towards the reconstruction of the shallow plumbing system of the barombi mbo maar cameroon implications for diatreme growth processes of a polygenetic maar volcano abstract understanding the mechanisms involved in the formation of maars and their diatreme growth processes has been a subject of contention while there is no direct evidence of the presence of diatremes beneath most of the young maars their existence is inferred based on the amount and type of country rocks excavated at different depths and deposited as pyroclastic ejecta around their craters properly tracing fragmented country rocks in ejecta to interpret their depths of origin and thus the depths of phreatomagmatic explosions require good and detailed information on the substrate geology that is generally lacking at many maars as an alternative this paper explores the role of juvenile components in deposits of a maar for understanding the cratering and growth of diatremes during maar forming eruptions based on field investigations pyroclast distribution componentry and grain morphology examinations this study reports on the eruptive mechanisms that led to the formation of the barombi mbo maar bmm a polygenetic maar volcano in cameroon the bmm consists of three diatremes that formed during distinct eruptive events and coalesced to produce an amalgamated maar diatreme two end member types of eruption styles from the dry magmatic to the wet phreatomagmatic explosions governed the formation of the maar in total a minimum of 0 0658 km 3 of magma dense rock equivalent corrected was ejected based on calculation by applying interpolation techniques on digital elevation models obtained from srtm30m data corrected by rock textural data collected from the field the distribution of juvenile clasts throughout the stratigraphic sequence suggests a complex subsurface eruptive process which originated probably within the uppermost part of the diatreme from the distribution and morphology of juvenile clasts in the deposits it is inferred that cratering and country rock excavation during the growth of each of the small diatremes developed mainly from shallow level explosions sometimes with lateral and vertical variations in the position of the explosion loci a prospective juvenile based conceptual model is proposed for the formation of the bmm the model suggests that during maar forming eruptions explosions taking place at a deeper position might entrain extensive amount of lithics from the mostly lithic dominated upper crater infill to deposit juvenile poor 90 vol

origin of the lethal gas burst from lake monoun cameroun abstract on 15 august 1984 a lethal gas burst issued from a submerged 96 m deep crater in lake monoun in cameroun western africa killing 37 people the event was associated with a landslide from the eastern crater rim which slumped into deep water waters below 50 m are anoxic dominated by high fe 2 600 mg l and hco 3 1900 mg l anoxic and supersaturated with siderite which is a major component of the crater floor sediments the unusually high fe 2 levels are attributed to reduction of laterite derived ferric iron gradually brought into the lake as loess and in river input sulfur compounds are below detection limits in both water and gas gases effervescing from depressurized deep waters are dominantly co 2 with minor ch 4 having 13 c of 7 18 and 54 8 per mil respectively bacterial decomposition of organic matter may account for the methane but 14 c of lake water indicates that only 10 of the carbon is modern giving an apparent age of 18 000 years the dominant source of carbon is therefore attributed to long term emission of co 2 as volcanic exhalation from vents within the crater which led to gradual build up of hco 3 in the lake the density stratification of the lake may have been upset by an earthquake and underwater landslide on 15 august which triggered overturn of the lake and caused nucleation of co 2 in the deep water the resultant ebullition of co 2 from deep lake waters led to a gas burst at the surface and locally generated a water wave up to 5 m high people travelling through the gas cloud were asphyxiated presumably from co 2 and suffered skin discoloration from unidentified components

a scaling growth model for bubbles in basaltic lava flows abstract pahoehoe an and massive lavas from mount etna show common statistical properties from one sample to another which are independent of scale size over certain ranges the gas vesicle distribution shows two scale invariant regimes with number density n v v b 1 where v is the volume and empirically b 0 for small bubbles and b 1 for medium to large bubbles we introduce a bubble growth model which explains the b 1 range by a strongly non linear cascading growth regime dominated by a quasi steady state coalescence process the small bubble region is dominated by diffusion its role is to supply small bubbles to the coalescence regime the presence of measured dissolved gas in the matrix glass is consistent with the notion that bubbles generally grow in quasi steady state conditions the basic model assumptions are quite robust with respect to the action of a wide variety of processes since we only require that the dynamics are scaled over the relevant range of scales and that during the coalescence process bubble volumes are approximately conserved the model also predicts a decaying coalescence regime with b 1 associated with a depletion of the gas source or alternatively a loss of large vesicles through the surface of the flow our model thus explains the empirical evidence pointing to the coexistence of two different growth mechanisms in subsurface lava flows but acting over distinct ranges of scale with non linear coalescence as the primary growth process the total vesicularity of each sample can then be well estimated from the partial vesicularity of each growth regime without any outlier problems

witness accounts of the catastrophic event of august 1986 at lake nyos cameroon abstract the catastrophic event at lake nyos in august 1986 has resulted in a major scientific debate concerning its origin and how to prevent new casualties of this nature in future we have tried in the present paper to interrelate the testimonies in time and place and to interpret them in geological terms it has been possible to draw a hazard map of the catastrophe and reconstruct the sequence of the events it began on august 20 1986 with minor upwelling of hot water on august 21 1986 a small explosion occurred in lake nyos followed in the evening by an intermittent jet of water topped by a white plume at 10 p m a major detonation occurred in the lake and carbon dioxide invaded the low lying valleys killing more than 1500 people and 6000 head of cattle the all scientific community agree gases have a magmatic origin two scenarios have been used to describe the catastrophe the volcanic origin scenario a gas jet splitted across the lake water and the limnic origin scenario gases were stored in the lake water and an internal or external phenomenon triggered the degassing in the volcanic origin scenario prevention of degassing is impossible any volcanic area can present this danger in or outside lakes prediction will proceed with usual methods in the limnic scenario both prediction and prevention are possible the only dangerous area are located around lakes containing dissolved gases prevention can be obtain by pumping and degassing the deep waters to the surface in the present paper testimonies have been used to test both hypotheses

sediment transfer by shallow landsliding in the queen charlotte islands british columbia despite the importance of landsliding in routing sediment through mountainous drainage basins few studies have documented landsliding rates over extended time and space scales we have investigated landsliding in surficial material in the queen charlotte islands using a large inventory of events derived from aerial photography covering an area of 166 7 km 2 the mean erosion rate for shallow landsliding is 0 10 mm a 1 which is at the upper end of shallow landsliding rates observed in the pacific northwest and coastal british columbia but several orders of magnitude lower than rock based landsliding rates reported in the literature probability distributions for landslide area and volume are somewhat convex in form flattening of the curve found at low magnitudes may be due to sampling bias or physical mechanisms inhibiting failure and the steepening for high values may exist because the sampling period is not long enough to adequately represent large events landslides generally initiate on hillslope gradients greater than 0 50 0 60 the largest numbers of landslides occur on south to southwest facing slopes and east to northeast facing slopes most events occur on concave and straight hillslopes in upper slope positions landsliding rates were found not to be af fected by rock type hillslopes in the queen charlotte islands are often mantled by weathered quaternary deposits and hence landsliding events are not directly controlled by weathering of bedrock about 31 of landslides identified in this study deposited material in stream reaches with about 83 of these landslides deposited in reaches with gradients between 3 and 10 resume malgre la grande contribution des glissements de terrain a acheminer des sediments a travers des bassins de drainage montagneux peu d etudes ont documente les taux de glissements de terrain sur une longue periode de temps et sur de grandes superficies nous avons fait des recherches sur des glissements de materiaux de surface dans les iles de la reine charlotte en utilisant un grand inventaire d evenements tires de photographies aeriennes couvrant une re

theology and disaster studies the need for dialogue abstract in hazard analysis the conventional wisdom holds that disasters are features of either human vulnerability and or de moralised nature the notion of the act of god has been almost completely replaced using examples of volcanic eruptions and christian theology it is argued that many actual and potential victims of hazards continue to explain losses in theistic terms even in societies where individuals are aware of alternative scientific and social explanations in christianity attempts to reconcile god s love justice and omnipotence on the one hand and human suffering on the other is termed theodicy and it is proposed that recent developments allow more fruitful dialogue to take place between hazard analysts and theologians than has been the case hitherto during the international decade for natural disaster reduction 1990 2000 a consensus emerged that if responses to disaster are to be successfully managed then an awareness of local culture is vitally important this consensus has continued as research agendas are currently being formulated for the international strategy for disaster reduction in many disaster prone regions religion is an essential element of culture and must be carefully considered in the planning process and not simply dismissed as a symptom of ignorance superstition and backwardness

extreme events in the sedimentary record of maar lake pavin implications for natural hazards assessment in the french massif central a set of sedimentary cores high resolution swath bathymetry and subbottom profiler data provides new insights on sedimentary processes in meromictic maar lake pavin france three sedimentary environments i e littoral plateau and basin have been identified in the lake from sediment composition using bulk organic geochemistry and the analysis of hydroacoustic images various forms of rapidly deposited layers rdls have been identified and radiocarbon dated an up to date stratigraphy of sedimentary events matching coeval rdls across the lake is presented and illustrates a wide range of natural hazards linked to lake pavin during the last 2000 years in ad 600 a sudden lake outburst triggered a slump deposit along with a 9 m lake level drop that drove shifts in sedimentary organic matter composition outside the lake outburst flood deposits have been described downstream and provide sedimentary evidence for this event the lake level drop also favored the generation of gravity reworking processes as shown by 1 a regional earthquake triggered large slope failure on the plateau connected to a masswasting deposit in the basin dated to ad 1300 and 2 a succession of turbidites in ad 1825 and ad 1860 contemporaneous to two historic earthquakes suggesting that this lake is sensitive to earthquakes with a minimum epicentral intensity of v finally past observations of lake water color changes in ad 1783 and ad 1936 similar to reports in other meromictic lakes match iron rich deposits identified in maar lake sediments and suggest that lake pavin could have undergone limnic eruptions

the gas cloud of lake nyos cameroon 1986 results of the italian technical mission abstract on august 21 1986 a gas cloud issued from lake nyos in cameroon killed over 1700 people an italian technical mission reached the area seven days later and obtained the first field evidences of the catastrophe on the basis of observations and measurements in the field and of samples collected the origin of the gas outburst is attributed to a phreatic explosion from beneath the bed of the lake this interpretation appears to fit well the observed and reported phenomena and seems perfectly consistent with the geological geothermal conditions of the area

water and gas chemistry of lake nyos and its bearing on the eruptive process abstract the isotopic and chemical composition of water samples collected from lake nyos some two and eight weeks after the eruption of august 21 1986 point to the existence of three distinct mixing regimes involving three water components an essentially homogeneous unmixed body of water at depths 100 m overlain by water increasingly affected by surface evaporation and a 5 10 m layer containing recent but pre eruption rain water the cationic constituents na k mg ca mn fe of the lake water correspond to the dissolution of around 0 1 g of local rock the waters are close to saturation with respect to siderite the composition of the gas dissolved in the deep lake waters 0 65 b w of co2 pco2 4 4b corresponds in mmol mol 1 to 996 co2 2 0 ch4 2 0 n2 0 05 ar 0 004 he 0 0002 h2 0 0001 ne co 2 13 c 3 4 and of he rair 5 5 suggest deep magmatic origins the 13c and 2h content of ch4 organic sedimentary origin the presence of aromatic hydrocarbons indicates very high temperatures of hydrocarbon formation exsolution of gas will first lead to the precipitation of siderite then iron hydroxide the chemistry of the lake waters points to a loss of some 240 000 t of co2 from the upper 100 m of the lake their isotopic composition is consistent with the assumption that the eruption was triggered by the accumulation of cold rain waters at the lake surface prior to the eruption inducing partial convective overturn there is no need to invoke addition of chemical or isotopic constituents from deeper levels during the eruption

timing and extent of allerod and younger dryas age ca 12 500 10 000 14c yr b p oscillations of the cordilleran ice sheet in the fraser lowland western north america the use of shaded digital topographic models to visualizes suites of topographic features stratigraphy and field mapping reveals newly recognized multiple moraines associated with oscillations of the remnants of the cordilleran ice sheet in the fraser lowland along the western washington british columbia border morphologic features show the extent of ice represented by sumas drift ca 11 600 10 000 14c yr b p following ca 3000 yr of retreat from the glacial maximum fraser glaciation positions 80 km south of seattle and in the strait of juan de fuca the paleogeography of the ice margin and timing of ice retreat during the sumas stade is reconstructed and bracketed by 70 radiocarbon dates 24 on marine shells 46 on wood and peat which are secured by morphologic and stratigraphic evidence four topographically distinct phases of the sumas deglaciation model are suggested phase si 11 600 11 400 14c yr b p outermost drift scattered remnants of ice contact deposits phase sii 11 600 11 400 14c yr b p glacier readvance building prominent moraine followed by glacier retreat phase siii 10 980 10 250 14c yr b p glacier readvance building of multiple moraines followed by glacier retreat phase siv 10 250 10 000 14c yr b p glacier readvance building of inner moraine followed by glacier retreat

mechanisms of the nyos carbon dioxide disaster and of so called phreatic steam eruptions abstract during the night of august 21 1986 a huge volume of concentrated co 2 was emitted by the crater maar of nyos cameroon it killed more than 1700 people and all animal life as far as 14 km away two hypotheses have been put forward to account for this disaster the chronologically first one imputes it to have been a phreatic eruption exceptionally co 2 rich as had been the case in february 1979 on the dieng plateau in central java indonesia where the erupting crater was lake less the second one claims a limnic origin for the co 2 release through an overturn of the 220 m deep lake nyos the hypolimnium of which was supposed to be oversaturated by dissolved gas of volcanic origin the present paper points to six observed facts for which the eruptive hypothesis easily accounts and which the authors of the limnic one do ignore

natural and industrial analogues for leakage of co2 from storage reservoirs identification of features events and processes and lessons learned instances of gas leakage from naturally occurring co2 reservoirs and natural gas storage sites serve as analogues for the potential release of co2 from geologic storage sites this paper summarizes and compares the features events and processes that can be identified from these analogues which include both naturally occurring releases and those associated with industrial processes the following conclusions are drawn 1 carbon dioxide can accumulate beneath and be released from primary and secondary shallower reservoirs with capping units located at a wide range of depths 2 many natural releases of co2 are correlated with a specific event that triggered the release 3 unsealed fault and fracture zones may act as conduits for co2 flow from depth to the surface 4 improperly constructed or abandoned wells can rapidly release large quantities of co2 5 the types of co2 release at the surface vary widely between and within different leakage sites 6 the hazard to human health was small in most cases possibly because of implementation of post leakage public education and monitoring programs 7 while changes in groundwater chemistry were related to co2 leakage waters often remained potable lessons learned for risk assessment associated with geologic carbon sequestration are discussed

are there biomedical criteria to assess an acute carbon dioxide intoxication by a volcanic emission abstract on august 21 1987 more than 1800 people thousands of head of cattle and countless wild animals including birds were killed by a gas release which occurred during about 4 hours at the lake in the crater iwi at nyos in cameroon plant life was mostly unaffected an international inquiry was performed by british french italian japanese and u s volcanologists and physicians to determine what had been the cause of this disaster an international conference organised by united nations educational scientific and cultural organisation u n e s c o the cameroon government and the u n economic commission for africa held in yaounde march 1987 concluded that the cause of sudden death was suffocation asphyxia in a carbon dioxide atmosphere the medical findings have been explained by asphyxia caused by carbon dioxide the presence of other volcanic gases e g hydrogen sulfide cannot be ruled out sigvaldason 1989 this issue this paper reviews what is mainly known about an acute carbon dioxide intoxication in order to disprove or confirm the diagnosis and helps to interpret the field observations and testimonies to provide a basis to discuss the prevention of such an intoxication

on the problems of translation in the investigation of the lake nyos disaster abstract problems of translation where one word in a local african language may be used to cover two or more concepts for which separate words would be used in a european language have created serious difficulties for the scientists who have been investigating the 1986 lake nyos gas disaster the most obvious example and the one which caused the greatest confusion amongst the investigators and a long running dispute in the scientific literature being the use in the languages of the people who lived near lake nyos of a single word to cover both smell and taste thus reports that the gas cloud had a bad smell could have been translated with equal accuracy as reports that the gas cloud had a bad taste had this been appreciated during the initial investigation many of the subsequent disputes over the origin of the gas and the mechanism by which it was released might have been avoided a second example and one which well illustrates the extraordinary differences between linguistic groups and the potential for confusion which is inherent in such differences can be found in the lack of separate words for the primary colours in some african languages this is further complicated by the use in the pidgin english of western cameroon of the word red to refer to all the primary colours thus when the surface water of lake nyos turned a yellow brown after the disaster the people who lived in the area would have said that it had turned red and when the lake water cleared and returned to its normal bright blue the people would still have said that it was red

sediment yield from disturbed earth systems changes of sediment yield rates through time reflect evolutionary changes within a landscape when a drainage basin is perturbed significantly by base level climatic or tectonic change sediment yields increase dramatically but with no further disturbance they decline rapidly these sediment yield changes have been documented at all scales from small experimental studies to incised channels to the colorado river basin and to the himalaya mountains thus the shape of the sediment yield curve can be used to estimate future sediment yields and to interpret past tectonic events

quantitative analysis of debris torrent hazards for design of remedial measures debris torrents which are rapid flows of soil and organic debris down steep mountain channels are a major natural hazard in many parts of british columbia a series of recent occurrences along the

the lake nyos gas disaster chemical and isotopic evidence in waters and dissolved gases from three cameroonian crater lakes nyos monoun and wum abstract to better understand the cause of the nyos gas disaster of august 21 1986 we conducted geochemical and limnological surveys in october 1986 of three lakes nyos monoun and wum which are located in the cameroon volcanic zone that is characterized by a prevalence of young alkaline basalts and basanitoids lake wum was studied as a non active control co2 is dissolved in significant concentrations about 1 5 of saturation in gas active lakes nyos and monoun but is virtually absent in lake wum stable isotopic ratios of total dissolved carbon 13c 3 for nyos and 5 5 for monoun and of helium 5 7 ratm for nyos and 3 6 ratm for monoun indicate a mantle origin of these gases however so42 and cl concentrations are found to be very low concentrations of dissolved chemical species like fe2 mg2 ca2 and hco3 are high in the two gas active lakes whereas they are very low in the gas inactive lake high salinities in the gas active lakes are probably due to dissolution of indigenous mafic rocks and transported lateritic soil in acidic co2 rich warm water the gas active lakes are characterized by increasing temperature and salinity with increasing depth indicating an active influx of heat and dissolved materials at the bottom density estimates show that the lake water is stably stratified in spite of the inverse temperature profile of the lakes on account of dissolved chemical species the concentrations of dissolved carbonate species co2 aq and hco3 are positively correlated with those of ionic dissolved species indicating their common occurrence in the bottom water the august 1986 gas bursts from lake nyos were most likely caused by rapid exsolution of dissolved co2 within the lake an explosive process such as a phreatic eruption or a co2 gas jetting from beneath the bottom is unlikely because of low concentrations of cl and so42 no oxygen isotopic shift low turbidity and no reported perturbation of the bottom sediments exsolution of co2 bubbles could occur if co2 saturated bottom water was displaced upwards by an increased influx of high salinity water from the bottom during the rainy season exsolution of co2 at the upper layers was possibly accelerated by upwelling of a two phase fluid co2 bubbles and solution a mechanism known as a pneumatic lift pump resulting in discharge of a large amount of co2 gas the h2s concentration in the gas cloud must have been kept far below the lethal level because of a high fe2 concentration of the lake water

the significance of siderite in the sediments from lake nyos cameroon abstract small amounts 1 3 wt of endogenic siderite feco3 and traces of pyrite fes2 are present in a 1 m long sediment core from lake nyos thermodynamic modeling shows that the deep waters are supersaturated with respect to siderite and pyrite no other carbonates were found to be stable this rare occurrence of siderite is symptomatic of the build up of large concentrations of co2 and fe2 in the lake nyos waters a search for siderite in the deeper sediments could reveal the existence of previous gas burst events that have occurred at lake nyos or in other cameroon lakes

the anecdotal evidence did it help or hinder investigation of the lake nyos gas disaster abstract in the aftermath of the lake nyos disaster it was widely reported that a smell af bad eggs or gunpowder was associated with the cloud of toxic gas in general these reports have been accepted at face value by scientists working on the disaster and used with varying degrees of emphasis to support favoured hypotheses six possible explanations for the reported smell are considered in this paper and three of them are either rejected or regarded as very unlikely 1 1 volcanic gas from beneath the lake very unlikely 2 2 hydrogen sulphide exolved from the lake water rejected 3 3 high concentrations of carbon dioxide causing olfactory hallucinations rejected 4 4 an illusion reflecting the expectation of some of those who questioned the survivors and of stories which subsequently started to circulate most likely 5 5 an illusion reflecting an association between death and the smell of gunpowder in the culture of some of the peoples of the area a possible contributary factor 6 6 confusion between the smell of gas and the taste of lake water in the toxic cloud a probable contributing factor my general conclusion is that an over reliance on anecdotal evidence has seriously hindered investigation of the lake nyos disaster and will continue to do so if hypotheses which rely heavily on such evidence are taken too seriously

reconnaissance sediment budgets for lynn valley british columbia holocene and contemporary time scales volumes of erosional and depositional landforms were estimated by reconnaissance methods in a steep forested drainage basin in the coast mountains british columbia to examine what insight might be gained into the sediment budget in the absence of direct measurements of sediment transfer processes sediment transfers in postglacial and contemporary time were inferred on hillslopes from hillslopes to stream channels and within stream channels data were collected by aerial photographic analysis and field observation postglacial sediment sources are major gullies created by debris slides and flows failures in glaciolacustrine terraces and stream channel degradation depositional landforms consist of talus slopes and colluvial and alluvial fans contemporary sediment sources include debris slides and flows in established gullies and minor processes on hillslopes debris slide and debris flow volumes were calculated and other processes were estimated from regional values erosion rate averaged over postglacial time is 276 t km 2 a 1 0 15 mm a 1 surface lowering with gullies and stream channel degradation contributing 170 and 82 t km 2 a 1 respectively a terminal alluvial fan provides an independent check of the results in contemporary time erosion rates are calculated to be 350 t km 2 a 1 with debris flows and slides contributing nearly all of this sediment the contemporary rate is probably perturbed by recent land use history mass movement processes appear to be the dominant mechanism of sediment transfer and contributions from pleistocene valley deposits have declined significantly during holocene time resume les volumes de terrain erodes et deposes ont ete estimes par des methodes de reconnaissance dans un bassin de drainage boise a pentes abruptes des montagnes cotieres de la colombie britannique afin d etudier quelles connaissances sur le budget sedimentaire pourraient etre acquises en l absence de mesures directes du processus de transfert de sediments les transferts de sediments a l epoque post glaciaire et contemporaine ont ete inferes sur les flancs des cotes des flancs des cotes vers les chenaux des rivieres et dans les chenaux des rivieres les donnees proviennent de l analyse de photographies aeriennes et d observations sur le terrain les sources de sediments post glaciaires sont des ravines creees par des glissements et des coulees de debris des effondrements de terrasses glacio lacustres et la degradation de chenaux les formes de terrain creees par deposition comprennent des tabliers d eboulis et des deltas colluviaux et alluvionnaires les sources contemporaines de sediments comprennent des glissements et des coulees de debris dans des ravines etablies et des processus mineurs sur des pentes les volumes des glissements et des coulees de debris ont ete calcules et d autres processus ont ete evalues a partir de valeurs regionales la moyenne du taux d erosion pour la periode post glaciaire est de 276 tonnes km 2 a 1 abaissement de la surface de 0 15 mm a les ravines et la degradation des chenaux des ruisseaux contribuant respectivement 170 et 82 tonnes km 2 a 1 un delta alluvionnaire terminal permet une verification independante des resultats a l epoque contemporaine les taux d erosion sont calcules comme etant 350 tonnes km 2 a 1 et les glissements et des coulees de debris y contribueraient pour la presque totalite le taux contemporain est probablement perturbe par l utilisation recente du terrain les processus de mouvements de masse semblent etre le mecanisme dominant de transfert de sediments et les contributions provenant des depositions dans les vallees au pleistocene ont diminue de facon significative durant l holocene traduit par la redaction campbell and church 713

representing the landslide magnitude frequency relation capilano river basin british columbia we use magnitude frequency analysis as a statistical tool to quantify the erosion caused by landslides and debris ows using air photo and ground derived data we show that the departure from power law distribution customarily observed for small magnitude is an artefact of sampling de ciencies nonetheless the total distribution is not sensitive to the frequency of small slides and total erosion remains adequately represented in the air photo derived data our data also demonstrate a real departure from simple scaling at much larger magnitudes the cause of which is not de nitively established copyright 2004 john wiley sons ltd

an example of health hazard people killed by gas during a phreatic eruption dieng plateau java indonesia february 20th 1979 on february 20th 1979 142 inhabitants of dieng plateau indonesia were asphyxiated by poisonous gases during a mild phreatic eruption from later fields gas collection and analysis the casualties are considered to be due to co2 rich volcanic gases

geomorphic and tectonic process rates effects of measured time interval analysis of the original numerical components of diverse geomorphic and tectonic process rates indicates that process rate is not independent of measured time interval this implies that direct comparison of geologic process rates measured over variable time intervals may not be valid and that conclusions based on those comparisons regarding changes in rates through geologic time may be misleading in some cases calculation of statistically derived scaling functions is one approach that can be used to account for this measurement interval bias and to improve comparisons of geologic process rate data when this approach is used a 10 4 or 10 5 yr variation in the measured time interval accounts for approximately one order of magnitude change in the measured process rate the magnitude of the correction can substantially affect conclusions of studies that compare uncorrected process rates calculated from variable time intervals

loihi seamount hawaii a mid plate volcano with a distinctive hydrothermal system the initial discovery of deep sea hydrothermal vents at the galapagos rift1 2 has resulted in a decade of exploration and experimentation subsequent discoveries in the pacific3 8 and atlantic9 ocean basins have established the importance of these features as sources of mantle derived gases and solutes10 2 and as loci for heat dissipation13 14 polymetallic sulphide mineral deposition15 16 and geochemical exchange17 19 the presence of dense communities of bacteria and specialized macrofauna20 22 has called into question the absolute role of sunlight as the principal energy source for marine organisms until recently these deep sea vents were known only at or near plate boundaries but recent dredging23 24 near bottom water sampling25 27 and sea floor camera survey28 programmes have indicated that hydrothermal vents are present at the summit of loihi seamount a mid plate hotspot submarine volcano at the southern end of the hawaiian island chain29 here we report results obtained from sampling two active vent fields the fluid chemistry especially high co2 and fe presence of alkalic lavas and iron depositing bacteria and absence of macrofauna suggest that mid plate vents may differ from the hydrothermal vents found at mid ocean ridges

carbon dioxide bursts of lake nyos cameroon modelled as periodic supersaturation in a countercurrent reactor abstract large scale degassing of carbon dioxide from lake nyos cameroon on august 21 1986 was caused by local gas supersaturation within the lake water carbon dioxide of volcanic origin accumulates in the lake but the dissolved solids originate from leaching of the bedrock atmospheric and organic nitrogen diffuses into the lake from its surface the lake is modelled as a countercurrent chemical reactor carbon dioxide bubbles rising from the bottom sediment dissolve as aqueous co2 which control the ph of the water at about 3 8 siderite formed within the lake settles and counteracts the upwards transport of co2 rising co2 bubbles also account for upwards transport of dissolved nitrogen local gass supersaturation causes a spontaneous large scale degassing event giving rise to catastrophic bursts of co2 chemical hazard evaluation at lake nyos can only be based on monitoring of total dissolved gases since variables such as conductivity and ph are insensitive to changes in aqueous co2 hazard prevention at lake nyos can be accomplished due to the great volume of annual precipitation relative to the volume of the lake by damming of the natural outlet of the lake and draining of the co2 rich bottom layer through a pipeline resulting in the gradual replacement of the gas rich bottom layer