groundwater nearer the surface. The mixture produces sulfate water that escapes through park hydrothermal features at temperatures about 200 degrees Fahrenheit (93 degrees Celsius)
Bumpass Hell is the largest “escape valve” for the underground boiler or hydrothermal system and is the main upward vent. Lesser upward flows exit as Sulfur Works, Devil’s Kitchen, Boiling Springs Lake and Little Hot Springs Valley. One Furnace, One System
