Friday, February 23, 2018

Capulín Volcano, Inside and Out

Capulín cinder cone, with lava flow (left) from a vent at the base of the cone.
On the west edge of the Great Plains in the northeast corner of New Mexico, at the northeast end of the mysterious lineup of volcanic features known as the Jemez Lineament, stands Capulín Volcano. It’s one of the youngest in the Raton Volcanic Field, having erupted just 60,000 years ago. Erosion has not yet destroyed its beauty, and much rock remains exposed, revealing some of its life story.
Capulín displays its beautiful symmetry.
Capulín's partially-vegetated lava flows are fascinating to explore.

Capulín is a cinder cone, a common and simple type of volcano. In shape, construction and composition, it very much resembles Paricutín in central Mexico, which erupted in a farmer's field just 75 years ago. Scientists were on hand to observe and describe Paricutín, from its birth in 1943 to its final gasp in 1952. Because the present is the key to the past, we can infer much about Capulín’s life from this modern-day example.
The infant Paricutín, just two days old. The cone is already 30 m tall (source).
Paricutín in the prime of life (1943; source).
Dead Paricutín, in 1997; note flow from side vent, a boca (source).

Now back to Capulín. Earthquakes probably were the first signs of imminent birth. For weeks they grew in intensity, until an “especially violent tremor” opened a fissure that spewed steam and smoke, followed by glowing red magma. These first stage eruptions were relatively calm—lava oozed and flowed.
Black line marks extent of a first-stage lava flow, later covered by cinders and now grass (Sayer & Ort 2011).
But it wasn’t long before all hell broke loose. Gas-rich magma exploded upon reaching the surface, producing tall “fiery fountains” of fine volcanic ash, coarser cinders, and even bombs!—some weighing hundreds of pounds. Debris from repeated eruptions accumulated layer by layer to form a cinder cone more than 1500 feet tall. The road to the summit of Capulín crosses great exposures of layered volcanic debris. Unfortunately, there's no place to pull over before the parking lot at the top. However, the road is closed to traffic at the end of the working day and open to walkers.
Pale gray ash, coarse cinders and small bombs from the violent second stage of Capulín activity.
Large dark volcanic bomb, with medium dog for scale.
The Capulín crater is asymmetric, presumably because more debris accumulated downwind. It’s wonderfully accessible, with trails to the bottom and around the rim.
Source.
View into crater from trailhead.
Crater floor.
View north; prominent volcano on left and lava-capped mesa with snow in distance.

As gas was depleted, the dramatic eruptions subsided, giving way to a third stage of activity. No longer gas-propelled, magma couldn’t reach the top of cone, and instead flowed out vents on the sides, called bocas. (Spanish for mouth). These flows are the freshest of Capulín’s remains, still only partially vegetated. Two trails and the picnic area provide fine opportunities to examine the “rocky desolate wasteland.”
Lava flows from Capulín and its neighbors (from Sayer & Ort 2011).

I saw plants colonizing rock everywhere I went. Some of the older flows appear mostly vegetated from a distance, but up close they're still rather rocky—just try walking across.
Partially vegetated flow along Lava Trail; Sierra Grande (volcano) on skyline.
Darker rocky tongue in grassland is an earlier lava flow (but post-cinder cone).
Gooseberry (Ribes sp.).
Young fringed sagebrush (Artemisia frigida).
Capulines on the crater rim. Capulín is the Spanish name for several wild cherries. The species in northern New Mexico is Prunus virginana—the chokecherry.
Flow surfaces cooled first, hardening into crust. But lava continued to ooze beneath, occasionally pushing through the crust to form tumuli or squeeze-ups. Some nice ones can be seen from the road to the park and along the lower trails.
Squeeze-up on Visitor Center Nature Trail.
Another tumulus, on the Lava Trail.
One more, near park entrance; vegetated lava flow in distance.
Not surprisingly, the Boca Trail tours the boca that was the source of Capulín’s final lava flows. The trail is relatively new—wear tough shoes and watch for trail signs.
Tastefully subdued sign (click on image to view).
This flat area is considered the remains of a lava lake, one of several in the Boca Trail area.

Geologists think Capulín was active for only a few years, but its life hasn't been dated precisely, only narrowed down to sometime between 62,000 and 56,000 years ago. Cinder cones typically are short-lived, erupting until they become clogged. Then they're done; they don't lie dormant. The Raton Volcanic Field probably is still active, but if Capulín’s magma source builds to erupt again, it will have to start all over, with another fissure spewing steam and smoke.
Baby Capulín is close by. Its lava covers parts of Capulin’s youngest flows, thus Baby is indeed younger.
A small part of the Raton Volcanic Field, viewed from the flank of Capulín.


Sources

Muehlberger, WR, Muehlberger, SJ, and Price, LG. 2005. High Plains of northeastern New Mexico, a guide to geology and culture. NM Bureau of Geology and Mineral Resources.

Parent, L, McCristal, J, and Mathis, A. 1991 (and 2006). Capulín Volcano National Moment. Western National Parks Association (recommended; for sale at the Visitor Center, $3.95).

Sayer, WO, and Ort, MH. 2011. A geologic study of the Capulín Volcano National Monument and surrounding areas, Union and Colfax Counties, New Mexico. New Mexico Bureau of Geology and Mineral Resources. PDF


Friday, February 16, 2018

A Plant Friend Most Would Pass By

Green leaves and red stems just above center are the plant of interest.
“When I discovered a new plant, I sat down beside it for a minute or a day, to make its acquaintance and hear what it had to tell.” John Muir, in Explorations in the Great Tuolumne Cañon, 1873.

John Muir—our great naturalist and conservationist—often wandered alone in the Sierra Nevada of California, passionately admiring and studying the plants. The vast wilderness enraptured him, but it also brought on feelings of loneliness at times. Perhaps that’s why he referred to plants as “friends” (1).

Muir came to mind last June, as I got to know a new plant friend near South Pass, at the southern end of the Wind River Mountains. For days I wandered through expansive sagebrush gardens bright with displays of pink, yellow, blue and white spring flowers. But I had to ignore them. I was being paid to search for rockcresses (genus Boechera, formerly Arabis)—small thin drab easily-overlooked plants.
But I didn't mind too much. I love the sweeping landscapes and granite blobs of the South Pass area. So does my field assistant.
Strolling with eyes glued to the ground, I pondered my fate—consigned to survey a challenging and esthetically unremarkable plant, the russeola rockcress (Boechera pendulina var. russeola). It is neither showy nor rare. Even worse, it no longer exists according to the latest treatment of the genus Boechera. So or course the more I thought about it, the more I became enamored of this plant! (I’m biased towards underdogs)
“But we know that however faint, and however shaded, no part of it is lost, for all color is received into the eyes of God.” John Muir (unpublished Pelican Bay Lodge manuscript)
The flowers of the all various rockcresses are small, white-to-purple, and 4-petaled. They’re useless for identifying plants to species. Mature seedpods (siliques) and basal leaves are required. One of the first things I learned from the russeola rockcress was that it can be recognized by the combination of pendulous siliques, reddish stems (hence russeola), and ciliate-margined but otherwise bare basal leaves. This probably sounds impossible to spot at the scale of these plants (a few inches tall at most), but the power of a well-developed search image is astonishing. Let’s have a look.

Below is a specimen from the Rocky Mountain Herbarium, University of Wyoming. Note the tiny white flowers. The normally pendulous arrangement of the siliques was distorted with pressing. The reddish color of the stems disappeared with drying.
The next photos show just how un-photogenic russeola rockcress is in the field, in part because the area is often windy. Still, the distinguishing features are obvious once one gets to know them. And fortunately, russeola prefers sparsely vegetated microsites.
Green leaves with ciliate margins (coarse hairs), reddish stems, pendulous blurry siliques.
Handlens is 2.5 cm long (1 in).
Sometimes the shadows are more obvious than the seedpods that cast them.
Distinctive upright green basal leaves at pencil tip, with reddish stem waving in the wind.
Ciliate-margined leaves; up close those hairs look gnarly! (click on image to view)
Though not rare overall, the russeola rockcress is uncommon in the South Pass area, which makes hunting for it fascinating—why does it only grow where it does? Muir pondered the same question; for him, learning why plants grow where they do was learning a bit more about the marvelous work of God.

After four long days of searching, I had learned that russeola (we're now on a first-name basis) is indeed restricted to rock. But it doesn’t grow in rock, i.e., not in crevices. That’s the habitat of the littleleaf rockcress, Boechera microphylla. Russeola prefers pockets of gravelly soil (decomposed granite) that develop in low, almost ground-level exposures of rock at the base of the big granite blobs.
Collection of littleleaf rockcress from South Pass area. Note upright very thin siliques.
Low rock outcrops such as this are prime targets for russeola survey.
Russeola grows on coarse granitic soil that develops in pockets in the low outcrops.
Russeola generally prefers less vegetated areas, such as this low ridge (dike?).
What's going on here?!
Dropseed rockcress, Boechera pendulocarpa (not to be confused with "pendulina"), frequently occurs with russeola on the same microsites. It’s the gray plant in the middle of the photo above, along with two russeola plants. But dropseed rockcress is a less picky plant, and it grows in a variety of habitats.

Though we’re now good friends, russeola has not revealed all of its secrets. I looked at a LOT of what appeared to be perfectly good habitat, but russeola wasn’t there. I wasn’t disappointed, or even surprised. After all these years I know that plants often don't grow everywhere it seems they could. In fact we should expect that, for a plant has to get to those perfect places—a seed has to land there. The great plant ecologist Henry A. Gleason made this clear, yet we often forget, perhaps driven by the human need to predict.
“Does a plant always grow in every habitat suitable to it and over the whole extent of the habitat? The answer is emphatically no. As previously stated, plants attain their range by migration. Possibly this plant is on its migratory way and has not yet arrived. … Possibly it has only recently arrived and has not yet had time to spread over the whole extent of the habitat. Possibly it is meeting with such strenuous competition from other plants that only a few individuals have a chance to grow.” Gleason and Cronquist, The Natural Geography of Plants, 1964 (2)
Russeola grows on bare gravelly soil at the base of this small outcrop.

Finally, some readers may wonder why was I paid to look for a plant that’s neither showy nor rare, nor even recognized by “experts.” I will try to explain. This is a long and winding tale that the faint of heart may wish to skip.

The main objective of our project was to locate additional populations of the small rockcress, Boechera pusilla, a globally-rare plant known from a single population (near South Pass). However, in the latest revision of the genus, authors Al-Shehbaz and Windham inadvertently (I think) expanded B. pusilla to include plants formerly called B. pendulina var. russeola. Does this mean that the small rockcress is no longer rare? No. It means the key and species descriptions were poorly constructed.

The authors lumped together the two varieties of Boechera pendulina—the typical one and russeola—though they acknowledged there’s no evidence they are conspecific. As a result (unintended), their key and descriptions do not address the plants we call russeola. Russeola material now keys to small rockcress (the very rare one), but only because there is no better match. As we discovered during post-field season herbarium study, russeola rockcress and small rockcress clearly are different. Hoping to eliminate the confusion, we collected and preserved leaves for DNA analysis, but Al-Shehbaz and Windham declined the offer, explaining they had insufficient funding to add another sample.

Thus russeola’s taxonomic status remains in limbo (3). But who cares?! The plants certainly don’t. Whatever we call them, these plants are real, and I’m happy to have made their acquaintance.
A dense “stand” of russeola—not a common situation.


Notes

(1) Muir’s passion for plants and his botany adventures are wonderfully recounted in Nature’s Beloved Son; rediscovering John Muir’s botanical legacy (Gisel and Joseph 2008).

(2) The first 10 chapters of The Natural Geography of Plants, including the discussion of why plants are restricted in distribution, were written by Gleason. Arthur Cronquist completed the book (second half) at Gleason’s request.

(3) Other experts recognize the russeola rockcress as a valid taxon. For example, our material clearly keys to and fits descriptions of Boechera pendulina var. russeola in Vascular Plants of Wyoming 3rd ed. (Dorn 2001) and Rollins’s 1982 treatment of North American Arabis (Boechera).