dynamic landscapes and human dispersal patterns tectonics coastlines and the reconstruction of human habitats studies of the impact of physical environment on human evolution usually focus on climate as the main external forcing agent of evolutionary and cultural change in this paper we focus on changes in the physical character of the landscape driven by geophysical processes as an equally potent factor most of the landscapes where finds of early human fossils and artefacts are concentrated are ones that have been subjected to high levels of geological instability either because of especially active tectonic processes associated with faulting and volcanic activity or because of proximity to coastlines subject to dramatic changes of geographical position and physical character by changes of relative sea level these processes can have both beneficial effects creating ecologically attractive conditions for human settlement and deleterious or disruptive ones creating barriers to movement disruption of ecological conditions or hazards to survival both positive and negative factors can have powerful selective effects on human behaviour and patterns of settlement and dispersal we consider both these aspects of the interaction develop a framework for the reconstruction and comparison of landscapes and landscape change at a variety of scales and illustrate this with selected examples drawn from africa and arabia

an integrated lightweight ice penetrating radar system we describe a portable low frequency impulse radar system intended for ground based surveys that employs off the shelf hardware integrated with custom designed software the hardware comprises a 1 200 mhz transmitter digitizer computer and gps receiver which together weigh 1 5 kg the entire system including waterproof enclosures and batteries suited for 8 hours of continuous operation weighs 10 kg plus the weight of the antenna housing the system design is flexible permitting hardware components such as the digitizer or navigation device to be exchanged the software includes acquisition parameter control real time visual ice depth rendering and data management capabilities using a hierarchical data format the system described here has been successfully used to sound polythermal ice up to 220 m thick in ski based surveys in the yukon canada and temperate ice up to 550 m thick in machine based surveys in iceland

spatial variation of radar derived basal conditions on kamb ice stream west antarctica radar profiles of bed echo intensity can survey conditions at the ice bed interface and test for the presence or absence of water however extracting information about basal conditions from bed echo intensities requires an estimate of the attenuation loss through the ice we used the relationship between bed echo intensities from constant offset radar data and ice thickness to estimate depth averaged attenuation rates at several locations on and near kamb ice stream kis west antarctica we found values varying from 29 db km 1 at siple dome to 15 db km 1 in the main trunk region of kis in agreement with a previous measurement and models using these attenuation rate values we calculated the relative bed reflectivity throughout our kis surveys and found that most of the bed in the trunk has high basal reflectivities similar to those obtained in the location of boreholes that found water at the bed areas of lower bed reflectivity are limited to the sticky spot where a borehole found a dry bed and along the margins of kis these results support previous hypotheses that the basal conditions at locations like the sticky spot on kis control its stagnation and possible reactivation

modeling cultural responses to volcanic disaster in the ancient jama coaque tradition coastal ecuador a case study in cultural collapse and social resilience the cultural impacts of catastrophic late pleistocene and holocene volcanism are characteristically variable throughout the world due to a wide range of factors such as magnitude of the eruptive event proximity to the eruption the geographic and ecological settings of the eruptive footprint and relative social and political complexity of the societies affected the reasons why one society succumbs to a volcanic disaster while another may recover are complex and not subject to invariant laws likewise even in cases where recovery is possible different pathways may be followed depending on a host of contingent factors in archaeological cases it is sometimes difficult to distinguish between cultural developments that may be caused by volcanic disasters and those that are merely coincidental with these events but not all volcanic eruptions lead to cultural collapse archaeological research in the jama valley of coastal ecuador has revealed evidence of three volcanic eruptions emanating from the northern ecuadorian highlands some 200 km to the east all three of which represent major stratigraphic breaks in the regional archaeological record the third of these volcanic events now thought to have occurred at 90 ad significantly affected the muchique phase 1 chiefdoms of the jama coaque tradition that occupied much of northern manabi province and like the first two eruptive events in the formative period that led to centuries long valley abandonment this eruption also resulted in valley abandonment for several centuries but it also ushered in a new ceramic phase muchique phase 2 of the jama coaque tradition and a notable change in settlement hierarchy ceramic figural sculpture evidence for warfare agricultural intensification and diversification surplus storage facilities and new forms of political complexity and chiefly authority this paper offers a model of differential human response to catastrophic volcanism that focuses attention on human resource imbalances resulting from such events and identifies a series of contingent circumstances in which complex chiefdoms may cope and even flourish in the aftermath of disaster

some comparisons between mining induced and laboratory earthquakes although laboratory stick slip friction experiments have long been regarded as analogs to natural crustal earthquakes the potential use of laboratory results for understanding the earthquake source mechanism has not been fully exploited because of essential difficulties in relating seismographic data to measurements made in the controlled laboratory environment mining induced earthquakes however provide a means of calibrating the seismic data in terms of laboratory results because in contrast to natural earthquakes the causative forces as well as the hypocentral conditions are known a comparison of stick slip friction events in a large granite sample with mining induced earthquakes in south africa and canada indicates both similarities and differences between the two phenomena the physics of unstable fault slip appears to be largely the same for both types of events for example both laboratory and mining induced earthquakes have very low seismic efficiencies eta tau a bar tau where a is the apparent stress and bar tau is the average stress acting on the fault plane to cause slip nearly all of the energy released by faulting is consumed in overcoming friction in more detail the mining induced earthquakes differ from the laboratory events in the behavior of as a function of seismic momentm0 whereas for the laboratory events 0 06 independent ofm0 depends quite strongly onm0 for each set of induced earthquakes with 0 06 serving apparently as an upper bound it seems most likely that this observed scaling difference is due to variations in slip distribution over the fault plane in the laboratory a stick slip event entails homogeneous slip over a fault of fixed area for each set of induced earthquakes the fault area appears to be approximately fixed but the slip is inhomogeneous due presumably to barriers zones of no slip distributed over the fault plane at constant bar tau larger events correspond to larger a as a consequence of fewer barriers to slip if the inequality a bar tau 0 06 has general validity then measurements of a ea m0 where is the modulus of rigidity andea is the seismically radiated energy can be used to infer the absolute level of deviatoric stress at the hypocenter

full depth englacial vertical ice sheet velocities measured using phase sensitive radar we describe a geophysical technique to measure englacial vertical velocities through to the beds of ice sheets without the need for borehole drilling using a ground based phase sensitive radio echo sounder pres during seven antarctic field seasons we measure the temporal changes in the position of englacial reflectors within ice divides up to 900 m thick on berkner island roosevelt island fletcher promontory and adelaide island recorded changes in reflector positions yield full depth profiles of vertical ice velocity that we use to examine spatial variations in ice flow near the divides we interpret these variations by comparing them to the results of a full stokes simulation of ice divide flow qualitatively validating the model and demonstrating that we are directly detecting an ice dynamical phenomenon called the raymond effect using pres englacial vertical ice velocities can be measured in higher spatial resolution than is possible using instruments installed within the ice we discuss how these measurements could be used with inverse methods to measure ice rheology and to improve ice core dating by incorporating pres measured vertical velocities into age modeling

a single southern exit of modern humans from africa before or after toba abstract during the late pleistocene anatomically modern humans amh dispersed out of africa they first spread north with game across the sahara to the levant during the eemian interglacial c 125 ka and there is some recent evidence they may also have spread via arabia to the far east at the same time however they failed to continue to europe then occupied by neanderthals the sahara and arabia then reverted to aridity and amh vanished from the fossil record after 92 ka being later replaced in the levant again by neanderthals there is recent fragmentary evidence amh may also have spread via arabia to the far east but the archaeological record fades similarly long before the toba eruption there is no evidence of surviving non african dna lineages dating from anywhere near the eemian to contradict this narrative genetic evidence indicates that amh successfully left africa much later as a single group by the southern route to india since all non african uniparental lineages date to this later exit this appears to have been the only ultimately successful amh exit amh reached the isolated sahul continent at least by 48 ka and possibly by 60 50 ka amh only finally arrived in europe from south asia before 46 ka probably linked to climatic amelioration during mis 3 dating the definitive exit without adequate fossil evidence relies on disputed genetic dates with wide confidence intervals at the top end independent genetic dates combined with ash associated data from malaysia and from india argue for a pre toba exit although the consensus view is still largely post toba recent correction for non linearity due to purifying selection and recalibration of the mtdna clock has improved confidence in genetic dating but reduced the age of the main exit lineage l3 which effectively embodies its maximum estimate to just below that of toba 71 6 ka although relevant 95 confidence intervals ci 57 1 86 6 ka still include the toba event this weakening of the genetic argument puts more pressure on the archaeological evidence associated with toba ash and the need for diagnostic well dated fossil data between 90 70 ka

radio echo sounding studies of englacial water movement in variegated glacier alaska une crue glaciaire du variegated a ete enregistree a l aide d un emetteur mono impulsion de 3mhz les discontinuites intraglaciaires ont ete observees dans le domaine des 12 a 30 mhz les changements dans la forme des echos sont interpretes en terme de redistribution de l eau dans les canaux glaciaires et les cavites reliees au lit a quelque distance a l aval

precise measurement of changes in ice shelf thickness by phase sensitive radar to determine basal melt rates 1 we describe a novel technique for measuring the basal melt rate at a point on an ice shelf the method uses a phase sensitive radar to observe the change in thickness of the ice column between an upper reference horizon and the ice shelf base the observed thickness change is a combination of basal melting horizontal ice divergence and firn compaction the latter two components are determined independently by the repeat survey of surface markers and from estimates of surface accumulation rate and density at the depth of the reference horizon the technique has been applied at a site on george vi ice shelf antarctica where a melt rate of 2 78 0 08 m yr 1 was observed over a twelve day period our technique is applicable to almost any ice shelf or floating glacier tongue and its high precision over short time intervals will permit the measurement of seasonal variations in melt rate

recent volume and area changes of kaskawulsh glacier yukon canada recent surface elevation changes of kaskawulsh glacier yukon canada are quantified by comparing an air photo derived dem from 1977 and airborne lidar measurements from 1995 2000 and 2007 surface area changes are assessed using historical aerial photography from 1956 and satellite imagery from 1977 to 2007 combined these measurements provide some of the first detailed records of volume change of a large yukon glacier between 1977 and 2007 kaskawulsh glacier underwent a decrease in area of 1 53 and a decrease in volume of 3 27 5 94 km 3 w e the terminus also retreated by 655 m over the period 1956 2007 there was relatively minor volume change over the period 1977 95 0 01 km 3 w e a 1 while over the periods 1995 2000 and 2000 07 volume losses occurred at a relatively constant rate of 0 51 and 0 50 km 3 a 1 w e respectively since 1995 thinning has been prominent throughout the ablation zone while relative stability and even slight thickening has occurred in the accumulation zone these findings are similar to those recently observed at other nearby alaskan glaciers

high resolution hydrothermal structure of hansbreen spitsbergen mapped by ground penetrating radar detailed ground penetrating radar gpr surveys at 50 and 200 mhz on hansbreen a polythermal glacier in southern svalbard are presented and interpreted comparison of the variations in character of the radar reflections with borehole thermometry and water levels in moulins suggests that gpr can be used to study the hydrothermal properties of the glacier the high resolution of the gpr data shows that the hydrothermal structure of the glacier is highly variable both along the centre line and on transverse profiles water contents for many places and depths within the glacier were calculated by estimating radar wave velocities to point reflectors we find typical water contents of 1 2 for the temperate ice but wetter ice associated with surface crevassing and moulins typically 4 water content there is evidence that wet ice sometimes overlays drier ice the hydrothermal structure is thus shown to be very complex temperature gradients in the cold ice indicate freezing rates of temperate ice below cold ice of 0 1 0 5 m a while isolated point reflectors within the cold ice indicate large water filled bodies that are probably related to the regular drainage structure of the glacier

geochemical sources for the terminal pleistocene early holocene obsidian artifacts of the site of beseka central ethiopia twenty obsidian artifacts from the terminal pleistocene early holocene phase of the site of beseka central ethiopia have been instrumentally characterized using edxrf and electron microprobe results show that most of the artifacts were derived from the silicic centers of fentale and kone a nearby source of abadir although with better quality raw material does not seem to have been utilized

a stationary impulse radar system for autonomous deployment in cold and temperate environments l mingo acknowledges the sr ed tax incentive program of the cra for offsetting some r d costs of the sipr g flowers and d bigelow are grateful to nserc cfi csa nstp pcsp and sfu for funding kluane first nation yukon government and parks canada for access to yukon field sites and s williams l goodwin a pulwicki j crompton f beaud and canadian astronaut d saint jacques for support and field assistance c schoof and c rada provided time lapse imagery and 2017 water pressure data a crawford and d mueller acknowledge funding from nserc transport canada pkc nstp and the garfield weston foundation as well as support from arctic net the ccgs amundsen crew and pilots o talbot a roy and g carpentier

probabilistic seismic hazard assessment for eritrea to date little is known about seismic hazard in eritrea despite its location in a volcanically and tectonically active region and the gathering pace of major infrastructure projects in response we report the findings of a comprehensive probabilistic seismic hazard assessment for eritrea and adjacent areas seismic source and ground motion models are constructed separately we use an adaptive spatiotemporal smoothing method to map expected patterns of seismicity to construct a consistent earthquake catalog from different data sets we use orthogonal regression to convert and unify different magnitude scales a sensitivity analysis of the different input parameters helps constrain them and disaggregation of site specific hazard estimates yields insights into the relative contribution from seismic sources of different magnitudes and distances the results highlight seismic hazard in proximity to the red sea gulf of aden afar depression and along the boundaries of the danakil microplate we estimate a 10 chance over 50 years of observing pseudospectral accelerations psas at 0 2 s exceeding 0 16g in the port city of massawa population 32 000 and the town of bada population 4000 for the capital asmara population 520 000 we calculate a psa of 0 11g at 0 2 s compared with previous studies our results provide greater spatial resolution use more recent ground motion models and benefit from a smoothed seismicity method our aims are to stimulate further studies and contribute to the safe development of the region in light of its exposure to seismic hazards

in situquantification of ice rheology and direct measurement of the raymond effect at summit greenland using a phase sensitive radar 1 the glen exponent ncharacterizes the stress dependence of ice deformation directly influencing the rate at which ice masses respond to external forcing the slow deformation in large ice sheets makes laboratory rheometry at representative strain rates difficult we develop a new technique to estimaten in situ deploying a phase sensitive radar to measure vertical strain rates of around 10 4 yr 1within the top 1000 m of ice across ice divides at summit and neem greenland a fluid dynamical feature the raymond effect predicts strong vertical strain rate variation across divides over distances of a few ice thicknesses we achieve sufficient resolution to show this pattern enabling us to estimaten 4 5 by inverting our observations with flow modelling this is higher than values previously used but consistent with other indirect measurements implying laboratory measurements do not explore the full range of ice rheology and the consequent possibility of a greater sensitivity and responsiveness in ice sheet dynamics

largest known historical eruption in africa dubbi volcano eritrea 1861 dubbi volcano located in the northeast part of the afar triangle erupted explosively in may 1861 showering maritime traffic in the red sea with pumice and plunging coastal settlements into darkness earthquakes associated with the opening phase of the eruption were felt in yemen and explosions were heard as far as massawa 330 km distant more than 100 local inhabitants were reported killed possibly as a result of pyroclastic flow emplacement by october 1861 activity switched to basaltic fire fountaining focused along a 4 km long summit fissure that fed several lava flows that traveled as far as 22 km we present a reconstruction of this unusual explosive and effusive eruption sequence based on interpretation of contemporary accounts analysis of satellite imagery field work and laboratory geochemistry the volume of lava flows alone 3 5 km3 makes this the largest reported historical eruption in africa an anomalously cold northern hemisphere summer in 1862 recorded in tree ring records could be the result of dubbi s sulfate aerosol veil

obsidian sources in highland yemen and their relevance to archaeological research in the red sea region the red sea and surrounding area formed through dynamic uplift and rifting of afro arabia and associated volcanism both oceanic and continental in character as a result volcanic landforms and products are widespread and play a vital role in the natural and cultural landscapes of humans occupying the highlands and lowlands on both sides of the red sea archaeologists have suggested for some time that afro arabian trade in obsidian had its roots in the prehistoric period and that the region was very likely the source of an abundance of obsidian artefacts found as far afield as egypt the persian gulf and mesopotamia and which do not match the well known anatolian transcaucasian or mediterranean sources nonetheless the southern red sea is one of the few obsidian rich regions exploited in antiquity that has been barely investigated in this paper we highlight new geochemical analyses carried out by la icp ms of obsidian sources in southern arabia and beyond that enhance our knowledge of obsidian exploitation from as early as the neolithic period and which enable us to evaluate the role that highland yemen obsidian sources played in prehistoric long distance trade in addition we present new evidence for explosive volcanic eruptions that likely affected the highland populations of yemen in the 4th millennium bc

a ground based radar for measuring vertical strain rates and time varying basal melt rates in ice sheets and shelves the apres autonomous phase sensitive radio echo sounder instrument is a robust lightweight and relatively inexpensive radar that has been designed to allow long term unattended monitoring of ice shelf and ice sheet thinning we describe the instrument and demonstrate its capabilities and limitations by presenting results from three trial campaigns conducted in different antarctic settings two campaigns were ice sheet based pine island glacier and dome c and one was conducted on the ross ice shelf the ice shelf site demonstrates the ability of the instrument to collect a time series of basal melt rates the two grounded ice applications show the potential to recover profiles of vertical strain rate and also demonstrate some of the limitations of the present system

temporal englacial water content variability associated with a rapidly retreating glacier this study uses a combination of evidence from ground penetrating radar borehole video and wireless probe data to assess temporal changes in englacial water content associated with briksdalsbreen a rapidly retreating norwegian glacier over a 13 day period in 2006 ice radar wave velocity varied between 0 135 m ns 0 009 and 0 159 m ns 0 003 and water content from 7 8 2 6 2 8 to 2 5 0 9 1 1 derived from the looyenga physica31 3 401 406 1965 formula it is suggested that during warm precipitation free days void spaces within the glacier become filled with water resulting in low radar wave velocity this stored water then drained during cold high precipitation days allowing the radar wave velocity to rise these changes in englacial storage were caused by the enhanced crevassing generated by the newly floating ice margin and were associated with accelerated glacier retreat

human evolution in a variable environment the amplifier lakes of eastern africa abstract the development of the cenozoic east african rift system ears profoundly re shaped the landscape and significantly increased the amplitude of short term environmental response to climate variation in particular the development of amplifier lakes in rift basins after three million years ago significantly contributed to the exceptional sensitivity of east africa to climate change compared to elsewhere on the african continent amplifier lakes are characterized by tectonically formed graben morphologies in combination with an extreme contrast between high precipitation in the elevated parts of the catchment and high evaporation in the lake area such amplifier lakes respond rapidly to moderate precessional forced climate shifts and as they do so apply dramatic environmental pressure to the biosphere rift basins when either extremely dry or lake filled form important barriers for migration mixing and competition of different populations of animals and hominins amplifier lakes link long term high amplitude tectonic processes and short term environmental fluctuations east africa may have become the place where early humans evolved as a consequence of this strong link between different time scales

deformation warming and softening of greenland s ice by refreezing meltwater when basal meltwater refreezes the resulting warm ice can influence the flow dynamics of the ice sheet above an analysis of airborne gravity and radar data identifies extensive basal ice units across the northern greenland ice sheet that coincide with areas of deformed ice and fast ice flow

radar derived bed roughness characterization of institute and moller ice streams west antarctica and comparison with siple coast ice streams 1 subglacial bed conditions exert a significant control on ice stream behavior and evolution and can be characterized by determining bed roughness from fft analysis of radar imaged basal reflectors here we assess bed roughness across institute and moller ice streams west antarctica and compare our findings with bed roughness determined across the siple coast ice streams we find that variations in bed roughness are spatially organized and attribute this to the varying efficacy of subglacial erosion and deposition with rougher inland slow flowing regions largely manifesting preglacial topography and smoother downstream fast flowing regions evincing significant postglacial modification to the subglacial landscape the observed similarities between bed roughness characteristics of iis mis and the siple ice streams suggest that iis and mis are largely underlain by wet poorly consolidated sediments and may therefore be vulnerable to the types of dynamical instabilities experienced by the siple ice streams

middle stone age msa site distributions in eastern africa and their relationship to quaternary environmental change refugia and the evolution of homo sapiens this paper considers the evolution of homo sapiens in eastern africa in relation to refugia and bottlenecks around 200 ka bp at a macro scale middle stone age msa lithics site distributions and locations are analysed in relation to palaeovegetation maps of the last glacial interglacial cycle which are used as a proxy for earlier climate cycles a push and pull model is then postulated for the spread of homo sapiens out of refugia in eastern africa involving both volcanism push and habitat availability pull a date within ois 5 is suggested for this expansion to other parts of the continent and potentially further afield contrary to a frequently proposed expansion within ois 3

distortion of isochronous layers in ice revealed by ground penetrating radar in addition to measuring ice sheet thickness ground penetrating radar can be used to delineate reflections in ice sheets1 2 3 these reflections are generally accepted to result from layers of isochronous deposition of snow and can reveal much about the dynamics of the ice flow here we present ground penetrating radar data from fletcher promontory antarctica which show arches and troughs in isochronous ice layers to a depth of 100 m we demonstrate that the origin of these features can be determined by their growth with depth and many features result from local anomalies in accumulation rate which can be correlated with the ice surface slope one arch appears to be the result of a local anomaly in vertical strain rate its proximity to the ice divide width and growth with depth indicate that this arch is one of a class of features postulated by raymond4 but not previously shown to exist in the field such a feature is an indication of the nonlinear rheology of ice and requires that palaeoclimate records from ice cores extracted from the vicinity of ice divides underlain by similar features should be specifically corrected for such effects on ice flow

resolving the internal and basal geometry of ice masses using imaging phase sensitive radar the phase sensitive radio echo sounder pres is a powerful new instrument that can measure the depth of internal layers and the glacier bed to millimetre accuracy we use a stationary 16 antenna pres array on store glacier in west greenland to measure the three dimensional orientation of dipping internal reflectors extending the capabilities of pres beyond conventional depth sounding this novel technique portrays the effectiveness of pres in deriving the orientation of dipping internal layers that may complement profiles obtained through other geophysical surveying methods deriving ice vertical strain rates from changes in layer depth as measured by a sequence of pres observations assumes that the internal reflections come from vertically beneath the antenna by revealing the orientation of internal reflectors and the potential deviation from nadir of their associated reflections the use of an antenna array can correct this assumption while the array configuration was able to resolve the geometry of englacial layers the same configuration could not be used to accurately image the glacier bed here we use simulations of the performance of different array geometries to identify configurations that can be tailored to study different types of basal geometry for future deployments

derivation and analysis of a complete modern date glacier inventory for alaska and northwest canada we present a detailed complete glacier inventory for alaska and neighboring canada using multi sensor satellite data from 2000 to 2011 for each glacier we derive outlines and 51 variables including center line lengths outline types and debris cover we find 86 723 km 2 of glacier area 27 109 glaciers 0 025 km 2 similar to 12 of the global glacierized area outside ice sheets of this area 12 0 is drained by 39 marine terminating glaciers 74 km of tidewater margin and 19 3 by 148 lake and river terminating glaciers 420 km of lake river margin the overall debris cover is 11 with considerable differences among regions ranging from 1 4 in the kenai mountains to 28 in the central alaska range comparison of outlines from different sources on 2500 km 2 of glacierized area yields a total area difference of similar to 10 emphasizing the difficulties in accurately delineating debris covered glaciers assuming fully correlated systematic errors uncertainties in area reach 6 for all alaska glaciers but further analysis is needed to explore adequate error correlation scales preliminary analysis of the glacier database yields a new set of well constrained area length scaling parameters and shows good agreement between our area altitude distributions and previously established synthetic hypsometries the new glacier database will be valuable to further explore relations between glacier variables and glacier behavior

continuous profiles of electromagnetic wave velocity and water content in glaciers an example from bench glacier alaska usa we conducted two dimensional continuous multi offset georadar surveys on bench glacier south central alaska usa to measure the distribution of englacial water we acquired data with a multichannel 25 mhz radar system using transmitter receiver offsets ranging from 5 to 150 m we towed the radar system at 5 10 km h 1 with a snow machine with transmitter receiver positions established by geodetic grade kinematic differentially corrected gps nominal 0 5 m trace spacing for radar velocity analyses we employed reflection tomography in the pre stack depth migrated domain to attain an estimated 2 velocity uncertainty when averaged over three to five wavelengths we estimated water content from the velocity structure using the complex refractive index method equation and use a three phase model ice water air that accounts for compression of air bubbles as a function of depth our analysis produced laterally continuous profiles of glacier water content over several kilometers these profiles show a laterally variable stratified velocity structure with a low water content 0 0 5 shallow layer 20 30 m underlain by high water content 1 2 5 ice

risk and reward explosive eruptions and obsidian lithic resource at nabro volcano eritrea abstract despite abundant pleistocene calderas in the east african rift and afar and the significance of regional tephra horizons for archaeological and paleoenvironmental dating the entanglements of volcanoes and their eruptions with human behaviour and paleoecology have received little attention here we focus on the intertwined human and eruptive history at nabro a caldera topped volcanic massif close to the red sea littoral of eritrea nabro exemplifies the antagonism of opportunities and threats posed by a large silicic volcano active at least since the middle pleistocene and as recently as 2011 using argon isotopic measurements we establish the first chronology of key eruptive stages of nabro and neighbouring mallahle revealing a history of explosive and effusive volcanism in the middle and late pleistocene past eruptions were an important source of obsidian that was exchanged over long distances across land and sea during the neolithic we infer that the availability of high quality obsidian combined with nabro s favourable microclimate and proximity to the red sea coast likely attracted humans to this volcanic landmark since the later middle pleistocene drawing on observations of the immediate consequences of the 2011 eruption on landscape and local pastoralist communities we consider also the impacts of past volcanic cataclysms on human populations in addition to the threat to life explosive eruptions of nabro circa 130 ka and 62 ka ago would have abruptly curtailed procurement of its obsidian resource our findings suggest further attention be paid to evaluating the significance of east african volcanic landscapes eruptions and resources for understanding human behaviour in deep antiquity

multiple inflation and deflation events at kenyan volcanoes east african rift the presence or absence of magma exerts a fundamental control on the distribution of strain in continental rift zones yet the time scales of magma intrusion remain unconstrained using more than a decade of measurements from interferometric synthetic aperture radar insar we detected geodetic activity at four of the eleven central rift volcanoes in the kenyan sector of the east african rift subsidence of 2 5 cm occurred at suswa and menengai over the period 1997 2000 9 cm of uplift was recorded at longonot in 2004 2006 and 21 cm of uplift occurred at paka during 2006 2007 the deformation is episodic and no deformation was observed at these volcanoes during other time periods preceding the infl ation at paka we observed transient uplift and subsidence of a second nearby source likely associated with fl ow through a complex plumbing system the best fi tting source models for each episode include infl ation or defl ation of a horizontal penny shaped crack at a depth of 2 5 km the episodic nature of the activity its lack of correlation with seasons and the preferred source geometry are all consistent with activity in the volatile rich cap to a crystal rich magma chamber beneath each of the four volcanoes the presence of active magmatic systems beneath more than 40 of the volcanoes and the 2007 2008 explosive eruptions at nearby oldoinyo lengai volcano have implications for models of continental rifting caldera volcanoes geothermal resources and volcanic and seismic hazard in rift zones

characteristics of surge type glaciers glaciers can be divided into two classes according to their flow behavior normal relatively steady annually averaged flow rate and surge type pronounced cyclic flow variations having a typical periodicity of 10 100 years we have examined the population statistics of 2356 glaciers in the st elias mountains yukon territory canada and estimate that 151 6 4 of these glaciers are surge type to explore how various glacier attributes are associated with surging we compare the probability of surging associated with various subsets of the complete population to appropriate reference values in this way potential influences on surge tendency can be examined for the 55 drainage basins analyzed there is a pronounced spatial variation in the concentration of surge type glaciers but no obvious environmental control can be evinced within the study area the greatest concentration lies in the northern st elias mountains a region of high topographic elevation that is experiencing rapid tectonic uplift analysis of the influence of length on surge tendency reveals that long glaciers have a significantly greater probability of being surge type than short glaciers the surge probability increases monotonically from 0 61 for very short glaciers 0 1 km to 65 1 for long glaciers 10 75 km this result suggests that ice sheets and ice caps or at least portions of them should have a high probability of surging tributary glaciers have a greater tendency to surge than trunk glaciers presumably because they may themselves be surge type and may additionally participate in surges of the trunk glacier the nonrandom geographical distribution of surge type glaciers is not simply a consequence of the variation from basin to basin of the glacier length distribution surge type glaciers tend to have a higher overall elevation than normal glaciers the elevation of the highest point of the accumulation zone the elevation of the snow line and the elevation of the lowest point of the ablation zone on average exceed the corresponding elevations for normal glaciers there is no significant difference between the overall slopes of surge type and normal glaciers although there is a tendency for surge type glaciers to have greater slope in the accumulation zone and lesser slope in the ablation zone than normal glaciers although the prevalent flow direction for glaciers in the yukon data set is to the north surge type glaciers tend to flow to the east and southeast this orientation influence is probably explained by the fact that many of the longest glaciers also flow to the east and southeast

recovery lakes east antarctica radar assessment of sub glacial water extent 1 a fast flowing tributary of recovery ice stream penetrates more than 500 km into the interior of east antarctica recent satellite based studies found surface features in the onset area of this tributary that indicate a significant subglacial hydraulic system including four large smooth basins the typical surface expression of large subglacial lakes as well as eleven smaller areas over which ice sheet surface elevations rapidly changed by discharge filling of subglacial water here we present the first ice penetrating radar evidence of subglacial conditions in this area we identified a distinct ice water interface only over a limited area within the boundaries of the investigated large smooth basins previously hypothesized to be water filled lakes the radar characteristics in some areas are similar to those of a drained lake indicating that parts of the bed are wet but not a typical lake we also find evidence for discrete water bodies outside of the lake boundaries the lines of evidence indicate that the northern most two recovery lakes have recently drained

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

experimental constraints on the textures and origin of obsidian pyroclasts obsidian pyroclasts are commonly preserved in the fall deposits of explosive silicic eruptions recent work has suggested that they form by sintering of ash particles on the conduit walls above the fragmentation depth and are subsequently torn out and transported in the gas particle dispersion although the sintering hypothesis is consistent with the general vesicle textures and dissolved volatiles in obsidian pyroclasts previous sintering experiments do not capture all of the textural complexities observed in the natural pyroclasts here we design experiments in which unimodal and bimodal distributions of rhyolitic ash are sintered at temperatures and h2o pressures relevant to shallow volcanic conduits and under variable cooling rates the experiments produce dense welded obsidian that have a range of textures similar to those observed in natural pyroclasts we find that using a unimodal distribution of particles produces obsidian with evenly distributed trapped vesicles while a bimodal initial particle distribution produces obsidian with domains of poorly vesicular glass among domains of more vesicle rich glass we also find that slow cooling leads to resorption of trapped vesicles producing fully dense obsidian these broad features match those found in obsidian pyroclasts from the north mono california usa rhyolite eruption providing strong support to the hypothesis that obsidian can be produced by ash sintering above the fragmentation depth during explosive eruptions

social resilience and long term adaptation to volcanic disasters the archaeology of continuity and innovation in the willaumez peninsula papua new guinea abstract a review of archaeological research on the impacts of multiple volcanic events in the willaumez peninsula papua new guinea during the past 40 000 years demonstrates that disaster studies in archaeology would benefit from considering resilience and innovation in addition to the more common emphasis on vulnerability often glossed as collapse when analytical time frames are extended beyond the immediate environmental impacts continuity in cultural practices is often observed the long term exchange of obsidian in the willaumez peninsula may have been adaptive because the resulting social ties enabled impacted populations to find refuge with other communities in contrast a series of novelties were much less resilient a hypothetical reconstruction of cultural responses to the high magnitude w k2 volcanic event is used to illustrate how disasters can provide opportunities for innovative behavior leading to culture change

radiostratigraphy and age structure of the greenland ice sheet 2015 the authors several decades of ice penetrating radar surveys of the greenland and antarctic ice sheets have observed numerous widespread internal reflections analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections here we present a comprehensive deep radiostratigraphy of the greenland ice sheet from airborne deep ice penetrating radar data collected over greenland by the university of kansas between 1993 and 2013 to map this radiostratigraphy efficiently we developed new techniques for predicting reflection slope from the phase recorded by coherent radars when integrated along track these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing core intersecting reflections were dated using synchronized depth age relationships for six deep ice cores additional reflections were dated by matching reflections between transects and by extending reflection inferred depth age relationships using the local effective vertical strain rate the oldest reflections dating to the eemian period are found mostly in the northern part of the ice sheet within the onset regions of several fast flowing outlet glaciers and ice streams reflections typically do not conform to the bed topography disrupted radiostratigraphy is also observed in a region north of the northeast greenland ice stream that is not presently flowing rapidly dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly this radiostratigraphy provides a new constraint on the dynamics and history of the greenland ice sheet

interactions between ice and ocean observed with phase sensitive radar near an antarctic ice shelf grounding line precise measurements of basal melting have been made at a series of 14 sites lying within a few kilometres of the grounding line of the ronne ice shelf antarctica where the ice thickness ranges from 1570 to 1940 m the study was conducted over the course of 1 year and included a detailed survey of the horizontal deformation as well as phase sensitive radar measurements of the vertical displacement of both internal reflecting horizons and the ice shelf base results from the surface survey show that the long term viscous strain rate is modulated at tidal frequencies by probably elastic strains of order 10 5 per metre of tidal elevation the radar measurements show a similar modulation of the long term thinning thickening of the ice shelf with thickness oscillations up to a few centimetres in range the long term trends in ice thickness determined at points moving with the ice shelf flow are consistent with a steady state thickness profile vertical strain rates within the ice shelf were determined from the relative motion of internal reflectors at two sites the observations were sufficient to discern the effect of tidal bending about a neutral surface 60 of the way down the ice column coincident measurements of horizontal and vertical strain imply a poisson s ratio of 0 5 and this combined with the asymmetric bending gives rise to the observed oscillations in thickness at a number of sites the long term viscous strain rates were found to be a linear function of depth for an ice shelf this is an unexpected result it can be attributed to the presence of significant vertical shear stresses set up close to the grounding line where the ice is still adjusting to flotation additional vertical motion arising from firn compaction was observed within the upper layers of the ice shelf the additional motion was consistent with the assumption that firn density is a function only of the time since burial by steady surface accumulation with both spatial and temporal fluctuations in the vertical strain rate accurately quantified it was possible to estimate the vertical motion of the ice shelf base in response differences between the calculated and observed motion of the basal reflector arise because of basal melting derived melt rates at the 14 sites ranged from 0 11 0 31 to 2 51 0 10 ma 1 with a mean of 0 85 m a 1 and a standard deviation of 0 69 m a 1 and showed no signs of significant sub annual temporal variability there was no obvious global correlation with either ice thickness or distance from the grounding line although melt rates tended to decrease downstream along each of the flowlines studied previous estimates of basal melting in this region have been obtained indirectly from an assumption that the ice shelf is locally in equilibrium and have included a broad range of values only those at the lower end of the published range are consistent with the directly measured melt rates reported here

obsidian tempered pottery in the southern caucasus a new approach to obsidian as a ceramic temper this research deals with the obsidian tempered ceramics of the chalcolithic period in the southern caucasus in order to assess their viability for provenance studies samples of obsidian tempered ceramics from the site of aratashen armenia were analysed by means of laser ablation high resolution inductively coupled plasma mass spectrometry a similar procedure was applied to some experimentally fired clays tempered with the same obsidians as the archaeological samples the results of these analyses show that there are not modifications in concentration of heavy and rare earths elements in the obsidians employed as a ceramic temper consequently obsidian temper can be used for provenance studies these analyses have shown that obsidians coming from different sources were employed for ceramic tempering in some of these cases a local production of these ceramics can be suggested a new model of acquisition and use of the obsidians related to different craft activities tool knapping and ceramic production is also proposed for the site of aratashen

velocity of radio waves in glaciers as an indicator of their hydrothermal state structure and regime the results of measurements of radio wave velocities rwv by wide angle reflection war methods in the temperate abramov glacier in the alai mountain ridge and the two layered sub polar fridtjovbreen and hansbreen on svalbard using a low frequency 2 13 mhz radar are considered and discussed the experimental data obtained and the data from the literature show that the values of rwv could be a good indicator of the hydrothermal state of glaciers as such these data enable the identification of cold temperate and transitional two layered glaciers and can be used for estimation of the water content in glaciers and changes in the hydrothermal state

late stone age variability in the main ethiopian rift new data from the bulbula river ziway shala basin abstract research conducted along the bulbula river ziway shala basin main ethiopian rift has yielded archaeological assemblages that document various phases of the upper pleistocene and the early holocene the oldest period documented is dated to 34 33 000 cal bp dw1 and the second is dated to the pleistocene holocene transition between 14 000 and 11 000 cal bp b1s1 dw2s2 and dw2s1 the analysis of these assemblages and their comparison offer new perspectives on early lsa industries and on the development and diversity of partially microlithic industries at the end the pleistocene and the beginning of the holocene through the characterization of techno economic changes in the context of shifting environments and their exploitation by humans our results intend to provide new insights into human behavioral evolution on a local scale and for a time period that is currently insufficiently known this study highlights the existence of major breaks in the archaeological record of the area during mis 3 1

a new framework for estimating englacial water content and pore geometry using combined radar and seismic wave velocities 1 ice mechanical properties and hence the response of glaciers to climate change depend strongly on the presence of liquid water at ice grain boundaries the propagation velocities of radar and seismic waves are also highly sensitive to this water mixing laws typically the looyenga and riznichenko formulae have traditionally been used to quantify liquid water content within glaciers from such velocity data however it has become apparent that these mixing laws are geometrically inconsistent we present an inclusion based effective medium approximation in which we model water inclusions within solid ice two types of inclusions are used spherical inclusions to represent water in the grain junction nodes and high aspect ratio spheroidal inclusions to represent water in the grain boundary veins we apply this model to radar and seismic data from a polythermal glacier in svalbard to quantify both inclusion geometry and the unfrozen water content within the warm ice

interannual changes of the floating ice shelf of petermann gletscher north greenland from 2000 to 2012 petermann gletscher northwest greenland drains 4 of the greenland ice sheet into nares strait its floating ice shelf retreated from 81 to 48 km in length during two large calving events in 2010 and 2012 we document changes in the three dimensional ice shelf structure from 2000 to 2012 using repeated tracks of airborne laser altimetry and ice radio echo sounding icesat laser altimetry and modis visible imagery the recent ice shelf velocity measured by tracking surface features between flights in 2010 and 2011 is 1 25 km a 1 15 30 faster than estimates made before 2010 the steady state along flow ice divergence represents 6 3 gt a 1 mass loss through basal melting 5 gt a 1 and surface melting and sublimation 1 0 gt a 1 airborne laser altimeter data reveal thinning both along a thin central channel and on the thicker ambient ice shelf from 2007 to 2010 the ice shelf thinned by 5 m a 1 which represents a non steady mass loss of 4 1 gt a 1 we suggest that thinning in the basal channels structurally weakened the ice shelf and may have played a role in the recent calving events

automated monitoring of subglacial hydrological processes with ground penetrating radar gpr at high temporal resolution scope and potential pitfalls kulessa b a d booth a hobbs and a l hubbard 2008 automated monitoring of subglacial hydrological processes with ground penetrating radar gpr at high temporal resolution scope and potential pitfalls geophysical research letters 35 24 l24502

the great arc of dispersal of modern humans africa to australia abstract during the late pleistocene anatomically modern humans amh dispersed out of africa across the continents their routes obeyed the limitations placed on any large terrestrial mammal dependent on daily drinking water following certain climate permissive corridors amh first spread north with game across the sahara to the levant during the eemian interglacial c 125 ka but failed to continue to europe then occupied by neanderthals the savannah ecosystem in north africa and the middle east then dried up and amh vanished from the levantine fossil record being replaced there by neanderthals later amh successfully left africa as a single group by the southern route to india the added ability to make short but deliberate open water crossings allowed them first to cross the mouth of the red sea from eritrea and subsequently wallace s line to reach the isolated sahul continent at least by 48 000 years ago and possibly by 60 50 000 years ago they only finally arrived in europe from south asia around 45 50 000 years ago probably linked to climatic amelioration during ois 3

re evaluating the resource potential of lomas fog oasis environments for preceramic hunter gatherers under past enso modes on the south coast of peru lomas ephemeral seasonal oases sustained by ocean fogs were critical to ancient human ecology on the desert pacific coast of peru one of humanity s few independent hearths of agriculture and pristine civilisation the role of climate change since the late pleistocene in determining productivity and extent of past lomas ecosystems has been much debated here we reassess the resource potential of the poorly studied lomas of the south coast of peru during the long middle pre ceramic period c 8000 4500 bp a period critical in the transition to agriculture the onset of modern el nino southern oscillation enso conditions and eustatic sea level rise and stabilisation and beach progradation our method combines vegetation survey and herbarium collection with archaeological survey and excavation to make inferences about both preceramic hunter gatherer ecology and the changed palaeoenvironments in which it took place our analysis of newly discovered archaeological sites and their resource context show how lomas formations defined human ecology until the end of the middle preceramic period thereby corroborating recent reconstructions of enso history based on other data together these suggest that a five millennia period of significantly colder seas on the south coast induced conditions of abundance and seasonal predictability in lomas and maritime ecosystems that enabled middle preceramic hunter gatherers to reduce mobility by settling in strategic locations at the confluence of multiple eco zones at the river estuaries here the foundations of agriculture lay in a broad spectrum revolution that unfolded not through population pressure in deteriorating environments but rather as an outcome of resource abundance

short pulse radar wavelet recovery and resolution of dielectric contrasts within englacial and basal ice of matanuska glacier alaska u s a wavelets transmitted by short pulse radar are recovered from continuous profiles and used to determine interfacial dielectric contrasts within the englacial and basal ice at the terminus area of matanuska glacier alaska u s a the field studies were in the ablation region where radar horizons could at some point be identified with interfaces between clear ice and air water or basal ice and were performed in early spring before drainage fully developed the profiles usedclosely spaced antennas with bandwidths centered near 50 and 400 mhz transmitted wavelets reflected from interfaces of known dielectric contrasts are used to establish a phase reference for other events from interfaces between unknown contrasts migration and fourier transform filtering are then applied to the profiles and shown to recover these wavelets from diffractions and reflections interfacial dielectric contrasts are determined from the relative phase of the wavelets near the terminus lake some basal ice events above 8 m depth are interpreted as voids further up glacier most englacial events are interpreted as voids but deeper localized reflectors and horizons to 90 m depth and within the basal zone are interpreted as voids water or debris phase cannot be determined for the basal substrate transition reflections recommendations are made for improving the wavelet recovery process and the quality of gpr migration

spatial extent and temporal variability of greenland firn aquifers detected by ground and airborne radars we document the existence of widespread firn aquifers in an elevation range of 1200 2000 m in the high snow accumulation regions of the greenland ice sheet we use nasa operation icebridge accumulation radar data from five campaigns 2010 2014 to estimate a firn aquifer total extent of 21 900 km2 we investigate two locations in southeast greenland where repeated radar profiles allow mapping of aquifer extent and water table variations in the upper part of helheim glacier the water table rises in spring following above average summer melt showing the direct firn aquifer response to surface meltwater production changes after spring 2012 a drainage of the firn aquifer lower margin 5 km is inferred from both 750 mhz accumulation radar and 195 mhz multicoherent radar depth sounder data for 2011 2014 we use a ground penetrating radar profile located at our ridgeline field site and find a spatially stable aquifer with a water table fluctuating less than 2 5 m vertically when combining radar data with surface topography we find that the upper elevation edge of firn aquifers is located directly downstream of locally high surface slopes using a steady state 2 d groundwater flow model water is simulated to flow laterally in an unconfined aquifer topographically driven by ice sheet surface undulations until the water encounters crevasses simulations suggest that local flow cells form within the helheim aquifer allowing water to discharge in the firn at the steep to flat transitions of surface topography supported by visible imagery we infer that water drains into crevasses but its volume and rate remain unconstrained

volcanism and human prehistory in arabia abstract the cenozoic harrats lavafields of western arabia constitute one of the major volcanic areas of the world recent precise chronometric dating of volcanic rocks in harrat rahat makes it possible to outline a detailed chronology of volcanic activity likewise recent advances in archaeology have demonstrated that early humans repeatedly occupied the arabian peninsula in the pleistocene most archaeological sites in arabia correlate with phases of increased rainfall such as interglacials however we should be cautious about reducing the prehistory of arabia to simply the story of rainfall fluctuation this paper explores the impacts of volcanism on human populations in arabia as a case study of causality and scale in human environment interactions periodic environmental windows of opportunity allowed early human groups to expand into western arabia however the western highlands are also home to volcanically active areas that saw repeated eruptions in the holocene a major eruption occurred in western arabia around every 300 years and the emerging evidence for pleistocene volcanism demonstrates repeated major eruptions at the same times as early humans were occupying the area as well as offering a review of human volcanism interactions in arabian prehistory a model is proposed in which volcanic activity in western arabia may have facilitated further population dispersal as well as negative health impacts as a push factor a balanced perspective on the impacts of volcanism and associated phenomena such as earthquakes emphasises possibly positive impacts in terms of factors such as water availability and the formation of fertile volcanic soils these positive impacts may have offered pull factors and facilitated regional occupation longer than would be predicted based on climatic variables alone this framework offers not only an explanation for some of the characteristics of the arabian archaeological record but potentially offers part of the explanation for how early human populations were able to pass through the saharo arabian arid belt from our african birthplace to populate the rest of the world