Hydrothermal (hot water) features at Lassen Volcanic National Park fascinate visitors to this region of northeastern California. Boiling mudpots, steaming ground, roaring fumaroles, and sulfurous gases are linked to active volcanism and are all reminders of the ongoing potential for eruptions in the Lassen area. Nowhere else in the Cascade Range of volcanoes can such an array of hydrothermal features be seen. Recent work by scientists with the U.S. Geological Survey (USGS), in cooperation with the National Park Service, is shedding new light on the inner workings of the Lassen hydrothermal system.

Most of the hydrothermal features in the park contain mixtures of condensed steam and near-surface ground water and have temperatures that are near boiling. The steam-heated waters of the features are typically acidic and, even if cool enough, are not safe for bathing.

Water from rain and snow (meteoric water) that falls on the highlands of Lassen Volcanic National Park feeds the Lassen hydrothermal system. Once deep underground, the water is heated by a body of hot or molten rock beneath Lassen Peak. The deeper part of the system, where hot water saturates the rock, is called the liquid-dominated zone. At shallower depths, lower pressure allows rising hot water to boil. The subsurface area in which steam and gas prevail in open fractures is called the vapor-dominated zone. Although most of the steam condenses near the surface, some reaches the surface through conduits to form fumaroles (steam and volcanic-gas vents), such as those at Bumpass Hell.

Many argue that a trip to Lassen is not complete without a visit to Bumpass Hell. The largest hydrothermal area in the park got its name from Kendall Bumpass who severely burned his leg after breaking through a thin crust into a boiling pool. Beginning at the Bumpass Hell parking area, the trail traverses the rocky slope of Bumpass Mountain. The trail changes little in elevation until the basin overlook where it drops 100 feet into the hydrothermal area basin. Here, a boardwalk provides a safe way to explore the steaming pools, boiling mudpots, and array of unusual colors.

Credits and Sources:

“Bumpass Hell Trail Guide,” National Park Service,http://www.nps.gov/lavo/planyourvisit/upload/Bumpass-Hell-trail-guide-booklet.pdf, Accessed on June 29, 2015.