Kilbourne and Hunts Holes and White Sands

Kilbourne Hole is a

maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallo ...

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 seat of El Paso County in the western corner of the U.S. state of Texas. The 2020 population of the city from the U.S. Census Bureau was 678,815, making it the 23rd-largest city in the U.S., the ...

, 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 A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

xenolith A xenolith ("foreign rock") is a rock fragment ( country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ig ...

s, 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 Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...

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 subsiden ...

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

forms when rising

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...

encounters sediment beds saturated with

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

. The magma heats the groundwater to the point where the

vapor pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed pha ...

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 Country rock is a genre of music which fuses rock and country. It was developed by rock musicians who began to record country-flavored records in the late 1960s and early 1970s. These musicians recorded rock records using country themes, vocal ...

is fragmented and expelled into the atmosphere together with fragments of the

, 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 A pyroclastic surge is a fluidised mass of turbulent gas and rock fragments that is ejected during some volcanic eruptions. It is similar to a pyroclastic flow but it has a lower density or contains a much higher ratio of gas to rock, which makes ...

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

s 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, sand ...

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 Lherzolite is a type of ultramafic igneous rock. It is a coarse-grained rock consisting of 40 to 90% olivine along with significant orthopyroxene and lesser amounts of calcic chromium-rich clinopyroxene. Minor minerals include chromium and a ...

, a rock composed mostly of

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...

and

pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe I ...

. The olivine has a distinctive pale green color in which the pyroxene forms black flecks.

Wehrlite Wehrlite is an ultramafic and ultrabasic rock that is a mixture of olivine and clinopyroxene. It is a subdivision of the peridotites. The nomenclature allows up to a few percent of orthopyroxene. Accessory minerals include ilmenite, chromite, ...

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 In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, wh ...

) and low-silica (

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...

) 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 agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

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

Apollo 12 Apollo 12 (November 14–24, 1969) was the sixth crewed flight in the United States Apollo program and the second to land on the Moon. It was launched on November 14, 1969, by NASA from the Kennedy Space Center, Florida. Commander Charles ...

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 Apollo 14 (January 31, 1971February 9, 1971) was the eighth crewed mission in the United States Apollo program, the third to land on the Moon, and the first to land in the lunar highlands. It was the last of the " H missions", landings at ...

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 Edgar Dean Mitchell (September 17, 1930 – February 4, 2016) was a United States Navy officer and aviator, test pilot, aeronautical engineer, ufologist, and NASA astronaut. As the Lunar Module Pilot of Apollo 14 in 1971 he spent nine ...

Apollo 15 Apollo 15 (July 26August 7, 1971) was the ninth crewed mission in the United States' Apollo program and the fourth to land on the Moon. It was the first J mission, with a longer stay on the Moon and a greater focus on science than ear ...

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 Apollo 16 (April 1627, 1972) was the tenth human spaceflight, crewed mission in the United States Apollo program, Apollo space program, administered by NASA, and the fifth and penultimate to Moon landing, land on the Moon. It was the second o ...

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 Coll ...

and

Charlie Duke Charles Moss Duke Jr. (born October 3, 1935) is an American former astronaut, United States Air Force (USAF) officer and test pilot. As Lunar Module pilot of Apollo 16 in 1972, he became the tenth and youngest person to walk on the Moon, at ag ...

, and

Apollo 17 Apollo 17 (December 7–19, 1972) was the final mission of NASA's Apollo program, the most recent time humans have set foot on the Moon or traveled beyond low Earth orbit. Commander Gene Cernan and Lunar Module Pilot Harrison Schmitt walke ...

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 The Bureau of Land Management (BLM) is an agency within the United States Department of the Interior responsible for administering federal lands. Headquartered in Washington DC, and with oversight over , it governs one eighth of the country's ...

. 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