Volcanic Rock Mass Research Articles

Submarine volcanism in the Sicilian Channel revisited

The origin and role of volcanism in continental rifts remains poorly understood in comparison to other volcano-tectonic settings. The Sicilian Channel (central Mediterranean Sea) is largely floored by continental crust and represents an area affected by pronounced crustal extension and strike-slip tectonism. It hosts a variety of volcanic landforms closely associated with faults, which can be used to better understand the nature and distribution of rift-related volcanism. A paucity of appropriate seafloor data in the Sicilian Channel has led to uncertainties regarding the location, volume, sources and timing of submarine volcanism. To improve on this situation, we use newly acquired geophysical data (multibeam echosounder and magnetic data, sub-bottom profiles) and dredged seafloor samples to: (i) re-assess the evidence for submarine volcanism in the Sicilian Channel and define its spatial pattern, (ii) infer the relative age and style of magmatism, and (iii) relate this to the dominant tectonic structures in the region. Quaternary rift-related volcanism has been focused at Pantelleria and Linosa, at the northwest boundaries of their respective NW-SE trending grabens. Subsidiary and older volcanic sites potentially occur at the Linosa III and Pantelleria SE seamounts, collectively representing the only sites of recent volcanism that can be directly related to the main rift process. These long-lived polygenetic volcanic landforms have been shaped by magmatism that is directly correlated with extensional faulting and buried igneous bodies. Older volcanic landforms, sharing a similar scale and alignment, occur to the north at Nameless Bank and Adventure Bank. These deeply eroded volcanoes have likely been inactive since the Pliocene and are probably related to earlier stages of crustal thinning and underlying feeder structures in the northern region of the Sicilian Channel. Along a similar alignment, Pinne Bank, SE Pinne Bank and Cimotoe in the northern Sicilian Channel lack a surface volcanic signature but are associated with intrusive bodies or deeply buried volcanic rock masses. Terrible Bank, in the same region, also shows evidence of ancient, polygenetic magmatism, but was subject to significant erosion and lacks a prominent alignment. The much younger volcanism at Graham Volcanic Field and along the northern Capo-Granitola-Sciacca Fault Zone differs markedly from that observed in the other study areas. Here, the low-volume and scattered volcanic activity is driven by shallow-water mafic magma eruptions, which gave rise to small individual cones. These sites are associated with large fault structures away from the main rift axis and may have a distinct magmatic origin. Dispersed active fluid venting occurs across both ancient and young volcanic sites in the region and is directly associated with shallow magmatic bodies within tectonically-controlled basins. Our study provides the foundation for an updated tectonic and magmatic framework for the Sicilian Channel, and for future detailed chronological and geochemical assessment of the sources and evolution of magmatic processes in the region.

Influence of nappe structure on the Carboniferous volcanic reservoir in the middle of the Hongche Fault Zone, Junggar Basin, China

Abstract This work presents an in-depth examination of the Carboniferous volcanic reservoir within the CH471 well area, situated in the central portion of the Hongche fault zone on the northwestern margin of the Junggar Basin. Leveraging seismic data and well connection comparisons, we scrutinize the tectonic evolution model and elucidate the impact of the nappe structure of the Hongche fault zone on the volcanic reservoir. The study has obtained the following understanding: after the formation of Carboniferous volcanic rocks, affected by the Hongche fault structure, a series of structural superpositions from extension to extrusion and finally thrust occurred, resulting in a northwestward tilt of the volcanic rock mass, and a large number of cracks were generated inside the rock mass. At the same time, the top was uplifted and affected by weathering and leaching to form a weathering crust, eventually forming a reservoir. The northern part is located in the edge area of the eruption center, and the rock mass has good stratification. The rock strata have certain constraints on the reservoir distribution, and the reservoir is inclined along the rock mass. The southern part is close to the eruption center and features large volcanic breccia accumulation bodies with strong internal heterogeneity. The reservoir developed mainly in the superposition of the range of control of the weathering crust and dense fracture development, and the rock mass morphology does not control the area. Structure is the key to forming a volcanic rock reservoir, mainly reflected in the following aspects. First, tectonic activity is accompanied by fracture development, and fractures are densely developed in areas with strong activity, which can effectively improve the physical properties of volcanic reservoirs. Second, tectonic activity leads to the strata uplift and weathering denudation, forming a weathering crust. Within the range of control of weathering and leaching, the physical properties of volcanic rocks are improved, and it is easier to form high-quality reservoirs. Third, the distribution of volcanic rock masses is controlled by tectonic activity, which affects the reservoir controlled by the dominant lithology.

Genesis and Accumulation Period of CO2 Gas Reservoir in Hailar Basin

Gas reservoirs with high CO2 have been found in several wells in the Hailar Basin. In this paper, a composition analysis, stable carbon isotope analysis, and a rare gas helium isotope 3He/4He and argon isotope 40Ar/36Ar analysis were carried out. These comprehensive analyses show that the CO2 in the Hailar Basin is inorganic-origin gas, which generally has the characteristics of crust–mantle-mixed CO2, and the fraction of helium of mantle source can reach 15.12~18.76%. There are various types of CO2 gas reservoirs. CO2 gas mainly comes from deep crust. The distribution of gas reservoirs is mainly controlled by deep faults and volcanic rocks, as well as by reservoir properties and preservation conditions. Magmatic rocks provide gas source conditions for the formation of inorganic CO2 reservoirs. Deep–large faults provide the main migration channels for CO2 gas. The sandy conglomerate and bedrock weathering crust of the Nantun Formation and the Tongbomiao Formation provide favorable reservoir spaces for the formation of CO2 gas reservoirs. The combination of volcanic rock mass and deep–large faults creates a favorable area for CO2 gas accumulation. The age of magmatic intrusion and the homogenization temperature of oil–gas inclusions in Dawsonite-bearing sandstone indicate that 120 Ma in the Early Cretaceous was the initial gas generation period of the CO2 reservoir and that oil and gas were injected into the reservoir in large quantities in 122~88 Ma. This period is the peak period of magmatic activity in Northeast China, as well as when the crust of Northeast China greatly changed. A large-scale CO2 injection period occurred in 100~80 Ma, slightly later than the large-scale injection period of the oil and gas. Since the Cenozoic, the structure has been reversed, and the gas reservoir has been adjusted.

The reservoir property modeling of volcanic reservoir: An application to the Shahejie Formation, Zaoyuan oilfield, eastern China

As an increasing number of volcanic reservoirs has been discovered all over the world, the study of volcanic reservoirs has caught more attention. However, researchers mainly focus on the characterization of the external architecture of volcanic rock mass and the superimposed relationship between the rock mass, while paying little attention to the fine anatomy of the internal structure of the rock mass, making it difficult to effectively guide the development of the volcanic reservoir. Taking Zao35 block in Huanghua depression, Bohai Bay Basin, China, as an example, we find a workflow of establishing a high-resolution volcanic stratigraphic structure model and reservoir properties models by integrating well- and seismic-data analysis. The seismic data indicate that the volcanic activities consist of three stages: Stages I and III have positive seismic amplitude reflections, whereas stage II has a negative seismic reflection. The well data indicate that the lithology column of target formation in our study area consists of eight volcanic strata and seven mudstone strata. According to the lithology interpreted using well data, stages III, II, and I consist of five, one, and two volcanic eruption periods, respectively. We have established a structure and stratigraphy model with eight zones of volcanic rock and seven zones of mudstone barrier (15 zones in total) to effectively distinguish volcanic rocks (products of the eruption period) from sedimentary rocks (products of the volcanic dormant period). Based on the seismic attribute analysis, we have combined the sequential indicator simulation and local anisotropy from the seismic amplitude attribute. The model of volcanism can be reproduced by sequential indication simulation of local variogram with variable range directions. Based on the principle of “facies control” (perform lithology simulation in different regions according to lithofacies), we have used the sequential indication method to simulate volcanic rocks. The simulation results have a very good agreement with the shape of lava flows spreading around the crater. To describe the internal structure of the volcanic rock body, reveal internal lithology distribution characteristics, and reservoir physical properties, we provide an effective research method for the development of volcanic reservoir geologic research.

Challenges of Tunnelling in Volcanic Rock Masses

Volcanic rock masses exhibit temporal and spatial variability, even at the scale and duration of engineering projects. Volcanic processes are dynamic, resulting in rock masses ranging from high-porosity, clay-rich, fractured, and soil-like to low-porosity, high-strength, brittle, and massive. Based on a number of studies in a variety of geological settings, such as active and fossil geothermal systems, on the surface of active volcanoes and up to 3000 m below the surface, the work presented in this article shows the relationship between geological characteristics and mechanical parameters of volcanic rocks. These are then linked to the resultant challenges to tunnelling associated with the mechanical behaviour of volcanic rocks and rock masses, ranging from ductile failure such as squeezing and swelling to dynamic failure such as spalling and rockburst.This article highlights some of the key parameters that should be incorporated in site and laboratory investigations to build representative ground models in volcanic rocks and rock masses. Rock mass characterisation needs to address the highly variable and anisotropic nature of volcanic rocks, ranging from millimetre to decametre scale. Ground models must include not only the mechanical properties, such as strength and stiffness, of typical lab investigations, but also petrophysical properties, such as porosity, and geological conditions, such as alteration. Geomechanical characterisation of these rock masses requires an understanding of geological processes to select appropriate field, lab and design tools. In volcanic rocks, perhaps more than any other rock types, the geology is critical to characterising and understanding the behaviour in response to tunnelling.

Calculating the cohesion and internal friction angle of volcanic rocks and rock masses

Rock failure criteria are key input parameters for models designed to better understand the stability of volcanic rock masses. Cohesion and friction angle are the two defining material variables for the Mohr-Coulomb failure criterion. Although these can be determined from laboratory deformation experiments, they are rarely reported. Tabulated data for volcanic rocks, calculated using published triaxial results, show that cohesion and friction angle decrease with increasing porosity. If porosity is known, these empirical fits can provide laboratory-scale cohesion and friction angle estimations. We present a method to upscale these parameters using the generalised Hoek-Brown failure criterion, discuss the considerations and assumptions associated with the upscaling, and provide recommendations for potential end-users. A spreadsheet is provided so that modellers can (1) estimate cohesion and friction angle and (2) upscale these values for use in large-scale volcano modelling. Better constrained input parameters will increase the accuracy of large-scale volcano stability models.

Engineering geological characterisation of rock masses for design of excavation method and support system of Tanju Tunnel, West Nusa Tenggara, Indonesia

This paper presents experiences with design and construction process of the Tanju Tunnel, West Nusa Tenggara. The objective of this research was to characterize the volcanic and intrusive rock masses for designs of the tunnel excavation method and support system. Engineering geological investigations were carried out, upon which the tunnel stand-up time was estimated and the tunnel excavation method and support system were determined based on the rock mass classifications of RMR (Bieniawski, 1989). The investigation results showed that the tunnel construction area consisted of colluvium, andesite, and tuff breccia. The rock masses were dominated by the andesite, which had UCS of intact rock ranging from 200 to 300 MPa classified as strong intact rock. Based on the RMR value, the andesite was classified as a good quality rock mass. The tunnel had unsupported roof stand-up time approximately 20.000 hours for a 3 m tunnel span. The recommended tunnel excavation method was full face, 1.0-1.5 m advance, and complete support 20 m from face, while the support systems were locally bolt in crown 3 m long and 2.5 m spacing, with occasional wire mesh, 50 mm thick shotcrete in crown where required.

An active large rock slide in the Andean paraglacial environment: the Yerba Loca landslide, central Chile

A ca. 2.5 million m3 landslide occurred in August 2018 in the Yerba Loca valley, Andes Main Cordillera (33° 15′ S), at about 4000 m a.s.l. The Yerba Loca landslide is a multirotational slide, with a main scarp and failure surface developed in a volcanic rock mass, with secondary scarps and tilted blocks disturbing the colluvial soil cover. No clear trigger could be identified, although the failure took place some weeks after the largest winter precipitation and a sequence of snowfall and snowmelt, in the context of a severe drought. Inspection of optical satellite images suggests that the landslide suffered slow deformation for at least 15 years, increasing in the months prior to the failure. To corroborate these precursor deformations, InSAR analyses were performed at two time and spatial scales. For over 3 years, deformation in the landslide area was detected, while the local, short-term analysis from the 7 months before failure shows line-of-sight deformation rates at the landslide site of over 10 cm/year. Deformation continues after the failure with decreasing speed, with indications of further activity and expansion of the failure zone. This implies a hazard of rock avalanche, debris flows and/or river damming and subsequent outburst floods that may endanger communities downstream. The Yerba Loca landslide is an example of rock slope failure in paraglacial conditions and the influence of climatic factors in the context of climate change for the central Andes. This event represents an opportunity for learning on landslide mechanisms, remote sensing monitoring and hazard assessment of slow, large volume landslides in the Andean highlands.

Application of soft computing methods in predicting uniaxial compressive strength of the volcanic rocks with different weathering degree

Uniaxial compressive strength (UCS) of rock material is very important parameter for rock engineering applications such as rock mass classification, numerical modelling bearing capacity, mechanical excavation, slope stability and supporting with respect to the engineering behaviors’ of rock. UCS is obtained directly or can be predicted by different methods including using existing tables and diagrams, regression, Bayesian approach and soft computing methods. The main purpose of this study is to examine the applicability and capability of the Extreme Learning Machine (ELM), Minimax Probability Machine Regression (MPMR) for prediction of UCS of the volcanic rocks and to compare its performance with Least Square Support Vector Machine (LS-SVM). The samples tested were taken from the volcanic rock masses exposed at the eastern Pontides (NE Turkey). In the soft computing model to estimate UCS of the samples investigated, porosity and slake durability index were used as input parameters. In this study, the root mean square error (RMSE), variance account factor (VAF), maximum determination coefficient value (R2), adjusted determination coefficient (Adj. R2) and performance index (PI), regression error characteristic (REC) curve and Taylor diagram were used to determine the accuracy of the ELM, MPMR and LS-SVM models developed.

Toppling and sliding in volcanic bimrocks around Bayrakli (Izmir, Turkey)

Discontinuities have significant role on the behavior of rock masses with respect to several types of instabilities. Excavability, deformability, bearing capacity and slope stability of the rock masses should be investigated considering the discontinuity characteristics with particular emphasis on the geomechanical properties. Kinematic analyses mostly provide an insight to the instabilities, however the dimensions of the blocks bounded by discontinuities, their geomechanical properties and the geometry of the slope should also to be taken into account. The study area is in the abandoned stone quarry in Bayrakli district of Izmir residential area. Due to the excavations and discontinuity orientations, instabilities have occured. Miocene aged andesites and altered agglomerates of Yamanlar Volcanics form the bimrock mass. The study area is located within a sheared zone, bounded by strike slip fault zone. Intact andesite blocks were encountered in altered agglomerate matrix, forming a volcanic bimrock. Wedge and planar sliding and block toppling were observed within the area. Detailed discontinuity surveying was conducted, combined with core drillings. Several typical locations were detected where prismatic blocks of andesites are bound to experience block toppling. Such locations are nearby the top of the steep slopes. Agglomerates are subjected to mainly sliding and the blocks have been formed not by gravity but by peculiarities of the volcanic sedimentation and, probably by subsequent tectonics. In order to determine the mechanism of the sliding and toppling in more details, the relation of the blocks and the slope geometry were investigated. Bimrock type volcanic rock masses sometimes do not tend to accommodate the general rules of toppling and sliding due to their anisotropic settings.

Towards more realistic values of elastic moduli for volcano modelling

The accuracy of elastic analytical solutions and numerical models, widely used in volcanology to interpret surface ground deformation, depends heavily on the Young’s modulus chosen to represent the medium. The paucity of laboratory studies that provide Young’s moduli for volcanic rocks, and studies that tackle the topic of upscaling these values to the relevant lengthscale, has left volcano modellers ill-equipped to select appropriate Young’s moduli for their models. Here we present a wealth of laboratory data and suggest tools, widely used in geotechnics but adapted here to better suit volcanic rocks, to upscale these values to the scale of a volcanic rock mass. We provide the means to estimate upscaled values of Young’s modulus, Poisson’s ratio, shear modulus, and bulk modulus for a volcanic rock mass that can be improved with laboratory measurements and/or structural assessments of the studied area, but do not rely on them. In the absence of information, we estimate upscaled values of Young’s modulus, Poisson’s ratio, shear modulus, and bulk modulus for volcanic rock with an average porosity and an average fracture density/quality to be 5.4GPa, 0.3, 2.1GPa, and 4.5GPa, respectively. The proposed Young’s modulus for a typical volcanic rock mass of 5.4GPa is much lower than the values typically used in volcano modelling. We also offer two methods to estimate depth-dependent rock mass Young’s moduli, and provide two examples, using published data from boreholes within Kīlauea volcano (USA) and Mt. Unzen (Japan), to demonstrate how to apply our approach to real datasets. It is our hope that the data and analysis presented herein will assist in the selection of elastic moduli for volcano modelling. To this end, we provide a Microsoft Excel© spreadsheet containing the data and necessary equations to calculate rock mass elastic moduli that can be updated when new data become available. The selection of the most appropriate elastic moduli will provide the most accurate model predictions and therefore the most reliable information regarding the unrest of a particular volcano or volcanic terrain.

Time–Frequency Electromagnetic Method for Exploring Favorable Deep Igneous Rock Targets: A Case Study from North Xinjiang

The detection of deep targets has always been a challenging topic for controlled source electromagnetic methods; however, the time–frequency electromagnetic method (TFEM) can overcome some of these challenges. In this paper, we introduce the method and showcase the technique for imaging deep targets using optimal offsets and transmission periods. In addition, we implement a simulated annealing constrained inversion, based on well-seismic data, to illustrate improvement in the effective detection depth and the ability to identify deep targets. We apply TFEM for two targets in North Xinjiang to show that internal multiple sets of layered series in a deep Carboniferous system and the volcanic rock mass developed in this area can be imaged. We conclude that the low-resistivity layer inside the Carboniferous system is the response of hydrocarbon source beds of muddy clastic rocks and predict that the high-resistivity layer is a favorable reservoir of volcanic rocks. Subsequent drilling confirmed the structural characteristics of the Carboniferous system revealed by TFEM data.

Preliminary geological, geochemical and numerical study on the first EGS project in Turkey

Geothermal energy is attracting more and more attention due to its large capacity and lack of dependency on the weather. Currently, many countries have planned enhanced geothermal system (EGS) projects. In this paper the first EGS project in Turkey, which is being implemented at the license area of SDS Energy Inc., in Dikili of the Izmir province, is introduced. Extensive geological, paleostress (279 fault-slip data from 33 locations), geophysical (magnetotelluric and vertical electrical sounding at 80 and 129 locations, respectively) and geochemical studies as well as paleostress measurements have been conducted in this area within the scope of this project. In the light of all these studies, it has been determined that the Dikili region is remarkable in terms of its high thermal gradient of about 7 °C/100 m. The geothermal reservoir formation “the Kozak granodiorite” is a homogeneous, crystalline volcanic rock mass with high radiogenic heat production, and suitable for an EGS application. The analysis shows that the dominating fault system is normal, and the corresponding primary stress regime is extensional. Based on the geological, geophysical surveys and the estimated in situ stresses, numerical studies were carried out to assess the results of the hydraulic fracturing and geothermal energy production using the numerical codes FLAC3Dplus and TOUGH2MP, respectively, in the area A of the Dikili site. The simulation results show that the stimulated reservoir volume and area could reach 44.5 million m3 and 1 km2, respectively, with an injection volume of 122,931 m3. Assuming the fractured zone has a height of 1000 m and a half-length of 1200 m (the distance between injection and production wells being 1000 m), an average overall geothermal capacity of 83.7 MWth in 20 years could be reached with an injection rate of 250 l/s. The injection strategy and design parameters of the reservoir stimulation and geothermal production will be further optimized with the project running.

Açıksaray “Open Palace”: a Byzantine rock-cut settlement in Cappadocia

AbstractCourtyard complexes formed entirely out of the volcanic rock mass in Cappadocia, in Central Anatolia, differ from the other rock-cut structures in the region, in both scale and elaboration of design. There are more than forty such complexes in Cappadocia, either gathered in one location or isolated. Located on the Nevşehir-Gülşehir road, Açıksaray contains nine such complexes in close proximity, many of which feature monumental façades as well as reception areas and utilitarian spaces such as large stables around a courtyard. This paper, in the light of survey results, presents site analysis and architectural readings that lead the discussion of the nature and stages of occupation at Açıksaray. By doing this, the paper aims to bring new insights to the discussion on courtyard complexes, adding details and nuance to our understanding of the Açıksaray settlement, while noting similarities with other settlements in the region. Underlining the secular and elite character of the Açıksaray settlement, this study contributes in particular to enlarging the picture of medieval life in Cappadocia, and in general to the studies of Byzantine domestic architecture, for which architectural evidence is still scarce.

Geological and geomechanical models of the pre-landslide volcanic edifice of Güímar and La Orotava mega-landslides (Tenerife)

The geological and geomechanical characterizations of the volcanic rock mass succession affected by the Güímar and La Orotava mega-landslides (Tenerife, Canary Island) are presented here for the first time. The estimated subaerial volume of rocks mobilized by each of these landslides is in the range of 30–50km3, one of the largest known in the world. Field data, gallery surveys and borehole drilling have allowed the main types of materials and their structural arrangement to be identified. Based on these information a geological model of the pre-landslide volcanic edifice is proposed. A palaeo-morphological reconstruction has been produced and possible slope angles and heights of the pre-landslide volcanic edifice are presented. Five main lithological units have been identified in the emerged part of the edifice, three of them forming the flanks and two forming the structural axis of the island. On the flanks, lava flows predominate with different degrees of alteration and proportion of dikes increasing near the structural axis. The predominant materials on the structural axis are pyroclastic deposits, lava flows and dikes. In the submarine edifice four main lithological units have been distinguished, formed by hyaloclastites, pillow-lavas, dikes and gravitational deposits (slope and basin facies). The geomechanical characterization of these materials has been obtained from field data, boreholes, laboratory tests and literature review. The geological and geomechanical models obtained provide the fundamental basis for the explanation of the instability processes that generated the Güímar and La Orotava mega-landslides.

EPR dating and evolution of the Elbrus volcano

This study is devoted to the reconstruction of the Elbrus volcano evolution by electron paramagnetic resonance (EPR) dating. The following ages have been obtained for the Elbrus activity cycles: early caldera cycle was apparent between 340 and 250 ka ago and changed into the denudation of volcano. Resumption of volcanic activity (late stage of caldera cycle) resulted in accumulation of thick volcanic rock mass (up to 2 km) took place about 170 ka ago. The end of this stage came 70–60 ka ago soon after the intrusion of subvolcanic bodies 90–70 ka ago. After Late Pleistocene glaciation, volcanic activity resumed several times, however, we have dated with EPR only one eruption which occurred 6.7 ka ago. Comparison with the results of geomorphological,14C, K−Ar and U-Th sensitive high-resolution ion microprobe dating show that EPR dating of quartz from volcanic rocks may be used for the reconstruction of the Late Neo-Pleistocene and Holocene history of the Elbrus. For older rocks, EPR ages are younger than those obtained with conventional methods. The causes of this disagreement are discussed.

Megabreccia Deposits in an Extensional Basin: the Miocene-Pliocene Horse Camp Formation, East-Central Nevada

Three varieties of megabreccia deposits are present in alluvial-lacustrine extensional basin fill of the Miocene-Pliocene Horse Camp Formation of east-central Nevada. Coherent debris sheets (150-300 m thick; up to 1,500 m long) consist of Oligocene-Miocene volcanic rock masses which are internally fractured yet retain their stratigraphic integrity. Fracture zones show variable amounts of displacement (up to 5 cm) and brecciation. These debris sheets overlie horizontally stratified sandstone and laminated claystone interpreted as playa deposits and are overlain by lithified grus. Emplacement of these coherent debris sheets was by landslide or block slide. Associated deposits of large boulders within playa facies suggest gliding of blocks broken from the edges of the landslides across wet playa surfaces. Large (1.6 - 2.4 km-long) allochthonous blocks consist of intact Paleozoic and Tertiary volcanic stratigraphic sequences which are brecciated and attenuated. Brecciation is accompanied in places by incorporation of muddy sand matrix. These blocks may be fragments of the upper plate of low-angle detachment faults which broke away as gravity-driven blocks from the nearby Horse Range and slid along the uplifted former detachment surface into the adjacent Horse Camp basin. Megabreccia deposits characterize Teritary extensional basins in western North America. Detailed analysis of their stratigraphic,more » sedimentologic, and structural relations can provide a better understanding of the complex tectonosedimentary history of these basins.« less

千葉県館山市船形磨崖仏十一面観音像の劣化と水・岩石相互作用

Daifukuji Temple rock-cliff Budda sculpture which is located halfway up on the hill near the coast of Tateyama, Chiba Prefecture was carved in 8th century on the Neogene andesitic tuff and tuff breccia alternated bed. It is sheltered by a beautiful wooden construction. The Neogene andesitic tuff and tuff breccia are composed chiefly of augite, hypersthene, hornblende, plagioclase, and volcanic glass with subordinate amounts of fine-grained magnetite, pyrite (probably biogenic), hematite and limonite. The surface of Budda sculpture is covered by a thick, up to several mm, crust or scab composed chiefly of minerals such as gypsum, thenardite, epsomite, mirabilite with minor amounts of halite, sylvite, aragonite and copiapite. Rain water penetrates into the rock of the hill where sculpture is located and the water easily comes out after interaction with rocks and evaporates from the surface of rock-cliff. The water coming out from rock mass has high contents of Ca, Na, Cl, HCO3 and SO4 with subordinate amounts of K and Mg. Gypsum-rich scab or crust was formed by the evaporation of such type of groundwater on the rock-mass surface. The growth of thus formed scabs or crusts and their falling off must be major reasons why the sculpture has been decayed so badly as shown by Fig 4. Modes of occurrence of gypsum-rich scabs and indoor experiments using bore-hole cores taken from the Neogene volcanogenic sediments mass on which the sculpture was carved indicate that the increase in the thickness of the gypsum-rich scabs is unbelievably fast, probably more than 0.15mm/year. The repeated cycle of the growth of gypsum-rich scab or crust on the surface of Neogene volcanic sedimentary rock mass and their falling off should be stopped to prevent the forth decay of this Budda sculpture. The best ways to solve this problem are considered to be (1) to minimize the down permeation of groundwater from the top surface through interstitial void and joint of Neogene volcanogenic formation by making open drainage space at the above and/or back side of the rock-cliff sculpture or by covering the top surface of the hill by unpermeable facing and (2) to keep the humidity of the room of rock-cilff sculpture as high as possible to minimize the evaporation of water extracted from the surface of the sculpture.

Partition of trace elements between rock-forming minerals and the host volcanic rocks

Partition coefficients for +1 to +4 valent trace ions between ground mass of volcanic rocks and the coexisting phenocrysts of plagioclase, biotite, hornblende and olivine have been determined by neutron activation analysis. The result supports the mechanism proposed by Onuma et al. [1] that the trace element partition between phenocryst and ground mass is determined by crystal structure of the phenocryst.

On some Tufaceous Rhyolitic Rocks from Dufton Pike (Westmorland)

The specimens which form the subject of this paper were selected for examination on account of their peculiar appearance, and because it was thought probable that they might afford some evidence of solfataric action on British rhyolites of considerable geological age. Through the kindness of my friend Mr. H. B. Woodward, F.R.S., I have been able to learn a few particulars concerning the geology of Dufton Pike. From these it appears that the central portion of the Pike consists of volcaninc rocks of the Borrowdale Series, bounded by four faults, those on the east and west being approximately parallel and running in a north-north-westerly direction. The rocks faulted against this central mass of volcanic rocks are of Lower Silurian age on the north, south, and east; while those on the west are Upper Silurian, consisting of Stockdale Shales and Coniston Flags. The specimens about to be described were collected by the late Prof. A. H. Green, F.R.S., and Mr. J. G. Goodchild, F.G.S., and were evidently procured from the Borrowdale Volcanic Series which constitutes the central mass of Dufton Pike. The specimens were given to me many years ago, so that, never having visited that part of Westmorland, I am ignorant of the precise spots from which they were derived. The chief interest which attaches to them lies in the peculiar character of the alteration that they have undergone: an alteration which appears to me to have been probably due to solfataric action. For the careful analyses which accompany this