radiocarbon studies of latest pleistocene and holocene lava flows of the snake river plain idaho data lessons interpretations abstract latest pleistocene holocene basaltic lava fields of the snake river plain idaho have been dated by the radiocarbon method backhoe excavations beneath lava flows typically yielded carbon bearing charred eolian sediment this material provided most of the samples for this study the sediment typically contains less than 0 2 carbon charcoal fragments were obtained from tree molds but only from a few backhoe excavations contamination of the charred sediments and charcoal by younger carbon components is extensive the effects of contamination were mitigated but appropriate pretreatment of samples using acid and alkali leaches twenty of the more than 60 lava flows of the craters of the moon lava field have been dated their ages range from about 15 000 to about 2000 yr b p the ages permit assignment of the flows to eight distinct eruptive periods with an average recurrence interval of about 2000 yr the seven other latest pleistocene holocene lava fields were all emplaced in short eruptive bursts their 14 c ages yr b p are kings bowl 2222 100 wapi 2270 50 hells half acre 5200 150 shoshone 10 130 350 north robbers and south robbers 11 980 300 and cerro grande 13 380 350

what are the best radar wavelengths incidence angles and polanzations for discrimination among lava flows and sedimentary rocks a statistical approach linear discriminant analysis of multifrequency and multipolarization radar scatterometer data of lava flows and sedimentary rocks indicates that the lava flows sampled at the snake river plain idaho and the sedimentary formations sampled at the san rafael swell utah can be discriminated from one another the necessary radar backscatter data and optimum wavelengths polarizations and incidence angles among those available for these problems are indicated by the discriminant analysis program for separation of the lava flows shorter wavelengths and smaller incidence angles are best for the sedimentary rocks conversely the longer wavelengths and somewhat larger incidence angles are preferred separation among the lava flows was slightly better using horizontally polarized data while vertical polarization gave better separation with the sedimentary rocks the method developed here may provide a rationale for user selection tion of operating parameters for advanced radar systems such as the shuttle imaging radar c sir c and that proposed for the earth observation system eos the analysis is being extended to other study sites for which we have scatterometer data to determine the generality of the results reported here

idaho beginnings a review of the evidence abstract evidence sought here for a pre clovis presence in the snake river basin of idaho and northeastern oregon in the millennium ending at 11 600 yr bp includes radiocarbon and tephrochronological dates extinct pleistocene faunal associations depositional context and living floor and feature integrity and typologically or technologically legible lithic industries results of a review of eleven sites found ambiguous evidence for pre clovis hearths in two caves but no convincing support for the temporal priority of the western stemmed over the clovis tradition however intact sites of the western stemmed tradition dating to 10 200 9800 yr bp survive at 4 m below surface in deep quaternary alluvium in canyon floors in west central idaho below 610 m elevation deeper and earlier deposits may be found in the same settings

paleoseismology and seismic hazards evaluations in extensional volcanic terrains extensional structures in volcanic terrains are the surface expression of shallow dike intrusion and can be misinterpreted as structures associated with major tectonic faults dike induced structures can be distinguished from their tectonic counterparts by their association with cogenetic volcanic rocks and by several geometric relationships tensile fissures with little or no vertical displacement fissure swarms flexural monoclines and normal faults are commonly symmetrically distributed about a central eruptive fissure sometimes forming a graben above shallow dikes the structures typically occur within broad zones not narrow belts near a main fault zone reflecting their origin by repeated dike injection colluvial wedges containing records of single large earthquakes generally do not form instead fault scarps with several meter vertical displacements in volcanic bedrock may reflect the cumulative effects of many decimeter scale displacement events from several dike injection episodes the mechanism of dike intrusion and the nature of cointrusive seismicity have important implications for determination of the maximum magnitude and recurrence of earthquakes in extensional volcanic terrains observational seismicity from volcanic rift zones worldwide suggests the maximum magnitudes of dike induced earthquakes are 3 8 0 8 earthquakes are generally small to moderate because downdip extents of faults and fissures are controlled by the depth to the top of the associated dike usually 5 km permitting only small rupture areas also rupture and displacement on faults and fissures migrate incrementally at about the velocity of propagating dikes 0 5 m s as dike dilation stresses the zone above and ahead of the dike earthquake recurrence is tied to recurrence of volcanic cycles based on the geochronology of the associated volcanic materials based on these concepts innovative approaches have led to estimates of the maximum magnitude and recurrence for magma induced seismicity in eastern snake river plain esrp volcanic rift zones the most conservative approach uses surface length fault width downdip extent and rupture areas of normal faults and fissures produced by dike injection to estimate a maximum m5 5 earthquake for an episode of rift zone volcanism chronology of volcanic rocks suggests annual probabilities of 10 4 to 10 5 for volcanic rift zones near idaho national engineering laboratory facilities probabilistic assessments show that ground motion hazard due to volcanic rift zone seismicity is lower than the hazard from other earthquake sources this is because of the relatively low magnitudes and long recurrence intervals of cointrusive earthquakes in volcanic rift zones

age and duration of volcanic activity at diamond craters southeastern oregon abstract diamond craters one of several young basalt lava fields dotted across southeastern oregon was active in the time between about 7320 and 7790 years ago calibrated ages this timing is determined by a two step analysis first new radiocarbon ages from samples that underlie the lava field and existing ages from overlying deposits constrain the volcanic activity to between 6130 and 7790 years ago second paleomagnetic directions specifically a steep inclination of about 71 further constrain the age of emplacement to the older part of that interval the time before 7320 years ago paleomagnetic directions for lava emplaced early and late in the eruptive activity are essentially the same the duration of diamond craters eruptive activity must have been at least 1 2 decades in order to account for the extrusion of 1 6 km 3 of dense rock equivalent magma at rates typical of long lived basaltic eruptions whether the duration was only that brief or persisted to a century or more is irresolvable from paleomagnetic directions although the coincidence of directions from beginning to end is evidence that the eruption certainly was not protracted over many centuries

compositional heterogeneity of the 3 4 km3 blue dragon flow craters of the moon volcanic field idaho abstract the blue dragon lava flow in southern idaho is one of the largest holocene basaltic flows in the contiguous u s multispectral remote sensing and field mapping of the flow have revealed its 280 km2 surface is divided into five large sub areas with different spectral reflectance and morphology that correspond with distinct periods of the eruption the flow grew outward from its source fissures primarily via a complex system of lava tubes and stratigraphic relations at the boundaries of the mapped sub areas provide temporal information about their order of emplacement this offers a unique opportunity to reconstruct chemical and mineralogical changes in the source magmas as the eruption progressed in this first comprehensive study of the compositional diversity of the blue dragon flow geochemical data from 28 rock samples show that over the course of the eruption the lavas became progressively more primitive and depleted in incompatible trace elements and pb isotopes show subtle increases these observations are best explained by eruption from a zoned magma source due to variable assimilation fractional crystallization afc with the initial eruption of more evolved and enriched magmas that may have been residual from the previous eruption followed by progressively higher proportions of a more primitive and depleted component from deeper in the system differences in lava surface color and morphology among the five mapped eruptive phases may indicate changes in eruptive temperature flow rate or both as the blue dragon eruption progressed the results support a growing body of evidence that systematic studies of geochemical variations in monogenetic and short duration lava flows can reveal the relative influence of processes that affect single batches of magma

small scale deformation structures and physical properties related to convergence in japan trench slope sediments diatomaceous mudstones cored on dsdp legs 56 57 off japan contain numerous postdepositional veins healed fractures and microfaults beneath the forearc basin these secondary structures occur only at depths greater than 620 m miocene in a zone of normal faulting beneath the landward slope of the trench however they occur at depths as shallow as 250 m pliocene in hemipelagic sediments which are inferred to blanket tectonically accreted deposits the intensity of deformation in the trench slope deposits increases in a seaward direction bulk densities indicate that the trench slope deposits have not dewatered normally but are above 400 m more consolidated than sediment deposited on the deep sea terrace a decline in sediment bulk density with increasing depth suggests that open fractures may exist in situ perhaps induced and or maintained by excess pore pressure below about 550 m a normal pattern of increasing density with increasing depth may reflect fracture closure and consolidation under lithostatic load we suggest that tectonic stress related to plate convergence has been communicated to the sediment on the landward japan trench slope causing tectonic dewatering within the subduction complex and inducing pervasive but small scale veining fracturing and faulting in near surface 700 m hemipelagic deposits this deformation occurs in sediment which has not been subject to large tectonic movement and does not eradicate larger 50 100 m thick structural depositional units which are apparent on seismic reflection records the brecciation induced by deformation may reflect natural hydrofracturing under abnormally high pore pressures or opening of fractures formed earlier at shallower depths during the dewatering process the overpressures may in turn locally reduce the sediment shear strength at shallow levels in the sediment column and induce downslope mass sediment movement

holocene bison diminution on the snake river plain idaho usa researchers have established a holocene pattern of bison spp diminution on the great plains of north america this pattern however is less clear west of the rocky mountains this lack of clarity stems from a relative paucity of paleontological and archaeological bison assemblages sufficiently large enough to understand local bison diminution to begin filling this important gap in knowledge we analyze a large bison assemblage from baker cave a late holocene archaeological site located on idaho s snake river plain measurements of humeri radii tibiae metatarsals and calcanei demonstrate that these animals were significantly smaller than early holocene bison from both the great plains and snake river plain middle holocene bison from the great plains are generally larger than those from baker cave but this size difference varies by skeletal element the baker cave bison do fall within the range of late holocene morphological variation present in both snake river plain and great plains bison popula

induced thermoluminescence as a method for dating recent volcanism eastern snake river plain idaho usa the induced thermoluminescence properties of 24 samples of basalts from volcanoes in the eastern snake river plain idaho were measured as part of an investigation into the possibility of using this technique for dating purposes the volcanic flows sampled ranged in age from 2200 years to 400 000 years the tl sensitivity values obtained i e maximum induced tl normalized to that of the dhajala meteorite where dhajala 1000 ranged from 1 6 0 3 to 226 15 and showed a correlation between log tl and age with an r2 value of 0 47 thus tl sensitivity values correlate with age in the manner expected although there is a high level of scatter we discuss various mechanisms for the correlation and scatter particularly 1 the role of primary igneous processes and secondary solid state processes 2 composition of the plagioclase feldspar 3 weathering the induced tl signal from feldspars the mineral responsible for the tl is strongly dependent on their composition and correcting for this improved the correlation r2 0 7 variations in primary feldspar are affecting the data but we find no evidence that weathering of the samples is important further work is required to explore the remaining causes for the scatter and the tl age trend however it is clear from the present study that induced tl has the potential for dating volcanism on the 2200 to 400 000 year time frame this dating method if successful would be well suited to spacecraft use since it requires low mass and low power instruments with a low data demand

contrasting magma types and steady state volume predictable basaltic volcanism along the great rift idaho the great rift is an 85 km long 2 to 8 km wide volcanic rift zone in the snake river plain idaho three latest pleistocene to holocene basaltic lava fields craters of the moon kings bowl and wapi are located along the great rift the craters of the moon lava field is a composite of more than 60 lava flows 25 cinder cones and at least 8 eruptive fissure systems it covers 1 600 km2 and contains 30 km3 of lava flows and associated pyroclastic deposits field radiocarbon and paleomagnetic data show that the craters of the moon lava field formed in eight eruptive periods each of which was typically several hundred years or less in duration and was separated from others before and after by intervals of several hundred to several thousand years the first eruptive period began 15 000 yr b p and the latest eruptive period ended 2100 yr b p the small kings bowl lava field 3 3 km2 0 01 km3 and the larger wapi lava field 330 km2 6 km3 both formed 2250 yr b p three magma types have fed flows along the great rift the types are 1 a contaminated type that has a sio2 range of 49 64 and commonly shows petrographic evidence of contamination 2 a fractionated type that has a sio2 range of 44 54 and shows no evidence of contamination and whose chemical and mineralogical variation can be accounted for mainly by crystal fractionation and 3 a snake river plain type that has a sio2 range of 45 48 shows little evidence of fractionation and is represented by kings bowl wapi flows and olivine basalts of the snake river plain the contaminated and fractionated magma types were erupted at the craters of the moon lava field and the snake river plain magma type was erupted at the kings bowl and wapi lava fields these relations imply that the magma reservoirs are spatially isolated the magma output rate for the craters of the moon segment of the great rift was constant at 1 5 km3 1 000 yr for the period from 15 000 to 7000 yr b p the rate increased to 2 8 km3 1 000 yr from 7000 to 2000 yr b p mainly as a result of the addition of contaminated magma to the nearly constant output rate of fractionated magma the craters of the moon segment of the great rift has experienced quasi steady state volume predictable volcanism for the last 15 000 yr the recurrence interval of eruptive activity for the craters of the moon lava field ranges from several hundred to 3 000 yr because the present interval has lasted 2 100 yr another eruptive period seems likely to occur within the next 1 000 yr the steady state volume predictable relationship suggests that 5 6 km3 of lava will be erupted in the next eruptive period

assessing the accuracy of thermoluminescence for dating baked sediments beneath late quaternary lava flows snake river plain idaho baked sediments beneath lava flows on the snake river plain idaho with independent age control by either 14c or k ar dating were analyzed to evaluate the accuracy of the thermoluminescence tl technique the age of flows ranges from 2 to 100 ka and multiple tl analyses by the total bleach method yielded ages that overlap at one sigma with independent chronologic control the tl signal of one sample of baked sediment beneath a lava flow with an inferred age of at least 641 54 ka was near saturation perhaps reflecting a relatively high environmental dose rate and is not datable by tl this study underscores several major limitations of luminescence geochronology the natural spatial and temporal variability in environmental radioactivity and the susceptibility of silicate minerals to the growth and retention of a luminescence signal despite these limitations the results demonstrate the utility of luminescence geochronology to date volcanic eruptive events during the quaternary

a summary of cenozoic tectonic history along the ipod japan trench transect along the international program of ocean drilling ipod japan trench transect a mid cenozoic period of tectonism without arc volcanism separated an earlier cretaceous to paleogene and a later neogene period of plate convergence and subduction the cretaceous to early paleogene period of convergence is evidenced by andesitic volcanism associated with a large syncline probably a forearc basin the seaward flank of the basin is a tectonically thickened sediment sequence inferred to be an accretionary complex the arc the syncline and the thickened sediment sequence resemble an arc trench system of the size and structure of the great valley forearc basin and franciscan accretionary complex of california and they were probably continuations of the yezo geosyncline and associated sequences exposed to the north on hokkaido the arc trench system is contemporaneous with the adjacent shimanto arc trench system southwest of tokyo bay in the early paleogene volcanism ceased and part of the thickened sediment sequence of the cretaceous paleogene margin was emergent as a 160 km wide landmass which is recognized in seismic records as a later paleogene sediment source at the end of the paleogene this landmass began to subside and volcanism began again but it was located first briefly on the east and then on the west of the cretaceous arc along the present arc of northern honshu the land mass erosion surface is clearly visible as an angular unconformity in multichannel seismic reflection records the sequence of neogene sediment explosive volcanism and benthic foraminiferal assemblages recording subsidence from subareal conditions to the present bathyal depths have been studied in deep sea drilling project dsdp cores cretaceous subduction appears to have resulted in a very extensive accretionary complex whereas the neogene subduction period appears to have been marked by little net accretion in the forearc area but massive subsidence and some erosion of the front of the convergent margin

cosmic ray exposure dating with in situ produced cosmogenic 3he results from young hawaiian lava flows in an effort to determine the in situ production rate of spallation produced cosmogenic 3 he and evaluate its use as a surface exposure chronometer we have measured cosmogenic helium contents in a suite of hawaiian radiocarbon dated lava flows the lava flows ranging in age from 600 to 13 000 years were collected from hualalai and mauna loa volcanoes on the island of hawaii because cosmic ray surface exposure dating requires the complete absence of erosion or soil cover these lava flows were selected specifically for this purpose the 3 he production rate measured within olivine phenocrysts was found to vary significantly ranging from 47 to 150 atoms g 1 yr 1 normalized to sea level although there is considerable scatter in the data the samples younger than 10 000 years are well preserved and exposed and the production rate variations are therefore not related to erosion or soil cover data averaged over the past 2000 years indicate a sea level 3 he production rate of 125 30atoms g 1 yr 1 which agrees well with previous estimates the longer record suggests a minimum in sea level normalized 3 he production rate between 2000 and 7000 years 55 15atoms g 1 yr 1 as compared to samples younger than 2000 years 125 30 atoms g 1 yr 1 and those between 7000 and 10 000 years 127 19atoms g 1 yr 1 the minimum in production rate is similar in age to that which would be produced by variations in geomagnetic field strength as indicated by archeomagnetic data however the production rate variations a factor of 2 3 0 8 are poorly determined due to the large uncertainties in the youngest samples and questions of surface preservation for the older samples calculations using the atmospheric production model of o brien 1979 35 and the method of lal and peters 1967 11 predict smaller production rate variations for similar variation in dipole moment a factor of 1 15 1 65 because the production rate variations archeomagnetic data and theoretical estimates are not well determined at present the relationship between dipole moment and production rate will require further study precise determination of the production rate is an important uncertainty in the surface exposure technique but the data demonstrate that it is feasible to date samples as young as 600 years of age providing that there has been no erosion or soil cover therefore the technique will have important applications for volcanology glacial geology geomorphology and archaeology

late pleistocene hansel valley basaltic ash northern lake bonneville utah usa abstract the hansel valley ash bed lies within 5 cm of the base of deposits of lake bonneville 28 ka in the vicinity of great salt lake and provides a useful stratigraphic marker for this area of the lake basin however it has not been matched to an eruptive edifice presumably because such an edifice was eroded by waves of lake bonneville we present data for the chemical composition of the tephra and for possible matching lavas and tephras of the region as well as grain size data for the tephra in an attempt to identify the location of the eruption matches with other tephras are negative but lavas near the coarsest ash deposits match well with the distinctive high values of tio2 and p2o5 of the ash neither chemistry nor grain size data points uniquely to a source area but an area near the northwest shore of great salt lake and within curlew valley is most likely the hansel valley ash is an example of an ash that has no direct numerical date from proximal deposits despite considerable study yet nonetheless is useful for stratigraphic studies by virtue of its known stratigraphic position and approximate age basaltic tephras commonly are not as widespread as their rhyolitic counterparts and in some cases apparently are produced by eruptive sources that are short lived and whose edifices are not persistent

the origin of ina evidence for inflated lava flows on the moon 1 ina is an enigmatic volcanic feature on the moon known for its irregularly shaped mounds the origin of which has been debated since the apollo missions three main units are observed on the floor of the depression 2 9 km across 64 m deep located at the summit of a low shield volcano irregularly shaped mounds up to 20 m tall a lower unit 1 to 5 m in relief that surrounds the mounds and blocky material analyses of lunar reconnaissance orbiter camera images and topography show that features in ina are morphologically similar to terrestrial inflated lava flows comparison of these unusual lunar mounds and possible terrestrial analogs leads us to hypothesize that features in ina were formed through lava flow inflation processes while the source of the lava remains unclear this new model suggests that as the mounds inflated breakouts along their margins served as sources for surface flows that created the lower morphologic unit over time mass wasting of both morphologic units has exposed fresh surfaces observed in the blocky unit ina is different than the terrestrial analogs presented in this study in that the lunar features formed within a depression no vent sources are observed and no cracks are observed on the mounds however lava flow inflation processes explain many of the morphologic relationships observed in ina and are proposed to be analogous with inflated lava flows on earth

basaltic volcanism in the bering sea geochronology and volcanic evolution of st paul island pribilof islands alaska abstract the evolution of a pleistocene to holocene basaltic volcanic field in the back arc region of the aleutian subduction system is investigated at st paul island alaska one of the youngest eruptive centers in the bering sea basalt province new 40ar 39ar and 14c age determinations indicate that subaerial volcanic activity forming the island began as early as 540 ka and has continued nearly to the present the youngest eruption occurred approximately 3230 years bp magmas erupted on st paul are basaltic with mgo contents ranging from 14 to 4 wt and phenocryst assemblages of olivine clinopyroxene plagioclase all are alkalic the surface of st paul is composed mainly of numerous tephra cones surrounded by coalescing low viscosity pahoehoe lava flows a central highland spans the island from east to west and is constructed of relatively young eruptive centers where rocks show a minimum of weathering and little deformation by faulting in contrast older lava flows forming the wave eroded base of the island are gently to moderately tilted and faulted geochronologic stratigraphic and geochemical data indicate that eruptive styles on st paul evolved from early mostly effusive eruptions of chemically little evolved lavas that form the base of the island to more explosive monogenetic scoria cones to polygenetic centers forming shields by repeated effusive eruptions of evolved low viscosity lavas localization of the monogenetic and polygenetic centers appears to be related to east west and northeast southwest trending fault and fissure systems with polygenetic centers located at intersections of major structures the combined volcanic and compositional changes on st paul island suggest that the magmatic system as a whole may be trending toward eruption of more evolved magmas related to the progressive development of crustal magma chambers in which crystal fractionation and magmatic differentiation are occurring

terrestrial maria the origins of large basalt plateaus hotspot tracks and spreading ridges large lava plateaus which form abruptly within plates without apparent tectonic cause appear to be the terrestrial equivalents of lunar maria deep erosion of lava plateaus reveals that their magma chambers are gabbro and granophyre complexes the classic lopoliths the close association of the deccan plateau with the timing of the terminal cretaceous boundary clay suggests that it is an impact crater large enough to cause pressure relief melting in the asthenosphere basalt then flooded the crater to form a lava lake the terrestrial equivalent of a lunar mare part of the crater rim survives in the amirante ridge the carlsberg oceanic ridge and chagos laccadive hotspot track formed simultaneously with the deccan plateau several other mesozoic and cenozoic lava plateaus are parts of similar arrays of simultaneous features one of those is the southern oregon part of the columbia plateau with its associated continental rifting in the northern basin and range and the yellowstone hotspot track along t

timing of late quaternary glaciations in the western united states based on the age of loess on the eastern snake river plain idaho the most viable sources for ubiquitous loess deposits on the eastern snake river plain idaho are aggraded river valleys active alluvial fans and fluctuating pluvial lake margins associated with regional late pleistocene glaciation of the northern rocky mountains stratigraphic studies on the idaho national engineering laboratory document two distinct loess deposits separated by a well developed paleosol resting on basaltic lava baked sediments beneath this lava yielded thermoluminescence tl age estimates of 108 000 13 000 and 101 000 7000 yr and baked organic matter gave radiocarbon ages of 32 000 yr b p consistent with an earlier k ar age for the flow of 95 000 25 000 yr the overlying two loess deposits yielded tl age estimates of 74 000 6000 and 28 000 3000 yr the available geochronology indicates that the latest period of loess deposition commenced ca 40 000 to 35 000 yr ago and ceased approximately 10 000 yr ago which is generally coincident with the inferred timing of regional pinedale glaciation and pluvial lake expansion we estimate that the penultimate loess depositional episode dates between 80 000 and 60 000 yr ago which is significantly younger than previous age estimates of 140 000 to 150 000 yr based on stratigraphic position we speculate that this period of loess deposition may correlate with documented early to middle wisconsinan glaciation and a high stand of pluvial lakes in the basin and range province

contemporary seismicity in the eastern snake river plain idaho based on microearthquake monitoring microearthquake monitoring by a permanent network operated since 1971 and two recent temporary surveys performed by the idaho national engineering laboratory suggest that infrequent small magnitude earthquakes are characteristic of eastern snake river plain esrp seismicity although a total of only 19 earthquakes have been observed to date and not all have well constrained focal depths their relatively shallow occurrence at depths of 8 km is consistent with the hypothesis that elevated crustal temperatures in the esrp confine the brittle portion of the crust and hence seismogenesis to the upper 6 to 10 km a composite focal mechanism of two microearthquakes located near the axis of the esrp indicates normal faulting with a minor component of strike slip motion the northeast southwest trending t axis indicated by this composite mechanism is consistent with the direction of extension indicated by holocene volcanic rift zones within the esrp and normal faults in the adjacent basin and range province to the northwest based on this low level of small magnitude seismicity deviatoric stresses appear to be small in the esrp

duration of eruption at the giant crater lava field medicine lake volcano california based on paleomagnetic secular variation nearly 500 cores were collected from the postglacial giant crater lava field on the south flank of medicine lake volcano the basaltic lavas form a continuous set of lava flows which display strong chemical zonation from initially erupted calc alkaline basaltic andesite to final primitive basalt of tholeiitic affinity six chemical stratigraphic groups have been recognized and mapped the eruptive sequence was sampled at numerous sites both to determine the characteristic paleomagnetic direction of each chemical group and to estimate the duration of the eruption inferred from secular variation of the geomagnetic field well grouped mean directions of magnetization were obtained for 41 sites in the giant crater lava field mean directions of magnetization determined for the lava field are nearly identical the likelihood of any extended time interval for the eruption of the different lava types is extremely small and the data suggest an eruptive event of less than 30 years duration analogous to historic hawaiian eruptions however the average of groups 1 4 which cannot be distinguished paleomagnetically from each other is slightly different statistically from that of the average of groups 5 and 6 which have similar directions a time gap of 10 5 years is inferred between eruption of group 4 and 5 lavas based on analysis of the probability of the observed angular difference of 1 27 0 84 between their mean directions and by comparison of this angular difference to calculated field directions with similar declination and inclination determined from spherical harmonic models of the geomagnetic field for the time period 1945 1990 about 200 oriented cores were also collected from predecessor and successor basaltic lava flows on the upper flanks of the volcano together with remanent directions from lavas of the snake river plain the data define a clockwise loop of secular variation

spatial distribution of high frequency energy radiation on the fault of the 1995 hyogo ken nanbu japan earthquake mw 6 9 on the basis of the seismogram envelope inversion abstract we studied the generation and propagation of high frequency above 1 hz s wave energy from the 1995 hyogo ken nanbu kobe japan earthquake m w 6 9 by analyzing seismogram envelopes of the mainshock and aftershocks we first investigated the propagation characteristics of high frequency s wave energy in the heterogeneous lithosphere around the source region by applying the multiple lapse time window analysis method to aftershock records we estimated two parameters that quantitatively characterize the heterogeneity of the medium the total scattering coefficient and the intrinsic absorption of the medium for s waves observed envelopes of aftershocks were well reproduced by the envelope green functions synthesized based on the radiative transfer theory with the obtained parameters next we applied the envelope inversion method to 13 strong motion records of the mainshock we divided the mainshock fault plane of 49 21 km into 21 subfaults of 7 7 km square and estimated the spatial distribution of the high frequency energy radiation on that plane the average constant rupture velocity and the duration of energy radiation for each subfault were determined by grid searching to be 3 0 km sec and 5 0 sec respectively energy radiated from the whole fault plane was estimated as 4 9 10 14 j for 1 to 2 hz 3 3 10 14 j for 2 to 4 hz 1 5 10 14 j for 4 to 8 hz 8 9 10 12 j for 8 to 16 hz and 9 8 10 14 j in all four frequency bands we found that strong energy was mainly radiated from three regions on the mainshock fault plane around the initial rupture point near the surface at awaji island and a shallow portion beneath kobe we interpret that energetic portions were associated with rupture acceleration a fault surface break and rupture termination respectively

last glacial loess in the conterminous usa the conterminous united states contains an extensive and generally well studied record of last glacial loess the loess occurs in diverse physiographic provinces and under a wide range of climatic and ecological conditions both glacial and non glacial loess sources are present and many properties of the loess vary systematically with distance from loess sources united states midcontinent last glacial loess is probably the thickest in the world and our calculated mass accumulation rates mars are as high as 17 500 g m 2 yr at the bignell hill locality in nebraska and many near source localities have mars greater than 1500 g m 2 yr these mars are high relative to rates calculated in other loess provinces around the world recent models of last glacial dust sources fail to predict the extent and magnitude of dust flux from the mid continent of the united states a better understanding of linkages between climate ice sheet behaviour routing of glacial meltwater land surface processes beyond the ice margin and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region r 2003 elsevier ltd all rights reserved

investigating physical and thermal interactions between lava and trees the case of kīlauea s july 1974 flow to examine whether there was any physical or thermal interaction between trees and lava when a lava flow inundates a forest we studied the k lauea s july 1974 lava flow we mapped the location of 600 lava trees and the lava type p hoehoe versus a and sampled an additional ten lava trees for chemical and textural analysis to infer flow viscosity and dynamics the emplacement event lasted 3 5 h and markers on the outer surface of the lava trees allowed us to define initial high effusion rate and velocity 400 m3 s and 5 10 m s that then declined to 9 m3 s and 4 m s during a waning phase we find that lava passing through the forest underwent an initial cooling rate of 4 c km which increased to 10 c km late in the eruption this is no different to cooling rates recorded at k lauea for tree free cases there thus appears to be no effect on cooling for this case the lava trees did though form a network of vertical cylinder obstacles and evidence for local diversion of flow lines are noticed however this varies with lava type as almost no lava trees form in a we find a relation between the percentage of a and the number of lava trees per hectare the p hoehoe a transition for this flow occurs at a viscosity of 103 pa s and this appears to be a threshold below which lava trees can form so as to behave as a network of obstacles and above which they cannot

the snake river plain idaho representative of a new category of volcanism studies of the volcanic geology of the snake river plain idaho and comparison with other basaltic regions suggest a new category of volcanic activity termed basaltic plains volcanism typified by the snake river plain this style of volcanism is intermediate between basaltic flood or plateau eruptions and hawaiian volcanism characteristics that are common to both hawaiian and plains volcanism are multiple lava flow units which erupt primarily from point sources formation of low shields and frequent emplacement through lava tubes or channels characteristics that are common to both flood basalts and plains volcanism are high volume flows vents aligned along rift zones and planar surfaces the recognition of plains volcanism in other areas provides a means to interpret the style of eruption and volcanic history

a new interpretation of deformation rates in the snake river plain and adjacent basin and range regions based on gps measurements we evaluate horizontal global positioning system gps velocities together with geologic volcanic and seismic data to interpret extension shear and contraction within the snake river plain and the northern basin and range province u s a we estimate horizontal surface velocities using gps data collected at 385 sites from 1994 to 2009 and present an updated velocity field within the stable north american reference frame snarf our results show an ene oriented extensional strain rate of 5 9 0 7 x 10 sup 9 yr sup 1 in the centennial tectonic belt and an e oriented extensional strain rate of 6 2 0 3 x 10 sup 9 yr sup 1 in the intermountain seismic belt combined with the northern great basin these extensional strain rates contrast with the regional north south contraction of 2 6 1 1 x 10 sup 9 yr sup 1 calculated in the snake river plain and owyhee oregon plateau over a 125 x 650 km region tests that include dike opening reveal that rapid extension by dike intrusion in volcanic rift zones does not occur in the snake river plain at present this slow internal deformation in the snake river plain is in contrast to the rapidly extending adjacent basin and range provinces and implies shear along boundaries of the snakemore river plain we estimate right lateral shear with slip rates of 0 5 1 5 mm yr along the northwestern boundary adjacent to the centennial tectonic belt and left lateral oblique extension with slip rates of 10 sup 6 yrs the low strain field in the snake river plain and owyhee oregon plateau would extend through the quaternary less

a reevaluation of cosmogenic 36cl production rates in terrestrial rocks we have measured 36cl in a suite of 33 rock samples having well constrained exposure histories and ages the 36cl production parameters were estimated by minimizing the squared deviations between the 36cl and independent ages yielding the following production parameters spallation and muon production from ca 2940 200 atoms 36cl mole ca 1 yr 1 spallation from k 6020 400 atoms 36cl mole k 1 yr 1 and neutron production in air 586 40 fast neutrons g air 1 yr 1 the new production constants for spallation on ca and thermal neutron activation are in good agreement with previous results but that for spallation on k is about 50 larger the past decade has seen a rapid growth in the application of terrestrial cosmogenic nuclides produced by cosmic ray particles within rocks at the earth surface nuclear cross sections particularly for reactions initiated by neutrons and muons are not known with sufficient accuracy so production rates for these nuclides must be empirically calibrated using independently dated geological samples direct production estimates for 36cl were first obtained by zreda et al 1991 who measured 36c1 in mineral separates from granitic boulders on moraine crests at chiatovitch creek in the eastern white mountains of california and nevada this data set was the best available at the time but since then several factors have prompted a reevaluation of the 36cl production rates one is that zreda et al 1994 have shown that there can be significant scatter of the cosmogenic ages of individual glacial boulders toward ages younger than that of the moraine due to soil erosion a second factor is that a much wider range of samples is now available for this purpose finally recent theoretical advances in calculating production by thermal neutron absorption liu et al 1994 now permit more realistic calibration of this reaction

seismicity of the eastern snake river plain region idaho prior to the borah peak idaho earthquake october 1972 october 1983 abstract in december 1971 the idaho national engineering laboratory deployed a network of short period high gain vertical seismographs to monitor earthquake activity within a designated study area 43 0 to 44 5 n 111 5 to 114 0 w centered on the eastern snake river plain in the 11 yr prior to the 28 october 1983 borah peak idaho earthquake there were 102 events located within the study area with a duration magnitude m range of 0 7 m 3 2 three microearthquakes m 1 were detected on the eastern snake river plain seventy five microearthquakes were located northwest of the eastern snake river plain primarily in the birch creek valley beaverhead mountains region during the 11 yr period that the idaho national engineering laboratory seismograph stations have been active there were only two events located inside the study area within 35 km of the epicenter of the borah peak idaho earthquake in the 2 6 yr prior to the borah peak idaho earthquake there were no foreshocks with magnitudes 1 observed within a 20 km radius of the epicenter future large earthquakes in the lost river range lemhi range and segments of the beaverhead mountains may also occur without significant foreshock activity

a holocene paleosecular variation record from 14c dated volcanic rocks in western north america 1 a paleosecular variation psv curve for western north america is presented on the basis of 94 virtual geomagnetic poles vgps from dated volcanic rocks sampled at 446 sites approximately 60 of the paleomagnetic database has been previously published a curve defined by spherical smoothed splines is fitted to the vgps ranked by the quality of the age determinations where the data density is highest between 3690 and 30 years before present b p a d 1950 between 7800 and 7050 years b p and between 14 060 and 12 700 years b p the younger segments of the curve derived from volcanic rocks are similar but less complex than other high resolution psv curves derived from lacustrine sediments particularly the record at fish lake oregon the psv record from lava flows psvl however is perhaps more reliable in its general shape and chronology because of the higher fidelity of volcanic rocks as magnetic field recorders and because of the greater density of 14c dates the new psvl record provides a partial holocene master curve for western north america and will be of particular value in dating geological and archeological materials using paleomagnetic directions