calculated volumes of individual shield volcanoes at the young end of the hawaiian ridge abstract high resolution multibeam bathymetry and a digital elevation model of the hawaiian islands are used to calculate the volumes of individual shield volcanoes and island complexes niihau kauai oahu the maui nui complex and hawaii taking into account subsidence of the pacific plate under the load of the hawaiian ridge our calculated volume for the island of hawaii and its submarine extent 213 103 km3 is nearly twice the previous estimate 113 103 km3 due primarily to crustal subsidence that had not been accounted for in the earlier work the volcanoes that make up the island of hawaii mahukona kohala mauna kea hualalai mauna loa kilauea and loihi are generally considered to have been formed within the past million years and our revised volume for the island indicates that magma supply rates are greater than previously estimated 0 21 km3 yr as opposed to 0 1 km3 yr this result also shows that compared with rates calculated for the hawaiian islands 0 6 ma 0 095 km3 yr the hawaiian ridge 0 45 ma 0 017 km3 yr and the emperor seamounts 45 80 ma 0 010 km3 yr magma supply rates have increased dramatically to build the island of hawaii

pyrometamorphic processes at the magma hydrothermal system interface of active volcanoes evidence from buchite ejecta of stromboli aeolian islands italy pyrometamorphic ejecta erupted during recent paroxysmal explosions and hydrothermally altered volcanic and subvolcanic rocks from stromboli volcano aeolian islands italy were studied by combined polarizing microscopy electron microprobe scanning electron microscope x ray diffraction transmission electron microscope and whole rock inductively coupled plasma optical emission spectrometry mass spectrometry analysis the pyrometamorphic ejecta are compositionally heterogeneous at the macroand micro scale and are classified as buchites that is glass coupled with a high temperature low pressure modal mineralogy three distinct facies i e cordierite plagioclase mullite plagioclase palisade and tridymite clinopyroxene are recognized among the buchites whose bulk rock chemistry is compatible with aluminousto silica rich protoliths abundant mineral growth e g plagioclase palisades and clinopyroxene coronae occurs at the contact between the ejecta and the crystal rich host shoshonitic basalt which typically coats the pyrometamorphic blocks mineral constraints pseudoporphyritic microstructures plagioclase relict phenocrysts and major and trace element compositions strongly support the origin of the buchite ejecta as hydrothermally altered rocks from thevancori edifice a period of activity spanning 410 kyr which underwent high temperature low pressure contact metamorphism in the uppermost magmatic system of an active island arc volcano such as stromboli volcanic and subvolcanic rocks usually undergo alteration processes induced by acid sulphate hydrothermal systems the circulation of acidic fluids results in leaching of the stromboli rocks in the upper part of the volcano edifice and depending on the ph temperature and exposure time to the hydrothermal fluids production of different alteration facies the hydrothermally altered stromboli rocks show facies consistent with argillic to silicic alteration containing abundant hydrous sulphate and hydroxy sulphate minerals such as the alunite group minerals hexahydrite millosevichite pickeringite and kieserite the hydrothermally altered wall rocks heated by contact with the basaltic magma of the feeder dyke system of stromboli can easily undergo pyrometamorphic processes inducing partial melting and subsolidus crystallization of the volcanic protoliths this results in the development of buchite rocks at the magma hydrothermal system interface

tectonic controls on the yamanlar volcano and yuntdagi volcanic region western turkey implications for an incremental deformation abstract over the past ten years it has been proposed that the western part of the menderes massif was strongly structurally controlled by the izmir balikesir transfer zone ibtz yamanlar volcano is a key area for understanding the deformation of miocene volcanoes in western turkey because of its progressive extensional tectonics structural analysis provides that this volcano has undergone the incremental tectonic controls in western turkey since early miocene the volcano experienced deformation and erosional processes associated with activity of intense tectonic regime that resulted in the dissection of the southern flank of the volcano mostly by ne sw striking oblique and strike slip faults together with cross cutting faults during and after miocene period the orientation of volcanic domes dykes and intrusive bodies indicates successive and reactive tectonic phases that caused incremental complex movements of numerous fault blocks during the destruction area of the yamanlar volcano structural data documents that the region around izmir bay and yuntdagi volcanic complex is prevailed by far more than three deformation phases cross faults do not reflect to the ne sw trending transtensional deformation thereafter early middle miocene for just the area of the yuntdagi volcanic system the nearly e w oriented faults are inferred to be the most likely cause of the destruction of both the yamanlar and dumanlidag volcanoes coincident with the last stage of the deformation phases the region experienced this study proposed that the western part of the mmcc was affected by different deformational phases instead of ibtz resulting in different stage magma ascents i early miocene transtensional tectonic ii middle miocene extensional tectonic related to slab retreat and iii late miocene tectonic block rotation

crustal kinematics and deep structure of the northern rhine graben germany surface and subsurface geological data unpublished information gleaned from industrial seismic surveys and results from a deep reflection seismic profile across the tertiary northern rhine graben indicate that crustal extension in excess of 6 km was achieved by asymmetric detachment of the upper crust at a depth of about 15 km comparison of a simple geometric kinematic cross sectional model and its depth extrapolation with the dekorp 9 n deep crustal reflection data suggests that extension below the graben was achieved by slip along a gently westward dipping shear zone which truncated and offset lower crustal planar fabrics and which continues into the uppermost mantle the planar lower crustal reflectors probably originated mainly during late variscan permocarboniferous crustal extension and or magmatic underplating

tectonic evolution of the gediz graben field evidence for an episodic two stage extension in western turkey western turkey is one of the most spectacular regions of widespread active continental extension in the world the most prominent structures of this region are e w trending grabens e g gediz and buyuk menderes grabens and intervening horsts exposing the menderes massif this paper documents the result of a recent field campaign field geological mapping and structural analysis along the southern margin of the modern gediz graben of pliocene 5 ma age this work provides field evidence that the presently low angle ductile brittle detachment fault is cut and displaced by the high angle graben bounding normal faults with total displacement exceeding 2 0 km the evolution of the n s extension along the gediz graben occurred during two episodes each characterized by a distinct structural styles 1 rapid exhumation of menderes massif in the footwall of low angle normal fault core complex mode during the miocene 2 late stretching of crust producing e w grabens along high angle normal faults rift mode during pliocene quaternary times separated by a short time gap the later phase is characterized by the deposition of now nearly horizontal sediments of pliocene age in the hanging walls of the high angle normal faults and present day graben floor sediments the evolution of extension is at variance with orogenic collapse and or back arc extension followed by the combined effect of tectonic escape and subduction rollback processes along the aegean cyprean subduction zone consequently it is misleading to describe the miocene sediments exhumed on shoulders of the gediz graben as simple graben fill

a deep reflection seismic line across the northern rhine graben abstract two reflection seismic lines across the tertiary rhine graben in central europe were recorded in 1988 as a joint venture of the french ecors and the german dekorp deep seismic reflection programs in this paper the line across the northern graben is presented the main results are the asymmetry of the graben as documented by the sedimentary fill is accompanied by asymmetric features throughout the entire deep crystalline crust a thin 3 7 s twt reflective lower crust in the east a thick 5 5 s twt relatively transparent lower crust in the west total crustal thicknesses of 8 7 s twt in the east vs 10 5 s twt in the west provided a laterally homogeneous crust existed prior to rifting significant differences in upper and lower crustal thinning must be postulated extension occurred along localized shear zones that are located in the upper crust and at the crust mantle boundary the entire lower crustal layer acts as a decoupling zone

an active bivergent rolling hinge detachment system central menderes metamorphic core complex in western turkey two symmetrically arranged detachment systems delimit the central menderes metamorphic core complex and define a bivergent continental breakaway zone in the anatolide belt of western turkey structural analysis and apatite fission track thermochronology show that a large east trending syncline within the alpine nappe stack in the central part of the orogen is related to late miocene early pliocene to recent core complex formation the syncline formed as a result of two opposite facing rolling hinges in the footwalls of each of the two detachments back rotation of the syncline limbs suggests that the detachments rotated from an initial dip of 408 608 to a currently shallow orientation of 08 208

isotopic evidence for a transition from subduction to slab tear related volcanism in western anatolia turkey abstract volcanic rocks in western turkey show age progressive magmatism migrating from northeast to southwest that reflects a southward shift of the aegean subduction zone during the miocene slab segmentation during this period of trench roll back is thought to have imposed source region heterogeneity trending northwest to southeast in this study we present new sr nd pb and o isotopic analyses from the miocene volcanic rocks of the usak gure basin and compare these to previously published data the data demonstrate a change from subduction related sources around the menderes core complex to more asthenospheric sources in the afyon region isotopic compositions sr nd pb of volcanic rocks from the demirci and selendi basins to the west and the afyon volcanic area to the east indicate minimal upper crustal contamination the most primitive lavas also reveal increasing k contents from west the ne sw trending basins to east afyon region it is suggested that the composition of the western anatolian volcanic rocks change from orogenic with lithospheric mantle sources associated to denudation of the menderes massif core complex mmcc to anorogenic with asthenospheric mantle sources in the vicinity of the kirka afyon isparta kai volcanic province with time from early miocene to quaternary there is no asthenospheric contribution during the late miocene onwards in the eastern margin of the mmcc while the asthenospheric upwelling occurred only in a small area beneath the exhuming core complex we interpret the usak gure basin to reflect a structural boundary showing a transition from a subduction influenced metasomatized mantle source to asthenospheric mantle source volcanism driven by slab tearing between the hellenic and cyprus slab segments the usak mugla transfer zone umtz most likely corresponds to slab tear related westernmost faults that were induced by initiation of slab segmentation processes following the late miocene circa 11 ma and possibly since the early miocene

gravity interpretation along seismic reflection profile dekorp 9 n northern rhine graben a 2 d gravity model incorporating geophysical and geological data is presented for a 110 km long transect across the northern rhine graben coinciding with the 92 km long dekorp 9 n seismic reflection profile the upper rhine graben is marked by a prominent nne striking negative anomaly of 30 40 mgal on bouguer gravity maps of sw germany surface geological contacts borehole data and the seismic reflection profile provide boundary constraints during forward modelling short wavelength 5 10 km gravity features can be correlated with geologic structures in the upper few km at deeper levels the model reflects the asymmetry visible in the seismic profile a thicker mostly transparent lower crust in the west and a thinner reflective lower crust in the east from west to east moho depth changes from 31 to 26 28 km the entire 40 mgal minimum can be accounted for by the 2 3 km of light sedimentary fdl in the graben which masks the gravitational effects of the elevated moho the thickened lower crust in the west partly compensates for the mass deficit from the depressed moho a further compensating feature is a relatively low density contrast at the crust mantle boundary of 0 25 g cm 3 the variscan must displays heterogeneity along the profile which cuts at an angle across the strike of variscan structures the asymmetry of the integrated crustal model both at the surface and at depth suggests an asymmetric mechanism of rift development

growth destruction and volcanic facies architecture of three volcanic centres in the miocene usak gure basin western turkey subaqueous subaerial volcanism in a lacustrine setting abstract early to mid miocene extension in western anatolia related to plate tectonic motions resulted in the development of a number of normal fault bounded sedimentary basins as well as different styles and compositions of volcanic activity the usak and gure basins accumulated a thick fluvio lacustrine fill in which three distinct volcanic edifices elmadag itecektepe and beydagi and their deposits can overlap with each other and with the sediments produced by the background sedimentation in addition complete facies architectures of small volume monogenetic volcanoes have been recognised in association with the three large complex polygenetic volcanoes providing a complex mixed siliciclastic and volcaniclastic basin infill in the respective basins where volcanism took place all three volcanic centres display a complex succession of effusive and explosive volcanisms and their reworked deposits with abundant evidences of magma water interaction such as peperites for non explosive magma water interaction with the lacustrine water saturated sediment and standing water body in a large alkaline lake during the constructive phase proximal successions of pyroclastic flows pyroclastic falls and rarely surge deposits are associated with distally emplaced debris flow deposits sometimes of mixed volcanogenic and terrestrial origins and are interbedded with lacustrine sediments of the inay group all three volcanic centres then experienced a phase of volcano growth and degradation between 17 and 15 ma ago most likely related to a combination of tectonic movements on ne sw trending basement faults which triggered multiple flank collapses and volcanic debris avalanches elmadag and voluminous ignimbrite eruptions that triggered caldera formation itecektepe and beydagi volcanic centres lacustrine conditions persisted during the destruction and post destruction stages of the volcano s evolution as evidenced by indications of magma water interactions within the central collapse structures which also contain uplifted basement metamorphic rocks now exhumed in their eroded cores

progress in birps deep seismic reflection profiling around the british isles abstract the results of 4000 km of new birps profiles are briefly outlined as an introduction to other birps papers in this volume highlights of these profiles include the tracing for 900 km of a reflection pattern in the lower crust associated with the lapetus suture and the observation of more than 20 separate reflections from the mantle while progress in solving the problem of deep water multiples has enabled the joining of the continental and oceanic moho reflections off sw england developments in old interpretational problems are reviewed and the new problem of dating reflections is mentioned

petrogenesis and 40ar 39ar geochronology of the volcanic rocks of the usak gure basin western turkiye abstract in spite of much research over the past 30 years the dynamic evolution origin of the volcanism and geometrical stratigraphical relations of the ne sw trending basins in western anatolia are poorly understood the usak gure basin is one of the prominent ne sw trending basins developed on the northern part of the menderes massif core complex three distinct volcanic successions are found in the usak gure basin 1 the beydagi volcanic unit composed of shoshonite latites and rhyolitic lavas followed by dacitic and andesitic pyroclastic deposits 2 the payamtepe volcanic unit composed of potassic intermediate composition lavas latites and trachytes and 3 the karaagac dikes composed of andesite and latite the beydagi volcanic unit occurs in three different ne sw trending volcanic centers beydagi itecektepe and elmadag calderas from southwest to northeast respectively the oldest radiometric ages for the beydagi volcanic unit are from the elmadag volcanic center in the north and range from 17 to 16 ma the data indicate that volcanism was active during the latest early miocene the youngest radiometric age for the beydagi volcanic unit is obtained from the beydagi caldera located 12 ma in the south the data indicate that beydagi volcanism was active in the late middle miocene and migrated from north to south with time 40ar 39ar ages of the payamtepe volcanic unit are restricted to a short period between 16 0 and 15 9 ma volcanic rocks of the usak gure basin are characterized by strong enrichment in lile and lree and depletions of nb ta and ti on morb normalized multi element diagrams geochemical features of the volcanic rocks suggest that they experienced mixing processes between mafic and felsic end members and also fractional crystallization of dominantly plagioclase and pyroxenes from mixed magma compositions crustal contributions to the magma sources may also have occurred during magmatic evolution these processes have resulted in scattered major and trace element variations with respect to increasing silica contents geochemical features of the most mafic samples agree with the results of previous studies from other volcanic areas in western anatolia suggesting that the volcanic rocks in the region were derived from a mainly lithospheric mantle source that had been heterogeneously metasomatized by previous subduction events during convergence between the african and eurasia plates the volcanic activity in the region which developed synchronously with the formation of the menderes massif core complex is best explained by delamination of lithospheric mantle slices that were heterogeneously enriched by previous subduction related processes

controls on accumulation of a volcaniclastic fan ruapehu composite volcano new zealand the whangaehu fan is the youngest sedimentary component on the eastern ring plain surrounding ruapehu volcano fan history comprises constructional 830 200 years bp and dissectional 200 years bp phases the constructional phase includes four aggradational periods associated with both syneruptive and inter eruptive behavior all four aggradational periods began when deposition by large lahars changed flow conditions on the fan from channelized to unchannelized subsequent behavior was a function of the rate of sediment influx to the fan the rate of sediment influx in turn was controlled by frequency and magnitude of volcanic eruptions short term climate change and the amount of sediment stored on the volcano flanks fanwide aggradation occurred when rates of sediment influx and deposition on the fan were high enough to maintain unchannelized flow conditions on the fan surface maintenance of an undissected surface required sedimentation from frequent and large lahars that prevented major dissection between events these conditions were best met during major eruptive episodes when high frequency and magnitude eruptions blanketed the volcano flanks with tephra and rates of lahar initiation were high during major eruptive episodes volcanism is the primary control on sedimentation climatic variations do not influence sediment accumulation local aggradation occurred when lahars were too small to maintain unchannelized flow across the entire fan in this case only the major channel system received much sediment following the deposition from the initial lahar this localized aggradation occurred if 1 the sediment reservoir on the flank was large enough for floods to bulk into debris flows and 2 sedimentation events were frequent enough to maintain sediment supply to only some parts of the fan these conditions were met during both minor eruptive and inter eruptive episodes in both cases a large sediment reservoir remained on the volcano flanks from previous major eruptive intervals periods of increased storm activity produced floods that bulked to relatively small debris flows when the sediment reservoir was depleted the fan entered the present dissectional phase syneruptive and noneruptive lahars are mostly channelized and sediment bypasses the fan fan deposits are rapidly reworked this is the present case at ruapehu even though the volcano is in a minor eruptive episode and the climate favors generation of intense storm floods

crustal evolution of the rhinegraben area 1 exploring the lower crust in the rhinegraben rift by unified geophysical experiments abstract unified geophysical investigations of the lithosphere in the rhinegraben rift system have revealed new details of the lower crust and its role in the rifting process the new findings allow an assessment of the compatibility of four different geophysical notions and properties of the lower crust 1 1 the lower crust as the layer beneath the conrad discontinuity with a p wave velocity of about 6 5 km s or greater refraction seismics 2 2 the laminated band of reflections as seen in the near vertical reflection seismic experiments in many parts of the continents 3 3 the ductile part of the crust below the brittle ductile transition devoid of earthquakes in seismically active regions 4 4 the electrical conductivity of the lower crust indicative of dry or wet conditions or still unknown conduction phenomena in the rhinegraben area the lamination of the lower crust serves as an outstanding marker of deep tectonic activity during the rifting process in which the crust of the rhinegraben rift system has been subjected to three different natural dynamic processes 1 uplift by 2 to 3 km with subsequent erosion of the rhinegraben shoulders black forest and vosges mountains caused decompression possibly leading to the formation of a low velocity high electrical conductivity zone right on top of the laminated lower crust beneath the elevated shoulders of the black forest 2 the brittle crystalline wedge of the graben proper subsided nearly undeformed into the lower crust which became about 5 to 7 km thinner below the graben than below the shoulders 3 the deepest hypocentres in the black forest dinkelberg area if projected onto the neighbouring reflection profile would be located 7 to 8 km within the laminated lower crust beneath the southern black forest indicating a discrepancy between the top of the lower crust as defined by the brittle ductile transition as seen by the deepest earthquakes and by the top of the laminated reflection band the rhinegraben rift system reveals the properties and behaviour of the lower crust under a wide variety of tectonic situations

olivine basalt and trachyandesite peperites formed at the subsurface surface interface of a semi arid lake an example from the early miocene bigadic basin western turkey abstract miocene successions in western turkey are dominated by lacustrine fluvial and evaporitic sedimentary deposits these deposits include considerable amounts of volcaniclastic detritus derived from numerous ne trending volcanic centres in western turkey as well as in the bigadic region early miocene syn depositional ne trending olivine basalt and trachyandesite bodies that formed as intrusions and lava flows occur within the bigadic borate basin olivine basalts occur as partly emergent intrusions and trachyandesite dykes fed extensive lava flows emplaced in a semi arid lacustrine environment peperites associated with the olivine basalt and trachyandesites appear to display contrasting textural features although all the localities include a large variety of clast morphologies from blocky to fluidal fluidal clasts mainly globular ameboidal and pillow like varieties are widespread in the peperite domains associated with olivine basalts apparently due to large volume sediment fluidisation in contrast fluidal clasts related to trachyandesites are restricted to narrow zones near the margins of the intrusions and have commonly elongate and polyhedral shapes with digitate margins rather than globular and equant varieties blocky and fluidal clasts in the olivine basalt peperite display progressive disintegration suggesting decreasing temperature and increasing viscosity during fragmentation abundance of blocky clasts with respect to fluidal clasts in the trachyandesite peperite indicates that the fluidal emplacement and low volume sediment fluidisation in the early stages were immediately followed by quench fragmentation due to the high viscosity of the magma size texture and abundance of the blocky and fluidal clasts in the olivine basalt and trachyandesite peperites were mainly controlled by sediment fluidisation pulsatory magma injection and magma properties such as composition viscosity vesicularity and size abundance and orientation of phenocrysts variously combining these contrasting features to varying degrees may form diverse juvenile clast shapes in peperitic domains

southern menderes massif an incipient metamorphic core complex in western anatolia turkey in the southern sector of the menderes massif north of selimiye milas augen gneisses interpreted as a deformed peraluminous granite have been dynamothermally metamorphosed and are surrounded by and intrude a regionally metamorphosed palaeozoic envelope the granitic rocks exhibit a moderately dipping mylonitic foliation and nne ssw trending mineral elongation lineation the progressive deformation of the granitic rocks produces a structural sequence typical of an extensional shear zone marked from bottom to top by a very thick extensive zone of mylonites followed in turn by brecciated mylonite and cataclasite the kinematic indicators exhibit a top to the south down dip sense of shear these structures are attributed to exhumation of the granitic rocks of the massif along a major south dipping normal sense shear zone that accommodated crustal extension during late oligocene collapse of the orogen in western turkey thus the southern menderes massif may be interpreted as the exhumed footwall of a major extensional shear zone and possibly as an incipient core complex

structural evolution of the usak gure supra detachment basin during miocene extensional denudation in western turkey the usak gure basin is a ne sw trending extensional basin located in the northern part of the menderes massif in western anatolia the usak gure basin contains a lower to upper miocene volcano sedimentary succession that records the unroofing of the metamorphic rocks of the menderes metamorphic core complex we propose a new structural mechanism based on geological mapping and detailed kinematic fault analysis from each of the evolutionary phases we also propose that north to ne dipping low angle detachment surfaces define the basin boundaries and have identified three stages of deformation throughout the miocene the early miocene deformation phase d 2 is characterized by low angle normal faulting simav detachment fault in the supra detachment usak gure basin which marks the initiation of the extensional tectonics during the latest oligocene the middle miocene deformation phase d 3 refers to volcano tectonic activities during accumulation of the inay group the late miocene deformation phase d 4 is related to late miocene tectonic activity widely responsible for deposition of the asartepe formations and uplift of the metamorphic rocks in the usak basin margin in addition we propose that the eastern part of the menderes massif was delimited by the usak mugla transtensional transfer zone from middle miocene time throughout the eastern part of the menderes metamorphic core complex

growth destruction and facies architecture of effusive and explosive volcanics in the miocene shama basin southwest of saudi arabia subaqueous subaerial volcanism in a lacustrine setting abstract this paper presents for the first time detailed stratigraphical and petrographical analyses of the harrat shama volcanic basin hsvb of miocene age in sw saudi arabia this basin is filled by abundant volcanics intercalated with fluvio lacustrine sedimentary successions these successions are characterized by a syneruptive intereruptive cycle which results from the intercalation periods of volcanics and volcaniclastic sedimentation along with periods of fluvial incision two depositional sequences showing an overall fining upward trend are preserved within the hsvb the first comprises hyaloclastites zeolite bearing bedded tuffs and bedded accretionary lapilli tuffs interpreted as deep lake whereas the second is made up of extensive pumiceous pyroclastic flows peperitic breccias and basaltic lava flows which are in turn capped by siliciclastic deposits of lacustrine deposits the passage between two sequences is defined by lateral variations of the lithofacies and textural features reflecting a change in paleogeography the fining upward volcaniclastic deposits of the hsvb sequence are interpreted to represent the sedimentation pattern induced by tectonic subsidence with the influence of volcaniclastic sediment input indicating well established proximal distal relationship hsvb was evolved through three stages including pre syn and post caldera stages the first two stages correspond to proximal aggradational syn eruptive event whereas the latter stage refers to distal degradational inter eruptive event these stages overlap in time as shown by the alternation of explosive effusive and their resedimented deposits reflecting diverse eruptive sequences formed by different fragmentation processes the difference in the latter coupled with the variability in the magma water interaction and the nature of substrate are responsible for such diversity resulting in progressive environmental changes from subaqueous to subaerial regime from bottom to top the development of such contrast in the depositional sequences reflects variation in the sediment flux and subsidence rate during the evolution of the hsvb

cone building block and ash flows the senyama volcanic products of o e takayama volcano sw japan the senyama volcanic products of the late pliocene to early pleistocene o e takayama volcano overlie a 100 m thick late pliocene coastal quartz sandstone and are intruded by an early pleistocene dacite dome the senyama volcanic products are the remains of a cone that retains a basal part 1 5 km across and 150 250 m high from the substrate the cone comprises dacite block and ash flow deposits and minor base surge deposits occur at the base single beds of the block and ash flow deposits are 1 16 m thick and dip inward 20 40 at the base of the cone and inward or outward 10 20 at the summit juvenile fragments in the block and ash flow deposits are non to poorly vesicular and commonly have curviplanar surfaces and prismatic joints extending inward from the surfaces which imply quenching and brittle fracturing of dacite lava they are variably hydrothermally altered nevertheless juvenile blocks appear to retain a uniform direction of the magnetization vector residual during thermal demagnetization between 280 c and 625 c at the time of the eruption the well sorted sand of the substrate was at the coast and a good aquifer that facilitated explosive interaction of water and the ascending dacite lava the mechanism of the explosion perhaps involved thermal contraction cracking of the dacite lava water inflow into the interior of the lava and explosive expansion of the water initial phreatomagmatic explosions opened the vent succeeding phreatomagmatic or phreatomagmatic vulcanian explosions produced block and ash flow deposits around the vent hydrothermal silver ore deposits and manganese oxide deposits occur in the senyama volcanic products and the underlying sandstone respectively they could represent post eruptive activity of the hydrothermal system developed in and around the cone

pyroclastic phases of a rhyolitic dome building eruption puketarata tuff ring taupo volcanic zone new zealand the 14 ka puketarata eruption of maroa caldera in taupo volcanic zone was a dome related event in which the bulk of the 0 25 km3 of eruption products were emplaced as phreatomagmatic fall and surge deposits a rhyolitic dike encountered shallow groundwater during emplacement along a ne trending normal fault leading to shallow seated explosions characterised by low to moderate water magma ratios the eruption products consist of two lava domes a proximal tuff ring three phreatic collapse craters and a widespread fall deposit the pyroclastic deposits contain dominantly dense juvenile clasts and few foreign lithics and relate to very shallow level disruption of the growing dome and its feeder dike with relatively little involvement of country rock the distal fall deposit representing 88 of the eruption products is despite its uniform appearance and apparently subplinian dispersal a composite feature equivalent to numerous discrete proximal phreatomagmatic lapilli fall layers each deposited from a short lived eruption column the puketarata products are subdivided into four units related to successive phases of a shallow lava intrusion and initial dome growth b rapid growth and destruction of dome lobes c slower sustained dome growth and restriction of explosive disruption to the dome margins and d post dome withdrawal of magma and crater collapse phase d was phreatic phases a and c had moderate water magma ratios and phase b a low water magma ratio dome extrusion was most rapid during phase b but so was destruction and hence dome growth was largely accomplished during phase c the puketarata eruption illustrates how vent geometry and the presence of groundwater may control the style of silicic volcanism early activity was dominated by these external influences and sustained dome growth only followed after effective exclusion of external water from newly emplaced magma

the menderes massif of western turkey and the cycladic massif in the aegean do they really correlate based on lithostratigraphic comparisons the menderes massif has been correlated with the cycladic massif thereby implying that the eastern mediterranean consists of a narrow pre alpine basement belt which is laterally continuous over a long distance and which experienced a similar alpine orogenic history our work indicates that the architecture the age of basement and the pre alpine and alpine tectonometamorphic history of both massifs differ fundamentally from each other the menderes massif consists of remnants of the cycladic massif which overly an exotic unit the menderes nappes both massifs do not represent lateral continuations which has implications for palaeogeographic reconstructions

a medial to distal volcaniclastic record of an andesite stratovolcano detailed stratigraphy of the ring plain succession of south west taranaki new zealand the 25 ka volcaniclastic ring plain succession in south west taranaki has been remapped to establish a much more detailed understanding of the older stratigraphic record of mt taranaki coastal cliff exposures show a range of volcaniclastic lithofacies including debris avalanche and lahar deposits and allow a detailed chronological reconstruction of past volcanic and sedimentary events five new debris avalanche deposits were identified and their distribution in coastal cross sections mapped in addition four previously described units were renamed and their stratigraphic position and lateral extent redefined chronostratigraphic control of the younger 50 ka sequence was obtained by radiocarbon dating of wood found within or peat interbedded with the deposits emplacement ages of the older units were estimated from their stratigraphic position and underlying marine wave cut surfaces overall at least 14 widespread debris avalanche deposits occur within the 200 ka ring plain record of mt taranaki suggesting one major edifice failure on average every 14 000 years with an increase in frequency since 40 ka the stratigraphic reconstruction of the ring plain succession showed that the same pattern of deposition was repeatedly produced throughout the existence of mt taranaki depending on their sedimentological characteristics the different volcanic and sedimentary lithofacies can be related to phases of edifice construction or collapse events based on the identified cyclic sedimentation pattern we present a new episodic stratigraphy that integrates existing and new lithostratigraphic units into a coherent chronostratigraphic framework that can be applied to the entire volcanic and volcaniclastic succession at mt taranaki this model takes into account the complex geological processes that have taken place on the volcano and provides a more uniform stratigraphic terminology that could be applied to repeatedly collapsing stratovolcanoes elsewhere

composite volcanoes in the south eastern part of izmir balikesir transfer zone western anatolia turkey abstract during the early middle miocene western anatolia several volcanic fields occur along a ne sw trending shear zone known as izmir balikesir transfer zone this is a deformed crustal scale sinistral strike slip fault zone crossing the bornova flysch and extending along the nw boundary of the menderes massif by accommodating the differential deformation between the cycladic and menderes core complexes within the aegean extensional system here we discuss the volcanic activity in yamanlar and yuntdagi fields that is closely related to the extensional tectonics of the izmir balikesir transfer zone and in the same time with the episodic core complex denudation of the menderes massif this study documents two composite volcanoes yamanlar and yuntdagi whose present vent area is strongly eroded and cut by a variety of strike slip and normal fault systems the transcurrent nw se being the dominant one the erosional remnants of the vent areas resembling a shallow crater intrusive complex illustrate the presence of numerous dykes or variably sized neck like intrusions and lava flows typically associated with hydrothermal alteration processes propylitic and argillic such vent areas were observed in both the examined volcanic fields having 6 km in diameter and being much more eroded toward the south along the nw se fault system lava flows and lava domes are sometimes associated with proximal block and ash flow deposits in the cone building association part besides lava flows and remnants of lava domes rare block and ash and pumice rich pyroclastic flow deposits as well as a series of debris flow deposits have been observed the rocks display a porphyritic texture and contain various proportions of plagioclase clinopyroxene orthopyroxene amphibole rare biotite and corroded quartz the examined rocks fall at the limit between calc alkaline to alkaline field and plot predominantly in high k andesite and dacite fields and one is rhyolite the trace element distribution suggests fractional crystallization processes and mixing in upper crustal magma chambers and suggests a metasomatized lithospheric mantle lower crust source this preliminary volcanological petrological and geochronological base study allowed documenting the yamanlar and yuntdagi as composite volcanoes generated during post collisional early middle miocene transtensional tectonic movements

tectono stratigraphic evolution of the ne sw trending superimposed selendi basin implications for late cenozoic crustal extension in western anatolia turkey abstract selendi basin is located in the eastern part of western anatolia that is the easternmost part of the aegean extensional province in western anatolia crustal extension resulted in exhumation of the mid crustal units the menderes massif synchronously with volcano sedimentary basin formation the stratigraphic and tectonic features of the volcano sedimentary succession reflect the exhumation processes and the modes of extension we present new stratigraphical sedimentological structural and 40ar 39ar age data from the neogene volcano sedimentary fill of the ne sw trending selendi basin the data show that crustal extension in the region occurred in four distinct episodes and accommodated the exhumation of the menderes massif and the basin formation throughout the late cenozoic late oligocene to early miocene detachment faulting the simav detachment fault sdf is attributed to the first episode clastic sedimentation and bimodal volcanism of 20 0 17 5 ma the hacibekir group age was formed in the hanging wall of the sdf during the exhumation of northern menderes massif in the footwall during second episode the menderes collapse occurred and was manifest by formation of the gediz detachment fault gdf during the middle miocene activity on the gdf has resulted in the exhumation of the central menderes massif in the bozdag area during this period the hanging wall of the gdf was dissected by ne sw trending high angle oblique slip cross faults and accommodated clastic to lacustrine carbonate deposition and syn sedimentary bimodal volcanism of 16 15 ma the inay group the third episode is represented by formation of nw se trending sinistral and ne sw trending dextral strike to oblique slip faults and associated dip to oblique slip normal faults during the late miocene indicating that the area was deformed under a strike slip tectonic regime the faults localized alluvial sedimentation the kocakuz formation and basaltic volcanism of 7 8 ma the kabaklar basalt in the selendi basin the last episode commenced by the start of the plio quaternary this period is represented by the currently active n s extensional tectonic regime that resulted in the formation of e w trending high angle normal faults that controls the present day e w trending graben type basin formation e g gediz and simav grabens and the quaternary 1200 60 ka basaltic volcanism

a comparison of geodetic and finite strain pattern in the aegean geodynamic implications abstract a comparison of the active strain pattern of the aegean constrained by global positioning system measurements and the oligo miocene finite strain field shows some striking similarities in terms of direction and rates of extension the geometry of extension at crustal scale is also very similar with north dipping normal faults connecting near the brittle ductile transition to shallow north dipping shear zones this pattern of extension is not significantly modified by the recent extrusion of the motion of anatolia and aegea the persistence over more than 25 myr of the same pattern of extension suggests that the cause for extension resides within the aegean lithosphere gravitational collapse allowed by extensional boundary conditions after 30 ma slab retreat is the primary cause for post orogenic extension in the aegean and western anatolia

crumbling of dacite dome lava and generation of pyroclastic flows at unzen volcano recent modelling of volcanic eruptions has shown that the efficiency of subsurface degassing of magmas determines whether magma erupts explosively or effuses quietly1 2 slow uprise of magma is often accompanied by effective degassing leading to the extrusion of lava flows and domes although lava dome extrusion is one of the less explosive modes of eruption it is often accompanied by explosive pyroclastic activities3 5 the 1991 eruption of unzen volcano provided an opportunity to observe at close range several types of small scale pyroclastic flow glowing avalanches originating from lava domes most of the pyroclastic flows are of merapi type caused by blocks falling from a collapsing dome others are of pelean type originating in an explosion from the side of a dome the lavas apparently show variable degrees of self explosivity we suggest that variable degrees of degassing of the magma produced a wide range of excess pore pressures in the extruded lava domes resulting in both merapi type and pelean type pyroclastic flows from the domes

compositional modes in the ash fraction of some modern pyroclastic deposits their determination and significance this paper illustrates some problems involved in the quantitative compositional study of pyroclastic deposits and proposes criteria for selecting the main petrographic and textural classes for modal analysis the relative proportions of the different classes are obtained using a point counting procedure applied to medium coarse ash samples that reduces the dependence of the modal composition on grain size and avoids tedious counting of different grain size fractions the major purposes of a quantified measure of component distributions are to a document the nature of the fragmenting magma b define the eruptive dynamics of the eruptions on a detailed scale and c ensure accuracy in classifying pyroclastic deposits compositional modes of the ash fraction of pyroclastic deposits vary systematically and their graphical representation defines the compositional and textural characteristics of pyroclastic fragments associated with different eruptive styles textural features of the glass component can be very helpful for inferring aspects of eruptive dynamics four major parameters can be used to represent the component composition of pyroclastic ash deposits a juvenile index ji b crystallinity index cri c juvenile vesicularity index jvi and d free crystal index fcri the fcri is defined as the ratio between single and total crystal fragments in the juvenile component single crystals crystals in juvenile glass this parameter may provide an effective estimate of the mechanical energy of eruptions variations in fcri vs jvi discriminate among pyroclastic deposits of different origin and define compositional fields that represent ash derived from different fragmentation styles

sedimentary and geomorphic responses to ignimbrite emplacement readjustment of the waikato river after the a d 181 taupo eruption new zealand abstract the posteruption readjustment of landscapes to major explosive volcanic eruptions is one of the most dramatic processes in physical sedimentology and geomorphology large ignimbrite emplacing eruptions from rhyolitic caldera volcanoes can form new landscapes over 104 km2 create new depocenters in calderas and bury existing topography and drainage systems beneath hundreds of meters of pyroclastic material subsequent remobilization of this debris constitutes a widespread and enduring hazard in the central north island of new zealand the a d 181 taupo eruption destroyed hydrologic systems over 20 000 km2 when emplacement of the climactic ignimbrite filled valleys and depressions with up to 70 m of pyroclastic material and blocked the waikato river outlet to the intracaldera lake basin posteruption remobilization of this material in the waikato catchment was associated with axial stream reestablishment vertical lateral and proximal distal changes in volcaniclastic lithofacies preserved al

geology of the ignimbrites and the associated volcano plutonic complex of the ezine area northwestern anatolia abstract the ezine region is located in the northwestern part of anatolia where young granitic and volcanic rocks are widespread and show close spatial and temporal association in this region magmatism began with the kestanbol granite which intruded into metamorphic basement rocks and formed contact metamorphic aureole to the east and southeast the pluton is surrounded by hypabyssal rocks which in turn are surrounded by volcanic associations the volcanic rocks may be divided into two main groups on the basis of their lithological properties lavas and lahar deposits dominate the northern sector while ignimbrites dominate the southern sector the ignimbrite eruptions were formed partly coevally with the plutonic and the associated volcanic rocks during the early miocene they appear to have been associated in a caldera collapse environment geochemical properties of the plutonic and the associated volcanic assemblages indicate that the magmas are hybrid and co genetic and were formed from a similar mantle source under a compressional regime prior to the opening of the present e w trending graben of the aegean western anatolian region

supergene alteration of sulphides vii distribution of elements during the gossan forming process abstract the results of many electrochemical weathering experiments involving sulphide ore assemblages are brought together and discussed in terms of the mechanism of reaction of sulphide minerals through to oxide gossan minerals the observed reactions of various sulphide minerals are compared and the behaviour of the resultant cations and anions in solution including their hydrolysis and adsorption properties as they effect the types of gossan materials that are formed is given the interaction between the ph of the reactions and the amount of fe in the sulphides is shown to be the dominant feature which controls the mobility of many elements the experiments demonstrate how a low ph develops near to the surface of oxidising sulphides giving a scale at this point that is depleted in most base metals relative to gossan materials that precipitate from solution gangue minerals are shown to be leached and the elements leached play a role in the formation of gossan materials there is a complex interaction between the fe ii fe iii couple and the cu i cu ii couple that should favour the formation of hematite native cu at low ph and malachite hematite goethite at ph above 6 5

bivergent extension in orogenic belts the menderes massif southwestern turkey the central menderes massif is characterized by an overall dome shaped foliation pattern and a north northeast trending stretching lineation the asymmetry of shear bands and quartz c axis fabrics on either side of the structural dome demonstrate a top to thenorth northeastshearsenseinthenorthernpartandatoptothesouth southwestshear sense in the southern part of the submassif i e a bivergent downdip movement this suggests a symmetric collapse of the alpine menderes orogenic belt along two extensional shearzones conjugateshearbandsandsymmetricquartzc axisfabricsintheeast trendingtransitionzonedemonstrateacoaxialdeformationbetweenthetwoextensiondomains bivergent extension in the menderes massif is in contrast to asymmetric extension in the aegeansea here thestill activehellenicsubductionzoneevolvedfromanadvancingplate boundary associated with crustal thickening into a retreating plate boundary in oligocene miocene time southward rollback of the subducting plate during continuous northward subduction allowed asymmetric top to the north northeast extension in the back arc region during the exhumation of the cycladic core complexes in western turkey the arrival of the thick continental crust of the menderes massif halted subduction and probably caused the symmetric collapse of the massif because the high potential energy of the thickened crust was no longer supported by subduction

reconstructing the evolution of an eroded miocene caldera volcano yamanlar volcano izmir turkey abstract the miocene yamanlar composite volcano is located in the central part of a shear zone in western turkey the volcano s deeply eroded interior provides excellent three dimensional exposure of a faulted caldera floor and caldera fill rocks as well as surrounding extracaldera ignimbrites we present a much revised stratigraphy and geological map of yamanlar in order to quantify the evolutionary stages of the volcano the yamanlar volcanic cone was composed of 800 m of basaltic andesite to andesite lavas and lava domes the volcano underwent at least one phase of caldera formation associated with an explosive eruption that deposited an ignimbrite sheet within and outside the caldera lithofacies architecture analysis is applied to the proximal and medial exposures of the early middle yamanlar formation which occurs outside of the caldera field evidence of the succession indicates a caldera forming eruption our results indicate that the formation of the yamanlar caldera resulted from one major catastrophic eruption that generated several sustained pyroclastic density currents pdcs subdivided by fall deposits with sharp contacts the ignimbrite sheet is composed of four flow units the presence of numerous coarse grained lithic rich horizons within the ignimbrite sheet is consistent with caldera subsidence post caldera volcanism is indicated by intrusions and lava domes erupted along the inferred caldera bounding faults some of which record 90 m of displacement widespread coarse grained breccias that overlie the ignimbrite sheet are interpreted as debris avalanche deposits resulting from gravitational failure of the flanks of the volcano or the caldera wall during or after caldera subsidence

a pulsed extension model for the neogene recent e w trending alasehir graben and the ne sw trending selendi and gordes basins western turkey abstract we have developed a significant body of new field based evidence relating to the history of crustal extension in western turkey we establish that two of the ne sw trending basins in this region the gordes and selendi basins whose sedimentary successions begin in the early miocene are unlikely to relate to late stage alpine compressional orogeny or to e w extension of tibetan type grabens as previously suggested we argue instead that these basins are the result of earlier late oligocene low angle normal faulting that created approximately n s scoop shaped depressions in which clastic to lacustine and later tuffaceous sediments accumulated during early mid miocene time separated by elongate structural highs these basins were later cut by e w trending plio quaternary normal faults that post date accumulation of the neogene deposits in addition we interpret the alasehir gediz graben in terms of two phases of extension an early phase lasting from the early miocene to the late miocene and a young plio quaternary phase that is still active taking into account our inferred earlier phase of regional extension we thus propose a new three phase pulsed extension model for western turkey we relate the first two phases to roll back of the south aegean subduction zone and the third phase to the westward tectonic escape of anatolia

sedimentation and palaeoenvironments of late cretaceous crater lake deposits in bushmanland south africa a large diameter borehole core from an epiclastic kimberlite remnant on the farm stompoor in the prieska district cape province contains a continuous 76 m section of fossiliferous sediments interpreted as having accumulated within a crater lake during the late cretaceous three distinct facies associations reflect depositional processes that prevailed in offshore areas of the original lake facies association a matrix supported pebble conglomerates comprising a chaotic assemblage of pyroclastic basement and country rocks set in a fine grained matrix flat non erosional basal surfaces with frozen rip up clasts the protrusion of matrix supported clasts above the upper surfaces and a direct relationship between maximum clast size and bed thickness suggest deposition from debris flows that originated subaerially on pyroclastic talus cones surrounding the crater facies association b alternating thin beds of matrix supported granule conglomerate structureless fine grained sandstone and parallel laminated mudrock small fining upward sequences within these beds are comparable to turbidite bouma tade tde numerous partings display petrified fish and frog skeletons as well as bivalve gastropod and ostracode shells leaf impressions insect wings and a possible bird bone these beds were deposited by thin debris flows and turbidity underflows interspersed with periods of pelagic sedimentation facies association c microlaminated mudstone beds containing scattered dropstone lapilli the lamination is imparted by alternating ca rich ca poor layers which may reflect climatic seasonality they are interpreted as the result of seasonally influenced suspension settling through a thermally stratified water column short term periodicities in conglomerate bed thicknesses are interpreted as the result of successive block caving of a slump scar giving rise to several debris flows from the same source area seismic shock from nearby volcanism may have simultaneously triggered slumps on both subaerial and subaqueous slopes dropstone lapilli in type c beds and the preponderance of load casting in type b beds support this interpretation an estimate of the time span involved in accumulating 76 m of crater lake sediments based on the possible seasonal imprint of type c beds gives a figure of some 220 000 yr

koroglu caldera mid west anatolia turkey volcanological and magmatological evolution abstract the koroglu caldera is a result of the eruption of seydiler ignimbrites which have been emplaced in two sequences known as lower seydiler ls and upper seydiler us the koroglu caldera measures 13 km 18 km contains a resurgent dome in the center and produced low aspect ratio ignimbrites which have been transported up to 50 km away from the source the ignimbrites show argillaceous weathering which decreases from the bottom towards the top of the deposits such a transition from ignimbrites to reworked tuffs indicates the development of a lacustrine environment over the ignimbrites spot image analysis shows that tectonic activity continued after the caldera collapse two main trends of tectonic elements ne sw and nw se have been distinguished the latter being the younger a nw se striking fault was used by lamprophyric magmas which were extruded into the post ignimbrite lacustrine deposits the lava flows and dikes trachybasalte trachyandesite also occur along the ring fractures of the caldera the dikes are composed of olivine phlogopite cr diopside salite k feldspar ba feldspar hyalophane the lava flows contain scarce cognate inclusions

environmental impact of the 1 8 ka taupo eruption new zealand landscape responses to a large scale explosive rhyolite eruption abstract large scale ignimbrite eruptions from rhyolitic caldera volcanoes can trigger geologically instantaneous changes in sedimentary systems over huge areas by either burying existing environments or overloading them with vast quantities of unconsolidated particulate material the post eruption readjustment of the landscape to such perturbations is one of the most dramatic processes in physical sedimentology exemplified here by the 1 8 ka taupo eruption in the central north island of new zealand this eruption generated voluminous fall deposits then climaxed with emplacement of a c 30 km 3 non welded ignimbrite over a near circular area of c 20 000 km 2 approximately 90 of the area but the headwaters of many of the north island s largest rivers were impacted by both the primary pyroclastic fall and flow material large scale post eruption remobilisation of this material coupled with the re establishment of fluvial systems occurred in a distinct sequence as recorded by the evolution of sedimentary facies in different sub environments following an initial period dominated by mass flows re establishment of fluvial systems began with the headward erosion of box canyons through the ponded ignimbrite deposits a process often associated with the break out of temporary lakes aggradational streams developed in these channels rapidly evolved from shallow ephemeral sediment laden outbursts associated with flash flood events to deeper permanent braided rivers before declining sediment yields led to retrenchment of single thread rivers and a return to pre eruption gradients and bedloads years to decades later typically the modern profile of many streams and rivers follow closely their pre eruption profiles and incision and erosion is overwhelmingly confined to the deposits of the eruption itself although the general remobilisation pattern is similar for all impacted river systems detailed studies of the waikato rangitaiki mohaka ngaruroro and whanganui catchments show that the relative timing and scale of each eruption response phase differs between each catchment these reflect differences in catchment physiography and hydrology and the volume and type of pyroclastic material deposited in each ultimately the landscape response reflects the relative spatial distributions of and the volumetric ratios between the volumes of pyroclastic debris water and accommodation space in the basin cf kataoka and manville this volume

miocene sedimentary evolution of the ne sw trending selendi and gordes basins w turkey implications for extensional processes abstract western turkey is one of the classic regions for the study of extensional processes in a recent interpretation the regional metamorphic basement the menderes massif was exhumed related to large scale extensional processes possibly during latest oligocene time regional scale ne sw trending basins including the gordes and selendi basins were created associated with this exhumation the ne sw trending basins are seen as regional scale corrugations 10 15 km across in the surface of an extensional detachment orientated parallel to the direction of extension the detached upper plate is represented by erosional remnants of unmetamorphosed tethyan ophiolitic melange we describe and interpret the gordes and selendi basins separately and then show that their sedimentary facies and evolution are very similar basal coarse alluvial fan deposits accumulated after extensional removal of the upper plate these basal sediments rarely exposed were rotated by up to 50 probably as a result of local extension or transtension later during the early miocene the gordes and selendi basins were infilled by a generally fining upward succession derived from the south based on palaeocurrent evidence coarse alluvial fan deposition was followed by the deposition of finer grained alluvial deposits from braided streams flowing northwards over a topographically subdued flood plain later deposition was within shallow ephemeral lakes after a possible change to a moister climate calc alkaline magmatism was initiated with the fall out of fine grained silicic ash followed by coarser grained tuff derived from local magmatic centres during early pliocene time the basins were dissected by e w extensional faults associated with the establishment of the modern pattern of westward drainage to the aegean sea we use the assembled sedimentary evidence to test alternative tectonic models for miocene basin formation in western turkey our preferred tectonic model emphasises the importance of deposition in regional basins created by exhumation of metamorphic basement that was previously assembled during early tertiary closure of the tethys ocean

transport and emplacement mechanisms of large volcanic debris avalanches evidence from the northwest sector of cantal volcano france abstract large volcanic debris avalanche vda deposits of miocene age occur within the stratigraphic sequence of cantal stratovolcano central france the vda of cantal volcano were initiated by sector collapse of a cone of high elevation up to 4500 m a s l two distinct superimposed vda deposit units breccias i and ii resulted from at least two successive large scale collapse events during the evolution of the volcanic complex breccia i the oldest one is very thick up to 200 m and heterolithologic it is overlain by breccia ii which is thinner up to 50 m and contains more heterometric clasts ranging from hectometer to millimeter size the vda deposits are poorly sorted clasts are angular and highly fractured at different scales often with jigsaw fit in breccia ii jigsaw megaclasts have usually subspheric shapes with size decreasing distally basal deposits commonly display thin inversely graded layers reorientated clasts along ramp structures and cataclasis of the substratum some units have a distal fabric in the form of a poorly developed clast imbrication the clasts are commonly sub rounded thereby indicating abrasion during viscous flow anisotropy of magnetic susceptibility a m s measurements indicate absence of a preferentially oriented matrix fabric magnetic foliation parallel to the bedding suggests that the depositional process is dominated by particle settling the magnetic fabric is better organized in distal deposits where magnetic carriers are imbricated moreover the fragmented clasts and megaclasts are not abraded rather inflation led to isotropic spherical dispersion of clastic material isotropic dispersive inflation which fed the interclast matrix this is also confirmed by the lack of rotation at the individual crystal level all these data strongly suggest transport of vda by liquified non turbulent granular flows distally imbricated deposits suggest more turbulent flow emplacement of the vda results from progressive upward aggradation of the particles by volume reduction and deflation loss the non turbulent liquified stage of the vda disappears the vda behaves as a sliding rigid mass plug flow that exerts strong friction on the basement leading to gouge formation

permian rhyolitic volcanism changing from subaqueous to subaerial in post variscan intra continental sirinia basin sw romania eastern europe abstract the sirinia basin is a well exposed upper carboniferous lower permian intra continental extensional basin containing 1 2 km of permian interbedded terrigeneous sediments and primary volcanic and volcaniclastic rocks of rhyolitic composition these are mostly the products of subaqueous volcanism passing into a subaerial volcanism the intra continental basin lies on the danubian metamorphic units in the south westernmost part of the carpathians sw romania and is n s oriented 18 8 km as result of alpine tectonic evolution and deformation the sirinia basin setting formed a dynamic closed intra continental sedimentary system that experienced a successive subsidence it started with lacustrine sediments and then with large volumes of rhyolitic volcanic and volcaniclastic material dominantly sited in the central part of the basin volcanism included 1 subaqueous extrusion of domes surrounded by hyaloclastite deposits closely associated with secondary sedimentation 2 extrusive and explosive surtseyan type and subaerial eruptions from shallow water to emergent volcanoes on dome cap and associated reworked deposits towards the southern side of the basin and 3 subaerial extrusive domes fluvial erosion and deposition completed the evolution of the emerged marginal part of the basin most of the erupted material of the first and second phase filling the central part of the basin along extensional normal faults was rapidly transported on sides of the basin by turbidite sedimentation debris flows slumping and sliding while turbidites prevail toward the central part of the basin the debris flow sedimentation predominated at the margin of the basin infrequently interrupted by deposition of fallout ash from hydromagmatic explosive eruptions related to the dome cap tuff and pumice cones

explosive activity associated with the growth of volcanic domes abstract domes offer unique opportunities to measure or infer the characteristics of magmas that at domes and elsewhere control explosive activity a review of explosive activity associated with historical dome growth shows that 1 1 explosive activity has occurred in close association with nearly all historical dome growth 2 2 whole rock sio 2 content a crude but widely reported indicator of magma viscosity shows no systematic relationship to the timing and character of explosions 3 3 the average rate of dome growth a crude indicator of the rate of supply of magma and volatiles to the near surface enviornment shows no systematic relationship to the timing or character of explosions and 4 4 new studies at arenal and mount st helens suggest that water content is the dominant control on explosions from water rich magmas whereas the crystal content and composition of the interstitial melt and hence magma viscosity are equally or more important controls on explosions from water poor magmas new efforts should be made to improve current rather limited techniques for monitoring pre eruption volatile content and magma viscosity and thus the explosive potential of magmas

accumulation of volcaniclastic aprons in the mount dutton formation oligocene miocene marysvale volcanic field utah volcaniclastic rocks in the mount dutton formation form coalescing aprons of lahar deposits around several volcanoes the aprons accumulated across a featureless alluvial plain in an arid to semi arid climate under these conditions debris flows dominated apron construction building large aprons extending as much as 27 km from the flank of the source volcano three distinct but gradational lithofacies assemblages within the aprons show a proximal to distal change from thickly bedded coarse lahar deposits to thinly bedded fine grained ones this lithofacies change represents a change from channelized flow on the proximal apron to unchannelized flow on the medial apron unconfined flow on the medial apron together with lower slope caused lahars to deposit the bulk of their sediment load most deposition in distal areas resulted from small dilute lahars large lahars capable of transporting coarse sediment into distal areas were rare the aprons also show a down apron decrease in abundance of debris flow deposits corresponding to an increase in hyperconcentrated flow deposits this trend represents reworking of more proximal deposits by floods that did not form debris flows rather than flow transformation from debris flow to hyperconcentrated flow arid climate and unchannelized flow prevented the flow transformation that is a common feature of volcaniclastic deposits in the pacific northwest where glacially dissected valleys with permanent streams control flow of lahars away from the volcanoes

volcaniclastic debris flows in the clanio valley campania italy insights for the assessment of hazard potential abstract the rugged and steep slopes of the clanio valley campania southern italy mantled by volcaniclastic deposits from explosive eruptions of somma vesuvius and phlegraean fields volcanoes have a great potential for generating volcaniclastic debris flows during the well known meteorological event of may 5 6 1998 which triggered tens of debris flows causing enormous damage and casualties in the area of sarno quindici siano bracigliano sqsb the clanio valley was also affected by these hazardous phenomena debris flows were triggered by the failure of the volcaniclastic cover of the carbonate relief in the form of soil slips mainly on the sides of steep valleys slope between 26 and 45 a map of the hazard potential was created on the basis of both field and computer assisted morphometric data three classes characterised by a high medium and low hazard potential were distinguished within the higher class a better and more detailed zonation was obtained by studying the shape of the disrupted and undisrupted basins during the may 5 6 1998 event in the nearby sarno quindici siano bracigliano area this type of morphometric analysis can be applied rapidly by using a digital elevation model dem which allows a rapid investigation of large scale areas such an approach can be useful in areas characterised by similar geological and geomorphological settings

construction and destruction of a volcanic island developed inside an oceanic rift graciosa island terceira rift azores abstract there is a great lack of knowledge regarding the evolution of islands inside active oceanic rifts in particular the meaning of the different evolutionary steps therefore we conducted an investigation in graciosa island which lies at the northwestern end of the terceira rift in the azores triple junction with the objective of constraining the evolution of the island in terms of volcanic growth and mass wasting in particular the meaning and age of the destruction events from digital elevation model dem analysis stratigraphic and tectonic observations k ar dating on key samples and available bathymetry and gravity data we propose that graciosa comprises five main volcanic complexes separated by major unconformities related to large scale mass wasting 1 the older volcanic edifice serra das fontes complex grew until ca 700 ka and was affected by a major flank collapse towards the southwest which removed the whole sw flank the summit and a part of the ne flank 2 the baia do filipe complex developed between at least 472 ka and 433 ka in two different ways in the sw presently offshore as a main volcano and in the ne unconformably over the sub aerial remnants of the serra das fontes complex as secondary volcanic edifices 3 the baia do filipe complex was affected by a major flank collapse towards the sw again removing most of the edifice 4 the remnants of the baia do filipe complex were covered in unconformity by the serra dormida complex between ca 330 and 300 ka which in turn was unconformably covered by the younger basaltic cover complex between ca 300 ka and 214 ka these two units were affected by a third major sector collapse that removed the whole western flank the summit and part of the eastern flank of the serra dormida and basaltic cover complexes 5 despite the relatively young age of graciosa the collapse scars are not well preserved and not active anymore 6 a central type volcano has been growing since at least 60 ka at the southeastern end of the island inside the scar left by a fourth sector collapse towards the se which affected most previous complexes contemporaneously parasitic strombolian cones formed all over the island despite the location of graciosa inside the active terceira rift the new data indicate that the evolution of the island has been driven by a competition between volcano growth and repeated destruction by catastrophic sector collapses rather than by slow incremental faulting associated with the tectonics of the rift

abiogenic silica layers within a fluvio lacustrine succession bolzano volcanic complex northern italy a permian analogue for magadi type cherts thin layers of chert occur within a fluvio lacustrine succession sandwiched between acidic volcanic rocks of the lower permian bolzano volcanic complex in northern italy these cherts are interpreted as analogues to magadi type abiogenic chert known from modern volcanic lake settings soft sediment deformation features shrinkage cracks and well preserved palynomorphs document very early diagenetic silica precipitation volume loss by dehydration and consolidation prior to mechanical compaction of the sediment transformation to quartz and concomitant re crystallization resulted in a variety of silica textures dominated by microflamboyant quartz the oxygen isotopic composition of chert samples ranges from 25 4 to 29 0 and is negatively correlated with crystal size and ordering

tephra deposits associated with a large lava dome collapse soufriere hills volcano montserrat 12 15 july 2003 abstract the 12 13 july 2003 dome collapse at soufriere hills volcano montserrat was the largest event of its kind during the eruption thus far 1995 2005 involving the removal of 210 million m 3 of the lava dome complex over 18 h less than 2 of the total volume of material involved in the dome collapse was deposited on land a pyroclastic density current deposit alongshore and inland from the tar river fan was generated from a single blast originating at the shoreline the blast was caused by the interaction of pyroclastic flows with seawater we propose that at the peak of the lava dome collapse a sharp increase in the volume flux of pyroclastic flows caused substantial displacement of seawater from the shoreline followed by inrush of seawater when the flux decreased a few minutes later the tsunami allowed penetration of seawater into the main body of the pyroclastic flow at the shoreline which led to explosive fragmentation of pyroclastic blocks tephra fall deposits accumulated at a high rate on montserrat causing extensive damage to vegetation and buildings their stratigraphy recorded fallout from high co pyroclastic flow clouds from a vulcanian explosion cloud at the peak in collapse rate caused by the fragmentation of degassed lava dome and from four vulcanian explosion clouds after the dome collapse caused by fragmentation of bubbly magma in the conduit the total tephra fall volume is estimated at 10 20 million m 3

crustal scale thrusting and extension in the hercynian schwarzwald and vosges central europe the hercynian outcrop areas in the schwarzwald of sw germany and vosges of easternmost france consist from north to south of three major lithotectonic complexes very low to medium grade metamorphics of the saxothuringian belt the polymetamorphic central gneiss complex and the tectonic melange of the southern complex juxtaposition of these three complexes occurred by oblique convergent motions in early carboniferous time the saxothuringian belt is part of a major se dipping accretionary wedge that consists of lower paleozoic meta sedimentary and metaigneous rocks and superimposed upper devonian to lower carboniferous synorogenic volcanics and elastics the central gneiss complex consists of polymetamorphic paragneisses orthogneisses metabasites and meta ultramafics dipping to the nw the southern complex consists of an imbricated melange of north to nw dipping synorogenic elastics volcanics and blocks of ultramafics and gneissic basement the central gneiss complex cgc experienced pervasive hercynian low pressure high temperature metamorphisrn before it was emplaced against and thrust over the sedimentary and volcanic fill of the adjacent synorogenic basins this convergence 340 330 ma produced mylonitic cataclastic shear zones in the cgc the most significant shear zones are the se verging todtnau fault zone between the cgc and the southern complex and the nw verging lubine fault zone between the central gneiss complex and the rocks of the saxothuringian belt these two fault zones enclose a bivergent pop up of the polymetamorphic basement the todtnau fault zone probably extends for more than 100 km along strike and can be traced to a depth of 10 km by deep seismic reflection studies detachment probably occurred along a mid crustal zone of anatexis expressed by a domain of low seismic reflectivity between about 10 and 15 km crustal thickening during early carboniferous convergence led to an extensional phase of crustal reordering between about 330 and 280 ma that was accompanied by the massive rise of posttectonic granitic plutons from middle to high crustal levels simultaneous creation of a structural lamination in the refractory lower crust neglected the main convergent tectonic boundaries it produced a basin and range type lower crust and mantle crust transition in early permian time and involved a major advective input of heat

the strength of intraplate lithosphere abstract the deformation of intraplate lithosphere in response to laterally applied stress has been investigated using a mathematical model of the elastic brittle and viscous response of the lithosphere fundamental to the model is the conservation of the horizontal force associated with the applied stress and the redistribution of stress within the lithosphere after stress release by ductile or brittle failure ductile deformation is assumed to be controlled by dislocation creep in quartz in the crust and by dislocation and dorn law creep in olivine in the mantle brittle failure is predicted using griffith theory the redistribution of stress after brittle and ductile deformation results in large levels of stress in the middle and lower crust immediately above the elastic ductile or brittle ductile transition lithosphere deformation is controlled critically by the lithosphere thermal structure of which surface heat flow q is taken as a convenient indicator for hotter lithosphere stress release by ductile deformation in the middle and lower lithosphere is more extensive and rapidly leads to larger levels of stress in the upper lithosphere for sufficiently large levels of applied stress or sufficiently hot lithosphere complete failure whole lithosphere failure of the lithosphere occurs by ductile and brittle deformation resulting in geologically significant strains critical levels of applied stress required to produce whole lithosphere failure have been computed as a function of the lithosphere surface heat flow the predicted strength of the lithosphere has been compared with expected levels of intraplate stress arising from plate boundary forces and isostatically compensated loads the model predicts significant extensional intraplate deformation in regions of moderate heat flow with q 60 m w m 2 for compressional deformation however a hotter lithosphere is required with q c 75 m w m 2 the model predictions are in general agreement with the comparatively widespread occurrence of extensional intraplate deformation and the restricted occurrence of compressional deformation the model has also been used to investigate the relationship between the depth of the brittle ductile transition and lithosphere temperature structure the brittle ductile transition depth is shown to become shallower with increasing heat flow in good agreement with seismic evidence

pyroclastic flows generated by gravitational instability of the 1996 97 lava dome of soufriere hills volcano montserrat numerous pyroclastic flows were produced during 1996 97 by collapse of the growing andesitic lava dome at soufriere hills volcano montserrat measured deposit volumes from these flows range from 0 2 to 9 106 m flows range from discrete single pulse events to sustained large scale dome collapse events flows entered the sea on the eastern and southern coasts depositing large fans of material at the coast small runout distance 1 km flows had average flow front velocities in the order of 3 10 m s while flow fronts of the larger runout distance flows up to 6 5 km advanced in the order of 15 30 m s many flows were locally highly erosive field relations show that development of the fine grained ash cloud surge component was enhanced during the larger sustained events periods of elevated pyroclastic flow productivity and sustained dome collapse events are linked to pulses of high magma extrusion rates

late cenozoic tectono sedimentary development of the selendi and usak gure basins a contribution to the discussion on the development of east west and north trending basins in western turkey

incision of a river curvature due to exhumed miocene volcanic landforms danube bend hungary a new model for the formation and relief evolution of the danube bend northern hungary is discussed on geomorphological and volcanological grounds we propose that the present day u shaped loop of the danube bend was partly inherited from the horseshoe caldera morphology of keser s hill volcano a mid miocene ca 15 ma lava dome complex with an eroded central depression open to the north according to combined palaeogeographical data and erosion rate calculations the drainage pattern in the danube bend region was formed when pleistocene tectonic movements resulted in river incision and sedimentary cover removal formation of the present curvature of the river was due to the exhumation of the horseshoe shaped caldera as well as the surrounding resistant volcaniclastic successions i e visegrad castle hill and a hilltop lava dome szent mihaly hill the process accelerated and the present narrow gorge of the danube bend was formed by very rapid as young as late quaternary differential tectonic uplift also enhancing the original volcanic morphology on the basis of comparative long term erosion rate calculations we estimated successive elevation changes of the volcanic edifice including partial burial in late miocene time in comparison with various order of magnitude changes the mid to late quaternary vertical movements show increased rates and or base level drop in the pannonian basin

eruptive history of south sister oregon cascades abstract south sister is southernmost and highest of the three sisters three geologically dissimilar stratovolcanoes that together form a spectacular 20 km reach along the cascade crest in oregon north sister is a monotonously mafic edifice as old as middle pleistocene middle sister a basalt andesite dacite cone built between 48 and 14 ka and south sister is a basalt free edifice that alternated rhyolitic and intermediate modes from 50 ka to 2 ka largely contemporaneous with middle sister detailed mapping 330 chemical analyses and 42 radioisotopic ages show that the oldest exposed south sister lavas were initially rhyolitic 50 ka by 37 ka rhyolitic lava flows and domes 72 74 sio2 began alternating with radially emplaced dacite 63 68 sio2 and andesite 59 63 sio2 lava flows construction of a broad cone of silicic andesite dacite 61 64 sio2 culminated 30 ka in a dominantly explosive sequence that began with crater forming andesitic eruptions that left fragmental deposits at least 200 m thick this was followed at 27 ka by growth of a steeply dipping summit cone of agglutinate dominated andesite 56 60 5 sio2 and formation of a summit crater 800 m wide this crater was soon filled and overtopped by a thick dacite lava flow and then by 150 m of dacitic pyroclastic ejecta small volume dacite lavas 63 67 sio2 locally cap the pyroclastic pile a final sheet of mafic agglutinate 54 56 sio2 the most mafic product of south sister erupted from and drapes the small 300 m wide present day summit crater ending a summit building sequence that lasted until 22 ka a 20 kyr long hiatus was broken by rhyolite eruptions that produced 1 the rock mesa coulee tephra and satellite domelets 73 5 sio2 and 2 the devils chain of 20 domes and short coulees 72 3 72 8 sio2 from n s vent alignments on south sister s flanks the compositional reversal from mafic summit agglutinate to recent rhyolites epitomizes the frequently changing compositional modes of the south sister locus throughout its lifetime south sister is part of a reach of the cascades unusually active in the last 50 kyr characterized by high vent density n s vent alignments and numerous eruptive units of true rhyolite 72 sio2 that distinguishes it from much of the quaternary cascade arc these are eruptive expressions of the complex confluence of arc and intraplate magmatic tectonic regimes

stratigraphy mineralogy and genesis of the bigadic borate deposits western turkey the bigadic borates are the largest colemanite and ulexite deposits in the world and the high grade colemanite and ulexite ores 30 and 29 b 2 o 3 respectively should supply a substantial proportion of the world9s needs for many years the bigadic deposits formed within neogene perennial saline lakes sediments located in a northeast southwest trending basin the volcano sedimentary sequence in the deposits consists of from bottom to top basement volcanics lower limestone lower tuff lower borate zone upper tuff upper borate zone and olivine basalt the borate deposits formed under arid conditions in perennial saline lakes fed by hydrothermal springs associated with local volcanic activity the deposits are interbedded with tuffs clay and limestones borate minerals formed in two zones separated by thick tuff beds that have been transformed to montmorillonite chlorite and zeolites mainly heulandite during diagenesis colemanite and ulexite predominate in both borate zones but other borates including howlite probertite and hydroboracite are present in the lower borate zone whereas inyoite meyerhofferite pandermite tertschite hydroboracite howlite tunellite and rivadavite are found in the upper borate zone calcite anydrite gypsum celestite k feldspar analcime heulandite clinoptilolite quartz opal ct montmorillonite chlorite and illite are also found in the deposit colemanite nodules in both borate zones probably formed directly from solution within unconsolidated sediments just below the sediment water interface and continued to grow as the sediments were compacted it is unlikely that the colemanite formed by dehydration of inyoite and or by replacement of ulexite after burial later generations of colemanite and ulexite are found in vugs and veins and as fibrous margins of early formed nodules other diagenetic changes include the partial replacement of colemanite by howlite and hydroboracite and ulexite by tunellite nodular shaped colemanite and ulexite minerals predominate in both borate zones colemanite and ulexite show alternating horizons and the transformation of one mineral to another has not been observed and the

reflectivity patterns in the variscan mountain belts and adjacent areas an attempt for a pattern recognition and correlation to tectonic units abstract the seismic reflection profiles of dekorp deutsches kontinentales reflexionsseismisches programm in the federal republic of germany to date have been limited to areas of the variscan orogeny nevertheless the character of their reflections differs considerably and may be correlated to certain variscan and post variscan developments lower crust lamellae develop in areas of high heat flow mostly associated with post variscan extensional processes crocodile and nappe tectonics are best preserved in the cores and at the flanks of older massifs which were incorporated into the variscan orogeny so far poor reflectivity has been observed only in the area of the london brabant massif which was not involved in any of the phanerozoic orogenies

volcanic and deformation history of the bodrum resurgent caldera system southwestern turkey abstract the volcanic rocks of the bodrum peninsula in sw turkey and ne of the hellenic arc outcrop over an area of 138 km 2 a monzonitic intrusion is exposed in the western part of the peninsula upper miocene volcanism is represented by high k hk andesitic andesitic lava flows and pillows sparse hk andesitic and dacitic lava domes and associated block and ash flows a hk andesitic ignimbrite sequence with two stratigraphic units is associated with the collapse of a complex caldera system breccias formed as a result of slumping of the caldera walls are observed inside the caldera post caldera activity is represented by hk andesitic hk basaltic andesitic lava flows domes and associated block and ash flows numerous dykes hk andesitic and shoshonitic in composition cut all volcanic units the structure of the bodrum caldera was investigated using spot image digital elevation model dem aerial photographs as well as field data the bodrum caldera is a ne sw elongated semi elliptical deeply eroded caldera with dimensions of 18 7 7 7 km it is partly submerged in the sw part the complex caldera system can be described in terms of two structural domains the collapse of the dagbelen domain is interpreted as a piston type subsidence while the karakaya domain represents a piecemeal collapse both domains exhibit two separate resurgence events the elongation of the caldera may be related to pre existing regional tectonic structures the caldera is also affected and cut by late stage faults related to regional extensional events moreover pre caldera volcanism is dispersed and cannot be related to a pre existing stratovolcano bodrum volcanism is therefore interpreted as a complex ignimbritic shield volcano

multistage exhumation of the menderes massif western anatolia turkey structural analyses along selected transects across the menderes massif and incorporation of existing data have resulted in a synthetic cross section across southwestern turkey the tectonic interpretation has been combined with 40ar 39ar laser probe experiments on two syn kinematic white mica populations which respectively predate and overprint documented early miocene deformational fabrics our results indicate that the regional extension had initiated by eocene oligocene times a 36 2 ma 40ar 39ar age derived from white mica which formed during a regionally observed northward directed tectonic transport suggests that the extension was contemporaneous with the tectonic emplacement of mid crustal continental basement alternatively the age may relate to the regional cooling of the basement sequence and thus postdates the tectonic emplacement in the latter scenario the analysis fails to solve the present ambiguity on the pan african or alpine affinity of the northward directed transport further exhumation of basement rocks is characterized by a dominant displacement along the north dipping gediz detachment at the northern margin of the massif which developed under ductile conditions in the early miocene by partial exploitation of older zones of weakness which originated from an earlier phase of basement emplacement youngest semi ductile activity along the gediz detachment has been recorded as having a 7 1 ma 40ar 39ar age derived from syn kinematic white mica in the top of the detachment following the initiation of the ductile gediz detachment an antithetic semibrittle and south dipping buyuk menderes detachment had developed in the center of the massif which together with the gediz detachment accommodated further doming of the central part of the menderes massif and controlled the architecture of the surrounding supradetachment basins

entrance of hot pyroclastic flows into the sea experimental observations the entrance of hot pyroclastic flows into water has been observed in a series of experiments in which shooting granular flows of hot ignimbrite ash 403 c of bulk density near that of water run down a smooth chute and enter a water filled tank at an angle of 26 flows of relatively cool ash 250 c mixing across the water surface over some distance from shore generates steam explosions forming fountains of wet and dry ash and convectively rising fine ash plumes steam explosions increase in strength and lateral extent towards higher ash temperatures and mass fluxes the explosions generate water waves that remain driven by massive fountain fallout across some distance from shore the ash fountains feed pyroclastic surges which advance down tank over water at high speeds underwater plumes of sediment falling from the ash fountains and surges drop coarse load onto the floor whereas the finer load forms a turbidity current high temperature and poor size sorting of pyroclastic flows are key parameters that determine the processes of interaction with water and the associated hazards poor sorting allows for the formation of ash cloud surges moving over water even from cool flows high temperatures cause littoral explosions and facilitate extensive mass transport over water all flows generate tsunami waves by different mechanisms

landscape and sedimentary response to catastrophic debris avalanches western taranaki new zealand abstract catastrophic volcanic debris avalanches reshape volcanic edifices with up to half of pre collapse cone volumes being removed deposition from this debris avalanche deposit often fills and inundates the surrounding landscape and may permanently change the distribution of drainage networks on the weakly incised mt taranaki ring plain volcanic debris avalanche deposits typically form a large wedge shape in plan view over all flat lying fans following volcanic debris avalanches a period of intense re sedimentation commonly begins on ring plain areas particularly in wet or temperate climates this is exacerbated by large areas of denuded landscape ongoing instability in the scarp source region damming of river stream systems and in some cases inherent instability of the volcanic debris avalanche deposits in addition on mt taranaki the collapse of a segment of the cone by volcanic debris avalanche often generates long periods of renewed volcanism generating large volumes of juvenile tephra onto unstable and unvegetated slopes or construction of new domes with associated rock falls and block and ash flows the distal ring plain impact from these post debris avalanche conditions and processes is primarily accumulation of long run out debris flow and hyperconcentrated flow deposits with a variety of lithologies and sedimentary character common to these post debris avalanche units is evidence for high water content flows that are typically non cohesive hence sedimentary variations in these units are high in lateral and longitudinal exposure in relation to local topography the post collapse deposits flank large scale fans and hence similar lithological and chronological sequences can form on widely disparate sectors of the ring plain these deposits on mt taranaki provide a record of landscape response and ring plain evolution in three stages that divide the currently identified warea formation 1 the deposition of broad fans of material adjacent to the debris avalanche unit 2 channel formation and erosion of stage 1 deposits primarily at the contact between debris avalanche deposits and the stage 1 deposits and the refilling of these channels and 3 the development of broad tabular sheet flows on top of the debris avalanche leaving sediments between debris avalanche mounds after a volcanic debris avalanche these processes represent an ever changing and evolving hazard scape with hazard maps needing to be regularly updated to take account of which stage the sedimentary system is in