flowgo a kinematic thermo rheological model for lava flowing in a channel we present a kinematic self adaptive numerical model to describe the down flow thermal and rheological evolution of channel contained lava as our control volume of lava advances down a channel it cools and crystallizes an increasingly thick and extensive surface crust grows and its heat budget and rheology evolve by estimating down flow heat and velocity loss our model calculates the point at which the control volume becomes stationary giving the maximum distance lava flowing in the channel can extend modeled effusion rates velocities widths surface crust parameters heat budget cooling temperature crystallinity viscosity and yield strength all compare well with field data collected during eruptions at mauna loa k lauea and etna modeled lengths of 25 27 2 5 5 7 and 0 59 0 83 km compare with measured lengths of 25 27 4 and 0 75 km for the three flows respectively over proximal flow portions we calculate cooling crystallization viscosity and yield strength of 1 10 c km 1 0 001 0 01 volume fraction km 1 103 104 pa s and 10 3 102 pa respectively at the flow front cooling crystallization viscosity and yield strength increase to 100 c km 1 0 1 volume fraction km 1 106 107 pa s and 103 104 pa respectively all of which combine to cause the lava to stop flowing our model presents a means of a analyzing lava flow thermo rheological relationships b identifying important factors in determining how far a channel fed flow can extend c assessing lava flow hazard and d reconstructing flow regimes at prehistoric unobserved or remote flows

bayesian time lapse inversion a new fast inversion approach for time lapse seismic data is developed where the uncertainty of the inversion results is an integral part of the solution the inversion method estimates changes in the elastic material properties of a reservoir because of production of hydrocarbons including uncertainty bounds on these estimates the changes in elastic properties then can be related to changes in hydrocarbon saturation and reservoir pressure by using rock physics relations the inversion operates directly on the difference between a repeat survey and a baseline survey this is advantageous with respect to the uncertainty calculation because an estimate of the seismic uncertainty can be obtained directly from the difference data in zones not affected by production the method is formulated in a bayesian setting and the solution is represented by explicit expressions for the posterior expectation and the covariance of the elastic parameter changes the explicit analytical form of the posterior distributi

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

a new model for the emplacement of columbia river basalts as large inflated pahoehoe lava flow fields extensive flows of the columbia river basalt crb group in washington oregon and idaho are dominantly inflated compound pahoehoe sheet lavas early studies recognized that crb lavas are compound pahoehoe flows with textures suggesting low flow velocities but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks however small volume 1 km compound pahoehoe flows on kilauea hawai i demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger 10 20 km3 pahoehoe flows in iceland the vertical distribution of vesicles and other morphologic features within crb lava flows indicate that they grew similarly by inflation small pahoehoe lobes at the base and top of many crb pahoehoe lava flows indicate emplacement in a gradual piecemeal manner rather than as a single flood we propose that each thick crb sheet flow was active for months to years and that each group of flows produced by a single eruption a flow field was emplaced slowly over many years

in situ cosmogenic radiocarbon production and 2 d ice flow line modeling for an antarctic blue ice area surface 14 c activity that differs by up to 25 from the activity calculated using an ablation only approximation which is used in all prior work and 3 that at high ablation margin sites solar modulation of the cosmic ray flux may change the strength of the dominant spallogenic production by up to 10 as part of this effort we model twodimensional ice flow along the central flow line of taylor glacier we present two methods for parameterizing vertical strain rates and assess which method is more reliable for taylor glacier finally we present a sensitivity study from which we conclude that uncertainties in published cosmogenic production rates are the largest source of potential error the results presented here can inform ongoing and future 14 c and ice flow studies at ice margin

pleistocene ice and paleo strain rates at taylor glacier antarctica ice exposed in ablation zones of ice sheets can be a valuable source of samples for paleoclimate studies and information about long term ice dynamics we report a 28 km long stable isotope sampling transect along a flowline on lower taylor glacier antarctica and show that ice from the last glacial period is exposed here over tens of kilometers gas isotope analyses on a small number of samples confirm our age hypothesis these chronostratigraphic data contain information about past ice dynamics and in particular should be sensitive to the longitudinal strain rate on the north flank of taylor dome averaged over millennia the imprint of climatic changes on ice dynamics may be discernible in these data

cosmogenic 36cl accumulation in unstable landforms 1 effects of the thermal neutron distribution cosmogenic nuclides produced in situ within minerals at the surface of the earth are proving to be an effective means of assessing geomorphic histories the use of multiple cosmogenic nuclides permits both exposure times and erosion rates to be determined however if two nuclides are produced only by spallation reactions the systematic differences in their accumulation rates depend only on the differences in their production rates and half lives the relatively small differences that result require a high degree of analytical precision to yield useful results in contrast to other spallogenic nuclides sup 36 cl is also produced by low energy neutron absorption which creates a different pattern of production as a function of depth we have measured the thermal flux with depth in a concrete block using sup 3 he filled neutron detectors the measured thermal neutron profile agrees well with predictions from a simple diffusion based thermal neutron distribution model calculations of sup 36 cl production using the model suggest that the use of sup 36 cl along with a purely spallogenic nuclide to determine erosion rates and exposure times should be less sensitive to analytical error than are determinations from two purely spallogenic nuclides 31 refs 7 figs 3 tabs

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

pahoehoe transport as a correlated random walk 1 transport and emplacement of pahoehoe lava is often dominated by random influences such as budding small scale variations in topography degree of inflation and variations in how the skin cools stretches and cracks a random walk model is used to describe the transport of small pahoehoe lobes when random effects are a significant influence on emplacement we derive the stochastic formalism for random movements on a two dimensional grid our formulation features correlation and bias that determine the degree of randomness in the random walk of each parcel of lava qualitative and quantitative predictions of the random walk are compared with observations and data for pahoehoe lobes in hawaii the correlated random walk quantitatively describes lobe thickness transects whereas the uncorrelated random walk only reproduces the meandering of small filaments of a few toes correlation expresses momentum effects and a chain of memory from the flow front to the source of lava supply the correlated random walk features a channel forming regime that decays with distance from the source of lava supply the theory can also be interpreted in the context of a time dependent planar flow when many parcels of lava participate the overall shape of a one dimensional lobe has the appearance of a continuum wave the types of processes contained in this basic random walk model explain the multitude of concurrent or overriding features found in broad fields of toes the formalism can thus be extended to simulate large fields of emplaced pahoehoe in either terrestrial or planetary settings

pahoehoe toe dimensions morphology and branching relationships at mauna ulu kilauea volcano hawai i pahoehoe toe dimensions morphology and branching relationships were analyzed in flows emplaced during 1972 at mauna ulu a satellitic shield on the east rift zone of kilauea volcano hawai i in order to characterize regions within flow fields dominated by networks of pahoehoe toes measurements of toe length width thickness and orientation were completed for 445 toes at 13 sites variations in site characteristics including slope substrate and position in the flow field allow an evaluation of the effects of such parameters on toe dimensions toe surface morphology ropy or smooth local flow lobe position interior or margin and connective relationships between toes were documented in the form of detailed toe maps these maps show the number of branches connecting a given toe to other toes in its local pahoehoe network and illustrate branching patterns statistical analyses of toe dimensions and comparisons of pahoehoe toe study sites and sub populations combined with field observations evaluation of toe maps and qualitative examination of toe dimension size distributions show the following a although there are significant variations at a given site toes typically have mean lengths 101 cm greater than mean widths 74 cm and mean widths greater than mean thicknesses 19 cm sites that have mean widths greater than mean lengths are those with lower slopes b where significant site to site variations in mean values of a given toe dimension were apparent these differences could not be directly related to site characteristics c ropy toes have significantly larger mean values of length width and number of branches than smooth toes and toes with three or more branches have greater lengths widths and thicknesses than toes with two or fewer branches suggesting concentration of flow in these toe types d the skewness of all size distributions of toe length and width to larger values suggests that toes are transitional to larger sheets and channels consistent with field observations and e two distinct types of branching patterns called monolayer and centrally ridged were observed in preserved pahoehoe flow lobes the significant variability in measured toe dimensions at mauna ulu suggests that toe dimensions are influenced by numerous locally defined random factors and that an approach based on stochastic methods can be used to model pahoehoe flow emplacement

interpreting ancient ice in a shallow ice core from the south yamato antarctica blue ice area using flow modeling and compositional matching to deep ice cores 1 we explore methods of dating a 101 m ice core from a bare ice ablation area in the yamato mountains dronning maud land east antarctica there are two unknowns the age of the ice at the surface and the age spanned by the core the ice crystal growth rate was used to estimate the age span of the core at about 5 kyr co2 ch4 and n2o data on the core were compared with well dated records from deep cores leading to two plausible matches both within isotope stage c detailed comparison of high resolution dep records from this core and the dome fuji core support the 55 61 kyr bp fit best oxygen isotope values in the core were then used to constrain the source elevation of the snow in the core and hence the velocities in a simple flow line model we inverted the ice core surface age age span and origin site and their confidence intervals in a sensitivity study of flow model parameter space the flow line model predicts good matches to the core by reducing glacial flow rates to 70 of present day accumulation rates by 45 with 10 confidence intervals the modeled surface age for the whole meteorite field yields maximum surface ages of about 90 kyr which is consistent with known but poorly constrained tephra dating meteorite terrestrial ages and the frequency of meteorite discoveries this approach can be used quite generally to link deep ice cores to surface outcrops on blue ice fields

radiometric 81kr dating identifies 120 000 year old ice at taylor glacier antarctica we present successful 81kr kr radiometric dating of ancient polar ice krypton was extracted from the air bubbles in four 350 kg polar ice samples from taylor glacier in the mcmurdo dry valleys antarctica and dated using atom trap trace analysis atta the 81kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 2 5 ka our experimental methods and sampling strategy are validated by i 85kr and 39ar analyses that show the samples to be free of modern air contamination and ii air content measurements that show the ice did not experience gas loss we estimate the error in the 81kr ages due to past geomagnetic variability to be below 3 ka we show that ice from the previous interglacial period marine isotope stage 5e 130 115 ka before present can be found in abundance near the surface of taylor glacier our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available greatly enhancing their scientific value as archives of old ice and meteorites at present atta 81kr analysis requires a 40 80 kg ice sample as sample requirements continue to decrease 81kr dating of ice cores is a future possibility

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

time lapse inverse theory with applications abstractcompaction in the reservoir overburden can impact production facilities and lead to a significant risk of well bore failures prevalent practices of time lapse seismic processing of 4d data above compacting reservoirs rely on picking time displacements and converting them into estimated velocity changes and subsurface deformation this approach relies on prior data equalization and requires a significant amount of manual interpretation and quality control we have developed methods for automatic detection of production induced subsurface velocity changes from seismic data we have evaluated a time lapse inversion technique based on a simultaneous regularized full waveform inversion fwi of multiple surveys in our approach baseline and monitor surveys are inverted simultaneously with a model difference regularization penalizing nonphysical differences in the inverted models that are due to survey or computational repeatability issues the primary focus of our work was the inversion of long wavel

ice stratigraphy at the pakitsoq ice margin west greenland derived from gas records horizontal ice core sites where ancient ice is exposed at the glacier surface offer unique opportunities for paleo studies of trace components requiring large sample volumes following previous work at the pakitsoq ice margin in west greenland we use a combination of geochemical parameters measured in the ice matrix d 18 oice and air occlusions d 18 oatm d 15 no f n 2 and methane concentration to date ice layers from specific climatic intervals the data presented here expand our understanding of the stratigraphy and three dimensional structure of ice layers outcropping at pakitsoq sections containing ice from every distinct climatic interval during termination i including last glacial maximum bolling allerod younger dryas and the early holocene are identified in the early holocene we find evidence for climatic fluctuations similar to signals found in deep ice cores from greenland a second glacial interglacial transition exposed at the extreme margin of the ice is identified as another outcrop of termination i rather than the onset of the eemian interglacial as postulated in earlier work consequently the main structural feature at pakitsoq is a large scale anticline with accordion type folding in both exposed sequences of the glacial holocene transition leading to multiple layer duplications and age reversals

estimation of changes in saturation and pressure from 4d seismic avo and time shift analysis a reliable estimate of reservoir pressure and fluid saturation changes from time lapse seismic data is difficult to obtain existing methods generally suffer from leakage between the estimated parameters we propose a new method using different combinations of time lapse seismic attributes based on four equations two expressing changes in prestack avo attributes zero offset and gradient reflectivities and two expressing poststack time shifts of compressional and shear waves as functions of production induced changes in fluid properties the effect of using different approximations of these equations was tested on a realistic synthetic reservoir where seismic data have been simulated during the 30 year lifetime of a water flooded oil reservoir results found the importance of the porosity in the inversion with a clear attenuation of the porosity imprint on the final estimates in case the porosity field or the vertically averaged porosity field is known a priori the use of a first order approximation of the gradient reflectivity equation leads to severely biased estimates of changes in saturation and leakage between the two different parameters both the bias and the leakage can be reduced if not eliminated by including higher order terms in the description of the gradient or by replacing the gradient equation with p and or s wave time shift data the final estimates are relatively robust to random noise as they present fairly high accuracy in the presence of white noise with a standard deviation of 15 the introduction of systematic noise decreases the inversion accuracy more severely

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

inverting for reservoir pressure change using time lapse time strain application to genesis field gulf of mexico there are increasing numbers of published examples from around the world in which significant 4d time shifts have been observed in the overburden above producing reservoirs

comparison between greenland ice margin an ice core oxygen 18 records old ice for paleoenvironmental studies retrieved by deep core drilling in the central regions of the big ice sheets can also be retrieved from the ice sheet margins the d18o content of the surface ice was studied at 15 different greenland ice margin locations at some locations two or more records were obtained along closely spaced parallel sampling profiles showing good reproducibility of the records we present ice margin d18o records reaching back into the pleistocene many of the characteristic d18o variations known from greenland deep ice cores can be recognized allowing an approximate time scale to be established along the ice margin records a flow line model is used to determine the location on the ice sheet where the margin ice was originally deposited as snow the pleistocene holocene d18o change at the deposition sites is determined by comparing the d18o values in the ice margin record to the present 18o values of the surface snow at the deposition sites on the northern slope of the greenland ice sheet the pleistocene holocene d18o change is c 10 per mil in contrast to a change of 6 7 per mil at locations near the central ice divide this is in accordance with deep ice core results we conclude that d18o records measured on ice from the greenland ice sheet margin provide useful information about past climate and dynamics of the ice sheet and thus are important and cheap supplements to deep ice core records

gas records from the west greenland ice margin covering the last glacial termination a horizontal ice core abstract certain sites along ice sheet margins provide an easily accessible and almost unlimited supply of ancient ice at the surface measurements of gases in trapped air from ice outcropping at pakitsoq west greenland demonstrate that ancient air is mostly well preserved no alterations in 18 o atm and 15 n of n 2 are apparent and alterations in methane are found in only a few ice sections using measurements of these gases we have unambiguously identified a stratigraphic section containing ice from the end of last glacial period as well as bolling allerod younger dryas and preboreal intervals extensive sections of ice from the holocene and most ages within the last glacial period are probably also present very accurate dating has been possible in the ice section containing the younger dryas preboreal abrupt climate transition signal the ice at pakitsoq is folded and non uniformly thinned with many cross cutting bands of bubble free ice and dust the cross cutting features are associated with anomalies in both the gas and the ice records with careful sampling to avoid these the ice at pakitsoq is suitable for recovery of large volume samples of the ancient atmosphere for analysis of trace constituents such as 14 ch 4

high precision 14c measurements demonstrate production of in situ cosmogenic 14ch4 and rapid loss of in situ cosmogenic 14co in shallow greenland firn abstract measurements of radiocarbon 14 c in carbon dioxide co 2 methane ch 4 and carbon monoxide co from glacial ice are potentially useful for absolute dating of ice cores studies of the past atmospheric ch 4 budget and for reconstructing the past cosmic ray flux and solar activity interpretation of 14 c signals in ice is complicated by the fact that the two major 14 c components trapped atmospheric and in situ cosmogenic are present in a combined form as well as by a very limited understanding of the in situ component this study measured 14 ch 4 and 14 co content in glacial firn with unprecedented precision to advance understanding of the in situ 14 c component 14 ch 4 and 14 co were melt extracted on site at summit greenland from three very large 1000 kg each replicate samples of firn that spanned a depth range of 3 6 5 6 m non cosmogenic 14 c contributions were carefully characterized through simulated extractions and a suite of supporting measurements in situ cosmogenic 14 co was quantified to better than 0 6 molecules g 1 ice improving on the precision of the best prior ice 14 co measurements by an order of magnitude the 14 co measurements indicate that most 99 of the in situ cosmogenic 14 c is rapidly lost from shallow summit firn to the atmosphere despite this rapid 14 c loss our measurements successfully quantified 14 ch 4 in the retained fraction of cosmogenic 14 c to 0 01 molecules g 1 ice or better and demonstrate for the first time that a significant amount of 14 ch 4 is produced by cosmic rays in natural ice this conclusion increases the confidence in the results of an earlier study that used measurements of 14 ch 4 in glacial ice to show that wetlands were the likely main driver of the large and rapid atmospheric ch 4 increase approximately 11 6 kyr ago

dynamics and mass balance of taylor glacier antarctica 1 geometry and surface velocities 1 taylor glacier antarctica exemplifies a little studied type of outlet glacier one that flows slowly through a region of rugged topography and dry climate this glacier in addition connects the east antarctic ice sheet with the mcmurdo dry valleys a region much studied for geomorphology paleoclimate and ecology here we report extensive new measurements of surface velocities ice thicknesses and surface elevations acquired with insar gps and gpr the latter two were used to construct elevation models of the glacier s surface and bed ice velocities in 2002 2004 closely matched those in 2000 and the mid 1970s indicating negligible interannual variations of flow comparing velocities with bed elevations shows that along much of the glacier flow concentrates in a narrow axis of relatively fast flowing ice that overlies a bedrock trough the flow of the glacier over major undulations in its bed can be regarded as a cascade it speeds up over bedrock highs and through valley narrows and slows down over deep basins and in wide spots this pattern is an expected consequence of mass conservation for a glacier near steady state neither theory nor data from this taylor glacier study support the alternative view recently proposed that an outlet glacier of this type trickles slowly over bedrock highs and flows fastest over deep basins

dynamics and mass balance of taylor glacier antarctica 2 force balance and longitudinal coupling 1 taylor glacier antarctica exemplifies an ice sheet outlet that flows through a region of rugged topography and dry climate in contrast to other well studied outlets taylor glacier moves very slowly despite a thickness of order 1 km and driving stresses averaging 1 5 bars here we analyze new measurements of glacier geometry and surface velocity to elucidate flow dynamics of taylor glacier force balance and basal temperatures are calculated at six locations along the glacier s length using an algorithm developed for this study the effects of stress gradient coupling on longitudinal flow variations are also examined we ask whether kamb and echelmeyer s 1986 linearized theory adequately describes the observed response of flow to large amplitude variations in driving stress the force balance calculations indicate that no basal motion is needed to explain the observed flow of taylor glacier inferred basal temperatures are within a few degrees of the melting point in regions of kilometer thick ice and well below the melting point elsewhere deformation of subfreezing ice largely controls the flow of taylor glacier basal drags are mostly in the range 0 9 to 1 2 bars and lateral drags are in the range 0 2 to 0 5 bar stress gradient coupling strongly reduces the variability of velocities along the glacier the velocity variations can be described as the convolution of a forcing function with a spatial filter as kamb and echelmeyer suggested but the form of the forcing function differs from the theoretical relation derived for small amplitude perturbations the power on driving stress is one not three

record of cosmogenic in situ produced 14c in vostok and taylor dome ice samples implications for strong role of wind ventilation processes we present results of studies of in situ cosmogenic 14 c in several ice samples from the vostok and taylor dome cores spanning the time intervals of 20 and 11 k y b p respectively the results are in variance with our findings for the greenland ice sheet project 2 gisp 2 samples where near quantitative 14 c retention was observed the partitioning of 14 c in the co and co 2 phases is however quite similar in the gisp and two antarctic ice samples noting that most of the in situ 14 c is produced in the ice during its accumulation to thicknesses of up to 10 m we interpret the observed 14 c deficiencies in antarctic ice samples as due to grain metamorphism recrystallization and sublimation or evaporation caused by wind ventilation simplified models for wind ventilation exhibit an interesting feature of the firnification processes they differently affect the concentrations of in situ 14 c and of the cosmogenic nuclides 10 be and 36 cl scavenged from the atmosphere in the accumulating firn by studying the concentrations of in situ cosmogenic 14 c and the atmospheric cosmogenic nuclides in the same ice samples one can hope to obtain fairly realistic models of the chemical impacts of firnification processes specifically relationships between precipitation and accumulation and the main processes contributing to modifications in the nuclide concentrations

nearest neighbor analysis of small features on mars applications to tumuli and rootless cones 1 fields of low relief cones domes and mounds on mars have been interpreted as tumuli rootless cones and pingos the spatial distribution of such features can be characterized by their nearest neighbor nn distances the nn distributions can provide insight into the physical processes that affected field formation and can possibly provide a future diagnostic of the feature type present on mars the conventional approach for analyzing the observed nn distribution is based on the poisson probability distribution and uses one statistic c our simulations of spatial randomness show that there is an unrecognized bias in c that often leads to erroneous conclusions three alternative extensions of the poisson distribution are proposed here the first accounts for a minimum threshold on the size of features discerned the second considers the scavenging of the resources necessary to form neighboring features e g inflation pressurization and subsurface volatiles and the third models self limiting growth of the feature population three statistical tests are proposed to improve the conventional nn analysis we provide the critical regions needed to perform these tests for common sample sizes of these geologic features our methodology is applied to tumuli at mauna ulu hawaii and conjectured tumuli and rootless cones on mars each example exhibits a different aspect of spatial randomness these applications suggest avenues for further field and theoretical studies to develop this approach as a remote sensing diagnostic

a new approach to separate seismic time lapse time shifts in the reservoir and overburden abstractfor a robust way of estimating time shifts near horizontal boreholes we have developed a method for separating the reflection responses above and below a horizontal borehole together with the surface reflection data the method uses the direct arrivals from borehole data in the marchenko method the first step is to retrieve the focusing functions and the up down wavefields at the borehole level using an iterative marchenko scheme the second step is to solve two linear equations using a least squares minimizing method for the two desired reflection responses then the time shifts that are directly linked to the changes on either side of the borehole are calculated using a standard crosscorrelation technique the method is applied with good results to synthetic 2d pressure data from the north sea one example uses purely artificial velocity changes negative above the borehole and positive below and the other example uses more realistic changes based on well logs in the 2d case with an adequ

in situ stress dependence of wave velocities in reservoir and overburden rocks seismic waves propagate through a stressed earth sonic waves recorded by a borehole sonic logging tool propagate in the near well environment which is also stressed albeit under different stress conditions than the untouched formation far away cores excavated from within the earth undergo stress release and are then reloaded in the laboratory but hardly ever to the complete fully anisotropic in situ state of stress and pore pressure based on this we easily recognize that stress sensitivity affects our ability to compare and correlate geophysical and petrophysical measurements of wave velocities on the other hand it also provides an avenue to extract information about rock stresses as an example the presence of abnormally low velocities in seismic or log data is evidence of high pore pressure

simulation of inflated pahoehoe lava flows a new stochastic model simulates late stage pahoehoe lobes where random processes dominate emplacement the model prescribes probabilistic rules for determining where and when parcels of lava move within the lobe unlike a classical brownian motion random walk the model allows individual parcels to remain dormant but fluid for multiple time steps the randomness of parcel volume transfers within the lobe interior as well as at the margins qualitatively reflects inflation processes observed in the field the fraction of inflated volume to total volume increases with the total volume with greater than 75 of the lobe volume contributed through inflation for typical lobes the influence on planform shape and topographic cross sectional profiles of total volume source area and shape topographic confinement and sequential breakouts at the lobe margins are all explored with the stochastic model each of these factors influences the overall lobe thickness and width the model provides a means for assessing the relative importance of these processes through comparisons with field data for the first time gaussian and parabolic functions are quantitatively fit to field measurements of pahoehoe lobes both functional forms provide adequate description of the cross sectional flow shapes when comparing simulated lobes to field data sequential breakouts at the lobe margins are found to be an important process controlling the final topographic distribution of observed pahoehoe lobes

topographic and stochastic influences on pahoehoe lava lobe emplacement a detailed understanding of p hoehoe emplacement is necessary for developing accurate models of flow field development assessing hazards and interpreting the significance of lava morphology on earth and other planetary surfaces active p hoehoe lobes on k lauea volcano hawai i were examined on 21 26 february 2006 using oblique time series stereo photogrammetry and differential global positioning system measurements during this time the local discharge rate for peripheral lava lobes was generally constant at 0 0061 0 0019 m3 s but the areal coverage rate of the lobes exhibited a periodic increase every 4 13 0 64 min this periodicity is attributed to the time required for the pressure within the liquid lava core to exceed the cooling induced strength of its margins the p hoehoe flow advanced through a series of down slope and cross slope breakouts which began as 0 2 m thick units i e toes that coalesced and inflated to become approximately meter thick lobes the lobes were thickest above the lowest points of the initial topography and above shallow to reverse facing slopes defined relative to the local flow direction the flow path was typically controlled by high standing topography with the zone directly adjacent to the final lobe margin having an average relief that was a few centimeters higher than the lava inundated region this suggests that toe scale topography can at least temporarily exert strong controls on p hoehoe flow paths by impeding the lateral spreading of the lobe observed cycles of enhanced areal spreading and inflated lobe morphology are also explored using a model that considers the statistical likelihood of sequential breakouts from active flow margins and the effects of topographic barriers

statistical distribution of tumuli on pahoehoe flow surfaces analysis of examples in hawaii and iceland and potential applications to lava flows on mars 1 spatial distributions of tumuli on lava flow surfaces can be quantitatively linked to subsurface inflation processes three distinct styles of flow emplacement are studied 1 lava flows undergo inflation that changes as a function of space and time resulting in random spatial distributions of tumuli 2 lava flows with preferred pathways result in systematic clustering of inflation features and 3 established tubes or narrow pahoehoe flows produce chains of tumuli statistical analyses are required to distinguish between styles one and two comparison of the spatial distribution of tumuli on a portion of a lava flow at mauna ulu with the poisson distribution indicates that tumuli are randomly distributed on the flow surface typical of style one emplacement where small scale topographic variability and low slope influence development of preferred pathways that evolve over time at thrainsskjoldur direct statistical comparisons to the poisson spatial distribution are inconclusive but nearest neighbor analysis indicates significant clustering an initially random spatial distribution is inferred that developed preferred pathways and systematic clustering of inflation features as with style two at elysium planitia on mars the flow margin is significantly deficient in inflation features while away from the margin the flow exhibits a random spatial distribution of tumuli typical of style one emplacement the flow is interpreted as multiple units or a single flow that migrated in space during emplacement at the 1843 flow on mauna loa tumuli occur on a linear trend consistent with style three emplacement

a hybrid model for leveed lava flows implications for eruption styles on mars 1 many channelized lava flows on the plains of mars have substantial embanking margins and levees inferred to have been stationary while the central channel was active levee formation can be attributed to two end member processes during emplacement construction during passage of the flow front and growth along the entire length of the flow while it is active it is shown here that the amount of lava that can be deposited by the flow front alone is limited estimates of the levee volume for many mars plains flows exceed this limit and must have formed by processes that continued after the passage of the front experimental studies of analogous laboratory flows also indicate a combination of both modes of emplacement a model that combines both modes of levee formation is presented including a method for estimating volumetric flow rate eruption duration and viscosity six lava flows on the plains of the tharsis volcanic province are used as illustrative examples crustal thicknesses for the six flows examined range from 9 to 23 m estimated emplacement times required to cool crusts of these thicknesses range from 1 year to 10 years corresponding viscosities are on the order of 105 106 pa s effusion rates range from 25 to 840 m3 s 1 and are all within the range of terrestrial observations therefore the large leveed plains flows on mars are not dramatically different in eruption rate or lava viscosity from large terrestrial analogs

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

measurements of 14c in ancient ice from taylor glacier antarctica constrain in situ cosmogenic 14ch4 and 14co production rates abstract carbon 14 14c is incorporated into glacial ice by trapping of atmospheric gases as well as direct near surface in situ cosmogenic production 14c of trapped methane 14ch4 is a powerful tracer for past ch4 emissions from old carbon sources such as permafrost and marine ch4 clathrates 14c in trapped carbon dioxide 14co2 can be used for absolute dating of ice cores in situ produced cosmogenic 14c in carbon monoxide 14co can potentially be used to reconstruct the past cosmic ray flux and past solar activity unfortunately the trapped atmospheric and in situ cosmogenic components of 14c in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core 14c we analyzed very large 1000 kg ice samples in the 2 26 19 53 m depth range from the ablation zone of taylor glacier antarctica to study in situ cosmogenic production of 14ch4 and 14co all sampled ice is 50 ka in age allowing for the assumption that most of the measured 14c originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation our results place the first constraints on cosmogenic 14ch4 production rates and improve on prior estimates of 14co production rates in ice we find a constant 14ch4 14co production ratio 0 0076 0 0003 for samples deeper than 3 m which allows the use of 14co for correcting the 14ch4 signals for the in situ cosmogenic component our results also provide the first unambiguous confirmation of 14c production by fast muons in a natural setting ice or rock and suggest that the 14c production rates in ice commonly used in the literature may be too high

sublimation and surface energy budget of taylor glacier antarctica taylor glacier an outlet of the east antarctic ice sheet flows through the transantarctic mountains and terminates in the dry valleys understanding how this glacier fluctuates is important for studies of glacial geology paleoclimate ice dynamics and ecology sublimation is the primary mass loss process for most of the glacier four years of specific balance measurements from the ablation zone show sublimation rates up to 40 cma 1 we used data from an array of weather stations as inputs to a model for latent heat flux and hence sublimation rate calculated and measured ablation rates agree to within uncertainties indicating that wind speed and vapour pressure gradient a function of temperature and humidity are the governing variables as expected from theory measurements and model results together allowed us to examine the spatial and temporal variations of sublimation on the glacier on average sublimation is about two times faster in summer than winter rapid sublimation occurs during storms and katabatic wind events but such periods contribute less to the annual total than do slow persistent losses spatially sublimation reaches a maximum midway along the glacier where descending surface air currents are focused by the topography of the aptly named tributary windy gully

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

seismic time lapse effects and stress changes examples from a compacting reservoir compaction of unconsolidated reservoir rock represents a major drive mechanism in many oil and gas reservoirs significant volumes of produced hydrocarbons may be credited to this effect however compaction might also result in surface subsidence a dynamic overburden and local permeability losses in the reservoir

jotun 4d characterization of fluid contact movement from time lapse seismic and production logging tool data time lapse or 4d seismic is a reservoir monitoring technology that has matured to the point where it can be considered a reliable reservoir surveillance tool by analyzing differences of multiple seismic surveys acquired over a producing reservoir and by integration with conventional reservoir monitoring tools 4d seismic data can provide valuable insight on dynamic reservoir properties such as fluid saturation pressure and temperature many published case studies demonstrate that 4d seismic technology can optimize reservoir management and improve production efficiency in this paper we describe the application of time lapse seismic methods to the norwegian north sea jotun field to determine the extent of the oil water contact owc movement during the first three years of production

dating antarctic blue ice areas using a novel ice flow model 1 we present a new type of flow model suitable for antarctic blue ice areas with application to dating ice for paleoclimate purposes the volume conserving model uses field data for surface velocities mass balance and ice thickness along a flow line with parameterized variation of ice rheology with depth to produce particle trajectories and isochrones the model is tested on the contrasting allan hills near western ice field and the scharffenbergbotnen blue ice fields in antarctica by comparing predicted ages with ages inferred from meteorites and 14c data during the glacial periods ice surface velocities at the allan hills must have been 25 less and accumulation rates 50 less than present day values in order to match meteorite ages in contrast scharffenbergbotnen velocities have probably been fairly constant over time due to the atypical valley where it resides

bayesian inversion of time lapse seismic data for the estimation of static reservoir properties and dynamic property changes seismic conditioning of static reservoir model properties such as porosity and lithology has traditionally been faced as a solution of an inverse problem dynamic reservoir model properties have been constrained by time lapse seismic data here we propose a methodology to jointly estimate rock properties such as porosity and dynamic property changes such as pressure and saturation changes from time lapse seismic data the methodology is based on a full bayesian approach to seismic inversion and can be divided into two steps first we estimate the conditional probability of elastic properties and their relative changes then we estimate the posterior probability of rock properties and dynamic property changes we apply the proposed methodology to a synthetic reservoir study where we have created a synthetic seismic survey for a real dynamic reservoir model including pre production and production scenarios the final result is a set of point wise probability distributions that allow us to predict the most probable reservoir models at each time step and to evaluate the associated uncertainty finally we also show an application to real field data from the norwegian sea where we estimate changes in gas saturation and pressure from time lapse seismic amplitude differences the inverted results show the hydrocarbon displacement at the times of two repeated seismic surveys

a self replication model for long channelized lava flows on the mars plains 1 a model is presented for channelized lava flows emplaced by a self replicating levee building process over long distances on the plains of mars such flows may exhibit morphologic evidence of stagnation overspills and upstream breakouts however these processes do not inhibit the formation and persistence of a prominent central channel that can often be traced for more than 100 km the two central assumptions of the self replication model are 1 the flow advances at the average upstream velocity of the molten core and 2 the fraction of the lava that travels faster than the average upstream velocity forms stationary margins in the advancing distal zone to preserve the self replication process for an exemplary 300 km long flow north of pavonis mons the model indicates that 8 m of crust must have formed during emplacement as determined from the channel and levee dimensions when combined with independent thermal dynamic estimates for the crustal growth rate relatively narrow constraints are obtained for the flow rate 2250 m3 s 1 emplacement duration 600 d and the lava viscosity of the molten interior 106 pa s minor transient overspills and breakouts increase the emplacement time by only a factor of 2 the primary difference between the prodigious channelized martian flows and their smaller terrestrial counterparts is that high volumetric flow rates must have persisted for many hundreds of days on mars in contrast to a few hours or days on earth

dynamics and mass balance of taylor glacier antarctica 3 state of mass balance 1 taylor glacier flows from the east antarctic ice sheet and terminates in the mcmurdo dry valleys where it has left a geomorphologic record of past incursions here we use new data on the flow thickness and surface balance of taylor glacier to calculate ice fluxes and assess the current state of mass balance overall the glacier is close to a state of zero net balance and has largely adjusted to reduced snowfall on the taylor dome source region in the mid holocene one region of the upper ablation zone appears to be losing mass evidence from ice surface morphology and stable isotope profiles suggests that this mass loss is a long term phenomenon hence probably a lingering response to the earlier drying of taylor dome our data give a general indication of the size of ablation or accumulation changes needed for ice to advance far into taylor valley as occurred 70 to 130 ka ago

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

diffraction tomography and multisource holography applied to seismic imaging seismic tomography is emerging as an imaging method for determining subsurface structure when the view angle coverage is limited and the scale of the medium inhomogeneities is comparable with the wavelength as is often true in geophysical applications the performance of ordinary ray tomography becomes poor other tomographic methods are needed to improve the imaging process here we study diffraction tomography and multisource holography and evaluate their performances for surface reflection profiling srp vertical seismic profiling vsp and cross hole measurements theoretical formulations are derived for two dimensional geometry in terms of line sources along a source line and line receivers along a receiver line the theory for diffraction tomography is based on the born or rytov approximation the performances of diffraction tomography and multisource holography are evaluated by examining the information coverage in the spatial frequency domain and by numerical examples multisource holography

instruments and methods a novel method for obtaining very large ancient air samples from ablating glacial ice for analyses of methane radiocarbon we present techniques for obtaining large 100 l stp samples of ancient air for analysis of 14 c of methane 14 ch4 and other trace constituents paleoatmospheric 14 ch4 measurements should constrain the fossil fraction of past methane budgets as well as provide a definitive test of methane clathrate involvement in large and rapid methane concentration ch4 increases that accompanied rapid warming events during the last deglaciation air dating to the younger dryas preboreal and oldest dryas bolling abrupt climatic transitions was obtained by melt extraction from old glacial ice outcropping at an ablation margin in west greenland the outcropping ice and occluded air were dated using a combination of d 15 no f n 2 d 18 oo f o 2 d 18 oice and ch4 measurements the ch4 blank of the melt extractions was 4 ppb measurements of d 18 o and d 15 n indicated no significant gas isotopic fractionation from handling measured ar n2 cfc 11 and cfc 12 in the samples indicated no significant contamination from ambient air ar n2 kr ar and xe ar ratios in the samples were used to quantify effects of gas dissolution during the melt extractions and correct the sample ch4 corrected ch4 is elevated over expected values by up to 132 ppb for most samples suggesting some in situ ch4 production in ice at this site

ages and composition of gas trapped in allan hills and byrd core ice gas is extracted from large 6 31 kg antarctic ice samples to obtain sufficient co2 for14c measurements with small low level proportional counters the14c ages of byrd core ice are in accord with glaciological estimates ranging from 2 2 1 1 1 4 103 yr at 271 m depth to more than 8 103 yr at 1071 m depth the co2 abundances in gas extracted from byrd core ice range from 0 0216 to 0 051 with below present day atmosphere co2 abundances for ice from 1068 and 1469 m depths the co2 abundance in gas from allan hills surface ice samples ranges between four and six times the atmospheric value and the co2 had a specific activity three times that of contemporary carbon a possible explanation for the anomalously high specific activity is surface melting with the incorporation into co2 of14c produced by cosmic ray spallation of oxygen in ice the co2 abundance in gas extracted from subsurface allan hills ice ranged from 0 030 to 0 065 and the specific activities are below contemporary carbon indicating ages greater than 5 103 yr the18o 16o ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the18o 16o ratio in the ice the o2 n2 and ar abundances and isotopic compositions are similar to those in contemporary air except for positive15n 14n ratios in a few samples

4d time strain and the seismic signature of geomechanical compaction at genesis genesis field which lies in the green canyon area of the gulf of mexico at a water depth of 790 m consists of a series of unconsolidated pleistocene pliocene aged turbidite sands dipping up against a salt cored ridge since first oil in 1999 the field has been under primary production and although there is a moderate natural water drive in parts of the field much of it has undergone significant compaction resulting from pressure depletion the compaction has had severe economic ramifications as recently several wells have been lost due to compaction related shear failure