The 1996 Eruption of Karymsky Volcano, Kamchatka: Historical Record of Basaltic Replenishment of an Andesite Reservoir

The simultaneous eruption in 1996 of andesite from Karymskyvolcano and of basalt from the Academy Nauk vent 6 km away appearsto provide a case of mafic recharge of an andesite reservoirfor which the time of recharge is exactly known and direct samplesof the recharging magma are available. The explosive phreato-magmaticeruption of basalt was terminated in less than 24 h, whereasandesite erupted continuously during the following 4 years.Detailed petrological study of volcanic ash, bombs and lavasof Karymsky andesite erupted during the period 1996–1999provides evidence for basaltic replenishment at the beginningof the eruptive cycle, as well as a record of compositionalvariations within the Karymsky magma reservoir induced by basalticrecharge. Shortly after the beginning of the eruption the compositionof the matrix glass of the Karymsky tephra became more maficand then, within 2 months, gradually returned to its originalstate and remained almost constant for the following 3 years.Further evidence for basaltic replenishment is provided by thepresence of xenocrysts of basaltic origin in the andesite ofKarymsky. A conspicuous portion of the plagioclase phenocrystsin the Karymsky andesite has calcic cores, with compositionsand textures resembling those of plagioclases in the AcademyNauk basalt. Similarly, the earlier portion of the andesiteof the eruption sequence contains rare olivines, which occuras resorbed cores in pyroxenes. The composition of the olivinematches that of olivines in the Academy Nauk basalt. The sequenceof events appears to be: (1) injection of basaltic magma intothe Karymsky chamber with immediate, compensating expulsionof pre-existing chamber magma from the Karymsky central vent;(2) direct mixing of basaltic and andesitic magmas with dispersalof phenocrysts associated with the basalt throughout the andesiteso that newly mixed magma appeared at the vent within 2 months;(3) re-establishment of thermal and chemical equilibrium withinthe reservoir involving crystallization in the new hybrid liquid,which returned the melt composition to ‘normal’,formed rims on inherited calcic plagioclase, and caused theresorption of dispersed olivine xenocrysts. Taken together,these findings indicate that the Karymsky magma reservoir wasrecharged by basalt at the onset of the 1996 eruptive cycle.The rapidity and thoroughness of mixing of the basalt with thepre-existing andesite probably reflects the modest contrastin temperature, viscosity, and density between the two magmas. KEY WORDS: Karymsky; Kamchatka; magma mixing; andesite; volcanic glass; plagioclase     

Plio-Pleistocene sedimentation in coastal grabens,north-east Rhodes,Greece

The stratigraphy of marine Plio-Pleistocene sediments from northeast Rhodes (Dodecanese islands, Greece) is revised in the light of facies mapping and the recognition of three major transgression–regression cycles. Before late Pliocene submergence, metamorphosed Mesozoic limestones formed a high-relief karstic landscape. During subsequent transgressions, subsiding basins with spectacular cliffed and bioeroded margins were infilled by a mosaic of carbonate-dominated sediments, sourced by high rates of carbonate productivity on narrow shelves rimming the basins and their drowning islands. Periods of relative sea-level fall superimposed a complex series of ‘fossil’ coastal geomorphological features such as cliffs, abrasion platforms, surf caves, notches, boulder beaches and palaeokarsts. These created the rugged present day topography of the island's northeast coast. Three main lithostratigraphic units, the Kritika, Rhodes and Lindos Acropolis Formations, are defined. The Rhodes and Lindos Acropolis Formations are subdivided into mappable facies groups rather than members, as the lithofacies are strongly diachronous. The Kritika and Rhodes Formations were each subaerially exposed and partly eroded before re-transgression. Although there is a general pattern of lithological succession, details vary across the study area and some facies groups are restricted in development, indicating differences in tectonic behaviour and palaeo-geomorphology between neighbouring basins. A preliminary process-response model is presented for the sedimentation history of the Rhodes and Lindos Acropolis Formations, using sedimentological, palaeontological, palaeoecological and ichnological data.     

Determination of the effect of surface water irrigation on the groundwater chemistry of a hard rock terrain in central India

Abstract

The Bundelkhand area of central India consists of weathered granitic bedrock. The aim of the present study was to identify the effects of surface water irrigation on groundwater quality in shallow aquifers used for domestic supply. A set of 37, 58 and 17 samples were collected, respectively, from the non-irrigated area, the irrigated area and surface waters. Concentrations of major ions (including NO₃ ^?), PO₄ = and Fe⁺⁺ were determined. A statistical comparison of the data groups was carried out assuming that the only difference between the two areas was in agricultural practice. It was discovered that, despite the better quality of the surface waters, the irrigated area groundwaters were higher in concentration than those of the non-irrigated area. The main causes for that appear to be evaporation/transpiration and fertilizer application, modified by calcite precipitation and ion exchange. The proposed approach is simple enough to be used routinely in monitoring.     

POTENTIAL EFFECTS OF CLIMATE CHANGE ON FRESHWATER ECOSYSTEMS OF THE NEW ENGLAND/MID-ATLANTIC REGION

Numerous freshwater ecosystems, dense concentrations of humans along the eastern seaboard, extensive forests and a history of intensive land use distinguish the New England/Mid-Atlantic Region. Human population densities are forecast to increase in portions of the region at the same time that climate is expected to be changing. Consequently, the effects of humans and climatic change are likely to affect freshwater ecosystems within the region interactively. The general climate, at present, is humid continental, and the region receives abundant precipitation. Climatic projections for a 2 × CO₂ atmosphere, however, suggest warmer and drier conditions for much of this region. Annual temperature increases ranging from 3–5°C are projected, with the greatest increases occurring in autumn or winter. According to a water balance model, the projected increase in temperature will result in greater rates of evaporation and evapotranspiration. This could cause a 21 and 31% reduction in annual stream flow in the southern and northern sections of the region, respectively, with greatest reductions occurring in autumn and winter. The amount and duration of snow cover is also projected to decrease across the region, and summer convective thunderstorms are likely to decrease in frequency but increase in intensity. The dual effects of climate change and direct anthropogenic stress will most likely alter hydrological and biogeochemical processes, and, hence, the floral and faunal communities of the region's freshwater ecosystems. For example, the projected increase in evapotranspiration and evaporation could eliminate most bog ecosystems, and increases in water temperature may increase bioaccumulation, and possibly biomagnification, of organic and inorganic contaminants. Not all change may be adverse. For example, a decrease in runoff may reduce the intensity of ongoing estuarine eutrophication, and acidification of aquatic habitats during the spring snowmelt period may be ameliorated. Recommendations for future monitoring efforts include: (1) extending and improving data on the distribution, abundance and effect of anthropogenic stressors (non-point pollution) within the region; and (2) improving scientific knowledge regarding the contemporary distribution and abundance of aquatic species. Research recommendations include: (1) establishing a research centre(s) where field studies designed to understand interactions between freshwater ecosystems and climate change can be conducted; (2) projecting the future distribution, activities and direct effects of humans within the region; (3) developing mathematical analyses, experimental designs and aquatic indicators that distinguish between climatic and anthropogenic effects on aquatic systems; (4) developing and refining projections of climate variability such that the magnitude, frequency and seasonal timing of extreme events can be forecast; and (5) describing quantitatively the flux of materials (sediments, nutrients, metals) from watersheds characterized by a mosaic of land uses. © 1997 John Wiley & Sons, Ltd.     

MULTIVARIATE GEOMORPHIC ANALYSIS OF FOREST STREAMS: IMPLICATIONS FOR ASSESSMENT OF LAND USE IMPACTS ON CHANNEL CONDITION

Multivariate statistical analyses of geomorphic variables from 23 forest stream reaches in southeast Alaska result in successful discrimination between pristine streams and those disturbed by land management, specifically timber harvesting and associated road building. Results of discriminant function analysis indicate that a three-variable model discriminates 10 disturbed from 13 undisturbed reaches with 90 per cent and 92 per cent correct classification respectively. These variables are the total number of pools per reach, the ratio of mean residual pool depth to mean bankfull depth, and the ratio of critical shear stress of the median surface grain size to bankfull shear stress. The last variable can be dropped without a decrease in rate of correct classification; however, the resulting two-variable model may be less robust. Analysis of the distribution of channel units, including pool types, can also be used to discriminate disturbed from undisturbed reaches and is particularly useful for assessment of aquatic habitat condition. However, channel unit classification and inventory can be subject to considerable error and observer bias. Abundance of pool-related large woody debris is highly correlated with pool frequency and is an important factor determining channel morphology. Results of this study yield a much needed, objective, geomorphic discrimination of pristine and disturbed channel conditions, providing a reference standard for channel assessment and restoration efforts.     

A LATE PLEISTOCENE INTERTIDAL BOULDER PAVEMENT FROM AN ISOSTATICALLY EMERGENT COAST,DUNDALK BAY,EASTERN IRELAND

Late Pleistocene sequences around Dundalk Bay, eastern Ireland, record glaciomarine sedimentation near the margin of a grounded ice lobe around 15 ka BP. A coastal exposure at Cooley Point consists of four major facies deposited outside this ice limit. (1) A basal mud facies deposited from sediment plumes accumulated following the initial ice marginal retreat inland. It contains a well-preserved Arctic microfauna dominated by the foram Elphidium clavatum and the ostracod Roundstonia globulifera. (2) A flat to undulating boulder facies (pavement), mostly one clast thick, is found pressed into the mud and is characterized by bevelled and striated upper clast surfaces. Pavement attributes are a result of intertidal activity in a cold climate. The boulder source is due to rafting by ice floes from glacigenic debris deposited during an ice advance. (3) Laminated sand facies drape the pavement and are a result of variable current activity. (4) The overlying gravel facies is separated from the sand facies by a marine erosion surface. The gravel facies is subaqueous, channelized and is overlain by late glacial raised beach ridges. Locally the gravels have been deformed by ice pressure from partially floating ice floes. Facies changes record terrestrial submergence and provide evidence for changes in relative sea level during part of the last deglacial cycle. The boulder pavement and deformed gravel facies suggest that ice floes and sea ice effects may be more common within stratigraphies along emergent coasts than previously thought, though they have a low preservation potential. Extreme conditions during the deglacial favoured opportunistic microfaunas during mud deposition. This event may be related to a major meltwater event within the Irish Sea Basin.     

Thermal Emplacement Model for the Alpine Lherzolite Massif at Balmuccia, Italy

The spinel lherzolite massif at Balmuccia, northwest Italy,forms an elongate north-south trending lens (4.5 x 0.5 x 1.1km) within the pre-Alpine granulite basement complex of theIvrea zone. The western contact is a mylonite fault zone formedduring late emplacement cataclastic flow near the Insubric line;to the east the lherzolite massif is separated from the granulitesby a magmatic sheath of layered pyroxenites, pyroxene pegmatitesand meta-gabbros. Pyroxene reaction zones on gabbro dikes indunite pods which lie east of the main lherzolite massif showthat emplacement occurred at pressures >9 kb, based on peridotiteequilibria studies. Phase chemistry calculations on pyroxenitesand granulites show ambient P–T conditions to have been850 °C (Cpx–Opx equilibria) and 10–13 kb (Opx–Gt;Plg–Gt–Sill–Qtz) during emplacement of thelherzolite massif. Temperature calculations on 12 peridotitesfrom throughout the massif suggest an earlier high-T stage (1200°C; Ol–Px–Sp) followed by partial re-equilibrationat lower T (850–950 °C; Cpx–Opx). The areaswithin the lherzolite massif with the highest calculated Ol–Px–Sptemperatures have the lowest Cpx–Opx temperatures, suggestingthat the apparent Cpx–Opx temperatures are due to re-equilibrationduring emplacement. The spinel lherzolite probably originatedat 12 and 20 kb, based on the mineral assemblage Ol + Opx +Cpx + Sp + Hnbd. The inferred P–T ranges put both themassif and the granulites on a geotherm that is high for continentalcrust and implies a high surface heat flow at the time of emplacement(2.2 µcal/cm² sec). The Balmuccia area later became thelocus of early Mesozoic rifting between the North and SouthAlpine plates. These relationships at Balmuccia are similarto the Great Basin of the western United States, where mantlexenoliths in young basalts that show P–T conditions of1100–1300 °C at 17–20 kb, occur in an area ofhigh heat flow (2.0 µCal/cm² sec average) and extension.This suggests an association between up-welling of mantle peridotitesbelow continents and ensialic tensional tectonics.     

The Scots Bay formation, Nova Scotia, Canada, a Jurassic carbonate lake with Silica-rich hydrothermal springs

During Early Jurassic time, the Scots Bay Formation accumulated in an aerobic lake on the floor of the subtropical Fundy rift valley. A diverse biota flourished in the lake as evidenced by algal stromatolites, oncolites, charophytes, ostracods, gastropods, conchostracans, fish bones, calcispheres and logs. Carbonate wackestone and packstone were deposited in the littoral zone and lime mudstone accumulated offshore on a proximal slope. Silica-rich hydrothermal springs and seeps around and on the floor of the lake precipitated siliceous tufa and silicified adjacent carbonate strata. The tufa is characterized by the progressive sequence: (1) open-framework, porous substrate of goethite spheres, (2) encrusting chalcedony spherulites where goethite inclusions decrease in size and number outwards towards the surfaces of the spherulites, (3) a fringe of quartz on the chalcedony spherulites and (4) coarsening inwards mosaics of quartz that filled the remaining voids. Carbonate diagenesis included conversion of low-Mg calcite ooze to micrite and microspar-pseudospar, and local dissolution and reprecipitation of calcite cement. At times the lake shrank in size, concentrating silica in increasingly alkaline lake water which then silicified some of the carbonate strata and logs. The latest cements were calcite, zeolites and celadonite.