Kilbourne and Hunts Holes and White Sands

Kilbourne Hole is a maar

volcanic crater A volcanic crater is an approximately circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During volcanic eruptions, molten magma and volcanic gases rise from an und ...

, located west of the Franklin Mountains of

El Paso, Texas El Paso (; "the pass") is a city in and the county seat, seat of El Paso County, Texas, El Paso County in the western corner of the U.S. state of Texas. The 2020 population of the city from the United States Census Bureau, U.S. Census Bureau w ...

, in the

Potrillo volcanic field The Potrillo volcanic field is a Monogenetic volcanic field, monogenetic volcanic field located on the Rio Grande Rift in southern New Mexico, United States and northern Chihuahua (state), Chihuahua, Mexico. The volcanic field lies southwest of ...

Doña Ana County, New Mexico Doña Ana County is located in the southern part of the State of New Mexico, United States. As of the 2020 U.S. Census, its population was 219,561, which makes it the second-most populated county in New Mexico. Its county seat is Las Cruces, t ...

. Another maar, Hunt's Hole, lies just two miles south of Kilbourne Hole. Kilbourne Hole is notable for the large number of mantle xenoliths, solid fragments of mantle rock, that were carried to the surface by the eruption. Estimates of the age of the crater vary from about 24,000 to about 80,000 years. In 1975, Kilbourne Hole was designated as a National Natural Landmark by the National Park Service. It is now part of Organ Mountains–Desert Peaks National Monument.

Geologic setting and formation

Kilbourne Hole and Hunt's Hole are found in the central part of the

, which also contains the Afton-Aden

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

flows. The area is part of the

Rio Grande rift The Rio Grande rift is a north-trending continental rift zone. It separates the Colorado Plateau in the west from the interior of the North American craton on the east. The rift extends from central Colorado in the north to the state of Chihuahu ...

, where the Earth's crust is being stretched and thinned. The rift is characterized by deep

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subside ...

s, recent faulting and volcanic activity, and unusually high heat flow upwards from the

Earth's mantle Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of 4.01 × 1024 kg and thus makes up 67% of the mass of Earth. It has a thickness of making up about 84% of Earth's volume. It is predominantly so ...

. Kilbourne Hole and Hunt's Hole are located on the same north-trending fault of the Fitzgerald-Robledo fault system. A maar forms when rising magma encounters sediment beds saturated with

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...

. The magma heats the groundwater to the point where the vapor pressure overcomes the weight of the overlying beds (the

overburden pressure Pressure is force magnitude applied over an area. Overburden pressure is a geology term that denotes the pressure caused by the weight of the overlying layers of material at a specific depth under the earth's surface. Overburden pressure is also ...

) and the beds are catastrophically blown out. Country rock is fragmented and expelled into the atmosphere together with fragments of the magma, creating a deep crater, the bottom of which sits below the pre-eruptive ground surface. Kilbourne Hole erupted through

alluvium Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. ...

(unconsolidated water-deposited sediments) and through a thin basalt flow. Like most maars, it has a shallow rim, composed of erupted material that was deposited as thin pyroclastic surge deposits.

Description of the crater

The crater is at an elevation of . It has a diameter of by and a depth of .2016 National Land Cover (NLCD) dataset
Kilbourne Hole The hole is over a mile wide, and over deep, with crumbling

cliffs all around except at the southwest corner. The basalt cliffs resemble the cliffs of the Devils Postpile National Monument near

Yosemite National Park Yosemite National Park ( ) is an American national park in California, surrounded on the southeast by Sierra National Forest and on the northwest by Stanislaus National Forest. The park is managed by the National Park Service and covers an ...

, with the characteristic reddish purple hexagonal columns, except that they are not as tall. The cliffs are about high. The base of the cliffs is covered with a

scree Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. Talus deposits typically ...

of basalt blocks. The basalt thins and disappears on the southwestern rim of the hole. Dropstone at Kilbourne Hole

The eastern and northern rim of the hole have low rim deposits of ejecta from the maar eruptions. These rest on the basalt flow where it is present or on older sediments. The ejecta at Kilbourne Hole contains dropstones and a large number of xenoliths derived from the lower crust and mantle. These have been closely studied by geologists to learn more about geologic processes deep underground. Hunt's Hole is a little smaller, with basalt cliffs only at the northeast and southeast sides of the crater. Layers of ashfall and crumbling

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

also rise about high, on the south rim of the crater. Sand dunes have collected on the east sides of the both craters, rising about above the desert floor. A dry lakebed lies on the floor of each crater.

Xenoliths

Kilbourne Hole is notable for the abundance of xenoliths in the crater ejecta. These are fragments of country rock carried intact to the surface by the eruption. Xenoliths at Kilbourne Hole include both upper mantle rocks and lower crustal rocks and are most abundant in the northern and eastern rim. Because these are samples of portions of the Earth that are inaccessible by mining or drilling, they are of great scientific interest. Most of the mantle xenoliths at Kilbourne Hole are composed of lherzolite, a rock composed mostly of olivine and pyroxene. The olivine has a distinctive pale green color in which the pyroxene forms black flecks. Wehrlite is occasionally found here as well. Deep crustal rocks include a variety of

granulite Granulites are a class of high-grade metamorphic rocks of the granulite facies that have experienced high-temperature and moderate-pressure metamorphism. They are medium to coarse–grained and mainly composed of feldspars sometimes associated ...

s of both high-silica ( felsic) and low-silica ( mafic) compositions. These likely took less than three days to reach the surface from their place of origin, and show pristine composition and texture. Their characteristics show that they were little altered from their formation 1.6 to 1.8 billion years ago, other than some reheating during the opening of the Rio Grande rift. Xenoliths are almost entirely absent in the ejecta from Hunt's Hole, but xenoliths are found in Potrillo maar to the south. File:Kilbourne Hole embedded xenolith.jpg, Mantle xenolith embedded in basalt File:Kilbourne Hole lxenoliths.jpg, Mantle xenoliths File:Kilbourne Hole lower crust xenolith.jpg, Lower crust xenolith

NASA training

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

geologically trained the

Apollo Astronauts As part of the Apollo program by NASA, 24 astronauts flew 9 missions to the Moon between December 1968 and December 1972. During six successful two-man landing missions, 12 men walked on the lunar surface, six of whom drove Lunar Roving Vehicl ...

in April and Nov. 1969, June 1970, and Jan. and Dec. 1971. Astronauts who would use this training on the Moon included Apollo 12's

Pete Conrad Charles "Pete" Conrad Jr. (June 2, 1930 – July 8, 1999) was an American NASA astronaut, aeronautical engineer, naval officer and aviator, and test pilot, and commanded the Apollo 12 space mission, on which he became the third person to ...

and

Alan Bean Alan LaVern Bean (March 15, 1932 – May 26, 2018) was an American naval officer and aviator, aeronautical engineer, test pilot, NASA astronaut and painter; he was the fourth person to walk on the Moon. He was selected to become an astron ...

, Apollo 14's

Alan Shepard Alan Bartlett Shepard Jr. (November 18, 1923 – July 21, 1998) was an American astronaut, naval aviator, test pilot, and businessman. In 1961, he became the second person and the first American to travel into space and, in 1971, he beca ...

and Edgar Mitchell, Apollo 15's

David Scott David Randolph Scott (born June 6, 1932) is an American retired test pilot and NASA astronaut who was the seventh person to walk on the Moon. Selected as part of the third group of astronauts in 1963, Scott flew to space three times and ...

and

James Irwin James Benson Irwin (March 17, 1930 – August 8, 1991) was an American astronaut, aeronautical engineer, test pilot, and a United States Air Force pilot. He served as Apollo Lunar Module pilot for Apollo 15, the fourth human lunar landi ...

, Apollo 16's

John Young John Young may refer to: Academics * John Young (professor of Greek) (died 1820), Scottish professor of Greek at the University of Glasgow * John C. Young (college president) (1803–1857), American educator, pastor, and president of Centre Col ...

and Charlie Duke, and Apollo 17's

Gene Cernan Eugene Andrew Cernan (; March 14, 1934 – January 16, 2017) was an American astronaut, naval aviator, electrical engineer, aeronautical engineer, and fighter pilot. During the Apollo 17 mission, Cernan became the eleventh human being to ...

and

Jack Schmitt Harrison Hagan Schmitt (born July 3, 1935) is an American geologist, retired NASA astronaut, university professor, former U.S. senator from New Mexico, and the most recent living person—and only person without a background in military aviation� ...

Access

Kilbourne Hole is located within Organ Mountains–Desert Peaks National Monument and administered by the Bureau of Land Management. It is accessed via Doña Ana County Road A-011, driving 8 miles west from the railroad. The hole is "on the right, past the big tan dirt bank." Much of the land inside the hole is private property. Hunt's Hole is about 2 miles south on A-013.

References