aerial view of a snowy mountainside with steaming fumaroles
Active fumaroles on Fourpeaked Mountain in Katmai National Park. (2006 photo)

USGS photo.


Fumaroles are vents or openings at the surface where volcanic gases and vapors are emitted. Fumaroles are common features on active volcanoes, and are an important sign that a volcano is active in that fumaroles indicate the presence of heat from volcanic sources.

In between eruptions, fumaroles are one of the most dynamic features on volcanoes. Fumaroles hiss, growl, can put out noxious gases, and also present significant geohazards.

Fumaroles may be holes or be found at small cracks or along fissures. Multiple fumaroles often occur together. They are most common in or near the vent areas or craters on volcanoes, but may occur elsewhere where hot gases and steam escape at the surface.

Fumaroles emit a variety of gases, including water vapor, sulfur dioxide, carbon dioxide, hydrogen chloride, and hydrogen sulfide. Water vapor is generally the main component of fumarolic emissions and is usually from meteoric groundwater. Carbon dioxide, sulfur dioxide, and other gases originate from volcanic sources.

Because they contain volcanic gases, fumaroles provide important information to geologists about active volcanoes. An increase in a fumarole activity is often associated with unrest and may be an indication that magma is moving within a volcano. Volcanologists monitor the temperature of fumaroles as well as the composition of the gases.

Deposits of sulfur, sulfide minerals, opal, gypsum, hematite, and or other minerals may be found around fumaroles. Fumaroles also cause extensive hydrothermal alteration where the presence of sulfuric acid alters minerals in volcanic rocks to clays.

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Katmai National Park

Katmai NP is the site of the largest eruption of the 1900s and also contains ten active volcanoes, most of which have active fumaroles.

Katmai NP was first established as part of the National Park System in 1918 in the years following the 1912 eruption of Novarupta-Mount Katmai, which was the largest eruption of the 20th century. This Colossal (VEI 6) eruption deposited a vast ignimbrite (ash flow tuff) which was still emitting steam and volcanic gases from thousands of fumaroles when scientists first visited the site in 1916 and named it the Valley of Ten Thousand Smokes.

photo of canvas tents set up adjacent to a valley of steaming fumaroles with mountains in the distance
The camp of the National Geographic expedition to the Valley of Ten Thousand Smokes, led by Robert Griggs, in 1917.
black and white photo of numerous fumaroles steaming in a valley with mountain peak in the distance
Valley of Ten Thousand Smokes from the rim of Novarupta, taken sometime between 1916 and 1922.

Photograph by E.C. Kolb and published in Griggs, 1922.

The 1912 eruption of Novarupta-Mount Katmai deposited an ignimbrite that was up to 660 ft thick (200 m) thick that was emplaced at a temperature of 1380 °F (750 °C). In 1917, the ignimbrite was still very hot as 3-foot (1-m) deep pits dug into its surface approached the boiling temperature and Griggs estimated that more than 1,000 fumaroles had plumes of steam and volcanic gases more than 500 ft (150 m) in height. By 1929 only a few hundred fumaroles were still present and by the 1990s, the last fumaroles had extinquished.

Extinct Fumaroles

The locations of extinct fumaroles on the Valley of Ten Thousand Smokes ignimbrite are evident today by discoloration and alteration of the rock. Both linear and circular orifices are seen in the barren surface of the valley. Most of the steam released in the fumaroles came from buried snow fields, precipitation and groundwater.

photo of a barren arctic landscape with oval features from extinct fumaroles on the surface. Mountains and snowy peaks are visible in the distance
Extinct Fumarole in the Valley of Ten Thousand Smokes.

NPS photo by M. Fitz.

Active Volcanoes

Fumaroles are present on most of the active volcanoes in Katmai National Park, including Trident, Martin, Mageik, Mount Griggs, and Douglas.

volcanic summit crater with steaming fumaroles
Vigorous fumaroles in the summit crater of Mount Martin.

USGS photo taken August 26, 2006.

Lassen Volcanic National Park

Fumaroles are present in several geothermal areas in Lassen Volcanic NP, including Sulphur Works, Little Hot Springs Valley, Bumpass Hell, and Devils Kitchen. The temperature and vigor of fumaroles in the park vary from year-to-year and season-to-season. Fumaroles have a lower temperature in the spring because of mixing with abundant shallow groundwater, and are hotter and dryer in the late summer and during periods of drought.

photo of a steaming fumarole surrounded by hydrothermally altered soils
Big Boiler, a fumarole in Bumpass Hell, is one of the hottest in the world. Measured temperatures are as high as 322 °F (161°C).

NPS photo.

Mount Rainier National Park

Fumaroles at Mount Rainier’s summit have created a network of ice caves in the glaciers that fill the volcano’s craters. These fumaroles emit largely steam from shallow groundwater which is heated by an underlying magmatic hydrothermal system.

Yellowstone National Park

Fumaroles are present in several geothermal areas in Yellowstone NP, including Norris Geyser Basin, Roaring Mountain, and the Mud Volcano Thermal Area. Approximately 2,000 fumaroles are found within Yellowstone.

Fumaroles are the hottest geothermal features in Yellowstone NP. They also typically have a different chemistry than geysers and hot springs. Fumaroles and mudpots have acid-sulfate water, and are acidic with a low pH. Geysers and hot springs are rich in chlorine and silica and have a high pH.

These fumaroles consist of meteoric water (water from precipitation) that has been charged with hot gases from a magmatic source.

steam coming out of the ground
Roaring Mountain, Yellowstone National Park.
photo of steaming fumaroles
Black Growler Steam Vent in Norris Geyser Basin, Yellowstone National Park.

John St. James photo (Flickr).

Sound Recording—Yellowstone NP

Redoubt Volcano, Lake Clark National Park

mountain peak with steam vents

Both Redoubt and Iliamna volcanoes have active fumaroles on them, which sometimes produce steam plumes that can be viewed from a distance.

Redoubt experienced an increase in fumarolic activity in the months prior to its 2009 eruption.

Photo (right): Fumaroles near the summit of Iliamna in 2019.

USGS photo/Matt Loewen.

steaming fumaroles on a snow covered mountain
View of vigorous hot fumarolic emission from two holes (at about 7000 feet in elevation) located under the Drift glacier on Mount Redoubt in Lake Clark National Park and Preserve, Alaska. Water vapor and volcanic gas emanating from these holes in the ice are forming the visible white plume. (January 31, 2009.)

USGS Alaska Volcano Observatory photo.

snow covered volcanic peak with steam plume above its summit crater.
Steam plume from fumaroles on Redoubt Volcano in 2014.

USGS Alaska Volcano Observatory photo.

Hawai’i Volcanoes National Park

Fumaroles are located in places in and around the caldera at the Kīlauea summit. Wahinekapu (Steaming Bluff) and Ha'akulamanu (Sulphur Banks) are two of the fumarolic features. Steaming Bluff emits steam formed from groundwater that has been heated by magma deep in the subsurface. The fumaroles at Sulphur Banks emit volcanic gases including sulfur dioxide and hydrogen sulfur as well as steam from heated groundwater.

steaming fumaroles alone the crater rim
Steaming Bluff (Wahinekapu) in Hawai’i Volcanoes National Park.

NPS photo by J. Wei.

National Park Sites containing Fumaroles

Part of a series of articles titled Volcanic Features.

Previous: Crater Lakes

Next: Lava Lakes

Aniakchak National Monument & Preserve, Hawaiʻi Volcanoes National Park, Katmai National Park & Preserve, Lake Clark National Park & Preserve, Lassen Volcanic National Park, Mount Rainier National Park, Valles Caldera National Preserve, Wrangell - St Elias National Park & Preserve, Yellowstone National Park more »

Last updated: April 18, 2023