Valles Caldera Research Articles

Valleys of fire: historical fire regimes of forest-grassland ecotones across the montane landscape of the Valles Caldera National Preserve, New Mexico, USA

Montane grasslands and forest-grassland ecotones are unique and dynamic components of many landscapes, but the processes that regulate their dynamics are difficult to observe over ecologically relevant time spans. We aimed to demonstrate the efficacy of using grassland-forest ecotone trees to reconstruct spatial and temporal properties of the historical fire regime in a complex landscape of montane forests and adjacent grasslands. We sampled and crossdated fire-scarred trees along ecotones and compared variations in historical fire occurrence within and among nine adjoining valle basins in a 10,158 ha landscape. We analyzed fire year extensiveness, climate regulation, and the occurrence of consecutive fire years. The resulting tree-ring record covers 1240–2005 AD, with 296 trees recording 125 replicated fire years during the analysis period 1601–1902 AD. Mean fire intervals for all events recorded on two or more trees ranged from 4.7 to 13.6 years in individual valles, and a mean of 2.4 ± 1.7 (SD) years at the landscape scale. Between 1660 and 1902, extensive fires occurring in six or more valles occurred 15 times, on average at ~ 17-year intervals; 29 moderately widespread fires (3–5 valles) occurred during this period, at 8.7 year intervals on average. Widespread events occurred in years with a significantly lower Palmer Drought Severity Index (PDSI) preceded by years of significantly positive PDSI, indicating conditions favorable for fine fuel production. Spatial reconstruction of fire extent revealed multiple occurrences of consecutive-year fires burning non-overlapping areas, associated with persistent low PDSI anomalies preceded by positive conditions in antecedent years. A landscape spatiotemporal approach to reconstructing fire regimes of montane forest-grassland complexes provides a valuable baseline for guiding prescribed and natural fire management at large spatial scales.

Arcyria versicolor of western mountains, U.S.A. (Myxomycetes: Trichiales: Trichiaceae): a morphological and taxonomic study with observations of nivicolous species

Arcyria versicolor (Trichiales: Trichiaceae) is a distinct myxomycete species described by William Phillips in 1877. The genus Arcyria dates back to Linnaeus in 1753 through the species A. denudata. Arcyria sporangia are brightly colored red, yellow, grey or white, mostly stalked, often in large groups easily seen with the naked eye. Approximately 54 species are known, many are common, and distributed worldwide. Collectors often encounter these colorful species on decaying logs as clusters of many sporangia often covering extensive areas. Arcyria versicolor, collected in the Valles Caldera National Preserve located in the Jemez Mountains of north central New Mexico, is a new record for the state. The nomenclatural history of this species is reviewed and the justification for selection of the species name versicolor is discussed. Arcyria versicolor is accepted as the valid species name and A. vitellina a synonym after examination of type specimens. Environmental parameters for coloration are discussed in general for fruiting bodies of Arcyria and more specifically for nivicolous snowbank species. Transitional stages of plasmodial color to mature fruiting body formation are described for Arcyria versicolor. More than 140 specimens of Arcyria versicolor fruiting bodies were examined with light microscopy and in part illustrated with multifocal computer stacked imaging. Higher magnifications were highlighted using scanning electron microscopy. A more complete and accurate species description is provided for Arcyria versicolor. Differences of fruiting body morphology including habit, color, dehiscence, peridial inner and outer surface features, capillitial ornamentation and size, spore color, size, and ornamentation, and stalk spore-like bodies are described and illustrated. Observation of type specimens from the type locality is illustrated, discussed, and nomenclatural evaluation given for the name selected. Mountain myxomycetes are reviewed based on the observations of T.H. Macbride and his early 1914 paper published in Mycologia. Collection data is presented that compares the dark-spored and light spored nivicolous myxomycetes in the French Alps. The history of renown collectors of nivicolous myxomycetes in western mountains of U.S.A. documents the discovery and study of this special ecological group of myxomycetes. This current paper is the first in a series from an ongoing research project entitled Myxomycetes of New Mexico.

Responses of Ground-Dwelling Spider (Arachnida: Araneae) Communities to Wildfire in Three Habitats in Northern New Mexico, USA, with Notes on Mites and Harvestmen (Arachnida: Acari, Opiliones)

Catastrophic wildfire is increasingly common in forests of the western United States because climate change is increasing ambient temperatures and periods of drought. In 2011, the Las Conchas wildfire burned in the Santa Fe National Forest of New Mexico, including portions of ponderosa pine and mixed-conifer forests, and grasslands in the Valles Caldera National Preserve, a large, high-elevation volcanic caldera. Following the fire, Caldera staff began monitoring abiotic, plant, and animal responses. In this study, ground-dwelling arachnids were collected in pitfall traps in burned and unburned habitats from 2011–2015. Permutational multivariate analysis of variance (PERMANOVA) mostly at the genus level with some higher taxon levels showed significant fire, year, and interaction effects. Abundance was at or near unburned levels by 2014, but species composition changed in burned areas. Pardosa and Haplodrassus were dominant genera across habitats. Linyphiids were strong indicators of unburned sites. Harvestmen were among the dominant species in the forest habitats, and erythraeid mites were abundant in the burned ponderosa pine forest and the grassland. Years were not significantly autocorrelated, unsurprising given the interannual variation in precipitation in this generally arid region. Although fire is a common feature of these habitats, future fires may be outside of historical patterns, preventing spider communities from re-establishing fully.

Anatomy of a Recharge Magma: Hornblende Dacite Pumice from the rhyolitic Tshirege Member of the Bandelier Tuff, Valles Caldera, New Mexico, USA

The 1.26 Ma Tshirege Member of the Bandelier Tuff is the second of two major (~ 400 km3, dense rock equivalent) compositionally zoned rhyolitic eruptions from the Valles caldera. Here we analyze 25 samples of a minor component of compositionally and texturally variable silicic dacite pumice (~ 67 to 72% SiO2) that is widely distributed through the unit. The dacite has a phenocryst assemblage dominated by feldspar and hornblende and is presumed to be a recharge magma. Quenching of dacite against cooler rhyolite, melting of rhyolitic crystal mush, and mixing between dacite and rhyolite contributed to textural complexity. The dacite can be broken into three petrographic pumice types resulting from different degrees of dacite–rhyolite interaction. The earliest stage in the history of the dacite discernable from mineral chemistry, thermobarometry and hygrometry is mid-crustal storage at temperatures close to 900 °C and water content ~ 5 wt%. Plagioclase zoning suggests that the dacite was subject to more mafic recharge at this stage. The dacite was then injected into rhyolitic crystal mush at temperatures between 700 and 800 °C and pressures ~ 0.3 GPa. Consequences of mixing with mushy rhyolite include the following: (1) cooling and partial crystallization of dacite; (2) growth of large, dendritic feldspars with ternary compositions; (3) ingestion of and melting of feldspar and quartz from the rhyolitic mush; (4) enrichment in fluorine due to melting of biotite in the mush; (5) enrichment in light REE contents in some samples due to melting of chevkinite-rich domain(s) in the mush; (6) second boiling of quenched dacite rendering it buoyant and distributing dacite ‘enclaves’ through the zoned rhyolite magma column. The dacite was likely injected into the rhyolite over a protracted period and eventually triggered the Tshirege eruption.

Titanium diffusion profiles and melt inclusion chemistry and morphology in quartz from the Tshirege Member of the Bandelier Tuff

AbstractMany rhyolites contain quartz crystals with relatively Ti-rich rims and Ti-poor cores, with a sharp interface between zones, attributed to partial dissolution followed by overgrowth following a heating event due to mafic recharge of the system. Quartz crystals in the compositionally zoned, high-silica rhyolite Tshirege Member of the Bandelier Tuff erupted at 1.26 Ma from the Valles caldera, New Mexico, show a range in zoning styles with Ti-rich rims becoming more abundant upward in the ignimbrite sheet among progressively less evolved magma compositions. Here we compare times between quartz overgrowth and eruption obtained by applying Ti diffusion coefficients to Ti concentration profiles in Tshirege Member quartz crystals with those from cathodoluminescence (CL) brightness profiles and show that panchromatic CL provides only a crude proxy for Ti in quartz in this unit. Titanium concentrations are measured to detection limits of ~1.2 ppm with small analytical errors (<5%) using MAN backgrounds, blank corrections, and oblique corrected transects to resolve diffusion-relaxed zone boundaries as thin as ~10 μm. Timescales derived from Ti profiles using the widely applied Tiin-quartz diffusion coefficients of Cherniak et al. (2007) range from 60 to 10 000 years, suggesting heating and mobilization events at different times prior to the eruption. However, the use of the newer Ti diffusivities reported by Jollands et al. (2020) yields timescales up to three orders of magnitude longer, including results that are geologically unreasonable for the Bandelier system. We suggest that assumptions commonly made in diffusion modeling, specifically about the form of the Ti zoning profile prior to diffusive relaxation, may be invalid.Melt inclusions in the Ti-poor cores of late-erupted quartz are chemically akin to early erupted melt compositions, while adhering and groundmass glasses more closely reflect the composition of the host pumice. Heating and mobilization events identified from quartz Ti zoning are thus linked to overall compositional zoning of the tuff, which may have been produced by repeated episodes of melting of a crystal cumulate cognate to the early-erupted, evolved rhyolite. Quartz-hosted melt inclusion faceting suggests the development of a crystal mush over a minimum time frame of 1000–10 000 years prior to the recharge events that produced the erupted Tshirege magma at 1.26 Ma.

Use of a portable ultrasound machine to determine pregnancy and uterine litter size for wild Gunnison’s prairie dogs (Cynomys gunnisoni)

Accurate estimates of population dynamics play a major role in formulating conservation strategies for Gunnison’s prairie dogs (Cynomys gunnisoni) and other keystone species. Over 5 years (2014–2018) at Valles Caldera National Preserve in NM, USA, we used a portable ultrasound machine (PUM) to investigate the presence or absence of pregnancy, and to determine uterine litter size for 238 pregnant female Gunnison’s prairie dogs from two colonies. We compared litter size at weaning for 168 of these 238 females and we found no significant difference between uterine litter size and litter size at weaning. For 76 of these 168 females (45%), estimates of uterine litter size and litter size at weaning were identical. We detected no significant variation among years for uterine litter size versus litter size at weaning. To our knowledge, our research is the first to compare uterine litter size to litter size at weaning for the same group of females living under natural conditions.

Relentless Predation on Gunnison's Prairie Dogs (Cynomys Gunnisoni) by a Single American Badger (Taxidea Taxus)

Predation affects the demography and population dynamics of prey species. Because predators commonly stalk prey from concealed routes, attack quickly, and frequently avoid areas with human observers, documenting predation under natural conditions is often difficult. An adult female American badger (Taxidea taxus) with offspring moved into a colony of Gunnison's prairie dogs (Cynomys gunnisoni) living under natural conditions at Valles Caldera National Preserve in New Mexico, United States, and provided an excellent opportunity to record predations over a period of 33 consecutive days in June–July 2018. Badgers are commonly nocturnal, but the badger at our study area captured a total of 100 Gunnison's prairie dogs during daylight hours. Sixty-two of the victims were adults (≥1 year old), 32 were juveniles (≤3 months since birth), and 6 were of unknown age. Most predations occurred in mid-morning and early afternoon. Our results, which do not account for nighttime predations and therefore underestimate numbers of successful attacks, suggest that a single predatory individual can have a sudden, devastating effect on a prey species.

FOOD HABITS OF COYOTES (CANIS LATRANS) IN THE VALLES CALDERA NATIONAL PRESERVE, NEW MEXICO

Wildlife managers needed to understand coyote (Canis latrans) ecology in order to develop management plans on the nascent Valles Caldera National Preserve in northern New Mexico. Managers concerned about low elk (Cervus elaphus) recruitment had observed an increase in sightings of coyotes and observations of coyote predation on elk calves. Our objective was to identify and quantify coyote diet, and assess the temporal variation in coyote diet on the Valles Caldera National Preserve, particularly as related to elk calf consumption. We examined coyote food habits using 1,385 scats analyzed monthly from May 2005 to November 2008. The most frequent taxa were rodents (predominantly voles from the genus Microtus, and northern pocket gophers, Thomomys talpoides), elk, insects from the orders Orthoptera (grasshoppers and crickets) and Coleoptera (beetles), mountain cottontail rabbit (Sylvilagus nuttallii), and plant material (mainly grass). We detected rodent and elk in scats during all months of the study and were each present in 54% of scats overall. We identified elk remains in 43% of spring scats, 72% of winter scats, and 56% of fall scats. During summers, we could distinguish calf from adult elk hair: 8% of summer the scats contained adult elk hair and 39% contained calf elk hair. The frequency of prey items varied significantly over most seasons and years, with notable exceptions being that elk did not vary among summers and winters, and rabbits were a consistent diet item through all seasons. The high frequency of elk in the coyote diet bears further study on the density of elk calves, the vulnerability of elk to predation, the nutritional impacts from the quality of forage available to elk, and the role of hunting and other mammalian predators in providing carcasses.

Rhyolite lava emplacement dynamics inferred from surface morphology

The morphology of a silicic lava is created by the fluid dynamic conditions that operated during flow. Careful analysis of these features can thus be used to reconstruct emplacement processes. We used unoccupied aerial system and structure-from-motion photogrammetry techniques to collect centimeter-scale spatial resolution imagery of the surfaces of South Coulee and Obsidian Dome rhyolite lavas (Mono-Inyo Craters, USA). We supplement the newly acquired orthomosaics and digital elevation models with existing imagery of other Holocene rhyolite lavas from across the western USA, including Rock Mesa Dome (South Sister, OR), Newberry Flow (South Sister, OR), Obsidian Flow (Newberry, OR), Interlake Flow (Newberry, OR), and Banco Bonito Flow (Valles Caldera, NM). Although many morphologic features exist, we restrict our quantitative analyses to the recurrent ridges and blocks of loose rubble that are common to the flows. Ridge spacing and ridge vergence indicate the ridges are likely folds produced by compression during emplacement. Pressure ridge spacings range from 27 to 45 m at South Coulee and 18 to 34 m on Obsidian Dome. Spacing generally decreases with distance from the vent across both lavas. Ridge amplitudes range from 4 to 17 m at both lavas and show little correlation with distance from the vent. The vergence of the crest of the ridges in the flow interiors points back to the source vent, which provides strong evidence for endogenous flow and the backward rotation of folds produced by undertow of the underlying lava. Ridges near flow margins verge towards the flow front, demonstrating that exogenous flow becomes increasingly important at the point of advance. In both South Coulee and Obsidian Dome block sizes are largest near the vent, and gradually decrease towards the flow front. The gradual decrease in block size with increasing distance from the vent likely reflects decreasing effusion rates from the conduit. We interpret our high-resolution field measurements under the lens of analytical solutions to fluid dynamic models to estimate emplacement timescales and associated rates. We calculate relatively abbreviated eruptive timescales ranging from 1 month to <2 years. Such values predict eruptive fluxes <135 m3 s−1 and velocities <100 m day−1, providing helpful criterion for volcanic monitoring or hazard forecasting efforts.

Resolving Deep Critical Zone Architecture in Complex Volcanic Terrain

AbstractCritical zone (CZ) structure, including the spatial distribution of minerals, elements, and fluid‐filled pores, evolves on geologic time scales resulting from both top‐down climatic forcing and bottom‐up geologic controls. Climate and lithology may be imprinted in subsurface structure as depth‐dependent trends in geophysical, geochemical, mineralogical, and biological datasets. As the weathering profile is as much (or more) a product of past environmental conditions, development of predictive models requires understanding the relative roles of climatic forcing and the geologic template on which CZ processes evolve. Doing so in complex volcanic terrains with high initial bedrock porosity and distinct depositional and hydrothermal alteration histories is particularly challenging. To resolve CZ structure in a rhyolitic catchment in the Valles Caldera National Preserve (NM, USA), this study combined geophysics, drilling, and laboratory analyses to produce depth‐resolved porosity, geochemistry, and mineralogy datasets to &gt;40 m in depth. Quantitative X‐ray diffraction analysis showed that local mineral transformations control complex chemical enrichment/depletion (τ) patterns. Using linear discriminant analysis, key variables enabled separation of complex‐layered geology into discrete zones. Contemporary, matrix‐dominated weathering processes and modern hydrologic fluxes occur dominantly within the top 15 m of the weathering profile. This zone is convoluted by incomplete primary mineral weathering and overprinted by post‐eruption weathering and metasomatism. Matrix weathering transitions to fracture surface weathering driven by deep percolation of slower moving, longer residence time meteoric waters at depth. By altering initial conditions and weathering trajectory, geologic legacy is a critical factor in how this subsurface landscape evolved and functions.

Petrogenesis of three East Fork Member rhyolites of the Jemez volcanic field, Valles caldera, New Mexico, USA

The most recent volcanism in the Valles caldera is represented, in stratigraphic order, by the El Cajete Pyroclastic Beds (ECPB), Battleship Rock Ignimbrite (BRI), the VC-1 rhyolite (not studied herein), and Banco Bonito Flow (BBF), which are collectively known as the East Fork Member (EFM) of the Valles Rhyolite. The EFM was erupted approximately 74 to 68 ka after an approximate 460 ka lull in ring-fracture volcanism.Crystal assemblages consist of plagioclase, biotite, clinopyroxene, orthopyroxene, amphibole, sanidine, quartz, and oxides, in order of abundance. Electron probe microanalysis and detailed petrography indicates that two distinct crystal populations are present in the ECPB, BRI, and BBF. Large (≥1 mm), typically resorbed or subhedral crystals represent one population, and small (≤0.5 mm), generally euhedral crystals represent the other. The large resorbed plagioclase crystals typically have oligoclase to andesine rim overgrowths. 40Ar/39Ar geochronology performed on euhedral biotite and groundmass glass from the BBF returned isochron ages of 478 ± 3 ka and 575 ± 2 ka and total gas ages of 125 ± 1 ka and 129 ± 1 ka, respectively. High molar Mg numbers of large euhedral biotite and 40Ar/39Ar ages older than the accepted age range indicate these crystals are xenocrystic. Radiogenic isotopes are consistent with mixing between the mantle and lower crustal reservoirs. General trends are evident between whole-rock major and trace elements with increasing SiO2 and Nb, respectively. In general, incompatible trace elements increase and compatible trace elements decrease with increasing Nb. For the major elements, MgO, P2O5, Al2O3, FeO* show decreasing trends while K2O and Na2O show increasing trends with increasing SiO2. Incompatible trace element ratios (Ta/Yb, Y/Yb, Th/Yb, Th/Nb) indicate the presence of a single magma batch.The heterogeneity in crystal morphology and chemistry can be explained by a model in which partial melting of mid- to deep continental crust occurred due to an intrusion of an intermediate composition magma. Magma mixing and an exchange of crystals took place between the partial melt and the intruding magma. The hybrid magma rose to the upper crust, where it underwent fractional crystallization prior to eruption. The geochemical and isotopic data from this study are best explained by a modified version of the rapid production and eruption model put forth by Huppert and Sparks (1988).

Seismicity Monitoring in North-Central New Mexico by the Los Alamos Seismic Network

AbstractThe first seismic stations of the Los Alamos Seismic Network (LASN) were installed in 1973, as a part of research on monitoring of nuclear testing. The extent of the network rapidly expanded by the late 1970s. By the middle 1980s, spatial coverage of the network was drastically reduced, due to a loss of funding. Since then, however, it has been possible to expand the coverage of the network with additional stations and to slowly upgrade network equipment to match contemporary instrument standards. These improvements will make it possible to keep recording the network’s data and to initiate real-time exchange of data with other institutions to improve earthquake monitoring throughout New Mexico and neighboring states. During more than 40 yr of operation, the network has provided a slow but steady increase in the volume of earthquake seismograms available to study seismicity and tectonics in north-central New Mexico. The current network covers an area from the Valles Caldera on the west, to within the Rio Grande rift on the east. LASN has yielded locations for about 900 earthquakes in north-central New Mexico between 1973 and 2013 (the most recent locations available). Epicenters of these have a complex pattern, with some that can be attributed to the deformation of the rift, though most are spread in areas west of the rift. A lack of seismicity in and near the Valles Caldera reinforces an earlier observation, based on far fewer earthquakes, which first called attention to this paucity of seismicity and attributed it to ductile deformation resulting from elevated crustal temperatures.

Hot spring hydrochemistry of the Rio Grande rift in northern New Mexico reveals a distal geochemical connection between Valles Caldera and Ojo Caliente

Warm and hot springs occur within and on both sides of the Rio Grande rift (RGR) of northern New Mexico. Springs on the western side of the RGR are along the Ojo Caliente fault zone, which intersects the Embudo fault transfer zone that extends northeast of the Valles Caldera. Springs on the eastern side occur along north-south rift-bounding faults near Taos, NM. We compared spring water geochemical data from the western and eastern sides of the RGR to discover spring water origins. Included in our discussion was spring chemistry of the Valles Caldera located to the southwest of our study area. The Valles Caldera is a significant feature because it had major rhyolite eruptions 1.65 and 1.26 Ma, continued rhyolite eruptions until ~30 ka, and an active magmatically-driven geothermal system. The latest volcanic events in the Taos Plateau were basalt flows occurring about ~ 2 Ma. Our spring chemistry findings showed elevated levels of geothermal input in the western spring group, with the greatest input in Ojo Caliente spring waters. The elevated geothermal tracers include CO2, Li, B, Na, Cl, HCO3, Cext, He, Sr, mantle-like δ13C-CO2 values (−3.5 to −6.8‰), radiogenic basement-like 87Sr/86Sr ratios (0.747), and mantle-derived 3He (up to 4.8%) in the presence of highly elevated crustal 4He. Eastern springs had fewer magmatic inputs including tracers listed above and notably lower 87Sr/86Sr ratios ranging from 0.708 to 0.713. Nevertheless, eastern springs contain endogenic carbon and helium isotope values showing up to 4% mantle-derived helium. We interpret the elevated tracer results discovered in Ojo Caliente spring waters as distal influences of the Valles geothermal system, which is about 60 km away. The most conclusive evidence for these results stem from significant contributions of magmatically-derived volatiles including CO2, He, and their isotopes. With evidence of far-traveled water and volatiles, we concluded that the RGR transfer zone fault systems provide conduits for long-distance migration of deep fluids and gases that mix with meteoric water in the shallow subsurface.

Composition Variation and Eruption Dynamics of the El Cajete Series, Valles Caldera, New Mexico

Composition Variation and Eruption Dynamics of the El Cajete Series, Valles Caldera, New Mexico

Quaternary tephra from the Valles caldera in the volcanic field of the Jemez Mountains of New Mexico identified in western Canada

AbstractA fine-grained, up to 3-m-thick tephra bed in southwestern Saskatchewan, herein named Duncairn tephra (Dt), is derived from an early Pleistocene eruption in the Jemez Mountains volcanic field of New Mexico, requiring a trajectory of northward tephra dispersal of ~1500 km. An unusually low CaO content in its glass shards denies a source in the closer Yellowstone and Heise volcanic fields, whereas a Pleistocene tephra bed (LSMt) in the La Sal Mountains of Utah has a very similar glass chemistry to that of the Dt, supporting a more southerly source. Comprehensive characterization of these two distal tephra beds along with samples collected near the Valles caldera in New Mexico, including grain size, mineral assemblage, major- and trace-element composition of glass and minerals, paleomagnetism, and fission-track dating, justify this correlation. Two glass populations each exist in the Dt and LSMt. The proximal correlative of Dt1 is the plinian Tsankawi Pumice and co-ignimbritic ash of the first ignimbrite (Qbt1g) of the 1.24 Ma Tshirege Member of the Bandelier Tuff. The correlative of Dt2 and LSMt is the co-ignimbritic ash of Qbt2. Mixing of Dt1 and Dt2 probably occurred during northward transport in a jet stream.

Sulfur cycle in the Valles Caldera volcanic complex, New Mexico – Letter 2: Aqueous sulfate budget and implications for hydrological transport on early Mars

There is a large disagreement about what sulfur sources participated in formation and transport of aqueous sulfate (SO42−) on early Mars. Previous geochemical models mainly focused on volcanic degassing and atmospheric deposition via acid rainfall. Generally, it is unclear whether chemical weathering of sulfur mineralization present in volcanic bedrock might have been an important source of aqueous SO42− on Mars. Therefore, we selected the watershed of Valles Caldera to better constrain the quantities (fluxes) of SO42− from chemical weathering compared to direct oxidation of hydrothermal sulfur-rich (H2S) gases and atmospheric deposition. Our results show that in the presence of various oxidants (e.g., oxygen, metals) the SO42− contributions from these sources significantly vary between dry and wet seasons. In the dry seasons of Nov 2012 and May 2013, the aqueous SO42− flux from bedrock weathering was the highest (5992 to 8142 kg/month; ∼81% of total flux) with minor SO42− contributions from atmospheric deposition (1110 to 1508 kg/month; ∼15%) and hydrothermal H2S gas emission (314 to 404 kg/month; ∼4%). Conversely, in the wet season (Mar 2014) the bedrock weathering showed SO42− fluxes of 4070 kg/month (∼34%) and gas emission of 6088 kg/month (51%) compared to smaller inputs from atmospheric deposition (1796 kg/month; ∼15%). The volume of water interacting with a particular sulfur reservoir appears to define the amount (flux) of SO42− transported in the aqueous system of active volcanoes. While H2S emission more effectively increased SO42− fluxes in surface water under wet conditions, the SO42− fluxes from chemical weathering only slightly varied between investigated wet and dry seasons. We demonstrate that in addition to hydrothermal sulfur emissions the chemical weathering should be included in geochemical source-to-sink models of sulfur cycles on Mars, particularly when assuming prevailing dry surface conditions in the past.

Sulfur cycle in the Valles Caldera volcanic complex, New Mexico – Letter 1: Sulfate sources in aqueous system, and implications for S isotope record in Gale Crater on Mars

Initial in situ sulfur (S) isotope measurements of the Martian bedrock in Gale Crater have revealed an unexpectedly wide range of δ34S values (−47 to +28‰). Generally, it is unclear what processes could have contributed to these large isotope fractionations. Therefore, we studied S sources and aqueous SO42− cycling in the Valles Caldera volcanic complex, New Mexico to better understand S isotope fractionations related to S degassing, hydrothermal activity, and low-temperature processes in aqueous environment. Overall, our study demonstrates that volcanic systems show large spatial heterogeneity in δ34S. Magmatic S sources are obvious in steam-dominated H2S degassing and precipitation of secondary minerals from hydrothermal fluids with low δ34S values of +0.9 ± 3‰. Locally, however, hydrothermal processes have resulted in more negative δ34S values in sulfide minerals (−18 to −4‰) and more positive δ34S values in sulfate minerals (−1 to +3‰). Major aqueous SO42− sources are oxidation of H2S from modern hydrothermal gas emission, and oxidation and dissolution of sulfide and sulfate minerals present in the hydrothermally altered bedrock and crater-lake sediments. The δ34S of aqueous SO42− in surface water and groundwater varies widely (−8 to +5‰) and is similar to major S endmembers that undergo oxidation and/or dissolution by active hydrological system. Minor SO42− contributions with more positive δ34S values (+9 to +14‰) come from deeply circulating geothermal fluids and negligible amounts from atmospheric deposition (+5 to +7‰ in snow). Elevated SO42− contents are mainly associated with modern and past H2S emissions and oxidations near the surface. On regional scale, however, most of the intracaldera bedrock is S-depleted, thus the SO42− contents are usually low in the surface aquatic system and younger sedimentary lake deposits formed at times of negligible near surface hydrothermal activity. In general, magmatic-hydrothermal processes apparently cause the largest δ34S variation in S-bearing minerals on volcanic terrains. Therefore, we infer that the measured wide range of δ34S values in the Gale sediments by the Curiosity rover on Mars can be explained by S isotope composition of magmatic-hydrothermal sulfide and sulfate minerals that were present in the initial igneous/volcanic rocks prior to crater formation. Later aqueous processes involved oxidation and dissolution of S minerals initially present in these rocks and led to subsequent formation of diagenetic fluids and alteration products enriched in SO42− with relatively large δ34S variation. Additionally, physical erosion, transport and deposition of detrital hydrothermal S minerals from igneous/volcanic rocks might be in part responsible for the measured wide range of δ34S in Gale Crater. These unique S isotope results, measured in situ on another planet for the first time, imply the importance of magmatic-hydrothermal fluids in S transport on early Mars and their subsequent alteration in low-temperature aqueous environments.

RESPONSE TO SHACKLEY AND MOORE

Shackley and Moore's Comment misrepresents the focus of my 2017 article, which is not “regional” in nature but rather attempts a focused study of one community's relationship with the Valles Caldera; furthermore, the vast majority of the data they present do not correspond temporally with my study.

MORE THAN JUST JEMEZ PUEBLO OBSIDIAN: COMMENT ON LIEBMANN'S “… LANDSCAPES OF SIGNIFICATION IN THE AMERICAN SOUTHWEST”

Liebmann's (2017) essay on the relationship between Jemez Pueblo and the Valles Caldera of northern New Mexico seems to imply that the Jemez Pueblo had an exclusive relationship with the caldera, particularly Redondo Peak, and the major obsidian source Cerro del Medio (CDM). This is curious given that abundant obsidian provenance studies from the region exhibit equal to or nearly equal proportions of Cerro del Medio obsidian that are not considered ancestral to Jemez Pueblo. Liebmann's regional perspective based on landscape theory appears flawed by a lack of regionally specific data.

The effects of a catastrophic forest fire on the biomass of submerged stream macrophytes

Primary production during the growing season in the low-gradient meadow streams of the Valles Caldera in northern New Mexico (USA) is dominated by submerged aquatic macrophytes. A catastrophic wildfire beginning on June 28, 2011, the Las Conchas fire, burned 36% of the East Fork Jemez River catchment above an intensively instrumented stream reach where water quality, hydrology, and aquatic ecology are being studied. Submerged macrophyte biomass in the late summer of 2011 was reduced about 20% after a series of high turbidity spates (>1200 NTU) in late July through early September. Stable flows and deposition of fire-related nutrient-rich sediments in the fall of 2011 led to maximum mean macrophyte biomass during the three-year period of study of 234 g ash free dry-mass (AFDM) m−2 in October of 2011. Peak mean biomass in 2012 was 228 g AFDM m−2 in September, during a growing season with only minor hydrologic and water quality disruptions. A major regional storm over multiple days in mid-September of 2013 produced the highest discharge during the three years of study with turbidities reaching ∼400 NTU. Peak mean biomass in 2013 did not reach levels measured in 2011 and 2012. Elodea canadensis was more sensitive to biomass removal during these high flow conditions while Ranunculus aquatilis added biomass following higher flow conditions in 2011 and 2013. Disturbance impacts on submerged macrophytes from major wildfires can be both negative and positive depending upon species types, stream hydrology, catchment geomorphology and water quality.