Geology

Raton-Clayton Volcanic Field

The cinder cone we know as Capulin Volcano serves as the centerpiece for an amazing display of volcanic features in and around the national monument. It shares the landscape with hundreds of other cinder cones and basaltic lava flows, rhyolitic volcanic domes and a large andesitic shield volcano. This volcanic field includes lavas of wide chemical range: from rhyolite (> 68 weight % SiO2), to dacite (63-68 wt % SiO2), to basalt (< 52 wt % SiO2), as well as varieties of these end-member compositions.

Beginning in the Cretaceous Period, about 146 to 65 million years ago (Ma), prior to the volcanic eruptions in the area that would become northeastern New Mexico, this region was covered by an interior seaway that initially connected the Arctic Ocean and the Gulf of Mexico. This seaway expanded and contracted throughout the Cretaceous. When it expanded, dark-colored, fine-grained marine sediments were deposited, such as the Pierre Shale, which can be seen in outcrop along Interstate 25 between Las Vegas and Raton.

When the seaway contracted, beach, river, and delta deposits covered the marine sediments. As the Rocky Mountain Range began to rise, this seaway retreated forever. Beginning about 9 million years ago, in the western region that is bounded today by the New Mexico towns of Raton and Clayton, called the Raton-Clayton Volcanic Field (RCVF), large volumes of lava were erupted onto either the Ogallala Formation (Miocene age) or the Poison Canyon Formation (Paleocene age). The Ogallala Formation was formed from the deposition of sediment carried by rivers from the Sangre de Cristo Mountains, and today serves as a major source of groundwater for much of the Great Plains. These lavas also erupted on the northern and southern perimeters of the RCVF. Chemically the majority of the lavas erupted during this time are classified as either olivine basalts or alkali basalts. Another type of lava erupted here is the Red Mountain rhyodacite, which erupted between 6.8 and 6.3 Ma; this lava comprises Red Mountain, a rhyolitic volcanic dome, on Johnson Mesa. These lavas are grouped together in what is referred to as the "Raton Phase" of RCVF activity. The next phase of volcanic activity began approximately 3.0 Ma at Rabbit Ears, which today is an eroded vent near Clayton, New Mexico. This stage of volcanism is referred to as the "Clayton Phase" as the majority of lavas erupted during this time are found between Clayton and Sierra Grande; although, Jose Butte and Robinson Peak are located west of Capulin. The Clayton lavas typically have very low SiO2 content (42-45 wt %) and are classified as nephelinite and basanite. The Capulin Phase lavas were also erupted onto the Ogallala Formation, as well as onto the light-brown sandstone called the Dakota Sandstone (Cretaceous Age), which locally crops out near the towns of Folsom and Des Moines. Presently, there is no evidence to suggest that the volcanism in this phase has ended, and it may only be in an eruptive hiatus. However, since the last known eruption occurred more than 30,000 years ago, the RCVF is considered dormant.

Volcanic Field Features

The processes that created Capulin Volcano also created extraordinary forms around its base. The lava flows formed a resistant cap on the easily weathered sedimentary rocks, which protected this underlying rock from erosion while all the surrounding rock washed away. The result is the high, flat-topped mesas, such as Raton Mesa, Mesa de Maya, and Johnson Mesa.

At Capulin Volcano moving lava developed a crust on the surface as it cooled and in places this surface was “wrinkled” by the flowing lava beneath producing pressure ridges.

Lava cascades and levees formed as the lava flowed, while caves and lava tubes formed beneath the crust as the lava drained away. These lava tubes and caves are quite fragile, and so no intact lava tubes or caves may be found in the park today.

Partially cooled lava, pushing through cracks like toothpaste from a tube, solidified into semi-rounded squeeze-ups called tumuli.

Environmental Factors

Erosion, fire, and non-native species play an important part in shaping the monument landscape.  

Erosion on the volcano is primarily associated with the road which circles the mountain to the crater rim. Culverts under the road provide narrow paths for water run off which create erosion channels and gullies down the sides of the mountain. Heavy rain and high winds also regularly shift the ash and cinders which built the mountain.

Capulin Volcano National Monument was set aside from public use in 1891 and was designated a National Monument in 1916. Fire was considered destructive and dangerous. All fires were suppressed and the natural fire cycle of both grasslands and woodlands disrupted.

Until recently, the Monument has not experienced any form of fire management. The first prescribed fire was conducted in April, 2005. This prescribed burn, as well as others conducted in the future, will help restore a natural fire cycle to the monument ecosystems. It will also lessen the possibility for devastating wildfires, which could result from a build-up of fuel sources within the Monument.

Nonnative or exotic species are those that evolved elsewhere and have been transported and purposefully or accidentally disseminated by humans. These species “disrupt the functioning of native ecosystems” and become problematic by rapidly dispersing into communities in which they have not evolved, and by displacing native species because of evolutionary mismatches. Eventually the introduced species may dominate an ecosystem, thereby making conditions impossible for the native species to exist. At Capulin Volcano, there are several exotic species of plants present.

Geology

Between 58,000 to 62,000 years ago, just yesterday on the clock of geologic time, the scene near Capulin would have been one of fire, ash, glowing lava, and ear-shattering explosions.

Capulin Volcano formed during the most recent period of activity in the Raton-Clayton Volcanic Field. The cone rises more than 1,000 feet above the plains to 8,182 feet above sea level and consists chiefly of loose cinders, ash, and other rock debris. These materials were ejected during successive eruptions and fell back upon the vent, piling up to form the conical mountain. The symmetry of Capulin Volcano was preserved because lava did not flow from the main crater but from secondary vents located at the western base of the cone.

Evidence of the other episodes of activity can be seen in nearly 100 nearby volcanic peaks and lava capped mesas. The largest of these volcanic peaks is the Sierra Grande, an extinct volcano rising some 2,200 feet above the surrounding plain, about 10 miles to the southeast. The largest lava flow is Johnson Mesa, 14 miles long and 7 miles wide, to the west of Capulin.