reply to comment on cobenas g thouret j c bonadonna c boivin p 2012 the c 2030 yr bp plinian eruption of el misti volcano peru eruption dynamics and hazard implications journal of volcanology and geothermal research 241 242 105 120 by harpel et al jvgr 2013 abstract the comment provided by harpel et al challenges our interpretation of the most recent plinian eruption of el misti c 2070 yr bp situated near the city of arequipa peru revised age from our previously stated date of c 2030 bp in our view the sequence of deposits points to another example of a plinian pumice rich tephra fall followed by lithic rich pyroclastic density currents pdcs locally late rockslide avalanches have emplaced mass flow deposits on top of pdcs while elsewhere post eruption lahars have led to their remobilization one of the main criticisms from harpel et al was in our interpretation of the deposits as being of pdc origin rather than post eruption lahars we revise each of the diagnostic features that harpel et al have used for attributing the deposits to lahars we present two tables of the revised age of the eruption and criteria based on lithofacies lithological components grain size distribution and statistical indices for each of the c 2070 yr bp old pdc lahar and mass flow deposits our maps and simulations of pdcs and lahars based on two numerical codes with volume inputs from identified deposits around el misti do not fall short of the hazard assessment goal

jokulhlaups a reassessment of floodwater flow through glaciers 1 in glaciated catchments glacier generated floods jokulhlaups put human activity at risk with large sporadic jokulhlaups accounting for most flood related fatalities and damage to infrastructure in studies of jokulhlaup hydrodynamics the view predominates that floodwater travels within a distinct conduit eroded into the underside of a glacier however some jokulhlaups produce subglacial responses wholly inconsistent with the conventional theory of drainage by focusing on icelandic jokulhlaups this article reassesses how floodwater flows through glaciers it is argued that two physically separable classes of jokulhlaup exist and that not all jokulhlaups are an upward extrapolation of processes inherent in events of lesser magnitude and smaller scale the hydraulic coupling of multiple nonlinear components to the flood circuit of a glacier can induce extreme responses including pressure impulses in subglacial drainage representing such complexity in mathematical form should be the basis for upcoming research as future modeling results may help to determine the glaciological processes behind heinrich events moreover such an approach would lead to more accurate predictive models of jokulhlaup timing and intensity

vapour discharges on nevado del ruiz during the recent activity clues on the composition of the deep hydrothermal system and its effects on thermal springs abstract the nevado del ruiz volcano is considered one of the most active volcanoes in colombia which can potentially threaten approximately 600 000 inhabitants the existence of a glacier and several streams channelling in some main rivers flowing downslope increases the risk for the population living on the flank of the volcano in case of unrest because of the generation of lahars and mudflows indeed during the november 1985 subplinian eruption a lahar generated by the sudden melting of the glacier killed twenty thousand people in the town of armero moreover the involvement of the local hydrothermal system has produced in the past phreatic and phreatomagmatic activity as occurred in 1989 therefore the physico chemical conditions of the hydrothermal system as well as its contribution to the shallow thermal groundwater and freshwater in terms of enthalpy and chemicals require a close monitoring the phase of unrest occurred since 2010 and culminated with an eruption in 2012 after several years of relative stability still maintains a moderate alert as required by the high seismicity and so 2 degassing in october 2013 a sampling campaign has been performed on thermal springs and stream water located at 2600 5000 m of elevation on the slope of nevado del ruiz analyzed for water chemistry and stable isotopes some of these waters are typically steam heated low ph and high sulfate content by the vapour probably separating from a zoned hydrothermal system by applying a model of steam heating based on mass and enthalpy balances we have estimated the mass rate of hydrothermal steam discharging in the different springs the composition of the hottest thermal spring botero londono is probably representative of a marginal part of the hydrothermal system having a temperature of 250 c and low salinity cl 1500 mg l which suggest along with the retrieved isotope composition a chiefly meteoric origin the vapour discharged at the steam vent nereidas 3600 m asl is hypothesized to be separated from a high temperature hydrothermal system based on its composition and on literature data on fluid inclusions we have retrieved the p t x conditions of the deep hydrothermal system as well as its ph and f o 2 the vapour feeding nereidas would separate from a biphasic hydrothermal system characterized by the following parameters t 315 c p 15 mpa nacl 10 wt co 2 5 wt and similar proportion between liquid and vapour considering also the equilibria involving s bearing gases and hcl ph would approach the value of 1 5 while f o 2 would correspond to the feo fe 2 o 3 buffer chlorine content is estimated at 10 300 mg l changes in the magmatic input into the hydrothermal system could modify its degree of vapourization and or p t x conditions thus inducing corresponding variations in vapour discharges and thermal waters these findings paralleled by contemporary measurements of water flow rates could give significant clues on risk evaluation

impact of the eruptive activity on glacier evolution at popocatepetl volcano mexico during 1994 2004 abstract distribution rate and magnitude of the glacier changes caused by eruptive activity over 1994 2001 at popocatepetl volcano were determined digital elevation models computed by scanned photographs within a digital photogrammetric workstation and the subsequent dem comparison allowed the determination of glacial changes the results show that drastic changes occurred in glacier geometry and morphology over 1996 2001 53 of the glacier surface area was lost due to melting processes the most important loss occurred over 2000 2001 when 19 of the glacier covered area disappeared the glacier volume losses increased over time during 1999 2000 the largest loss was observed however in february 2001 the glacier showed an apparent small increase in volume volcanic processes disturbed the mass balance of the glacier thereby accelerating the ablation processes the eruptive behavior of popocatepetl was characterized during this time by alternating periods of explosive events and low activity pyroclastic flow generation ejection of incandescent material and tephra fall affected the glacier the tephra volume distribution and remobilization produced considerable changes on glacier evolution tephra deposition on the glacier surface was the most frequent process the irregular distribution and thickness of tephra provoked differential ablation and tephra remobilization processes took place on the glacier surface together these processes incised the glacier surface over time based on these results and observations a model of glacier evolution is proposed involving an adjustment phase thinning phase areal retreat phase and fragmentation phase a complex interplay of factors and processes took place between eruptive activity and the glaciers at popocatepetl volcano the glacier evolution and subsequent extinction were induced by the eruptive behavior over the years while not the only process at work eruptive activity played the primary role in accelerating retreat and as a consequence in glacier extinction

paleoenvironmental changes and glacial stades of the last 50 000 years in the cordillera central colombia using data from glacial geomorphology tephra soil stratigraphy and mineralogy palynology and radiocarbon dating a sequence of glacial and bioclimatic stades and interstades has been identified for the past ca 50 000 yr in the ruiz tolima massif cordillera central six cold stades separated by warmer interstades occurred before 48 000 between 48 000 and 33 000 between 28 000 and 21 000 from 16 000 to ca 14 000 ca 13 000 12 400 and ca 11 000 10 000 yr b p although the radiocarbon ages are minimum limiting ages obtained from tephra layers on top of tills the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections two minor moraine stages likely reflect glacier pauses during cold intervals ca 7400 yr b p and slightly earlier finally glaciers readvanced between the 17th and 19th centuries in contrast to the glacier cover ca 34 km2 on volcanoes of the massif during the last glacial maximum lgm the ice cover expanded to 1200 km2and was still 800 km2during late glacial time lgt glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude ela by ca 1100 m during the lgm and 500 600 m during lgt relative to the modern ela which lies at ca 5100 m in the cordillera central glaciers in this region apparently reached their greatest extent when the climate was cold and moist e g during stades corresponding to marine isotope stage 3 glaciers were still expanding during the lgm ca 28 000 21 000 yr b p but they shrank considerably after 21 000 yr b p because of greatly reduced precipitation

effects of the november 13 1985 eruption on the snow pack and ice cap of nevado del ruiz volcano colombia abstract about twenty five to thirty percent of the ice on the ice cap of nevado del ruiz was fractured and destabilized by earthquakes and explosive activity on november 13 1985 comparison of aerial and ground photographs taken before and after the eruption allows calculation of the volume of snow and ice removed from each glacial basin during the eruption about 16 4 2 km 2 of the surface area of the ice and snow was lost the corresponding volume is estimated to be close to 0 06 km 3 or 9 of the total volume of ice and snow at least four distinct processes including explosions ice avalanches surficial erosion of snow and slush avalanches were responsible for transporting snow firn and ice downslope heat from pyroclastic flows and surges and their deposits was responsible for melting snow and ice both at the surface of the ice cap in situ and during its downslope transport voluminous lahars were triggered in 3 of the 4 main drainages on the volcano by the approximately 43 million m 3 of liquid water about 62 million m 3 of snow firn and ice produced by these combined processes thermal and mechanical effects of the pyroclastic flows and surges included scouring direct melting and entraining snow firn and ice which left several erosional features on the ice cap and deposits both on the ice and on the edges of the ice cap subsurface and englacial drainage of water through crevasses was deduced from depositional and morphological features at the ice margins some meltwater might have been trapped in reservoirs but some water was also released shortly after the eruption the estimated volume of released meltwater is about 43 million m 3 i e 2 4 times more than the approximate 11 12 million m 3 of water incorporated into the lahars thus roughly 21 million m 3 of water were released but did not contribute to lahar generation this non contributing water was 1 included in snow avalanches and sediment laden slush avalanches outside the lahars channels or bound up in the wet pyroclastic surge deposits 2 incorporated in the phreatic explosive products or saturated firn by meltwater which issued from the thermal effect of the tephra fall 3 sublimated into steam during the passage of the pyroclastic flows or 4 stored within the ice meltwater may still be be trapped within the ice cap and may be a potential source of water for future lahars

a study of the taisho lahar generated by the 1926 eruption of tokachidake volcano central hokkaido japan and implications for the generation of cohesive lahars abstract understanding the generation mechanisms of lahars is important for improving volcanic hazard assessments the taisho lahar tl was generated during the 1926 eruption of tokachidake volcano japan and was considered a typical snowmelt lahar caused by the runout of hot debris onto a snow covered slope a similar mechanism produced a huge mud flow during the 1985 eruption of nevado del ruiz colombia however the origin of water in such lahars remains a controversial topic because the calculated water mass is based on the assumption that all of the snow on the runout area of the tl was melted although this is much less than the estimated water volume in the tl estimated by previous studies i have re examined proximal deposits of the tl and their paleomagnetic characteristics in order to better understand the eruption sequence and formation of the tl the tl produced two debris avalanche deposits and a surge like deposit that had relatively high emplacement temperature 350 c the deposits are composed of hydrothermally altered andesitic gravel sand and mud the high clay content 3 5 wt clay in the 6 m 3 water beneath the active crater this study indicates that hydrothermal system explosions can trigger cohesive lahars that contain both snow melt and hydrothermal pore water and this indicates the need to monitor hydrothermal systems

ice melt collapse pits and associated features in the 1991 lahar deposits of volcan hudson chile criteria to distinguish eruption induced glacier melt in subaerial volcaniclastic sequences structures formed by ice blocks can provide information about a volcano s history of lahar generation by glacier melt at volcan hudson in chile catastrophic lahars were initiated by eruption induced melting of glacier ice in august and october 1991 they transported large ice blocks 50 km down the rio de los huemules valley to the sea large current crescents with lee side lenses were formed where ice blocks were deposited during waning stages of the flood when stranded blocks of ice melted they left cone shaped and ring shaped heaps of ice rafted debris on the sediment surface several hundred ice blocks were completely buried within the aggrading lahar sediment and when these melted circular collapse pits formed in the sediment collapse types included subsided coherent blocks of sediment bounded by an outward dipping ring fracture trapdoor structures with horseshoe shaped fractures downsag pits with centroclinal dips locally up to 60 pits with peripheral graben and crevasses piecemeal highly fragmented collapse structures and funnel shaped pits containing disaggregated sediment a sequence of progressive collapse is inferred in which initial downsag and subsidence on an outward dipping ring fracture produces a small diameter pit this is followed by widening of the pit by progressive development of concentric ring fractures and downsag outside the early formed pit and by collapse of overhanging pit walls to produce vertical to inward dipping walls and aprons of collapse debris on the pit floor the various structures have potential for preservation even in regions prone to high rainfall and flooding and they can be used to indicate that former lahars contained abundant blocks of ice

glaciological response to distal tephra fallout from the 1947 eruption of hekla south iceland glacier responses to tephra deposition are shown to be highly variable where wind transported eruption plumes produce narrow distal fallout zones with steep lateral thickness gradients significant but short lived advances of faster flowing glaciers can be triggered by deposition from modest eruptions the 1947 eruption of hekla south iceland covered nearby glaciers with variable thicknesses of tephra causing dramatic spatial variations in ablation rate relative snow ablation increased by an estimated 80 at the eastern margin of eyjafjallajokull but decreased by 54 at the western margin relative ice ablation increased by only 4 in the east but decreased by 75 at the western margin only 15 km distant the effect on mass balance therefore depends on tephra distribution as well as on the nature of the glacier surface on gigjokull retardation of ablationwas greatest at the terminus associated with an anomalous advance of 328 m between 1947 and 1954 other glaciers in the fallout zone show either no recognizable response or accelerated retreat advances will be short lived due to the rapid redistribution of supraglacial tephra in a maritime climate and the potential for discriminating between volcanically and climatically forced advances in the glacio geomorphological record is low the long term glaciological effect of volcanism is to create thin low albedo covers after reworking which make conditions less favourable for glaciation

basanite glaciovolcanism at llangorse mountain northern british columbia canada the llangorse volcanic field is located in northwest british columbia canada and comprises erosional remnants of miocene to holocene volcanic edifices lava flows or dykes the focus of this study is a single overthickened 100 m thick valley filling lava flow that is middle pleistocene in age and located immediately south of llangorse mountain the lava flow is basanitic in composition and contains mantle derived peridotite xeno liths the lava directly overlies a sequence of poorly sorted crudely bedded volcaniclastic debris flow sediments the debris flow deposits contain a diverse suite of clast types including angular clasts of basanite lava blocks of peridotite coated by basanite and rounded boulders of granodiorite many of the basanite clasts have been palagonitized the presence and abundance of clasts of vesicular to scoriaceous palagonitized basanite and peridotite suggest that the debris flows are syngenetic to the overlying lava flow and sampled the same volcanic vent during the early stages of eruption they may represent lahars or outburst floods related to melting of a snow pack or ice cap during the eruption the debris flows were water saturated when deposited the rapid subse quent emplacement of a thick basanite flow over the sediments heated pore fluids to at least 80 100 c causing in situ palagonitization of glassy basanite clasts within the sediments the over thickened nature of the llangorse mountain lavas suggests ponding of the lava against a down stream barrier the distribution of similar aged glaciovolcanic features in the cordillera suggests the possibility that the barrier was a lower elevation valley wide ice sheet

major holocene block and ash fan at the western slope of ice capped pico de orizaba volcano mexico implications for future hazards abstract a major block and ash fan extends more than 14 km westward from the summit of pico de orizaba volcano in the eastern part of the trans mexican volcanic belt radiocarbon dating of charcoal within the fan deposits yielded holocene ages that range between 4040 80 and 4660 100 y b p stratigraphical sedimentological geochemical and scanning electron microscope studies indicate that this fan originated within a relatively short time span by multiple volcanic explosions at the summit crater this activity produced a series of pyroclastic flows mainly block and ash flows and lahars which were channelized by a glacial cirque and connecting u shaped valleys as they descended toward the base of the volcano a recurrence of a similar eruption today would pose severe hazards to the population of more than 50 000 people who live in a potentially dangerous zone a detailed reconstruction of the sequence of events that led to the formation of the block and ash fan is presented to help mitigate the risk special attention is given to the effects of an ice cap and the role of pre existing glacial morphology on the distribution of products from such an eruption

volcanic geomorphology an overview abstract the review examines the role of geomorphology in analyzing the volcanoes on earth five objectives are stressed first classifications of volcanic landforms should be improved to take care of the complexity in volcanic landform generation as magmatic systems style of eruption and the erupted material all influence the morphology second geomorphology should contribute to the science of volcanology through its capability in reconstructing growth stages in complex volcanoes and also in analyzing the structural factors which contribute to the catastrophic collapse of volcanoes third geomorphology can contribute to physical volcanology by assessing the effects of topography on transport erosion and deposition of volcanogenic flows and identifying the sources and climatic tectonic conditions which govern the emplacement of volcaniclastic deposits fourth volcanic geomorphology a identifies sedimentary facies associations b constructs facies models for dynamic volcano delivery systems and c analyzes the characteristics of sediment gravity flows in order to determine relevant parameters for modelling their behaviour fifth process oriented geomorphology is critical in developing accurate methods for measuring rates of geomorphic processes that shape ephemeral volcanic constructs and for evaluating and comparing geomorphic impacts on disturbed catchments and the related hydrologic response before during and after eruptions this should help to refine parameters for the exponential decay model finally volcanic geomorphology is essential for risk assessment through geomorphic hazard zonation and composite risk zonation such treatments are necessary in order to face the enhanced challenge posed by the combination of natural hazards and the increasing number of people who are at risk around volcanoes

monitoring and modeling ice rock avalanches from ice capped volcanoes a case study of frequent large avalanches on iliamna volcano alaska abstract iliamna is an andesitic stratovolcano of the aleutian arc with regular gas and steam emissions and mantled by several large glaciers iliamna volcano exhibits an unusual combination of frequent and large ice rock avalanches in the order of 1 10 6 m 3 to 3 10 7 m 3 with recent return periods of 2 4 years we have reconstructed an avalanche event record for the past 45 years that indicates iliamna avalanches occur at higher frequency at a given magnitude than other mass failures in volcanic and alpine environments iliamna volcano is thus an ideal site to study such mass failures and its relation to volcanic activity in this study we present different methods that fit into a concept of 1 long term monitoring 2 early warning and 3 event documentation and analysis of ice rock avalanches on ice capped active volcanoes long term monitoring methods include seismic signal analysis and space and airborne observations landsat and aster satellite data was used to study the extent of hydrothermally altered rocks and surface thermal anomalies at the summit region of iliamna subpixel heat source calculation for the summit regions where avalanches initiate yielded temperatures of 307 to 613 k assuming heat source areas of 1000 to 25 m 2 respectively indicating strong convective heat flux processes such heat flow causes ice melting conditions and is thus likely to reduce the strength at the base of the glacier we furthermore demonstrate typical seismic records of iliamna avalanches with rarely observed precursory signals up to two hours prior to failure and show how such signals could be used for a multi stage avalanche warning system in the future for event analysis and documentation space and airborne observations and seismic records in combination with srtm and aster derived terrain data allowed us to reconstruct avalanche dynamics and to identify remarkably similar failure and propagation mechanisms of iliamna avalanches for the past 45 years simple avalanche flow modeling was able to reasonably replicate iliamna avalanches and can thus be applied for hazard assessments hazards at iliamna volcano are low due to its remote location however we emphasize the transfer potential of the methods presented here to other ice capped volcanoes with much higher hazards such as those in the cascades or the andes

late quaternary glacial stades in the cordillera central colombia based on glacial geomorphology tephra soil stratigraphy palynology and radiocarbon dating using data from glacial geomorphology tephra soil stratigraphy and mineralogy palynology and radiocarbon dating a sequence of glacial and bioclimatic stades and interstades has been identified for the last ca 50000 yr in the ruiz tolima massif cordillera central colombia six pleistocene cold stades separated by warmer interstades occurred before 48000 between 48000 and 33000 between 28000 and 21000 from 16000 to ca 14000 ca 13000 12400 and ca 11000 10000 yr bp although these radiocarbon ages are minimum limiting ages obtained from tephra layers on top of tills the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections two minor moraine stages likely reflect glacier standstill during cold intervals ca 7400 yr bp and slightly earlier finally glaciers readvanced between the seventeenth and nineteenth centuries in contrast to the ice clad volcanoes of the massif ca 34 km2 in area above an altitude of ca 4800 m the ice cover expanded to 1200 km2 during the last glacial maximum lgm and was still 800 km2 during late glacial time lgt glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude ela by ca 1100 m during the lgm and 500 600 m during lgt relative to the modern ela which lies at ca 5100 m in the cordillera central glaciers in this region apparently reached their greatest extent when the climate was cold and wet e g during stades corresponding to oxygen isotope stage 3 glaciers were still expanding during the lgm ca 28000 21000 yr bp but they shrank considerably after 21000 yr bp because of greatly reduced precipitation 1997 john wiley sons ltd

the 1985 nevado del ruiz volcano catastrophe anatomy and retrospection abstract this paper seeks to analyze in an objective way the circumstances and events that contributed to the 1985 nevado del ruiz catastrophe in order to provide useful guidelines for future emergencies the paper is organized into two principal parts in the first part an anatomy of the catastrophe is developed as a step by step chronicle of events and actions taken by individuals and organizations during the period november 1984 through november 1985 this chronicle provides the essential background for the crucial events of november 13 this year long period is broken down further to emphasize important chapters the gradual awareness of the awakening of the volcano a long period of institutional skepticism reflecting an absence of credibility the closure of the credibility gap with the september 11 phreatic eruption followed by an intensive effort to gird for the worst and a detailed account of the day of reckoning the second part of the paper retrospection examines the numerous complicated factors that influenced the catastrophic outcome and attempts to cull a few lessons from armero in order to avoid similar occurrences in the future in a nutshell the government on the whole acted responsibly but was not willing to bear the economic or political costs of early evacuation or a false alarm science accurately foresaw the hazards but was insufficiently precise to render reliable warning of the crucial event at the last possible minute catastrophe was therefore a calculated risk and this combination the limitations of prediction detection the refusal to bear a false alarm and the lack of will to act on the uncertain information available provided its immediate and most obvious causes but because the crucial event occurred just two days before the armero emergency management plan was to be critically examined and improved the numerous circumstances which delayed progress of emergency management over the previous year also may be said to have contributed to the outcome thus the catastrophe was not caused by technological ineffectiveness or defectiveness nor by an overwhelming eruption or by an improbable run of bad luck but rather by cumulative human error by misjudgment indecision and bureaucratic shortsightedness armero could have produced no victims and therein dwells its immense tragedy

the stratigraphy depositional processes and environment of the late pleistocene polallie period deposits at mount hood volcano oregon usa the polallie eruptive period of mt hood oregon is the last major episode of eruption and dome growth before the late holocene activity which was centered at crater rock avolume of 4 8 km 3 of polallie deposits forms an apron of ca 60 km 2 on the east northeast and southeast flanks the polallie deposits can be divided stratigraphically into four groups group i rockslide avalanche and pyroclastic flow deposits group ii debris flow and pyroclastic flow deposits that suggest some explosive activity and remobilization of pyroclastic debris in a glacial environment group iii block and ash flow deposits that attest to summit dome growth group ivalternating debris flow deposits glacial sediments and reworked pyroclastic flow deposits that indicate a decrease in dome activity and an increase in erosion and transport group iii clearly indicates frequent episodes of dome growth and collapse whereas groups ii and iv imply increasing erosion and conversely decreasing volcanic activity the polallie period occurred in the late pleistocene during and just after the last alpine glaciation which is named evans creek in the cascade range according to four k ar age dates on lava flows interbedded with polallie deposits and to published minimum 14 c ages on tephra and soils overlying these deposits the polallie period had lasted 15 000 22 000 years between 28 34 ka and 12 13 ka from stratigraphic subdivisions sedimentary lithofacies and features and from the grain size and geochemical data we infer that the polallie depositional record is a result of the interplay of several processes acting during a long lasting period of dome growth and destruction the growth of several domes near the present summit was intermittent because each group of sediments encompasses primary pyroclastic and secondary volcaniclastic and epiclastic deposition direct deposition of primary material has occurred within intervals of erosion that have probably included meltwater processes from snow and ice fields interactions of hot pyroclastic debris with glacier ice that capped the mountain at that time contributed to release meltwater enhancing the remobilization of primary deposits d 2005 elsevier b v all rights reserved

quaternary eruptive history of nevado del ruiz colombia abstract nevado del ruiz has a 1 8 m y long eruptive record that includes alternate construction and destruction of three edifices during three main eruptive periods termed ancestral ruiz older ruiz and ruiz nevado del ruiz is located on a complex intersection of four groups of faults the most significant being the n20 e palestina strike slip fault and the n50 w villamaria termales normal fault ancestral ruiz was a broad stratovolcano built by two eruptive stages of lava flows starting about 1 8 ma ago and ending 1 0 ma ago a partial collapse and formation of a caldera are thought to have occurred between 1 0 and 0 8 ma ago older ruiz was a stratovolcano constructed by lava flows in three stages starting about 0 8 ma ago and ending about 0 2 ma ago extensive and voluminous welded and nonwelded pyroclastic flow deposits that partly fill preexisting valleys record the formation of a young summit caldera between 0 2 and 0 15 ma ago present ruiz is formed by a cluster of composite lava domes that probably filled the summit caldera of older ruiz present ruiz eruptive activity is mostly explosive but also includes dome growth and parasitic dome activity of la olleta and alto la piramide twelve eruptive stages occurred during the last 11 000 years accompanied by rockslide debris avalanches pyroclastic flows or surges and their subsequent interactions with the ice cap as well as by glacial erosion and mass wasting diverse processes within these twelve stages have led to a partial destruction of the summit domes this long and complex pleistocene and holocene eruptive sequence helps to put the november 13 1985 eruption into a broader perspective

ice volcano interactions during the 2010 eyjafjallajokull eruption as revealed by airborne imaging radar 1 during the eruption of the ice covered eyjafjallajokull volcano a series of images from an airborne synthetic aperture radar sar were obtained by the icelandic coast guard cloud obscured the summit from view during the first three days of the eruption making the weather independent sar a valuable monitoring resource radar images revealed the development of ice cauldrons in a 200 m thick ice cover within the summit caldera as well as the formation of cauldrons to the immediate south of the caldera additionally radar images were used to document the subglacial and supraglacial passage of floodwater to the north and south of the eruption site the eruption breached the ice surface about four hours after its onset at about 01 30 utc on 14 april 2010 the first sar images obtained between 08 55 and 10 42 utc show signs of limited supraglacial drainage from the eruption site floodwater began to drain from the ice cap almost 5 5 h after the beginning of the eruption implying storage of meltwater at the eruption site due to initially constricted subglacial drainage from the caldera heat transfer rates from magma to ice during early stages of cauldron formation were about 1 mw m 2 in the radial direction and about 4 mw m 2 vertically meltwater release was characterized by accumulation and drainage with most of the volcanic material in the ice cauldrons being drained in hyperconcentrated floods after the third day of the eruption meltwater generation at the eruption site diminished due to an insulating lag of tephra

quaternary eruptive history and hazard zone model at nevado del tolima and cerro machin volcanoes colombia the ice clad and fumarolic nevado del tourna volcano 4 39 n 75 20 w south of nevado del ruiz is offset toward the southeast from the axis of the volcanic ruiz tolima massif with respect to the major ne trending strike slip palestina fault it is composed of four units 1 a pre tolima plateau like basement of basaltic andesite lava flows of early quaternary age 2 a dissected ancestral tourna stratovolcano cut by a presumed collapse caldera of middle pleistocene age 3 an older tolima stratovolcano of late pleistocene age partly destroyed by a summit caldera and 4 composite domes of the cone shaped young and present tolima young tolima volcano is an andesitic and dacitic composite cone formed over the past 40 000 years within a 3 km wide caldera that opened around 0 14 ma deposits of welded and nonwelded pumice and scoria flows were emplaced toward the southeast rio combeima and northeast rio totare repeated growth of lava domes over the past 16 000 years is witnessed by thick block lava flows on the southern and eastern flanks and by block and ash or scoria rich pyroclastic flow deposits this activity occurred during at least six eruptives stages as follows el placer ca 16 200 14 000 yr b p romerales ca 13 000 12 300 yr b p canalones ca 11 500 9750 yr b p mesetas ca 7200 4600 yr b p encanto ca 3600 1700 yr b p and nieves historical interactions with the ice cap probably triggered debris flows that partly filled the combeima and totare valleys and formed the holocene terraces on the upper pleistocene volcaniclastic fans of ibagueand venadillo as much as 60 km from the source the latest major activity was a plinian eruption which deposited a pumice fall layer ca 3600 yr b p 0 5 km3 actual volume mainly toward the west and northwest minor tephra falls and debris flows occurred during the historical period before the reported 1918 and 1943 small phreatic events a general hazard zone map shows areas potentially affected by future eruptions both at nevado del tolima and at active cerro machin 12 km southward the extent of areas likely to be affected by tephra falls debris flows pyroclastic flows or surges debris avalanches and lava flows is shown subplinian and plinian eruptions of nevado del tolima were used to represent the moderate and large events to be expected 300 000 people live within a 35 km distance from those volcanoes which have exhibited a behaviour more explosive than nevado del ruiz despite the small sized ice cap debris flows are the most probable hazard for even a minor eruption because of the very steep slope gradient and because of probable interactions of hot eruptive products with ice and snow additionally scoria flows and debris avalanches can be directed toward the southeast and could be transformed into debris flows that would devastate the combeima valley and suburbs of ibaguecity where about 50 000 people live

the relative importance of supraglacial versus subglacial meltwater escape in basaltic subglacial tuya eruptions an important unresolved conundrum the hydraulic behaviour of meltwater during subglacial basaltic eruptions in temperate ice is of paramount importance in understanding the eruptive processes lithofacies and architecture of the edifices formed hydraulics also determines the timing location and volume of meltwater discharge which may be sudden and catastrophic and via subglacial and or supraglacial routes increasing our knowledge of meltwater hydraulics is therefore important for understanding predicting and mitigating the impact of meltwater release on vulnerable human communities new observations about eruption related meltwater hydraulics are presented for well exposed glaciovolcanic lava fed deltas on james ross island antarctica and accounts of historical eruptions are also re examined to identify the major meltwater discharge routes the study provides the first conceptual model for how meltwater escapes supraglacially in the absence of a crevassed layer which will dominate any meltwater flow overflowing may be initiated by enhanced rates of seepage despite the intrinsically low hydraulic conductivities of snow and firn once overflowing is established the rate of spillway incision is a likely overriding control on the evolution of the system and whether the discharge is unstable fast or stable slower the james ross island sequences demonstrate that meltwater discharge is highly dynamic and may have involved both subglacial and supraglacial escape subglacial discharge probably occurs throughout basaltic tuya eruptions but some periods may be dominated by concurrent overflowing it is still unclear if overflowing systems are sufficiently stable to enable the growth of laterally extensive glaciovolcanic lava fed deltas

tomographic constraints on the geodynamic evolution of the italian region in this paper we present p wave tomographic images of the mantle beneath italy obtained by inverting 6000 teleseismic p and pkp wave arrival times accurately repicked recorded in the time period 1988 1994 by the stations of the national seismic network of the istituto nazionale di geofisica we pay great attention in the data selection and picking procedure of seismic phases to obtain a very high quality data set the data were inverted with the well established aki christofferson husebye tomographic technique different reference models and residuals computation have been tried to verify the stability of the results the high quality of the repicked arrival times allows us to enhance the definition of the deep structures beneath both the alps and the apennines looking for their lateral and vertical continuity down to 800 km depth the main finding of this study is a continuous high velocity body located between 250 and 670 km depth beneath the entire apenninic system dipping toward the tyrrhenian area which continues upward segmented in two main anomalies in the northern apenninic and the calabrian arcs we interpret this high velocity feature as the subducted oceanic lithosphere between the eurasian and african plates dipping down to the upper lower mantle boundary beneath the tyrrhenian sea the retrieved images of the lithosphere subducting beneath apennines are reliable in terms of thickness about 80 90 km and p wave velocity contrast 2 4 higher than the normal mantle furthermore our tomographic images which focus on the deep geometry and continuity of the velocity structures provide new keys to understanding the geodynamic evolution of the italian region the segmentation of the high velocity slab upward suggests a complex evolution of the arc trench system and the initially continuous subduction of the ionian adriatic plate progressively developed in subordinate arcs probably due to lateral heterogeneity of the subducting lithosphere

eruption of the nevado del ruiz volcano colombia on 13 november 1985 tephra fall and lahars a small plinian eruption of the nevado del ruiz volcano in colombia ejected 3 5 x 1010 kilograms of mixed dacite and andesite tephra on 13 november 1985 with a maximum column height of 31 kilometers above sea level small pyroclastic flows and surges generated during the initial stage of the eruption caused surface melting of approximately 10 of the volcano9s ice cap leading to meltwater floods the erosive floods incorporated soils and loose sediments from the volcano9s flanks and developed into lahars which claimed at least 25 000 lives

magma mixing and petrogenesis of the 13 november 1985 eruptive products at nevado del ruiz colombia abstract magma erupted on november 13 1985 at nevado del ruiz colombia was compositionally diverse with bulk compositions ranging from andesite 59 sio2 and 6 mgo to dacite 65 sio2 and 3 mgo the textural heterogeneity of juvenile products is emphasized by clasts of black scoria gray scoria black scoria with white pumiceous inclusions banded scoria banded pumices and white pumices numerous phenocrysts are out of equilibrium in the andesitic component including magnesian olivine sodic plagioclase and hypersthene plagioclase compositions are bimodal such features and textural heterogeneities are interpreted to result from transfers of phenocrysts by a mechanical mixing process mainly from the felsic component to the mafic one three mineralogical associations have been observed dacitic association andesine an 35 50 hypersthene en 68 70 edenite augite phlogopite magnetite and ilmenite andesitic association labradorite an 55 65 bronzite en 75 78 pargasite augite phlogopite magnetite and ilmenite mafic association magnesian olivine fo 79 87 and bronzite en 78 83 basic magma was not erupted but is thought to be responsible for triggering the eruption it could have been injected into a shallow dacitic reservoir ph2o about 1 kbar destabilized it and mechanical mixing could have started in the magma chamber or through a conduit just before eruption the basic magma evolved completely to andesite as suggested by the experiments of kouchi and sunagawa in 1983 while some original dacitic magma was preserved as complete homogenization was not attained the resulting products are texturally heterogeneous such a genesis explains the mineralogical disequilibria

isotopic composition of carbonaceous chondrite kerogen evidence for an interstellar origin of organic matter in meteorites abstract stepwise combustion has revealed systematic patterns of isotopic heterogeneity for c h and n in the insoluble organic fraction m kerogen from the orgueil and murray carbonaceous chondrites those patterns are essentially identical for both meteorites indicating a common source of m kerogen the data cannot be reconciled with a single mass fractionation process acting upon a single precursor composition this indicates either a multi path history of mass dependent processing or a significant nucleogenetic contribution or both if mass fractionation were the dominant process the magnitude of the observed isotopic variability strongly suggests that ion molecule reactions at very low temperatures probably in interstellar clouds were responsible in any case an interstellar rather than solar nebular origin for at least some of the meteoritic organic matter is indicated this has interesting implications for the origin of prebiotic molecules temperatures in the early solar system and the isotopic compositions of volatiles accreted by the terrestrial planets