Weathering Of Volcanic Rocks Research Articles

GEOCARBSULF: A combined model for Phanerozoic atmospheric O 2 and CO 2

A model for the combined long-term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the GEOCARB III model [Berner R.A., Kothavala Z., 2001. GEOCARB III: a revised model of atmospheric CO 2 over Phanerozoic time. Am. J. Sci. 301, 182–204] for CO 2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for O 2 [Berner R.A., 2001. Modeling atmospheric O 2 over Phanerozoic time. Geochim. Cosmochim. Acta 65, 685–694]. New isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models. Sensitivity analysis is done by determining (1) the effect on weathering rates of using rapid recycling (rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks); (2) the effect on O 2 of using different initial starting conditions; (3) the effect on O 2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic δ 13C for the past 200 million years; (4) the effect on sulfur isotope fractionation and on O 2 of varying the size of O 2 feedback during sedimentary pyrite formation; (5) the effect on O 2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion, and the degree of exposure of coastal lands by sea level change; (6) the effect on CO 2 of adding the variability of volcanic rock weathering over time [Berner, R.A., 2006. Inclusion of the weathering of volcanic rocks in the GEOCARBSULF model. Am. J. Sci. 306 (in press)]. Results show a similar trend of atmospheric CO 2 over the Phanerozoic to the results of GEOCARB III, but with some differences during the early Paleozoic and, for variable volcanic rock weathering, lower CO 2 values during the Mesozoic. Atmospheric oxygen shows a major broad late Paleozoic peak with a maximum value of about 30% O 2 in the Permian, a secondary less-broad peak centered near the Silurian/Devonian boundary, variation between 15% and 20% O 2 during the Cambrian and Ordovician, a very sharp drop from 30% to 15% O 2 at the Permo-Triassic boundary, and a more-or less continuous rise in O 2 from the late Triassic to the present.

Inclusion of the Weathering of Volcanic Rocks in the GEOCARBSULF Model

The carbon cycle model GEOCARBSULF is extended by dividing the weathering of silicates into volcanic and non-volcanic rocks. The proportion of volcanic weathering is calculated as a function of time from the oceanic record of ^87^Sr/^86^Sr. The volcanic proportion is then used to modify the equations for calculating atmospheric CO~2~ by the addition of a new non-dimensional volcanic weathering factor. The effect of uplift and physical erosion on weathering is also modified by using only the distribution over time of the abundance of sandstones and shales, and not Sr isotopic data that had been used previously. Results indicate moderate change from GEOCARBSULF in the distribution of atmospheric CO~2~ over Phanerozoic time. This includes an increased minimum in CO~2~ during the Late Ordovician, in agreement with the presence of a continental glaciation at that time, and a shift of maximum Mesozoic values from the Jurassic to the Early Cretaceous.

Statistical evaluation of compositional changes in volcanic gas chemistry: a case study

The geochemical analysis of fumarolic gases collected at quiescent and active volcanic systems over time is one of the main tools to understand changes in the state of activity for surveillance and risk assessment. The continuous output of chemical species through fumarolic activity, which characterizes the inter-eruptive intervals, has also a major and general influence on the environment. The mobilization of chemical species due to weathering of volcanic rocks, or the input of gaseous components from fumarolic activity, results in some kind of modification of the environment affecting, in particular, water, soils, and the consequent growth of the plants present in these areas. In this paper, an investigation on the chemical composition of fumarolic gases collected at Vulcano island (Sicily, southern Italy) is performed, with the aim to discover how data changes during the monitored period of time, and to design a strategy for the environmental surveillance of volcanic systems taking into account the nature of the analyzed data. In order to summarize the contribution of all the components that can affect the chemical composition of volcanic gases, a multivariate statistical approach appears to be suitable. Since many of those methods assume independent observations, the possible presence of time-dependent structures should be carefully verified. In this framework, given the compositional nature of geochemical data, we have applied recent theoretical and practical developments in the field of compositional data analysis to work in the correct sample space and to isolate groups of parts responsible for significant changes in the gas chemistry. The proposed approach can be generalized to the investigation of complex environmental systems.

Diverse Mn(II)-Oxidizing Bacteria Isolated from Submarine Basalts at Loihi Seamount

Metal-oxidizing bacteria may play a key role in the submarine weathering of volcanic rocks and the formation of ferromanganese crusts. Putative fossil microbes encrusted in Mn oxide phases are commonly observed on volcanic glasses recovered from the deep ocean; however, no known Mn(II)-oxidizing bacteria have been directly identified or cultured from natural weathered basalts. To isolate epilithic Mn(II) oxidizing bacteria, we collected young, oxidized pillow basalts from the cold, outer portions of Loihi Seamount, and from nearby exposures of pillow basalts at South Point and Kealakekua Bay, HI. SEM imaging, EDS spectra and X-ray absorption spectroscopy data show that microbial biofilms and associated Mn oxides were abundant on the basalt surfaces. Using a series of seawater-based media that range from highly oligotrophic to organic-rich, we have obtained 26 mesophilic, heterotrophic Mn(II)-oxidizing isolates dominated by α- and γ-Proteobacteria, such as Sulfitobacter, Methylarcula and Pseudoalteromonas spp. Additional isolates include Microbulbifer, Alteromonas, Marinobacter, and Halomonas spp. None of the isolates, nor their closest relatives, were previously recognized as Mn(II) oxidizing bacteria. The physiological function of Mn(II) oxidation is clearly spread amongst many phylogenetically diverse organisms colonizing basalt surfaces. Our findings support a biological catalysis of Mn(II) oxidation during basalt-weathering, and suggest heterotrophic Mn(II) oxidizing bacteria may be ubiquitously associated with submarine glasses within epilithic and endolithic biofilms.

The origin of brines and salts in Chilean salars: a hydrochemical review

Northern Chile is characterized by a succession of north–south-trending ranges and basins occupied by numerous saline lakes and salt crusts, collectively called salars. Fossil salt crusts are found to the west in the extremely arid Central Valley, while active salars receiving permanent inflows fill many intravolcanic basins to the east in the semiarid Cordillera. Sea salts and desert dust are blown eastward over the Cordillera, where they constitute an appreciable fraction of the solute load of very dilute waters (salt content<0.1 g/l). The weathering of volcanic rocks contributes most components to inflow waters with salt content ranging from 0.1 to 0.6 g/l. However, the average salt content of all inflows is much higher: about 3.2 g/l. Chemical composition, Cl/Br ratio, and 18O– 2H isotope contents point to the mixing of very dilute meteoric waters with present lake brines for the origin of saline inflows. Ancient gypsum in deep sedimentary formations seems to be the only evaporitic mineral recycled in present salars. Saline lakes and subsurface brines are under steady-state regime. The average residence time of conservative components ranges from a few years to some thousands years, which indicates a permanent leakage of the brines through bottom sediments. The infiltrating brines are recycled in the hydrologic system where they mix with dilute meteoric waters. High heat flow is the likely driving force that moves the deep waters in this magmatic arc region. Active Chilean salars cannot be considered as terminal lakes nor, strictly speaking, as closed basin lakes. Almost all incoming salts leave the basin and are transported elsewhere. Moreover, the dissolution of fossil salt crusts in some active salars also carries away important fluxes of components in percolating brines. Evaporative concentration of inflow waters leads to sulfate-rich or calcium-rich, near-neutral brines. Alkaline brines are almost completely lacking. The alkalinity/calcium ratio of inflow waters is lowered by the oxidation of native sulfur (reducing alkalinity) and the deposition of eolian gypsum (increasing Ca concentration). Theoretically, SO 4-rich inflow waters and their derived SO 4-rich brines should be found in the intravolcanic basins of the Cordillera because of the ubiquity of native sulfur, while Ca-rich brines should prevail in sedimentary basins where Ca-rich minerals are abundant. This relation is perfectly observed in the salar de Atacama, the largest in Chile. However, several salars located within the volcanic Cordillera belong to the Ca-rich group. Inflows and brines may have acquired their Ca-rich composition in Pleistocene time when their drainage basins were mainly sedimentary. Later on, recent lava flows and ignimbrites covered the sedimentary formations. Underground waters may have kept their early sedimentary signature by continuous recycling. However, the weathering of volcanic rocks tend to slowly shift the water compositions from the Ca-rich to the SO 4-rich type.

Spatial and temporal variability of trace element concentrations in an urban subtropical watershed, Honolulu, Hawaii

Trace metal concentrations in soils and in stream and estuarine sediments from a subtropical urban watershed in Hawaii are presented. The results are placed in the context of historical studies of environmental quality (water, soils, and sediment) in Hawaii to elucidate sources of trace elements and the processes responsible for their distribution. This work builds on earlier studies on sediments of Ala Wai Canal of urban Honolulu by examining spatial and temporal variations in the trace elements throughout the watershed. Natural processes and anthropogenic activity in urban Honolulu contribute to spatial and temporal variations of trace element concentrations throughout the watershed. Enrichment of trace elements in watershed soils result, in some cases, from contributions attributed to the weathering of volcanic rocks, as well as to a more variable anthropogenic input that reflects changes in land use in Honolulu. Varying concentrations of As, Cd, Cu, Pb and Zn in sediments reflect about 60 a of anthropogenic activity in Honolulu. Land use has a strong impact on the spatial distribution and abundance of selected trace elements in soils and stream sediments. As noted in continental US settings, the phasing out of Pb-alkyl fuel additives has decreased Pb inputs to recently deposited estuarine sediments. Yet, a substantial historical anthropogenic Pb inventory remains in soils of the watershed and erosion of surface soils continues to contribute to its enrichment in estuarine sediments. Concentrations of other elements (e.g., Cu, Zn, Cd), however, have not decreased with time, suggesting continued active inputs. Concentrations of Ba, Co, Cr, Ni, V and U, although elevated in some cases, typically reflect greater proportions attributed to natural sources rather than anthropogenic input.

Weathering mechanisms and indices of the igneous rocks of Hong Kong

Weathering mechanisms of volcanic and granitic rocks in Hong Kong have been studied by chemical analysis, optical microscopy on thin sections and magnetic susceptibility measurements. The mobility of elements of calcium, sodium, iron, potassium, magnesium, silicon, aluminium and constitutional water is investigated in detail using the Mobility Index. Chemical weathering processes in Hong Kong are dominated by decomposition of feldspars and biotite, leaching of alkali and alkaline earth metals, and enrichment of ferric oxide under prolonged subtropical climate conditions. Data for some granitic residual soils from five neighbouring regions in Southern China are also gathered and examined. It is found that the residual soils in Hong Kong are abnormal and immature with respect to its latitude. By examining various quantitative chemical indices and comparing them with the current six-grade material classification scheme, WPI , LOI and I mob are found to be good indicators of the degree of weathering for both volcanic and granitic rocks in Hong Kong. Regarding the optical microscopy, the micropetrographic index ( I p ) is only suitable for granitic rock but not for volcanic rock due to the presence of fine-grained minerals and small voids. For the magnetic susceptibility measurements, consistent results with weathering grades for volcanic rocks are obtained by applying a moving average technique. However, due to the low content of Al 2 O 3 and Fe 2 O 3 in granitic rock, SOC and the magnetic susceptibility index, which are appropriate for quantifying the degree of weathering of volcanic rock, are not quite suitable for the granitic rock.

Characterization of weathered volcanic rocks in Hong Kong

Abstract The mineralogical and fabric characteristics of weathered volcanic rocks, which are widespread in Hong Kong, are poorly documented. Consequently, the significant variations commonly observed, even at the same locality, in engineering properties and in situ behaviour of these rocks and the resulting soils cannot be adequately related to their basic mineralogical and fabric characteristics. A model for weathering of volcanic rocks, particularly those of pyroclastic origin, is presented in this paper. Modifications, similar to those recently proposed for granites by Irfan, are proposed to the material and mass weathering schemes commonly adopted in Hong Kong for the characterization of weathered volcanic rocks in engineering use. The appropriateness of various proposed petrographic and chemical weathering indices to generally fine-grained volcanic rocks is examined. A number of modifications are proposed to the standard soil preparation and testing methods for the soils formed from tropical weathering of volcanic rocks in order to obtain meaningful and more repeatable results.

Marine Sr (Ca) input in Quaternary volcanic rock weathering profiles from the Mediterranean coast of Morocco: Sr isotopic approach

Carbonate commonly accumulates in weathering profiles developed on noncalcareous parent material under arid and semiarid climatic conditions. Such weathering profile types are widespread in Morocco, making it critical to know the sources of the calcium in order to understand the genesis of carbonate‐rich soils. In this study, we use 87Sr/86Sr as a geochemical tracer of the Ca sources in weathering profiles developed on volcanic rocks (basalt, tuff, andesite and latite) in the Mediterranean coast of Morocco. The results show that the most of the Sr, and hence Ca, is of an external origin, derived from (i) sea‐water for the profiles located near to the coast or (ii) sea‐water plus Liassic carbonate outcropping in the catchment for the profiles more distant from the coastline. The contribution of the host rock is small, being less than 25%. The ratio of the Sr (Ca) from the parent material to that from the external sources is controlled by the degree of porosity developed in the profile.

Present Chemical Weathering of Basalt in Iceland

Before the initiation of the water cycle on the 'early Earth' all the rocks were volcanogenic (e.g. Ronov, 1964). At present, volcanic rocks cover about 8 % of the land surface of the Earth and more than half of that is of basaltic composition (Meybeck, 1987). The present contribution of the weathering of volcanic rocks to the dissolved load of the world's rivers is less than 3%, the most important contribution comes from carbonate rocks (45%) and shale (20%; Meybeck, 1987). The high contribution of shale is primarily due to the weathering of small portions of the shale, i.e. calcareousand pyritic-shales. The chemical weathering of Ca-Mg silicate rocks is important for the atmospheric COz on a multimillion-year time scale and may therefore influence the temperature of the atmosphere (e.g. Berner, 1992). Thus, even to day, the weathering of basalt is an important factor in the net loss of CO2 from the atmosphere, and it's general importance increases with geological age because the ratio of basalt to sedimentary rocks increases with the age of the crust (e.g. Ronov, 1964). Iceland provides an opportunity to study the effects of the age of rocks, glaciation and vegetation on the nature and rate of chemical weathering of basalts. About 10% of the country is covered with glaciers, and one fourth is covered with vegetation. The interior of the country is unpopulated, providing pristine unpolluted catchment areas of uniform temperature and rock composition (basalt) with a variable glacier-and vegetation cover and variable runoff. The objective of this paper is to define and interpret, the source of supply for the dissolved constituents in Icelandic rivers, the relative mobility of the elements during weathering of basalt, the rate of chemical denudation in Iceland and the effect of age of rocks, and glacier/ vegetation cover on the chemical weathering of basalt.

Weathering of volcanic rocks from Mt. Vesuvius associated with the lichen Stereocaulon vesuvianum

Weathering of volcanic rocks from Mt. Vesuvius associated with the lichen Stereocaulon vesuvianum

REE mobilities during incipient weathering of volcanic rocks of the Parana Basin, Brazil

REE mobilities during incipient weathering of volcanic rocks of the Parana Basin, Brazil

Lithium and rubidium in the Waikato River, New Zealand

Abstract Lithium and rubidium in the Waikato River originate partly from geothermal fluids and partly from weathering of surficial volcanic rocks. This paper reports on the distribution and behaviour of these metals in the river system. Total Li concentrations in the river water increased from 0.079 g/m3 at the Lake Taupo outlet to 0.435 g/m3 at Mercer, but the ratios of filtrable to particulate metal decreased from 1.82 to 0.322, respectively. The corresponding concentrations for Rb were 0.038 and 0.626 g/m3, and the ratios were 0.095 and 0.040. Geothermal fluids are the source of about 80% of filtrable Li but only 50% of filtrable Rb. Weathering of volcanic rocks contributes the remainder of the metals. Approximately 11001 each of total Li and total Rb flow annually past Lake Aratiatia and more than 99% of these totals flow into the Tasman Sea. About 3 t of Li and 6 t of Rb accumulate each year into reservoir sediment; reservoir macrophytes, which probably turn over each year, could contain up to 0.5 t ...

Modern carbonate-siliciclastic transitions: Humid and arid tropical examples

Climate and tectonic setting largely control characteristics of transitions between carbonate and siliciclastic sediments in depositional systems. Three examples, selected from both humid and arid tropical settings, are discussed order to illustrate details of these relationships. The eastern shelf area of Nicaragua is an area where siliciclastic and carbonate sediments actively interfinger under humid tropical conditions. Extremely high rainfall (4.5 m yr −1 in the southern part of coastal plain), coupled with a correspondently high sediment flux to the nearshore shelf, results in an inner shelf that is dominated by siliciclastics. Density gradients and persistent momentum provided by the trade winds force turbid coastal waters to the south and confine siliciclastic sediments to a coast-parallel zone approximately 20 km wide. The remainder of the broad shelf is characterized by carbonate sediments and reefs. The mid-shelf area has a coarse carbonate sediment cover composed largely of the calcareous green alga Halimeda. The outer shelf displays rugged topography associated with reef development. Skeletal carbonates containing abundant coral and coralline algal grains are characteristic of the seaward margin of the shelf. Significant amounts of siliciclastic sediment are confined to the nearshore part of the shelf, and the transition from siliclastics to carbonates occurs over a distance of 20 km or less. A second example from the humid tropics focuses on the living reefs of Indonesia that are surrounded by fine-grained siliciclastics. A warm, rainy climate results in rapid weathering of volcanic rocks from the Indonesian archipelago and abundant sediment input to the shallow (40–70 m deep) Sunda Shelf. In the northern hemisphere winter, monsoonally driven marine processes rrive water and sediment to the east down the axis of the Java Sea. During summer the direction of transport is reversed. This bidirectional process regime not only leaves its imprint in reef and carbonate platform morphology but also results in widespread distribution of siliciclastics from adjacent source areas. Isolated reefs as well as small and generally elongate reef-rimmed carbonate platforms (0.5–10 km long) rise 40–50 m above a sea floor composed largely of siliciclastic sediments. In these cases, facies transitions are very abrupt. Until environmental conditions curtail the carbonate-producing communities of these platforms, carbonate buildups and associated skeletal sediments will coexist with wider spread and more abundant siliciclastics. A third example from a low-latitude arid setting shows that facies transitions from carbonates to siliciclastics typically take place over short distances. The lack of significant rainfall, coupled with high relief along fault-controlled basin margins, promotes aperiodic but powerful episodes of siliciclastic that build directly into the marine environment. High-sloping and narrow coastal plains composed of overlapping fans result. The steep seaward ends of these fans are maintained and protected from marine erosion by coral reefs and associated carbonates. Regionally, siliciclastic to carbonate facies changes in these arid settings take place over very shor distances, a few kilometers at most. However, on a local scale, carbonates may be replaced by siliciclastics over distances as small as a few tens of meters.

Two potential sources for Holocene clay sedimentation in the Caribbean Basin: The Lesser Antilles Arc and the South American continent

Clay sedimentation in the Caribbean Basin is the result of the mixing of two types of materials of different origin. (1) Those derived from weathered volcanic products of the Lesser Antilles (Martinique) Island Arc and identified in the Bay of Fort-de-France are made up of ferriferous montmorillonites and beidellites rich in Mg and poor in Si, K, trace elements and halloysite. Materials derived from the meteoric weathering of volcanic rocks (andesites-dacites) are transported to deeper facies by turbidity and bottom currents. The contribution of these materials to the sedimentation of the Grenada Basin and the eastern flank of the Aves Ridge is relatively important. (2) South American terrigenous materials identified in the Venezuela Basin consist of illites, kaolinites and ferriferous beidellites; they are poor in Mg and relatively rich in Si, K and trace elements. These materials are formed of weathered metamorphic and magmatic acid rocks from the northern provinces of the South American continent, brought into the Grenada Basin by Guyana and Equatorial surface currents. The contribution of these materials to sedimentation on the Island Arc platform of the Lesser Antilles is relatively significant. This work shows that during the transport of fine-grained materials variations in the composition of clays took place only on the insular platform.

Possible Influences upon Lake Development in the East African Rift Valleys

The rift valley lakes of East Africa exhibit considerable variety in size, hydrology, hydrochemistry, and sedimentary regime. Although tectonics and climate are ultimately responsible for lake formation, vol-canism may exert a significant influence upon the lake characteristics. In the Eastern Rift (Kenya, Ethiopia), extensive volcanic activity has disrupted drainage and helped create small, shallow lake basins. Weathering of volcanic rocks produces runoff waters rich in $$Na^{+}$$ and $$HCO_{3}^{-}$$, and smectite is a common clay mineral. In contrast, the Western Rift (Uganda, Mozambique) has localized volcanism; the lakes are large and deep with significant fluvial influents and effluents. Dissolved $$Mg^{2+}, K^{+}$$ and $$SO_{4}^{-}$$ are proportionately greater and detrital mineralogy is more variable. Carbonates and evaporites also reflect the hy-drochemical differences. In addition, the topographic elevation of the lake within the rift may determine the composition and rate of sedimentation.

静岡県富士市における地下水の水質の研究

The Southern foot area of Mt. Fuji, including its lower flank and the coastal plain to the south in Shizuoka Prefecture, is a suitable field to study the relationship between hydrogeology and chemical characters of ground water.Aquifers in the area are distributed in the volcanic strata from the volcanoes [Ko(Old)-Fuji, Fuji, and Ashitaka] and in the alluvial deposits. These aquifers are under a mineralogically uniform condition. Analytical data of natural ground water and leaching experiments on the rocks indicate that the ground water can be grouped by the water temperature, ratio of chemical constituents, bicarbonate (HCO3-) content, total dissolved solids, and others. The g -ound water borne at the depth of 150-250 m in coastal area has a matked discontinuity of HCO3- concentration, which is related with the geology.Chemical constituents in water of the volcanic layers seem to originate from processes of weathering of volcanic rocks. The constituents in water can be explained as a results of weathering reactions.

変質火山岩に由来する過圧密粘土地盤における切土斜面の崩壊

On the 24th June 1978 a landslide occurred at Shiraki, Okuchi-shi, located in the north of Kagoshimaken, Japan; destroying two inhabitants and two houses and causing the damage in a road and a paddy field.The landslide occurred during the improvement-work of road and at the time of heavy rainfall, in the cuttingslope of weathered and fissured overconsolidated clays derived from volcanic rocks. In this paper the originand mechanism of the landslide are described and analysed from the standpoint of geotechnical engineering.In order to investigate strata, geological structure and ground water condition in the landslide area, electricprospecting, electric logging, drilling survey, groundwater tracing and interpretations of aerial photograph andof topographic map were performed. The dependence of the landslide on rainfall also was investigated.Physical and mechanical properties of clays were cleared by means of laboratory soil tests.The strata consisting of lava, upper tuff and lower tuff with a great may of joints and fissures wereformed by the hydrothermal alteration and the weathering of volcanic rocks. The slip surface observed waslocated in the dipping joints with the seam contained montmorillonite between clayey upper tuff and clayeylower tuff.The condition of rainfall was 300 mm in the effective accumulated amount of rainfall and 26 mm in theamount of hourly rainfall preceding the time of activation of the landslide, and fully satisfied the rainfalllevel of threshold value of slope-movements in the southern Kyushu.This landslide is classified as the rockslide of weathered materials derived from volcanic rocks in a ridgyterrain.Physical properties of upper clay (clayey upper tuff) are typically Gs=2.70, ω=82%, ωL=103%, ωP=69%, clay fraction (<2μm) =35% and bulk density=1.40 (t/m3). Its mechanical properties are c'=0.5 tf/m2and φ=34°C in the peak strength, φ=14°C in the residual strength, overconsolidation ratio=3.0, residual factorR=0 and brittleness index IB=1.00-0.64.Stability analyses using the conventional slice-method based on the effective stress gave the decrease incalculated factor of safety owing to the cutting of hillside and the saturation of ground.