DESCRIPTION:
Craters of the Moon Volcanic Field, Idaho

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Idaho and Craters of the Moon National Monument

Craters of the Moon is 29 kilometers southwest of Arco, Idaho, on U.S. Alternate Route 93 in Butte and Blaine counties. Paved roads are found within the National Monument open to vehicular traffic; the southern part of the Monument is a wilderness area closed to vehicles.

Craters of the Moon is in the Picabo Volcanic Field.

The monument is a geologic wonder cast in a wild and remote landscape. Its central focus is the Great Rift, a 62-mile long crack in the earth's crust. The Great Rift is the source of a remarkably preserved volcanic landscape with an array of exceptional features. Craters, cinder coves, lava tubes, deep cracks, and vast lava fields form a strangely beautiful volcanic sea on central Idaho's Snake River Plain.

Volcanic eruptions first occurred at Craters of the Moon about 15,000 years ago. The most recent eruptions ended about 2,100 years ago and were likely witnessed by the Shoshone people. A Shoshone legend speaks of a serpent on a mountain who, angered by lightening, coiled around and squeezed the mountain until liquid rock flowed, fire shot from cracks, and the mountain exploded.

The volcanic area now lies dormant, but its eight eruptive periods formed 60 lava flows which traveled as far as 45 miles from their vents. Some of the lava flowed around areas of higher ground, forming isolated islands of vegetation called "kipukas". Today, these kipukas provide a window on the vegetation communities of the past. They contain some of the last pristine vegetation in the Snake River Plain, including 700-year-old juniper trees and relic stands of sagebrush and native bunchgrass.

The Craters of the Moon National Monument was established by President Coolidge on May 2, 1924. Since 1924, the monument has been expanded through five presidential proclamations issued in accordance with the Antiquities Act. The most recent and largest expansion of the monument occurred November 9, 2000 when President Clinton signed a Proclamation enlarging the monument 13-fold. The monument now contains 715,000 acres of federal land.

Craters of the Moon
Location: Idaho
Latitude: 43.42 N
Longitude: 113.50 W
Height: 1,630 to 1,810 meters
Type: CinderCones
Eruptive History: Eight eruptive periods from 15,000 to around 2,000 years ago ²
Remarks: Composition is Olivine basalt²

Craters of the Moon sits astride the "Great Rift." Eight times in the past 15,000 years lava poured from cracks which opened along this weak spot in the earth's crust. Expanding gases in the lava ejected bubbly rocks hundreds of feet into the air. In some cases these cinders showered the ground to form cones. Less explosive lava flowed in sheets and rivers. The lava moving beneath the congealing crust sometimes tugged the surface into folds resembling coils of rope. This type of lava is called pahoehoe, which means "ropy" in Hawaiian. Cooler, thicker aa lava -- with a consistency much like peanut butter -- inched along, twisting and shattering into tumbled masses of jagged rocks. Aa is a Hawaiian word loosely translated as "rough on the feet," a description worth keeping in mind as you select your hiking shoes.

Of the more than 60 lava flows of the Craters of the Moon lava field, 20 have been dated: their ages were found to range from about 15,000 years before present to about 2,100 years before present. The flows were laid down in eight distinct eruptive periods that recurred on an average of every 2,000 years. On the basis of recent eruptive history, the Craters rift set is due for another eruption within the next thousand years, perhaps as soon as within 200 years. Craters of the Moon lava flows are classified as aa, pahoehoe, or blocky pahoehoe.

Craters of the Moon lava field lies along the northern border of the Snake River Plain, midway between Arco and Carey, Idaho. It consists of Holocene to Pleistocene lava flows, cinder cones, spatter cones, lava tubes, and other features typical of basaltic volcanism. Much of the field lies within the Craters of the Moon National Monument, administered by the National Park Service. The lava field covers, 1,600 square kilometers and consists of more than 60 mappable flows, around 25 cinder cones, and eight fissures/fissure systems. Detailed mapping and evaluation of dated flows have allowed USGS scientists to determine that the magma output rate was constant at around 1.5 cubic kilometers per 1000 years during 15,000-7,000 years B.P., then increased to 2.8 cubic kilometers per 1000 years from 7,000-2,000 years B.P.

The primary fissure system, called the Great Rift, passes through the Monument as a set of en echelon fissures which strikes N35degreesW and occurs in a zone up to 3 kilometers wide. Many of the flows and cinder cones have been described in detail.

Much of the volcanism of the Snake River Plain was confined to volcanic rift zones. A volcanic rift zone is a concentration of volcanic landforms and structures along a linear zone of cracks in the earth's crust. The Great Rift volcanic rift zone is a zone of cracks running approximately northwest to southeast across almost the entire eastern part of the Snake River Plain. The entire Great Rift is 62 miles long.

The Great Rift is an example of basaltic fissure eruption. This type of volcanic activity is characterized by extrusion of lavas from fissures or vents that is relatively quiet in comparison with highly explosive eruptions such as the 1980 Mount Saint Helens eruption. Where the Great Rift intersects the earth's surface, there is an array of cinder cones, lava cones, eruptive fissures, fresh-appearing lava flows, noneruptive fissures, and shield volcanoes.

One explanation for the existence of the Snake River Plain and the Craters of the Moon lava field is called the mantle plume theory. This theory states that beneath the crust of the Snake River Plain lies a "hot spot" or localized heat source. Periodically, this hot spot consists of a "plume" of molten rock (magma) which rises buoyantly to the surface of the earth. The hot spot does not move but rather remains in a fixed position. What does move is the crust of the earth; as the North American plate slides southwestward over the hot spot. As the plate moves over the hot spot volcanic eruptions occur on the surface.

Initially these eruptions are very violent and produce a lava known as rhyolite. Huge calderas of up to 30 miles in diameter are formed when these devastating eruptions take place. Later a more fluid lava known as basalt flows onto the surface and covers the rhyolitic flows. Yellowstone National Park, the area where the hot spot is believed to be located at this time, is the place where catastrophic rhyolitic eruptions last occurred 600,000 years ago. Craters of the Moon represents the second stage of the eruptions where fluid basaltic lava covered the landscape as recently as 2,000 years ago.

Big Cinder Butte

• the highest cone within the monument - has a total volume of 2 x 10^8 cubic meters, and rises 250 meters above the plain. It has no summit crater. Many bombs are found on the cone, including cow dung, breadcrust, and spindle types. The rims of five or six older volcanoes are visible around its base. Several flows issued from Big Cinder Butte. The youngest originated from a fissure on the north side of the cone and is a "Blue Dragon" - type pahoehoe flow. This type of flow is characterized by a shining iridescent surface. -- Excerpt from: R. Greeley, 1990, IN: Wood and Kienle

Big Craters

• Big Craters is a series of spatter cones and open fissure flows. The slope of each cone is 50-60 degrees near the summit and decreased to approximately 30 degrees near the base. The upper slopes are angular and rough, but the lower slopes are smoother and have profiles similar to those of cinder cones. The cones range in height from 12 to 20 meters and have chimneylike vent areas, most of which have collapsed, displaying a rubbly interior. Toward the northwest portion of the Big Crater area, however, two vents remain intact. -- Excerpt from: R. Greeley, 1990, IN: Wood and Kienle

Blue Dragon Flow

• The trail winds through shrubs and stands of limber pine before reaching the edge of the Blue Dragon Flow. While still molten, this lava flow knocked down and ignited trees. The charred tree trunks left impressions in the lava rock. In other places, the trees remained standing as the lava encased them, leaving vertical molds in the cooling lava. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

• The Blue Dragon and Green Dragon pahoehoe flows and the Vermilion Chasm are named for the striking lava colors in those areas. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

Broken Top Cinder Cone, Buffalo Caves, and Echo Crater

• You will have a sense of solitude as you travel into the Craters of the Moon Wilderness. The trailhead is 1/10 mile from the parking lot back along the road. The trail goes over Broken Top cinder cone and crosses a pahoehoe flow close to Buffalo Caves. The caves are located 100 yards northwest of the trail against the south side of Broken Top. You then pass a series of lava trees and several cinder cones before reaching Echo Crater, Some people backpack to this point and camp overnight. Backcountry permits are required for overnight trips and are available free of charge at the visitor center. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

• The Broken Top Loop Trail is one of the most outstanding trails within Craters of the Moon. Along its 2-mile length you can observe nearly every type of volcanic feature characteristic of the basaltic eruptions that created this unearthly landscape. A wide variety of phenomenon such as bombs, lava tubes, pahoehoe, lava toes, pressure ridges, and cinder cones can be found along this trail. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

Craters of the Moon Volcanic Field

• Craters of the Moon is a monogenetic volcanic field, 1,630 to 1,810 meters in elevation, of olivine basalt composition. Craters of the Moon had 8 eruptive episodes from 15,000 to approximately 2,000 years ago. ... Craters of the Moon lava field lies along the northern border of the Snake River Plain, midway between Arco and Carey, Idaho. It consists of Holocene to Pleistocene lava flows, cinder cones, spatter cones, lava tubes, and other features typical of basaltic volcanism. Much of the field lies within the Crater of the Moon National Monument, administered by the National Park Service. ... Craters of the Moon is 29 kilometers southwest of Arco, Idaho, on U.S. Alternate Route 93 in Butte and Blaine counties. Paved roads are found within the National Monument open to vehicular traffic; the southern part of the Monument is a wilderness area closed to vehicles. -- Excerpt from: R. Greeley and J.S. King, 1990, IN: Wood and Kienle

Devil's Orchard

• This paved trail explores an area of cinder beds scattered with pieces of the North Crater wall. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

Great Rift

• The primary fissure system, called the Great Rift, passes through the Monument as a set of en echelon fissures which strikes N35degreesW and occurs in a zone up to 3 kilometers wide. Many of the flows and cinder cones have been described in detail. -- Excerpt from: R. Greeley, 1990, IN: Wood and Kienle

• The Great Rift is an example of basaltic fissure eruption. This type of volcanic activity is characterized by extrusion of lavas from fissures or vents that is relatively quiet in comparison with highly explosive eruptions such as the 1980 Mount Saint Helens eruption. Where the Great Rift intersects the earth's surface, there is an array of cinder cones, lava cones, eruptive fissures, fresh-appearing lava flows, noneruptive fissures, and shield volcanoes. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

Green Dragon Flow

• The Blue Dragon and Green Dragon pahoehoe flows and the Vermilion Chasm are named for the striking lava colors in those areas. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

Indian Tunnel

• Indian Tunnel is one of the largest lava tubes in the Monument, reaching widths of over 15 meters. Concentric rock heaps in this area were probably used to secure tepees of the Indians who frequented the caves. Numerous other tunnels and caves are common in this area, ranging from centimeters to meters in size. -- Excerpt from: R. Greeley, 1990, IN: Wood and Kienle

Inferno Cone

• The area east of Inferno Cone consists of a series of lava "domes". Many of the flow units contain lava tubes, and individual flow units are generally "Blue Dragon" pahoehoe. The lava tubes in this area may be part of an extensive network in a single flow. Indian Tunnel is one of the largest tubes in the Monument, reaching widths of over 15 meters. Concentric rock heaps in this area were probably used to secure tepees of the Indians who frequented the caves. Numerous other tunnels and caves are common in this area, ranging from centimeters to meters in size. -- Excerpt from: R. Greeley, 1990, IN: Wood and Kienle

North Crater Flow

• North Crater Flow, a pahoehoe flow that spilled from the North Crater vent about 2,200 years ago. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

• The North Crater flow possesses features termed "monoliths" which appear to be fragments of cinder cones broken apart and rafted to their present positions by flowing lava. They range in length from approximately 0.5 to 300 meters long; some are up to 25 meters high. The massive Highway flow issued northward from the North Crater vent and was confined to the valley between Sunset and Grassy Cones. Its surface is braided with channels 3-6 meters deep, and its flow margins range from 3 to 15 meters high. -- Excerpt from: R. Greeley, 1990, IN: Wood and Kienle

Picabo Volcanic Field

• Craters of the Moon is in the Picabo Volcanic Field. -- U.S. Bureau of Land Management Website, Idaho State Office, 2001

Spatter Cones

• Like Yellowstone's Old Faithful, the spatter cone chain at Craters of the Moon best symbolizes the essence of this special place. Created during a dwindling stage of an eruption, the spatter cones formed as hot lumps of lava were thrown a short distance into the air only to fall back to earth around a small central vent. As the still molten blobs landed on top of each other, they cooled and adhered to nearby pieces to form the walls of what could be considered a mini-volcano. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

Sunset and Grassy Cones

• Sunset and Grassy cones rise around 160 meters above the surrounding plain. Three flows issue from Sunset cone but are largely blanketed with ash and soil. Two pahoehoe flows breached the crater in the northeast and in the west. On the northwest flank of the crater, an aa flow approximately 6 meters thick issued from a small parasitic cone. Both cones represent some of the earliest eruptive activity in the Monument. Two craters on the north side of Grassy Cone erupted lava simultaneously to produce flows which merged and extended northward. A network of lava tubes, some as large as 5 meters in diameter, developed within the flows. -- Excerpt from: R. Greeley, 1990, IN: Wood and Kienle

Tree Molds

• The trail winds through shrubs and stands of limber pine before reaching the edge of the Blue Dragon Flow. While still molten, this lava flow knocked down and ignited trees. The charred tree trunks left impressions in the lava rock. In other places, the trees remained standing as the lava encased them, leaving vertical molds in the cooling lava. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

Vermilion Chasm

• The Blue Dragon and Green Dragon pahoehoe flows and the Vermilion Chasm are named for the striking lava colors in those areas. -- Excerpt from: U.S. National Park Service, Craters of the Moon National Monument Website, 2002

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