Inactive Volcanoes Research Articles

Species Richness and Similarity of New Zealand Mayfly Communities (Ephemeroptera) Decline with Increasing Latitude and Altitude.

The distribution of species in relation to latitude and altitude is of fundamental interest to ecologists and is expected to attain increasing importance as the Earth's climate continues to change. Species diversity is commonly greater at lower than higher latitudes on a global scale, and the similarity of communities frequently decreases with distance. Nevertheless, reasons for such patterns are not well understood. We investigated species richness and changes in community composition of mayflies (Ephemeroptera) over 13 degrees of latitude at 81 locations throughout New Zealand by light-trapping and the benthic sampling of streams. Mayflies were also sampled along an altitudinal gradient on a prominent inactive volcano in the east of North Island. Sampled streams were predominantly in the native forest, at a wide range of altitudes from sea level to c. 1000 m a. s. l. A total of 47 of the 59 described New Zealand mayflies were recorded during the study, along with five undescribed morphospecies. Species richness declined and the degree of dissimilarity (beta diversity) of mayfly communities increased significantly from north to south but less strongly with increasing altitude. Our results suggest that the southward decline in species richness has historical origins with the north of the country having acted as a major refuge and region of speciation during the Pleistocene. The increasing dissimilarity of the northern and southern communities may reflect an increasingly harsh climate, variable amounts of subsequent southward dispersal of northern species and, in the South Island, the presence of species which may have evolved in the newly uplifted mountains during the Miocene-Pliocene.

Hydrothermal Vent Complexes Control Seepage and Hydrocarbon Release on the Overriding Plate of the Tyrrhenian-Ionian Subduction System (Paola Basin)

Active fluid seeps have been described in a wide range of geological environments and geodynamic contexts, which include continental shelves of non-volcanic passive margins and accretionary wedges. Fluids seeping in hybrid volcanic-sedimentary basins, characterized by the presence of magmatic intrusive complexes, have always received less attention. We detected and imaged dozens of distinct gas flares, as high as 700 m, on the continental slope of the Paola Basin in the southeastern Tyrrhenian Sea, at 550–850 m water depth. The sedimentary basin is surrounded by Pleistocene active and inactive volcanoes and volcanic-intrusive complexes, which formed in the back-arc basin of the Calabrian subduction zone, in response to subduction-induced mantle flow. Gas flares develop above pockmarks, craters and mud flows that form over and along the scarps of mound structures and correspond to seismic zones of free gas accumulation in the sub-seafloor. Here, methane-derived siderite shows enrichment in δ13C and δ18O isotopes likely related to methanogenesis and intermittent venting of deep-sourced CO2. Multichannel seismic reflection data showed that the gas flares develop in correspondence of doming and diapirism apparently originating from the top of the Messinian evaporites and nearby magmatic sills, that are present in the lower part of the Plio-Quaternary succession. These diapiric structures can be related to seafloor hydrothermal vent complexes fed by the igneous intrusions. Our data suggest that the vent complexes acted as fluid migration pathways and gas conduits, which at times are bounded by deep-rooted normal faults, leading to post-explosive near-surface microbial activity and seep carbonate formation. Fluids being mobilised by magmatism in the study area include: hydrocarbons and hydrothermal fluids generated at depth, interstitial water expelled during formation of polygonal faults. The close spatial correlation between seafloor seep manifestations, fluid migration pathways in the sub-surface involving part of the Messinian units and igneous features indicates that magmatic activity has been the main driver of fluid flow and can have a long-term effect in the southern Tyrrhenian Sea.

Wind-snow interactions at the Ojos del Salado region as a potential Mars analogue site in the Altiplano - Atacama desert region

We describe the general characteristics and interactions happening at a unique, potential new Mars analogue site, located in the Altiplano and Atacama Desert region: the Ojos del Salado inactive volcano. The interaction between rare snowing events and strong winds transported large masses of porous volcanic grains there could produce decimeter - meter thick buried snow masses fast, shielded against sublimation for extended periods (years). Subsurface temperature logging suggests that water ice melting is rare and surface modification is dominated by desiccation of the cryosphere and wind activity – just like on Mars. The first analysis of aeolian transported grains in the area points to immature material sized between coarse sand and coarse silt, and indicates the possibility of larger snow occurrence in winter when the site is inaccessible – however further observations are necessary The site contains decameter scale megaripples, which are unusual for Earth and also support the understanding of resemble features on Mars. The shallow subsurface analysis with Mars relevance is supported here by drilled cores of evaporitic sediments presented carbonate, aragonite, anhydrite, talc and clay minerals in the shallow subsurface with Mars relevance. Though the region is generally felsic in composition, basalts can be found at a hillside near Laguna Verde where the effect of extreme conditions (including the strong UV radiation) on rock weathering could be analysed. The temperature, dryness, wind exposure, decreased atmospheric pressure and elevated UV radiation together make Ojos del Salado a unique Mars analogue site, and it is accessible up to 5200 m altitude by regular pick-up trucks via a 5–6 h driving from the Copiapo airport.

KARAKTERISTIK FISIK MATAAIR PANAS DAERAH SAMBOJA, KUTAI KARTANEGARA

Geothermal features can be observed in areas of active volcanism, or areas that have inactive volcanoes. In non-volcanic areas, the temperature of rocks within the Earth also increases with depth. This temperature increase is known as the Geothermal Gradient. If water percolates deeply enough into the crust, it comes into contact with hot rocks and can circulate to the surface to form hot springs. The collection of field hydrothermal data during field study with the help of portable instruments. The different physical parameters of the thermal springs such as temperature, pH, colour, and odour of thermal fluid are noted. The temperature of the thermal springs ranges from 43oC to 48oC. The pH value of the thermal waters shows a neutral (pH 6-6.6) and sulphur odour is discernible particularly. Based on geological, the system geothermal energy that develops is geopressured.

Associated analysis of groundwater qualities and inactive volcano distributions in Burirum province, northeastern Thailand

Associated analysis of groundwater qualities and inactive volcano distributions in Burirum province, northeastern Thailand

Zircon geochronology suggests a long-living and active magmatic system beneath the Ciomadul volcanic dome field (eastern-central Europe)

Ciomadul is the youngest volcano in eastern-central Europe. Although its last eruption occurred at ca. 30 ka, there are independent indications for a high-crystallinity magma reservoir persisting beneath the volcano until present. In order to further test the hypothesis of long-lived melt presence and to better constrain the nature and timescales associated with the subvolcanic magma storage system, over 500 zircon U-Th and U-Pb spot ages (crystal interiors and outer surfaces) were interpreted from dacitic rocks of the most productive eruptive period (the Young Ciomadul Eruptive Period; YCEP, 160-30 ka). Zircon surface ages from lava dome and pumice samples range from ca. 600 ka up to the youngest eruption event at 30 ka. They form a continuous age distribution and some single crystals reveal significant age zonation (>150 kyr difference from core to rim). The oldest zircon ages of YCEP overlap with the last eruption events of the Old Ciomadul Eruptive Period (1000–330 ka). The zircon age spectra, combined with textural data, point to a prolonged (several 100's kyr) residence in a highly crystalline mush state. The range in zircon crystallization temperature (from ∼750°C to the solidus at ∼680°C) is consistent with the results of thermometry on amphibole and plagioclase from felsic crystal clots, which represent crystal mush fragments. To maintain magma reservoir for such a long time above solidus, continuous magma input by deeper recharge is required. Zircon crystallization model calculations constrained by thermal modelling imply an average rate of magma input of about 1.3 × 10−4 km3/yr over 2 Myr. Such estimate allows us to calculate an extrusive/intrusive ratio of 1:25–1:30. The model calculations suggest that a crystal mush zone of about 35 km3 is still present within the subvolcanic magma reservoir. Importantly, the Ciomadul plumbing system thus remains thermally primed and renewed magma injection could lead to rapid reawakening and eruption of the apparently inactive volcano.

Rapid alteration of fractured volcanic conduits beneath Mt Unzen

The nature of sub-volcanic alteration is usually only observable after erosion and exhumation at old inactive volcanoes, via geochemical changes in hydrothermal fluids sampled at the surface, via relatively low-resolution geophysical methods or can be inferred from erupted products. These methods are spatially or temporally removed from the real subsurface and thus provide only indirect information. In contrast, the ICDP deep drilling of the Mt Unzen volcano subsurface affords a snapshot into the in situ interaction between the dacitic dykes that fed dome-forming eruptions and the sub-volcanic hydrothermal system, where the most recent lava dome eruption occurred between 1990 and 1995. Here, we analyse drill core samples from hole USDP-4, constraining their degree and type of alteration. We identify and characterize two clay alteration stages: (1) an unusual argillic alteration infill of fractured or partially dissolved plagioclase and hornblende phenocryst domains with kaolinite and Reichweite 1 illite (70)-smectite and (2) propylitic alteration of amphibole and biotite phenocrysts with the fracture-hosted precipitation of chlorite, sulfide and carbonate minerals. These observations imply that the early clay-forming fluid was acidic and probably had a magmatic component, which is indicated for the fluids related to the second chlorite-carbonate stage by our stable carbon and oxygen isotope data. The porosity in the dyke samples is dominantly fracture-hosted, and fracture-filling mineralization is common, suggesting that the dykes were fractured during magma transport, emplacement and cooling, and that subsequent permeable circulation of hydrothermal fluids led to pore clogging and potential partial sealing of the pore network on a timescale of ~ 9 years from cessation of the last eruption. These observations, in concert with evidence that intermediate, crystal-bearing magmas are susceptible to fracturing during ascent and emplacement, lead us to suggest that arc volcanoes enclosed in highly fractured country rock are susceptible to rapid hydrothermal circulation and alteration, with implications for the development of fluid flow, mineralization, stress regime and volcanic edifice structural stability. We explore these possibilities in the context of alteration at other similar volcanoes.

Positron Annihilation Spectroscopy of Basaltic Rocks from Plio-Qaternary Volcanics, Sana’a-Amran Volcanic Field, Yemen

We focus a new application of positron annihilation lifetime spectroscopy and Doppler broadening techniques at the annihilation sites have been applied on some basaltic rocks from inactive volcano related to Sana’a-Amrana volcanic Field (SAVF). A brief geologic set up and the main petrographic signature of this inactive volcano are given. To gain an insight into geological environment, open nanospaces in the well-characterized basaltic rocks were investigated by positron annihilation spectroscopy. The analysis of the lifetime spectra yielded two lifetime components. The olivine basalt samples contain less mono- vacancies than those found in the trachybasalt and vesicular basalt samples. The overall defect (vacancy) concentration and its variation in the samples were estimated using the mean positron lifetime (τm). The Doppler broadening parameters (S and W-Parameters) were measured. A little variation of the S-parameter values has been observed for all the studied samples indicating that the valance electron contribution to annihilation is not significant.

Alexander von Humboldt (1769-1859): early high-altitude explorer and renowned plant naturalist.

Alexander von Humboldt (1769-1859) was one of the most distinguished German scientists of the late 18th and early 19th centuries. His fame came chiefly from his extensive explorations in South America and his eminence as a plant naturalist. He attempted to climb the inactive volcano Chimborazo in Ecuador, which was thought to be the highest mountain in the world at the time, and he reached an altitude of about 5,543 m, which was a record height for humans. During the climb, he had typical symptoms of acute mountain sickness, which he correctly attributed to the low level of oxygen, and he was apparently the first person to make this connection. His ability as a naturalist enabled him to recognize the effect of high altitude on the distribution of plants, and by comparing his observations on Chimborazo with those in the European Alps and elsewhere, he inferred that the deleterious effects of high altitude were universal. During his return trip to Europe, he called on President Thomas Jefferson in Washington, where he was given a warm reception, and discussed conservation issues. He then returned to Paris, where he produced 29 volumes over a period of 31 years describing his travels. Here the effects of high altitude on the distribution of plants compared with animals are briefly reviewed. Following Humboldt's death in 1859, there was extensive coverage of his contributions, but curiously, his fame has diminished over the years, and inexplicably, he now has a lower profile in North America.

Dynamics and physical parameters of the Lastarria debris avalanche, Central Andes

Volcanic debris avalanches are extremely destructive phenomena, with the potential to travel many kilometers from their source region, either as rockslides or as mass flows. Given that they may even be triggered at inactive volcanoes, their hazard is often underestimated. Understanding the dynamics of such mass movements is essential for evaluating and mitigating hazards. A number of case studies have been carried out around the world, but there is still a need for further studies of flow-dominated avalanches, which remain poorly constrained. These studies would have high educational value, providing striking examples to teach decision makers and at-risk populations about the hazard.In this study, we investigate the 7500 cal. year B.P. Lastarria debris avalanche. It is a 7 km-long deposit, with exceptional preservation of both the flow structures and the collapse scar. Detailed fieldwork, morphometric mapping of over 600 surface features, and numerical modelling was carried out to constrain the avalanche's trigger and flow parameters. Numerical models and field scaling relationships are in good agreement, suggesting maximum velocities of 210 to 270 km h−1, negligible basal friction, low cohesion (50 kPa) and an intermediate friction coefficient. Structures are dominantly oriented parallel to transport direction, suggesting minimal influence from a smooth paleotopography. Lastarria provides an example of a shallow flank failure, initiated along stratigraphic planes, that allowed low strength pyroclastic strata to disaggregate rapidly and then quickly accelerate to flow as a granular material at high velocity beyond the base of the volcano. Overall, Lastarria provides excellent constraints on granular avalanche initiation and flow, which are valuable for hazard assessments and for the study of less well-preserved flow deposits elsewhere. The question of which precursory signs may warn of such a flank failure remains open, and is important to address in future studies.

Morphotectonic of volcanic area in Rawa Danau, Banten Province

Rawa Danau is a caldera and considered as an inactive volcano. Based on landscape characteristic the morphology was influenced from volcanic processes. However, many geological structures such as fractures were also found. Our research is trying to understand that the landscape in the Rawa Danau area whether it was controlled by tectonic activity or only by volcanic activity. The analysis of this study compared three different data: ridge linearity and river linearity that were obtained from analysis of satellite imagery. All the data then be compared with the fracture azimuth data obtained through field surveys. The three data were compared with each other by statistical analysis (Mann-Whitney U test), to test the relationship between the three. Based on the data analysis that has been carried out, it can be seen the results of the statistical analysis shows the average difference between the two independent samples, it shows that the area’s landscape is controlled by the volcanic process.

The potential use of volcanic deposits for geopolymer materials

Volcanic deposits are abundant in the vicinity of an active and inactive volcano. They are produced from the cooling of magma during explosive volcanic eruptions. They have varying physical properties and can range in size from sub-millimetric ash up to boulder size. As Indonesia is considered as an active volcanic region, volcanic materials are abundant but they are still unexploited to full capacity such as geopolymer raw material. Geopolymers are generally understood as alkali-activated aluminosilicates. They may be considered as an inorganic two-component system which consists of: [1] a reactive solid source of SiO2 and Al2O3, and [2] an alkaline activation solution. The aim of the research is to identify the chemical and mineralogical properties of Merapi and Mt. Sinabung volcanic ashes as the raw material of geopolymers. Results showed that Mt. Merapi contained amorphous volcanic glass and crystalline [feldspar] minerals with 61.13% SiO2; 17.78% Al2O3; 3.47% Fe2O3; 6.22% CaO. Mount Sinabung deposit contains amorphous volcanic glass also and crystalline [feldspar] minerals with an oxide content of 49.33% SiO2; 15.93% Al2O3; 6.48% Fe2O3; 5.87% CaO. The high content of silica and alumina in this material showed that it was pozzolan material which can be synthesized to geopolymers. The molar ratio of SiO2/Al2O3 was high, Merapi is 5.84 and Sinabung is 5.26.

Two distinct mechanisms of fluoride enrichment and associated health risk in springs' water near an inactive volcano, southeast Iran.

Groundwater fluoride contamination is a major issue of water pollution in the world with health hazards such as dental and skeletal fluorosis. This research focused on exposure to the high concentration of fluoride in the springs water in the Bazman volcanic area, southeast Iran. The combination of chemical/isotopic analysis, geochemical modeling, health risk assessment and multivariate statistical methods were applied to investigate the contamination and sources of fluoride in the samples. Groundwater samples were collected from cold and thermal springs. Major ions, fluoride, trace elements and stable isotopes δ18O and δD were measured in the samples using standard methods, ICP-MS and OA-ICOS, respectively. Fluoride content in springs varied from 0.5 to 3.75mg/L with an average value of 1.66mg/L. The highest fluoride concentrations were observed in the eastern cold springs while thermal springs showed the minimum fluoride contents. The majority of samples showed F contents higher than the calculated optimal concentration of fluoride (0.75mg/L). Reaction of fluorite mineral with HCO3 and replacement of F in clay minerals and metal oxy-hydroxides with OH- in water were likely cause fluoride enrichment in the eastern springs. Whereas, in the western springs and thermal springs, origin of fluoride was related to weathering of muscovite, cryolite, apatite and fluoroapatite minerals. The δ18O and δ2H of the water samples displayed the impact on evaporation on fluoride enrichment in all spring water samples. The average value of contamination index (Cd) in the water samples was 1.94 categorizing medium risk level while springs S7, S8, S9 and S4 were above the threshold value of Cd index. The fluoride hazard quotient (HQ) showed that 25%, 44%, 56% and 0% of springs' water resources had high risk level for age group of adults, teenager, children and infants, respectively. Therefore, health risk of fluoride in drinking water resources were in the following order: children>teenager>adults>infants.

Volcano growth versus deformation by strike-slip faults: Morphometric characterization through analogue modelling

Volcanoes display diverse morphologies as a result of the complex interplay of several constructive and destructive processes. Scaled analogue models offer a tool to isolate and characterize the different processes. Here, we investigate the interplay between volcano growth and deformation caused by an underlying strike-slip fault through simple analogue models. In particular, we analyze the morphometry of analogue volcanoes resulting from different growth-to-deformation ratios. Deformation elongates the volcano edifice at an angle of 10–45° from the fault trace along the extensional quadrants and generates a summit graben structure oriented perpendicular to the edifice elongation. The overall steepness of the edifice decreases, but steep slopes are preserved or increased on the lower compressional flanks, commonly related to small avalanches. Growth can partially to totally mask these features depending on the growth rate to strike-slip velocity ratio. The summit graben is easily masked even by low growth rates, whereas edifice elongation has the best preservation potential. Scaling of the experiments suggests that at volcanoes with growth rate (km3/yr) to strike-slip velocity (km/yr) ratios ≤3.8 km3/km, deformation features should be clearly preserved, whereas at volcanoes with ratios ≥15 km3/km, deformation features should be completely masked. The typical growth rates of volcanoes (0.01 to 1 km3/ka) and the typical velocities of strike-slip faults (1 to 20 mm/yr) suggest that in nature, growth rate to strike-slip velocity ratios can range over 3 orders of magnitude, spanning both types of end-members. Using examples of both active and inactive volcanoes located on strike-slip faults with variable elongation intensities and orientations, we highlight that the analogue models account for some of the morphometric variability observed at volcanoes in nature, although the role of vent distribution can be a key factor.

Evidence for a persistent magma reservoir with large melt content beneath an apparently extinct volcano

Most active volcanoes display eruption frequencies of 10-1000s years but a class of volcanic systems has extremely long repose-time (>10's kyr), and are deemed as extinct. Yet, some reawaken, posing a particular threat because little is known about the way they endure and stir back to life. Reawakening primarily depends on the nature of the subvolcanic magma reservoir, especially the presence and distribution of melt. Here, we integrate petrology, thermobarometry, thermomechanical models, geophysics and in situ electrical conductivity measurements to show that the magma storage beneath Ciomadul, a seemingly inactive volcano in eastern-central Europe that last erupted 30 ka, may still hold 20 to 58 km3 of water-rich silicic melt, constituting up to 20-58% in parts of the upper crustal crystal mush body. Such a melt volume exceeds the volume of erupted lava over the entire history of the volcano. This illustrates the important longevity of a magmatic reservoir at temperature above the solidus, which implies that there is still a potential for rapid mush rejuvenation. That a seemingly dead volcano like Ciomadul is actually capable of erupting in the future calls for renewed attention to “inactive” volcanoes worldwide and perhaps for a redefinition of their activity/inactivity status.

Deeply buried ancient volcanoes control hydrocarbon migration in the South China Sea

AbstractSeismic reflection data image now‐buried and inactive volcanoes, both onshore and along the submarine portions of continental margins. However, the impact that these volcanoes have on later, post‐eruption fluid flow events (e.g., hydrocarbon migration and accumulation) is poorly understood. Determining how buried volcanoes and their underlying plumbing systems influence subsurface fluid or gas flow, or form traps for hydrocarbon accumulations, is critical to de‐risk hydrocarbon exploration and production. Here, we focus on evaluating how buried volcanoes affect the bulk permeability of hydrocarbon seals, and channel and focus hydrocarbons. We use high‐resolution 3D seismic reflection and borehole data from the northern South China Sea to show how ca. <10 km wide, ca. <590 m high Miocene volcanoes, buried several kilometres (ca. 1.9 km) below the seabed and fed by a sub‐volcanic plumbing system that exploited rift‐related faults: (i) acted as long‐lived migration pathways, and perhaps reservoirs, for hydrocarbons generated from even more deeply buried (ca. 8–10 km) source rocks; and (ii) instigated differential compaction and doming of the overburden during subsequent burial, producing extensional faults that breached regional seal rocks. Considering that volcanism and related deformation are both common on many magma‐rich passive margins, the interplay between the magmatic products and hydrocarbon migration documented here may be more common than currently thought. Our results demonstrate that now‐buried and inactive volcanoes can locally degrade hydrocarbon reservoir seals and control the migration of hydrocarbon‐rich fluids and gas. These fluids and gases can migrate into and be stored in shallower reservoirs, where they may then represent geohazards to drilling and impact slope stability.

Light rooms in Tindaya Mountain and the Roden Crater: Turrell’s realization and Chillida’s proposal

Late in his life, in 1995/96, Eduardo Chillida designed a project to create a huge space in the inactive Tindaya volcano on Fuerteventura, in which visitors would be able to experience moonlight or sunlight falling in through two different lightshafts. The shafts would project the incoming light in a geometrical form into the space. Unfortunately, Chillida’s proposal could not be realized. James Turrell’s project for the Roden Crater in Arizona, however, has been built in stages since 1972. This, too, involves an inactive volcano and it is therefore instructive to compare both artists’ visions in these projects. What were Chillida’s plans and why could they not be realized? My own experiences on the Tindaya Mountain in 2018 help me to find some answers.

Favorable Birth Outcomes in the Population of Tacna, Peru, despite Chronic Arsenic Exposure in Drinking Water

Tacna is a southern region of Peru, bordering with Chile and Bolivia. It presents valleys, sandy soils and inactive volcanoes. As it happens with Northern Chile and Argentina, Tacna possess high levels of arsenic in water, reaching values of 0.6812 mg/L, many times above the limit established by WHO (0.01 mg/L). The arsenic present have a geogenic origin derived from volcanic rocks. It is well known that continuous exposure leads increases risks of morbidity and mortality as different kinds of cancers, cardiovascular diseases and diabetes. Arsenic is able to cross the placenta, causing low birth weight, small for gestational age (SGA) and preterm birth.A recent work from our laboratory found extreme arsenic chronic exposure measured in drinking water in several districts of Tacna, without affecting negatively birth weight, or SGA and preterm birth prevalence as expected. In fact, these reproductive outcomes were not different according to exposure levels defined in quartiles [Q1 (0.0001-0.01 mg/L), Q2 (0.0220-0.0537 mg/L), Q3 (0.0545-0.2261 mg/L) and Q4 (0.2520-0.6812 mg/L)]. Nonetheless, arsenic speciation data was not available.These favorable birth outcomes could be evidence of 1) presence of non-toxic arsenic (organic Dimethylarsenic rather than inorganic) or 2) a positive selection for genetic polymorphisms in the gene as3mt; in charge of arsenic methylation, as those found in northern Chile and Argentina (San Antonio de los Cobres), conferring the fetuses a natural protection against arsenic toxicity.Given the reasons above, and the public interest, it is necessary conduct a research aimed to identify why high arsenic exposure is not associated with adverse reproductive outcome. These include measurements of urine, hair to detect different arsenic species and blood for polymorphisms e.g. as3mt. Group of study will be pregnant women in Tacna, in which different designs will be performed starting with a preliminary pilot study and finally a cohort study.

Forms of trace arsenic, cesium, cadmium, and lead transported into river water for the irrigation of Japanese paddy rice fields

In this study, we focus on the behavior of geogenic, toxic trace elements, particularly As, Cs, Cd, and Pb, during their transportation in two rivers for irrigation commonly used in monsoon Asia; one river originates from an active volcano, Mt. Asama, and the other originates from a currently inactive volcano, Yatsugatake Mountains in Nagano, Japan. These rivers were investigated to understand the role of river water as a pollutant of rice and other aquatic plants (via irrigation) and aquatic animals. The results indicated that the behavior of toxic trace elements in river water are likely controlled by their interactions with particulate Fe, Al, and Ti compounds. The majority of Pb and Cd is transported as particulate matter with Fe, Al, and Ti, while the majority of As is transported in the dissolved form, predominantly as arsenate, with low abundance of particulate matter. Cs is transported either as the dissolved form or as particulate matter in both rivers. The investigated elements are transported in the rivers as particulate and dissolved forms, and the ratio of these forms is controlled by the pH and presence of particulate Fe, Al, and Ti phases in the river water. With respect to Cs in both rivers, the parameter governing the concentration and transportation of Cs, in the bimodal form (i.e., particulate and dissolved forms), through the river possibly shifts from sorption to pH by particulate Fe–Al–Ti, according to the abrupt increase in the concentration of Cs in the river. The chemical attraction of particulate Fe–Al–Ti for Cs is weaker than that for Pb and Cd, indicating that the lower electronegativity of Cs weakens the chemical attraction on a colloid for the competitive sorption with the other trace elements. The different relationships between As and Fe in the river and in the irrigation water and soil water, as well as those in paddy rice, suggested that As in paddy rice is not directly derived from As in the irrigation water from the river under flooding.

Spatially Variable CO2 Degassing in the Main Ethiopian Rift: Implications for Magma Storage, Volatile Transport, and Rift‐Related Emissions

AbstractDeep carbon emissions from historically inactive volcanoes, hydrothermal, and tectonic structures are among the greatest unknowns in the long‐term (∼Myr) carbon cycle. Recent estimates of diffuse CO2 flux from the Eastern Rift of the East African Rift System (EARS) suggest this could equal emissions from the entire mid‐ocean ridge system. We report new CO2 surveys from the Main Ethiopian Rift (MER, northernmost EARS), and reassess the rift‐related CO2 flux. Since degassing in the MER is concentrated in discrete areas of volcanic and off‐edifice activity, characterization of such areas is important for extrapolation to a rift‐scale budget. Locations of hot springs and fumaroles along the rift show numerous geothermal areas away from volcanic edifices. With these new data, we estimate total CO2 emissions from the central and northern MER as 0.52–4.36 Mt yr−1. Our extrapolated flux from the Eastern Rift is 3.9–32.7 Mt yr−1 CO2, overlapping with lower end of the range presented in recent estimates. By scaling, we suggest that 6–18 Mt yr−1 CO2 flux can be accounted for by magmatic extension, which implies an important role for volatile‐enriched lithosphere, crustal assimilation, and/or additional magmatic intrusion to account for the upper range of flux estimates. Our results also have implications for the nature of volcanism in the MER. Many geothermal areas are found >10 km from the nearest volcanic center, suggesting ongoing hazards associated with regional volcanism.