morphometry of subaerial shield volcanoes and glaciovolcanoes from reykjanes peninsula iceland effects of eruption environment abstract we present a morphometric study of 33 basaltic volcanic edifices from the reykjanes peninsula iceland using a 20 m resolution digital elevation model dem slope values distinguish subaerial from intraglacial eruption environments with glaciovolcanic edifices having average slope values that are 5 higher than subaerial shields the 26 analyzed glaciovolcanic edifices are separated into 3 groups based on size and are also categorized following the new classification scheme of tuyas by russell et al 2014 into 15 tindars 1 conical tuya 3 flat topped tuyas and 7 complex tuyas the glaciovolcanic edifices show a continuum of landforms ranging from small elongated tindars to large equidimensional flat topped tuyas the smaller edifices 3 are all tindars and the larger edifices 0 1 km 3 are flat topped tuyas the mid sized edifices 0 01 0 1 km 3 show a wide variety of shapes and classify either as tindars or as complex tuyas with only one edifice classifying as a conical tuya edifice elongation tends to decrease with volume suggesting that small edifices are primarily fissure controlled whereas larger edifices are mainly controlled by a central vent the mid sized complex tuyas are transitional edifices suggesting that some intraglacial eruptions start as fissure eruptions that subsequently concentrate into one or more central vents whereas the mid sized tindars suggest a sustained fissure eruption there is a tectonic control on the orientation of the edifices evidenced by a strong correlation between edifice elongation azimuth and mapped faults and fractures most edifice elongations cluster between 020 and 080 coinciding with the strike of normal faults within and at the boundary of regional volcanic systems but some edifices have elongations that correlate with n s striking book shelf faults this implies that intraglacial eruptions are controlled by pre existing pathways in the crust as has been previously observed for subaerial fissure eruptions in terms of classification quantification of the limits between the four tuya types proposed by russell et al 2014 is difficult because of the transitional nature shown by several edifices a threshold of 1 8 in ellipticity index e i values can be used to distinguish tindars from the other three types flat topped tuyas are distinguished by their greater overall size their large and relatively flat summit regions reflected in bimodal slope distributions and their low e i and low to intermediate irregularity index i i values the only analyzed conical tuya has very low e i and i i values very small summit regions and very steep flank slopes the complex tuyas have variable morphometries but are in general characterized by high i i values and very irregular slope distributions no correlation is observed between edifice scale morphology and lithology e g pillow dominated or hyaloclastite dominated

paleo glacier reconstruction in southwestern british columbia canada a glaciovolcanic model abstract volcanic rocks erupted within glacial environments offer powerful paleoenvironmental insights these glaciovolcanoes and their deposits serve as proxies that inform on the paleo presence distribution and thickness of past glaciers we investigate the paleoenvironmental implications of three mid to late pleistocene volcanic deposits in the garibaldi volcanic belt of southwestern british columbia canada we use these data to inform a simple geometric model that constrains paleo glacier distributions in the southern canadian cordillera the three volcanoes are used to recover i a coalesced mountain ice sheet in late marine isotope stage mis 4 and possibly into mis 3 up to 49 1 5 5 ka ii major and rapid degradation of glaciers during the late mis 6 to 5e transition by 141 12 9 ka and iii a coalesced mountain ice sheet or continental ice sheet that existed during mis 15 598 7 5 ka

breccias and ores part 1 history organization and petrography of breccias abstract although the term breccia is one of the oldest rock names still in use and proliferating in its application a satisfactory definition remains problematic and an overall classification of breccias is non existent the names of breccia varieties several hundred please the heart rather than the computer and there is little interdisciplinary correlation among the more than fifty specialized schools of breccia study this contribution reviews briefly the history of breccia research and provides a list of the present study trends complete with references with emphasis on ore associated breccias wherever possible conventional breccia definitions and their shortcomings are discussed and a case is made for the introduction of the petrographic category of coarse fragmentites of which the typical sedimentary breccias and conglomerates as well as volcanic tectonic hydrothermal impact and other fragmental materials are members whether designated or not as breccia in the conventional literature this is followed by a proposed rational organization classification of coarse fragmentites and breccias based on the regime of formation and architecture fabric gefuge two fundamental end member sequences a b and a transitional suite c can be recognized a disaggregation fragmentites d breccias produced from a solid progenitor by increasing rate of fracturing expansion rotation mixing and attrition the transitional sequence is crackle mosaic rubble melange milled breccia b aggregation fragmentites a breccias generated by gathering aggregation and accumulation of originally dispersed fragments at the site of deposition these materials form a sequence ranging from tightly packed fragment supported matrix free fragmentites through matrix infilled matrix supported fragmentites to lonestone rocks c in transport fragmentites t breccias formed by redeposition of an aggregate gathered in an earlier phase of development as an a fragmentite or by transportation and redeposition of an advanced member i e rubble melange or milled fragmental aggregate of a d fragmentite examples of metallic mineralizations coeval with or superimposed on the fragmentite sequences are reviewed

subaqueous explosive eruption and welding of pyroclastic deposits silicic tuffs infilling an ancient submarine caldera at mineral king in california show microscopic fabrics indicative of welding of glass shards and pumice at temperatures 500 degrees c the occurrence indicates that subaqueous explosive eruption and emplacement of pyroclastic materials can occur without substantial admixture of the ambient water which would cause chilling intracaldera progressive aggradation of pumice and ash from a thick fast moving pyroclastic flow occurred during a short lived explosive eruption of approximately 26 cubic kilometers of magma in water 150 meters deep the thickness high velocity and abundant fine material of the erupted gas solids mixture prevented substantial incorporation of ambient water into the flow stripping of pyroclasts from upper surfaces of subaqueous pyroclastic flows in general both above the vent and along any flow path may be the main process giving rise to buoyant convective subaqueous eruption columns and attendant fallout deposits

emplacement of the 18 may 1980 lateral blast deposit ene of mount st helens washington facies variations east northeast of mount st helens preserve a record of depositional processes in the 18 may 1980 lateral blast cloud this paper reports new field grain size and component data from the ene sector of the timber blowdown zone and presents a model for blast flow and sedimentation the first erupted ejecta was rich in juvenile components and extends to the distal blowdown limit the last erupted ejecta was rich in accidental lithics and reached no further than a few kilometres from the mountain due to waning discharge the blast cloud was a turbulent stratified flow which transported and deposited sediment in the manner of a high density turbidity current the possibility that the blast was emplaced as a giant shearing fluidised bed is not favoured by compositional zoning patterns depositional conditions were strongly influenced by the rate of suspended load fallout from the blast within about 8 km from vent rapid sedimentation caused deposition under moderate to high concentration conditions and formation of a basal hindered settling zone able to detach gravitationally and drain into local depressions the resulting proximal facies resembles a low aspect ratio ignimbrite fines depletion in the proximal facies is attributed to a combination of residual turbulence and rapid gas escape during particle settling and compaction through the hindered settling zone component data suggest that the blast head played no significant role in the generation of fines depletion in the blast deposit as suggested by previous workers with increasing distance from vent the rate of particle fallout declined and sedimentation took place under increasingly dilute and tractional conditions building up antidune like bedforms wavelengths of these bedforms range from 20 to 1 m and decrease away from vent there is a systematic relationship between antidune migration direction and depositional slope the transition from proximal ignimbrite like to distal surge like facies suggests a possible gradation in transport and deposition processes between conventional pyroclastic surges and high velocity pyroclastic flows

a high resolution record of late holocene moisture variability from a michigan raised bog usa we reconstructed the late holocene surface moisture history and vegetation dynamics of a raised bog in michigan using testate amoebae peat humification pollen stomata and plant macrofossils our primary objective was to compare bog palaeohydrology with the water level history of lake michigan and to regional and local vegetation changes hydrologic histories inferred from testate amoebae and humification show similar trends and correspond with records of past water level variability in lake michigan the bog clearly shows effective moisture increases during the algoma highstand 3200 2300 cal bp and a later unnamed highstand 1900 1300 cal bp some higher frequency fluctuations are also similar the good correspondence indicates that bog hydrology and the water levels of lake michigan have been driven by changes in large scale atmospheric circulation patterns for at least the past 3500 years climate during the algoma highstand may have been spatiotemporally complex with increasing moisture oc

quantitative experiments on phreatomagmatic explosions abstract an experimental set up for controlled generation of thermal explosions fuel coolant interactions has been built by an interdisciplinary research group of volcanologists physicists and engineering scientists the tee haus thermal explosion experiment during the last 3 years more than 500 experimental runs were performed aim of the project was not to build a mini volcano but to produce igniteable mixtures of water and hot melt on a small scale in order to investigate basic physical aspects such small scale mixtures however most probably also occur during phreatomagmatic events in nature mixtures of water and magma on a large scale may be modelled by combination of small elements earlier experimental studies of thermal explosions were carried out with the use of metal melts nearly exclusively therefore a carbonate melt approx 0 3 kg of 1 1 mass ratio na2co3 k2co3 was used for initial experimental series because of easy handling and more magma similarity by injection of water into this melt explosive mixtures were produced and ignited self triggering explosive interactions occurred in a wide melt temperature range 720 to 1040 c at melt temperatures exceeding 1000 c co2 increasingly degassed presence of non condensible gas bubbles in the melt strongly reduced the explosivity the intensity of explosions only slightly increased with higher melt temperatures but strongly increased with higher water injection velocities because of more intensive mixing a minimum injection velocity was found to be approx 0 7 m s 1 experiments with silicate melts derived from diverse remelted volcanic rocks were carried out with a slightly modified set up explosions were ignited by an additional trigger a shock wave of approx 8 j in volcanic systems shock waves of this magnitude are abundant volcanic tremor etc strong explosions with silicate melts were produced at melt temperatures between 1350 and 1750 c the produced explosions exerted repulsion forces of up to 24 000 n with a typical pulse duration of 1 ms carbonate melt resp 1 5 ms silicate melts the ejection velocity was found to be in a range between 200 and 400 m s 1 explosion energy values up to 500 j were calculated the maximum explosion pressure was calculated to be in the range between 10 and 100 mpa only part of the melt so called interactive melt reacts explosively with injected water most of the melt is passively ejected by and after the thermal explosion different fragmentation processes result in specific grain size and grain shape populations that can be distinguished from each other particles resulting from the fine fragmentation process that precedes and causes the thermal explosion are characterized by angular to subrounded shapes and grain sizes ranging from 20 m to 180 m the amount of interactive melt is proportional to the intensity of the explosion the maximum amount of water vapourized at the explosive interaction so called interactive water was estimated thus the water melt mass ratio for explosive interactions could be calculated the values range between 1 25 and 1 35 carbonate melt resp between 1 6 and 1 25 silicate melts

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

subaqueous basaltic magmatic explosions trigger phreatomagmatism a case study from askja iceland abstract sequences of basaltic pillow lavas that transition upward with systematic gradation from pillow fragment breccias to fluidal bomb bearing breccias to bomb bearing lapilli tuffs are common at askja volcano iceland based on the detailed textural investigation of three of these sequences we argue that they record temporally continuous transitions from effusive to explosive products that were erupted from and deposited at or near a single subaqueous vent the recognition of such sequences is important as they provide evidence for controls on the onset of explosive activity in subaqueous environments such investigations are complicated by the interplay of magmatic gas expansion and phreatomagmatic and mechanical granulation fragmentation mechanisms in the subaqueous eruptive environment all of the sequences studied at askja have textural componentry and sedimentological characteristics suggestive of a close genetic and spatial relationship between the pillow lavas and all of the overlying glassy clastic deposits the identification of magma fragmentation signatures in pyroclasts was accomplished through detailed textural studies of pyroclasts within the full range of grain sizes of a given deposit i e bomb blocks lapilli and fine ash these textural characteristics were compared and evaluated as discriminators of fragmentation in pyroclastic deposits the presence of angular vitric clasts within the breccia and lapilli tuff displaying fragile glassy projections indicates little or no post depositional textural modification a shift in vesicle and clast textures between the pillow lavas and the large concentration of fluidal bombs in the breccia indicates that the phreatomagmatic explosions were initially triggered by magmatic vesiculation the initial magmatic gas expansion may have been triggered by depressurization caused by the drainage of the ice confined lake surrounding askja the fuel coolant interactions fcis of the more efficient phreatomagmatic explosions were enabled by the increase in the surface area to volume ratio of the fluidal bombs in the water producing a premix of magma and water the onset and increasing influence of phreatomagmatic fragmentation is preserved in the presence of very fine blocky ash particles and diminished presence of larger particles such as fluidal bombs the textural sedimentological and environmental characteristics of these deposits suggest that phreatomagmatic explosions can be triggered by initial magmatic gas expansion but that it is likely one of many mechanisms for triggering such explosions

may 18 1980 mount st helens deposits in south coldwater creek washington beginning at 0832 pacific daylight time pdt mount st helens washington produced a rockslide debris avalanche and a lateral explosion blast that generated a laterally directed pyroclastic surge called here a blast surge the resulting deposits are thickest in the east west trending valley of north fork toutle river immediately north of the volcano but are almost as thick in south coldwater creek a small tributary of the toutle river in the lee of an east west trending ridge johnston ridge just north of the north fork toutle river the avalanche surmounted johnston ridge 300 m relief and flowed down the valley of south coldwater creek closely following the avalanche and in part contemporaneously with it the blast surge left thin up to 0 5 m deposits on johnston ridge and thick up to 15 m deposits in south coldwater creek these deposits have a lower layer layer a1 which is friable massive poorer in fines particles 1 16 mm and more poorly sorted than the upper layer layer a2 layer a2 is less friable because it contains more silt and clay sized material beneath layer a1 is a zone containing a small percentage of debris from the blast surge mixed with products eroded from the underlying surface this zone designated as layer a0 is a poorly mixed layer containing schlieren of soil shattered volcanic fragments and considerable quantities of organic material layer a1 is strongly sorted and fines depleted and is interpreted to have been deposited from just behind the turbulent head of the blast surge layer a2 is interpreted to have been deposited from the body of the blast surge which is believed to have been less turbulent than the head layer a0 is interpreted to have formed by shearing at the base of the head of the blast surge in the region between the front and the back of the head of the blast surge it is concluded that a strongly fines depleted basal layer of a pyroclastic flow or surge deposit underlain by a thin sheared zone is the signature of an extremely high velocity particulate density current

use of scanning electron microscopy to investigate records of soil weathering preserved in lake sediment reconstruction of soil weathering is one of the more difficult problems for palaeoecologists interested in landscape scale environmental changes here we use scanning electron microscopy and energy dispersive x ray analysis sem eds to study the pitting of feldspars in soils and lake sediments at two sites in the great lakes region usa a semi quantitative feldspar weathering index fwi allows description of the weathering status for large numbers of individual grains and reveals differences among soil horizons and strata of lake sediment as well as between the two sites feldspars in upper soil horizons generally have greater fwi than those in lower horizons but analyses also suggest considerable weathering in the soil c horizon at the site with more rapid water infiltration at one site the fwi of upper soil horizons and surface lake sediment are similar implying that lake sediments have the potential to record changes in soil over time however differences between upper soil horizons and surface sediment at the other site highlight the need to examine more sites and more profiles within sites to better relate catchment and sediment characteristics we interpret increases in the fwi over time within lake sediments as evidence of progressive weathering of soils and conclude that the sites had different histories of soil development however the complexities of sediment deposition in lakes and the paucity of information relating fwi to soil characteristics prevent straightforward reconstruction of soil development variability within each record appears tied to initial grain chemistry depositions environment changes in lake level and progressive degradation of grains as more information relating micromorphology to soil characteristics becomes available this technique should become a more useful complement to chemical studies of lake sediment

middle holocene dry period in the northern midwestern united states lake levels and pollen stratigraphy abstract four cores from lake mendota in the yahara river valley of south central wisconsin provide pollen charcoal and sediment stratigraphic evidence of a middle holocene dry period in the northern midwest the lake level was lower between about 6500 and 3500 yr b p indicating that runoff from the upper yahara river basin may have ceased during the drier seasons of the year derived estimates of precipitation between 6500 and 3500 yr b p indicate a decrease of about 10 down to about 700 mm from the present precipitation value of 800 mm a warming between 6500 and 3500 yr b p is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr b p to quercus savanna with increased charcoal abundances after that time after 3500 yr b p a closed quercus forest and decreased charcoal suggest a cooler and wetter climate the qualitative paleoecological interpretations quantitative precipitation reconstructions based on pollen from the region including the lake mendota data and estimates of hydrologic budget based on lake level changes all show indications of a dry and warm middle holocene evidence from a large regional array of sites also supports these interpretations

mechanisms of slope failure on pyramid mountain a subglacial volcano in wells gray provincial park british columbia pyramid mountain is a subglacial volcano in wells gray provincial park in east central british columbia landslides deform the north and east flanks of the volcano field strength testing and rock mass classification designate the hyaloclastite breccia in which the landslides originated as a weak massive rock mass uniaxial compressive strengths ucs range from 24 to 35 mpa and geologic strength index gsi and rock mass rating rmr values are 60 70 the shear strength of fracture surfaces in the hyaloclastite breccia as measured by laboratory direct shear tests can be characterized by a friction angle of 18 and cohesion c of 0 11 0 66 mpa limit equilibrium slope stability analyses show that the landslides were probably triggered by the rapid drawdown of a surrounding englacial lake with no seismic ground acceleration required slope measurements and slope stability modeling indicate that pyramid mountain was asymmetric prior to failure the north and east flanks had slope angles of 35 40 and

lake level fluctuations at ljustjarnen central sweden and their implications for the holocene climate of scandinavia abstract a detailed reconstruction of water level fluctuations in ljustjarnen a small kettle lake in south central sweden provides a preliminary outline of holocene changes in water balance for that region lake levels were generally high from 9200 to 8000 yr b p falling from then until c 6500 6000 yr b p and rising again by 5000 yr b p temporary lowerings were recorded c 4000 yr b p and c 2000 yr b p and water levels have risen dramatically since c 500 yr b p the reconstruction is based on sedimentologic and fossil analyses of multiple cores as well as on geomorphological evidence comparison of lake level fluctuations in south central sweden with those from southern sweden and western finnish lapland and with records of glacier fluctuations in the scandinavian mountains suggest a distinct north south contrast in water balance from 9000 to 5000 yr b p consistent with strongly zonal atmospheric circulation during that period between 7000 and 5000 yr b p the mid holocene dry period appears to have been time transgressive across scandinavia perhaps as a result of a gradual shift in the position of the atlantic polar front and its associated cyclonic stormtrack since 4000 yr b p however most detectable fluctuations are synchronous across scandinavia with the most prominent and widespread change being increased net moisture during the little ice age

tuyas a descriptive genetic classification we present a descriptive genetic classification scheme and accompanying nomenclature for glaciovolcanic edifices herein defined as tuyas positive relief volcanoes having a morphology resulting from ice confinement during eruption and comprising a set of lithofacies reflecting direct interaction between magma and ice melt water the combinations of lithofacies within tuyas record the interplay between volcanic eruption and the attending glaciohydraulic conditions although tuyas can range in composition from basaltic to rhyolitic many of the characteristics diagnostic of glaciovolcanic environments are largely independent of lava composition e g edifice morphology columnar jointing patterns glass distributions pyroclast shapes our classification consolidates the diverse nomenclature resulting from early isolated contributions of geoscientists working mainly in iceland and canada and the nomenclature that has developed subsequently over the past 30 years tuya subtypes are first recognized on the basis of variations in edifice scale morphologies e g flat topped tuya then on the proportions of the essential lithofacies e g lava dominated flat topped tuya and lastly on magma composition e g basaltic lava dominated flat topped tuya these descriptive modifiers potentially supply additional genetic information and we show how the combination of edifice morphologies and lithofacies can be directly linked to general glaciohydraulic conditions we identify nine distinct glaciovolcanic model edifices that potentially result from the interplay between volcanism and glaciohydrology detailed studies of tuya types are critical for recovering paleo environmental information through geological time including ice sheet locations extents thicknesses and glaciohydraulics such paleo environmental information represents a new innovative underutilized resource for constraining global paleoclimate models

subglacial volcanism in north central british columbia and iceland the subglacial genesis of five volcanoes in british columbia has been confirmed by field and laboratory studies and by comparison with the stapar table mountains of iceland two of the canadian tuyas are flat topped piles of hyaloclastite overlain by basalt flows these mountains are almost identical in form to their icelandic counterparts three other tuyas are large conical piles of unconsolidated lapilli two of which overlie vitric tuff and pillow basalt layers and may be analogous to relatively rare icelandic subglacial scoria cones all five volcanoes can be accounted for by eruption into englacial meltwater lakes the differences in gross morphology and physical composition can be accounted for by minor variations in the relative importance of magmatic versus phreatomagmatic eruption

alteration of basaltic glasses from north central british columbia canada abstract evidence of palagonitization glass replacement by poorly crystallized clay like material is seen on all glasses studied from three pleistocene subglacial volcanoes in north central british columbia canada samples from foreset breccias of tuya butte are more highly palagonitized than those from the tephra cones of ash mountain and southern tuya extensive palagonitization is generally associated with authigenic mineralization clays zeolites palagonite composition varies widely relative to glass composition and palagonite can be broadly categorized as either high al or low al depending on whether al was retained or lost to aqueous solutions during palagonitization the lowest al palagonites are those from the foreset breccias of tuya butte loss of al during palagonitization is related to closed system alteration including precipitation of aluminosilicate authigenic cements low initial ph is suggested for al depletion consistent with the behavior of ni co and cr which are retained in high al and depleted in low al palagonite microenvironment appears to be more influential than macroenvironment in determining the composition of palagonite palagonite rinds are compositionally zoned generally becoming progressively higher in al and ca and lower in fe and mg towards the innermost later formed portions of the rinds this apparently reflects changing solution composition increasing ph with time compositional zoning does not change the overall stoichiometry of palagonite which resembles smectite clay mineral paragenesis is related to the ca content of the palagonite with partial replacement of palagonite by smectite fe saponite occurring when ca is retained in the rind this replacement phenomenon occurs prior to zeolitization no such replacement clay occurs with low ca palagonite but a late stage nontronite film overgrows zeolite phillipsite is the first zeolite formed followed by chabazite analcime and calcite occur in the most highly palagonitized samples mass balance considerations indicate higher mass loss where palagonitization has not proceeded to the point where zeolite solubility limits were attained in the local solution zeolites occur in closed system conditions low flow rates where little net system mass loss or gain has occurred the colloidal nature of palagonite allows the effective adsorption of rb cs sr ba and rees

paleohydrological implications of holocene peatland development in northern michigan daphne sphagnum peatlands provide data about local hydrologic changes in northern michigan during the holocene gleason bog started about 8000 yr b p as a shallow pond that supported rich fen vegetation after it was partly filled with peat and sand about 4000 yr b p the vegetation changed to oligotrophic bog at gates bog paludification starting about 3800 yr b p caused peat accumulation over sand without an initial pond phase the onset of peat accumulation at both sites is attributed to a rise in the water table resulting from the onset of cool and moist late holocene climates the water table of gleason bog is linked to the water level of adjacent douglas lake which may have undergone a simultaneous rise the results emphasize the individuality of hydrological conditions and hydroseral development in northern michigan peatlands q

stratigraphy of the fort selkirk volcanogenic complex in central yukon and its paleoclimatic significance ar ar and paleomagnetic data brunhes matuyama kaena and mammoth age basaltic lava flows tertiary quaternary selkirk volcanics were sampled in west central yukon the mean characteristic remanent magnetization chrm direction of the flows sampled in this and previous studies has a declination of 348 7 and an inclination of 70 8 n 42 k 99 6 95 2 2 all on lower hemisphere the time range represented in this study ca 3 25 to ca 0 004 ma is great enough to have confidently averaged secular variation sediment associated with the basalt has a mean declination of 7 6 and inclination of 78 8 n 5 k 5 6 95 35 7 a new 40ar 39ar date on the reversely magnetized basal basalts at ne ch e ddhawa places the eruption in the mammoth subchron of the gauss normal chron the newly dated basal basalt at ne ch e ddhawa precedes the initial continental glaciation in yukon and is older than the fort selkirk vent lower mushroom which was previously thought to be the oldest eruption at fort selkirk volcanic complex

the dynamics of mountain erosion cirque growth slows as landscapes age glacial cirques are widely used palaeoenvironmental indicators and are key to understanding the role of glaciers in shaping mountain topography however notable uncertainty persists regarding the rate and timing of cirque erosion in order to address this uncertainty we analyse the dimensions of 2208 cirques in britain and ireland and model ice accumulation to investigate the degree of coupling between glacier occupation times and cirque growth results indicate that during the last 120 ka cirques were glacier free for an average of 52 0 21 2 ka 43 18 occupied by small largely cirque confined glaciers for 16 2 9 9 ka 14 8 and occupied by large glaciers including ice sheets for 51 8 18 6 ka 43 16 over the entire quaternary i e 2 6 ma we estimate that cirques were glacier free for 1 1 0 5 ma occupied by small glaciers for 0 3 0 2 ma and occupied by large glaciers for 1 1 0 4 ma comparing occupation times to cirque depths and calculating required erosion rates reveals that continuous cirque growth during glacier occupation is unlikely instead we propose that cirques attained much of their size during the first occupation of a non glacially sculpted landscape perhaps during the timeframe of a single glacial cycle during subsequent glacier occupations cirque growth may have slowed considerably with the highest rates of subglacial erosion focused during periods of marginal small glacier glaciation we propose comparatively slow rates of growth following initial cirque development because a least resistance shape is formed and as cirques deepen sediment becomes trapped subglacially partly protecting the bedrock from subsequent erosion in support of the idea of rapid cirque growth we present evidence from northern british columbia where cirques of comparable size to those in britain and ireland developed in less than 140 ka

intraglacial volcanism in the wells gray clearwater volcanic field east central british columbia canada small volume subaerial subaqueous and subglacial basaltic eruptions occurred in the wells gray clearwater area during quaternary time part of this time significant thicknesses of glacial ice were present dating of intraglacial volcanic features corroborates other evidence of an early pleistocene cordilleran wide ice sheet of the intraglacial volcanoes investigated three were studied in detail and of these two probably erupted during the fraser glaciation 11 20 ka when maximum ice level exceeded 2100 m elevation major element and sulphur concentrations were measured in glass from the volcanoes to provide insight into vent conditions at the time of eruption hyalo ridge 2102 m elevation whole rock k ar age of 0 02 0 01 ma is a small volcanic edifice capped by lava flows with coherent pillowed lavas and interbedded hyaloclastite exposed over nearly 400 m altitude on its east flank low sulphur content 0 03 wt in pillow rim glasses indicates that the lavas are degassed it is interprete

holocene climatic change and the development of the lake effect snowbelt in michigan usa lake effect snow is an important constraint on ecological and socio economic systems near the north american great lakes little is known about the holocene history of lake effect snowbelts and it is difficult to decipher how lake effect snowfall abundance affected ecosystem development we conducted oxygen isotope analysis of calcite in lake sediment cores from northern lower michigan to infer holocene climatic variation and assess snowbelt development the two lakes experience the same synoptic scale climatic systems but only one of them huffman lake receives a significant amount of lake effect snow a 177 cm difference in annual snowfall causes groundwater inflow at huffman lake to be 18o depleted by 2 3 relative to o brien lake to assess when the lake effect snowbelt became established we compared calcite 18o profiles of the last 11 500 years from these two sites the chronologies are based on accelerator mass spectrometry 14c ages of 11 and 17 terrestrial plant samples from huffman and o brien lakes respectively the values of 18o are low at both sites from 11 500 to 9500 cal yr bp when the laurentide ice sheet lis exerted a dominant control over the regional climate and provided periodic pulses of meltwater to the great lakes basin carbonate 18o increases by 2 6 at o brien lake and by 1 4 at huffman lake between 9500 and 7000 cal yr bp suggesting a regional decline in the proportion of runoff derived from winter precipitation the great lakes snowbelt probably developed between 9500 and 5500 cal yr bp as inferred from the progressive 18o depletion at huffman lake relative to o brien lake with the largest increase of lake effect snow around 7000 cal yr bp lake effect snow became possible at this time because of increasing contact between the great lakes and frigid arctic air these changes resulted from enhanced westerly flow over the great lakes as the lis collapsed and from rapidly rising great lakes levels during the nipissing transgression the 18o difference between huffman and o brien lakes declines after 5500 cal yr bp probably because of a northward shift of the polar vortex that brought increasing winter precipitation to the entire region however 18o remains depleted at huffman lake relative to o brien lake because of the continued production of lake effect snow

tholeiitic alkalic transition at subglacial volcanoes tuya region british columbia canada ash mountain south tuya and tuya butte are three small basaltic volcanoes in the stikine volcanic belt of northern british columbia the volcanoes rise 700 500 and 400 m above their bases and are about 3 2 1 6 and 2 6 km3 in volume respectively they began eruptive activity under several hundred meters of overlying glacial ice or water in an ice impounded lake and undegassed pillow lava was erupted and forms the bases of all three later as the vents grew into shallow water explosive phreatomagmatic activity erupted partly degassed glassy tuffs finally when the volcano emerged through the surface of the ice or water or the water was drained degassed subaerial lava flows were erupted and were converted to assemblages of foreset bedded pillow breccia and pillow lava when subaerial flows crossed a shoreline and flowed into meltwater lakes the undegassed subglacial pillow base of ash mountain is overlain by partly degassed pillows and hyaloclastite tuff cut by dikes at south tuya the pillow base is overlain by hyaloclastite tuffs and lenses of pillow lava at tuya butte the pillow base is overlain by foreset bedded pillow lava pillow breccias and hyaloclastite tuffs which in turn are overlain by subaerial lava flows composing a small shield volcano the undegassed basal subglacial pillow lava of the three volcanoes contain 0 10 0 01 wt sulfur and 0 5 wt h2o the overlying partly degassed assemblages contain 0 06 0 02 sulfur and 0 2 h2o at ash mountain 0 07 0 01 sulfur at south tuya and 0 03 0 01 sulfur at tuya butte the differences in the degree of degassing can be related to the nature of eruption and quenching and the distance of flow of the subaerial lava when the volcanoes switched from subglacial to shallow water or subaerial eruptions as shown by change to more explosive activity and then to subaerial lava flows and by a marked reduction of sulfur in volcanic glass the magma shifted from tholeiitic to alkalic composition this transition occurs at each of the three volcanoes the tholeiitic and alkalic magmas cannot be related by shallow crystal fractionation and apparently originated by differing degrees of deep melting at a mantle source prior to eruption the tholeiitic melts overlay alkalic melts in shallow chambers underlying each of the volcanoes because of their lower density and were therefore the first to erupt under subglacial conditions as the volcano grew through the ice or ice impounded water the volcanic conduit vented to the atmosphere producing a partial depressurization of the conduit and the subsurface chamber this sudden reduction in confining pressure caused enhanced vesiculation of volatile saturated melts particularly of the more volatile rich alkalic melts causing them to rise to the top of the chamber and erupt

paleoecology of a northern michigan lake and the relationship among climate vegetation and great lakes water levels abstract we reconstructed holocene water level and vegetation dynamics based on pollen and plant macrofossils from a coastal lake in upper michigan our primary objective was to test the hypothesis that major fluctuations in great lakes water levels resulted in part from climatic changes we also used our data to provide temporal constraints to the mid holocene dry period in upper michigan from 9600 to 8600 cal yr b p a shallow lacustrine environment characterized the mud lake basin a sphagnum dominated wetland occupied the basin during the mid holocene dry period 8600 to 6600 cal yr b p the basin flooded at 6600 cal yr b p as a result of rising water levels associated with the onset of the nipissing i phase of ancestral lake superior this flooding event occurred contemporaneously with a well documented regional expansion of tsuga betula pollen increased during the nipissing ii phase 4500 cal yr b p macrofossil evidence from mud lake suggests that betula alleghaniensis expansion was primarily responsible for the rising betula pollen percentages major regional and local vegetational changes were associated with all the major holocene highstands of the western great lakes nipissing i nipissing ii and algoma traditional interpretations of great lakes water level history should be revised to include a major role of climate

evolution of an englacial volcanic ridge pillow ridge tindar mount edziza volcanic complex ncvp british columbia canada abstract glaciovolcanic deposits are critical for documenting the presence and thickness of terrestrial ice sheets and for testing hypotheses about inferred terrestrial ice volumes based on the marine record deposits formed by the coincidence of volcanism and ice at the mount edziza volcanic complex mevc in northern british columbia canada preserve an important record for documenting local and possibly regional ice dynamics pillow ridge located at the northwestern end of the mevc formed by ice confined fissure fed eruptions it comprises predominantly pillow lavas and volcanic breccias of alkaline basalt composition with subordinate finer grained volcaniclastic deposits and dykes the ridge is presently 4 km long 1000 m in maximum width and 600 m high fifteen syn and post eruptive lithofacies are recognized in excellent exposures along the glacially dissected western side of the ridge we recognize five lithofacies associations 1 poorly sorted tuff breccia and dykes 2 proximal pillow lava dykes and tuff breccia 3 distal pillow lava poorly sorted conglomerate and well sorted volcanic sandstone 4 interbedded tuff lapilli tuff and tuff breccia units and 5 heterolithic volcanogenic conglomerate and sandstone given the abundance of pillow lavas and the lack of surrounding topographic barriers capable of impounding water we agree with souther souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp that the bulk of the edifice formed while confined by ice but have found evidence for a more complex and variable eruption history than that which he proposed preliminary estimates of water ice depths derived from ftir analyses of h2o give ranges of 300 to 680 m assuming 0 ppm co2 and 857 to 1297 m assuming 25 ppm co2 variations in depth estimates among samples may indicate that water ice depths changed during the evolution of the ridge which is consistent with our interpretations for the origins of different lithofacies associations given that the age of the units are likely to be ca 0 9 ma souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp pillow ridge may be the best documentation of a regional high stand of the cordilleran ice sheet cis in the middle pleistocene and an excellent example of the lithofacies and stratigraphic complexities produced by variations in water levels during a prolonged glaciovolcanic eruption

fragmentation of foamed silicic melts an experimental study we present the first experimental investigation of the fragmentation behavior of two phase melt gas rhyolitic systems under rapid decompression two phase samples have been generated by foaming water oversaturated rhyolitic melts up to 900 c and up to 18 mpa prior to rapid decompression in a fragmentation bomb the fragmented particles or experimental pyroclasts were recovered for analysis several features of naturally foamed pumices have been reproduced including the generation of both isotropic and tube pumices we focus here on the fragmentation behavior fragmentation occurred through a layer by layer process in the brittle regime of melt response we investigated the influence of the magnitude of the decompression 4 to 18 mpa the porosity 0 to 85 vol and the pore morphology tube versus isotropic on the fragment size distribution less vesicular samples porosity 50 vol yield coarser fragments when decompressed below 15 mpa and finer fragments when decompressed above 15 mpa increasing decompression of the vesicular samples results in a decrease in fragment size of 0 2 unit mpa the presence of tubes instead of isotropic pores in vesicular samples generates finer fragments under decompression implications for dome eruptions are discussed

pyroclastic flows and surges over water an example from the 1883 krakatau eruption pyroclastic deposits from the 1883 eruption of krakatau are described from areas northeast of the volcano on the islands of sebesi sebuku and lagoendi and the southeast coast of sumatra massive and poorly stratified units formed predominantly from pyroclastic flows and surges that traveled over the sea for distances up to 80 km granulometric and lithologic characteristics of the deposits indicate that they represent the complement of proximal subaerial and submarine pyroclastic flow deposits laid down on and close to the krakatau islands the distal deposits exhibit a decrease in sorting coefficient median grain size and thickness with increasing distance from krakatau crystal fractionation is consistent with the distal facies being derived from the upper part of gravitationally segregated pyroclastic flows in which the relative amount of crystal enrichment and abundance of dense lithic clasts diminished upwards the deposits are correlated to a major pyroclastic flow phase that occurred on the morning of 27 august at approximately 10 a m energetic flows spread out away from the volcano at speeds in excess of 100 km h and traveled up to 80 km from source the flows retained temperatures high enough to burn victims on the sw coast of sumatra historical accounts from ships in the sunda straits constrain the area affected by the flows to a minimum of 4x103 km2 at the distal edge of this area the flows were relatively dilute and turbulent yet carried enough material to deposit several tens of centimeters of tephra the great mobility of the krakatau flows from the 10 a m activity may be the result of enhanced runout over the sea it is proposed that the generation of steam at the flow seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective the buoyant distal edge of these ash and steam laden clouds lifted off into the atmosphere leading to cooling condensation and mud rain

stable isotope ratios in swale sequences of lake superior as indicators of climate and lake level fluctuations during the late holocene abstract beach ridges along the coastline of lake superior provide a long term and detailed record of lake level fluctuations for the past 4000 cal bp although climate change has been invoked to explain these fluctuations its role is still in debate here we reconstruct water balance by employing peat samples collected from swale deposits present between beach ridge sequences at two locations along the coastline of lake superior carbon isotope ratios for sphagnum remains from these peat deposits are used as a proxy for water balance because the presence or absence of water films on sphagnum controls the overall isotope discrimination effects consequently increased average water content in sphagnum produces elevated 13c values two maxima of sphagnum 13c values interpreted to reflect wetter conditions prevailed from 3400 to 2400 cal bp and from about 1900 to 1400 cal bp there are two relatively short drier periods as inferred from low sphagnum 13c values one is centered at about 2300 cal bp and one begins at 1400 cal bp a good covariance was found between sphagnum 13c values and reconstructed lake levels for lake michigan in which elevated carbon isotope values correlate well with higher lake levels based on this covariance we conclude that climate exerts a strong influence on lake levels in lake superior for the past 4000 cal bp

thermodetrital and crystallodetrital magnetization in an icelandic hyaloclastite an icelandic hyaloclastite mostly composed of millimetric fragments of basaltic glass that is fresh at the bottom of the unit but largely palagonitized in the upper part has been studied by petrologic mineralogical and magnetic means with the aim of determining the nature and characteristics of the natural remanent magnetization nrm the nrm was generally found to consist of two components a thermodetrital remanent magnetization thermo drm and a crystallodetrital remanent magnetization crystallo drm thermo drm and crystallo drm are defined here as the remanences acquired as a result of the deposition of magnetic particles of detrital origin individually carrying either a trm thermoremanent magnetization or a crm crystallization remanent magnetization respectively regardless of the chemistry and size and of these particles thellier experiments carried out on samples carrying a thermo drm provide apparent paleointensities close to the expected geomagnetic paleointensity which suggests that in the present case the fractional alignment of individual magnetic moments is similar for drm and trm in the upper part of this outcrop grain growth crm was acquired by individual grains of magnetite which crystallized as a result of palagonitization of basaltic glass at low temperature 100 c no systematic difference could be observed between the directions of characteristic remanence in the layers richest in magmatic magnetic grains and the layer where secondary magnetite is the main remanence carrier in both cases the overall remanence exhibits a large inclination error 20 and the samples have a marked anisotropy of magnetic susceptibility which is typical of sedimentary fabrics thus secondary magnetite probably formed prior to the deposition of particles and the bulk remanence in the palagonitized layers is a crystallo drm rather than a crm throughout the entire stratigraphic thickness thellier paleointensity data are of good or excellent quality regardless of the nature of the primary remanence in agreement with previous theoretical inferences and experimental results the layers carrying a crystallo drm provide a much lower by a factor of 2 apparent paleointensity than the layers where the remanence is a thermo drm this suggests that palagonitized basaltic glasses should not be used for paleointensity determinations our study shows that application of the thellier thermal paleointensity method to sedimentary rocks can be a useful tool for distinguishing crystalline versus thermal blocking of the magnetic moments of the individual particles which after deposition carry a drm more generally discrepancies between relative paleointensities obtained from sediments can be expected if rocks with different proportions of thermo drm crystallo drm or crm are compared

moisture changes in northeast china since the last deglaciation spatiotemporal out of phase patterns and possible forcing mechanisms abstract there is a strong chance that the 21 st century warming will cause differences in precipitation distribution over the globe northeast ne china is a unique area whose atmospheric circulation is still a controversial subject and is likely to be strongly impacted by global warming thus a good understanding of the past variations in effective moisture in ne china will be benefit for the prediction of future hydrological changes in this study we use basal peat ages and published paleoclimate records to evaluate the spatial and temporal patterns and possible forcing mechanisms for the moisture changes in ne china over the past 16 000 years basal peat ages suggest that the moisture conditions in different regions of ne china show as a spatiotemporal out phase pattern in addition the paleoclimate records of 17 sites also indicate that ne china experienced a spatiotemporal out phase pattern of moisture changes along northwest southeast direction since the last deglaciation the moisture in southern ne china experienced increasing trend during the period of 16 8 cal ka bp with the maximum moisture occurring 8 3 cal ka bp and decreasing trend after 3 cal ka bp the moisture pattern in western ne china is similar to that in southern ne china it experienced increasing trend during the period of 16 8 cal ka bp the maximum moisture during the period 8 4 cal ka bp and decreasing trend from 4 cal ka bp to present the moisture in eastern ne china experienced wet conditions from 16 cal ka bp to 4 cal ka bp and decreasing trend after 4 cal ka bp in central ne china two relatively wet periods occurred during the periods of 13 8 cal ka bp and 6 3 cal ka bp respectively in addition two wet periods occurred during the periods of 14 11 cal ka bp and 7 1 cal ka bp in northern ne china respectively the moisture patterns between ne china and other regions of china are also compared in this study we propose that the possible forcing mechanisms for the moisture changes in ne china were different for each 4000 year interval during the period of 16 12 cal ka bp the weak east asian summer monsoon easm and strong northeast monsoon nem were the major water vapor sources of ne china during the period of 12 8 cal ka bp the increasing easm and strong nem were still the major water vapor sources of ne china during the period of 8 4 cal ka bp the strongest easm was the major water vapor sources of the whole ne china furthermore the increasing westerlies slightly penetrated into northern ne china during this period from 4 cal ka bp to present the decreasing easm provided precipitation for the most regions of ne china the westerlies reached the maximum and further penetrated into the whole northern ne china during this period

a geochronology supported soil chronosequence for establishing the timing of shoreline parabolic dune stabilization abstract detailed dune chronologies are required to understand the complex drivers of dune stabilization and activation stabilized parabolic dunes provide ideal study sites to examine dune stabilization because their geomorphic histories are more straightforward than other dune types here we present optically stimulated luminescence osl stabilization chronologies for two complexes of fully stabilized parabolic dunes along the eastern coast of lake michigan with the goal of clarifying the timing and consistency of dune stabilization along the shoreline further we use this chronology to calibrate a soil chronosequence for use in future dune chronologies we found periods of stabilization at 4 0 ka 2 8 2 0 ka and 1 2 0 4 ka that complement existing periods of stabilization identified as the nipissing the algoma and modern soils in the area appear to develop consistently and predictably over the last 4000 years the strongest indicators of age are depth to the b horizon and thickness of the e horizon well developed e horizons also appear to form between the algoma and modern stabilization periods creating a useful proxy for quickly differentiating between otherwise similar landforms the impact of leaching is also evident in the soil chemistry as zn co mg and fe all decrease in the eluvial zone through time while ba steadily increases overall our study closes a gap between chronologies further to the north and south clarifies the consistency of stabilization periods along the coastline and creates new tools for quickly estimating dune stabilization ages

paleoecology and high resolution paleohydrology of a kettle peatland in upper michigan we investigated the developmental and hydrological history of a sphagnum dominated kettle peatland in upper michigan using testate amoebae plant macrofossils and pollen our primary objective was to determine if the paleohydrological record of the peatland represents a record of past climate variability at subcentennial to millennial time scales to assess the role of millennial scale climate variability on peatland paleohydrology we compared the timing of peatland and upland vegetation changes to investigate the role of higher frequency climate variability on peatland paleohydrology we used testate amoebae to reconstruct a high resolution hydrologic history of the peatland for the past 5100 years and compared this record to other regional records of paleoclimate and vegetation comparisons revealed coherent patterns of hydrological vegetational and climatic changes suggesting that peatland paleohydrology responded to climate variability at millennial to sub centennial time scales although ombrotrophic peatlands have been the focus of most high resolution peatland paleoclimate research paleohydrological records from sphagnum dominated closed basin peatlands record high frequency and low magnitude climatic changes and thus represent a significant source of unexplored paleoclimate data

kaguyak dome field and its holocene caldera alaska peninsula abstract kaguyak caldera lies in a remote corner of katmai national park 375 km sw of anchorage alaska the 2 5 by 3 km caldera collapsed 5 8 0 2 ka 14c age during emplacement of a radial apron of poorly pumiceous crystal rich dacitic pyroclastic flows 61 67 sio2 proximal pumice fall deposits are thin and sparsely preserved but an oxidized coignimbrite ash is found as far as the valley of ten thousand smokes 80 km southwest postcaldera events include filling the 150 m deep caldera lake emplacement of two intracaldera domes 61 5 64 5 sio2 and phreatic ejection of lakefloor sediments onto the caldera rim co2 and h2s bubble up through the lake weakly but widely geochemical analyses n 148 including pre and post caldera lavas 53 74 sio2 define one of the lowest k arc suites in alaska the precaldera edifice was not a stratocone but was instead nine contiguous but discrete clusters of lava domes themselves stacks of rhyolite to basalt exogenous lobes and flows four extracaldera clusters are mid to late pleistocene but the other five are younger than 60 ka were truncated by the collapse and now make up the steep inner walls the climactic ignimbrite was preceded by 200 years by radial emplacement of a 100 m thick sheet of block rich glassy lava breccia 62 65 5 sio2 filling the notches between the truncated dome clusters the breccia now makes up three segments of the steep caldera wall which beheads gullies incised into the breccia deposit prior to caldera formation they were probably shed by a large lava dome extruding where the lake is today

distribution nature and origin of neogene quaternary magmatism in the northern cordilleran volcanic province canada the northern cordilleran volcanic province encompasses a broad area of neogene to quaternary volcanism in northwestern british columbia the yukon territory and adjacent eastern alaska volcanic rocks of the northern cordilleran volcanic province range in age from 20 ma to ca 200 yr b p and are dominantly alkali olivine basalt and hawaiite a variety of more strongly alkaline rock types not commonly found in the north american cordillera are locally abundant in the northern cordilleran volcanic province these include nephelinite basanite and peralkaline phonolite trachyte and comendite the most mgo rich nephelinites basanites and alkaline basalts from throughout the northern cordilleran volcanic province show trace element abundances and isotopic compositions that are consistent with an asthenospheric source region similar to that for average oceanic island basalt and for post 5 ma alkaline basalts from the basin and range our petrologic observations help constrain the origin of northern cordilleran volcanic province magmatism as well as lithosphere changes between the four major basement terranes that underlie the province results from phase equilibria calculations and the spatial distributions of volcanic rock types and magmatic inclusions are more consistent with the existence of thicker lithosphere beneath stikinia which underlies the southern part of the northern cordilleran volcanic province than beneath the cache creek and yukon tanana terranes which underlie the northern part of the northern cordilleran volcanic province our results support a model for initiation of northern cordilleran volcanic province magmatism due to incipient rifting of the northern cordillera driven by changes in relative plate motion between the pacific and north american plates ca 15 10 ma

volatiles in basaltic glasses from a subglacial volcano in northern british columbia canada implications for ice sheet thickness and mantle volatiles

holocene soil development on till and outwash inferred from lake sediment geochemistry in michigan and wisconsin abstract two geochemical techniques from soil mineralogy were used with lake sediment to reconstruct soil development in the catchments of two lakes one on outwash and the other on till in the great lakes region a sodium pyrophosphate extraction provides information about leaching of exchangeable and organically complexed cations from terrestrial sources while an acidified ammonium oxalate extraction removes mineral materials without well developed crystalline structure that are indicative of podzolization more evidence of pedogenesis is preserved in sediment of the lake on outwash likely a result of greater retention of material within the soil profile in the catchment on till this difference between the records suggests that excessively well drained leaky catchments may provide better records of soil development than those with higher water holding capacity evidence of acidification and podzolization appeared first at the lake on till and 4500 years later at the lake on outwash both records reveal a late holocene intensification of weathering that coincided with a regional climatic change to greater moisture availability the variability in weathering rates observed presents a more complex picture of weathering than the simple exponential functions often assumed in chronosequence studies use of lake sediment records provides better temporal resolution of significant events in soil formation than could be achieved using a chronosequence approach

patterns of hydroclimatic change in the rocky mountains and surrounding regions since the last glacial maximum abstract the paleohydrologic record of western north america since the last glacial maximum reveals a wide range of hydroclimatic variability in time and space to improve the understanding of abrupt hydroclimatic shifts and millennial scale hydrologic changes in the central rocky mountains we reconstruct the lake level histories of two small lakes in the beartooth and bighorn mountains in northern wyoming over the past 17 ka to do so we use ground penetrating radar gpr and sediment cores to track the elevations of shoreline sediments within the lakes through time we compare the stratigraphies with those from four other lakes in wyoming and colorado and find widespread evidence for a terminal pleistocene drought from 15 to 11 ka an early holocene humid period from 11 to 8 ka and mid holocene aridity from 8 to 5 5 ka the northern wyoming lakes also provide evidence of high levels in the pleistocene possibly before ca 15 ka and rapid hydroclimatic changes that may have correlated with heinrich event 1 ca 16 8 ka we place the changes in a broad context by summarizing and mapping water level changes from 107 additional previously studied lakes important patterns include 1 extensive drying across the western u s after 15 ka 2 sub regional differences during the pleistocene holocene transition 3 a north south contrast from 9 to 6 ka consistent with a northward shift in storm tracks as the influence of the laurentide ice sheet diminished and 4 rapid increases in effective moisture across much of western north america from 6 to 4 ka

holocene lake effect precipitation in northern michigan holocene sediments from nelson lake on michigan s eastern upper peninsula provide isotopic pollen and charcoal evidence for a two step sequence of changes in moisture source and increased lake effect precipitation during the late holocene between 8000 and 5300 cal yr b p a warm dry climate and zonal atmospheric circulation produced enriched stable oxygen and carbon isotopic values in combination with high percentages of pine pollen and sustained influx of charcoal particles after 5300 cal yr b p decreasing isotopic values in marl and increasing pollen percentages of mesic hardwoods and northern white cedar indicate increased meridional air flow and precipitation from cold winter storms generated in alberta canada after 3000 cal yr b p abrupt declines in values of 13c and 18o and increased pollen representation of hemlock american beech spruce and aquatic plants indicate paludification from increased lake effect snowfall the moisture was derived from the great lakes and transported by alberta cyclonic storms that were steered across lakes superior and michigan by a southward shift in the modal winter position of the polar jet stream

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

mid late holocene maar lake mire transition in northeast china triggered by hydroclimatic variability abstract the density of maar lake type peatlands in the changbai mountain areas northeast ne china is among the highest in the world these deposition systems include both peat and limnic deposits providing valuable sites to study their evolutionary history shaped by their sensitivity to climate forced state shifts to investigate the maar lake mire shift in response to hydroclimatic variability we examined developmental history of the jinchuan peatland based on sedimentary facies grain size physical and chemical properites plant macrofossils and peat basal age the results indicate that the jinchuan peatland mainly originated from paludification in a maar lake from approximately 7000 cal bp its water level continuously increased since the middle holocene reaching the peak during the period of 5000 4000 cal yr bp the outward expansions of jinchuan peatland suggest a climate driven model based on which water level variability superimposes the underlying basin morphology the hydroclimatic variability and peatland development history can be divided into three periods from 12 to 7 ka cal bp the increasing east asian summer monsoon easm was the major water vapor source of jinchuan peatland the strong evaporation effects induced by the strong winter asian winter monsoon wawm and the maximum sea surface temperatures ssts of japan sea might have changed the jinchuan maar lake into dry upland from 7 to 4 ka cal bp the maximum easm and increasing westerly jet wj provided water vapor for the peatland the decreasing eawm and ssts of japan sea resulted in decreased evaporation effects the moisture and water level in jinchuan peatland gradually increased the peat covered 68 97 of the area during this period since 4 ka cal bp the decreased easm and the maximum wj provided water vapor for the jinchuan peatland the weak eawm and the lower ssts of japan sea induced lower evaporation effects the moisture and water level in the peatland reached the maximum subsequently peat area further expanded and covered the remaining 31 03 area this study reveals a remarkable link between the maar lake mire shift and hydroclimatic variability which is significant for future prediction of maar lake mire ecosystem shifts under global climate change

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

holocene lake level rise in the upper peninsula of michigan usa as indicated by peatland growth we examined one sediment core from kerr lake and eight cores from the adjacent peatland in the sylvania wilderness area of the upper peninsula of michigan usa radiocarbon dating of the interface between peat and the underlying glacial till showed that the peatland grew by paludification of the surrounding uplands implying a rising water level in the lake pollen analysis of the cores showed that the peatland began expanding just before the arrival of tsuga in the surrounding forests the most rapid growth of the peatland occurred between 3900 and 3000 bp this is also the time when the forests were being transformed from dry pinus strobus dominated woodlands to moister tsuga and acer saccharum dominated northern hardwoods our results imply an increase in available moisture at the time of tsuga colonization

evolution of a subglacial basaltic lava flow field tennena volcanic center mount edziza volcanic complex british columbia canada abstract studies of terrestrial glaciovolcanic deposits have elucidated the utility of these deposits as tools to constrain ice conditions at the time of their emplacement very few studies however have documented the emplacement of effusion dominated basaltic glaciovolcanic eruptions the tennena volcanic center tvc located at 57 40 57 705 n 130 39 43 138 w on the western flank of mount edziza volcanic complex mevc in northwestern british columbia canada preserves a detailed record of interactions between coherent basaltic lavas and a local regional ice sheet inferred to be associated with the last glacial maximum lgm here we describe the field characteristics of five primary volcanic lithofacies and five associated glaciogenic lithofacies and discuss their spatial distribution within the volcanic center we find that 1 the distribution of primary hydrovolcanic clastic deposits tuff breccias and lapilli tuffs is confined to tennena cone 2 pillow lavas are present throughout the extent of the surrounding lava field with morphologies that include distinctive structures comprising vertically oriented distended pillows 3 multiple lobes of massive non pillowed lavas that represent high initial magma discharge rates are confined to medial distances from the cone and 4 associated glaciogenic facies that underlie or onlap the tvc lavas indicate a variable sediment water ratio during subglacial meltwater drainage at the time of the eruption or shortly afterwards analyses of h 2 o co 2 in pillow rim samples give broad constraints for emplacement pressures equivalent to 500 1400 m of overlying ice no subaerial lava morphologies are found on the cone or in the proximal medial and distal lithofacies and the sequence is interpreted as documenting an eruption of basaltic lava flows beneath either the lgm cordilleran ice sheet or a younger dryas expansion of the still extant edziza ice cap the tvc lavas especially medial and distal ones display excellent examples of textures and morphologies that can be used to 1 help identify other terrestrial and martian basaltic lava flows emplaced beneath ice and 2 further our understanding on how sub ice lava flows are emplaced

have the southern westerlies changed in a zonally symmetric manner over the last 14 000 years a hemisphere wide take on a controversial problem the prevailing view in the palaeoclimate literature of the last 20 years is that the southern westerly winds sww were intensified over southern australia and tasmania during the warmer than present early holocene 11e8 ka at similar latitudes on the opposite side of the southern mid latitudes palaeoclimate studies have suggested a poleward shift of the northern edge of the westerlies and focusing at 49 s in southern south america this zonal asymmetry contrasts with the modern day zonal symmetry displayed by the sww and poses a formidable challenge to an understanding of the modes of climatic variability of the southern extra tropics this paper presents an updated synthesis of continuous radiocarbon dated palaeoenvironmental data from the westerlies zone of influence in all southern hemisphere continents synchronous multi millennial trends in moisture vegetation fire and hydrologic balance are remarkably consistent with the way the sww changes impact upon the climate in southern hemisphere landmasses in the modern climate considering the modern relationships between local precipitation and zonal wind speeds it is suggested that the sww changed in a zonally symmetric manner at multi millennial scale between 14 and 5 ka regional asymmetry develops after 5 ka across the southern hemisphere with a pattern of precipitation anomalies akin to the modern functioning of el nino e southern oscillation which started w6200 years ago

diatom indicators of peatland development at pogonia bog pond minnesota usa sediment cores were taken from the central pond and fringing mat of a sphagnum peatland located in the big woods vegetation type pollen analysis of the pond core spanning 12 000 cal bp to the pre

a study of the palaeomagnetism of subglacial basalts sw iceland a comparison with oceanic crust summary subglacial volcanic sequences in iceland were used as analogues of oceanic crust to get an indication of the degree of primary heterogeneity of magnetic directions that can be expected within subaqueous volcanic sequences erupted in both deep and shallow water in the icelandic sequences the degree 6f tilt brecciation and the amount of hyaloclastite are known so it is possible to test for primary magnetic heterogeneity we measured magnetic directions of 119 oriented core samples 2 5 cm diameter collected from five sites in sw iceland where there is good exposure in quaternary subglacial volcanic sequences sample sites vary from compact pillowed flows most analogous to deep water volcanic sequences to pillow breccia with up to 40 per cent interpillow hyaloclastite more analogous to shallow water sequences magnetic directions of multiple samples from 16 individual pillows have angular differences of 2 66 with most being less than lo of the five sites sampled two sites have inclinations that approximate that of the centred axial dipole one site has steeper inclinations and two sites have shallower inclinations when the site averages of magnetic direction with their circles of ag5 are plotted there is little overlap there is little correlation between either the scatter of magnetic measurements or the percentage of non dipolar inclinations and the occurrence of pillow breccias hyaloclastite or depositional dips we doubt the tectonic significance of small amounts of tilt 30 estimated from drill cores on the basis of palaeomagnetic inclination as it is not uncommon for rocks to rotate by as much as 30 after they cool through the curie temperature or for such a scatter to be the result of secular variation with this in mind the same caution must be applied when orienting seafloor basalts for palaeomagnetic or structural studies using geopetal features such as drain away ledges or segregation vesicles because the rocks may rotate after these features form at 1200 1000 c but before the rocks cool through the curie temperature

volcanology and petrology of mathews tuya northern british columbia canada glaciovolcanic constraints on interpretations of the 0 730 ma cordilleran paleoclimate petrological volcanological and geochronological data collected at mathews tuya together provide constraints on paleoclimate conditions during formation of the edifice the basaltic tuya was produced via pleistocene glaciovolcanism in northern british columbia canada and is located within the tuya volcanic field 59 195 n 130 434 w which is part of the northern cordilleran volcanic province ncvp the edifice comprises a variety of lithofacies including columnar jointed lava pillow lava massive dikes and volcaniclastic rocks collectively these deposits record the transition from an explosive subaqueous to an effusive subaerial eruption environment dominated by pleistocene ice as is typical for tuyas the volcaniclastic facies record multiple fragmentation processes including explosive quench and mechanical fragmentation all samples from mathews tuya are olivine plagioclase porphyritic alkali olivine basalts they are mineralogically and geochemically similar to nearby glaciovolcanic centers from the southeastern part of the tuya volcanic field e g ash mountain south tuya tuya butte as well as the dominant ncvp rock type crystallization scenarios calculated with melts account for variations between whole rock and glass compositions via low pressure fractionation the presence of olivine microphenocrysts and the absence of pyroxene phenocrysts constrain initial crystallization pressures to less than 0 6 gpa the eruption of mathews tuya occurred between 0 718 0 054 ma and 0 742 0 081 ma based on 40ar 39ar geochronology weighted mean age of 0 730 ma the age determinations provide the first firm documentation for large 700 m thick pre fraser wisconsin glaciers in north central british columbia 0 730 ma and correlate in age with glaciovolcanic deposits in russia e g komatsu et al geomorph 88 352 366 2007 and with marine isotopic evidence for large global ice volumes 0 730 ma

the lateral facies of ignimbrites at laacher see volcano valley fill ignimbrites of the middle laacher see tephra mlst in the proximal depositional fan south of laacher see volcano are laterally continuous with fine grained overbank facies deposits 0 5 1 5 m thick covering higher elevations and interfluves between the paleovalleys the overbank deposits consist of up to 12 ash layers each 4 10 cm thick which show internal structures typical of ash flow transport such as poor sorting reverse size grading of pumice local normal grading of coarse ash sized lithics above a fine grained basal layer cross stratification behind obstacles and erosional unconformities thickness median grain size and number of individual layers decrease systematically with distance from the vent overbank ash layers thicken at the valley slopes and form discrete valley fill ignimbrite flow units in the paleochannels with median grain size increasing from 63 m to 350 m toward the center of paleochannels however the well defined overbank facies is obscured by mutual erosion of individual flow units overlapping data fields in ternary grain size variation diagrams indicate the overbank facies to have evolved from ash flows chiefly through depletion of lapilli and coarse ash overbank facies ash layers do not represent dust layers resulting from elutriation clouds of ash flows co ignimbrite ash or surge deposits developed on higher ground due to low concentration of solids they are similar in some parameters to taupo type ignimbrite veneer deposits but are interpreted differently the thin fine grained laacher see ash layers are thought to have been deposited from diluted portions of the flow proceeding directly from the eruption column while the main pyroclastic flows were confined to the paleovalleys radiating away from the eruptive center the wide distribution of the thin ash layers is attributed to the balance of deposition from various flow parts and turbulent entraining and heating of ambient air that sustained sufficient mobility of the diluted flows to spread across hills and level ground

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