effect of partial melting on rock deformation experimental and natural evidences on rocks of granitic compositions abstract deformation tests at constant strain rate 10 5 s 1 at 210 250 mpa confining pressure and at 560 900 c are performed on an aplite with varying water contents the mechanical behaviour is correlated with the microstructure after a stage of plastification depending on the temperature and on the water content the rock strength falls dramatically under such confining pressures before melting and before straining the pores of the wet rocks burst as the thermal expansion of water develops a local high pore pressure which causes cracking and fracturing in our opinion this pore bursting will increase the effects of thermal cracking due to the differential expansion of the minerals the rocks exhibit a uniform crack network with increasing temperature melting occurs in the cataclased rock the crack development and melting depend on the initial water content the loss of cohesion obtained either by cracking or by cracking and melting provokes a dramatic weakening axial shortening induces cracking parallel to 1 and melt transfer into extensional regions deformation is concentrated in dilatant shear bands at the highest temperature 900 c a melt film network is rapidly established and induces a very low flow stress melt effects in naturally deformed gneisses suggest that biotite breakdown furnishes a silicate fluid which induces hydraulic fracture and melt dispersion

a granular flow theory for the deformation of partially molten rock abstract a model is developed for deformation of partially molten rock in which the primary mechanism is the relative movement of grains and the strain rate is controlled by the rate at which the interferences to this movement are accommodated by local melting it is concluded that in multicomponent rocks with moderate melt fractions where this model is applicable the strain rate is generally determined by the rate of diffusion of the grain components in the melt with linear dependence on deviatoric stress quadratic dependence on melt fraction and inverse quadratic dependence on grain size where melt is free to escape the strain rate is somewhat higher than for a closed system but the melt escape rate is more strongly dependent on the pressure differential between grains and melt effective pressure than on the applied principal stress difference unless the stress difference is large compared with the effective pressure any substantial increase in rate of melt release due to deformation would have to come from other factors such as increase in permeability due to microfracturing

constraints on the evolution of crustal flow beneath northern tibet crustal flow is an important tectonic process active in continent continent collisions and which may be significant in the development of convergent plate boundaries in this study the results from multidimensional electrical conductivity modeling have been combined with laboratory studies of the rheology of partially molten rocks to characterize the rheological behavior of the middle to lower crust of both the songpan ganzi and kunlun terranes in the northern tibetan plateau two different methods are adopted to develop constraints on melt fraction temperature and crustal flow velocity in the study area the estimates of these parameters are then used to evaluate whether crustal flow can occur on the northern margin of the tibetan plateau in the songpan ganzi crust all conditions are satisfied for topography driven channel flow to be dominant with partial melt not being required for flow at temperature above 1000 c further north the kunlun fault defines the southern boundary of a transition zone between the tibetan plateau and the qaidam basin constrained by the estimated melt fractions it is shown that channel injection across the fault requires temperatures close to 900 c the composition of igneous rocks found at the surface confirm those conditions are met for the southern kunlun ranges to the north the qaidam basin is characterized by colder crust that may reflect an earlier stage in the channel injection process in the study area at least 10 of the eastward directed tibetan crustal flow could be deflected northward across the kunlun fault and injected into the transition zone defining the northern margin of the tibetan plateau

on the rheology of partially molten synthetic granite abstract in an attempt to obviate some of the difficulties inherent in using natural rocks to study experimentally the rheology of partially molten granitic rocks we report some preliminary experiments using hot pressed synthetic aggregates with quartz as the solid phase and a quartz albite glass to form the melt phase undrained constant displacement rate and stress relaxation experiments were performed at 1100 c and 300 mpa total confining pressure using nominally 16 and 28 wt anhydrous melt and at 980 c with 12 wt of water saturated melt strain rate varies non linearly with stress corresponding to a stress exponent of 3 6 for the anhydrous melt tests and 1 9 with the wet melt strain rate is enhanced about 160 fold through doubling the melt fraction from 16 wt intracrystalline plasticity appears to contribute insignificantly to the observed deformation and the preservation of relatively equant grains implies a granular flow process microcracking occurs during isostatic hot pressing and also contributes to subsequent non isostatic deformation at high stresses and strain rates models of flow of partially molten rock that assume diffusive transfer accommodation of granular flow predict linear viscosity but only at lower strain rates than accessed experimentally it is suggested that the non linear granular flow observed in these experiments involved the episodic unsticking of sintered contacts between grains by a rate dependent cracking and or dislocation accommodation process

the influence of melting and melt drainage on crustal rheology during orogenesis partial melting significantly weakens crustal rocks by introducing a low viscosity liquid phase however near concomitant melt drainage can remove this weak phase potentially reversing the rheological effects such that the strength of a specific lithology depends on when the prograde pressure temperature path intersects a melting reaction how much melt is produced and how long this melt is retained before it is lost phase equilibria and mixed rheology modeling of typical metapelite and metagreywacke compositions indicate that these rocks undergo continuous but pulsed melt production during prograde metamorphism depending on whether melt removal is continuous or episodic and assuming geological strain rates the lithologies can retain a very low strength less than 1 mpa or transiently strengthen to 5 mpa following melt loss lithologies undergoing episodic melt loss can therefore cycle between being relatively weak and relatively strong components within a composite crustal section melt production retention and weakening in the middle to lower crust as a whole is more sustained during heating and melt production consistent with geodynamic inferences of weak melt bearing lower crust however the long term consequence of melting and melt loss is a 50 400 increase in the strength of residual lithologies the strengthening is more pronounced in metapelite than metagreywacke and is achieved through a combination of dehydration and the removal of the weak mica framework coupled to increased proportions of strong feldspars and garnet despite prolonged weakness melting and melt loss therefore ultimately result in a dry and elastic lower crust

mobility of pyroclastic flows and surges at the soufriere hills volcano montserrat the soufriere hills volcano on montserrat has produced avalanche like pyroclastic flows formed by collapse of the unstable lava dome or explosive activity pyroclastic flows associated with dome collapse generate overlying dilute surges which detach from and travel beyond their parent flows the largest surges partially transform by rapid sedimentation into dense secondary pyroclastic flows that pose significant hazards to distal areas different kinds of pyroclastic density currents display contrasting mobilities indicated by ratios of total height of fall h run out distance l area inundated a and volume transported v dome collapse flow mobilities characterised by either l h or a v2 3 resemble those of terrestrial and extraterrestrial cold rockfalls dade and huppert 1998 in contrast fountain fed pumice flows and fine grained secondary pyroclastic flows travel slower but for comparable initial volumes and heights can inundate greater areas

variation of lithium isotope composition in the marine environment a preliminary report the li isotopic compositions of ocean waters lake water hydrothermal solutions altered and unaltered basalts have been determined using the technique of thermal ionization mass spectrometry of lithium tetraborate seawater appears to be homogeneous in li isotopic composition the mean delta sup 6 li value is minus 32 3 plus minus 0 5 per thousand relative to an isotopic standard three lakes studied lake tanganyika caspian sea and dead sea yield delta sup 6 li similar to the seawater isotopic composition a fresh basalt glass from 21 degree n east pacific rise displays a delta sup 6 li value of minus 4 7 per thousand a hydrothermal solution from a 21 degree n vent field has delta sup 6 li of minus 10 per thousand indicating incomplete extraction of li from the igneous minerals or partial retention in secondary phases the alteration margin of a basalt from the mid atlantic ridge has delta sup 6 li of minus 8 4 per thousand the isotope data of submarine basalts suggest preferential removal of sup 6 li from seawater into alteration minerals during low temperature weathering the delta sup 6 li values of two hydrothermal solutions from guaymas basin were found to be minus 5 per thousand and minus 10 per thousand the results can be interpreted as the net effect of li addition from basalt and sediments and incorporation in hydrothermal precipitates as the hydrothermalmore fluids interact with basin sediments the observed enrichment of sup 7 li in seawater relative to submarine hydrothermal solutions its principal li input is tentatively attributed to isotopic fractionation associated with low temperature alteration of sea floor basalt and incorporation in authigenic sediments it appears that the li isotope system may have characteristics that can resolve the mass balance of li in the ocean less

the relationship between riverine lithium isotope composition and silicate weathering rates in iceland abstract this study presents lithium isotope and elemental data for the dissolved phase and suspended and bedload sediments of the major icelandic rivers for the dissolved phase 7li values range between 10 1 and 23 8 while river sediments display lower and much more homogeneous values 7li 3 1 4 8 close to the composition of unweathered mid ocean ridge basalt morb high 7li values are associated with high k li na li and mg li ratios in waters draining mainly old and weathered basalt catchments whereas low 7li rivers are located in younger parts of the island simple mixing between precipitation li rich hydrothermal springs and basalt weathering is unable to explain the entire range of 7li values instead a simple model of li uptake by secondary minerals associated with clay water li isotope fractionation 7li ranging from 1 to 7 5 can explain both water and sediment 7li values a negative correlation is observed between basalt chemical erosion rates and 7li measured in icelandic rivers and an empirical law is inferred comparison with literature data suggests that this relationship may be applicable at a more global scale and if confirmed could be of particular use for estimating the evolution of continental weathering preserved in marine sedimentary records however more data are now needed for rivers draining silicates typical of the continental crust in order to refine large scale modelling

mechanisms and timescales of felsic magma segregation ascent and emplacement in the himalaya we combine field petrological geochemical and experimental observations to evaluate the time scales of compaction driven and shear assisted melt extraction and ascent in the himalayas the results show that melt migration via compaction and channelling is inescapable and operates on timescales less than 1 m y and possibly as short as 0 1 m y field and petrological data show that such a fast and efficient melt transfer result from a combination of favourable factors including 1 low but constant melt viscosity 104 5 pa s during extraction and ascent 2 grain size coarsening of the source rocks in response to prolonged heating prior to melting and 3 high source fertility and thus high melt fraction owing to elevated modal amounts of muscovite of leucogranite sources all three factors dramatically increase source permeability calculations show that shear assisted melt extraction had a time interval recurrence in the 10 100 kyr range leading to sill thicknesses of 1 30 m yet melts falling at the low end of the viscosity range when coupled to high shear velocities may lead to veins several hundred meters thick the deepest structural levels eg central zanskar range show that in situ melts formed where pure shear compaction was greatest and where simple shear was also operative magma extracted from migmatite leucosomes was injected along planes of weakness parallel to the ductile shear fabric probably by some sort of hydraulic fracturing crack propagation mechanism large hhl eg c 5 km thick sills at manaslu makalu and northern bhutan may thus represent inflated laccoliths assembled via dykes that tapped a 100 300 m melt layer produced by compaction of ghs thermal simulations show that such melt layers may have incubation times of several m y although transport time for magmas associated with the hhl is short the time for assembly may take several m y for the largest hhl as geochronological data indicate up to 5 m y for manaslu shisha pangma transport of leucogranite melt from mid crust levels towards the surface was concomitant with active low angle normal faulting along the south tibetan detachment normal fault a structure that effectively formed the lid to the extrusion of a partially molten layer of mid crustal rocks channel flow rapid cooling of the granites emplaced on top of ghs implies rapid extrusion and lateral flow of greater himalayan sequence rocks beneath the std during the period 20 17 ma weakening of the crust by partial melting is thus likely to be pulsatory in time and future thermomechanical models should incorporate such aspects to model tectonic evolution of hot orogens

pyroclastic flows from the 1991 eruption of unzen volcano japan pyroclastic flows from unzen were generated by gravitational collapse of the growing lava dome as soon as the parental lobe failed at the edge of the dome spontaneous shattering of lava occurred and induced a gravity flow of blocks and finer debris the flows had a overhanging tongue like head and cone or rollershaped vortices expanding outward and upward most of the flows traveled from 1 to 3 km but some flows reached more than 4 km burning houses and killing people in the evacuated zone of kita kamikoba on the eastern foot of the volcano the velocities of the flows ranged from 15 to 25 m s on the gentle middle flank observations of the flows and their deposits suggest that they consisted of a dense basal avalanche and an overlying turbulent ash cloud the basal avalanche swept down a topographic low and formed to tongue like lobe having well defined levees it is presumed to have moved as a non newtonian fluid the measured velocities and runout distances of the flows can be matched to a bingham model for the basal avalanche by the addition of turbulent resistance the rheologic model parameters for the 29 may flow are as follows the density is 1300 kg m3 the yield strength is 850 pa the viscosity is 90 pa s and the thickness of the avalanche is 2 m the ash cloud is interpreted as a turbulent mixing layer above the basal avalanche the buoyant portions of the cloud produced ash fall deposits whereas the dense portions moved as a surge separated from the parental avalanche the ash cloud surges formed a wide devastated zone covered by very thin debris the initial velocities of the 3 june surges when they detached from avalanches are determined by the runout distance and the angle of the energy line slope a comparison between the estimated velocities of the 3 june avalanches and the surges indicates that the surges that extended steep slopes along the avalanche path detached directly from the turbulent heads of the avalanches the over running surge that reached kita kamikoba had an estimated velocity higher than that of the avalanche this farther travelled surge is presumed to have been generated by collapse of a rising ash cloud plume

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

the 15 september 1991 pyroclastic flows at unzen volcano japan a flow model for associated ash cloud surges large scale collapse of a dacite dome in the late afternoon of 15 september 1991 generated a series of pyroclastic flow events at unzen volcano pyroclastic flows with a volume of 1 106 m3 as dre descended the northeastern slope of the volcano changing their courses to the southeast due to topographic control after they exited a narrow gorge an ash cloud surge rushed straight ahead detaching the main body of the flow that turned and followed the topographic lows to the east the surge swept the kita kamikoba area which had been devastated by the previous pyroclastic flow events and transported a car as far as 120 m following detachment the surge lost its force after it moved several hundred meters but maintained a high temperature the deposits consist of a bottom layer of better sorted ash unit 1 a thick layer of block and ash unit 2 and a thin top layer of fall out ash unit 3 unit 2 overlies unit 1 with an erosional contact the upper part of unit 2 grades into better sorted ash at distal block and ash flow deposits the bottom part of unit 2 also consists of better sorted ash and the contact with the unit 1 deposits becomes ambiguous video footage of cascading pyroclastic flows during the 1991 1995 eruption traveling over surfaces without any topographic barriers revealed that lobes of ash cloud protruded intermittently from the moving head and sides and that these lobes surged ahead on the ground surface this fact together with the inspection by helicopter shortly after the events suggests that the protruded lobes consisted of better sorted ash and resulted in the deposits of unit 1 the highest ash cloud plume at the oshigadani valley exit and the thickest deposition of fall out ash over kita kamikoba and ohnokoba indicate that abundant ash was also produced when the flow passed through a narrow gorge in the model presented here the ash clouds from the pyroclastic flows were composed of a basal turbulent current of high concentration main body an overriding and intermediate fluidization zone and an overlying dilute cloud release of pressurized gas in lava block pores due to collisions among blocks and the resulting upward current caused a zone of fluidization just above the main body the mixture of gas and ash sorted in the fluidization zone moved ahead and to the side of the main body as a gravitational current where the ash was deposited as surge deposits the main body which had high internal friction and shear near its base then overran the surge deposits partially eroding them when the upward current of gas fluidization waned better sorted ash suspended in the fluidization zone was deposited on block and ash deposits in the distal places of block and ash deposits unit 2 probably was deposited in non turbulent fashion without any erosion of the underlying layer unit 1

rapid topographic change measured by high resolution satellite radar at soufriere hills volcano montserrat 2008 2010 high resolution satellite radar observations of erupting volcanoes can yield valuable information on rapidly changing deposits and geomorphology using the terrasar x tsx radar with a spatial resolution of about 2 m and a repeat interval of 11 days we show how a variety of techniques were used to record some of the eruptive history of the soufriere hills volcano montserrat between july 2008 and february 2010 after a 15 month pause in lava dome growth a vulcanian explosion occurred on 28 july 2008 from a vent that was hidden by dense cloud we were able to show the civil authorities using tsx difference images of surface roughness change that this explosion had not disrupted the dome sufficiently to warrant continuation of a previous precautionary evacuation change difference images also proved to be valuable in mapping new pyroclastic flow deposits the valley occupying block and ash component tended to increase backscatter and the marginal surge deposits to reduce it with the pattern reversing after the event due to erosion and deposition by comparing east and west looking images acquired 12 h apart the deposition of some individual pyroclastic flows can be inferred from change differences some of the narrow upper sections of valleys draining the volcano received many tens of metres of rockfall and pyroclastic flow deposits over periods of a few weeks by measuring the changing radar shadows cast by these valleys in tsx images the changing depth of infill by deposits could be estimated in addition to using the amplitude data from the radar images we also used their phase information within the insar technique to calculate the topography during a period of no surface activity this enabled areas of transient topography crucial for directing future flows to be captured

experimental deformation of partially molten westerly granite under fluid absent conditions with implications for the extraction of granitic magmas the mechanical behavior of partially molten westerly granite was investigated in the temperature range 800 1100 c 250 mpa confining pressure by means of constant strain rate creep and stress relaxation tests the only water in the samples came from the breakdown of hydrous phases biotite minor chlorite and muscovite and alteration products of feldspars thus the amount of melt was controlled by the test temperature and ranged from 3 at 800 c to 50 at 1100 c over that temperature range strength decreased from 500 mpa to less than 1 mpa and a preliminary constitutive flow law for the partially molten rock was obtained to allow extrapolation to low strain rates the comparative viscosity of the melt alone was estimated at 950 and 1000 c from the distance it could be made to penetrate into a porous sand under a known pressure gradient under all conditions deformation of the matrix of solid grains was by brittle fracture only samples containing up to 10 vol melt failed with the formation of a shear fault zone at higher melt fractions melt filled pores collapsed by shear enhanced compaction squeezing the melt into axial cracks above 40 vol melt unfractured solid grains were carried about passively in the flowing liquid there was no evidence of a rheologically critical melt percentage in this system by analogy with the uniaxial compaction of water saturated soils a simple model is erected to describe a two stage process for the extraction of granitic melts from their protoliths with the aid of nonhydrostatic stress shear enhanced compaction is inferred to drive melt into a network of melt filled veins whereupon porous flow through the high permeability vein network allows rapid drainage of melt to higher crustal levels

microstructures and rheology of hydrous synthetic magmatic suspensions deformed in torsion at high pressure the relationship between magma rheology and characteristic magmatic microstructures was investigated by performing high temperature high pressure deformation experiments on hydrous synthetic magmatic suspensions in the range of 0 to 76 solid fraction alumina grains torsion experiments were conducted at 300 mpa confining pressure temperatures ranging from 475 c to 1000 c and shear strain rates ranging from 2 0 10 5 to 2 1 10 3 s 1 up to total strains of 21 3 flow is newtonian for a solid fraction of s 0 0 0 16 with a log dynamic viscosity 10 3 pa s t 500 c a deviation from newtonian behavior is observed for s 0 16 with an increase in apparent viscosity of about 1 order of magnitude between s 0 16 and 0 54 the shape fabric of the solid phase is characterized by a unimodal orientation that is almost stable and nearly parallel to the shear direction both shape fabric and deviation from newtonian behavior originate from the increase in the number of particle clusters in the suspension the apparent viscosity increases by 1 5 orders of magnitude between s 0 54 and 0 65 and extrapolation of the data suggests a very sharp increase in apparent viscosity for s 0 65 at t 550 c and s 0 54 the solid phase forms an almost entirely connected network composed of two alternating orientation domains at t 550 c and s 0 65 intragranular fracturing and tensile fractures result from high local stresses at contact points between neighboring particles the resulting bulk extensional fabric is almost parallel to the shortening direction

pyroclastic flow deposits of the 1991 eruption of volcan de colima mexico the april 16 1991 eruption of volcan de colima represents a classical example of partial dome collapse with the generation of progressively longer runout merapi type pyroclastic flows that traveled up to 4 km along the el cordoban gullies east central and west the flows filled the gullies with block and ash flow deposits up to 10 m thick of which after 7 years of erosion only remnants remained in the el cordoban west and east gullies the el cordoban central gully however provided a well preserved and incised longitudinal section of the 1991 deposits the deposits were emplaced as proximal and distal facies separated by a change in slope angle from 30 to 20 the proximal facies consists of massive clast supported flow units up to 1 m thick with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading the distal facies consists of a massive matrix supported deposit up to 8 m thick which contains dispersed andesite blocks in a fine ash matrix in the distal facies a train of blocks marks flow unit upper boundaries and although sorting is poor some grading is present thin finely stratified or dune bedded layers of fine ash material are locally present above or below units of both facies sedimentologic parameters show that the size or fraction of large pyroclasts larger than 1 decreases from proximal to distal facies as the percentage of matrix 0 to 4 increases especially immediately beyond the break in slope we propose that the propagation of the colima pyroclastic flows is critically dependent on local slope angle the presence of erodible slope debris and the decrease in grain size with distance from the vent the progressive fining is probably caused by some combination of erosion clast breakup and deposition of larger pyroclasts and is itself influenced by the slope angle in the proximal region the flows moved as granular avalanches in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud the maximum runout distance of the avalanches was controlled by the angle of repose of the material and the volume and grain size of source and eroded material because the slope angle is close to the repose angle for this debris granular avalanches were not able to propagate far beyond the change in slope if however an avalanche had enough mass in finer grain size fractions at least part of the flow continued beyond the break in slope and across the volcano apron propagating in a turbulent state and depositing surge layers or in an otherwise settling modified state and depositing block and ash flow layers

maximum and minimum water contents of granitic melts implications for chemical and physical properties of ascending magmas new results obtained by the investigation of liquidus and solidus phase relations in the system qz ab or and by the determination of h2o solubility in haplogranitic melts are used to discuss the evolution of granitic quartzo feldspathic magmas during their ascent in the crust particular attention is given to the role of h2o and its effect on physical properties of ascending magmas the evolution of melt fraction h2o content of the melt and viscosity of melt and magma during ascent are discussed for several examples adiabatic ascent ascent with cooling ascent with crystal fractionation it is shown that decompression melting processes may be very important significant increase of the melt proportion especially at low pressure in magmas ascending along adiabats or with slow cooling rates the comparison of the discussed examples shows that melts formed at low t are significantly less viscous than at high t although the degree of melting may remain very low in the case of dehydration melting at low temperature the low viscosity of the generated melts may enhance the extraction of these melts from the source area to produce leucogranites

preliminary report on the activity at unzen volcano japan november 1990 november 1991 dacite lava domes and pyroclastic flows abstract the eruption of unzen volcano commenced on 17 november 1990 phreatic and phreatomagmatic eruptions occurred by early may 1991 no large scale explosive eruptions preceded the extrusion of lava domes lava domes appeared in a summit crater on 20 may 1991 and they grew on the steep slope of mt fugen at unzen volcano rockfalls from the margins of the domes frequently generated pyroclastic flows major pyroclastic flows occurred on 3 june 8 june and 15 september 1991 the 3 june pyroclastic flow killed forty three persons many of the pyroclastic flows seem to have resulted from the simple rockfalls except one flow on 8 june which was accompanied by an explosion from the crater many of the rockfalls that generated pyroclastic flows were witnessed as of november 1991 unzen volcano was still active with a nearly constant magma supply rate of about 0 3 106 m3 d the total magma output exceeded 45 106 m3 by the beginning of november 1991 the volume of the lava domes is more than 23 106 m3

fluid dynamics of the 1997 boxing day volcanic blast on montserrat west indies 1 directed volcanic blasts are powerful explosions with a significant laterally directed component which can generate devastating high energy pyroclastic density currents pdcs such blasts are an important class of eruptive phenomena but quantified understanding of their dynamics and effects is still incomplete here we use 2 d and 3 d multiparticle thermofluid dynamic flow codes to examine a powerful volcanic blast that occurred on montserrat in december 1997 on the basis of the simulations we divide the blast into three phases an initial burst phase that lasts roughly 5 s and involves rapid expansion of the gas pyroclast mixture a gravitational collapse phase that occurs when the erupted material fails to mix with sufficient air to form a buoyant column and thus collapses asymmetrically and a pdc phase that is dominated by motion parallel to the ground surface and is influenced by topography we vary key input parameters such as total gas energy and total solid mass to understand their influence on simulations and we compare the simulations with independent field observations of damage and deposits demonstrating that the models generally capture important large scale features of the natural phenomenon we also examine the 2 d and 3 d model results to estimate the flow mach number and conclude that the range of damage sustained at villages on montserrat can be reasonably explained by the spatial and temporal distribution of the dynamic pressure associated with subsonic pdcs

behavior of lithium and its isotopes during weathering of hawaiian basalt 1 we examined the pedogenic behavior of lithium li and its isotopes in hawaii by sampling same age lava flows under mean annual rainfall ranging from 18 to 300 cm lithium concentrations in these soils vary from 1 to 29 ppm whereas na k and ca are completely leached from the soil at the most humid and severely weathered site li mg si and al show significant retention due to their association with secondary clay minerals in these soils allochthonous li delivered in marine and mineral aerosol mixes with basalt derived li modifying the isotopic composition of the li pool the ability of soil to retain li is related to its effective cation exchange capacity which in turn is governed by rainfall and leaching intensity and their resulting effect on mineralogy lithium isotope ratios have a large range 7li of 0 4 to 14 well beyond the intershield or temporal variation of the lavas of hawaiian volcanoes 2 5 to 5 7 the most unweathered samples have 7li 5 6 comparable to that of mauna kea and mauna loa lavas the li concentrations and isotope ratios together suggest that in arid to subhumid sites there is a net addition of isotopically heavier lithium from marine aerosol but that under greater rainfall there is a net loss of li and isotopically light li is preferentially retained thus during incongruent weathering of primary minerals li especially 6li is adsorbed and sequestered by the clay mineral fraction of high cation exchange capacity soils in drier regions but lost from highly weathered low cation exchange capacity acidic soils in the wetter regions

deformation and seismic precursors to dome collapse and fountain collapse nuees ardentes at merapi volcano java indonesia 1994 1998 abstract following the eruption of january 1992 episodes of lava dome growth accompanied by generation of dome collapse nuees ardentes occurred in 1994 1998 in addition nuees ardentes were generated by fountain collapse in january 1997 and the 1998 events also suggest an explosive component significant tilt and seismic precursors on varying time scales preceded these events deformation about the summit has been detected by electronic tiltmeters since november 1992 with inflation corresponding generally to lava dome growth and deflation or decreased inflation corresponding to loss of dome mass strong short term days to weeks accelerations in tilt rate and seismicity occurred prior to the major nuees ardentes episodes apart from those of 22 november 1994 which were preceded by steadily increasing tilt for over 200 days but lacked short term precursors because of the combination of populated hazardous areas and the lack of an issued warning about 100 casualties occurred in 1994 in contrast the strong precursors in 1997 and 1998 provided advance warning to observatory scientists enabled the stepped raising of alert levels and aided hazard management as a result of these factors but also the fortunate fact that the large nuees ardentes did not quite descend into populated areas no casualties occurred the nuee ardente episode of 1994 is interpreted as purely due to gravitational collapse whereas those of 1997 and 1998 were influenced by gas pressurization of the lava dome

the transition from magmatic to high temperature solid state deformation implications from the mount stuart batholith washington criteria for syntectonic emplacement of plutons are commonly ambiguous the strongest single criterion is probably the preservation of a continuous transition from submagmatic to high temperature solidstate deformation this transition is not commonly documented an exception is the mount stuart batholith which displays a variety of syntectonic structures within its sheared northeastern margin including the following 1 s c fabrics that range from submagmatic to high temperature solid state 2 solid state foliation and lineation defined by amphibolite facies assemblages that overprint and are parallel to magmatic foliation and lineation 3 folds of magmatic and solid state foliation that have hinge lines parallel to magmatic and solid state lineation and to equivalent structures in wall rocks 4 dikes that were folded and boudinaged over a wide range of rheological states with boudin necks locally filled by tonalite 5 pegmatite dikes and mineralized joints that are sub perpendicular to magmatic and solid state lineation and 6 submagmatic and high temperature solidstate ductile shear zones we suggest that many plutons emplaced during regional deformation do not preserve evidence for syntectonic deformation because of the transitory nature of the submagmatic state and the obscuring effects of postemplacement deformation syntectonic features are most likely preserved in plutons cooled at slow to moderate rates or in plutons deformed at high strain rates during emplacement the optimum conditions for preservation may occur in plutons emplaced along fault zones in the mid crust such as the mount stuart batholith and in intrusions at deeper levels that were rapidly exhumed and or intruded during the waning stages of regional deformation

a statistical study of trees damaged by the 22 november 1994 eruption of merapi volcano java indonesia relationships between ash cloud surges and block and ash flows abstract on 22 november 1994 after 2 years of dome growth merapi volcano generated pyroclastic flows and surges this eruption destroyed the south southwest flank that had been intact for several decades about 9 5 km 2 of forest were blown down a study of tree damage correlated with geological and eyewitness observations is used here to reconstruct the dynamics of the pyroclastic surges and block and ash flows of the 22 november eruption the main results are summarised in the form of maps showing blown down trunk directions and zones indicating the percentage of broken and downed trees these maps provide evidence for various aspects of the emplacement of the 1994 flows 1 pyroclastic flow generation from gravitational collapse of part of the active lava dome without significant initial explosion 2 the control of topography cliffs hills river channels on damage distribution and range 3 the genesis and decoupling of ash cloud surges from block and ash flows

nuees ardentes of 22 november 1994 at merapi volcano java indonesia nuees ardentes associated with dome collapse on 22 november 1994 at merapi volcano traveled to the south southwest as far as 6 5 km and collectively accumulated roughly 2 5 3 million cubic meters of deposits the damaged area comprises 9 5 km2 and is covered by two nuee ardente facies a conventional merapi type valley fill block and ash flow facies and a pyroclastic surge facies the proximal deposits reflect the accumulation of dozens of nuees ardentes with many subsidiary flow units the distal deposits are more simply organized as only a few individual events reached to distances 3 5 km the stratigraphic relationships north of turgo hill indicate that the surge deposits are a facies of particularly mobile nuees ardentes that also deposited channeled block and ash flow facies they further suggest that the surge facies beyond the channel margins correlate laterally with a finer grained sublayer locally developed at the base of the block and ash flow facies eyewitness reports suggest that the emplacement of the block and ash flow facies in the distal part of the boyong river may have followed by a short time interval the destruction and deposition of the surge facies at turgo village the stratigraphy is in accord with the eyewitness reports the surge facies was emplaced by a dilute surge current detached from the same dome collapse nuee ardente that as a separate flow unit subsequently emplaced the distal block and ash deposit in the boyong valley the detachment occurred at higher elevations likely at or above the slope break at about 2000 m elevation this flow separation enabled the surge current to shortcut over the landscape and to emplace its deposit even as the block and ash flow continued its tortuous southward movement in the boyong channel dome collapse nuee ardente activity formed the bulk of the eruption which was accompanied by virtually no significant vertical summit explosive activity

experimental investigation of melt topology in partially molten quartzo feldspathic aggregates under hydrostatic and non hydrostatic stress continental collision results in deep burial of crustal rocks and their subsequent partial melting field relations of melt along zones of intense deformation suggest that partially molten rocks may play an important role in regional tectonics however subsequent deformation may erase the microstructures produced by the earlier deformation mechanisms inhibiting our understanding of the rheology of partially molten crustal rocks thus in this paper we report the results of an experimental study of the distribution of 2 5 vol melt in quartzo feldspathic aggregates of various grain sizes 2 5 5 10 10 16 and 26 31 m three types of samples were examined all with the composition of 60 wt albite 25 wt potassium feldspar 10 wt quartz and 5 wt biotite the first group included mineral powders annealed at 1000 c 1 0 gpa for c 100 h the second group included commercially hot pressed mineral powders which yielded c 25 vol glass cores of this material were also annealed at 1000 c 1 0 gpa for c 100 h the third group included cores of hot pressed material that were annealed at 1000 c 1 0 gpa for c 45 h then deformed all samples were quenched rapidly in order to examine the melt distribution wetting angles are very similar in both the hydrostatically annealed and the deformed samples analysis of melt pool orientations reveal that melt migrates away from grain boundaries normal to the maximum compressive stress direction in response to the applied non hydrostatic stress this response is easily seen in the coarser grained samples in which melt pools elongated parallel to the maximum compressive stress direction formed during deformation if these results extrapolate to naturally deformed rocks it will be important to consider the orientation of the state of stress in a region during syn magmatic deformation because of its effect on the melt distribution

the effects of porphyroblast growth on the effective viscosity of metapelitic rocks implications for the strength of the middle crust numerical models are used to examine the effects of porphyroblast growth on the rheology of compositionally layered rocks metapelites and metapsammites and by extension the middle crust during prograde metamorphism as porphyroblast abundance increases during prograde metamorphism metapelitic layers will strengthen relative to porphyroblast free metapelitic units and potentially relative to quartzofeldspathic metapsammitic units as metapelitic layers become stronger the integrated strength of compositionally layered successions increases potentially causing large volumes of mid crustal rock to strengthen altering the strain rate distribution in the middle crust and affecting the geodynamic evolution of an orogenic belt the growth of effectively rigid porphyroblasts creates strength heterogeneities in the layer undergoing porphyroblast growth which leads to complex strain rate distributions within the layer at the orogen scale the strengthening of large crustal volumes on the order of thousands of cubic kilometres changes the strain rate distribution which may change exhumation rates of high grade metamorphic rocks the geothermal structure and the topography of the orogen the presence of a strong zone in the middle crust causes strain rate partitioning around the zone suppressed uplift rates within and above the zone and leads to the development of a basin on the surface

an experimental study of alteration of oceanic crust and terrigenous sediments at moderate temperatures 51 to 350 c insights as to chemical processes in near shore ridge flank hydrothermal systems studies of hydrothermal circulation within partly buried basement on the eastern flank of the juan de fuca ridge jfr have shown that ridge flank geochemical fluxes are potentially important for the global budgets of some elements there are major uncertainties in these flux calculations however because the composition of these basement fluids is strongly dependent on temperature and because they may be modified by interaction with the overlying terrigenous sediments either by diffusive exchange with basement or during upwelling to the seafloor to better understand the nature and temperature control of basalt fluid and sediment fluid reactions at the jfr flank we have conducted laboratory experiments between 51 and 350 c and at 400 bars pressure k rb and si are leached from basalt between 150 and 351 c and sr and u are taken up the direction of exchange of li and ca with basalt varies with temperature li and sr are removed from fluid at 150 c but isotope studies show that there is simultaneous release of both elements from basalt indicating that uptake is controlled by the formation of secondary minerals moreover our experiments confirm that sr isotope exchange with oceanic crust occurs at moderate temperature and is not confined to high temperature axial hydrothermal systems our data and field data from the jdr flank indicate that uptake of u into basalt at moderate temperature could remove between 9 9 and 15 106 mol u yr 1 from the oceans this is higher than a recent estimate based on measurements of u in altered ocean crust 5 7 3 3 106 mol yr 1 which concords with arguments that the element heat ratios of jdr flank fluids are too large to be representative of average global flank fluids k ca sr ba li si and b are leached from terrigenous sediments between 51 and 350 c and u is taken up cs and rb are removed from the fluid below 100 c and leached from the sediment at higher temperature sr isotope data show that sr is preferentially mobilised from volcanic components within terrigenous sediments which may lead to an overestimation of the ridge flank sr isotope flux at the jdr if there is exchange of sediment pore fluids with basement

evaluation of geophysical mass flow models using the 2006 block and ash flows of merapi volcano java indonesia towards a short term hazard assessment tool abstract the dynamics and depositional processes associated with block and ash flows bafs are most commonly inferred to be a function of granular or inertial grain flow similar to debris flows and cold rock avalanches existing geophysical mass flow models are either based on frictional mohr coulomb behavior the titan2d model developed at the state university of new york at buffalo usa or another rheological law i e a constant retarding stress eventually adding some viscous and turbulent components the volcflow model developed at the laboratoire magmas et volcans clermont ferrand france the 2006 bafs of merapi present a rare opportunity to test these two well established models against a well constrained field example integration of high resolution field based data into numerical simulations allows the validity of these models to be tested and rapid quantification of best fit input parameters we first show that with the incorporation of spatially varying bed friction angles titan2d is capable of reproducing the paths runout distances areas covered and deposited volumes of the 2006 merapi flows over highly complex topography however some discrepancies with field data are noted and the velocity and travel time of the flows do not match entirely using a single free parameter a constant retarding stress simulations obtained with the volcflow model also reproduce the morphology and distribution of the natural deposits as well as the time of emplacement and velocities of the flows the results suggest that the performance of these models in simulating actual events is critically dependent on 1 the calibration of the model by using extensive field based data such as deposit distribution and processes of flow generation transport and deposition 2 the incorporation of a suitable numerical topographic dataset i e high resolution digital elevation model and 3 the choice of input parameters such as location and volume of the initial pile of material and source characteristics single or multiple dome collapse dome collapse duration and total volume of collapsed material sensitivity analyses and inundation maps based on the probability of impact were used to produce a suite of potentially inundated areas from future gravitational dome collapse events affecting the gendol valley and adjacent areas on the southern flank of the volcano our results provide the basis for defining hazard zonations of key areas at risk from bafs which will be generated during future comparable eruptions at merapi

emplacement of pyroclastic flows during the 1998 1999 eruption of volcan de colima mexico after three years of quiescence volcan de colima reawakened with increasing seismic and rock fall activity that reached its peak on november 20 1998 when a new lava dome forced its way to the volcano s summit the new lava rapidly reached the s sw edge of the summit area beginning the generation of merapi type pyroclastic flows that traveled down la lumbre and the el cordoban western and eastern ravines reaching distances of 3 4 5 and 3 km respectively on december 1 1998 the lava flow split into three fronts that in early 1999 had reached 2 8 3 1 and 2 5 km in length advancing down the el cordoban ravines the lava flow fronts disaggregated into blocks forming pyroclastic flows one of the best examples occurred on december 10 1998 as the lava flow ceased moving in early 1999 activity became more explosive strong blasts were recorded on february 10 may 10 and july 17 1999 the last event developed a 10 km high eruptive column from which a pyroclastic flow developed from the base traveling 3 3 km sw from the summit into the san antonio montegrande ravines regardless of the mechanism of pyroclastic flow generation each flow immediately segregated into a basal avalanche that moved as a granular flow and an upper ash cloud in which particles were sustained in turbulent suspension when the basal avalanche lost velocity and eventually stopped the upper ash cloud continued to move independently as a dilute pyroclastic flow that produced a massive pyroclastic flow deposit and an upper dune bedded surge deposit the dilute pyroclastic flow scorched and toppled maguey plants and trees and sandblasted vegetation in the direction of the flow at the end of the dilute pyroclastic flow path the suspended particles lifted off in a cloud from which a terminal ash fall was deposited the basal avalanche emplaced block and ash flow deposits up to 8 m thick that filled the main ravines and consisted of several flow units each flow unit was massive monolithologic matrix supported and had a clast supported steep front ca 1 5 to 2 m thick composed of boulders up to 1 7 m in diameter the juvenile lithic clasts had an average density of 1800 kg m3 the dilute pyroclastic flow emplaced overbank deposits found on valley margins or beyond the tip of block and ash flow deposits they consist from bottom to top of a massive medium to coarse sand size flow layer 2 4 cm thick a dune bedded surge layer 2 10 cm thick and a massive silt size layer 0 5 cm thick the total estimated volume of the pyroclastic flow deposits produced during the 1998 1999 eruption is 24 105 m3

numerical modeling of mullions in the taili high deformation zone north china implications for the rheology of granitic rocks abstract this paper presents a combined field measurement and finite element modeling analysis of the mullions occurring on the contact of two granitic rocks with different grain size in the taili high strain deformation zone thdz west liaoning of north china all of the field data are located in the plot zone of the modeling results numerical modeling results indicate that 1 the inter angle between the tangent lines cross the cusp point and the ratio r of amplitude and width of mullions are the most effective parameters to describe the geometric shape and evolution of mullions as well as useful indicators of the rheology of rocks 2 the competence contrast controls the growth rate of mullions under shortening it determines the possible ratio r of final mullions moreover decreasing of the cusp angle in high competence contrast materials is faster than that in low competence contrast model 3 the initial disturbance is an essential factor for the generation of mullions those contacts with higher initial disturbance will develop into mullions more easily and have a high growth rate during the same shortening deformation regime 4 the rheology and deformation behavior of the granitic rocks in the study area are primarily controlled by the grain sizes of quartz and feldspar the effective viscosity ratio of biotite adamellite and granitic gneisses is about 0 01 0 5 the deformation mechanisms of these granitic rocks should be dominated by a grain size sensitive diffusion creep

centrifuge modelling of deformation of a multi layered sequence over a ductile substrate 1 style and 4d geometry of active cover folds during layer parallel shortening centrifuge analogue modelling illustrates the progressive development of active folds in multilayers upon a ductile substrate during layer parallel shortening models simulate folding of a mechanically stratified sedimentary sequence upon migmatitic gneisses in a large hot orogen or upon a thick basal evaporite shale sequence in deeper levels of fold belts the absence of a weak low viscosity and low density layer at the interface promotes infolding of the cover sequence and ductile substrate whereas a planar upper surface to the basal ductile substrate is preserved when it is present whilst fold style wavelength and deformation of the interface with the ductile substrate differ depending on whether a low viscosity and low density layer is present at the base of the cover sequence there is no marked systematic curvature of fold axes as seen in previous sandbox models for fault bend or fault propagation folding during bulk shortening bulk shortening of a layered sequence with relatively thick individual layers above a ductile substrate promotes a regular and upright train of buckle folds whereas thinner layers promote a more irregular distribution of buckle folds with variable vergence style and amplitude buckle folds above a ductile substrate progressively develop during bulk shortening from open and upright to angular and tight and may further develop into cuspate structures above relatively weak horizons relatively thick weak horizons within the layered sequence during bulk shortening interrupt regular fold patterns up structural section and allow out of phase folds to develop above and below the weak horizon

melt segregation in the continental crust distribution and movement of melt in anatectic rocks the grain and outcrop scale distribution of melt has been mapped in anatectic rocks from regional and contact metamorphic environments and used to infer melt movement paths at the grain scale anatectic melt is pervasively distributed in the grain boundaries and in small pools consequently most melt is located parallel to the principal fabric in the rock typically a foliation short branched arrays of linked melt bearing grain boundaries connect melt depleted parts of the matrix to diffuse zones of melt accumulation protoleucosomes where magmatic flow and alignment of euhedral crystals grown from the melt developed the distribution of melt leucosome and residual rocks normally melanocratic in outcrop provides different but complementary information the residual rocks show where the melt came from and the leucosomes preserve some of the channels through which the melt moved or sites where it pooled different stages of the melt segregation process are recorded in the leucosome melanosome arrays regions where melting and segregation had just begun when crystallization occurred are characterized by short arrays of thin branching leucosomes with little melanosome a more advanced stage of melting and segregation is marked by the development of residual rocks around extensive branched leucosome arrays generally oriented along the foliation or melting layer places where melting had stopped or slowed down before crystallization began are marked by a high ratio of melanosome to leucosome because most of the melt has drained away very few leucosomes remain to mark the melt escape path this is common in melt depleted granulite terranes many migmatites contain abundant leucosomes oriented parallel to the foliation mostly these represent places where foliation planes dilated and melt drained from the matrix via the branched grain boundary and larger branched melt channel leucosome arrays collected melt collected in the foliation planes was partially or fully expelled later when discordant leucosomes formed leucosomes or veins oriented at high angles to the foliation layering formed last and commonly lack melanocratic borders hence they were not involved in draining the matrix of the melting layer discordant leucosomes represent the channels through which melt flowed out of the melting layer

computer simulations of pyroclastic flows from dome collapse we present a method of simulating both the avalanche and surge components of pyroclastic flows generated by lava collapsing from a growing pelean dome this is used to successfully model the pyroclastic flows generated on 12 may 1996 by the soufriere hills volcano montserrat in simulating the avalanche component we use a simple 3 fold parameterisation of flow acceleration for which we choose values using an inverse method the surge component is simulated by a 1d hydraulic balance of sedimentation of clasts and entrainment of air away from the avalanche source we show how multiple simulations based on uncertainty of the starting conditions and parameters specifically location and size mass flux could be used to map hazard zones

the effect of pre tectonic reaction and annealing extent on behaviour during subsequent deformation insights from paired shear zones in the lower crust of fiordland new zealand granulite facies pargasite orthogneiss is partially to completely reacted to garnet granulite either side of narrow 20 mm felsic dykes in fiordland new zealand forming 10 80 mm wide garnet reaction zones the metamorphic reaction changed the abundance of minerals and their shape and grain size distribution the extent of reaction and annealing temperature related coarsening and nucleation is greatest close to the dykes whereas further away the reaction is incomplete as a consequence grain size and the abundance of garnet decreases away from the felsic dykes over a few centimetres the aspect ratios of clusters of s1 pyroxene and pargasite in the orthogneiss which are variably reacted to post s1 garnet decrease from high in the host to near equidimensional close to the dyke post reaction deformation localized in the fine grained partially reacted areas this produced a pattern of paired shear zones located at the outer parts of the garnet reaction zone our study shows that grain size sensitive deformation occurs where the grain size is sufficiently reduced by metamorphic reaction the weakening of the rock due to the change in grain size distribution outweighs the addition of nominally stronger garnet to the assemblage

transition from dislocation creep to melt enhanced diffusion creep in fine grained granitic aggregates abstract sintered aggregates composed of quartz albite and microcline of two different grain sizes 2 10 and 10 50 m each with two different melt contents

himalayan hinterland verging superstructure folds related to foreland directed infrastructure ductile flow insights from centrifuge analogue modelling abstract the orogenic superstructure ss and infrastructure is constitute two levels of a mountain belt with contrasting structural styles in the nepal himalaya n verging back folds which oppose the orogenic vergence dominate the ss competing explanations for these folds are tested using centrifuge analogue models modelling suggests that ss folding occurs during bulk shortening accompanied by is thickening before is flow focused erosion then instigates is lateral flow and stretching decoupling of the ss and transposition of the lower ss into a detachment zone decoupling at the is ss interface separates an ss dominated by older folds and an is characterised by younger horizontal transposition and stretching of early folds extrusive ductile flow of the is locally modifies fold vergence in the ss the fold asymmetry is thus controlled by the efficiency of coupling between is and ss a low viscosity at the is ss interface favours complete decoupling and hinders modification of fold vergence whereas a higher viscosity is ss interface favours fold vergence modification modelling supports a tectonic scenario in which himalayan hinterland verging folds are the product of early shortening of the ss followed by local modification of fold geometry when the is subsequently stretches and flows during focused erosion and melt enhanced is weakening

historical eruptions of merapi volcano central java indonesia 1768 1998 abstract information on merapi eruptive activity is scattered and much is remotely located a concise and well documented summary of this activity has been long needed to assist researchers and hazard mitigation efforts and the aim of this paper is to synthesize information from the mid 1700s to the present a descriptive chronology is given with an abbreviated chronology in a table that summarizes events by year assigns preliminary volcanic explosivity index vei ratings and hartmann classifications and provides key references the history of volcano monitoring is also outlined the study reveals that a major difference in eruption style exists between the twentieth and nineteenth centuries although the periodicity between larger events seems about the same during the twentieth century activity has comprised mainly the effusive growth of viscous lava domes and lava tongues with occasional gravitational collapses of parts of oversteepened domes to produce the nuees ardentes commonly defined as merapi type in the 1800s however explosive eruptions of relatively large size occurred to vei 4 and some associated fountain collapse nuees ardentes were larger and farther reaching than any produced in the twentieth century these events may also be regarded as typical eruptions for merapi the nineteenth century activity is consistent with the long term pattern of one relatively large event every one or two centuries based on the long term eruptive record deduced by others from volcanic stratigraphy it is uncertain whether or not a recurrence time model continues to apply to merapi but if so merapi could soon be due for another large event and its occurrence with only modest or inadequately appreciated precursors could lead to a disaster unprecedented in merapi s history because the area around the volcano is now much more densely populated

metamorphism transient mid crustal rheology strain localization and the exhumation of high grade metamorphic rocks 1 we present a series of three dimensional numerical models investigating the effects of metamorphic strengthening and weakening on the geodynamic evolution of convergent orogens that are constrained by observations from an exposed mid crustal section in the new england appalachians the natural mid crustal section records evidence for spatially and temporally variable mid crustal strength as a function of metamorphic grade during prograde polymetamorphism our models address changes in strain rate partitioning and topographic uplift as a function of strengthening weakening in the middle crust as well as the resultant changes in deformation kinematics and potential exhumation patterns of high grade metamorphic rock results suggest that strengthening leads to strain rate partitioning around the zone and suppressed topographic uplift rates whereas weakening leads to strain rate partitioning into the zone and enhanced topographic uplift rates deformation kinematics recorded in the orogen are also affected by strengthening weakening with complete reversals in shear sense occurring as a function of strengthening weakening without changes in plate boundary kinematics

on the rheologically critical melt fraction abstract with increasing melt fraction the strength of partially molten granite decreases from a value characteristic of solid competent rock to a value nearly equal to that of the melt previously published mechanical and microstructural data indicate that deformation in partially molten rocks often involves brittle processes thus the pressure in the melt is expected to be important in determining strength when the volume changes during deformation strength and fluid flow will be coupled by such parameters as permeability k storage capacity per unit volume or storativity s melt compressibility f grain size d fluid viscosity and strain rate experiments on brittle rock at low temperatures show that the strain rate at which the internal fluid pressure can be maintained constant is approximately proportional to k s an evaluation of published experimental data suggests that this relation also holds for partially molten granites indicating that the strength of these rocks depends on their transport properties since the permeability is related to below a critical melt fraction rcmf the melt pressure will change if deformation is not iso volumetric by assuming a power law relationship between k and we estimate that rcmf f d m 1 n 1 where m and n relate permeability to grain size and respectively

significance of a hiatus in down temperature fabric development within syn tectonic quartz diorite complexes channel islands uk detailed fabric development histories have been deduced for neoproterozoic foliated quartz diorite complexes of the channel islands uk the plutons were emplaced during regional d2 deformation magmatic fabrics formed at low crystal contents pre rheologically critical melt percent are only locally preserved due to overprinting by solid state deformation which occurred at moderate temperatures 400 550 c this is demonstrated by brittle microcracking of plagioclase and amphibole with only local ductile bending and dynamic recrystallization marginal recrystallization and myrmekite development on alkali feldspar ductile deformation of quartz to form types 2 3 ribbons quartz recrystallization by sub grain rotation associated with a slip but not c slip biotite recrystallization within micro shears and variable amphibole recrystallization the deformation histories display a distinct division between magmatic state and moderate temperature solid state deformation features with little evidence for intervening high temperature solid state fabrics this contrasts with criteria widely considered diagnostic of syn tectonic plutons which envisage development of a continuum of magmatic through high temperature solid state deformation fabrics however we consider the plutons syn tectonic and attribute the hiatus to contrasting strain and pluton cooling rates length and nature of deformation events and host rock ambient temperatures intermediate magmas emplaced at moderate to shallow levels in the crust may be more prone to develop such apparently punctuated deformation histories than sio 2 richer granitoids

high temperatures and inverted metamorphism in the schist of sierra de salinas california new field and thermobarometric work in the californian salinian block clarifies current and pre tertiary relationships between the schist of sierra de salinas and cretaceous arc related granitic rocks the contact is variably preserved as a brittle fault and hightemperature mylonite zone the salinas shear zone which represents the contact between north america and sediments accreted above the farallon slab between 76 ma and 70 ma near granulite facies prograde replacement of hornblende with clinopyroxene is associated with deformation of plutonic rocks at the base of the upper plate in the lower plate the schist of sierra de salinas garnet biotite thermometry indicates decreasing temperatures down section from at least 714 8c to 575 8c over an exposed thickness of 2 5 km consistent with petrologic evidence of an inverted metamorphic gradient the measured temperatures are significantly higher than observed at shallow levels above subducting slabs or predicted by 2d computational models assuming low shear stresses previous workers have called upon shear heating to explain similar observations in the correlative pelona schist an unlikely scenario given the results of recent rock deformation experiments which predict that feldspar quartz mica aggregates are far too weak to withstand stresses of 70 mpa required by the shear heating hypothesis as an alternative we propose that high temperatures resulted from conductive heating while the leading edge of the schist traveled 150 km beneath the recently active salinian continental arc during the initiation of shallow subduction weakening of the schist due to high temperatures helped facilitate the collapse of the salinian arc as the schist was emplaced schist emplacement coincided with loss of lower mafic portions of the arc and therefore evolution of the southern california crust towards a more felsic composition d 2005 elsevier b v all rights reserved

stress corrosion cracking of quartz a note on the influence of chemical environment abstract tensile mode i stress corrosion growth of cracks on the a plane of quartz in a direction normal to z has been studied in de ionized water in 2n hcl and in 2n naoh solutions at 20 c the double torsion testing method was used to obtain crack velocity v stress intensity factor ki curves the stress corrosion index n where v kin was 19 3 for 2n hcl 12 8 for deionized water and 9 5 for 2n naoh the degree of influence of reagent chemistry on crack velocity was most marked at low ki values at 0 5 kic 3 orders of magnitude increase in crack velocity results from substituting 2n naoh for 2n hcl as the corrosive medium but decreased monotonically on raising ki so that close to kic there was no clearly discernible influence on crack growth rates ca 10 3 m s 1 these observations are explained in terms of a model of crack propagation in which at low ki values the chemistry of the bulk fluid environment controls the corrosion reaction the rate of crack growth is enhanced by increasing environmental oh concentration at high ki or velocity however the chemical composition of the quartz surface may control crack propagation rates through its influence on the chemistry of the crack tip fluid as the ph of natural pore fluids is likely to vary widely in different geological environments these results should be noted when invoking stress corrosion to explain geophysical phenomena

constraints on melting and magma production in the crust major intrusions of granitic rocks are found in several tectonic settings and in all cases crustal melts may contribute to the volumes of granitic magma high grade metamorphism and partial melting of the crust take place predominantly under fluid absent conditions we present a model for calculating the amounts of melt that may be formed by fluid absent breakdown of micas and amphiboles in common crustal rock types pelitic quartzofeldspathic intermediate and mafic melt proportions depend mainly on the kind of source rock the pressure at which melting takes place the temperature and the hydrous mineral h2o content of the source as a consequence of the pressure dependence of water solubility in silicate melts any given source rock will produce more melt by a given fluid absent reaction at lower pressure at a given pressure higher temperature reactions can produce more melt from a given source rock based on a survey of the compositions of common rock types we show that the amounts of melt can vary from 50vol thus crustal rocks vary widely in their fertility as magma sources depending on the types and amounts of hydrous phases they contain in general muscovite breakdown in pelites will yield only small quantities of melt and lead to migmatite formation biotite breakdown in pelites occurs at higher temperature and because most high grade pelites below granulite grade are biotite rich can yield up to about 50 vol of granitoid melt rocks of intermediate composition and hornblende rich mafic rocks are potentially highly fertile magma sources also provided that the high temperatures necessary for biotite and hornblende breakdown are realized pyroxene rich mafic rocks and quartzofeldspathic rocks are much less potentially fertile data suggest that mechanisms exist for the efficient segregation of melt and restite in systems with 30and probably 20vol melt the pressure temperature history of a region can greatly influence crustal source fertility through its control over the occurrence of subsolidus dehydration and melting equilibria

the 2006 pyroclastic deposits of merapi volcano java indonesia high spatial resolution ikonos images and complementary ground based observations abstract on 16 june 2006 an overpass of ikonos coincided with the emplacement of an active block and ash flow fed by a lava dome collapse at merapi volcano java indonesia it was the first moving pyroclastic flow recorded on a satellite image the very high spatial resolution of the image indicated the extent and impact of pyroclastic material that was deposited during and prior to the day of image acquisition a number of features associated with the hazardous block and ash flows emplaced in narrow deep gorges were mapped interpreted and analysed the high spatial resolution ikonos imagery worked extremely well for identifying pyroclastic deposits the block and ash flow and surge deposits recognized in the ikonos images include 1 several channel confined flow lobes and tongues in the box shaped gorge 2 thin ash cloud surge deposit and knocked down trees in constricted areas on both slopes of the gorge 3 fan like overbank deposits on the gendol tlogo interfluves from which flows were re routed in the tlogo minor valley 4 massive overbank flow lobes on the right bank of the gendol river which destroyed the village of kaliadem 0 5 km from the main channel a small part of this flow was re channelled into the opak tributary valley the high resolution ikonos images also helped us to identify geomorphic obstacles that enabled flows to ramp up and spill out from the sinuous channel as flow avulsion flow avulsions are dangerous as the redirect flows to unexpected areas away from the main channel valley fills from previous deposits channel bends and anthropogenic barriers in the channel locally known as sabo dams influence the down valley passage of the flows sabo dams originally built to ameliorate the effect of high sediment load streams caused block and ash flows to avulse of the containing channel and devastate populated areas

parallel adaptive numerical simulation of dry avalanches over natural terrain high fidelity computational simulation can be an invaluable tool in planning strategies for hazard risk mitigation the accuracy and reliability of the predictions are crucial elements of these tools being successful we present here a new simulation tool for dry granular avalanches using several new techniques to create a highly accurate tool with a combination of good models and numerical methodologies highlights of our methodology are the use of a depth averaged model of the conservation laws and an adaptive grid godunov solver to solve the resulting equations the software is designed to run on distributed memory supercomputers and make use of digital elevation data dynamically i e refine the grid and input data to finer resolutions to better capture flow features as the flow evolves our simulations are validated using quantitative and qualitative comparisons to tabletop experiments and data from field observations our software is freely available and can be used on a range of hardware from inexpensive desktop computers to the largest supercomputers

kinematic characteristics of pyroclastic density currents at merapi and controls on their avulsion from natural and engineered channels we herein report an example of pyroclastic density current avulsion on 14 june 2006 at merapi indonesia four discrete series of multiple dome collapses led to the generation of four individual block and ash flows into kali gendol valley all four pyroclastic density currents locally overflowed the channel margins to devastate cultivated terraces along each side of the box shaped canyon while propagating as much as 2 2 km within adjacent tributaries the largest destruction was caused by the second and third pyroclastic density currents both of these flows partially spilled out of the gendol valley at a travel distance of 4 9 km bypassing a sabo dam just upstream of the village of kaliadem and leaving the village almost completely destroyed and buried by several meters of overbank deposits the main mechanism of flow avulsion on june 14 was the overflow of up to 20 vol of the dense basal part of the pyroclastic density currents onto interfluves the relative proportions of valley escaped material increased dramatically in the succession of each of the four pyroclastic density currents the main geometric parameters controlling flow avulsion and their critical values were quantified through high resolution real time kinetic global positioning system rtk gps data of the pre event topography for each of the 14 june flows this case highlights the way in which a sabo dam can significantly increase the potential of flow avulsion key lessons are derived for the future hazard mitigation in valleys subject to volcanic mass flows flow observational and geometric data are combined into a model to derive the kinematic characteristics of the basal valley ponding avalanche and the valley escaping veneer flows which are otherwise hidden by overriding clouds of elutriated ash

deformation mechanisms and rheology why marble is weaker than quartzite when deformed together in nature calcite rocks invariably appear weaker and more ductile than quartz rocks this can be reconciled with experimental flow data only by taking into account grain size sensitive gss flow in calcite rocks which is predicted to dominate even at grain sizes on the order of 1mm at middle metamorphic grades using new experimental data that demonstrate the transition between intracrystalline plastic and gss flow of quartz rocks we predict that unnaturally small grain sizes at temperatures of 700 c or higher are required for gss flow of quartz in nature thus natural flow of quartzite is expected to occur by intracrystalline plastic processes even after recrystallization to a fine grain size

modeling of pyroclastic flows of colima volcano mexico implications for hazard assessment the 18 24 january 1913 eruption of colima volcano consisted of three eruptive phases that produced a complex sequence of tephra fall pyroclastic surges and pyroclastic flows with a total volume of 1 1 km 3 0 31 km 3 dre among these events the pyroclastic flows are most interesting because their generation mechanisms changed with time they started with gravitanional dome collapse block and ash flow deposits merapi type changed to dome collapse triggered by a vulcanian explosion block and ash flow deposits soufriere type then ended with the partial collapse of a plinian column ash flow deposits rich in pumice or scoria the best exposures of these deposits occur in the southern gullies of the volcano where heim coefficients h l were obtained for the various types of flows average h l values of these deposits varied from 0 40 for the merapi type similar to the block and ash flow deposits produced during the 1991 and 1994 eruptions 0 26 for the soufriere type events and 0 17 0 26 for the column collapse ash flows additionally the information of 1991 1994 and 1998 1999 pyroclastic flow events was used to delimit hazard zones in order to reconstruct the paths velocities and extents of the 20th century pyroclastic flows a series of computer simulations were conducted using the program flow3d with appropriate heim coefficients and apparent viscosities the model results provide a basis for estimating the areas and levels of hazard that could be associated with the next probable worst case scenario eruption of the volcano three areas were traced according to the degree of hazard and pyroclastic flow type recurrence through time zone 1 has the largest probability to be reached by short runout b5 km merapi and soufriere pyroclastic flows that have occurred every 3 years during the last decade zone 2 might be affected by soufriere type pyroclastic flows 9 km long similar to those produced during phase ii of the 1913 eruption zone 3 will only be affected by pyroclastic flows 15 km long formed by the collapse of a plinian eruptive column like that of the 1913 climactic eruption today an eruption of the same magnitude as that of 1913 would affect about 15 000 inhabitants of small villages ranches and towns located within 15 km south of the volcano such towns

dilatancy during rock deformation at high temperatures and pressures the dilatancy during deformation at high pressure and temperature and at various pore pressures has been measured in carrara marble solnhofen limestone and gosford sandstone the method consists of monitoring the volume of pore fluid argon that flows into or out of the specimen at constant pore pressure the confining pressure was 300 mpa temperatures were up to 873 k and pore pressure ranged from 30 to 280 mpa positive dilatancy was observed in some cases in all three rocks in the ductile regime up to the highest temperature provided the difference between confining pressure and pore pressure was relatively small thus indicating the occurrence of microcracking even under these conditions however the behavior was complicated by the collapse of initial porosity in the limestone and sandstone and by microcracking due to intergranular thermal stresses upon heating especially in the marble the dilatancy observations have important implications for kinetics of fluid rock interactions under geological conditions

a two layer model for the evolution and propagation of dense and dilute regions of pyroclastic currents we present calculations of a simplified two layer pyroclastic flow model which incorporates different physics to represent the dense and dilute regions of column collapse pyroclastic density currents the two layers evolve separately but are coupled through mass exchange as suspended ash in the dilute cloud settles into the underlying dense basal layer the runout distance of the upper dilute current and the associated runout time are found to increase with increasing initial column height and decreasing particle size likewise steeper slopes increase the propagation velocity and thus the runout distance the independent runout distance of the basal flow exhibits opposite behaviour to that of the parent dilute current increasing with decreasing initial column height and increasing particle size observed runout distances can be calculated for basal flows using a coulomb friction law but deposit morphology is not well reproduced and is more realistic when an empirical slope dependent sedimentation rate is included dominant flow behaviour is controlled by the rate of mass transfer from the parent suspension current into the dense underflow tall column collapses which contain fine grained particles transfer their mass slowly to the dense basal flow and are well described by dilute cloud assumptions however for short columns containing coarse grains the particulate mass is rapidly transferred from the collapsing dilute current into the basal flow the bulk of the pyroclastic current material propagates as a concentrated suspension for the majority of its travel distance and is better described by the physics of granular avalanches

crustal channel flows 2 numerical models with implications for metamorphism in the himalayan tibetan orogen 1 results from a thermal mechanical model ht1 that includes midcrustal channel flow are compatible with many features of the himalayan tibetan system radioactive self heating and rheological weakening of thickened model orogenic crust lead to the formation of a hot low viscosity midcrustal channel and a broad plateau channel material corresponding to the greater himalayan sequence ghs flows outward from beneath the plateau in response to topographically induced differential pressure at the plateau flank it is exhumed by focused surface denudation and juxtaposed with cooler newly accreted material corresponding to the lesser himalayan sequence lhs the model channel is bounded by coeval thrust and normal sense ductile shear zones interpreted to represent the main central thrust mct zone and south tibetan detachment system respectively inverted metamorphism associated with the model mct zone results from distributed ductile shear along the mct and extrusion of the hot channel a variety of model p t t path styles resembling those observed in the ghs and lhs are produced for points traveling through contrasting tectonic regimes that coexist in different parts of the model predicted times of peak metamorphism cooling and erosion of metamorphic facies are generally compatible with observations although model ghs cooling ages are too young the times of m1 and m2 metamorphic events observed in the ghs correspond to model times of maximum burial and maximum heating respectively the results highlight the need to integrate tectonics and metamorphism in continental collision models and demonstrate the importance of lateral transport of both heat and material in large hot orogens

objective rapid delineation of areas at risk from block and ash pyroclastic flows and surges assessments of pyroclastic flow pf hazards are commonly based on mapping of pf and surge deposits and estimations of inundation limits and or computer models of varying degrees of sophistication in volcanic crises a pf hazard map may be sorely needed but limited time exposures or safety aspects may preclude fieldwork and insufficient time or baseline data may be available for reliable dynamic simulations we have developed a statistically constrained simulation model for block and ash type pfs to estimate potential areas of inundation by adapting methodology from iverson et al geol soc america bull 110 972 984 1998 for lahars the predictive equations for block and ash pfs are calibrated with data from several volcanoes and given by a 0 05 to 0 1 v2 3 b 35 to 40 v2 3 where a is cross sectional area of inundation b is planimetric area and v is deposit volume the proportionality coefficients were obtained from regression analyses and comparison of simulations to mapped deposits the method embeds the predictive equations in a gis program coupled with dem topography using the laharz program of schilling 1998 although the method is objective and reproducible any pf hazard zone so computed should be considered as an approximate guide only due to uncertainties on the coefficients applicable to individual pfs the authenticity of dem details and the volume of future collapses the statistical uncertainty of the predictive equations which imply a factor of two or more in predicting a or b for a specified v is superposed on the uncertainty of forecasting v for the next pf to descend a particular valley multiple inundation zones produced by simulations using a selected range of volumes partly accommodate these uncertainties the resulting maps show graphically that pf inundation potentials are highest nearest volcano sources and along valley thalwegs and diminish with distance from source and lateral distance from thalweg the model does not explicitly consider dynamic behavior which can be important ash cloud surge impact limits must be extended beyond pf hazard zones and we provide several approaches to do this the method has been used to supply pf and surge hazard maps in two crises merapi 2006 and montserrat 2006 2007

a comparison of the landsat image and laharz simulated lahar inundation hazard zone by the 2010 merapi eruption located above the java subduction zone merapi volcano is an active stratovolcano with a volcanic activity cycle of 1 5 years most merapi eruptions are relatively small with volcanic explosivity index vei of 1 3 however the most recent eruption which occurred in 2010 was quite violent with a vei of 4 and 386 people were killed in this study lahars and pyroclastic flow zones were detected using optical landsat images and the lahar and pyroclastic flow zone simulated using the laharz program to detect areal extents of lahar and pyroclastic flows using landsat images supervised classification was performed after atmospheric correction by using a cosine of the solar zenith correction cost model as a result the extracted dimensions of pyroclastic flows are nearly identical to the calatrava volcanic province cvp monthly reports then areas of potential lahar and pyroclastic flow inundation based on flow volume using the laharz program were simulated and mapped finally the detected lahars and pyroclastic flow zones were compared with the simulated potential zones using laharz program and verified results showed satisfactory similarity 55 63 between the detected and simulated zone the simulated zones using the laharz program can be used as an essential volcanic hazard map for preventing life and property damages for merapi volcano and other hazardous volcanic areas also the laharz program can be used to map volcano hazards in other hazardous volcanic areas

partial melt topology in statically and dynamically recrystallized granite microstructures of the murray granite pluton central ontario canada show evidence of both static and dynamic crystallization subsequent to partial melting backscattered electron analyses reveal interstitial k feldspar and plagioclase at triple junctions of strain free isometric quartz grains the geometry of the quartz feldspar boundaries mimics the original topology of the quartz melt contacts during crystallization this conclusion is suggested by the occurrence of both rounded and planar faces of quartz grains and by low 27 dihedral angles of quartz quartz feldspar boundaries similar to dihedral angles in experimentally crystallized quartz quartz silicic melt systems in contrast feldspar seams in deformed granites have high axial ratios are usually elongated perpendicular to the foliation plane and are located preferentially along individual grain boundaries quartz grains are dynamically recrystallized and occasionally transected by feldspar seams indicating that fracturing occurred in the presence of melt during crystal plastic deformation of quartz the subparallel orientation in quartz grains of intragranular feldspar bearing fractures and interstitial feldspar seams suggests that these features originated as intragranular and intergranular fractures respectively partial melt topology was therefore controlled by intergranular and occasionally by intragranular fracturing

preparation and deformation of synthetic aggregates of quartz synthetic quartz aggregates of low porosity have been fabricated from natural quartz powder impure silica gel and high purity silicic acid by hydrothermal isostatic pressing at 300 mpa the resulting specimens have water contents comparable to those of natural quartzites and have been used for deformation tests the flow stress at 1200 1300 k was found to vary in an inverse relationship to the water pressure estimated under the assumption that the measured water content homogeneously filled the measured porosity it is questionable that the natural quartz origin specimens were fully equilibrated in respect to the activity of the water but equilibration has probably been achieved in the amorphous silica origin specimens which crystallized under the experimental conditions in the deformation of the latter materials the experimental activation energy at water pressures approaching the confining pressure was found to be about 150 kj mol 1 for both however the impure gel origin material gave a stress exponent of about 2 3 whereas the high purity silicic acid origin material gave a stress exponent of about 4 in spite of the grain sizes being about 90 m and 20 m respectively it is concluded that while the impure specimens have higher intragranular strengths there is also a significant contribution of grain boundary processes to the strain in them which is absent in the high purity specimens

archean gravity driven tectonics on hot and flooded continents controls on long lived mineralised hydrothermal systems away from continental margins abstract we present the results of two dimensional numerical modelling experiments on the thermal evolution of archean greenstones as they sink into a less dense hot and weak felsic crust we compare this thermal evolution to that obtained via the analysis of isotopic data and fluid inclusion microthermometry data obtained in the paleoarchean to mesoarchean warrawoona synform eastern pilbara craton western australia our numerical experiments reveal a two stage evolution in the first stage cooling affects zones of downwelling as greenstone belts are advected downward whereas adjacent domes become warmer as deep and hot material is advected upward we show that this is consistent with stable isotopes data from the warrawoona synform which reveal an early episode of seafloor like alteration 90 160 c strongly focused along steeply dipping shear zones in a second long lived stage lateral heat exchanges between domes and basins dominate the system as domes cool down while downwelling zones become increasingly warmer in the warrawoona greenstone belt stable isotopes in gold bearing quartz veins post dating the sagduction related vertical fabrics reveal that rock fluid interaction occurred at much higher temperatures 234 372 c than seafloor like alteration we propose that emplacement of thick and dense continental flood basalts on flooded hot and weak continental plates led to conditions particularly favourable to hydrothermal processes and the formation of mineral deposits we further argue that sagduction was able to drive crustal scale deformation in the interior of continents away from plate margins on largely flooded continents sagduction related shear zones acted as fluid pathways promoting gold mineralisation far away from active plate boundaries continental rift zones or collisional mountain belts

distribution of partial melt in a felsic system the importance of surface energy the texture distribution and infiltration tendency of a quartz albite melt in equilibrium with a synthetic texturally equilibrated quartzite was examined in a series of distribution and infiltration experiments at 1 250 c and 8 kbar hydrostatic pressure wetting angle measurements from melt distribution experiments show a dihedral angle of 60 degrees implying a quartz quartz interfacial energy approximately 1 7 times the quartz melt value because of this specific relationship between interfacial energies the system can achieve its lowest surface free energy state with the melt either in pools or along grain edge intersections possibly forming some interconnected channels stability of melt in pockets and along grain edge intersections was observed in a fourteen day dispersed melt experiment yet melt pools failed to disperse into the quartzite during infiltration experiments comparison of the observed dihedral angle with previously measured surface energy values for the melt and quartz shows excellent agreement and also demonstrates that an aggregate of randomly orientated anisotropic grains acts approximately isotropically

objective delineation of lahar inundation hazard zones a new method of delineating lahar hazard zones in valleys that head on volcano flanks provides a rapid objective reproducible alternative to traditional methods the rationale for the method derives from scaling analyses of generic lahar paths and statistical analyses of 27 lahar paths documented at nine volcanoes together these analyses yield semiempirical equations that predict inundated valley cross sectional areas a and planimetric areas b as functions of lahar volume v the predictive equations a 0 05v 2 3 and b 200v 2 3 provide all information necessary to calculate and plot in

shear zone hosted migmatites eastern india the role of dynamic melting in the generation of ree depleted felsic melts and implications for disequilibrium melting in the ranmal migmatite complex non anatectic foliated granite protoliths can be traced to polyphase migmatites structural microtextural relations and thermobarometry indicate that syn deformational segregation crystallization of in situ stromatic and diatexite leucosomes occurred at 8008c and 8 kbar the protolith the neosome and the mesosome comprise quartz k feldspar plagioclase hornblende biotite sphene apatite zircon and ilmenite but the modal mineralogy differs widely the protolith composition is straddled by element abundances in the leucosome and the mesosome the leucosomes are characterized by lower cao feo mgo mg number tio2 p2o5 rb zr and total rare earth elements ree and higher sio2 k2o ba and sr than the protolith and the mesosome whereas na2o and al2o3 abundances are similar the protolith and the mesosome have negative eu anomalies but protolith normalized abundances of ree depleted leucosomes show positive eu anomalies the congruent melting reaction for leucosome production is inferred to be 0 325 quartz 0 288 k feldspar 0 32 plagioclase 0 05 biotite 0 014 hornblende 0 001 apatite 0 001 zircon 0 002 sphene1 4melt based on the reaction large ion lithophile element ree and zr abundances in model melts computed using dynamic melting approached the measured element abundances in leucosomes for40 5 mass fraction of unsegregated melts within the mesosome disequilibrium accommodated dynamic melting and equilibrium crystallization of melts led to uniform plagioclase composition in migmatites and ree depletion in leucosome

numerical simulations of block and ash flows using the titan2d flow model examples from the 2006 eruption of merapi volcano java indonesia we present titan2d simulations of two well characterized block and ash flow baf events of the 2006 eruption of merapi java indonesia that affected the gendol valley on the volcano s southern flank and adjacent densely populated interfluve non valley areas 1 a single dome collapse event to the south that generated one of the smaller post june 14 flows and 2 a sustained multiple dome collapse event also directed to the south that produced the largest flows of the 2006 eruption emplaced in the afternoon of june 14 using spatially varying bed friction angles titan2d is capable of reproducing the paths velocities runout distance areas covered and deposited volumes of these flows over highly complex topography the model results provide the basis for estimating the areas and levels of hazards associated with bafs generated during relatively short as well as prolonged dome collapse periods and guidance during future eruptive crises at merapi

towards an improved understanding of the mechanical properties and rheology of the lithosphere an introductory article to rock deformation from field experiments and theory a volume in honour of ernie rutter ernie rutter s influential contribution to our understanding of rock deformation spans the whole continental crust from deformation just under the grass e g rutter green 2011 to melt migration in the lower crust e g rutter neumann 1995 ernie has also worked on many aspects of the deformation of oceanic crust rutter brodie 1988 however here we reflect on the wide range of deformation conditions ernie has studied by presenting key aspects of the strength and rheology of the continental lithosphere as we understand it today with the aim of providing the context for the contributions included within this volume the continental crust forms just over a third of the earth s surface and it is different from the crust of any other planet in our solar system it is rich in those elements that partition in a silicate melt and its formation and evolution determined the composition of the mantle and that of the atmosphere hawkesworth 2006 thanks to its physical and chemical fingerprint the earth s crust has sustained life uninterrupted for 3 8 ga and it is the source of major natural resources such as hydrocarbons and mineral deposits and others such as geothermal energy the continental crust is less dense than its oceanic counterpart and is therefore more buoyant it forms a substantial part of the cold thermal layer of the earth and its rheology from greek r1v rhe flow and logia logia study the study of the flow of matter is a key factor controlling plate tectonic processes at the earth s surface and in its interior davies 2011 beneath the continental crust lies the lithospheric mantle and together they form the continental lithosphere considerable variations in structure thickness and composition of the continental lithosphere mean that despite its importance we currently have limited understanding of the rheology of this complex system thatcher pollitz 2008 significant advances in our knowledge of continental rheology have been possible through

decoupling of pyroclastic currents hazards assessments gravitational settling of fragments gas elutriation and boundary layer processes cause concentration values to change within different parts of sediment gravity flows during movement these processes result in flow transformations density stratification and decoupling of single currents into separate sediment gravity flows density can change by an increase in solids concentration in basal zones of currents by downward fall of particles or by incorporation of particles from the substrate thereby leaving their upper parts more dilute in some flows upward streaming gases and elutriation of fines cause dilute turbulent currents to develop at the top of a dense current increasing concentration dampens turbulent action transforming the turbulent to the nonturbulent state commonly at the current s base conversely dilute parts of currents become or remain turbulent currents consisting of turbulent and nonturbulent parts can decouple by shearing past one another because of differing flow properties with each part taking separate paths the manner by which a pyroclastic flow moves affects its predicted runout distance its distribution as continuous sheets or in isolated basins and whether it can cross barriers such as high mountain ranges or water bodies during the eruption of unzen volcano on june 3 1991 decoupling of a pyroclastic surge from the top of a pyroclastic flow caused the deaths of harry glicken maurice krafft katia krafft and 40 japanese citizens mapping volcanic hazard zones requires that consideration be given to decoupling processes to help prevent similar tragedies in the future

flow of synthetic wet partially molten granite under undrained conditions an experimental study 1 major problems in experimental studies of the flow of partially molten granitic rocks are 1 maintaining control of the grain size of the matrix of solid grains 2 controlling the melt fraction and 3 controlling the melt viscosity closely linked to water content to overcome these problems we used a synthetic granitoid comprising a solid matrix of quartz grains 50 m grain size mixed with an albite quartz melt prepared from oxides with added water 2 5 wt dissolved in the melt phase viscosity 9 104 pa s experiments were performed undrained with melt fractions of 0 1 0 2 0 25 and 0 3 constant strain rate creep and stress relaxation experiments were carried out in a gas medium apparatus at 1273 and 1173 k mostly at 300 mpa confining pressure up to 15 shortening strain strain rates ranged between 10 4 to less than 10 7 s 1 and fully ductile mechanical behavior was observed melt fraction has a more profound effect on strength than water content temperature or total confining pressure low strain rate 10 6 s 1 data were fitted to an empirical flow law of the form d dt a exp b m exp h rt n with the parameters loga 1 39 m 3 n 1 8 b 192 h 220 kjmol 1 where d dt is strain rate s 1 is flow stress mpa is melt fraction and t is temperature k strength is expected to fall rapidly above about 0 4 melt fraction to levels characteristic of flow of the melt containing suspended crystallites extrapolation to geological strain rates using this flow law shows that in nature migmatites bearing granitic melt will be extremely weak much weaker than silicate rocks deforming by intracrystalline plasticity microstructural study shows grains remain equant at all strains with no discernable formation of a grain flattening fabric nor a large strain contribution from microfracturing thus bulk intracrystalline plasticity is of minor importance and intergranular sliding is implied the nonlinear flow observed is tentatively attributed to a combination of sintering of grain contacts and sliding failure of such contacts with a substantial contribution from diffusive transfer processes

the structures of two ophiolite massifs bay of islands newfoundland a model for the oceanic crust and upper mantle abstract for a detailed analysis of their main structures accumulation planes foliation planes and lineations the peridotite gabbro units of table mountain and blow me down mountain bay of islands newfoundland have been divided into several structural units each one being characterized by specific microstructures of deformation or accumulation a fishbone pattern with the accumulation plane in the mafic cumulates dipping toward the ridge and the foliation plane in the ultramafic tectonites dipping away from it is postulated for the structure of the lithosphere formed at a spreading center the tectonic structures in the peridotites are related to asthenospheric flow in the uppermost mantle and the direction of the ridge is inferred from the lineation trend in the peridotites the structures in the cumulates are related to subsidence of the magma chamber floor during spreading at the base of the massifs the tectonic structures in the mafic metamorphic rocks are parallel to those observed the latter have been deformed at moderate temperatures under high stresses and display mylonitic textures at their contact with the mafic tectonites from these superimposed textures we infer a kinematic model for the oceanic thrusting of the lithosphere the direction of thrusting is given by the lineation trend and its sense by the analysis of shear all these data are combined into a paleogeographic scheme for the newfoundland caledonides

predicting the block and ash flow inundation areas at volcan de colima colima mexico based on the present day february 2010 status abstract maps of areas potentially affected by block and ash flows and associated ash clouds are here presented for the volcan de colima titan2d 2 0 1 code has been used to simulate block and ash flows using as an input volume that of the actual summit dome assessed at 2 10 6 m 3 while the energy cone model has been used to delimit the possible inundated area from associated ash clouds both merapi and soufriere type block and ash flows were generated using different basal friction angles and maintaining fixed the volume and the internal friction angle the setting of the input parameters takes into account some flow characteristics such as the stepwise aggradation of different pulses that piled up to form the total thickness of the block and ash flow deposits the outputs of the computational routines are reported as two maps describing the total thickness of the final deposits they predict that thick deposits will engulf the ravines descending from the main cone to the west south and southeast with expected maximum runouts between 4 5 and 7 km the associated ash clouds have slightly longer runouts and the model predicts they will inundate some higher grounds that are not affected by the concentrate underflows the presented maps represent useful tools for managing the current block and ash flow hazard at volcan de colima

modelling deformation of partially melted rock using a poroviscoelastic rheology with dynamic power law viscosity abstract a poroviscoelastic constitutive model is developed and used to study coupled rock deformation and fluid flow the model allows the relaxation of both shear and symmetric components of the effective stress experimental results are usually interpreted in terms of the power law viscous material however in this work the effect of strain damage on viscosity is considered by treating the viscosity as a dynamic time dependent parameter that varies proportionally to the second invariant of the strain rate healing is also taken into account so that the dynamic power law viscosity has a constant asymptotic at a given strain rate the theoretical model is implemented in a finite element fe formulation that couples fluid flow and mechanical equilibrium equations the fe method is applied to numerically study the triaxial compression of partially melted rocks at elevated pt conditions it is found that the numerically calculated stress strain curves demonstrate maxima similar to those observed in laboratory experiments also the computed pattern of melt redistribution and strain localization at the contact between the rock sample and a stiff spacer is qualitatively similar to the experimental observations the results also indicate that the matrix sensitivity to damage affects the scale of strain localization and melt redistribution

experimental deformation of partially melted granitic aggregates abstract the effects of varying amounts of partial melt on the deformation of granitic aggregates have been tested experimentally at conditions 900 c 1500 mpa 10 4 to 10 6 s where melt free samples deform by dislocation creep with microstructures approximately equivalent to those of upper greenschist facies experiments were performed on samples of various grain sizes including an aplite 150 m and sintered aggregates of quartz albitemicrocline 10 50 and 2 10 m water was added to the samples to obtain various amounts of melt 1 15 in the aplite 1 5 in the sintered aggregates optical and tem observations of the melt distribution in hydrostatically annealed samples show that the melt in the sintered aggregates is homogeneously distributed along an interconnected network of triple junction channels while the melt in the aplites is inhomogeneously distributed the effect of partial melt on deformation depends an melt amount and distribution grain size and strain rate for samples deformed with 1 melt all grain sizes exhibit microstructures indicative of dislocation creep for samples deformed with 3 5 melt the 150 m and 10 50 m grain size samples also exhibit dislocation creep microstructures but the 2 10 m grain size samples exhibit abundant tem scale evidence of dissolution precipitation and little evidence of dislocation activity suggesting a switch in deformation mechanism to predominantly melt enhanced diffusion creep at natural strain rates melt enhanced diffusion creep would predominate at larger grain sizes although probably not for most coarse grained granites the effects of melt percentage and strain rate have been studied for the 150 m aplites for samples with 5 and 10 melt deformation at 10 6 s squeezes excess melt out of the central compressed region allowing predominantly dislocation creep conversely deformation at 10 5 s produces considerable cataclasis presumably because the excess melt cannot flow laterally fast enough and a high pore fluid pressure results for samples with 15 melt deformation at both strain rates produces cataclasis presumably because the inhomogeneous melt distribution resulted in regions of decoupled grains which would produce high stress concentrations at point contacts at natural strain rates there should be little or no cataclasis if an equilibrium melt texture exists and if the melt can flow as fast as the imposed strain rate however if the melt is confined and cannot migrate a high pore fluid pressure should promote brittle deformation

decoupling of small volume pyroclastic flows and related hazards at merapi volcano indonesia the november 1994 eruption at merapi volcano provided good evidence of decoupling of dome collapse pyroclastic flows and of large scale detachment of an ash cloud surge acs component from the basal block and ash flow baf timing and stratigraphic relationships of the largest 1994 acs indicate that this escaped from the valleys travelled well ahead of the baf arrived at the termination tens of seconds before it and deposited a discrete acs deposit beneath the baf unit this suggests that the acs detachment mostly occurred relatively high on the volcano slope likely at the foot of the proximal cone later pyroclastic flow eruptions in january 1997 and july 1998 also showed evidence of acs detachment although to a lesser extent suggesting that acss could be a frequent hazard at merapi volcano based on an extensive review of the available literature and on field investigations of historical deposits we show here that flow decoupling and acs detachment in the way inferred from the 1994 eruption is a common process at merapi the acs related destructions outside valleys were frequently reported in the recent past activity of the volcano i e in at least 16 pyroclastic flow eruptions since 1927 destruction occurred systematically in eruptions where maximum runout of the bafs was 6 5 km or more and occurred rarely for baf runouts of 4 5 km or less the acs deposits have been recognized beneath some valley filling baf units we attribute to some recent destructive eruptions i e the 1930 1954 1961 and 1969 eruptions topographic conditions at merapi volcano favouring acs detachment include a the high slope 30 of the proximal cone leading to high proximal velocities of the pyroclastic flows and thus to the transfer of large amounts of particles into the ash cloud b the strong break in slope at the foot of the proximal cone where the velocity of the basal baf is strongly reduced and a major acs component is thought to form and detach by shearing over the baf and c the small depth of most valleys in the first kilometres beyond the foot of the cone which allows minor acs components to escape from the valleys during travel of the baf however flow decoupling and acs detachment occur for only some of the numerous pyroclastic flows that follow the same path in a given eruption this indicates that topography alone cannot lead to flow decoupling we suggest two factors that control flow decoupling and its extent the main one is flow volume and thus flux as both are correlated in almost instantaneous dome collapse events as suggested by the observed relationship between flow decoupling and the travel distance of the pyroclastic flows the second factor is the amount of available ash in the flow at its early stage which influences the mass and thus momentum of the ash cloud the amount of ash in the pyroclastic flows of merapi may depend on several factors among which are a the physical and thermal state of the part of the active dome that collapses and b the proportion of older cold rocks incorporated in the flow either by undermining of surrounding summit rocks by the current pyroclastic flow activity or by erosion on the upper slopes

melt segregation and far field melt transfer in the mid crust abstract migmatites in the damara belt in namibia preserve relationships between anatectic leucosomes and intrusive leucogranite sheets illustrating the consecutive stages of partial melting local melt segregation and far field mobilization of melts over hundreds of metres and out of the anatectic region initial melting and localized segregation of melts are controlled by gradients in fluid pressure created by pervasively developed shallowly dipping dilatant fractures subsequent melt transfer out of these initial sites of melting and melt storage occurs along subvertical disc shaped leucogranite sheets that intersect the leucosomes the leucogranite sheets propagate as isolated melt filled hydrofractures driven by the pressure differential along the subvertical fractures the collapse of wall rocks into former melt bearing fractures and the presence of residual peritectic phases of the melting reaction trapped in wall rocks testify to the efficient extraction of melt by the mobile hydrofractures during their ascent this process of melt drainage into and transport by hydrofractures leaves almost no trace of the ascent conduits this study also shows that melt transport and the stability of melt pathways in strongly layered mid crustal levels characterized by low deviatoric stresses are determined by the presence of pre existing anisotropies and the progressively evolving structure in deforming orogens