Linear fissure, young age, unusual vent structures, and proximity to a large city
The Rio Grande rift is segmented into a series of basins. The Albuquerque basin is one of these basins. It is bounded on the north by the La Bajada fault, which defines the southern margin of the Espanola basin, and to the south by the Socorro constriction.
Volcanism is widely distributed throughout the ABQ basin. Although most of the area covered by volcanic rocks is basaltic, andesitic and more silicic compositions are represented in local centers and within the basin fill at depth. This means that volcanism appears minor and recent, but in reality much of the volcanism is not represented at the surface but has instead been buried by continual filling of the Albuquerque basin segment of the Rio Grande rift over the past several million years.
The Albuquerque Volcanoes exhibit many unique volcanic features if you know where to look. For example, the larger cones appear to have swelled during their final stages. This resulted in radial cracks on the sides of the cones. In places the interior cinder has been exposed beneath the "carapice" of spatter and lava that coats the cone. Gradual weathering of the loose cinders in these places has caused cavernous holes. These look like lava tubes but actually were formed by a different process.
Two humps on the south side of Vulcan are actually baby volcanoes. You can stand on their tops and actually see the craters surrounded by outward-dipping spatter and lava.
The Albuquerque Volcanoes are the source of lavas that make up the Volcano Cliffs. Judging from the high cliffs at the edge of the lava field, one might suppose that the Volcanoes are old. But the Volcano Cliffs, as they are known locally, formed only because the Rio Grande flowed near the edges of the lava flows at one time and undercut them.
Few large cities in the United States have young volcanoes near them as does Albuquerque. The Albuquerque Volcanoes are geologically young (about 200,000 years old) such that many details of small eruptions are well preserved.
They are also an excellent example of the results of a "fissure eruption" in which a "curtain of fire" erupts from a long, linear crack. Fissure eruptions like the Albuquerque Volcanoes are common in many parts of the world, particularly oceanic island volcanoes, but are not as well-expressed throughout much of the Southwest.
Fissure eruptions form because molten rock, or "magma", tends to rise along vertical cracks. When the cracks reach the surface, they cause long surface fissures. Lava and ash then erupt from the fissure. As magma quickly cools and solidifies along most of the crack, only a few points continue to erupt. Small cones of ash, spatter, and lava are built as these points of eruption continue. The Albuquerque Volcanoes we see today are the result of a fissure eruption associated with the Rio Grand rift.
The Albuquerque Volcanoes are as young as 140,000 years. This is very young by the standards of geologic time. Volcanoes younger than 200,000 years in the Southwest are all very well preserved and look much like they did immediately after they erupted.
Rather than erupting individually like many small fields of volcanoes in the Southwest, the Albuquerque Volcanoes all formed simultaneously. This is because they all erupted from the same fissure eruption. The actual eruption probably took place over a period of months to years. To the south and west of Belen and Los Lunas there is another series of cinder cones called the Cat Hills volcanoes. These are slightly younger and consist of more typical cinders and agglomerate.
2. Will they erupt again?
Small volcanoes do not reactivate like big volcanoes, but the area around Albuquerque remains potentially active, mainly because of its location in the Rio Grande Rift. A new volcano could erupt, if not along the Albuquerque Volcanoes, at least somewhere within the rift.
One of the larger earthquake swarms in New Mexico occurred in 1972 beneath the Volcanoes. There is no particular evidence that this was new magma moving up a crack. Instead, the earthquake swarm may have been re-adjustments of dikes and faults at great depth as the deeper portions of the dike continue to cool and contract.
Many people visiting the Volcanoes in the winter months have noticed "warm" air in the caves. This is probably not "volcanic heat", but instead is ambient air trapped in subsurface that feels warm compared with the cold outside air. If one were to visit the same caves during the summer, one would find them cool compared with the outside air. The caves simply record the temperature of Albuquerque "averaged" over a year, which is around 55 degrees F, a temperature that feels warm in the winter and cool in the summer.
3. How did they form?
If you were to look down on the Albuquerque Volcanoes (Figure 1) you would see that they are arranged in a nearly straight line. This also is apparent if you stand on top of one volcano and look across to the next one (Figure 2). This is simply because they erupted along a fracture in the crust. Fractures of this type along which eruptions take place are referred to as "fissure eruptions". Many of the eruptions in Hawaii are fissure eruptions in which the fissures frequently extend outward from summit craters or calderas. The fractures in Hawaii are thought to result from the gradual sliding of parts of the sides of the large volcanoes that make up the Hawaiian islands.
Fissures also occur in Iceland where the crust is being pulled apart along the Mid Atlantic ridge. In New Mexico the fractures have an origin similar to those in Iceland. Here the fractures are part of the faults that formed where the crust has been pulled apart by forces similar to those in Iceland. The eruption that resulted in the Albuquerque Volcanoes probably looked similar to eruptions in Iceland (Figure 3). Although the Albuquerque Volcanoes appear to occur in a straight line, they are actually arranged in slightly offset segments like the fissure in this example from Iceland. This is probably a good analogy of what the Albuquerque Volcanoes looked like when they started erupting and before the eruptions centralized on several spots. Once the eruptions centralized on these spots, the cones that we see today began to build up.
The stretching that helped create the Albuquerque Volcanoes has resulted in the development of the Rio Grande Rift. The rift valleys of eastern Africa are another example of similar stretching and pulling apart of Earth's crust. The East African Rift and the Rio Grande Rift are two of the youngest and larger continental rifts currently active on Earth. (This is probably one reason why East African and New Mexico are among the most geologically, and ecologically, interesting and exotic places on Earth.)
Fissure eruptions occur when conditions are right in the mantle for the existence of partially melted rock (magma) and faults act as conduits for the rise of magma to the surface. When a vertical crack filled with molten magma (known as a "dike") intersects the surface, a line of eruption takes place. If the dike is particularly large and deep, the line of eruption or fissure is long, like the Albuquerque Volcanoes. Other dikes are smaller and the associated fissure eruptions at the surface are short.
4. Why are the Albuquerque Volcanoes important and unusual?
Most of the scoria cones and volcanoes in New Mexico and throughout the Southwestern U.S. are the result of smaller fissure eruptions. This is one reason why the Albuquerque Volcanoes are so unusual and geologically interesting. They are an excellent example of fissure eruption. In addition, few large cities in the United States have such young basaltic volcanoes nearby (within a few minutes drive of downtown) that are also an important part of the metropolitan landscape.
The Albuquerque Volcanoes are also an unusual type of scoria cone. Many scoria cones in the Southwest are piles of cinder. Examples are Capulin Volcano, Bandera Crater, and Sunset Crater. Some of the Albuquerque Volcanoes like Vulcan, the largest cone, are cones formed from spatter and thin lava flows coating an interior of cinder.
5. What are they made of?
The Volcanoes are basalt, a type of lava that consists largely of the minerals plagioclase, olivine, pyroxene, and magnetite. There are two principal types of basaltic lava in Southwest: alkali basalt and tholeiite, defined on the basis of the relative abundances of sodium and potassium. The Albuquerque Volcanoes are made of tholeiite that is low in sodium and especially potassium. These different types of lava reflect the differences in the depth and composition of the mantle rocks that were melted and erupted. By comparison, the youngest lava of El Malpais (McCartys lava flow) is tholeiite. Many of the volcanic fields, like Mount Taylor's collection of small volcanoes, also on the western horizon of Albuquerque, are alkali basalt.
View NM Volcanoes - Albuquerque in a larger map
Albuquerque Basin Volcanic Field :Ten distinct volcanos in the greater Albuquerque area.
New Mexico Volcano Directory
A map of volcanoes and volcanic features around the state, with detailed discussion of each site.
Volcanoes of New Mexico
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General Geology/Relation to the Rift:
Kelley, V. C., 1982, Albuquerque: Its Mountains, Valley, Water, and Volcanoes. New Mexico Bureau of Mines and Mineral Resources, Scenic Trips to the Geologic Past Series, No. 9, 3rd edition.
Baldridge, W. S., 1979, Petrology and petrogenesis of Plio-Pleistocene basaltic rocks from the central Rio Grande rift New Mexico and their relationship to the Rift, in Riecker, R. E., editor, Rio Grande Rift: Tectonism and Magmatism, American Geophysical Union, Washington, D.C., p. 323-353.
Kelley, V. C., and A. M. Kudo, 1978, Volcanoes and related basalts of Albuquerque basin, New Mexico. New Mexico Bureau of Mines and Mineral Resources, Circular 156, 30p.
Kudo, A.M., 1982, Rift volcanics of the Albuquerque basin: overview with some new data., New Mexico Geological Society Guidebook, 33rd Field Conference, Albuquerque Country II, 285-289.
Perry, F. V., W. S. Baldridge, D. J. DePaolo, 1987, Role of asthenosphere and lithosphere in the genesis of late Cenozoic basaltic rocks from thge Rio Grande Rift and adjacent regions of the southwestern United States. Jour. Geophys. Res., 92, 9193-9213.
Crumpler, L. S., 1999, Ascent and Eruption at the Albuquerque Volcanoes: A physical volcanology perspective: New Mexico Geological Society Guidebook, 50th Field Conference, Albuquerque Country III, p. 221-233.
Smith, G.A., Florence, P.A., Castrounis, A. D., Luongo, M., Moore, J. D., Throne, J., and Zelley, K., 1999, Basaltic near-vent facies of Vulcan Cone, Albuquerque Volcanoes, New Mexico: New Mexico Geological Society 50th Field Conference Guidebook, Albuquerque Geology, p. 211-219.