volcano tectonic evolution of the santa maria island azores implications for paleostress evolution at the western eurasia nubia plate boundary abstract the growth and decay of oceanic volcanoes developed close to plate boundaries are intrinsically related to a competition between construction and destruction processes partly controlled by tectonic strain and stresses from morphologic stratigraphic tectonic and new high precision k ar data we present a comprehensive picture of the volcano tectonic evolution of santa maria and discuss its significance regarding the stress evolution and regional deformation in the azores our new data show that 1 the western flat portion of the island is mostly composed of west dipping volcanic rocks here dated between 5 70 0 08 and 5 33 0 08 ma which we consider the remnants of an older shield volcano 2 more than half of this early volcanic complex has been removed by an east directed large scale sector collapse 3 a second volcano here coined the younger shield volcano grew rapidly on the collapse scar between at least 4 32 0 06 and 3 94 0 06 ma 4 more than half of this new volcano was removed by a second large scale sector collapse most probably around 3 6 ma based on the ages of parasitic scoria cones sitting unconformably on the younger shield volcano 5 the latest parasitic volcanic activity is here dated at 2 84 0 04 ma extending significantly the known eruptive history of santa maria morpho structural data shape of the island faults dikes and distribution of volcanic cones show a significant control of construction and destruction along the n045 and n150 directions the age of the lavas intruded by dikes suggests that the n045 and the n150 trends are ca 5 3 ma old and younger than ca 4 3 ma respectively based on the new data we conclude that a change in the regional stress field occurred between 5 3 and 4 3 ma most likely associated with a major reconfiguration of the eurasia nubia plate boundary in the azores

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

in situ monitoring of frost heave pressure during cross passage construction using ground freezing method the artificial ground freezing method has the dual effect of ground reinforcement and waterproof sealing and the frozen curtain can be designed flexibly it is widely used in the construction of cross passages for shield tunnels in soft ground with high groundwater levels however due to the lack of in situ monitoring data it remains difficult to determine the frost heave pressure acting upon a tunnel in this study based on the use of an anti freezing pad type earth pressure gauge in situ monitoring was carried out to measure the frost heave pressure acting upon tunnel segments during the construction of cross passages for the shanghai yangtze river tunnel the monitoring results show that the earth pressure acting upon the tunnel could decrease dramatically during freezing and this kind of decrease can take place suddenly and unpredictably which can be illustrated using the finite element method the maximum measured frost heave pressure during freezing and cross passage excavation was approximat

a multichannel seismic study of lithospheric flexure across the hawaiian emperor seamount chain existing models assume that the thickened crust beneath seamounts is the result of a surface volcanic load flexing an elastic plate new results suggest that flexed oceanic crust beneath the hawaiian emperor seamount chain is underlain by a 4 km thick deep crustal body we intepret the body as a deep crustal sill complex associated with the tholeiitic stage of volcano building along the chain

a geomorphological reconnaissance of the submarine part of the east rift zone of kilauea volcano hawaii more than half of the intensely active east rift zone of kilauea volcano crops out underwater along the crest of the submarine puna ridge i present multibeam bathmetry of the entire ridge near bottom photographic and sonar observations of the plunging crest of its deeper distal half and seismic profiles across the ridge tip and the adjacent structural moat analysis of large scale relief small scale topography and superficial rock types indicates that the rift zone is actively propagating across the moat but is probably a superficial structure that does not penetrate the underlying oceanic crust that its tip is covered with large lava flows erupted at high rates and is surrounded with extensive debris flow deposits and that the axial topography at depths of 2 4 km is dominated by gaping fissures and collapse pits showing a preponderance of intrusive rather than extrusive events some aspects of this central volcano rift zone such as its geometry at small lateral offsets resemble those at interplate rift zones along fast spreading mid ocean rises but the great contrast in lithosphere thickness results in fundamental structural differences

density of basalt core from hilo drill hole hawaii abstract density measurements of 1600 samples of core from 889 to 3097 m depth below sea level in the hawaii scientific drilling program hole near hilo hawaii show marked differences between the basaltic rock types and help define stratigraphy in the hole water saturated densities of subaerial lava flows occurring above 1079 m depth have the broadest range because of the large density variation within a single lava flow water saturated densities commonly range from 2 0 to 3 0 with an average of 2 55 0 24 g cc dikes and sills range from 2 8 to 3 1 g cc densities of hyaloclastite commonly range from 2 3 to 2 7 with an overall average of about 2 5 g cc the low density of most hyaloclastite is due primarily to palagonitization of abundant glass and presence of secondary minerals in the interstices between fragments four principal zones of pillow lava separated by hyaloclastite occur in the drill core the shallowest 1983 2136 m is paradoxically the densest averaging 3 01 0 10 g cc the second 2234 2470 m is decidedly the lightest averaging 2 67 0 13 g cc the third 2640 2790 m and fourth 2918 bottom at 3097 m are high averaging 2 89 0 17 and 2 97 0 08 g cc respectively the first pillow zone includes degassed pillows i e lava erupted on land that flowed into the sea these pillows are poor in vesicles because the subaerial one atmosphere vesicles were compressed when the flow descended to deeper water and higher pressure the second low density non degassed pillow zone is the most vesicle rich apparently because it was erupted subaqueously at a shallow depth the higher densities of the third and fourth zones result from a low vesicularity of only a few percent and an olivine content averaging more than 5 for the third zone and about 10 for the fourth zone the uppermost hyaloclastite extending about 400 m below the bottom of the subaerial basalt is poorly cemented and absorbs up to 6 wt of water when immersed progressing downward the hyaloclastite absorbs less water and becomes better cemented this change is apparently due to palagonitization of glass and addition of secondary minerals in the deeper older hyaloclastite a process favored by the increase of temperature with depth the cementation is largely complete at 1800 m depth where the temperature attains about 20 c the zone of freshest uncemented hyaloclastite represents the weakest rock in the drill hole and is a likely level for tectonic or landslide disruption

volcanic spreading at kilauea 1976 1996 the rift system traversing about 80 km of the subaerial surface of kilauea volcano has extended continuously since the m 7 2 flank earthquake of november 1975 widening across the summit has amounted to more than 250 cm decelerating after 1975 from about 25 to 4 cm yr 1 since 1983 concurrently the summit has subsided more than 200 cm even as the adjacent south flank has risen more than 50 cm the axes of the upper zones about 10 km from the summit subsided before 1983 at average rates of 9 and 4 cm yr 1 respectively and at rates of 4 and 3 cm yr 1 since the middle southwest rift zone is also subsiding and at the other end of kilauea s subaerial rift system subsidence along the lower east rift zone has averaged 1 2 cm yr 1 deformation of kilauea s south flank has been continuous although subject as well to displacements caused by major rift zone seismic swarms whereas horizontal strains across the subaerial south flank seem to have been generally compressive after 1975 they have been extensional since about 1980 or 1981 interrupted only by the east rift zone dike intrusion of 1983 because the magnitudes of these contractions and extensions are much less than the extension across the rift system the subaerial south flank is apparently sliding seaward on its basal decollement more than it is accumulating horizontal strains within the overlying volcanic pile kilauea suffers from gravitational spreading made even more unstable by accumulation of magma along the rift system at depths in excess of about 4 5 km in the presence hot rock incapable of withstanding deviatoric stresses this seismicly quiescent zone decouples the south flank from the rest of hawaii s volcanic edifice the rift zones at lesser depths exhibit a more brittle and therefore sporadic extensional behavior judging from the modern extension record of the summit which both predates the m 7 2 earthquake of 1975 and has outlived its 10 year period of aftershocks kilauea will continue to spread along its rift system as its south flank slips seaward to accommodate the accretion of magma and its relatively dense olivine rich differentiate

synchronization of late glacial vegetation changes at crystal lake illinois usa with the north atlantic event stratigraphy abstract late glacial 17 11 cal ka bp pollen records from midwestern north america show similar vegetation trends however poor dating resolution wide interval pollen counts and variable sedimentation rates have prevented the direct correlation with the north atlantic event stratigraphy as represented in the greenland ice core records thus preventing the understanding of the teleconnections and mechanisms of late quaternary events in the northern hemisphere the widespread occurrence of late glacial vegetation and climates with no modern analogs also hinders late glacial climate reconstructions a high resolution pollen record with a well controlled age model from crystal lake in northeastern illinois reveals vegetation and climate conditions during the late glacial and early holocene intervals late glacial crystal lake pollen assemblages dominated by picea mariana and fraxinus nigra with lesser amounts of abies and larix suggest relatively wet climate despite fluctuations between colder and warmer temperatures vegetation changes at crystal lake are coeval with millennial scale trends in the ngrip ice core record but major shifts in vegetation at crystal lake lag the ngrip record by 300 400 yr this lag may be due to the proximity of the laurentide ice sheet the ice sheet s inherent slowness in response to rapid climate changes and its effect on frontal boundary conditions and lake effect temperatures

proboscidea from the big cypress creek fauna deweyville formation harris county texas abstract in 2008 a rich accumulation of vertebrate bones and teeth was discovered in a small tributary drainage to big cypress creek near the town of hockley in harris county texas the fossils were recovered from sandy sediments of fluvial origin interspersed with contemporaneous spring boil deposits attributed to the deweyville formation and the recovered remains consist entirely of disarticulated and dissociated skeletal elements and teeth distinct stratigraphic horizons are limited in extent in the fossiliferous sections along the drainage and the fossils are generally concentrated in close association with gravel lag deposits two radiocarbon dates on wood suggest that the fauna may have accumulated about 24 000 years ago but presence of spring deposits association with lag deposits and the aerial extent approximately 125 m of exposed section along the length of the tributary could indicate significant time averaging during the rancholabrean bison occurs in the fauna the unique faunal character of the site is emphasized by a single tooth of mixotoxodon a notoungulate mammal that provides the first evidence of this taxon from the united states the fauna is dominantly composed of herbivorous megafauna with two proboscideans mammuthus and cuvieronius mammut americanum has not yet been found in the fauna isotopic analyses of the proboscideans and some of the other megafauna suggest that an open environment with scattered woodland habitat existed in southeastern texas at the end of the last glacial period

evidence for the diet and habitat of two late pleistocene mastodons from the midwest usa we analyzed intestinal contents of two late glacial mastodons preserved in lake sediments in ohio burning tree mastodon and michigan heisler mastodon a multi proxy suite of macrofossils and microfossils provided unique insights into what these individuals had eaten just before they died and added significantly to knowledge of mastodon diets we reconstructed the mastodons habitats with similar multi proxy analyses of the embedding lake sediments non pollen palynomorphs especially spores of coprophilous fungi differentiated intestinal and environmental samples the burning tree mastodon gut sample originates from the small intestine the heisler mastodon sample is part of the large intestine to which humans had added clastic material to anchor parts of the carcass under water to cache the meat both carcasses had been dismembered suggesting that the mastodons had been hunted or scavenged in line with other contemporaneous mastodon finds and the timing of early human incursion into the midwest both mastodons lived in mixed coniferous deciduous late glacial forests they browsed tree leaves and twigs especially picea they also ate sedge swamp plants and drank the lake water our multi proxy estimates for a spring summer season of death contrast with autumn estimates derived from prior tusk analyses we document the recovered fossil remains with photographs

a linear gradient crustal model for south hawaii a new crustal model with linear velocity gradients within layers does as good a job of locating earthquakes on south hawaii as any model yet published incorporating linear gradients means the model can be simpler and free of artificial velocity discontinuities using travel time residuals from local earthquakes and consistency of focal mechanism solutions as tests it is seen that a low velocity zone at the base of the crust is not required

three dimensional structure of the submarine flanks of la reunion inferred from geophysical data 1 la reunion indian ocean constitutes a huge volcanic oceanic system of which most of the volume is submerged we present a study of its submarine part based on the interpretation of magnetic and gravity data compiled from old and recent surveys a model of the submarine internal structure is derived from 3 d and 2 d models using constraints from previous geological and geophysical studies two large scale previously unknown buried volcanic construction zones are discovered in continuation of the island s construction to the east the alizes submarine zone is interpreted as the remnants of les alizes volcano eastward flank whose center is marked by a large hypovolcanic intrusion complex to the southwest the etang sale submarine zone is interpreted as an extension of piton des neiges probably fed by a volcanic rift zone over a large extent they were predominantly built during the matuyama period and thus probably belong to early volcanism a correlation exists between their top and seismic horizons recognized in previous studies and interpreted as the base of the volcanic edifice their morphology suggested a lithospheric bulging beneath la reunion not required to explain our data since the seismic interfaces match the top of our volcanic constructions the coastal shelf coincides with a negative bouguer anomaly belt often associated with magnetic anomalies suggesting a shelf built by hyaloclastites a detailed analysis of the offshore continuation of la montagne massif to the north confirms this hypothesis the gravity analysis confirms that the bathymetric bulges forming the northern eastern southern and western submarine flanks are predominantly built by debris avalanche deposits at the surface

stabilization of volcanic flanks by dike intrusion an example from kilauea dike propagation and dilation increases the compression of adjacent rocks on volcanoes especially oceanic shields dikes are accordingly thought to be structurally destabilizing as compression is incremented volcanic flanks are driven outward or downslope and thus increase their susceptibility to destructive earthquakes and giant landslides we show however that the 2 m thick dike emplaced along the east rift zone of kilauea in 1983 actually stabilized that volcano s flank specifically production of flank earthquakes dropped more than twofold after 1983 as maximum downslope motion slowed to 6 cm year 1 from approximately 40 cm year 1 during 1980 1982 as much as 65 cm of deflationary subsidence above kilauea s summit and upper rift zones accompanied the dike intrusion according to recent estimates this deflation corresponds to a reduction in magma reservoir pressure of approximately 4 mpa probably about as much as the driving pressure of the 1983 dike the volume of the dike approximately 0 10 0 15 km3 is orders of magnitude less than the estimated 200 to 250 km3 volume of kilauea s reservoir of magma and nearby hot mushy rock thus deflation of that reservoir reduces the compressional load on the flank over a much larger area than intrusion of the dike adds to it particularly at the dominant depth of seismicity 8 9 km a coulomb block model for flank motion during intervals between major earthquakes requires the low angle fault beneath kilauea s flank to exhibit slip weakening conducive to earthquake instability accordingly the triggering mechanism of destructive earthquakes several of which have struck hawaii during the past 150 years need not require stresses accumulated by dike intrusions

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

comparative velocity structure of active hawaiian volcanoes from 3 d onshore offshore seismic tomography abstract we present a 3 d p wave velocity model of the combined subaerial and submarine portions of the southeastern part of the island of hawaii based on first arrival seismic tomography of marine airgun shots recorded by the onland seismic network our model shows that high velocity materials 6 5 7 0 km s lie beneath kilauea s summit koae fault zone and the upper southwest rift zone swrz and upper and middle east rift zone erz indicative of magma cumulates within the volcanic edifice a separate high velocity body of 6 5 6 9 km s within kilauea s lower erz and upper puna ridge suggests a distinct body of magma cumulates possibly connected to the summit magma cumulates at depth the two cumulate bodies within kilauea s erz may have undergone separate ductile flow seaward influencing the submarine morphology of kilauea s south flank low velocities 5 0 6 3 km s seaward of kilauea s hilina fault zone and along mauna loa s seaward facing kao iki fault zone are attributed to thick piles of volcaniclastic sediments deposited on the submarine flanks loihi seamount shows high velocity anomalies beneath the summit and along the rift zones similar to the interpreted magma cumulates below mauna loa and kilauea volcanoes and a low velocity anomaly beneath the oceanic crust probably indicative of melt within the upper mantle around kilauea s submarine flank a high velocity anomaly beneath the outer bench suggests the presence of an ancient seamount that may obstruct outward spreading of the flank mauna loa s southeast flank is also marked by a large anomalously high velocity feature 7 0 7 4 km s interpreted to define an inactive buried volcanic rift zone which might provide a new explanation for the westward migration of mauna loa s current swrz and the growth of kilauea s swrz

changing depths of magma fractionation and stagnation during the evolution of an oceanic island volcano la palma canary islands la palma canary islands represents an oceanic island volcano with an active rift zone inferred to have formed during the last 800 ka following southward growth of the former radial symmetrical stratovolcano taburiente we carried out clinopyroxene melt thermobarometry and microthermometry of fluid inclusions to reconstruct the evolution of the magma plumbing systems over time and to understand the genetic relationship between taburiente and the presently active cumbre vieja rift zone clinopyroxene melt equilibria of phenocryst rims and glassy groundmass indicate pressures of 0 60 1 04 gpa 19 34 km depth for taburiente 0 47 1 17 gpa 16 40 km for the former cumbre nueva rift arm of taburiente and 0 50 0 78 gpa 16 26 km for bejenado volcano that formed after collapse of the cumbre nueva rift these pressures are interpreted to reflect depths of magma storage and major crystal fractionation co2 dominated fluid inclusions hosted by clinopyroxenes and olivines indicate pressures of formation or re equilibration within an overall range of 0 25 0 61 gpa 8 19 km depth respective frequency maxima are at 0 41 0 50 gpa for taburiente dunite xenoliths 0 26 0 43 gpa for cumbre nueva ankaramites and 0 26 0 32 gpa for bejenado cumulate xenoliths these pressures are interpreted to reflect levels of temporary magma stagnation during ascent our data show that the magma pathways during all volcanic phases including the presently active cumbre vieja rift klugel a hansteen t h galipp k 2005 magma storage and underplating beneath cumbre vieja volcano la palma canary islands earth and planetary science letters 236 211 226 are characterized by two distinct storage levels a system of prolonged storage within the upper mantle and a system of short term stagnation within the lower crust or near to the moho both the mantle and crustal storage systems show a migration to shallower levels from 1 0 ma to present probably as a result of changing thermomechanical properties of the mantle and crust and possibly stoping our combined barometric data and field observations suggest that the extinct taburiente cumbre nueva and the active cumbre vieja represent two distinct volcanoes with separate magma plumbing systems in this case the present rift configuration does not reflect continuous growth of the taburiente shield volcano during the last 800 ka none of the la palma volcanoes shows any indicators of a long lived shallow magma reservoir where magmas fractionate and from which rift zones emanate which is an important difference to hawaiian shield volcanoes characterized by shallow subcaldera magma chambers

role of olivine cumulates in destabilizing the flanks of hawaiian volcanoes the south flank of kilauea volcano is unstable and has the structure of a huge landslide it is one of at least 17 enormous catastrophic landslides shed from the hawaiian islands mechanisms previously proposed for movement of the south flank invoke slip of the volcanic pile over seafloor sediments slip on a low friction decollement alone cannot explain why the thickest and widest sector of the flank moves more rapidly than the rest or why this section contains a 300 km3 aseismic volume above the seismically defined decollement it is proposed that this aseismic volume adjacent to the caldera in the direction of flank slip consists of olivine cumulates that creep outward pushing the south flank seawards average primary kilauea tholeiitic magma contains about 16 5 wt mgo compared with an average 10 wt mgo for erupted subaerial and submarine basalts this difference requires fractionation of 17 wt 14 vol olivine phenocrysts that accumulate near the base of the magma reservoir where they form cumulates submarine erupted kilauea lavas contain abundant deformed olivine xenocrysts derived from these cumulates deformed dunite formed during the tholeiitic shield stage is also erupted as xenoliths in subsequent alkalic lavas the deformation structures in olivine xenocrysts suggest that the cumulus olivine was densely packed probably with as little as 5 10 vol intercumulus liquid before entrainment of the xenocrysts the olivine cumulates were at magmatic temperatures 1100 c when the xenocrysts were entrained olivine at 1100 c has a rheology similar to ice and the olivine cumulates should flow down and away from the summit of the volcano flow of the olivine cumulates places constant pressure on the unbuttressed seaward flank leading to an extensional region that localizes deep intrusions behind the flank these intrusions add to the seaward push this mechanism ties the source of gravitational instability to the caldera complex and deep rift systems and therefore limits catastrophic sector failure of hawaiian volcanoes to their active growth phase when the core of olivine cumulates is still hot enough to flow

expanded response surfaces a new method to reconstruct paleoclimates from fossil pollen assemblages that lack modern analogues pollen based paleoclimatic interpretations of late glacial to early holocene climates 17 9 ka in midwestern north america are hampered by samples that lack modern analogues unresolved questions include the magnitude and direction of temperature seasonality i e were these climates more or less seasonal than present and the temporal changes in precipitation central to the no analogue problem is the truncation of modern pollen climate relationships for abundant late glacial taxa such as fraxinus here we present a new method called the expanded response surface ers method developed to reconstruct climates from no analogue pollen assemblages and applied to a high resolution late glacial pollen record from crystal lake illinois to test hypotheses about late glacial climates the key assumptions central to the ers method are 1 plant species and pollen abundances follow symmetrical unimodal distributions along climatic gradients 2 taxa with truncated distributions in modern climate space occupy a subset of their fundamental niche and 3 expansion of truncated distributions by mirroring around the distributional mode recovers the portion of the fundamental niche not realized in the modern climate space with the ers method we expanded modern pollen climate relationships by mirroring pollen abundances for each taxon around a mode defined with respect to four climate axes mean winter temperature mean summer temperature mean winter precipitation and mean summer precipitation the ers method reconstructed past temperatures and precipitation during the height of no analogue conditions 14 160 12 370 cal yr bp for 37 of the crystal lake samples where techniques that employed only modern observational data found matches for only 13 of the fossil samples the total climate space of the expanded taxa set allowed analogue matches under more seasonal than present climates with higher than present precipitation the ers climate reconstructions for the height of no analogue conditions indicated cooler than present summer and winter temperatures similar to present seasonal range in temperatures higher than present winter precipitation and similar to present summer precipitation these results thus suggest that high moisture availability helped drive the formation of the midwestern no analogue communities with high fraxinus nigra abundances but do not show higher than present temperature seasonality notwithstanding the higher than present insolation seasonality at this time during the no analogue late glacial interval picea mariana f nigra and larix stands probably grew on low lying poorly drained soils in the crystal lake region whereas abies picea glauca quercus and ostrya carpinus grew on upland positions with better soil drainage

the isotopic ecology of late pleistocene mammals in north america part 1 florida abstract mammoths and mastodons are common in pleistocene deposits yet these proboscideans and many other animals disappeared suddenly 10 000 years ago in this study we reconstruct the diets of proboscideans and associated mammals through isotopic analysis of carbonate in tooth enamel apatite in order to test nutritional hypotheses for late pleistocene extinction we analyzed specimens from six sites in florida ranging from full glacial 21 000 bp to late glacial 14 750 to 10 000 bp age the oxygen isotope composition of mammalian apatite covaries with meteoric water composition which in turn varies with climate consequently oxygen isotope analysis can be used to assess the potential for time averaging or mixing of specimens from different geographic regions within fossil assemblages the carbon isotope composition of an herbivore is controlled by the isotopic composition of the plants that it ingests carbon isotope analysis reveals that mastodons ate chiefly c3 plants presumably trees shrubs and herbs whereas mammoths consumed chiefly c4 grass several nutritional hypotheses for late pleistocene extinction entail the assumption that extinct taxa had specialized diets the resource partitioning and focused feeding preferences of florida s proboscideans corroborate this assumption but they do not in themselves prove that nutritional stress was the cause of the late pleistocene extinction

rapid deformation of the south flank of kilauea volcano hawaii the south flank of kilauea volcano has experienced two large magnitude m 7 2 and m 6 1 earthquakes in the past two decades global positioning system measurements conducted between 1990 and 1993 reveal seaward displacements of kilauea9s central south flank at rates of up to about 10 centimeters per year in contrast the northern side of the volcano and the distal ends of the south flank did not displace significantly the observations can be explained by slip on a low angle fault beneath the south flank combined with dilation deep within kilauea9s rift system both at rates of at least 15 centimeters per year

rapid deformation of kilauea volcano global positioning system measurements between 1990 and 1996 campaign global positioning system gps measurements from 1990 to 1996 are used to calculate surface displacement rates on kilauea volcano hawaii the gps data show that the south flank of the volcano which has generated several large earthquakes in the past 3 decades is displacing at up to 8 cm yr to the south southeast the summit and rift zones are subsiding with maximum subsidence rates of 8 cm yr observed a few kilometers south of the summit caldera elastic dislocation modeling of the gps data suggests that the active sources of deformation include deep rift opening along the upper east and east rift zone fault slip along a subhorizontal fault near the base of the volcano and deflation near the summit caldera a nonlinear optimization algorithm was used to explore the parameter space and to find the best fitting source geometry there is a broad range of model geometries that fit the data reasonably well however certain models can be ruled out including those that have shallow rift opening or shallow fault slip some offshore aseismic slip on a fault plane that dips between 258 north northwest and 88 south southeast is required best fitting slip and rift opening rates are 23 28 cm yr although rates as low as 10 cm yr are permitted by the data

a morphometric analysis of the submarine volcanic ridge south east of pico island azores a region of crustal extension the azores plateau contains excellent examples of submarine volcanic edifices constructed over a wide range of ocean depths along the pico ridge using bathymetric data and towed ocean bottom instrument tobi side scan sonar imagery we measured the dimensions diameter height slopes shape and texture of these volcanic edifices to further understanding of the geometric development of a submarine ridge our analysis and interpretation of the measurement and texture data suggest the following 1 the various edifice types do not correlate with depth ranges suggesting that ambient water pressure is not a controlling factor in configuration of the edifice formed 2 the cones have a mean diameter of 948 m height of 152 m and slope of 15 6 and are peaked rather than displaying flat topped summits and 3 while hummocky textured cones also occur smooth textured cones predominate the cones seem to develop preferentially outwards then upwards with only a weak correlation between diameter and height suggesting that the cone population does not evolve self similarly although smooth and hummocky cone populations are not statistically different in mean slope angle and eruption depth the hummocky cones have a significantly greater mean diameter than the smooth cones we suggest that hummocky textured cones probably involving eruption of pillow lavas are formed after voluminous smooth textured flows nearest neighbour analysis suggests that submarine cones are distributed randomly whereas subaerial cones are not we interpret this finding to suggest subaerial cones being masked by over covering flows which tend to flow further than submarine lava flows furthermore the spatial distribution of cones away from the ridge centre is not easily explained by a magma supply fed via lava tubes from central eruptions because of a lack of consistent pathway down gradient fissure vents seem to be important in determining construction of the ridge and result in linear arrangements of edifices and cone elongation consistent with the regional tectonic trend of this part of the azores plateau cones form as each feeding dyke intrusion cools and the eruption becomes localized along point source vents along the fissure the ridge seems to be predominantly formed from fissure eruptions along the ridge axis with subordinate transport of lava down its flanks

mapping eastern north american vegetation change of the past 18 ka no analogs and the future the method of modern analogs and an extensive data base of modern and fossil pollen data were used to generate a new series of paleovegetation maps for eastern north america spanning the past 18 ka the maps illustrate the continuous nature of climate induced vegetation change and the development after about 10 ka of modern regional vegetation patterns before the holocene vegetation biomes without modern analogs were widespread in response to climate conditions without modern analogs and to a lesser extent to the rapidity of climate change over the last glacial interglacial transition this geological perspective suggests that possible future climate changes could force similarly complex changes in natural vegetation including the development of biomes without modern analogs

seismic detection of a low velocity layer beneath the southeast flank of mauna loa hawaii the authors have identified seismic phases reflected off the top and bottom of a low velocity layer lvl by analysis of seismograms from six small earthquakes in hawaii these events occurred almost directly beneath station ain of the hawaiian volcano observatory hvo seismic network located within the kaoiki seismic zone on the southeast flank of mauna loa the polarity reversals of the first reflected phases provide clear evidence for the existence of a lvl beneath this station the lvl is estimated to be at a depth of about 11 5 km with a thickness of about 800 m the estimated depth to the top of the lvl is consistent with the depth distribution of low angle thrust faulting events from the aftershock sequence of the 1983 kaoiki earthquake presumably this zone is the marine sediment layer buried beneath the volcanic pile along which the volcanic edifice may slip easily to cause large earthquakes mapping the interface between the volcanic pile and oceanic crust and thus determining the depth and thickness of the buried sediment layer is essential for understanding the tectonics of large earthquakes in hawaii

seismic stratigraphy of the frontal hawaiian moat implications for sedimentary processes at the leading edge of an oceanic hotspot trace multi channel seismic imaging reveals the seismic stratigraphy and associated sedimentary processes of the frontal hawaiian moat fhm to the southeast of the island of hawaii two sedimentary units are defined 1 a basal layer of pelagic sediment draping the oceanic basement and 2 a wedge of volcaniclastic material infilling the fhm and onlapping the frontal hawaiian arch three distinct seismic facies within the volcaniclastic unit are recognized a areas of chaotic or incoherent reflections interpreted as proximal debris avalanche or slump deposits b groups of hummocky and distorted reflections interpreted as distal debris avalanche or debris flow deposits and c regions of parallel and laterally continuous reflections interpreted as turbidite deposits the distribution of these facies delineates slope apron proximal basin and distal basin depositional environments respectively within the fhm the northwest drift of the pacific plate over the hawaiian hot spot results in the apparent southeasterly migration of the hawaiian chain advancement of the depositional environments within the fhm occurs as individual volcanoes evolve erode and are superseded by new volcanic centers the interplay between depositional processes and tectonic forces plate motion and lithospheric flexure predicts a coarsening upward stratigraphy within the fhm the combined accumulation of pelagic and volcaniclastic sediment defines a heterogeneous and potentially unstable layer of low strength material beneath the volcanic edifice that may influence the mobility of the island flanks

growth history of kilauea inferred from volatile concentrations in submarine collected basalts abstract major element and volatile h2o co2 s compositions of glasses from the submarine flanks of kilauea volcano record its growth from pre shield into tholeiite shield stage pillow lavas of mildly alkalic basalt at 2600 1900 mbsl on the upper slope of the south flank are an intermediate link between deeper alkalic volcaniclastics and the modern tholeiite shield lava clast glasses from the west flank of papau seamount are subaerial mauna loa like tholeiite and mark the contact between the two volcanoes h2o and co2 in sandstone and breccia glasses from the hilina bench and in alkalic to tholeiitic pillow glasses above and to the east were measured by ftir volatile saturation pressures equal sampling depths 10 mpa 1000 m water for south flank and puna ridge pillow lavas suggesting recovery near eruption depths and or vapor re equilibration during down slope flow south flank glasses are divisible into low pressure co2 0 5 wt s 1000 1700 ppm and high pressure groups co2 40 ppm s 1000 ppm corresponding to eruption sea level at moderate water depths 300 1000 m or shallower but in disequilibrium and in deep water 1000 m saturation pressures range widely in early alkalic to strongly alkalic breccia clast and sandstone glasses establishing that early k lauea s vents spanned much of mauna loa s submarine flank with some vents exceeding sea level later south flank alkalic pillow lavas expose a sizeable submarine edifice that grew concurrent with nearby subaerial alkalic eruptions the onset of the tholeiitic shield stage is marked by extension of eruptions eastward and into deeper water to 5500 m during growth of the puna ridge subaerial and shallow water eruptions from earliest kilauea show that it is underlain shallowly by mauna loa implying that mauna loa is larger and kilauea smaller than previously recognized

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

crustal structure flexure and subsidence history of the hawaiian islands seismic reflection profile data have been used to estimate the long term 106 years mechanical properties of the oceanic lithosphere underlying the hawaiian islands the data show prominent reflectors associated with the top of the oceanic crust reflector 2 the m discontinuity and the base of the crust reflector 3 the two way travel time to the reflectors has been depth converted using velocity depth functions derived from seismic refraction expanding spread profile data and compared to calculated depths based on simple three dimensional elastic plate models a good fit to the reflector depths was obtained for a model with an effective elastic thickness of the lithosphere te of 40 km the main discrepancies with the refraction data occur beneath oahu and molokai where the predicted depth of the base of the flexed crust is too shallow and beneath the southeast flank of hawaii where it is too deep we attribute the thickened crust beneath oahu to ponding of magma at the base of the crust following the last phases of tholeiitic shield building and the thinned crust beneath the flanks of hawaii to crustal melting beneath the youngest part of the chain the effective te of 40 km is higher than expected for 80 m y oceanic lithosphere possibly due to the effects of subsurface loads that act at or near the base of the flexed crust according to free air gravity anomaly and bathymetry data te does not change significantly along the island chain retaining a similar value for hawaii as it does for oahu we have used this result to estimate the pattern of subsidence and uplift that would be expected along the hawaiian islands because of flexural loading of hawaii the observed depth of the haleakala wave cut terrace northeast of maui can be generally explained by the flexure model the main discrepancies between observed and the predicted depths occur northwest of hawaii where they suggest a somewhat higher value of te possibly due to incomplete adjustment of the lithosphere we suggest that the addition of loads to the end of a volcanic chain generated as a plate moves over a mantle hotspot is accommodated by progressive flexing downstream causing subsidence of preexisting volcanos that lie in the flexural moat and uplift of islands on the flanking bulge the progressive flexure model predicts a characteristic pattern of offlap and onlap in the regions flanking the hawaiian islands that is generally similar to stratigraphic relationships observed along previously published seismic profiles of the moat a progressive flexure model may also apply to the case of a continental plate moving over a mantle hotspot and could explain the observations of 1 a clinoform pattern of stratigraphy in some flood basalt provinces and 2 a seaward dipping reflector sequence at some passive continental margins

oxygen isotope variation in the tusks of extinct proboscideans a measure of season of death and seasonality centimetre scale laminae in tusk and molar dentine of late pleistocene mastodonts and mammoths have been interpreted as annual growth bands produced in part by seasonal variation in growth rate to test this interpretation we measured the oxygen isotope composition 18 o of the co 3 fraction of dentinal hydroxyapatite from samples covering consecutive inferred years of growth in tusks in mammals changes in the 18 o value of dental tissues within individuals predominantly reflect variation in the 18 o value of body fluids which is controlled mainly by the isotopic composition of ingested water in northern hemisphere continental regions winter precipitation has substantially lower 18 o values than does precipitation in other seasons if ingested water tracks focal precipitation then seasonal variations in dentinal isotope composition should result the lowest 18 o values representing winter growth we demonstrate that there are substantial variations in the oxygen isotope composition of proboscidean dentinal apatite and that isotopic identifications of winter i e low 18 o values coincide with those based on growth rate i e slow growth zones finally the potential of oxygen isotope analyses of terrestrial mammals for assessing the seasonality of paleoclimates is considered

focal mechanisms and locations of earthquakes in the vicinity of the 1975 kalapana earthquake aftershock zone 1970 1979 implications for tectonics of the south flank of kilauea volcano island of hawaii the november 29 1975 kalapana earthquake of magnitude 7 1 on the south flank of kilauea volcano hawaii represents a major rift tectonic event it is generally understood that the earthquake resulted from movement on a nearly horizontal fault plane with the crustal block south of kilauea s east rift zone moving south southeastward up to several meters well recorded earthquakes on the south flank of kilauea from 1970 to 1979 were analyzed and focal mechanisms determined to obtain a better understanding of the details of south flank tectonics included are a large number of earthquakes from the aftershock sequence of the 1975 earthquake hypocenters are distributed in a subplanar zone that dips 2 to 3 to the west at a depth of about 8 9 km depth we interpret this pattern to coincide with a portion of the slip plane of the kalapana earthquake and to be consistent with the notion of the slip plane occurring in a weak layer at the top of the old oceanic crust focal mechanisms are remarkably constant throughout this time period both before and after the 1975 event and closely agree with the mainshock mechanism p axis azimuths and slip vectors for the low angle fault planes are normal to the middle and lower east rift zones of kilauea there is suggestion of a change in the orientation of p axes from shallower to steeper plunge at the time of the kalapana earthquake such a change is consistent with a general reduction in the horizontal compressional stress normal to the rift zone at the time of the large earthquake no other evidence of precursory reorientation of the stress field was found and the precise predictability of this event remains in doubt however a general model of the tectonics of the volcanic rift system is now available that satisfies a number of geological and geophysical observations

overlapping volcanoes the origin of hilo ridge hawaii the submarine hilo ridge has been interpreted as a part of mauna kea volcano but is crossed at 1100 m depth by a submerged shoreline terrace composed of basalts that are isotopically distinct from those of mauna kea and similar to those of kohala volcano this terrace evidently is a product of kohala instead of mauna kea almost all of hilo ridge below the terrace therefore must predate the principal growth of mauna kea which has superficially isolated the ridge from its kohala source by overlapping its proximal segment the mauna kea section penetrated by the hawaii scientific drilling project is predicted to be thinner than expected previously owing to the overlap similar overlaps are suspected among other volcanoes and may cause significant changes in the understanding of hawaiian volcanism

internal structure of puna ridge evolution of the submarine east rift zone of kilauea volcano hawai i abstract multichannel seismic reflection sonobuoy gravity and magnetics data collected over the submarine length of the 75 km long puna ridge hawai i resolve the internal structure of the active rift zone laterally continuous reflections are imaged deep beneath the axis of the east rift zone erz of kilauea volcano we interpret these reflections as a layer of abyssal sediments lying beneath the volcanic edifice of kilauea early arrival times or pull up of sediment reflections on time sections imply a region of high p wave velocity vp along the submarine erz refraction measurements along the axis of the ridge yield vp values of 2 7 4 85 km s within the upper 1 km of the volcanic pile and 6 5 7 km s deeper within the edifice few coherent reflections are observed on seismic reflection sections within the high velocity area suggesting steeply dipping dikes and or chaotic and fractured volcanic materials southeastward dipping reflections beneath the nw flank of puna ridge are interpreted as the buried flank of the older hilo ridge indicating that these two ridges overlap at depth gravity measurements define a high density anomaly coincident with the high velocity region and support the existence of a complex of intrusive dikes associated with the erz gravity modeling shows that the intrusive core of the erz is offset to the southeast of the topographic axis of the rift zone and that the surface of the core dips more steeply to the northwest than to the southeast suggesting that the dike complex has been progressively displaced to the southeast by subsequent intrusions the gravity signature of the dike complex decreases in width down rift and is absent in the distal portion of the rift zone based on these observations and analysis of puna ridge bathymetry we define three morphological and structural regimes of the submarine erz that correlate to down rift changes in rift zone dynamics and partitioning of intrusive materials we propose that these correspond to evolutionary stages of developing rift zones which may partially control volcano growth mobility and stability and may be observable at many other oceanic volcanoes

north kona slump submarine flank failure during the early tholeiitic shield stage of hualalai volcano abstract the north kona slump is an elliptical region about 20 by 60 km 1000 km 2 area of multiple geometrically intricate benches and scarps mostly at water depths of 2000 4500 m on the west flank of hualalai volcano two dives up steep scarps in the slump area were made in september 2001 using the rov kaiko of the japan marine science and technology center jamstec as part of a collaborative japan usa project to improve understanding of the submarine flanks of hawaiian volcanoes both dives at water depths of 2700 4000 m encountered pillow lavas draping the scarp and bench slopes intact to only slightly broken pillow lobes and cylinders that are downward elongate dominate on the steepest mid sections of scarps while more equant and spherical pillow shapes are common near the tops and bases of scarps and locally protrude through cover of muddy sediment on bench flats notably absent are subaerially erupted hualalai lava flows interbedded hyaloclastite pillow breccia and or coastal sandy sediment that might have accumulated downslope from an active coastline the general structure of the north kona flank is interpreted as an intricate assemblage of downdropped lenticular blocks bounded by steeply dipping normal faults the undisturbed pillow lava drape indicates that slumping occurred during shield stage tholeiitic volcanism all analyzed samples of the pillow lava drape are tholeiite similar to published analyses from the submarine northwest rift zone of hual lai relatively low sulfur 330 600 ppm and water 0 18 0 47 wt contents of glass rinds suggest that the eruptive sources were in shallow water perhaps 500 1000 m depth in contrast saturation pressures calculated from carbon dioxide concentrations 100 190 ppm indicate deeper equilibration at or near sample sites at water depths of 3900 to 2800 m either vents close to the sample sites erupted mixtures of undegassed and degassed magmas or volatiles were resorbed from vesicles during flowage downslope after eruption in shallow water the glass volatile compositions suggest that the tholeiitic lavas that drape the slump blocks were erupted either 1 early during shield stage tholeiitic volcanism prior to emergence of a large subaerial edifice or alternatively 2 from submarine radial vents during subaerial shield building because no radial vents have been documented on land or underwater for the unbuttressed flanks of any hawaii volcano alternative 1 is favored in comparison to other well documented hawaiian slumps and landslides north kona structures suggest a more incipient slump event with smaller down slope motions and lateral displacements

spores of coprophilous fungi from under the dawson tephra 25 300 14c years bp yukon territory northwestern canada based on the analysis of pollen and macrofossils zazula et al zazula g d froesne d g elias s a kuzmina s la farge c reyes a v sanborn p t schweger c e smith c a s mathewes r w 2006 vegetation buried under dawson tephra 25 300 14c yr bp and locally diverse late pleistocene paleoenvironments of goldbottom creek yukon canada palaeogeography palaeoclimatology palaeoecology 242 253 286 reported an in situ riparian grassy meadow ecosystem and regional well drained steppe tundra buried by dawson tephra ca 25 300 bp at goldbottom creek in the canadian yukon territory an additional study of fungal spores in pollen slides from that site was completed ascospores of the coprophilous sordaria type sporormiella type and podospora type appeared to be of common occurrence pointing to the former presence of herbivores the analysis of the various spore types of coprophilous fungi in pollen slides is useful and may lead to further knowledge of the role of different herbivore taxa in past ecosystems 2007 elsevier b v all rights reserved

flexure and seismicity beneath the south flank of kilauea volcano and tectonic implications we present a refined model for the tectonic behavior of kilauea volcano s south flank including flexure calculations and microearthquake data supportive of the model in our model the south flank moves seaward over the downwardly flexed ocean crust in a manner analogous to an accretionary prism in a subduction zone the flank is driven seaward by the gravitational stresses inherent in its shape this driving force is augmented by high density material in kilauea s rift zones elastic flexure calculations predict a configuration for the downwardly flexed crust which agrees with previous seismic refraction and gravity modeling this configuration in turn is consistent with the hypothesis that many earthquakes occur along the volcanic pile ocean crust interface focal mechanisms for these events predominantly indicate southeastward directed overthrusting we also propose a relationship between rift zone intrusion and south flank displacement including a suggestion that the decollement configuration controls the relative activity of kilauea s east and southwest rift zones

overthrusting and sediment accretion along kilauea s mobile south flank hawaii evidence for volcanic spreading from marine seismic reflection data a large intermittently active submarine landslide known as the hilina slump has been interpreted along the south flank of kilauea volcano seaward dipping faults on land mark its headwall and an offshore bench may define its uplifted toe geodetic data show that the entire south flank is also moving seaward by a process referred to as volcanic spreading this provides an alternative explanation for the bench i e overthrusting along the edge of the sliding flank the latter interpretation is consistent with new seismic reflection data across the submarine flank a prominent reflection near the top of the oceanic plate suggests the decollement upon which the mobile flank slides landward dipping reflections rise from this horizon and bound packages of bedded strata faulted and imbricated within the bench the absence of correlative seaward dipping faults and rotated strata on the upper flank suggests that the bench is not coupled to a slump moreover kinematic reconstructions of the bench indicate that it has accommodated 15 24 km of displacement this value is consistent with estimates for rift zone extension but too high for shortening at the toe of a slump we interpret the bench to result from overthrusting and accretion of volcaniclastic sediments to the edge of the mobile flank and suggest that morphologic benches develop preferentially where landslide debris has accumulated near the base of the volcano and can be accreted to its sliding edifice

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

taxonomic overview and tusk growth analyses of ziegler reservoir proboscideans abstract at an altitude of 2705 m in the colorado rockies usa the ziegler reservoir fossil site gives a rare look at a high elevation ecosystem from the late pleistocene especially mis 5 of north america remains of more than four mammoths and about 35 mastodons dominate the macrofossil assemblage mammoth remains are attributed to mammuthus columbi and mastodon remains are referred to the well known continent wide mammut americanum mastodon remains occur within and between several lake margin slump deposits their deposition must therefore have occurred as events that were to some degree separate in time we treat the mastodon assemblage in each stratigraphic unit as a source of information on environmental conditions during the lives of these individuals mastodon mandibular tusks are abundant at the site and represent both males and females from calves to full grown adults this study presents the first attempt to use microct thin section and isotope records from mandibular tusks to reconstruct features of life history we recognize an up section trend in 18o profiles toward higher values suggestive of warmer temperatures throughout this sequence mastodon growth histories show low mean sensitivities suggestive of low levels of environmental stress this work helps frame expectations for assessing environmental pressures on terminal pleistocene populations

what controls the along strike slopes of volcanic rift zones we investigate the dynamics of viscous pressure losses associated with lateral magma transport in volcanic rift zones by performing 1 coupled elastic hydrodynamic simulations of downrift magma flow in dikes and 2 analog experiments mimicking lateral dike propagation in the presence of an along rift topographic slope it is found that near source eruptions are likely to be favored by shallow slopes while distant downrift eruptions may be encouraged by steeper slopes provided that along rift variations in the tectonic stress are negligible or uncorrelated on the timescale of multiple dike intrusions this implies the existence of a critical slope to which a volcanic rift zone would naturally evolve such behavior is produced by three dimensional 3 d elastic effects and is controlled by the ratio of the driving pressure gradient due to the along strike topographic slope to the vertical gradient in the excess magma pressure in the dike this model may be viewed as complementary to commonly cited mechanisms that appeal to magma viscosity and the dynamics of freezing of lava flows at the surface to explain the low profiles of basaltic shield volcanoes our estimated values of the critical slopes are in general agreement with observations in hawaiian rift zones but further development of fully 3 d models is required for more accurate predictions

mastodon herbivory in mid latitude late pleistocene boreal forests of eastern north america skeletal remains of the extinct american mastodon have often been found with deposits of short decorticated twigs intermixed with plant fragments presumed to be gastrointestinal or fecal material if such deposits are digesta paleobotanical evidence may be used to analyze mastodon foraging strategy with implications for assessing habitat selection ecological roles and response to environmental change to identify components of mastodon diet in mid latitude late pleistocene boreall forests of eastern north america plant macrofossils and pollen from a molar socket hyde park site new york were compared with dispersed deposits associated with skeletal remains hiscock and chemung sites new york similar macrofossil condition and twig morphology among samples but difference from a modern boreal fen analog confirmed the deposits were digesta comparison of twigs with material from other paleontological sites and modern elephants suggested dimensions generally indicative of digesta picea formed the bulk of each sample but pinus may have been locally important wintertime browsing of salix and populus and springtime consumption of alnus were indicated evidence for cyperaceae gramineae and compositae was ambiguous if conifers broadleaf trees shrubs and herbs were necessary to fulfill dietary requirements mastodons would have been nutritionally stressed by rapid late pleistocene decrease in vegetational diversity

offshore continuation of volcanic rift zones el hierro canary islands el hierro is the youngest and most southwesterly of the seven canary islands the established view based on subaerial geology is that el hierro is a classic example of an oceanic island with 120 spaced volcanic rift arms vrzs forming a mercedes star however new offshore data do not support this simple interpretation instead of the discrete ridges of vrzs we observe to the nw and ne broad areas of irregular morphology which suggest that rifting activity might not be confined to narrow zones furthermore our data suggest that the anomalously long and steep flanked southern ridge could be part of an older eroded volcanic edifice that predates much of the other submarine flanks of el hierro the southern ridge has a distinctive gullied morphology which strongly contrasts with adjacent flanks there is also a 400 m deep saddle in its longitudinal profile 15 km from the coastline which we interpret as evidence that the southern ridge did not form by continuous dyke intrusion from the el hierro volcanic centre south of the saddle mean flank slopes are 10 steeper 30 with a sharp slope break at 3700 m between the ridge and smoothly sedimented seafloor these steeper slopes and lack of landslide scars to the south of the saddle indicate that the southern ridge is a stable edifice relative to the rest of el hierro surrounding sediments to the southeast appear to onlap the southern ridge a large landslide deposit el julan estimated age 200 ka occurs to the west of the ridge this landslide appears to have been constrained from spreading southeastwards by the southern ridge resulting in an elevation difference of 300 m for the seafloor on either side of the ridge

a comparison between subaerial and submarine eruptions at kilauea volcano hawaii implications for the thermal viability of lateral feeder dikes eruption styles on the subaerial east rift zone erz of kilauea volcano are reviewed and a classification scheme for the different types of eruption is proposed the various eruption types are produced by differing thermal and driving pressure behaviour in the feeder dikes existing evidence is reviewed and new evidence presented of the types and volumes of eruptions on the puna ridge which is the submarine extension of the erz eruptions on the puna ridge fall into the same five classes as and are of comparable volume to those on the subaerial erz evidence is presented which suggests that feeder dikes for puna ridge eruptions are more thermally viable than those feeding subaerial eruptions and this difference causes long lived large volume eruptions to be more common on the puna ridge than on the subaerial erz this systematic variation in thermal viability may be due to increased dike width for puna ridge dikes or increased pressure gradients driving magma flow lateral dike emplacement is common to many basaltic systems including on other hawaiian volcanoes in iceland and at mid ocean ridges the systematic trend inferred for the erz of kilauea implies that in the other systems large volume eruptions may also be more common at great distances than they are close to the magma centre

formation of submarine flat topped volcanic cones in hawai i high resolution bathymetric mapping has shown that submarine flat topped volcanic cones morphologically similar to ones on the deep sea floor and near mid ocean ridges are common on or near submarine rift zones of kilauea kohala or mauna kea mahukona and haleakala volcanoes four flat topped cones on kohala were explored and sampled with the pisces v submersible in october 1998 samples show that flat topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage similarly shaped flat topped cones on the northwest submarine flank of ni ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage submarine postshield stage eruptions on hilo ridge mahukona hana ridge and offshore ni ihau form pointed cones of alkalic basalt and hawaiite the shield stage flat topped cones have steep 25 sides remarkably flat horizontal tops basal diameters of 1 3 km and heights 300 m the flat tops commonly have either a low mound or a deep crater in the center the rejuvenated stage flat topped cones have the same shape with steep sides and flat horizontal tops but are much larger with basal diameters up to 5 5 km and heights commonly greater than 200 m the flat tops have a central low mound shallow crater or levees that surrounded lava ponds as large as 1 km across most of the rejuvenated stage flat topped cones formed on slopes 10 and formed adjacent semicircular steps down the flank of ni ihau rather than circular structures all the flat topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades these and other submarine volcanic cones of similar size and shape apparently form as continuously overflowing submarine lava ponds a lava pond surrounded by a levee forms above a sea floor vent as lava continues to flow into the pond the lava flow surface rises and overflows the lowest point on the levee forming elongate pillow lava flows that simultaneously build the rim outward and upward but also dam and fill in the low point on the rim the process repeats at the new lowest point forming a circular structure with a flat horizontal top and steep pillowed margins there is a delicate balance between lava heat supply to the pond and cooling and thickening of the floating crust factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents moderate to high confining pressure at moderate to great ocean depth long lived steady eruption years to decades moderate effusion rates probably ca 0 1 km3 year and low but not necessarily flat slopes with higher effusion rates sheet flows flood the slope with lower effusion rates pillow mounds form hawaiian shield stage eruptions begin as fissure eruptions if the eruption is too brief it will not consolidate activity at a point and fissure fed flows will form a pond with irregular levees the pond will solidify between eruptive pulses if the eruption is not steady lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones as occurs during the post shield stage the steady effusion of lava on land constructs lava shields which are probably the subaerial analogs to submarine flat topped cones but formed under different cooling conditions

submarine volcanic morphology of the western galapagos based on em300 bathymetry and mr1 side scan sonar 1 a compilation of high resolution em300 multibeam bathymetric and existing mr1 side scan sonar data was used to investigate the volcanic morphology of the flanks of the western galapagos islands the data portray an assortment of constructional volcanic features on the shallow to deep submarine flanks of fernandina isabela and santiago islands including rift zones and groups of cones that are considered to be the primary elements in constructing the archipelagic apron ten submarine rift zones were mapped ranging in length from 5 to 20 km comparable in length to western canary island rift zones but significantly shorter than hawaiian submarine rift zones a detailed analysis of the northwestern fernandina submarine rift including calculated magnetization from a surface towed magnetic study suggests that the most recent volcanism has focused at the shallow end of the rift small submarine volcanic cones with various morphologies e g pointed cratered and occasionally breached are common in the submarine western galapagos both on rift zones and on the island flanks where no rifts are present at depths greater than 3000 m large lava flow fields in regions of low bathymetric relief have been previously identified as a common seafloor feature in the western galapagos by geist et al 2006 however their source s remained enigmatic the new em300 data show that a number of the deep lava flows originate from small cones along the mid lower portion of the nw submarine rift of fernandina suggesting that the deep flows owe their origin at least in part to submarine rift zone volcanism

structure of the mobile south flank of kilauea volcano hawaii how do huge landslides occur in hawaii we can begin to address this question by examining an incipient landslide structure on the mobile south flank of kilauea volcano between 1970 and 1989 this part of the south flank moved in a southeast direction seaward by 4 m on its eastern end and by 10 m on its western end parallel to the western boundary of a large oifshore topographic bench we show that abrupt decreases in cumulative flank movement correspond to abrupt decreases in hypocenter concentration most of the earthquakes occur in a 7 to 10 km deep band beneath the south flank and relative relocation of a subset of these events shows that they are derived from a single horizontal plane which appears to be a decollement focal mechanisms for this deep seismicity are dominated by thrust fault mechanisms with the overlying block moving seaward a comparison of south flank bathymetry with decollement structures on other volcanoes suggests that the distal end of this decollement coincides with the distal end of the offshore topographic bench 30 50 km from shore and 5 km below sea level the fault system forming the hilina pali is connected with this decollement so that slip on the hilina pali s normal faults coincides with slip of the decollement and with reverse faulting of the distal end of the bench this interpretation is supported by studies of the events associated with the m7 2 kalapana earthquake in 1975 when the hilina pali is connected to the outer bench with a decollement inferred from seismicity a wedge 8 km thick adjacent to kilauea s magma system and 1 2 km thick along the edge of the outer bench an area over 3000 km2 is defined the thickness adjacent to the magma system decreases eastward along kilauea s east rift zone and southwestward from kilauea caldera whereas the thickness of the lip of the outer bench decreases only eastward geologic observations and geophysical studies of the subaerial flank reveal an extensive magma system beneath the koae fault system as well as beneath kilauea caldera and its east rift zone we infer that the boundary of the proximal end of the mobile flank is the southern boundary of this magma system and that this boundary coincides with the southern boundaries of both the koae fault system and kilauea s east rift zone

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

removal of overburden velocity anomaly effects for depth conversion a method of compensating for the presence of discrete overburden velocity anomalies during depth conversion of time horizons interpreted on conventional post stack time migrated seismic data is presented positive and negative time delays are estimated either from the push down or pull up of reflectors directly beneath the anomalies or from interpreted time thickness of the anomalous body and interval velocities estimated from well data the critical steps are pre stack simulation of seismic acquisition across the velocity anomalies incorporating the effects of a fresnel volume which changes its width as a function of depth and simulation of commonmidpoint cmp stacking using a linear regression of time delay at versus offset squared x 2 the time correction method predicts the time distortion for any target horizon and the distortion is removed as a correction in time depth conversion is then performed using a background velocity function the final average velocity map is calculated from the resulting depth structure and the raw times at the target horizon the method is implemented by manipulating time grids within an industry standard mapping package the final average velocity map shows steep lateral velocity gradients which are constrained by the interpreted boundaries of the velocity anomalies

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

constructing the upper crust of the mid atlantic ridge a reinterpretation based on the puna ridge kilauea volcano the volcanic morphology of a number of segments of the slow spreading mid atlantic ridge mar have been reinterpreted based on our understanding of dike emplacement dike propagation and eruption at the east rift zone of kilauea volcano hawaii and its submarine extension the puna ridge the styles of volcanic eruption at the submarine puna ridge are remarkably similar to those of the axial volcanic ridges avrs constructed on the median valley floor of the mar we use this observation to relate volcanic processes occurring at kilauea volcano to the mar we now consider that volcanic features e g seamounts and lava terraces built on the flanks of the avrs are secondary features that are fed from lava tubes or channels not primary features fed directly from an underlying dike we examine simple models of pipe flow and conclude that lava tubes can transport lava down the flanks of submarine rifts to build all of the volcanic features observed there in addition deep water lava tubes are strong enough to withstand the pressures of a few megapascals that the building of a volcanic structure 150 m high at the end of the tube would generate the volumes of individual volcanic terraces and seamounts on the puna ridge and at the mar are large 0 1 1 km3 and similar to the volumes of lava flows that are broadly distributed at the subaerial east rift zone of kilauea this striking difference in the volcanic morphology on a scale of 1 2 km producing terraces and seamounts underwater and low relief flows on land must be related to the enhanced cooling and to the greater mechanical stability of tubes in the submarine environment we suggest that at the mar a crustal magma reservoir most likely located beneath shallow flat sections of the segment provides magma to the rift axis through dikes that propagate laterally tens of kilometers the zone of dike intrusion at least in the neighborhood of the magma body is likely narrower than the width resurfaced by flows yielding a crustal structure that has a rapid vertical transition from lavas to sheeted dikes at segment ends the zone of dike intrusion is likely to be wider giving a resulting structure with a more gradual transition from lavas to dikes