Devils Postpile Research Articles

Tracing short-lived hydrothermal circulation systems and water–rock interactions around small-scale intrusions

Hydrothermal circulation around magmatic intrusions affects hazards, critical metal deposition, and heat transfer, however it is often difficult to directly observe. We combine stable isotope and thermochronologic measurements, hydrothermal circulation modeling, and forward thermal history modeling to understand the short-lived hydrothermal circulation system that developed around the Little Devils Postpile, a small-scale mafic intrusion in the eastern Sierra Nevada Mountains of western North America. Bedrock samples collected in transects orthogonal to the intrusion reveal reset and partially reset apatite (U-Th-Sm)/He and zircon (U-Th)/He ages up to ∼13m from the contact. Measurements of hydrogen isotopes in apatite crystals from the same samples show deuterium depletion near the contact; δD values vary between −120‰ and −132‰ within 3m of the contact, −112‰ to −104‰ at 4–6m from the contact, and −85‰ to −95‰ at distances of 12m to 40m from the contact. In contrast, oxygen isotopes do not vary spatially with a δ18O of +6.4 ± 0.4‰. This depletion of δD and consistency of δ18O suggests that short-lived water–rock interaction occurred following the intrusion emplacement, facilitating the exchange of hydrogen isotopes via diffusion rather than dissolution-precipitation processes. Conductive cooling calculations predict an alteration aureole ten times larger than is observed by the low-temperature thermochronometric ages. Numerical models of hydrothermal circulation, for a range of host bedrock permeabilities and magmatic emplacement temperatures, reveal that the geometry of alteration is most consistent with buoyancy-driven hydrothermal circulation and a relatively high crustal permeability. With this case study, we show that combining thermochronology and hydrothermal modeling allows for the opportunity to model hydrogen isotope exchange and predict plausible apatite-water hydrogen fractionation. These new constraints on the geometry of water–rock interactions coupled with hydrothermal circulation modeling provide (1) a rare window into the pressure–temperature evolution of a small magmatic intrusion, (2) constraints on crustal permeability, and (3) a useful tool for interpreting low-temperature thermochronometric data in volcanic settings.

Relief from summer warming: Devils Postpile National Monument’s cold air pool supports a refugium-based conservation strategy

Cold air pooling (CAP) occurs in low-lying areas where cold, dense air collects during nighttime hours, producing colder temperatures than surrounding higher elevations. Devils Postpile National Monument (DEPO) is confined by steep mountain ridges, which promote cold air drainage into lower-elevation meadows and river valleys. These low lying areas where CAP occurs could help facilitate a potential refugium from some of the greatest impacts of regional climate warming. A strong focus on CAP occurrence is part of a seven-step climate change refugia conservation cycle, outlined in Morelli et al. (2016), that DEPO has instituted, wherein resource management seeks to identify and focus on parts of the landscape that may be sheltered from the intensity and pace of rapid climate change. Locales that harbor persistent CAP may provide vulnerable species and ecosystems a sort of refuge, allowing more time to adapt to new conditions. Central to DEPO’s strategy is better monitoring and understanding of CAP occurrence. Based on observations from 10 years of temperature loggers in and around DEPO, CAP operates reliably throughout the year, and especially during summer. Importantly, CAP has occurred strongly during recent unusually warm years. These findings reinforce the value of monitoring and ongoing analysis as a way to guide conservation and adaptation using potential climate change refugia. As with this co-developed park–university investigation, other land managers could consider climate refugia-oriented management as a viable conservation and adaptation strategy.

Challenges characterizing N deposition to high elevation protected areas: A case study integrating instrument, simulated, and lichen inventory datasets for the Devils Postpile National Monument and surrounding region, USA

Excess N deposition is a common stressor of ecological health. Sensitive biota, including many lichens, respond to small differences in atmospheric N deposition. For lands with a conservation mandate, obtaining sufficient N data to evaluate risks is a challenge, especially in Mediterranean or arid landscapes. Managers in the Western U.S. commonly use epiphytic (“tree-dwelling”) lichens to supplement N assessments, although options for higher elevations lacking epiphytes are poorly developed. Managers instead rely on broad-scale air quality simulations like the Total Deposition Model (TDEP). The Sierra Nevada Range is an example where anthropogenic N reaches mid-to-high elevation protected areas but managers lack tools for monitoring at ecologically relevant spatial-scales. Our main goals were to demonstrate how well-studied epiphytic bioindicators can supplement N assessments and recommend saxicolous (“rock-dwelling”) candidates for similar development to improve coverage in higher elevations. As a case study, we characterized N deposition at a small (323 ha) protected area, Devils Postpile National Monument (DEPO), by integrating data from TDEP, air instruments, and assays of %N in the epiphyte Letharia vulpina. We used the regional N threshold associated with detrimental effects to epiphytic lichen communities, 2.9 kg N ha−1 yr−1 in throughfall (i.e. under a tree canopy), as a provisional critical load (CL) for indicating areas at risk of ecological impacts. Results clearly showed the need for empirical, diverse, and finer-scaled information, even for an area as small as DEPO. Importantly, simulations from TDEP overestimated dry deposition of oxidized N, making total N estimates nearly twice measured values (6.0 vs 3.03 – 3.66 kg N ha−1 yr−1, respectively). While small, our L. vulpina dataset (n = 5) from the Monument indicated highly variable N in throughfall (1.7 – 4.44 kg N ha−1 yr−1), with small-scale drivers, like proximity to the river canyon and the Central Valley, tipping the scale towards CL exceedance. Regional L. vulpina assays (n = 355) showed a distinct north-to-south gradient in California where N deposition at DEPO was highly similar to the nearby protected area, Yosemite National Park, where ecological impacts of excess N are well-documented. To expand N bio-monitoring into higher elevation areas, we recommend vetting five widespread saxicolous species, Rhizoplaca melanophthalma, Umbilicaria phaea, U. polaris, Xanthoparmelia coloradoënsis, and X. cumberlandia.

Coarse and Fine Particulate Matter Components of Wildland Fire Smoke at Devils Postpile National Monument, California, USA

ABSTRACT Fine (PM2.5) and coarse (PM10) particulate matter were monitored during the summer and fall of 2018 at Devils Postpile National Monument, California, USA. This remote site, located in the Sierra Nevada, was downwind of a number of wildland fires that were burning in California. The coarse (PM2.5-10) and the fine (PM2.5) fractions of the PM in the wildland fire smoke showed median PM2.5-10/PM2.5 ratios of .47 and 1.37 during periods with and without smoke, respectively. The concentrations at ground level were significantly (p < 0.001) higher during the periods with smoke for both the PM2.5-10 (10.3 µg m–3) and the PM2.5 (35.3 µg m–3), although the PM2.5 contributed most of the increase. These concentrations suggest that the fire size and intensity along with the distance and transport of smoke determine the exposure risk to humans. Current exposure estimates obtained via modeling and emission estimates may misrepresent ground-level concentrations due to a lack of understanding of the aerosol distribution in an aging wildland fire smoke plume.

Air Quality at Devils Postpile National Monument, Sierra Nevada Mountains, California, USA

Ambient concentrations of O_3, PM_(2.5), NH_3, NO, NO_2, HNO_3, SO_2 and VOCs were measured at Devils Postpile National Monument (DEPO) during the summer seasons of 2013 and 2014. The measurements were impacted by the Aspen and Rim Fires in 2013, and the French and King Fires in 2014. While O_3 concentrations were not discernibly perturbed by the fire events, the 70 ppb threshold (8-hour average) corresponding to both the current California Ambient Air Quality Standard (CAAQS) and the new National Ambient Air Quality Standard (NAAQS) was exceeded on five days during 2013, and on 16 days during 2014. The older NAAQS of 75 ppb (8-hour average) was exceeded once in 2013, and six times in 2014. Exceedances of the CAAQS or NAAQS occurred when background sources of O_3 were augmented by regional-scale transport, at higher altitudes, of polluted air masses that had passed through the San Joaquin Valley before arriving at the DEPO site. The 2013 Aspen Fire elevated PM_(2.5) to a maximum hourly concentration of 214 μg m^(-3) and a maximum 24 h mean of 92.7 μg m^(-3), and resulted in 13 exceedances of the 35 μg m^(-3) (24 h average) NAAQS for PM_(2.5). The 2013 Rim Fire increased PM_(2.5) to a maximum hourly concentration of 132 μg m^(-3) and a maximum 24 h mean of 69.6 μg m^(-3), and resulted in two exceedances of the 24 h NAAQS. Concentrations of NH_3 increased during all fires, as did those of NO_2 during the Aspen and Rim Fires. Concentrations of benzene increased substantially during the French Fire.

Vascular Flora Of Devils Postpile National Monument, Madera County, California

Abstract Devils Postpile National Monument is 319 ha in size, located in Madera County, California, on the western slope of the Sierra Nevada at an average elevation of 2280 m. Though small in size, the monument supports diverse habitats, including forests, chaparral, riparian corridors, meadows, seeps, and ponds. In 2001, the National Park Service conducted a survey to 1) inventory the vascular flora and document with vouchered specimens; and 2) describe the distribution and abundance of species of special management concern (rare and/or non-native). Methods coupled a species-level inventory with vegetation mapping, covered an estimated 70 percent of the monument's surface area, and combined broad and targeted search strategies. Survey results yielded a 121 percent increase (from 169 to 373) in the number of documented plant taxa, representing 60 families and 199 distinct genera. Forty-five percent of species were clustered within six families: Asteraceae, Poaceae, Cyperaceae, Brassicaceae, Onagraceae, a...

Field Note: Attributes of Windthrown Trees in a Sierra Nevada Mixed-Conifer Forest

On Nov. 30 to Dec. 1, 2011, an extreme wind event affected the central Sierra Nevada mountain region of California, causing extensive windthrow of trees. The wind event was caused by an extreme pressure gradient from north to south over Nevada and the Sierra that was unusual for the region in its duration, atypical wind direction, and high-intensity wind. Within Devils Postpile National Monument, there were approximately 118.5 windthrown trees km-1. The average diameter at 1.37 m of windthrown trees was 55.36 cm, 2.2 times greater than that for pre-windstorm standing trees. Trees differed in damage type; 86% of trees were uprooted, whereas 14% were snapped, and dead trees were more likely to snap than uproot relative to live trees. Tree species was not a factor in likelihood of windthrow because species composition and relative abundance of windthrown trees were representative of the preexisting forest composition. This wind event is the most extensive on record for California's Sierra Nevada range and may have long-lasting effects on forest composition and function.

Surface ozone at the Devils Postpile National Monument receptor site during low and high wildland fire years

Surface ozone (O3) was measured at the Devils Postpile National Monument (DEPO), eastern Sierra Nevada Mountains, California, during the 2007 (low-fire) and 2008 (high-fire) summer seasons. While mean and median values of O3 concentrations for the 2007 and 2008 summer seasons were similar, maximum O3 concentrations in June and August 2008 were higher than in any month of the 2007 summer season. This increase of maximum concentrations in the high-fire year is attributed to emissions of O3 precursors from wildland fires upwind of DEPO in addition to transport of polluted air from the California Central Valley (CCV) and the San Francisco Bay Area (SFBA). Analysis of backward trajectories for high O3 episodes in June 2007 and 2008 showed the lowest O3 pollution at DEPO when air masses originated over the Pacific Ocean (PO) and passed from West to East over PO and CCV at high altitudes. The highest O3 levels occurred when air masses originated in the vicinity of SFBA, swept through CCV in the NW–SE direction before reaching DEPO at low altitudes. Diurnal O3 concentrations were characterized by a sharp increase early morning and maximum values in late afternoon, followed by gradual evening decreases with very low pre-dawn minima, a phenomenon explained by local generation of O3 combined with the long range transport of polluted air masses from CCV, boundary layer destruction and surface deposition. Once in 2007, and 3 times in 2008, the 8-h average concentration exceeded 75 ppb, counting towards exceedance of the present primary Federal O3 standard (4th highest 8 h concentration <75 ppb over 3 years). The California 8-h average standard (<70 ppb) was exceeded 5 times in 2007 and 6 times in 2008, and these instances counted towards exceedance of the newly proposed primary Federal primary standard (4th highest 8-h concentration <70 ppb over 3 years). In addition, in 2008, the California 1-h average standard (<90 ppb) was exceeded 3 times. The proposed Federal secondary O3 standard of 13 ppm h was exceeded reaching 16 ppm h in 2007 and 15 ppm h in 2008 that indicates potentially phytotoxic effects on local flora.

Lichens in relation to management issues

The central and southern Sierra Nevada are subjected to high levels of ozone, high and increasing nitrogen deposition, and unknown quantities of pesticides such as organophosphates from agricultural emissions in the Central Valley. Fire regimes have changed greatly over time, from relatively frequent fire historically, to fire exclusion, to its reintroduction as prescribed fire. Parts of the Sierra parks have been grazed by livestock, and some of this persists today. On top of these factors, climate is likely to change rapidly. Although a large literature exists on human impacts on lichens, almost nothing is known on this topic in the Sierra Nevada specifically. We are largely ignorant of the biodiversity, ecology, and ecological roles of lichens in the Sierra Nevada Park system (the “Sierra parks”: Sequoia and Kings Canyon National Park, Yosemite National Park, and Devils Postpile National Monument ). This paper synthesizes existing data, written reports and other information about lichens in and near the Sierra Nevada parks, as a first step toward developing better baseline data and assessing lichen populations or communities as potential indicators of ecosystem change. Lichens are diverse in their ecosystem roles and functional significance. Organizing the hundreds of lichen species present in the Sierra parks into functional groups helps us to understand, interpret, inventory, and monitor the diversity of lichens. We therefore divided lichens of the Sierra parks into the following functional groups: forage lichens, nitrogen fixers, acidophiles, wolf lichens, crustose lichens on rock, crustose lichens on bark and wood, biotic soil crusts, aquatic, other green algal macrolichens, and pin lichens (calicioids). Management issues that relate to lichens include biodiversity, air quality, water quality, fire, grazing, and the possibility of draining Hetch Hetchy Reservoir. Existing lichen data from the west slope of the Sierra Nevada, of relevance to the management of Sierra parks include: extensive lichen community data from the Forest Inventory and Analysis program (FIA), a few floristic studies focused on the parks, photo points on prescribed fire transects, lichen biomass estimates from four locations, elemental analysis of lichens from a small number of locations, lichen communities in relation to various nitrogen species in Kings River watershed, the Western Airborne Contaminants Assessment Project, Bryoria fremontii studies at Teakettle Experimental Forest, and herbarium databases. We recommend the following short list for future inventory and monitoring work: population status and trend of Bryoria fremontii , macrolichen community monitoring, revise and update the inventory of lichen biodiversity, and preliminary surveys of lichens in neglected habitats.

Magmatic evolution of Quaternary mafic magmas at Long Valley Caldera and the Devils Postpile, California: Effects of crustal contamination on lithospheric mantle‐derived magmas

Isotopic variations in Cenozoic mafic volcanic rocks in the Basin and Range Province of the southwestern United States are considered by many to be due to differences in mantle sources, either subduction‐enriched subcontinental lithosphere or the asthenosphere. This is a detailed geochemical investigation of the magmatic evolution and mantle source(s) of Quaternary mafic volcanism at Long Valley Caldera and the Devils Postpile National Monument, Western Great Basin. The Quaternary mafic lavas are dominantly post‐Bishop Tuff (&lt;0.7 Ma) in age, occur as isolated cinder cones and small‐volume lava flows within the caldera, and range in composition from alkali basalt to trachyandesite. Whereas fractional crystallization is the dominant process effecting the evolution of Long Valley lavas with MgO &gt; 7%, assimilation of Sierra Nevada granitoids becomes increasingly important at MgO &lt; 7%, such that SiO2, K/La, and 87Sr/86Sr increase as P/K, Zr/Ba, and 143Nd/144Nd decrease. Assimilation‐fractional crystallization calculations suggest that the most evolved trachyandesites include ∼30% of upper crustal component. In lavas with &gt;7% MgO, 87Sr/86Sr and La/Sm decrease as 143Nd/144Nd, Nb/La, Zr/Ba and (to a lesser extent) Pb isotope ratios increase from the oldest to the youngest Quaternary lavas. The oldest lavas are chemically similar to other lavas in the western Basin and Range thought to have an enriched lithospheric mantle source. Whereas the shifts in Sr and Nd isotope ratios from oldest to youngest basalts might be consistent with a progressively increasing asthenospheric component in the lavas, the shifts in incompatible element ratios and lack of shifts in Pb isotope ratios with time are not. Instead, they indicate that with time the mafic lavas may have increasingly interacted with mafic crust, perhaps gabbroic/dioritic rocks at depth within the Sierra Nevada Batholith. Alternatively, a second, less enriched lithospheric mantle source is present beneath the Long Valley area that has only recently begun to undergo melt generation, and this source has made progressively larger contributions to the basaltic magmas erupted at the surface.

Three‐Dimensional Gravity Modeling of the Geologic Structure of Long Valley Caldera

A 48‐mGal gravity low coincides with Long Valley caldera and is mainly attributed to low‐density caldera fill. Gravity measurements by Unocal Geothermal have been integrated with U.S. Geological Survey data, vastly improving gravity station coverage throughout the caldera. A strong regional gravity trend is mainly attributed to isostasy. A “best fitting” (based on regional control of basement densities) Airy‐Heiskanen isostatic model was used for the regional correction. A three‐dimensional, multiple‐unit gravity modeling program with iterative capabilities was developed to model the residual gravity. The density structure of Long Valley caldera and vicinity was modeled with 22 discrete density units, most of which were based on geologic units. Information from drill hole lithologies, surface geology, and structural geology interpretations constrain the model. Some important points revealed by the three‐dimensional gravity modeling are that (1) the volume of ejected magma associated with the Bishop Tuff eruption is greater than previously thought, (2) the caldera structure is strongly influenced by precaldera topography and the extensions of major, active faults, (3) the main west ring fracture is coincident with the Inyo Domes‐Mono Craters fracture system, (4) a relatively low‐density region probably underlies the caldera, and (5) a silicic magma chamber may underlie Devils Postpile.

POTASSIUM-ARGON DATES OF THREE PLEISTOCENE INTERGLACIAL BASALT FLOWS FROM THE SIERRA NEVADA, CALIFORNIA

Potassium-argon dates of 90,000 ± 90,000 years and 60,000 ± 50,000 years on the basalt in Sawmill Canyon of the Sierra Nevada, California, that underlies a moraine correlated with the Tahoe Glaciation and overlies pre-Tahoe till show that the Tahoe is probably less than 100,000 years old. Pre-Tahoe basalt near Sonora Pass gives a date of 150,000 ± 30,000 years. These data support the correlation of the Tahoe with early Wisconsin. Tahoe Glaciation in the southernmost Sierra Nevada seems to have been no less extensive than pre-Tahoe glaciation. The basalt that forms the Devils Postpile, believed by Matthes (1960) to have been extruded between his El Portal (Sherwin?) and Wisconsin glaciations, gives a date of 940,000 ± 160,000 years.