simulation and analysis of conductively guided borehole radar wave in a borehole radar bhr survey a steel cable or a metallic drill pipe attached to a bhr can act as a waveguide and often gives measured radargrams with strong obliquely striped events these guided bhr wave events are commonly considered as interference noise for conventional bhr surveys and have not been fully investigated to better understand these events a 2 d cylindrical finite difference time domain method is used in this paper for simulation and investigation of the guided bhr wave propagation snapshots of wavefields and response profiles for different configurations are simulated and analyzed to understand the generation and interaction process of the guided waves with the borehole and the surrounding formation the simulation results confirm that if a conventional bhr is attached with a conductive waveguide the bhr wave can be coupled with the waveguide to generate guided bhr waves propagating along the borehole the backward looking or forward looking guided bhr reflections from the strata discontinuities are recorded on bhr profiles the generation of forward looking events makes it feasible to image ahead of a drill bit in real time while drilling using a conventional bhr a simple formula to estimate the location of the interface using the forward looking events is given based on the synthetic data with a bhr 3 7 m away from the interface it was demonstrated that the location of the interface can be accurately predicted with an error of about 1 cm finally the effect of the length of the waveguide on the guided waves is also discussed

estimation of permeable pathways and water content using tomographic radar data near surface environmental investigations often require monitoring of the spatial distribution of water content and identification of preferential fluid flow paths water content estimates are needed for example to model and predict pollutant transport through the vadose zone and to subsequently design an efficient and reliable remediation plan the characteristics of preferential flow paths as well as the location and geometry of these features are necessary to model and predict flow and transport in complex geological media such as fractured or strongly heterogeneous porous systems

sediment fluxes along the northeastern european margin inferring hydrological changes between 20 and 8 kyr abstract in an attempt to delineate past hydrographic conditions on the northeastern atlantic ocean margin along a latitudinal transect 37 63 n and link the eastern north atlantic ocean with the norwegian sea we have investigated planktonic and benthic stable oxygen isotopes as well as abundances and fluxes of planktonic and benthic foraminifera calcium carbonate organic carbon and detrital grains in six sediment cores studied by the enam project in our joint approach we focused on the major climatic events of the last 20 kyr that is the last glacial maximum lgm the heinrich event 1 h1 the younger dryas yd and the holocene climatic optimum hco simmax temperature estimates suggest glacial ssts off portugal similar to holocene values contradicting the proposed polar front position of climap project members 1976 besides increased planktonic and benthic foraminiferal fluxes in the norwegian sea and the faeroe islands cores point to nordic seas partially ice free with seasonally productive polynas multiple ird spikes observed at the faeroe islands and norwegian sea sites coeval with h1 suggest multiple pulses of the fenno scandian ice sheet at the same time the presence of ird on the portuguese margin cores confirms the southward influence of icebergs the increase in foraminiferal abundances and fluxes that parallel ird spikes at all sites suggests that times of increased productivity either succeed or occur simultaneously with the iceberg surges in the open north atlantic productivity conditions similar to those observed during h1 are also registered during the yd even though planktonic foraminiferal assemblages suggest less cold conditions

sea level estimates during the last deglaciation based on δ18o and accelerator mass spectrometry 14c ages measured in globigerina bulloides coupled measurements of 18o and accelerator mass spectrometry ams 14c in a particular species of planktonic foraminifera may be used to calculate sea level estimates for the last deglaciation of critical importance for this type of study is a knowledge of the seasonality of foraminiferal growth which can be provided by 18o measurements of modern shells core tops plankton tows isotopic 18o ams 14c dating and faunal records transfer function sea surface temperature were obtained from two cores in the north atlantic at about 37 n the locations were chosen to obtain high sedimentation rate records removed from the major ice melt discharge areas of the last deglaciation based upon globigerina bulloides data four 18o based sea level estimates were calculated 67 7 m at 12 200 yr b p and 24 8 m at about 8200 yr b p for core su 81 18 83 10 m at 12 200 yr b p and 13 11 m at about 8500 yr b p for core su 81 14 using a second working hypothesis concerning the seasonability of g bulloides growth it is suggested that the sea level rose by about 40 m during the millennium which followed 14 500 yr b p

analysis of a guided wave along a conducting structure in a borehole a guided wave along a borehole is often observed in borehole radar measurements these guided waves deform the antenna pattern and can cause artefacts in radar measurements a water filled borehole or a conducting logging cable can function as a waveguide for electromagnetic waves under some conditions we describe the theoretical characteristics of such a guided wave in a borehole and compare them with our experiments the measured signal discussed was obtained with a directional borehole radar this radar uses a cylindrical conformal array antenna as receiver and is a model of a conducting structure in a borehole the induced field around the borehole was compared with the theory the most fundamental symmetrical and asymmetrical modes were tm 01 and he 11 and they were identified in the measured signals using time frequency distribution analysis and by observation of the azimuthal field distribution of the magnetic field

basaltic calderas collapse dynamics edifice deformation and variations of magma withdrawal 1 the incremental caldera collapses of fernandina 1968 miyakejima 2000 and piton de la fournaise 2007 are analyzed in order to understand the collapse dynamics in basaltic setting and the associated edifice deformation for each caldera the collapse dynamics is assessed through the evolution of the 1 time interval t between two successive collapse increments 2 amount of vertical displacement during each collapse increment and 3 magma outflow rate during the whole collapse caldera process we show from the evolution of t that piton de la fournaise and fernandina were characterized by a similar collapse dynamics despite large differences in the caldera geometry and the duration of the whole collapse caldera process this evolution significantly differs from that of miyakejima where t strongly fluctuated throughout the whole collapse process quantification of the piston vertical displacements enables us to determine the magma outflow rates between each collapse increment displacement data tiltmeter and or gps for piton de la fournaise and miyakejima are used to constrain the edifice overall deformation and the edifice deformation rates these data reveal that both volcanoes experienced edifice inflation once the piston collapsed into the magma chamber such a deformation which lasts during the first collapse increments only is interpreted as the result of larger volume of piston intruded in the magma chamber than magma withdrawn before each collapse increment once the effect of the collapsing rock column vanishes edifice deflates we also determine for each caldera the critical amount of magma evacuated before collapse initiation and compare it to analog models the significant differences between models and nature are explained by the occurrence of preexisting weak zones in nature i e the ring faults that are not taken into account in analog models finally we show that t at piton de la fournaise and fernandina was equally controlled by the frictional resistance along the ring faults and the magma outflow rate in addition to these two parameters the collapse dynamics of miyakejima was also influenced by variations of the magma bulk modulus which changed after the influx of deep gas rich magma into the collapse related magma chamber altogether our results show that the dynamics of caldera collapse in basaltic volcanoes proceeds in two phases phase 1 starting with the first collapse is characterized by the largest collapse amplitude an incremental edifice inflation and a step by step increase of the rate of magma outflow phase 2 shows a rapid decrease of the magma discharge rate to a low level concomitant with the continuous edifice deflation if deep magma is injected into the magma chamber as at miyakejima an additional phase occurs phase 3

younger dryas style cooling events at glacial terminations i vi at odp site 658 associated benthic δ13c anomalies constrain meltwater hypothesis high resolution planktonic and epibenthic stable isotope records from ocean drilling program site 658 off northwest africa provide a basis for a detailed study of glacial terminations i vi during the last 650 000 years the duration of the terminations was about one half to one quarter of an orbital precession cycle 5800 10 700 years when its amplitude was high at low amplitudes the terminations lasted longer than half an obliquity cycle 29 000 years marked climatic rebounds similar to the younger dryas each with a duration of 1000 2500 years subdivided all six terminations into distinct steps a b and c important parts of the deglacial steps were as brief as 700 1000 years the speed of climatic change suggests that special associations existed between orbital forcing and inherent instability of the ice sheets in harmony with published models the more rapid pulses of glacial meltwater incursions to the northern north atlantic led to one or more brief short term shut downs of north atlantic deep water formation this process is reflected by pronounced benthic 13c minima that precisely coincide in most cases with the end of the 18o deglaciation steps and immediately terminate with succeeding younger dryas style cooling events thus we conclude that the rebounds resulted from a short term antecedent estuarine circulation regime in the north atlantic except for the younger dryas itself which succeeded the allerod with its well ventilated atlantic deepwater circulation and hence continues to be an enigma

chronology and products of the 2000 eruption of miyakejima volcano japan lateral migration of magma away from miyakejima volcanic island japan generated summit subsidence associated with summit explosions in the summer of 2000 an earthquake swarm beneath miyakejima began on the evening of 26 june 2000 followed by a submarine eruption the next morning strong seismic activity continued under the sea from beneath the coast of miyakejima to a few tens of kilometers northwest of the island summit eruptive event began with subsidence of the summit on 8 july and both explosions and subsidence continued intermittently through july and august the most intense eruptive event occurred on 18 august and was vulcanian to subplinian in type ash lofted into the stratosphere fell over the entire island and abundant volcanic bombs were erupted at this time another large explosion took place on 29 august this generated a low temperature pyroclastic surge which covered a residential area on the northern coast of the island the total volume of tephra erupted was 9 3 106 m3 dre much smaller than the volume of the resulting caldera 6 108 m3 migration of magma away from miyakejima was associated with crustal extension northwest of miyakejima and coincident shrinkage of miyakejima island itself during july august 2000 this magma migration probably caused stoping of roof rock into the magma reservoir generating subsurface cavities filled with hydrothermal fluid and or magmatic foam and formation of a caldera oyama caldera at the summit interaction of hydrothermal fluid with ascending magma drove a series of phreatic to phreatomagmatic eruptions it is likely that new magma was supplied to the reservoir from the bottom during waning stage of magma s migration resulting in explosive discharge on 18 august the 18 august event and phreatic explosions on 29 august produced a conduit system that allowed abundant so2 emission as high as 460 kg s 1 after the major eruptive events were over at the time of writing inhabitants of the island about 3 000 have been evacuated from miyakejima for more than 3 years

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

asymmetric growth of collapsed caldera by oblique subsidence during the 2000 eruption of miyakejima japan abstract oblique development of the ring faults reflecting the structural heterogeneities inside the volcano formed many asymmetric structures of miyakejima 2000 ad caldera the asymmetry includes a offset location of the ring faults with respect to the associated shallow magma chamber b unequal outward migration of the caldera wall 600 m at the southeastern rim but only 200 m at the northwestern rim c development of tilted terrace only at the southeastern caldera margin d eruption sites and fumaroles being confined to the southern part of the caldera geophysical data including ground deformation and seismic activity indicates the offset of the location of the magma chamber about 2 km south of the caldera center on the surface the ring faults propagated from the deflating magma chamber obliquely about 30 degrees toward the summit the oblique subsidence of the cylindrical block formed a wider instable zone particularly in the southeastern side of the ring fault that enhanced the larger outward migration of the caldera rim and also caused the formation of the outer half ring fault bordering the tilting slope at the southern part ascending pass of the buoyant magma along the tilted ring faults was concentrated in the southern half of the caldera and consequently the distributions of the eruption sites and fumaroles are localized in the southern half part of the caldera the structure of the miyakejima 2000 caldera with complete development of the ring faults its high roof aspect ratio and oblique subsidence is clearly distinguishable from trapdoor type caldera the oblique development of the ring faults can be controlled by the mechanical contrast between the solidified conduits and surrounding fragile volcanic edifice asymmetric development of the miyakejima caldera shows that the collapsed calderas are potential indicators of the heterogeneous structures inside of the volcano particularly in the case of small size caldera

evidence for two step deglaciation and its impact on north atlantic deep water circulation oxygen and carbon isotope records from benthic and planktonic foraminifera are presented for the past 35 000 years in the northeastern atlantic the results support the idea that the last deglaci ation took place in two major steps1 4 and conflict with theories calling for a strong reduction in north atlantic deep water formation to explain the abrupt cooling of the younger dryas cold period5 7

volcanic gas concentration and aquifer permeability estimated from tidal fluctuations in groundwater level case of koshimizu well in izu oshima japan in order to understand the mechanism of material transport induced by seismic and volcanic activities we analyzed chemical changes and permeability variations based on field observations on a recently active volcano izu oshima from march to august 1988 when the volcanic and seismic activities in izu oshima declined following an episode of those activities that ended in late 1987 the concentrations of co2 and h2 of volcanic origin increased 10 30 times above the previous levels in the koshimizu well located 1 km from the coast analysis of tidal frequency groundwater level variations in the well shows changes in tidal response of the groundwater level that are inferred to be associated with changes in shallow formation permeability a simple 1 dimensional diffusion model together with reasonable assumption about the local hydrologic structure suggest that the horizontal permeability in the upper few hundred meters of the island is high of the order of 10 8 m and varied by as much as 20 percent during recorded period we consider that these changes should be the results of vertical development of cracks which was caused by hot water intrusion from magma

a salt oscillator in the glacial atlantic 2 a scale analysis model a proposal has been made by broecker et al 1990 that rapid changes on a time scale of a thousand years or so seen over much of the last major glacial in the greenland ice core record represent significant climate changes and are caused by a salt oscillator in the glacial atlantic this proposal is examined in terms of a rudimentary quantitative model scale analysis asserts that heat transported to the high latitude atmosphere when the thermohaline circulation is turned on is large enough to produce the melting rates found by fairbanks 1989 for the time interval around that of the younger dryas event and that these melting rates are of the same order of magnitude as the mass flux associated with water vapor flux to the pacific ocean estimated by broecker 1989 scale analysis also suggests that the salinity fluxes associated with 1 the water vapor flux mechanism 2 the rapid melting episodes of fairbanks 3 possibly ice sheet growth events 4 net transport by the thermohaline circulation and 5 net transport by turbulent eddy mixing are roughly of the same order of magnitude and therefore may be important mechanisms for producing salinity oscillations on a time scale of a few thousands of years see broecker 1990 by integration of simple salt conservation equations it is found that model oscillations with a period of a few thousand years occur over a significant range of salinity fluxes estimated fluxes fall well within the range for which oscillations exist the model also suggests that there may exist close coupling between the european scandinavian ice sheets and the bimodal response of the oscillator that is significant increases or decreases in continental ice volume may accompany each complete cycle of the oscillator in addition it appears that continental ice may be required for the salt oscillator to function a crucial element which cannot adequately be investigated with the present model concerns the local effect of salinity source sinks associated with melt water production the proximity of these source regions on the neighboring ice sheets to the local regions where production of deep water occurs may play a critical role in the functioning of the proposed salt oscillator in addition further treatment of thermodynamics is needed to investigate the feasibility of a salinity driven oscillator

ba ca in neogloboquadrina pachyderma as an indicator of deglacial meltwater discharge into the western arctic ocean 1 down core samples of the planktonic foraminifer neogloboquadrina pachyderma sinistral from the mendeleyev ridge in the western arctic ocean have been analyzed for ba ca and 18o the apparent distribution coefficient for n pachyderma sin is estimated at dba 0 22 0 02 a meltwater event is identified at around 11 8 14c kyr bp and is coincident with elevated ba ca ratios the barium enrichment is believed to be the result of enhanced weathering and erosion following glaciation additionally barium may have desorbed from shelf sediments as sea level rose changes in ba ca correlate with the retreat of the laurentide ice sheet and the evolution of the mackenzie river drainage basin therefore maximum ba ca in arctic surface waters at 11 8 ka may be indicative of an increase in the export of freshwater from the arctic to the north atlantic potentially contributing to the onset of the younger dryas this work suggests that ba ca in planktonic foraminifera may be a useful indicator of the timing and processes associated with deglaciation

volcanology and eruptive styles of barren island an active mafic stratovolcano in the andaman sea ne indian ocean barren island india is a relatively little studied little known active volcano in the andaman sea and the northernmost active volcano of the great indonesian arc the volcano is built of prehistoric possibly late pleistocene lava flows dominantly basalt and basaltic andesite with minor andesite intercalated with volcaniclastic deposits tuff breccias and ash beds deposited by pyroclastic falls and surges which are exposed along a roughly circular caldera wall there are indications of a complete phreatomagmatic tephra ring around the exposed base of the volcano a polygenetic cinder cone has existed at the centre of the caldera and produced basalt basaltic andesite aa and blocky aa lava flows as well as tephra during historic eruptions 1787 1832 and three recent eruptions 1991 1994 95 2005 06 the recent aa flows include a toothpaste aa flow with tilted and overturned crustal slabs carried atop an aa core as well as locally developed tumuli like elliptical uplifts having corrugated crusts based on various evidence we infer that it belongs to either the 1991 or the 1994 95 eruptions the volcano has recently 2008 begun yet another eruption so far only of tephra we make significantly different interpretations of several features of the volcano than previous workers this study of the volcanology and eruptive styles of the barren island volcano lays the ground for detailed geochemical isotopic and petrogenetic work and provides clues to what the volcano can be expected to do in the future

mechanism of explosive eruptions of kilauea volcano hawaii a small explosive eruption of kilauea volcano hawaii occurred in may 1924 the eruption was preceded by rapid draining of a lava lake and transfer of a large volume of magma from the summit reservoir to the east rift zone this lowered the magma column which reduced hydrostatic pressure beneath halemaumau and allowed groundwater to flow rapidly into areas of hot rock producing a phreatic eruption a comparison with other events at kilauea shows that the transfer of a large volume of magma out of the summit reservoir is not sufficient to produce a phreatic eruption for example the volume transferred at the beginning of explosive activity in may 1924 was less than the volumes transferred in march 1955 and january february 1960 when no explosive activity occurred likewise draining of a lava lake and deepening of the floor of halemaumau which occurred in may 1922 and august 1923 were not sufficient to produce explosive activity a phreatic eruption of kilauea requires both the transfer of a large volume of magma from the summit reservoir and the rapid removal of magma from near the surface where the surrounding rocks have been heated to a sufficient temperature to produce steam explosions when suddenly contacted by groundwater

coal top detection by conductively guided borehole radar wave imaging for open cut blast hole drilling abstract damage to the top of coal seams caused by incorrect blast stand off distances results in coal losses of up to 10 15 to the australian open cut coal mining operations this is a serious issue to be addressed here we propose to use a new forward looking imaging technique based on the borehole radar technology to predict the coal seam top in real time while drilling blast holes this is achieved by coupling the conventional borehole radar waves on to a steel drill rod to induce a guided wave along the axial drill rod the drill rod ahead of the borehole radar behaves as a forward looking antenna for the guided waves both numerical modelling and field trials simulating a drill rod as an antenna are used to investigate the feasibility of the proposed technique for prediction of the coal top under typical open cut environments numerical modelling demonstrated that conductivity of the overburden is the most important factor affecting our ability to see coal seams ahead of the drill bit the guided borehole radar waves could be used for top coal prediction and a theoretical prediction error less than 10 cm and a forward looking capability of 4 6 m can be achieved field trials at australian open cut coal mines also demonstrated that guided borehole radar waves can be observed and used for prediction of coal top ahead of drill bit during blast hole drilling in resistive open cut environments the average resistivity should be higher than 75 m

on the late pleistocene ocean geochemistry and circulation a box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late pleistocene may have come about the model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric co2 13c and radiocarbon if the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the antarctic and if this increase is combined with a relative increase of the atlantic sector antarctic bottom water aabw versus north atlantic deep water nadw source ratio from 1 3 to about 2 1 then the model predicts several changes that seem to be recorded in the sedimentary record as follows 1 a global redistribution of nutrients and 12c from the intermediate to deep water takes place with the atlantic intermediate water phosphate decreasing 0 6 mole kg 1 and the 13c increasing 0 3 to 0 5 2 the dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 mole kg 1 but the intermediate water oxygen declines only a small amount 3 the decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean 4 the atmospheric co2 decreases by 90 to 110 ppm 5 initially a global increase in calcium carbonate dissolution occurs which is followed by a relaxation toward better preservation than exists for the present ocean in the model in this paper the reduction of nadw by itself does not produce these effects rather the nutrient decrease that does occur is found mostly in north pacific intermediate water and the model atmospheric co2 decrease is only 10 to 30 ppm it is observed that 92 of the atmospheric co2 change takes place according to a 200 year time constant in the model this corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric pco2 thus according to this model the time lag between the nutrient based cause and the atmospheric co2 response is not expected to be particularly large

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

improved accuracy of cross borehole radar velocity models for ice property analysis cross borehole radar xbhr is widely used for the quantification of pore scale liquid water in geologic materials inferred from bulk velocity variations caused by differences in electromagnetic properties between the water and the surrounding material the xbhr can accurately and repeatedly measure variation at depth with sampled material remaining under natural stresses while maintaining good lateral sampling however even small errors in measured radar velocities result in large errors in water content estimates emphasizing the need to quantify and minimize errors we have rigorously assessed the sources of uncertainty in xbhr surveys undertaken in a glaciological setting we have summarized and quantified the three main areas of uncertainty in data collection 1 instrument time drift 2 first break picking and 3 borehole geometry our analysis of field data indicated that contemporary acquisition procedures can produce velocity errors of 3 0 0 0050 m ns equivalent to 0 84 vol water content we have developed several revisions to produce improved data acquisition through enhancement of existing techniques the velocity uncertainties were improved to 1 5 we also found the measurement of borehole diameter during hot water drilling which could hypothetically further reduce the velocity uncertainty to 0 8 equivalent to 0 2 vol water content the need for such precise measurement is clear because an increase in englacial water content from 0 to 0 8 has been proven to triple the strain rate and soften the ice liquid water between ice crystals has also been linked to faster velocities in ice streams and surging events

water mass exchange between the north atlantic and the norwegian sea during the past 28 000 years the greenland iceland and norwegian gin seas are important regulators of heat transport in the northern hemisphere and of ocean atmosphere co2exchange1 5 rapid changes in the circulation of surface and deep waters in this region may induce nonlinear climatic effects and climate instabilities2 3 here we present carbon and oxygen isotope data that provide a record of circulation changes in the gin seas during and at the termination of the last glacial maximum lgm inflow of nutrient depleted waters from the gin seas to form intermediate waters of the north atlantic resulted in nutrient enrichment of north atlantic deep water and consequent enhanced drawdown of atmospheric co2 contributing to the lower atmospheric during the lgm the onset of deglaciation occurred at a time of low salinity in the gin seas and thus of reduced thermohaline circulation although strong thermohaline circulation was later reinitiated in the north atlantic as deglaciation proceeded it cannot therefore have caused the onset of warming similarly we find that rapid changes in thermohaline circulation cannot account for the transient return to a cooler climate during the younger dryas episode

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

magma plumbing system of the 2000 eruption of miyakejima volcano japan during the 2000 eruption at miyakejima volcano two magmas with different compositions erupted successively from different craters magma erupted as spatter from the submarine craters on 27 june is aphyric basaltic andesite 5 vol phenocrysts 51 4 52 2 wt sio2 whereas magma issued as volcanic bombs from the summit caldera on 18 august is plagioclase phyric basalt 20 vol phenocrysts 50 8 51 3 wt sio2 the submarine spatter contains two types of crystal clots a type and a type andesitic type the phenocryst assemblages plagioclase pyroxenes and magnetite and compositions of clinopyroxene in these clots are nearly the same but only a type clots contain ca poor plagioclase an 70 we consider that the a type clots could have crystallized from a more differentiated andesitic magma than the a type clots because feo mgo is not strongly influenced during shallow andesitic differentiation the summit bombs contain only b type basaltic type crystal clots of ca rich plagioclase olivine and clinopyroxene the a type and b type clots have often coexisted in miyakejima lavas of the period 1469 1983 suggesting that the magma storage system consists of independent batches of andesitic and basaltic magmas according to the temporal variations of mineral compositions in crystal clots the andesitic magma became less evolved and the basaltic magma more evolved over the past 500 years we conclude that gradually differentiating basaltic magma has been repeatedly injected into the shallower andesitic magma over this period causing the andesitic magma to become less evolved with time the mineral chemistries in crystal clots of the submarine spatter and 18 august summit bombs of the 2000 eruption fall on the evolution trends of the a type and b type clots respectively suggesting that the shallow andesitic and deeper basaltic magmas existing since 1469 had successively erupted from different craters the 2000 summit collapse occurred due to drainage of the andesitic magma from the shallower chamber as the collapse occurred it may have caused disruption of crustal cumulates which then contaminated the ascending deeper basalt thus porphyritic basaltic magma could erupt alone without mixing with the andesitic magma from the summit caldera the historical magma plumbing system of miyakejima was probably destroyed during the 2000 eruption and a new one may now form

timing of the younger dryas event in east africa from lake level changes the last deglaciation was interrupted by an abrupt cooling event the younger dryas at 11 000 ndash 10 000 yr bp uncalibrated radiocarbon timescale 1 originally recognized in climate records from northwest europe the younger dryas has now been identified in marine and ice core records worldwide2 6 in the tropics a broadly contemporaneous change in climate is recorded by decreases in water levels and increased salinity of lakes7 9 14 indicating a period of arid climate caused by a reduction in ocean to land moisture flux the exact timing of these changes in relation to the younger dryas event in high latitude records has remained unclear however here we present climate records based on analyses of diatom assemblages geochemistry and magnetic mineralogy of radiocarbon dated sequences of laminated lake sediments from lake magadi in the east african rift these records provide a detailed record of climate change in lowland equatorial africa throughout the last deglaciation 12 800 ndash 10 000 14c yr bp we find that lake level and humidity maxima coincide with the most rapid phases of ice melting in the northern hemisphere and that the climate changes including the younger dryas event were synchronous at low and high latitudes thus the effects of abrupt climate change appear to be felt at both high and low latitudes without a significant time lag

a convective model for the weddell polynya abstract mechanisms are considered which may induct the large over 105 km2 area of open water or polynya which frequently occurs within the weddell sea winter sea ice we propose that when surface cooling and ice formation decrease the temperature and increase the salinity of the surface water the latter by salt rejection during ice formation in a preconditioned area static instability with intense vertical mixing can occur the upwelled warm salty deep water can then supply enough heat to melt the ice or prohibit its formation even in the middle of winter a simple two level model is derived to test this theory and is found to agree well with observations the process is found to be irregular due to different times of ice onset from one year to the next and to a lesser extent from variations in surface heating and cooling further it is shown that unless the freshwater input exactly balances the increased salinity from the overturn each year the system will either gain or lose salt yearly an

the two step shape and timing of the last deglaciation in antarctica the two step character of the last deglaciation is well recognized in western europe in greenland and in the north atlantic for example in greenland a gradual temperature decrease started at the bolling b around 14 5 ky bp spanned through the allerod a and was followed by the cold younger dryas yd event which terminated abruptly around 11 5 ky bp recent results suggest that this ba yd sequence may have extended throughout all the northern hemisphere but the evidence of a late transition cooling is still poor for the southern hemisphere here we present a detailed isotopic record analyzed in a new ice core drilled at dome b in east antarctica that fully demonstrates the existence of an antarctic cold reversal acr these results suggest that the two step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences thus the coldest part of the acr which shows a temperature drop about three times weaker than that recorded during the yd in greenland may have preceded the yd antarctica did not experienced abrupt changes and the two warming periods started there before they started in greenland the links between southern and northern hemisphere climates throughout this period are discussed in the light of additional information derived from the antarctic dust record

greenland iceberg emissions constrained by 40ar 39ar hornblende ages implications for ocean climate variability during last deglaciation abstract interhemispheric climate variability during the last glacial period is commonly linked with semi periodic freshwater discharges into the north atlantic from surrounding ice sheets major iceberg emissions from the laurentide icesheet known as heinrich events have been frequently reported but little is known about the past dynamics of the greenland ice sheet gis here we apply 40ar 39ar dating of single hornblende grains 248 analyses derived from core sites in northeast labrador sea and davis strait with the aim to establish the provenance of ice rafted detritus ird during last glacial interglacial transition we associate ird derived from southern greenland with a bimodal paleoproterozoic mean of 1 88 ga and late archean mean of 2 67 ga age distribution which contrasts the dominant paleoproterozoic signature produced by laurentide icesheet icebergs issued from hudson strait younger dryas icebergs melting in the davis strait likewise carry a paleoproterozoic signal but at this site related to glacial weathering in the baffin bay region our results suggest that the gis was a prime source of icebergs melting in the labrador sea during pre bolling allerod younger dryas and early holocene intervals based on the timing of ablation events and the potential impact of greenland meltwater on north atlantic overturn circulation condron and winsor 2012 we surmise that the gis may have been a factor for bipolar ocean climate variability

benthic foraminiferal assemblages in labrador sea sediments relations with deep water mass changes since deglaciation surface sediment samples from the labrador sea and the irminger and iceland basins have been analysed for their benthic foraminiferal content to define the relationship between benthic foraminiferal assemblages and bottom water characteristics on the shelf 301 530 m and the upper slope 1364 and 1980 m the distribution of assemblages is complex and appears related to diversified microhabitats in the deep sea domain 2600 m three main assemblages have been identified the first dominated by epistominella exigua is related to the north east atlantic deep water neadw the second characterized by the co dominance of cibicides wuellerstorfi and e exigua seems to characterize the north west atlantic bottom water nwabw the third marked by the occurrence of nuttalides umbonifera is recorded at depths greater than 3500 m and is associated with the northern extent of the antarctic bottom water aabw microfaunal and isotopic analyses of two cores from the greenland slope 90 013 011 2800 m and

enhancing the detection of small coal structures by seismic diffraction imaging abstract faults are the most important geological structures that need to be detected in any modern underground coal mining project even a fault with a throw of a few metres can create safety issues and lead to costly delays in mine production while seismic surveys are usually successful at locating faults with throws greater than 5 10 m reliable techniques for resolving more subtle faults dykes and other minor features are yet to be developed in seismic data there are two types of seismic energy signatures that can be used for subsurface imaging specular reflections and diffractions specular reflections are created by relatively smooth surfaces between layers of differing impedance contrasts such as at coal rock interfaces specular reflections are used in conventional seismic reflection surveys diffractions are generated by local discontinuities caused by surface roughness faults dykes and fractures in this paper we describe the use of a moving average error filter which along with a process of reflection event flattening for accommodation of dips and undulations of coal seam reflections can be used to effectively extract diffraction signals from post stack reflection seismic data by identifying diffractions small faults and other minor features that are elusive using conventional seismic reflection processing can be detected suggesting that diffraction imaging may be a superior method to seismic reflection imaging both synthetic and real 2d and 3d coal seismic data are used to illustrate the feasibility of diffraction imaging for small fault detection it is demonstrated from synthetic examples that the extracted diffractions can be used to detect faults with a throw of 1 m while a real data example shows that it is possible to detect igneous dykes with widths of just 4 m

analysis of a borehole radar in cross hole mode a theoretical approach to cross hole radar measurements is presented an approximate analytical form for the current distribution on an antenna in a borehole is derived and the theoretical receiving signal of the borehole radar in the cross hole measurement is calculated theory is compared in the time domain with the measured borehole radar signal obtained in a salt deposit the radiation pattern of a borehole radar excited by a pulse is discussed the accuracy of tomographic analysis which is often applied to cross hole radar measurements is strongly governed by this radiation pattern it is found that in practice most borehole radars have a pattern of a lambda 2 dipole antenna however the radiation pattern can be deformed by short pulse excitation loading by the surrounding media and coupling to the logging cable

very long period seismic signals and caldera formation at miyake island japan over a period of roughly 40 days starting on 8 july 2000 a caldera structure 1 7 kilometers in diameter developed by means of gradual depression and expansion of the summit crater at miyake island japan at the same time very long period vlp seismic signals were observed once or twice a day source mechanism analyses of the vlp signals show that the moment tensor solutions are smooth step functions over a time scale of 50 seconds with dominant volumetric change components we developed a model to explain the caldera and the vlp signals in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber by lateral magma outflow this model offers potential for making quantitative estimations of the characteristic physical properties of magma systems

phreatomagmatic eruptions associated with the caldera collapse during the miyakejima 2000 eruption japan abstract the 2000 ad eruption of miyakejima was characterized by a series of phreatomagmatic eruptions from the subsiding caldera six major eruptive events occurred and they can be divided into the first and second periods separated by a 25 day hiatus the phreatomagmatic eruptions produced a total of 2 1010 kg of tephra which mainly comprised fine grained volcanic ash the tephra layers could be divided into six fall units corresponding to the six major eruptive events the grains of the 2000 tephra consisted mainly of accessory fragments derived from the previous edifice juvenile fragments were identified in four major units the angular and blocky shape of the juvenile fragments showed rapid cooling of magma by external water indicating the mechanical mixing of ground water and magma the removal of the load on the aquifer by caldera subsidence and the intrusion of magma into the decompressed aquifer caused a series of phreatomagmatic eruptions from the subsiding caldera the absence of surface water in the subsiding caldera during the eruption showed that groundwater participated in the phreatomagmatic eruptions rising magma along the ring faults intruded into the decompressed aquifer surrounding the caldera and caused phreatomagmatic explosions the 2000 eruption of miyakejima indicated that the fine grained tephra abundant in hydrothermally altered rock fragments is a possible indicator of the phreatomagmatic eruptions in the hydrothermal system during the caldera formation in basaltic volcanoes

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

borehole radar applied to the characterization of hydraulically conductive fracture zones in crystalline rock1 this paper discusses the borehole radar system ramac developed within the framework of the international stripa project which can be used in three different measuring modes single hole reflection cross hole reflection and cross hole tomography the reflection modes basically provide geometrical data on features located at some distance from the borehole in addition the strength of the reflections indicate the contrast in electrical properties single hole reflection data are cylindrically symmetrical with respect to the borehole which means that a unique fracture orientation cannot be obtained a method has been devised where absolute orientation of fracture zones is obtained by combining single hole reflection data from adjacent holes similar methods for the analysis of cross hole reflection data have also been developed and found to be efficient the radar operates in the frequency range 20 60 mhz which gives a resolution of 1 3 m in crystalline rock the investigation range obtained in the stripa granite is approximately 100 m in the single hole mode and 200 300 m in the cross hole model variations in the arrival time and amplitude of the direct wave between transmitter and receiver have been used for cross hole tomographic imaging to yield maps of radar velocity and attenuation the cross hole measurement configuration coupled withmore tomographic inversion has less resolution than the reflection methods but provides better quantitative estimates of the values of measured properties the analysis of the radar data has provided a consistent description of the fracture zones at the stripa cross hole site in agreement with both geological and geophysical observations less

finding eruptive mechanisms through pyroclasts from the current eruption 1984 present at nevado del ruiz volcanic complex colombia abstract the dominant fragmentation mechanisms in the magma involved in a volcanic eruption can be understood from the compositional and textural analysis of the fragments emitted as pyroclasts individual pyroclasts can be juvenile accessory and accidental and detailed analyses of their relative proportions as well as the juvenile clast features can shed light into the fragmentation processes involved in the eruption despite the multiple hundreds eruptive pulses since the nevado del ruiz re activation in 1984 following a quiescence of nearly 100 years such analyses have not been carried out for the ash emissions preceding the recently emplaced plug here four deposits related to the recent emissions were analysed from their pyroclasts the samples correspond to eruptive pulses from the years 1985 1986 1988 and 2012 their characterisation allowed proposing differences between likely juvenile fragments i e representative of involved magma and accessory fragments i e pre existing co magmatic the results indicate that alteration can be used as a criterion to distinguish them although this could not account for syn eruptive hydrothermal alteration of juvenile glass or for the preservation of accessory glass emplaced in glacial conditions this criterion could serve as a foundation to direct fresh glass fragment analyses following this criterion the fresh glass fragments which are assumed to be juvenile fragments are highly vesicular they exhibit spongy and fibrous textures that are related to the predominant vesicle shape their predominance suggests a magmatic fragmentation mechanism while blocky shaped poorly vesicular cracked glass shards suggest a phreato magmatic origin specifically november of 1985 and january of 1986 glassy ashes are primarily highly vesicular suggesting magmatic explosive events by contrast samples from the march of 1988 and may of 2012 events are primarily characterised by low fresh glass content they also exhibit quenched surfaces indicating that the magma water interaction acted as an important factor for triggering the eruptive pulses real time componentry petrography and glass characterisation in fine ash could significantly complement traditional geophysical monitoring and importantly improve the hazard assessments on the civil aviation during the ongoing nevado del ruiz activity

reduced meltwater outflow from the laurentide ice margin during the younger dryas the cause of the younger dryas cold event which interrupted the last deglaciation is still a matter of debate1 a prevalent hypothesis proposed by broecker et al 2 is that the abrupt climate change was driven by a decrease in the rate of north atlantic deep water production triggered by a sudden dilution of north atlantic surface water in response to the diversion of laurentide icesheet melt water from the mississippi drainage system to that of the st lawrence river here we investigate the feasibility of this triggering mechanism by reconstructing sea surface temperature salinity and sea ice cover records for the outlet of the gulf of st lawrence into the north atlantic ocean these reconstructions based on dinoflagellate cyst assemblages3 4 in sediment cores from the region show reduced meltwater runoff low temperatures and extensive sea ice cover during the younger dryas dated here between 10 800 and 10 300 bp meltwater pulses did occur before and after the younger dryas event as early as 11 700 bp during the development of the champlain sea in the st lawrence lowland and afterwards until 10 100 bp at the resolution of our salinity proxy 0 7 the meltwater pulses preceding the younger dryas did not affect sea surface salinity off the shelf break these constraint on the meltwater outflow through the st lawrence drainage system do not support the triggering mechanism of the broecker et al hypothesis2 unless the north atlantic thermohaline circulation is more sensitive to small salinity changes than most models suggest23

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

modeling the water masses of the atlantic ocean at the last glacial maximum 1 we produced gridded monthly sea surface boundary conditions for the atlantic ocean at the last glacial maximum lgm based on the sea surface temperature reconstruction of the glamap project we used an ocean general circulation model ogcm subject to these sea surface boundary conditions and a corresponding wind stress field from an atmospheric general circulation model to study the differences in the distribution of the main water masses between the lgm and the present our global ogcm is characterized by high vertical resolution low vertical diffusion and isopycnal mixing and hence allows for a realistic representation of the hydrology and circulation of the modern atlantic ocean according to a series of lgm experiments with an increasing sea surface salinity anomaly in the weddell sea the ventilated thermocline was colder than today by 2 3 c in the north atlantic ocean and in the experiment with the largest anomaly 1 0 beyond the global anomaly by 4 5 c in the south atlantic ocean its depth was reduced by 50 m on average most notably in the tropics in the north atlantic ocean the outcrop locations of the thermocline isopycnal surfaces migrated southward by 5 10 and the ventilation increased in the south atlantic ocean the mixed layer and thermocline water masses were dominated by cold water originating from drake passage and the import of warm water from the indian ocean was reduced to about 4 sv or 40 of its modern value antarctic intermediate water was colder by 3 4 c and could be traced as far as 10 n the meridional overturning rates of north atlantic deep water nadw and antarctic bottom water aabw in the atlantic ocean were similar to those of the present day experiment 9 10 sv and 4 sv respectively however nadw cooled by 2 5 c and aabw by 1 c aabw was near the freezing point of seawater at the surface and the saltiest water mass in the atlantic ocean even saltier than nadw we show that the differences between the lgm and the present day experiments can be traced back to the changes in the subpolar and interhemispheric sea surface density gradients

shift from magmatic to phreatomagmatic explosions controlled by the lateral evolution of a feeder dike in the suoana kazahaya eruption miyakejima volcano japan abstract explosive phreatomagmatic eruption is one of the most hazardous eruption styles particularly in basaltic systems as the instability of the conduit system can result in a sudden and unexpected shift of eruption style from a mild effusion of lavas to violently explosive activity the geological investigations on the phreatomagmatic activities in the 7th century suoana kazahaya eruption ske of miyakejima reveal that the drop of magmatic overpressure in conduit and the distribution of groundwater controlled the occurrence of phreatomagmatic explosion the dry magmatic eruption in the initial phase of the ske indicates that the positive overpressure of magma in the propagating feeder dike prevents the invasion of external groundwater into the conduit explosive phreatomagmatic eruption occurred at the later phase of the ske from the vents in the higher elevation the drop of magmatic overpressure in the upper part of the feeder dike caused by the downslope propagation of the eruption fissure allowed groundwater inflow to the still hot and molten feeder dikes the limited distribution of phreatomagmatic activities indicated the development of shallow groundwater hosted in the porous pyroclastic deposits within a basin of less permeable older edifice as shifts of eruption style from initial magmatic to later phreatomagmatic explosive eruption style in the top of mafic volcanoes are globally observed in many mafic volcanic systems such as kilauea and mt etna this is probably a far more common eruption mechanism than previously thought and hence it needs to be considered in volcanic hazard scenario descriptions the spatial distributions of phreatomagmatic activities in the ske suggest that the detection of buried caldera structure in a volcanic edifice can indicate a potential site for phreatomagmatic explosion the monitoring of the propagation of eruption fissure and drops of magmatic pressure and flux can indicate the potential of the phreatomagmatic explosion by the invasion of groundwater into the hot conduit

differences among sub orbital time scale events recorded in two high resolution loess sections china during the last deglaciation acquisition of high resolution loess sections allows study of climate change events on sub orbital time scales two high resolution loess section records from china wangguan and shagou located east and west of the liupanshan mountains respectively are compared with the grip record to evaluate climatic changes during the last deglaciation the results show that both sections recorded the younger dryas the heinrich 1 and the bolling and allerod events of the last deglaciation loess records of those events occurred almost simultaneously with those recorded in the grip the characteristics of the climate change events in the two loess sections were quite different it was found that 1 the heinrich 1 event was more obvious in the shagou section than in the wangguan section 2 the bolling and allerod events recorded in the shagou section have more fluctuations than in the wangguan section 3 the younger dryas terminated suddenly in the shagou section whereas in the wangguan section it came to a gradual end and 4 the records show a larger fluctuation range and higher frequency on the millennium scale in the shagou section than in the wangguan section it is suggested that the differences were caused by the effects of latitudinal differences

giant tuff cone and 12 km wide associated caldera at ambrym volcano vanuatu new hebrides arc abstract ambrym in the new hebrides arc has been considered as an effusive basaltic volcano the present paper discusses the general structure of this edifice which consists of a basal shield volcano topped by an exceptionally large tuff cone surrounding a 12 km wide summit caldera dacitic pyroclastic flow deposits are exposed in the lower part of the tuff series they grade upward into composite sequences of bedded surtseyan type hyaloclastites ash flow deposits and fallout tephra which are essentially basaltic in composition in such a way that the tuff cone may be considered as mainly basaltic the relationship between the eruption of pyroclastics and the collapse event precludes a classical model of caldera formation at a basaltic volcano in which quiet subsidence i e kilauea type is the dominant mechanism interpretation of the tuff series implies intervention of external water and suggests both explosive and collapse mechanisms a model of caldera formation which assumes an enlargement of the ring fracture during a first plinian and dacitic then essentially hydrobasaltic eruption is proposed

propagation linkage and interaction of caldera ring faults comparison between analogue experiments and caldera collapse at miyakejima japan in 2000 the formation of ring faults yields important implications for understanding the structural and dynamic evolution of collapse calderas and potentially associated ash flow eruptions caldera collapse occurred in 2000 at miyakejima island japan in response to a lateral intrusion based on geophysical data it is inferred that a set of caldera ring faults was propagating upward to understand the kinematics of ring fault propagation linkage and interac tion we describe new laboratory sand box experiments that were analyzed through digital image correlation dic and post processed using 2d strain analysis the results help us gain a better understanding of the processes occurring during caldera subsidence at miyakejima we show that magma chamber evacuation induces strain localization at the lateral chamber margin in the form of a set of reverse faults that sequentially develops and propagates upwards then a set of normal faults initiates from tension fractures at the surface propagating downwards to link with the reverse faults at depth with increasing amounts of subsidence interaction between the reverse and normal fault segments results in a deactivation of the reverse faults while displacement becomes focused on the outer normal faults modeling results show that the area of faulting and collapse migrates successively outward as peak displace ment transfers from the inner ring faults to later developed outer ring faults the final structural architecture of the faults bounding the subsiding piston like block is hence a consequence of the amount of subsidence in agreement with other caldera structures observed in nature the experimental simulations provide an analogy to the obser vations and seismic records of caldera collapse at miyake jima volcano but are also applicable to caldera collapse in general

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

electromagnetic logging technique based on borehole radar an electromagnetic logging technique based on borehole radar is introduced in this paper the tool consists of one transmitter and two receivers which can be used to cancel the effect of the antenna characteristics by taking the ratio of two receiver signals since receiver signals measured in the time domain can be converted into the frequency domain by fourier transformation the amplitude ratio and the phase difference between two receiver signals in a wide frequency band are obtainable the response of the tool to different formations is investigated and the algorithm that converts the amplitude and the phase information to the conductivity and the relative permittivity of the surrounding medium is given by a three dimensional finite difference time domain the effect of the borehole on measurement and the response of the tool to a formation interface are simulated and analyzed numerically the validity of this technique is confirmed by experiment this technique can be applied to detect physical properties including the conductivity and the relative permittivity of the surrounding medium and the locations of the fractures intersecting the borehole

palaeoecology of a late allerod peat bed at godoy western norway a peat bed found under solifluction deposits on godoya island western norway accumulated during a few decades around 11 000 yr bp at the end of the allerod period of the late weichselian palaeoecological investigations showed a local vegetation succession on wet sand culminating in a mire community dominated by carex nigra periodic flooding brought in sand and silt which decreased as drainage was impeded sufficiently for standing water to develop the surrounding terrestrial vegetation was dominated by salix scrub with some open heath and alpine habitats nearby apart from two aquatic species the 29 insect taxa recorded are characteristic of alpine heaths plant litter under salix scrub and stream sides their remains together with the terrestrial plant macrofossils were washed into the mire from nearby because the fossils are locally derived the environmental reconstructions are of the actual conditions at godoy at ca 11 000 yr bp palaeotemperature estimates from beetles and plants are in agreement the coleopteran estimates mutual climatic range method suggest mean july temperatures of 10 13 c slightly cooler than today 13 5 and january temperatures between 1 and 10 c similar to or much colder than today summer temperature estimates from individual plant taxa indicate that temperatures during the allerod period were similar to today s but estimates from the reconstructed vegetation and timber line positions give estimates up to 3 5 cooler temperatures fell 2 5 7 5 c at the younger dryas this abrupt and severe cooling initiated the solifluction processes on godoya that buried the peat the godoy peat bed and its contained fossils provide a rare glimpse of allerod biota and environments at the local site scale

rapid climate transitions in a coupled ocean atmosphere model recent geochemical data1 2 have challenged the view that rapid climate fluctuations in the north atlantic at the end of the last glacial were caused by the thermohaline circulation of the ocean being switched on or off instead these data suggest that the circulation pattern must have switched between a warm deep mode and a cold shallow mode probably associated with different sites of deep convection3 here i present simulations with a three dimensional ocean model coupled to an idealized atmosphere which show this kind of transition the mechanism for the transition is a rearrangement of convection in the north atlantic triggered by a brief freshwater pulse this results in a drop in sea surface temperature in the north atlantic by up to 5 c within less than 10 years the rate of north atlantic deep water nadw forma tion is the same in the cold climate as in the warm climate but nadw sinks to intermediate depths only while antarctic bottom water pushes north to fill the entire abyssal atlantic

april 2007 collapse of piton de la fournaise a new example of caldera formation collapse calderas are frequent in the evolution of volcanic systems but very few have formed during historical times piton de la fournaise is one of the world s most active basaltic shield volcanoes the caldera collapse which occurred during the april 2007 lateral eruption is one of the few large documented collapse events on this volcano it helps to understand the mode and origin of caldera collapses in basaltic volcanoes field observations gps and seismic data show that the collapse occurred at an early stage of the eruption the cyclic seismic signal suggests a step by step collapse that directly influenced the lateral eruption rate likely the caldera results from the combined effect of i the progressive collapse of the plumbing system above the magma chamber since 2000 and ii the large amount of magma withdrawal during the early stage of the eruption by both a significant intrusion within the edifice and an important emission rate

explosive activity of the summit cone of piton de la fournaise volcano la reunion island a historical and geological review summit explosive activity and collapses that form pit craters and calderas represent major volcanic hazards on a dominantly effusive frequently active volcano like piton de la fournaise only three summit collapse events 1986 2002 2007 have been recorded since the foundation of the piton de la fournaise volcano observatory ovpf in 1979 and two of them 1986 and 2007 were associated with weak phreatic activity at piton de la fournaise the normal explosive activity consists of short lived and mild 20 m high lava fountains which quickly evolve into strombolian activity during the eruptions based on comprehensive literature review and high resolution image analysis of surface outcrops and summit caldera walls we reconstructed the time distribution of recent explosive events phreatomagmatic phreatic and their link with summit collapses and lateral flank effusive eruptions in historical time post 1640 ce we recognise two main clusters of explosive events frequent and violent phreatomagmatic to phreatic explosions occurred during the oldest cluster 1708 1878 and alternated with long lasting periods years to decades of summit effusive activity in contrast scarce and on average weak explosions occurred during the youngest cluster 1897 2012 when discrete and short lived 6 months effusive eruptions represent the main eruptive dynamics historical summit collapses pit craters and caldera all localised at the top of the summit cone were related to voluminous lateral eruptions and were followed by a significant decrease in eruptive rate however magma draining during lateral eruptions was not systematically associated with summit collapses or explosions the long lasting occurrence of magma at very shallow depth below the volcano summit followed by a rapid lateral drainage apparently represents a critical condition favouring magma groundwater interaction to produce explosive activity the prehistoric growth of the piton de la fournaise summit cone results chiefly from long lasting to continuous activity centred below its western side bory crater containing lava lakes high lava fountains long lasting effusive activity lava lakes ash plumes and block ejections were common types of eruptive dynamics in the historical past between 1640 and 1878 in this perspective short lived small volume eruptions and long pauses up to six years during the last century of activity of piton de la fournaise can be considered as a lull despite the high frequency of eruption 1 eruption 9 months on average temporal and spatial variations in recurrence rate and eruptive dynamics of basaltic volcanism such as those recognised at piton de la fournaise should be considered in the formulation of hazard assessments and in the interpretation of precursory patterns

episodes of pit crater collapse documented by seismology at piton de la fournaise calderas are oval fault bounded depressions in volcanic regions the formation of a small analog a summit pit crater has followed a ten month cycle of eruptive activity at piton de la fournaise volcano reunion island indian ocean in 1985 six short episodes of summit seismic activity with shocks indicating shear failures have been followed by eruptions in five cases the eruptions occurred near the base of the summit cone which is at 2 5 km elevation inside the enclos fouque an ancient caldera 7 km in diameter in another instance the summit seismic crisis did not evolve to an eruption but was followed by a seismic crisis 4 km deeper in march 1986 low level activity both at shallow depth beneath the summit and around 4 km depth to the southeast a simultaneous occurrence not previously observed culminated by a summital swarm on march 18 activity resumed its low level and five hours later a small and short lived eruption occurred at mid distance between the summit and the rim of enclos fouque one day later a flank eruption began at 1000 m elevation outside of the enclos 9 km southeast of the summit four days later effusion began near sea level 14 km southeast of the summit the shift of activity from the vent inside to that outside the enclos occurred whilst both shallow summital and deeper flank seismicity were sustained but without notable shallow activity between one vent and the next then the seismic activity which in all five previous instances stopped when the vents opened persisted for ten days increasing in energy release rate activity only consisted of shallow shocks in the summit area whilst eruption was low on the flank 9 km then 14 km away the focal mechanisms are different from all those previously determined they correspond neither to shear failure nor tensile fracturing by fluid overpressure they suggest cracking due to volume increase in a low fluid flow environment which may be consistent with the simultaneous tapping of magma deeper in the edifice a final paroxysmal seismic crisis lasting one and a half days led to the collapse of a 200 m diameter 80 m deep pit crater inside the dolomieu summital caldera on march 29 this crisis released an order of magnitude more energy than previous activity the long period signature of these seismic events indicates low stress drop with respect to source dimensions sources are shallow however rather than directly marking the progressive development of a depression at the surface they appear to correspond to fractures opening above the retreating magma and progressive stoping of a cavity similarities with seismic observations during the last phase of the fernandina galapagos 8 km2 caldera collapse of june 1968 suggest that the same kind of mechanical behaviour occurred with a scaling of three orders of magnitude in seismic moments and in volumes of collapsed blocks between the two cases

understanding volcanic geomorphology from derivatives and wavelet analysis a case study at miyakejima volcano izu islands japan abstract from feature recognition to multiscale analysis the human brain does this computation almost instantaneously but reproducing this process for effective computation is still a challenge although it is a growing field in computational geomorphology there has been only limited investigation of those issues on volcanoes for the present study we investigated miyakejima a volcanic island in the izu archipelago located 200 km south of tokyo city japan the island has experienced numerous quaternary and historical eruptions which have been recorded in details and therefore provide a solid foundation to experiment remote sensing methods and compare the results to existing data in the present study the author examines the use of dem derivatives and wavelet decomposition 5 m dem available from the geographic authority of japan was used it was pre processed to generate grid data with qgis the data was then analyzed with remote sensing techniques and wavelet analysis in envi and matlab results have shown that the combination of elevation with local data range variation and relief mapping as a rgb image composite provides a powerful visual interpretation tool but the feature separation remains a subjective analysis provided a more appropriate dataset for computer based analysis and information extraction and understanding of topographic features at different scales in order to confirm the usefulness of these topographic derivatives the results were compared to known geological features and it was found to be in accordance with the data provided by geological topographic maps and field research at miyakejima the protocol presented in the discussion can therefore be re used at other volcanoes worldwide where less information is available on past eruption and geology in order to explain the volcanic geomorphology

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

a dike intrusion model in and around miyakejima niijima and kozushima in 2000 from june 26 2000 an earthquake swarm started in miyakejima about 50 km south off honshu central japan eruptions of miyakejima and five large earthquakes with magnitudes 6 0 and above occurred for the following 2 months together with a large number of smaller earthquakes over 100 000 in this study we focused on spatio temporal crustal deformation observed at gps stations in this area in order to explain the seismicity and the crustal deformation we considered a dike intrusion model placed between miyakejima and kozushima then we attempted to obtain spatio temporal distributions the amount of the dike intrusion deflation beneath miyakejima and fault slips of the seven large events by geodetic data inversion for this purpose we divided the time series of gps data from june 12 to august 27 into 10 periods which are related to significant events in order to find location depth strike and dip of the dike plane and a depth of deflation beneath miyakejima we used the monte carlo method and tested 10 000 models for each period as a result we estimated that the total amount of the dike intrusion and the deflation beneath miyakejima reached about 1 1 10 9 and 5 4 10 8 m 3 respectively the maximum amount of the dike intrusion and the deflation beneath miyakejima reached over 3 5 10 8 m 3 during the period from july 20 to july 28 2000 and over 1 7 10 8 m 3 during the period from june 15 to june 28 2000 respectively temporal change of the amount of the dike intrusion corresponds well to that of the deflation beneath miyakejima until the middle of july however since large amount of the dike intrusion from july 20 to 28 did not correspond to that of the deflation beneath miyakejima we deduced that the magma source changed from miyakejima to kozushima and the magma might come from sub crustal magma pockets from the middle of july if we assume the open crack associated with the dike intrusion and the deflation beneath miyakejima are filled with magma with a density of 2500 kg m 3 the mass would be about 2 75 10 9 and 1 35 10 9 tons respectively we deduced that at least 1 4 10 9 tons of magma came from sub crustal magma pockets d 2002 elsevier science b v all rights reserved

rapid late glacial atmospheric co2 changes reconstructed from the stomatal density record of fossil leaves the younger dryas stadial 11 000 10 000 yr bp was an abrupt return to a glacial climate during the termination of the last glaciation we have reconstructed atmospheric co2 concentrations from a high resolution sequence of fossil salix herbacea leaves through this climatic oscillation from krakenes western norway using the relationship between leaf stomatal density and atmospheric co2 concentration high allerod co2 values median 273 ppmv decreased rapidly during 130 200 14c years of the late allerod to ca 210 ppmv at the start of the younger dryas they then increased steadily through the younger dryas reaching typical interglacial values once more ca 275 ppmv in the holocene the rapid late allerod decrease in co2 concentration preceded the younger dryas temperature drop possibly by several decades this striking pattern of changes has not so far been recorded unambiguously in temporally coarse measurements of atmospheric co2 from ice cores our observed late glacial co2 changes have implications for global modelling of the ocean atmosphere biosphere over the last glacial interglacial transition

seeing coal seam top ahead of the drill bit through seismic while drilling blast damage to the tops of coal seams due to incorrect blast standoff distances is a serious issue costing the industry in australia about one open cut mine for every ten operating mines the current approach for mapping coal seam tops is through drilling and pierce point logging to provide appropriate depth control with accuracy of 0 2 m for blast hole drilling it is typically necessary to drill deep reconnaissance boreholes on a 50 m x 50 m grid well in advance of overburden removal pierce point mapping is expensive and can be inaccurate particularly when the seam is disturbed by rolls faults and other obstacles numerical modelling and prototype field testing are used in this paper to demonstrate the feasibility of two seismic while drillingbased approaches for predicting the approach to the top of coal during blast hole drilling i reverse walk away vertical seismic profiling recording in which the drill bit vibration provides the source signal and the geophones are planted on the surface near the drill rig and ii in seam seismic recording in which channel waves driven by the coupling to the coal of the seismic signal emitted by the approaching drill bit are guided by the seam to geophones located within the seam in nearby or remote boreholes

global nature of the younger dryas cooling event inferred from oxygen isotope data from sulu sea cores the younger dryas an approximately 1 000 year long return to near glacial conditions interrupted the glacial holocene climate transition during which most of the northern hemisphere ice sheets melted evidence for the younger dryas event has been found mainly in sediments from the north atlantic ocean and northwest europe and this has led to the idea that the event was caused by an injection of meltwater into the north atlantic ocean1 3 this model however has been recently questioned in the light of coral reef data on the rate of sea level changes during this transition4 here we present high resolution oxygen isotope records from benthic and planktonic foraminifera from two radiocarbon dated cores in the sulu sea showing that the younger dry as occurred synchronously in the surface and deep waters of the sulu sea and the northern atlantic ocean by combining our results with other palaeoclimate data we suggest that the younger dry as event was a global phenomenon and we believe it to have been caused by low atmospheric co2concentrations

from structure to erosion controlled subsiding calderas evidence thresholds and mechanics collapse calderas evolve by increasing their depth diameter ratio to properly characterize caldera evolution a structural s d ratio between structural subsidence and ring fault diameter ss ds and a topographic s d ratio between topographic caldera depth and topographic caldera width st dt are considered we review the evolution of the a d 2000 miyakejima caldera with two concentric ring faults at earlier collapsing stages and erosion of its wall accumulating debris on the floor at later collapsing stages while st dt and ss ds show a similar increase at initial stages when ss ds 0 33 the ss ds becomes significantly different from st dt while continuous caldera subsidence monotonically increases ss ds the erosion of the wall and the filling of the floor decrease st dt this evolution finds close similarities with recent caldera collapses of krakatau 1883 katmai 1912 fernandina 1968 tolbachik 1975 1976 pinatubo 1991 and dolomieu 2007 analog experiments mimic the observed variation evolving from a depression controlled by the activity of the double ring faults to that controlled by the erosion of the wall and sedimentation at the floor these natural and modeling results show that the control on the shape of mature calderas ss ds 0 07 and approaching ss ds 0 3 0 4 passes from a mainly structural to a mainly erosional control both st dt and ss ds are needed to describe the evolution of a collapse and the processes accompanying it evaluating st dt and ss ds allows proper description of the precise evolutionary stage of a caldera and of the relative importance of the structural and erosional processes and allows making semiquantitative comparisons between evolutionary stages

carbon and oxygen isotopic records of benthic foraminifera from the northeast indian ocean implications on glacial interglacial atmospheric co2 changes abstract we present here continuous records of 18o and 13c in benthic foraminifera extending well into the last ice age in two piston cores from the andaman sea sill depth 1 3 km and the bay of bengal 3 km these show that contrary to the previous reports the glacial to interglacial shift in 13c at mid depths in the northeast indian ocean was indistinguishable from the mean oceanic 13c change negating a more vigorous renewal of intermediate waters globally during the glacial time the corresponding 13c shift in deep waters is estimated to be about 50 larger than that reported previously jointly with some recent data from the pacific our results indicate a modest glacial holocene shift in the intermediate to deep water chemical gradients in the indo pacific as a whole implying that it was perhaps not the dominant mechanism for the glacial interglacial atmospheric co2 variations also in conflict with previous work our measurements suggest significant cooling of both the intermediate and deep waters during the glacial time the high resolution records from the andaman sea help reconstruct paleoenvironmental changes at intermediate depths during the last deglaciation rapid increases in 13c occurring in two stages during the early deglaciation appear to have been caused by the fluctuations in the north atlantic deep water production a negative excursion in 13c during the mid deglaciation is ascribed to enhanced nutrient regeneration at mid depths associated with the greatly intensified summer monsoon around the pleistocene holocene boundary

caldera collapse during the 2000 eruption of miyakejima volcano japan a collapsed caldera 1 6 km in diameter and 450 m in depth was formed at the summit of miyakejima volcano during the 2000 eruption the collapsed caldera appeared on 8 july with a minor phreatic eruption 12 days after seismic activity and magma intrusion occurred northwest of the volcano growth of the caldera took from 8 july to the middle of august with seismic swarms associated with the continuous intrusion of magma northwest of the volcano the growth rate of the caldera was about 1 4 107 m3 day and the final volume of the collapsed caldera was about 6 108 m3 major phreatomagmatic eruptions produced a total of about 1 6 1010 kg 1 1 107 m3 of volcanic ash after caldera growth the caldera structure and the nature of the eruptive materials of the first collapse on 8 july suggest that the surface subsidence was caused by the upward migration of a steam filled cavity with stoping of the roof rock above the magma reservoir the diameter of the stoping column was estimated to be 600 700 m from circumferential faults that developed in the caldera floor and the collapse of the caldera wall enlarged the diameter of the caldera to 1 6 km the total volume of the caldera and the horizontal diameter of the stoping column gave a subsidence of the caldera floor of 1 6 2 1 km

long distance magma transport from arc volcanoes inferred from the submarine eruptive fissures offshore izu oshima volcano izu bonin arc abstract long distance lateral magma transport away from volcanic centers in island arcs is emerging as a common phenomenon where the regional stress regime is favorable it should also be recognized as an important factor in the construction and growth of island arcs and a potential trigger for devastating eruptions in this contribution we report on recent investigations into the magma dynamics of izu oshima volcano an active basaltic volcano with an extensive fissure system izu oshima is flanked by numerous subparallel nw se trending submarine ridges extending up to 22 km to the nw and the se from the central vent during a recent submersible survey we have identified that these ridges are fissures which erupted basaltic spatter and lava flows furthermore lavas are petrographically similar along each ridge while there are noticeable differences between ridges the subparallel ridges are observed to transect a series of seamounts the izu tobu monogenetic volcanoes which are dispersed across this area of the rear arc however there are consistent petrographic and chemical differences between these seamounts and the ridges indicating that they have different magma sources yet they are essentially bounding each other in dive tracks the most appropriate scenario for their development is one where the izu tobu volcanoes are fed by an in situ underlying source while the nw se ridges are fed by lateral magma transport from izu oshima magma erupted from each ridge is of a consistent geochemistry along its length but has experienced crystal fractionation and some plagioclase accumulation compositions of the ridges are also very similar to lavas from the subaerial cones that can be traced down the flanks of izu oshima this implies that pairs of subaerial cones and submarine ridges represent the locus of magma transport events away from the storage system beneath izu oshima hence magma from this crustal reservoir moved upward to feed the on edifice cones as well as laterally to supply submarine fissures and dykes to a distance of 22 km

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

impact of end member mixing on depth distributions of δ13c cadmium and nutrients in the n atlantic ocean abstract the po 4 13 c and cd depth distributions measured in the n atlantic ocean during recent geotraces and clivar cruises are a result of biological and circulation processes with in situ uptake and remineralization of organic matter dominating in the upper 300 m and mixing of water masses dominating in the thermocline and deep sea the observed slopes of the no 3 po 4 preindustrial 13 c po 4 and by analogy cd po 4 along isopycnals deviate significantly from that expected from redfield in the thermocline and deep sea and in each case the observed slope is similar to the slopes of the end member water masses being mixed the depth increase in the cd po 4 slope resulting from end member mixing explains the observed kink at 1 m po 4 in the cd po 4 relationship in the n atlantic the observation that the po 4 preindustrial 13 c cd relationship in the modern n atlantic is heavily influenced by end member mixing throughout most of the water column complicates the use of 13 c and cd as proxies of the paleocean s nutrient distribution because changes in the po 4 13 c cd composition of locally and remotely produced end members water masses would change the po 4 13 c and cd depth distributions in the paleo n atlantic ocean

evidence for warm wet heinrich events in florida analyses of pollen and plant macrofossils from a new core spanning the past 60 000 years from lake tulane florida show a strong antiphase relationship in temperature between florida and the north atlantic region during the pleistocene oak scrub and prairie phases were coeval with long intense dansgaard oeschger interstadials warm periods that initiated bond cycles pine phases were coeval with the north atlantic long stadials cold periods that ended bond cycles and were terminated by heinrich events lake levels were higher during pine phases and climate was wetter however climate in florida was also warmer during these phases which were cold periods in the north atlantic perhaps diminution of thermohaline circulation before and during heinrich events reduced northward heat transport and retained warmth in the subtropical atlantic and gulf of mexico

submarine flank eruption preceding caldera subsidence during the 2000 eruption of miyakejima volcano japan during the early part of a seismic swarm preceding eruption and caldera formation at miyakejima volcano discoloured sea surfaces were observed 1 5 km off the western coast of miyakejima on 27 june 2000 a later survey of the area using a multi beam side scan sonar and a remotely operated small submarine revealed four craters of 20 30 m diameter aligned east west in a 100 10 30 m area on the seafloor with hot water at 140 c being released from one of the centres each crater consists of submarine spatter overlain in part by scoria lapilli dredged spatter from the craters was fresh and there was no evidence of activity of marine organisms on the spatter surface indicating that the discoloured sea surface resulted from magmatic eruption on the seafloor this eruption occurred when a westward propagating seismic swarm initiated beneath miyakejima s summit passed through the area finding new magma on the seafloor demonstrates that this seismic swarm was associated with intruding magma moving outward from beneath miyakejima submarine spatter shows flattened shapes with a brittle crust formed by cooling in water and its composition is aphyric andesite of 54 wt sio2 the spatter is similar in whole rock and mineral composition to spatter erupted in 1983 however the wide range of cl in melt inclusions in plagioclase of the 27 june submarine spatter shows that it is not simply a remnant of the 1983 magma which has only high cl melt inclusions in plagioclase the mixed character of melt inclusions suggests involvement of a magma with low cl melt inclusions the magma erupted explosively on 18 august from miyakejima s summit considered as the second juvenile magma in this eruption contains low cl melt inclusions in plagioclase based on these observations and the eruption sequence we present the following model 1 a shallow magma chamber was filled with a remnant of 1983 magma that had evolved to a composition of 54 55 wt sio2 2 injection of the 18 august magma into this chamber generated a mixed magma having a wide range of cl in melt inclusions contained plagioclase the magma mixing might have occurred shortly before the submarine eruption and could have been a trigger for the initiation of the removal of magma from the chamber as an extensive dyke which eventually led to caldera subsidence

shift and rotation of composition trends by magma mixing 1983 eruption at miyake jima volcano japan levels of ascent of the fountain in the host andesite magma analysis of compositional zoning in titanomagnetite crystals revealed that the eruption of the 1983 magmas was initiated soon after the replenishment of the basaltic magma in the 1kbar magma chamber

exploring the interior of salt domes from boreholes presently salt deposits are used for storage of energy from liquid or gaseous carrier materials another application being considered is the storage of radioactive material in order to avoid possible future environmental risk extremely high security has to be guaranteed in advance for a long period therefore a very precise exploration is absolutely necessary exploration methods already known which are applicable during and after drilling of test holes help in the recognition of structures in the salt only in the close vicinity of the holes radiowave electromagnetic methods developed for routine measurements in salt mines provide a penetration of some hundred meters appropriate well logging equipment has been designed here for measurements from surface boreholes discontinuities around one borehole in the salt can be detected through the electromagnetic reflection method when measuring between two boreholes additional reflecting zones can be detected and attenuation of directly pathed waves can point out material with greater absorption properties between the holes additional attempts to use acoustic waves of nearly the same wavelength proved that it is possible to recognize the direction of signals arriving at the receiver and allow separation of p and s waves instrumentation as well as recent results are reported

evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate