Volcanic Bedrock Research Articles

Provenance of modern sands from Baja California rivers (Mexico): petrographic constraints from light and heavy minerals

ABSTRACT We used high-resolution petrographic and dense-mineral data on modern sand to investigate erosion patterns of the El Rosario, San Fernando, and San Vicente river basins of Baja California (Mexico) to better understand the interrelationships between a complex magmatic arc terrane and surface processes. Modern sand composition of these three rivers reflects the nature of the source region, which lies in the central part of the Alisitos arc (Peninsular Ranges, Baja California, Mexico). The sand detrital modes correspond well with the main structural units drained by the El Rosario, San Fernando, and San Vicente rivers: 1) the Early Cretaceous oceanic arc of the Alisitos Group, 2) the Paleozoic to Mesozoic continental-margin metasedimentary rocks, 3) the Cretaceous plutons, 4) the Upper Cretaceous to Tertiary sedimentary rocks, and 5) the Tertiary volcanics. The modern sand of the San Vicente, San Fernando, and El Rosario rivers is fed chiefly from erosion of a magmatic arc and consists mostly of minor feldspatho-lithic (Fl) to quartzo-litho-feldspathic (qFL) sand and dominant quartzo-feldspatho-lithic (qLF) and litho-feldspatho-quartzose (lQF) sand. Framework petrography also suggests a progressive increase in quartz, K-feldspar, sedimentary and metamorphic lithic fragments, and a decrease in volcanic lithic fragments. Sand, in the Lv field, microlitic (Lvmi), felsitic (Lvf) and lathwork (Lvl) types, and trace amounts of vitric grains (Lvv), such as pumice particles. The andesitic volcanic province of the Alisitos arc sheds quartz-poor sand containing mainly microlitic lithic fragments and plagioclase, whereas sand derived from more felsic rhyolites and rhyodacitic and trachyandesitic products contains largely felsitic volcanic lithics and minor lathwork lithics are mainly derived from subordinate basalts. The abundance of intrusive rock fragments and volcanic and sedimentary lithics of the sampled river sands faithfully represents the relative abundance of a heterogeneous bedrock exposure consisting of sedimentary and metasedimentary rocks, as well as volcanic, plutonic, and medium- to high-grade metamorphic rocks in each drainage basin. Transparent heavy-mineral assemblages including major amounts of amphibole, pyroxene, epidote, titanite, zircon, and minor amounts of staurolite, rutile, actinolite, tourmaline, garnet, kyanite, andalusite, sillimanite, and apatite are in good agreement with a mixed provenance characterized mainly by magmatic, primarily volcanic (andesite, rhyolite, and basalt) and secondarily plutonic (granitoid rocks) and metamorphic source rocks. Some labile species such as hornblende and pyroxene grains show mainly corroded to etched morphologies due to dissolution processes and by chemical weathering processes occurring in a paleo and current semiarid climate. The Zircon+Tourmaline+Rutile index of the heavy-mineral modes, coupled with their subrounded to rounded grain surface texture, indicates recycling from the sedimentary source rocks. Heavy-mineral abundance and weathering textures in the San Fernando and San Vincente river sands match predominantly volcanic bedrock lithologies, while the El Rosario river sands match sedimentary and metasedimentary source rocks.

Probing environmental and tectonic changes underneath Mexico City with the urban seismic field

Abstract. The sediments underneath Mexico City have unique mechanical properties that give rise to strong site effects. We investigated temporal changes in the seismic velocity at strong-motion and broadband seismic stations throughout Mexico City, including sites with different geologic characteristics ranging from city center locations situated on lacustrine clay to hillside locations on volcanic bedrock. We used autocorrelations of urban seismic noise, enhanced by waveform clustering, to extract subtle seismic velocity changes by coda wave interferometry. We observed and modeled seasonal, co- and post-seismic changes, as well as a long-term linear trend in seismic velocity. Seasonal variations can be explained by self-consistent models of thermoelastic and poroelastic changes in the subsurface shear wave velocity. Overall, sites on lacustrine clay-rich sediments appear to be more sensitive to seasonal surface temperature changes, whereas sites on alluvial and volcaniclastic sediments and on bedrock are sensitive to precipitation. The 2017 Mw 7.1 Puebla and 2020 Mw 7.4 Oaxaca earthquakes both caused a clear drop in seismic velocity, followed by a time-logarithmic recovery that may still be ongoing for the 2017 event at several sites or that may remain incomplete. The slope of the linear trend in seismic velocity is correlated with the downward vertical displacement of the ground measured by interferometric synthetic aperture radar, suggesting a causative relationship and supporting earlier studies on changes in the resonance frequency of sites in the Mexico City basin due to groundwater extraction. Our findings show how sensitively shallow seismic velocity and, in consequence, site effects react to environmental, tectonic and anthropogenic processes. They also demonstrate that urban strong-motion stations provide useful data for coda wave monitoring given sufficiently high-amplitude urban seismic noise.

Physico-chemical and mineralogical changes of lithic xerorthent soils on volcanic rocks under semi-arid ecological conditions

This study investigates the mineralogical changes and soil development processes of young soils formed on various bedrocks of volcanic origin under the same land use/land cover and climate conditions. The current study was conducted in Lithic Xerorthent soils formed on tuff, trachybasalt, and trachyandesite bedrock between Sandıklı-Şuhut districts of Afyonkarahisar. The three soil profiles excavated in the study area were classified in Entisols order based on Soil taxonomy. The primary minerals, sanidine and muscovite, and the clay minerals, smectite, kaolinite, and illite, were widely determined in three soil profiles which were named Profile I (PI), Profile II (PII), and Profile III (PIII). According to the chemical alteration index (CIA) values, which indicate weathering, the soils formed on the tuff bedrock were slightly weathered (77.04%). The chemical weathering index (CIW) in the soils' surface horizons formed on the trachybasalt and trachyandesite bedrock are classified as non-weathering rocks with 24.43% and 33.88%. Basic cations are found at high levels in the tuff bedrock. The determination of phillipsite, gismondin and calcite minerals is an indication that the mineral content of the bedrock and the bedrocks have a significant effect on soil formation. The relationship between the bedrock and the soil has been revealed. As a result of the study, it was concluded that there were significant differences in their physico-chemical characteristics, weathering rates, and mineralogical properties. However, they were characterized as young soils since they do not contain any subsurface diagnostic horizons on the volcanic bedrock under the same climatic and land use/land cover conditions.

Water chemistry variation in tropical high‐mountain lakes on old volcanic bedrocks

AbstractWater chemistry and its ecological implications have been extensively investigated in temperate high‐mountain lakes because of their role as sentinels of global change. However, few studies have considered the drivers of water chemistry in tropical mountain lakes underlain by volcanic bedrock. A survey of 165 páramo lakes in the Cajas Massif of the Southern Ecuador Andes identified 4 independent chemical variation gradients, primarily characterized by divalent cations (hardness), organic carbon, silica, and iron levels. Hardness and silica factors showed contrasting relationships with parent rock type and age, vegetation, aquatic ecosystems in the watershed, and lake and watershed size. Geochemical considerations suggest that divalent cations (and related alkalinity, conductivity, and pH) mainly respond to the cumulative partial dissolution of primary aluminosilicates distributed throughout the subsurface of watersheds, and silica and monovalent cations are associated with the congruent dissolution of large amounts of secondary aluminosilicates localized in former hydrothermal or tectonic spots. Dissolved organic carbon was much higher than in temperate high‐mountain lakes, causing extra acidity in water. The smaller the lakes and their watersheds, the higher the likelihood of elevated organic carbon and metals and low hardness. The watershed wetland cover favored metal levels in the lakes but not organic carbon. Phosphorus, positively, and nitrate, negatively, weakly correlated with the metal gradient, indicating common influence by in‐lake processes. Overall, the study revealed that relatively small tropical lake districts on volcanic basins can show chemical variation equivalent to that in large mountain ranges with a combination of plutonic, metamorphic, and carbonate rock areas.

Analysis of preferred habitats of needlegrass (Hesperostipa spartea) and spotted knapweed (Centaurea biebersteinii) in the Crex Meadows State Wildlife Area

Invasive species threaten the health of native species by establishing in non-native habitats and outcompeting native species. The Crex Meadows State Wildlife Area (CMSWA) is 30,000 acres of native prairie and waterfowl habitat that is dedicated to the management of waterfowl and barrens habitat. Invasive species present in this area are inhibiting this management. Needlegrass (Hesperostipa spartea) and spotted knapweed (Centaurea biebersteinii) are two species that thrive in the CMSWA. Needlegrass is native to this area and is a key species for reintroduction, while spotted knapweed is an invasive species. The objective of this study was to document and analyze the locations of both species to determine if they prefer the same habitat types and identify possible sites of reintroduction for needlegrass and areas of vulnerability to invasion by spotted knapweed. Locations of both species were recorded and, using MaxEnt a species distribution model, the key environmental predictors of the locations of both species were identified. Results show that needlegrass habitat suitability was highest within 500 m of the nearest road, in the south-central and north-central areas of the CMSWA, away from the nearest major road, in sand/gravel, and igneous, metamorphic, and volcanic bedrock. Habitat suitability for spotted knapweed was highest at a slope of 20 degrees or steeper, within 500 m of the nearest road, in the southern part of the CMSWA, and at an elevation of 950 feet and greater. These results can help with management of both species on this property and beyond.

Cosmogenic nuclide exposure age scatter records glacial history and processes in McMurdo Sound, Antarctica

Abstract. The preservation of cosmogenic nuclides that accumulated during periods of prior exposure but were not subsequently removed by erosion or radioactive decay complicates interpretation of exposure, erosion, and burial ages used for a variety of geomorphological applications. In glacial settings, cold-based, non-erosive glacier ice may fail to remove inventories of inherited nuclides in glacially transported material. As a result, individual exposure ages can vary widely across a single landform (e.g., moraine) and exceed the expected or true depositional age. The surface processes that contribute to inheritance remain poorly understood, thus limiting interpretations of cosmogenic nuclide datasets in glacial environments. Here, we present a compilation of new and previously published exposure ages of multiple lithologies in local Last Glacial Maximum (LGM) and older Pleistocene glacial sediments in the McMurdo Sound region of Antarctica. Unlike most Antarctic exposure chronologies, we are able to compare exposure ages of local LGM sediments directly against an independent radiocarbon chronology of fossil algae from the same sedimentary unit that brackets the age of the local LGM between 12.3 and 19.6 ka. Cosmogenic exposure ages vary by lithology, suggesting that bedrock source and surface processes prior to, during, and after glacial entrainment explain scatter. 10Be exposure ages of quartz in granite, sourced from the base of the stratigraphic section in the Transantarctic Mountains, are scattered but young, suggesting that clasts entrained by sub-glacial plucking can generate reasonable apparent exposure ages. 3He exposure ages of pyroxene in Ferrar Dolerite, which crops out above outlet glaciers in the Transantarctic Mountains, are older, which suggests that clasts initially exposed on cliff faces and glacially entrained by rock fall carry inherited nuclides. 3He exposure ages of olivine in basalt from local volcanic bedrock in the McMurdo Sound region contain many excessively old ages but also have a bimodal distribution with peak probabilities that slightly pre-date and post-date the local LGM; this suggests that glacial clasts from local bedrock record local landscape exposure. With the magnitude and geological processes contributing to age scatter in mind, we examine exposure ages of older glacial sediments deposited by the most extensive ice sheet to inundate McMurdo Sound during the Pleistocene. These results underscore how surface processes operating in the Transantarctic Mountains are expressed in the cosmogenic nuclide inventories held in Antarctic glacial sediments.

Resolving the argument about volcanic bedrock under the West Antarctic Ice Sheet and implications for ice sheet stability and sea level change

We provide a test for recent arguments that the West Antarctic Ice Sheet (WAIS) is underlain by an extensive outcrop of volcanic rock (mainly basalt) by examining the non-clay and clay mineral composition of sediments collected in front of and under the Ross Ice Shelf. If the proposed large volume were present, then we posit that glacial erosion and transport would deliver sediments to the Ross Sea enriched in minerals diagnostic of alkaline basalt, namely olivine, pyroxene, and plagioclase, and no quartz. Using quantitative X-ray diffraction analysis, we determine the weight percent of minerals in West Antarctic alkaline basalt, dolerite, gneiss, and granite bedrock, and compare these with a suite of 49 surface and near-surface sediment samples from a 1400 km west to east transect across the Ross Sea. Fifty percent of the samples had quartz percentage values >25% and had very small wt percentages of diagnostic basalt minerals. A sediment unmixing algorithm, with basalt, dolerite, gneiss and granite bedrock, end members, showed that the sediment contained virtually no basalt, was dominated by granite compositions, but did show some samples with an admixture of material derived from the Ferrar dolerite, which crops out extensively in the Transantarctic Mountains. Indicators of possible late Cenozoic volcanic bedrock – pyroxene, forsterite, and smectite weight percentages – decrease from west to east across the Ross Sea opposite to the trend of the quartz weight percent. Our study provides no support for the presence of extensive basalt outcrop under the WAIS, hence indicates that any changes in ice stream stability will not be influenced by basal heat regime.

Sağlık Mahallesi Heyelanı (Ordu, TÜRKİYE)

Landslides cause loss of life and property from time to time. In Turkey, the Black Sea Region is the region where landslides are seen most frequently. In this study, Sağlık Neighborhood Landslide that occurred on May 15th, 2019 in the Central Black Sea Region was examined. This study aims to investigate the formation of the landslide and to discuss measures that can be taken in order to minimize the damage. For this purpose, area was visited and measurements were performed, soil samples and photos were taken. The region which has a rough terrain, receives precipitation throughout the year. The site has volcanic bedrock and thick debris and ground cover on it. The liquefaction limit of the soil is between 45.7 and 47.8 and the plasticity limit is between 20.51 and 22. Also, turning forests into agricultural areas, opening roads crossing the slopes, additional weights created by houses, water leaking from the sewer network to the ground and vibrations created by passing vehicles are among main causes of landslides. Stress cracks that started to occur in the crown part of the landslide three years ago started to expand on the day of the incident. The authorities who realized this evacuated the houses being under threat. Despite this, 22 buildings were destroyed and 8 hectares of agricultural land were damaged. To prevent damages, it has been proposed to prepare landslide susceptibility maps, to build new settlements away from potential landslide areas and to move residences in high-risk areas to safe places.

Soils in ancient irrigated agricultural terraces in the Atacama Desert, Chile

AbstractThe Atacama Desert is among the driest places on Earth, yet ancient agricultural systems are present in the region. Here, we present a study of terraced agricultural soils in the high‐altitude eastern margin of the Atacama Desert in northern Chile, mainly dating to the Late Intermediate Period (ca. 950–1400 AD) and Inka period (ca. 1400–1536 AD). Terraced fields were compartmentalized to distribute limited irrigation water originating mainly from springs. Natural soils used for agriculture are mostly Aridisols developed on Pleistocene alluvial fan terraces and hillslopes underlain by volcanic bedrock. One research objective is to evaluate long‐term soil change from agriculture. In this hyperarid climate, agriculture is only possible with irrigation, so natural soils on the same geomorphic surface adjacent to irrigated soils provide baseline data for assessing anthropogenic soil change. Data from soil profiles and surface transects indicate intentional soil change through terracing, removal of soil rock fragments, and probable fertilization. Agricultural soils have anthropogenic horizons ranging from 16 to 54 cm thick. Most agricultural soils have higher phosphorus levels, suggesting enrichment from fertilization. Changes in soil organic carbon and nitrogen are also evident. Unintentional anthropogenic soil change resulted from CaCO3 input through irrigation with calcareous spring water. Initial studies suggest that agriculture here was sustainable in the sense of conserving soils, and maintaining and possibly improving soil productivity over centuries.

Tectono‐Magmatic, Sedimentary, and Hydrothermal History of Arsinoes and Pyrrhae Chaos, Mars

AbstractArsinoes and Pyrrhae Chaos are two adjacent chaotic terrains located east of Valles Marineris and west of Arabia Terra, on Mars. In this work, we produced a morpho‐stratigraphic map of the area, characterized by a volcanic bedrock disrupted into polygonal mesas and knobs (Chaotic Terrain Unit) and two nondisrupted units. The latter present a spectral variation, likely associated with hydrated minerals, and they are here interpreted as sedimentary units. The reconstructed geological history of the area starts with the emplacement of the basaltic bedrock, followed by the collapse that caused the formation of the chaotic terrains. Since evidences of volcano‐tectonic activity are widespread across the area (e.g., fissure vents/graben, radial and concentric systems of faults, y‐shaped conjunctions, lava flows, and pit chains), and an intricate system of lava conduits is hypothesized for the occurrence of such features, we propose the possibility that the whole collapse was caused primarily by volcano‐tectonic processes. In a late stage, after the end of the volcano‐tectonic activity, a lacustrine/evaporitic depositional environment could have set, with the deposition of the nondisrupted units. The hydrated minerals found in the periphery of the Chaos could be the result of hydrothermal alteration of the basaltic bedrock.

Characterization of bioavailable Sr isotopic composition of Jeju Island, Korea

Stable isotope signatures of geologic, atmospheric, and hydrologic sources are transferred to the ecosystem through the food chain. The present study used Sr isotope data of soil and plant samples collected from Jeju Island to explore the roles of these sources in the local bioavailable Sr pool. X-ray diffraction and Sr isotope data revealed that the soil materials came from diverse sources such as weathered volcanic bedrock, marine carbonate sediments, and allochthonous aeolian dust. Dilute (1 M) ammonium nitrate- and acetic acid-leachates of the soil samples yielded 87Sr/86Sr ratios between 0.7047 and 0.7092, which were slightly but discernably higher than ratios for Jeju volcanic rocks reported in the literature (0.7045 ± 0.0004). This indicates that relatively more radiogenic Sr, probably in carbonate and aeolian dust, was preferentially released to the leachates. Geopedological control over the bioavailable Sr pool was demonstrated by the positive 87Sr/86Sr correlation between leachable soil fractions and the corresponding plant samples. The enhanced 87Sr/86Sr ratios of plants (0.7062–0.7092, average = 0.7077 ± 0.0012) reflect the influence of seawater. These Sr isotope data provide a scientific basis for addressing archaeological and historical questions related to Jeju Island.

The use of mineral interfaces in sand-sized volcanic rock fragments to infer mechanical durability

The use of mineral interfaces, in sand-sized rock fragments, to infer the influence exerted by mechanical durability on the generation of siliciclastic sediments, has been determined for plutoniclastic sand. Conversely, for volcaniclastic sand, it has received much less attention, and, to our knowledge, this is the first attempt to make use of the volcaniclastic interfacial modal mineralogy of epiclastic sandy fragments, to infer mechanical durability control at a modern beach environment. Volcaniclastic sand was collected along five beaches developed on five islands, of the southern Tyrrhenian Sea (Alicudi, Filicudi, Salina, Panarea and Stromboli) from the Aeolian Archipelago, and one sample was collected near the Stromboli Island volcanic crater. Each sample was sieved and thin sectioned for petrographic analysis. The modal mineralogy of the very coarse, coarse and medium sand fractions was determined by point-counting of the interfacial boundaries discriminating 36 types of interfaces categories, both no-isomineralic and/or no iso-structural (e.g., phenocrystal/glassy groundmass or phenocrystal/microlitic groundmass boundaries) and iso-mineralic interfaces, inside volcanic lithic grains with lathwork and porphyric textures. A total of 47,386 interfacial boundaries have been counted and, the most representative series of interfaces, from the highest to the lowest preservation, can be grouped as: a) ultrastable interfaces, categorized as Pl (Plagioclase)/Glgr (Glassy groundmass) > > Px (Pyroxene)/Glgr > > Ol (Olivine)/Glgr > > Op (Opaque)/Glgr > > Hbl (Hornblende)/Glgr> > Bt (Biotite)/Glgr > > Idd (Iddingsite)/Glgr > > Rt (Rutile) / Glgr; b) stable interfaces, categorized as Pl/Migr (Microlitic groundmass) > > Op/Migr > > Px/Migr > > Ol/Migr; c) moderately stable interfaces, categorized as Op/Px > > Op/Hbl > > Px/P > > Ol/Pl> > Bt/Op; and d) unstable interfaces, categorized as Pl/Pl > > Px/Px > > Ol/Ol > > Op/Op > > Hbl/Hbl > > Bt/Bt. Grains, eroded from the volcanic bedrock, if affected solely by abrasion, developed a rounded and smoothed form, with prevailing no-isostructural interfaces such as Plagioclase/Glassy groundmass, Pyroxene/Glassy groundmass and Olivine/Glassy groundmass interfaces. Grains that during transport suffered fracturing and percussion have a sharp and angular form: these combined transport mechanisms produce mainly volcanic sandy grains with iso-structural interfaces, such as Pl/Pl, Px/Px, Hbl/Hbl, and, to a lesser extent, Bt/Op and Bt/Glgr interfaces.

The mid holocene occupation of the Pearl Islands: A case of unusual insular adaptations on the Pacific Coast of Panama

A survey of the Pearl Island archipelago discovered a Preceramic shell-bearing midden on the island of Pedro González located in Panama Bay in the eastern tropical Pacific Ocean. This occupation dates between ca. 6200 and 5600 cal yr BP, and revealed a mixed marine and terrestrial economy including the exploitation of sea and terrestrial turtles, snakes, iguanas, dolphins, and land mammals such as dwarf deer. Test excavations in 2007–2010 provided well-preserved invertebrate and vertebrate samples, which were considerably more diverse taxonomically for fish than for other vertebrate categories. At that time, only boa among a large snake sample was identified to species. A 7 × 4 m pit dug in 2015 increased the faunal sample but added little to diversity. Development of the ophidian comparative collection, augmented by on-line research, enhanced snake diversity and highlighted the dietary importance of snakes. Two marine turtle species – hawksbill and Pacific green– remain the only ones exploited. Improvements in stratigraphic sectioning have fine-tuned chronological fluctuations of faunal populations as in the case of green iguana and terrestrial mammals. Birds have experienced the greatest increase in diversity, but not as much as expected on the basis of the present-day island avifauna. Only two terrestrial mammal genera – squirrel, and rabbit – were added to the inventory inferred during 2007–2010, which comprised deer, opossum, monkey, agouti, paca, spiny rat, furry spiny rat, and probable capybara. The occupants of Pedro González took advantage of the abundant agate nodules eroding from the island's volcanic bedrock. This latest study reveals the presence of a substantial microlithic component that relied on the specialized heat treatment of whole nodules of lithic raw materials. As an idea to be explored further, we suggest that these microliths may have been produced by women for the manufacture and maintenance of composite cutting and/or grating tools used for the preparation of various foods. Ongoing analyses from the 2015 excavations are providing new information on the impact of these early colonists on the local fauna and have demonstrated how the physical properties of the island's lithic raw materials influenced their reduction strategies.

Natural background radiation at Lab 2 of Callio Lab, Pyhäsalmi mine in Finland

In operating mines, as well as in deep locations for planned scientific activities, it is essential to recognize the natural background radiation from the point of view of both occupational hazard and experimental background. Callio Lab, located in the Pyhäsalmi Mine, Finland, is one of the underground laboratories participating in the Baltic Sea Underground Innovation Network (BSUIN). The characterization of the natural background radiation was done at the Lab 2, which is the deepest located in Callio Lab. It involved in-situ gamma spectrometry, thermal neutron flux measurements, radon concentration determination, and α∕β laboratory spectrometry of water and rock samples. At a depth of 1436 m (∼4000 m w.e.) within the felsic volcanic bedrock occurs a volcanogenic massive sulphide deposit, wherein a thermal neutron flux of (1.73 ± 0.10) × 10−5 cm−2s−1, a gamma-ray flux of 12.7 ± 1.5 cm−2s−1, a gamma-ray dose of 0.158 ± 0.029 μ Sv/h and a radon concentration of 213.3 Bq/m3 ± 11% were determined.

The origin of continental carbonates in Andean salars: A multi-tracer geochemical approach in Laguna Pastos Grandes (Bolivia)

In continental volcanic settings, abundant carbonate precipitation can occur with atypical facies compared to marine settings. The (bio-)chemical processes responsible for their development and early diagenesis are typically complex and not fully understood. In the Bolivian Altiplano, Laguna Pastos Grandes hosts a 40-km2 carbonate platform with a great diversity of facies and provides an ideal natural laboratory to understand the processes responsible for the precipitation of carbonates in a continental province dominated by volcanism. In order to trace the origin of both water and solutes in the lagoon, the major element and stable isotope compositions (δ2H-δ18O, δ37Cl, δ7Li, δ11B and 87Sr/86Sr) of the spring and stream waters were characterized, as well as the stable isotope compositions (δ13C, δ15N) and noble gas isotope ratios of hydrothermal gases associated with spring waters. The results show that thermal springs discharging on the carbonate platform are close to saturation with calcite. PHREEQC modeling, together with fluid geochemistry and temperature estimated from a combination of geothermometers, indicate that Ca in these springs is inherited from the alteration of the volcanic bedrock by aqueous fluids heated at ∼225 °C and enriched in magmatic mantle-derived CO2. Our results clearly show that the main driver for the precipitation of modern carbonates in Laguna Pastos Grandes is the deeply sourced CO2, which boosts the alteration of volcanic rocks at depth.

Assessment of seismic ground motion amplification and liquefaction at a volcanic area characterized by residual soils

A seismic hazard was assessed related to site effects at Abbadia San Salvatore, central Italy, on the Mt. Amiata slopes, an ancient volcanic area characterized by residual soils (thick layers of loose to dense sands originated from weathering of the trachydacitic lavas). The seismic ground amplification and soil liquefaction related to these layers were recognized as the major seismic hazards for the area. Geological, geophysical, and geotechnical surveys were carried out on the volcanic rocks. The Horizontal-to-Vertical Spectral Ratio (HVSR) analysis of 252 noise measurements and 29 shear-wave velocity models of the subsoil allowed a seismic microzonation of the studied area, distinguished by thick weathered volcanic sands and shear-wave impedance contrast with respect to the seismic bedrock (volcanic bedrock). The differentiation of classified zones allowed recognition of areas characterized by residual (almost undisturbed) soils from those with soils probably affected by flowing water. The analysis of hazards revealed that peak acceleration by seismic amplification of ground motion exceeded the value set by the national rules (0.175g) in a restricted area of the zone characterized by the most perturbed soils (Zone D); the potential occurrence of soil liquefaction was also greater in this zone. Finally, the study showed potential high hazards due to site effects of the volcanic mountainous area characterized by residual soils as opposed to an alluvial plain formed by volcanic debris where these effects have generally been more recognized.

Atmospheric contribution to cations cycling in highly weathered catchment, Guadeloupe (Lesser Antilles)

The important fertilizing role of atmospheric dust, and particularly African dust, in tropical rainforests is increasingly recognized but still poorly quantified. To better evaluate dust input into the Caribbean basin, we sampled critical zone compartments of a small forested volcanic catchment in Guadeloupe (soils, parent rock, atmospheric dust, plants, soil solutions, stream and rain waters). The aims of this study are to track sources of cation nutrients (Ca, Mg, K, Sr) developed on highly weathered soil in the rainforest of Guadeloupe, to quantify plant recycling of these nutrients, and to identify constraints on regolith development and its associated nutrient pool.In the Quiock Creek catchment, a large isotopic range of 87Sr/86Sr and εNd values was observed despite the small scale of observation. Sr isotopic composition of the dissolved load varied from 0.7084 in rainfall to 0.7110 in soil solution, whereas it ranges between 0.7068 and 0.7153 for soil samples and between 0.7096 and 0.7102 for plants. The Nd isotopic composition varied between -8.39 in near-surface soil samples to 2.71 in deeper soil. All samples had an intermediate signature between that of the bedrock endmember (87Sr/86Sr=0.7038; εNd=4.8) and the atmospheric endmember (sea salt: 87Sr/86Sr=0.7092 and Saharan dust: 87Sr/86Sr=0.7187, εNd=-11.5).The regolith was built on pyroclastic deposits, but, because of extreme leaching, the regolith has lost its original bedrock signature and inherited an exogenous atmospheric signature. Our results show that only the chemical weathering of the fresh near-surface minerals can provide nutrients to the ecosystem (first 30cm). However, this dust weathering is too low to sustain the tropical forest ecosystem on its own. The cationic mass balance at the catchment scale, as well as the Sr isotopic signature, show that cation and Sr fluxes are of atmospheric origin only and that original bedrock no longer participates in nutrient cycles. The vegetation reflects the 87Sr/86Sr of the dissolved pool of atmospheric Sr.At the soil-plant scale, the cation-nutrient fluxes provided by vegetation (litter fall+leaf excretion) are major compared to input and output fluxes. The annual Ca, K, Sr and Mg fluxes within the vegetation are, respectively, 31, 28, 20 and 3 times greater than the exported fluxes at the outlet of the basin. The residence time of nutrients in the vegetation is 16 years for K and close to 45 years for Sr, Ca and Mg. These results emphasize the highly efficient vegetative turnover that dominates the nutrient cycle in the Quiock Creek catchment.This first characterization of biogeochemical cycles in the Guadeloupean rainforest suggests that the forest community of Quiock Creek is sustained by a small near-surface nutrient pool disconnected from the deep volcanic bedrock. We also demonstrated that, even with efficient nutrient recycling, Saharan dust plays a significant role in maintaining ecosystem productivity in Guadeloupe over long-time scales.

Jeju ground water containing vanadium induces normal T cell development and immune activation in chronically stressed mice.

Containing high concentration of vanadium served by the volcanic bedrock, Jeju ground water has long been known for various implicit health benefits including immune-promotion. Exposure to stress has been reported to be associated with immunosuppression such as reducing lymphocyte population or antibody production due to stress hormones. In this study, we aimed at evaluating the effects of Jeju ground water on chronically stressed mice. C57BL/6 mice were subjected to various stressors such as restraint stress, water swimming stress, heat stress, acoustic stress, and Jeju ground water was supplied for 28days with two different concentrations, S1 (vanadium 15-20μg/l, pH 8.3) and S2 (vanadium 20-25μg/l, pH 8.5). Treatment with Jeju ground water increased CD4+CD8- or CD4-CD8+ single-positive thymocytes. It also increased the proliferation of splenocytes and the populations of CD4+ T cells, CD45R/B220+ B cells, CD11b+ macrophages or Gr-1+ granulocytes in spleen. In addition, the production of IgG was increased in chronically stressed mice by treatment with Jeju ground water. These results suggest vanadium-rich Jeju ground water may be helpful in T cell development in thymus and immune cell proliferation and its function in spleen against chronic stress.

Climate, Landforms, and Geology Affect Baseflow Sources in a Mountain Catchment

AbstractBaseflow is essential for stream ecosystems and human water uses, particularly in areas with Mediterranean climates. Yet the factors controlling the temporal and spatial variability of baseflow and its sources are poorly understood. Measurements of oxygen and hydrogen isotopic composition (δ18O and δ2H) were used to evaluate controls on baseflow in the stream network of a 64‐km2 catchment in western Oregon. A total of 607 water samples were collected to contrast baseflow in a year of near average precipitation (2016) to a year with low winter snowpack and subsequent summer drought conditions (2015). Spatial autocorrelation structures and relationships between surface water isotopic signatures and geologic and topographic metrics throughout the network were determined using Spatial Stream Network models. Isotope values varied widely in space and between years, indicating disparate baseflow water sources. During average flow conditions, the spatial variation in δ18O was primarily related to elevation, reflecting the influence of prior precipitation and input of water from snowmelt at higher elevation. In contrast, during drought conditions, the spatial variation in δ18O was also related to terrain slope and roughness—proxies for local water storage in deep‐seated earthflows and other Quaternary deposits. A prominent spring‐fed tributary with high unit baseflow discharge illustrated the importance of subsurface water storage in porous volcanic bedrock. As drought increases in a warming climate, baseflow in mountain catchments may become more dependent on storage in geologic and geomorphic features.

The sediment‐fill of Pago Pago Bay (Tutuila Island, American Samoa): New insights on the sediment record of past tsunamis

AbstractExtensive bathymetric and two‐dimensional seismic surveys have been carried out and cores collected in Pago Pago Bay (Tutuila, American Samoa) in order to describe and gain a better understanding of the sediment fill of the bay, which was affected by the 2009 South Pacific Tsunami. Eight sedimentary units were identified over the volcanic bedrock. The basal transgressive unit displays retrograding onlaps towards the shore, whereas the overlying seven aggradational layers alternate between four draping units and three pinching out seaward units. ‘Core to seismic’ correlation reveals that draping units are composed of homogeneous silts, while pinching out units are dominated by very coarse coral fragments showing fresh cuts, mixed with Halimeda plates. The basal unit is attributed to transgressive sedimentation in response to flooding of the bay after the last glacial maximum, followed by the upper aggradational units corresponding to highstand sedimentation. The changeovers in these upper units indicate an alternation between low‐energy silt units and high‐energy coral debris units interpreted as tsunami‐induced deposits. The 14C dating reveals that high‐energy sedimentation units can last up to approximately 2000 years while low‐energy sedimentation units can last up to approximately 1000 years. This alternation, deposited during the last highstand, may be explained by cycles of tectonic activity and quiescence of the Tonga Trench subduction, which is the main source of tsunamigenic earthquakes impacting the Samoan archipelago. In the uppermost silt unit, only the geochemical signature of the terrestrial input of the 2009 SPT backwash deposits was detected between 7 cm and 9 cm depth. Hence, Pago Pago Bay offers a unique sediment record of Holocene bay‐fill under the impact of past tsunamis intermittently during the last 7000 years.