control of pre rift lithospheric structure on the architecture and evolution of continental rifts insights from the main ethiopian rift east africa we investigate the along axis variations in architecture segmentation and evolution of the main ethiopian rift mer east africa and relate these characteristics to the regional geology lithospheric structure and surface processes we first illustrate significant along axis variations in basin architecture through analysis of simplified geological cross sections in different rift sectors we then integrate this information with a new analysis of ethiopian topography and hydrography to illustrate how rift architecture basin symmetry asymmetry is reflected in the margin topography and has been likely amplified by a positive feedback between tectonics flexural uplift and surface processes fluvial erosion unloading this analysis shows that 70 of the 500 km long mer is asymmetric with most of the asymmetric rift sectors being characterized by a master fault system on the eastern margin we finally relate rift architecture and segmentation to the regional geology and geophysical constraints on the lithosphere we provide strong evidence that rift architecture is controlled by the contrasting nature of the lithosphere beneath the homogeneous strong somalian plateau and the weaker more heterogeneous ethiopian plateau differences originating from the presence of pre rift zones of weakness on the ethiopian plateau and likely amplified by surface processes the data provided by this integrated analysis suggest that asymmetric rifts may directly progress to focused axial tectonic magmatic activity without transitioning into a symmetric rifting stage these observations have important implications for the asymmetry of continental rifts and conjugate passive margins worldwide

geochronology and distribution of silicic volcanic rocks of plio pleistocene age from the central sector of the main ethiopian rift abstract plio pleistocene silicic volcanoes calderas and their eruptive products are common throughout the main ethiopian rift mer a compllation of k ar and 40 ar 39 ar dating results for the central sector of the mer demonstrate that the most voluminous and widespread ignimbrites of this region are pliocene in age between 4 2 and 3 5 ma these units occur in and around 1 the awasa and wagebeta calderas 2 the guraghe and munesa escarpments where a major buried caldera is believed to occur in the adjacent rift floor 3 the addis ababa nazret area and 4 the foothills and shoulders of the northern sector of the main ethiopian rift the older units are overlain by less volumious and in most cases rift bound late pliocene and pleistocene pyroclastic rocks the pliocene ignimbrites in this area are likely to be the near source equivalents of widespread a ash fall units associated with fossil hominid deposits of the turkana and afar sedimentary basins

early mis 3 occupation of mochena borago rockshelter southwest ethiopian highlands implications for late pleistocene archaeology paleoenvironments and modern human dispersals abstract between 70 and 50 ka bp anatomically modern humans dispersed across and out of africa to eventually populate all inhabitable continents knowledge of paleoenvironments and human behavioral patterns in africa prior to and during these dispersals is crucial for understanding how and why hunter gatherers were able to adapt rapidly to the new environments they encountered however few well dated sites from this time period are known from the horn of africa one of the purported staging areas for population movements into southern arabia and asia excavations at mochena borago rockshelter situated on the western slopes of a dormant volcano where the sw ethiopian highlands meet the ethiopian rift have yielded the first securely dated archaeological sequence for later periods of the dispersal three major lithostratigraphic groups incorporating occupational episodes have yielded charcoal radiocarbon ages 53 38 ka calbp deeper deposits have been tested but remain undated archaeological assemblages consist mainly of obsidian flaked stone artifacts manufactured from small minimally prepared single to multi platform flake cores radially prepared cores are rare and blade cores are absent small unifacial to bifacial points from non radial cores dominate the earliest shaped tool assemblages and backed pieces first appear by 45 ka calbp by 43 ka calbp scrapers and backed pieces are predominant rather than points however there is little evidence for technological change other than the appearance of bipolar technology mochena borago s archaeological sequence thus cannot be neatly classified as middle stone age later stone age or transitional and calls into question some of the principles by which archaeologists have attempted to classify african toolmaking traditions

ground temperatures landforms and processes in an atlantic mountain cantabrian mountains northern spain abstract ground temperatures determine significant geomorphological processes in a wet and temperate mountain with a narrow high elevation range belt twenty five temperature data loggers were buried at a shallow depth in different locations and altitudes and at specifically cold locations at two massifs in the cantabrian mountains north spain picos de europa and fuentes carrionas this paper analyses the ground thermal regime and associated parameters e g freeze index duration and depth of freeze freeze and thaw cycles and correlates them with active geomorphological processes and landforms the thermal regime varies in accordance to the topoclimatic conditions and it was possible to determinate annual phases in function of snow cover behaviour main active processes and landforms stop their activity with a large snow cover which thermally protects the ground and in consequence avoids the freeze and thaw cycles during this period the records allow to asseverate the evidence of seasonal freeze grounds in several locations permafrost was not discover on the ground at any of the thermometers except one located at the vicinity of a relict ice patch with the help of geomorphological maps and previous works we got to establish the relation between geomorphological processes landforms snow cover and ground thermal regime

geology geochronology and rift basin development in the central sector of the main ethiopia rift based on stratigraphic relationships and k ar dating of volcanic rocks from both of the escarpments flanking plateaus and from the rift floor of the central sector of the main ethiopian rift six major volcanic episodes are recognized in the rift9s development over a time span from the late oligocene to the quaternary using the k ar data correlation of volcanic units from the six periods of activity throughout the study area forms the basis for establishing six time stratigraphic chronozones for the central sector that are related to volcanism in the ethiopian cenozoic volcanic province the oldest basalt and rhyolite flows exposed along the rift margins of the central sector are time correlative to or older than those in river canyons for example blue nile on the adjacent northwest plateau a thinned mesozoic stratigraphic sequence along the guraghe western rift margin suggests that doming may have preceded volcanism and rifting of the cenozoic by late miocene time at least by 8 3 ma and 9 7 ma the eastern and western faulted margins respectively of the rift had formed at guraghe and at agere selam as indicated by containment of flows of that age within the rift wall during eruption a paroxysm of calc alkaline ignimbrite activity produced voluminous flows nearly fully contained within the rift during the pliocene epoch the munesa crystal tuff 3 5 ma a prominent marker tuff exposed on both rift margins is present at depth in a geothermal well beneath the rift floor and indicates a minimum of 2 km of downthrow in the central sector since its eruption structural and stratigraphic relationships in the central sector indicate a two stage rift development this is characterized by an early phase late oligocene or early miocene of a series of alternating opposed half grabens along the rift with alternating polarity such as that in the present gregory and western rifts of east africa and symmetrical rifts that evolved from these grabens in late miocene or early pliocene time thus evolution from alternating half graben to a full symmetrical graben with a medially located neovolcanic zone that is bifurcated to marginal grabens in the northern part of the study area may be a fundamental part of the rifting process the study indicates that there are major petrologic and tectonic differences between the main ethiopian rift and the gregory kenyan rift

latest pleistocene and holocene river network evolution in the ethiopian lakes region abstract river network geomorphologic paleohydrologic stratigraphic and sedimentologic analyses document a dramatic reorganization of the drainage pattern in the northern part of the main ethiopian rift mer during latest pleistocene and early holocene the river network modification was induced by tectonic deformation volcanic activity and by the arid conditions connected with the last glacial maximum lgm this arid phase triggered the shrinking of a pleistocene megalake that formerly flooded large part of the main ethiopian rift the northern tributaries paleo awash and paleo mojo rivers extended following the lake shore retreat and incised the fesesa koye and cheleleka sulula hafa paleovalleys through the pleistocene deposits at the beginning of the holocene humid conditions induced a water level rise in the lacustrine basin ziway shala basin supplied from the north by the large awash mojo meki fluvial system a well exposed cross section of the cheleleka paleovalley at the confluence with the meki river and the use of paleohydrological methods allowed to infer the bankfull paleo discharge of the larger awash mojo river system tectonic events allowed the awash and mojo rivers to divert their courses to the east toward the afar depression depriving the ziway shala lacustrine basin of large volumes of water supply this and the further increase in aridity during the late holocene led to the separation of the ziway shala paleolake into the present four lakes ziway langano abjiata shala this study indicates that in the main ethiopian rift climatic changes cannot be inferred from lake level variations alone because changes in water supply are also influenced by the tectonic induced rearrangement of the fluvial drainage networks

contrasting styles of post caldera volcanism along the main ethiopian rift implications for contemporary volcanic hazards abstract the main ethiopian rift mer 7 9 n is the type example of a magma assisted continental rift the rift axis is populated with regularly spaced silicic caldera complexes and central stratovolcanoes interspersed with large fields of small mafic scoria cones the recent latest pleistocene to holocene history of volcanism in the mer is poorly known and no eruptions have occurred in the living memory of the local population assessment of contemporary volcanic hazards and associated risk is primarily based on the study of the most recent eruptive products typically those emplaced within the last 10 20 ky we integrate new and published field observations and geochemical data on tephra deposits from the main late quaternary volcanic centres in the central mer to assess contemporary volcanic hazards most central volcanoes in the mer host large mid pleistocene calderas with typical diameters of 5 15 km and associated ignimbrites of trachyte and peralkaline rhyolite composition in contrast post caldera activity at most centres comprises eruptions of peralkaline rhyolitic magmas as obsidian flows domes and pumice cones the frequency and magnitude of events varies between individual volcanoes some volcanoes have predominantly erupted obsidian lava flows in their most recent post caldera stage fentale whereas other have had up to 3 moderate scale vei 3 4 explosive eruptions per millennium aluto at some volcanoes we find evidence for multiple large explosive eruptions corbetti bora baricha boset bericha which have deposited several centimetres to metres of pumice and ash in currently densely populated regions this new overview has important implications when assessing the present day volcanic hazard in this rapidly developing region

the eruptive history and magmatic evolution of aluto volcano new insights into silicic peralkaline volcanism in the ethiopian rift the silicic peralkaline volcanoes of the east african rift are some of the least studied volcanoes on earth here we bring together new constraints from fieldwork remote sensing geochronology and geochemistry to present the first detailed account of the eruptive history of aluto a restless silicic volcano located in a densely populated section of the main ethiopian rift prior to the growth of the aluto volcanic complex before 500 ka the region was characterized by a significant period of fault development and mafic fissure eruptions the earliest volcanism at aluto built up a trachytic complex over 8 km in diameter aluto then underwent large volume ignimbrite eruptions at 316 19 ka and 306 12 ka developing a 42 km2 collapse structure after a hiatus of 250 ka a phase of post caldera volcanism initiated at 55 19 ka and the most recent eruption of aluto has a radiocarbon age of 0 40 0 05 cal ka bp during this post caldera phase highly evolved peralkaline rhyolite lavas ignimbrites and pumice fall deposits have erupted from vents across the complex geochemical modelling is consistent with rhyolite genesis from protracted fractionation 80 of basalt that is compositionally similar to rift related basalts found east of the complex based on the style and volume of recent eruptions we suggest that silicic eruptions occur at an average rate of 1 per 1000 years and that future eruptions of aluto will involve explosive emplacement of localised pumice cones and effusive obsidian coulees of volumes in the range 1 100 106 m3

volcanic vents rooted on extension fractures and their geodynamic implications in the ethiopian rift abstract most of the extension fractures located in the ethiopian rift are related to rift dynamics and they have consistently similar orientations for hundreds of kilometers the orientation of extension fracture gives the local extension direction which is perpendicular to its horns end segments of an extension fracture we have established clear geometrical relationships between tectonics and volcanism in the main ethiopian rift by interpreting high resolution images obtained from landsat tm and spot satellites and by quantitatively analyzing the geometry of extension fractures elongated vents and linear volcanic clusters applying the relationships obtained we show that extension fractures in the rift served as channels for magma rising to the surface and that extension fractures underlie most of the elongated volcanic vents and linear volcanic clusters the geometry of extension fractures beneath volcanic edifices can be deduced from the shape of elongated vents and pattern of linear volcanic clusters rooted on them utilizing the orientations of extension fractures directly observed and those inferred from elongated volcanic vents and linear clusters we found that the extension direction of the main ethiopian rift is northwest southeast and that the direction has been rotated clockwise for about 20 in the time interval 2 83 to 0 023 ma the recent axis of rift opening is oriented n40 and located closer to the southeastern escarpment giving an asymmetric geometry to the main ethiopian rift mer

soil temperatures in an atlantic high mountain environment the forcadona buried ice patch picos de europa nw spain the present study focuses on the analysis of the ground and near rock surface air thermal conditions at the forcadona glacial cirque 2227 m a s l located in the western massif of the picos de europa spain temperatures have been monitored in three distinct geomorphological and topographical sites in the forcadona area over the period 2006 11 the forcadona buried ice patch is the remnant of a little ice age glacier located in the bottom of a glacial cirque its location in a deep cirque determines abundant snow accumulation with snow cover between 8 and 12 months the presence of snow favours stable soil temperatures and geomorphic stability similarly to other cantabrian mountains the annual thermal regime of the soil is defined by two seasonal periods continuous thaw with daily oscillations and isothermal regime as well as two short transition periods however the results showed evidence of a significantly different annual thermal regime at the ground and near rock surface air relatively stable soil thermal regimes were observed at the moraine and talus sites while a more dynamic pattern was recorded at the rock wall site here a higher interannual variability in the number of freeze thaw days was also detected which showed evidence of the important role of the snow cover as a ground surface insulator in the area seasonal frost conditions are widespread today in the high lands of the massif no permafrost regime was detected in the area though mean temperatures measured at 0 5 m depth at the forcadona buried ice patch during 2006 07 0 1 c suggest that permanent negative values may be reached at deeper layers

correlation of plio pleistocene tephra in ethiopian and kenyan rift basins temporal calibration of geological features and hominid fossil records abstract the 200 m thick fossiliferous konso formation and overlying terrace deposits which crop out at the end of the southern sector of the main ethiopian rift mer contain more than 30 distal tephra layers local and regional tephra correlations of more than 20 tephra units were established using major and trace element data of discrete and purified bulk glass samples within the konso study area eleven correlative marker tuffs were recognized in stratigraphic sections of both the konso formation and the omo turkana basin sediments in southern ethiopia and northern kenya the turoha hope ivory bright white and boleshe tuffs in the konso formation and the upper white tuff in the overlying terrace deposits are securely correlated with the kbs akait lokapetamoi chari lower nariokotome and silbo tuffs of the omo turkana basin using least mobile major elements cao fe2o3 and tio2 and geochronology preliminary correlations are also suggested between the konso formation distal tephra and proximal units of the quaternary caldera forming silicic centers in the central sector of the mer the strongly peralkaline tuffs of the konso formation are compositionally similar to proximal eruptions mostly located along the quaternary axial rift zone of the southern central and northern sectors of the mer the tephra correlation provides information about the temporal and spatial features of the volcanic and tectonic processes recorded in the evolving basins thickness and sedimentation rate were determined for both the konso formation and the omo turkana basin sections measured between the turoha kbs 1 91 0 03 ma and the bright white chari 1 40 0 02 ma tuffs although the lithostratigraphic sequence at the konso study area is younger sedimentation rate within the konso formation was comparable to that of the koobi fora formation higher in the nachukui formation and lower in the shungura formation local and regional differences in thickness and sedimentation rates within the plio pleistocene deposits of the konso shungura nachukui and koobi fora formations may be attributed to erosion associated with increased topographic gradients maintained by continued subsidence mostly along axial fault zones of basins and uplift along the margins of the broadly rifted zone of the omo turkana basin and the southern sector of the mer

quaternary oblique extensional tectonics in the ethiopian rift horn of africa abstract the ethiopian rift extends in a northeasterly direction from southern ethiopia to the afar region it shows a complex fault pattern characterised by the interplay of a n30 e n40 e trending border fault system with the quaternary wonji fault belt which is constituted by right stepping en echelon n s to n20 e trending faults the wonji fault belt affects mainly the rift floor but it also overlaps with some segments of the margins its en echelon arrangement indicates a left lateral component of displacement along the rift trend the general fault pattern of the ethiopian rift as well as mesoscopic fault analyses and structural features of some key areas indicate the occurrence of a roughly e w extension which is compatible with the sinistral shear component of motion along the rift this paper proposes that oblique rifting related to the e w direction of extension has been active since the beginning of the quaternary and that it came after an earlier phase of roughly pure extension orthogonal to the rift trend

a depositional model for organic rich duvernay formation mudstones abstract the upper devonian duvernay formation of western canada is an organic rich shale formation now targeted as a hydrocarbon reservoir we present a detailed sedimentological analysis of the duvernay formation in order to better understand organic rich mudstone depositional processes and conditions and to characterize the vertical and lateral heterogeneity of mudstone lithofacies that affect petrophysical and geomechanical rock properties organic rich mudstone facies of the duvernay formation were deposited in a dynamic depositional environment by a variety of sediment transport mechanisms including suspension settling turbidity currents and bottom water currents in variably oxygenated bottom waters suspension settling dominated in distal relatively deep areas of the basin but evidence for weak turbidity currents and bottom water currents was observed in the form of graded beds and thin grain supported siltstone laminae organic enrichment primarily occurred in distal areas as a result of bottom water anoxia and low depositional rates of inorganic sediment in deep water locations near platform margins alternating silty sandy contourite beds and organic rich mudstone beds are present the former interpreted to have been deposited and reworked by bottom water currents flowing parallel to slope in shallower more oxygenated settings mudstone lithologies vary from calcareous to argillaceous these sediments were deposited from suspension settling turbidity currents and bottom water currents although primary sedimentary structures are often obscured by extensive bioturbation locally organic enrichment in dysoxic rather than anoxic bottom waters was driven by a slightly increased sedimentation rate and possibly also by aggregation of sedimentary particles in the water column due to interaction between organic matter and clay minerals large variations observed in sediment composition from siliceous to calcareous to argillaceous reflect multiple biogenic carbonate and clastic sediment sources sediment composition is influenced by basin morphology circulation patterns sea level variation and proximity to sediment sources

the dynamics of central main ethiopian rift waters evidence from δd δ18o and 87sr 86sr ratios abstract water samples from cold and geothermal boreholes hot springs lakes and rivers were analyzed for d 18o and 87sr 86sr compositions in order to investigate lake water groundwater mixing processes water rock interactions and to evaluate groundwater flow paths in the central main ethiopian rift mer of the ziway shala basin different ranges of isotopic values were recorded for different water types hot springs show 18o 3 36 to 3 69 and d 15 85 to 24 23 deep aluto langano geothermal wells show 18o 4 65 to 1 24 and d 12 39 to 9 31 groundwater wells show 18o 3 99 to 5 14 and d 19 69 to 32 27 whereas the lakes show 18o and d in the range 3 98 to 7 92 and 26 19 to 45 71 respectively the intersection of the local meteoric water line lmwl d 7 18o 11 2 r2 0 94 n 42 and the local evaporation line lel d 5 63 18o 8 n 14 r2 0 82 was used to estimate the average isotopic composition of recharge water into the basin d 5 15 and 18o 2 34 these values are depleted if compared with the modern day average precipitation presumably indicating paleo groundwater components recharged during previous humid climatic phases the measured stable isotope values indicate that the geothermal wells some of the hot springs and groundwater wells mainly consist of meteoric water the sr isotopic signatures in all waters are within the range of the sr isotopic composition of the rift basalts and rhyolites the variability of sr isotopic data also pinpoints complex water rock interaction and mixing processes in groundwater and surface water the 87sr 86sr ratio ranges from 0 70445 to 0 70756 in the hot springs from 0 70426 to 0 70537 in two deep geothermal wells and from 0 70673 to 0 70721 in the rift lakes ziway langano shala and awasa the radiogenic composition recorded by the lakes indicates that the input water was predominantly affected by progressive interaction with rhyolitic volcanics and lacustrine sediments there is a change in mer water composition between the recharge infiltration zone surrounding highlands and the discharge areas from depleted d 18o and less radiogenic sr isotope compositions to enriched d 18o and more radiogenic sr isotope compositions isotope analyses are therefore useful in providing further understanding of the hydrologeological processes occurring within a productive aquifer and the surface water system

long term soil temperature dynamics in the sierra nevada spain abstract soil temperatures play a key role on the dynamics of geomorphological processes in periglacial environments however little is known about soil thermal dynamics in periglacial environments of semiarid mid latitude mountains where seasonal frost is dominant from september 2006 to august 2012 we have monitored soil temperatures at different depths 2 10 20 50 and 100 cm in a solifluction landform located at 3005 m a s l in the summit area of the sierra nevada south spain mean annual temperatures in the first meter of the soil ranged from 3 6 to 3 9 c while the mean annual air temperature at the nearby veleta peak was 0 08 c therefore these data point out the inexistence of widespread permafrost conditions today in this massif seasonal frost controls the geomorphodynamics even in the highest lands climate conditions have shown a large interannual variability as it is characteristic in a high mountainous mediterranean environment these variations are reflected in the patterns of soil thermal dynamics the depth and duration of the frozen layer are strongly conditioned by the thickness of the snow cover the date of the first significant snowfalls conditioned the beginning and rhythm of freezing of the soil wet years resulted in a thick snow cover which insulated the ground from external climate oscillations and favored a shallow frost layer 2008 2009 2009 2010 and 2010 2011 on the other hand years with low precipitations promoted deeper freezing of the soil down to 60 70 cm extending until late may or early june 2006 2007 2007 2008 and 2011 2012 when snow melted a high increase of temperatures of 10 12 c in few weeks was recorded at all depths at this time of the year periglacial activity is enhanced due to higher water availability and the existence of freeze thaw cycles these were recorded mostly in spring and autumn in the first 50 cm depth of the soil ranging from 9 8 days at 2 cm to 3 7 days at 50 cm however the inactivity of solifluction landforms suggests that the combination of present day soil temperatures together with moisture conditions is not favorable to promote solifluction activity in the periglacial belt of the sierra nevada future climate scenarios point to a temperature increase and precipitation decrease in the area which would entail deeper but shorter frozen soil layers these conditions would not be favorable for active periglacial slope processes in the sierra nevada

hydrogeochemical study in the main ethiopian rift new insights to the source and enrichment mechanism of fluoride the central main ethiopian rift suffers a severe water quality problem characterized by an anomalously high fluoride f content that causes an endemic fluorosis disease the current study conducted in the ziway shala lakes basin indicates that the f content exceeds the permissible limit for drinking prescribed by the world health organization who 1 5 mg l in many important wells up to 20 mg l with even more extreme f concentration in hot springs and alkaline lakes up to 97 and 384 mg l respectively the groundwater and surface water from the highlands typically characterized by low total dissolved solids tds and ca mg hco3 hydrochemical facies do not show high f content the subsequent interaction of these waters with the various rocks of the rift valley induces a general increase of the tds and a variation of the chemical signature towards na hco3 compositions with a parallel enrichment of f the interacting matrixes are mainly rhyolites consisting of volcanic glass and only rare f bearing accessory minerals such as alkali amphibole comparing the abundance and the composition of the glassy groundmass with other mineral phases it appears that the former stores most of the total f budget this glassy material is extremely reactive and its weathering products i e fluvio volcano lacustrine sediments further concentrate the fluoride the interaction of these weathered reworked volcanic products with water and carbon dioxide at high ph causes the release of fluoride into the interacting water this mainly occurs by a process of base exchange softening with the neo formed clay minerals i e ca mg uptake by the aquifer matrix with release of na into the groundwater this is plausibly the main enrichment mechanism that explains the high f content of the local groundwater as evidenced by positive correlation between f ph and na and inverse correlation between f and ca mg saturation indices si have been calculated using phreeqc 2 for the different water groups highlighting that the studied waters are undersaturated in fluorite in these conditions fluoride cannot precipitate as caf2 and so mobilizes freely without forming other complexes these results have important implications for the development of new exploitation strategies and accurate planning of new drilling sites

quaternary volcano tectonic activity in the soddo region western margin of the southern main ethiopian rift 1 we present an analysis of the distribution timing and characteristics of the volcano tectonic activity on the western margin of the southern main ethiopian rift in the soddo area latitudes between 7 10 n and 6 30 n the margin is characterized by the presence of numerous normal faults with limited vertical offset and often sigmoidal in shape which accommodate a gentle transition from the rift floor to the ethiopian plateau new radiocarbon dating indicates post 30 ka fault activity pointing to a significant late pleistocene holocene tectonic activity of the soddo margin comparison of the fault architecture with analog models suggests that deformation has been controlled by a sub e w roughly n100 e extension direction resulting in an oblique extension with respect to the roughly ne sw trending rift this well accords with inversion of fault slip data collected on faults with pleistocene holocene activity and is also in good agreement with recent gps data from the southern main ethiopian rift our data support a close correlation between the recent volcanic activity and deformation in the study area with eruptive vents located along the recent border faults the axial tectono magmatic activity is subordinate in the area these findings support a transition from axial tectono magmatic deformation in the northern main ethiopian rift to marginal deformation in the central and southern main ethiopian rift in turn indicating an along axis north to south decrease in rift maturity

volcanic vent self similar clustering and crustal thickness in the northern main ethiopian rift 1 the spatial distribution of volcanic vents in the northern ethiopian rift has been analysed in terms of their self similar clustering the fractal distribution of vents has been computed for the monogenetic vents cones domes and maar occurring along the rift valley and in the rift margin the self similar clustering of vents has been computed through the analysis of vent centres coordinates by means of the two point correlation method the vents of the northern main ethiopian rift display a self similar clustering characterised by a correlation coefficient of 1 41 0 02 with a size range defined by a lower cut off of 1 1 km and an upper cut off of 26 5 km this analysis indicates a probable crustal thickness of 27 km as indicated by the value of the computed upper cut off this value compares well with other estimates for the crustal and lithosphere thickness in the ethiopian rift

tectonic control of complex slope failures in the ameka river valley lower gibe area central ethiopia implications for landslide formation abstract even though major faults represent important landslide controlling factors the role the tectonic setting in actively spreading rifts plays in the development of large complex landslides is seldom discussed the ameka complex landslide area is located on the eastern scarp of the gibe gorge approximately 45 km to the west of the main ethiopian rift and 175 km to the southwest of addis ababa investigation of the complex landslide failures required a combination of satellite and airborne data based geomorphology geological field survey complemented with structural analysis radiocarbon geochronology and vertical electric sounding the obtained observations confirmed the multiphase evolution of the landslide area we have documented that apart from climatic and lithological conditions the main triggering factor of the ameka complex landslide is the tectonic development of this area the e w extension along the nne ssw trending main ethiopian rift is associated with the formation of numerous parallel normal faults such as the gibe gorge fault and the almost perpendicular scissor faults the geometry of the slid blocks of coherent lithology have inherited the original tectonic framework which suggests the crucial role tectonics play in the fragmentation of the compact rock masses and the origin and development of the ameka complex landslide area similarly the main scarps were also parallel to the principal tectonic features the local tectonic framework is dominated by faults of the same orientation as the regional structures of the main ethiopian rift such parallel tectonic frameworks display clear links between the extension of the main ethiopian rift and the tectonic development of the landslide area the ameka complex landslide developed in several episodes over thousands of years according to the radiocarbon data the last of the larger displaced blocks representing only 2 of the total area most likely slid down in the seventh century ad the main scarps namely the high scarps in the western part are unstable over the long term and toppling and falling type slope movements can be expected here in the future

control of rift obliquity on the evolution and segmentation of the main ethiopian rift the main ethiopian rift has evolved in two stages with successive activation of differently oriented fault systems analogue modelling of the earth s lithosphere demonstrates that such a rift evolution requires neither magma weakening nor a change in plate kinematics the main ethiopian rift is an active rift in the break up stage and it marks the incipient boundary between the nubia and somalia plates1 rifting started with the activation of large boundary faults and diffuse volcanism followed by focused magmatism and faulting in the rift floor along step like segments oblique to the rift axis that now act as a protoridge for future seafloor spreading2 this concentration of volcano tectonic activity has been thought to be either magma assisted2 3 or controlled by a change in rift kinematics with a late oblique rifting phase that would have caused the development of the step like fault segments that focused magma upwelling4 5 geodetic6 7 seismic8 and stress field9 data confirm current oblique rifting kinematics but plate kinematics models do not predict a change in nubia somalia motion in the past 11 million years10 here i use lithospheric scale analogue models of oblique rifting to analyse the development of the main ethiopian rift i find that neither magma weakening nor a change in plate kinematics are required to simulate a two phase evolution with successive activation of differently oriented fault systems i conclude that rift evolution and segmentation are controlled by rift obliquity independent of magmatic processes

snow control on active layer thickness in steep alpine rock walls aiguille du midi 3842 m a s l mont blanc massif since the early 2000s a remarkable amount of rockfalls has been observed in permafrost areas of the mid latitude mountain ranges concurrently to hot summers this study explores the seasonal thaw st in permafrost rock walls of the aiguille du midi site 3842 m a s l mont blanc massif we first analyse six years of temperature records in three 10 m deep boreholes against air temperature at and a four year time series of pictures showing the snow conditions on two rock faces then we test the sensitivity of the active layer against eight snow fall scenarios using the 1 d surface energy balance and heat conduction model cryogrid 3 forced by in situ measurements from a vertical face snow falls occur all the year round at this elevation and play an important role for the active layer thickness alt but the snow cover and its control are highly heterogeneous a long lasting of a snow cover during spring early summer delays the st and reduces the alt the thicker and the more spatially continuous is the snow cover the stronger are the delay and alt reduction convective clouds could also reinforce this pattern the summer at and heat waves are the dominant controlling factors of the alt but summer snow falls can sometimes persist for several days on the rock surface and reduce the effect of the heat waves active layer can thicken during the early fall except if the snow starts to accumulate on the rock surface and favours the refreezing the timing of the snow fall is the most critical parameter to determine the snow effect on the alt this study suggests that the characteristics of the bedrock and snow accumulation steepness surface roughness and sun exposure must be taken into account to better understand the formation and changes of the active layer and its possible implications for rockfall triggering

spatial relationship between earthquakes and volcanic vents in the central northern main ethiopian rift abstract during the breakup of continents extension is commonly accommodated by connected networks of fluid filled fractures dykes and by faults despite the importance of these two extension mechanisms their spatial relationship in three dimensions is poorly understood primarily because it is difficult to quantify the subsurface distribution of faulting and intrusion in order to address this problem we conduct a quantitative analysis of the spatial distribution and clustering of earthquakes and volcanic vents in the main ethiopian rift in east africa in order to understand how extension by faulting and intrusion is distributed throughout the volcanic rift we use fractal analysis of earthquake epicentres in order to infer the 2d characteristics of the subsurface fault network and directly test our model results against the 3d distribution of earthquake hypocentres our results show that fractal analysis of these features is a reliable means to characterise the 3d properties of the fault network in addition the strong similarity between the properties of the fault network derived from earthquakes and properties of the magma filled fracture network derived from fractal analysis of volcanic vents strongly suggests that these are genetically linked we then explore their spatial link using computation of earthquake and vent density which shows that the zone of seismicity is generally around 20 30 km wide while the zone of vents is narrower and centred within the zone of seismicity this spatial relationship suggests that the faults which form rift axial grabens are induced above a narrower and central zone of diking we also demonstrate significant along rift variation in degree of magmatism and faulting with regions of increased degree of diking inferred from a higher cone density characterised by reduced degree of faulting

a new kinematic approach for the danakil block using a digital elevation model representation abstract data from the literature are integrated in a regional digital elevation model dem in order to analyse the motion of the danakil block with regard to the arabian and somalian plates the application of the poles and angles of rotation taken from the literature induces a superposition of the danakil block on the arabian plate and the formation of a gap in the afar region the determination of new poles of rotation using a best fitting procedure allows one to avoid these drawbacks in all cases calculations are carried out keeping the nubian plate stationary the present approach shows that the danakil block is an independent entity and is not related to the nubian and arabian plates between the oligocene and the miocene it has been submitted to a n20 e sinistral strike slip motion anterior to the rotation itself that was started in the middle miocene this rotation is directed by a mechanical couple due to the combination of the red sea and north afar extensions

mountain permafrost development and challenges of a young research field an overview is given of the relatively short history important issues and primary challenges of research on permafrost in cold mountain regions the systematic application of diverse approaches and technologies contributes to a rapidly growing knowledge base about the existence characteristics and evolution in time of perennially frozen ground at high altitudes and on steep slopes these approaches and technologies include 1 drilling borehole measurement geophysical sounding photogrammetry laser altimetry gps sar surveying and miniature temperature data logging in remote areas that are often difficult to access 2 laboratory investigations e g rheology and stability of ice rock mixtures 3 analyses of digital terrain information 4 numerical simulations e g subsurface thermal conditions under complex topography and 5 spatial models e g distribution of permafrost where surface and microclimatic conditions are highly variable spatially a sound knowledge base and improved understanding of governing processes are urgently needed to deal effectively with the consequences of climate change on the evolution of mountain landscapes and especially of steep mountain slope hazards as the stabilizing permafrost warms and degrades interactions between glaciers and permafrost in cold mountain regions have so far received comparatively little attention and need more systematic investigation

fault architecture in the main ethiopian rift and comparison with experimental models implications for rift evolution and nubia somalia kinematics abstract the main ethiopian rift mer offers a complete record of the time space evolution of a continental rift we have characterized the brittle deformation in different rift sectors through the statistical analysis of a new database of faults obtained from the integration between satellite images and digital elevation models and implemented with field controls this analysis has been compared with the results of lithospheric scale analogue models reproducing the kinematical conditions of orthogonal and oblique rifting integration of these approaches suggests substantial differences in fault architecture in the different rift sectors that in turn reflect an along axis variation of the rift development and southward decrease in rift evolution the northernmost mer sector is in a mature stage of incipient continental rupture with deformation localised within the rift floor along discrete tectono magmatic segments and almost inactive boundary faults the central mer sector records a transitional stage in which migration of deformation from boundary faults to faults internal to the rift valley is in an incipient phase the southernmost mer sector is instead in an early continental stage with the largest part of deformation being accommodated by boundary faults and almost absent internal faults the mer thus records along its axis the typical evolution of continental rifting from fault dominated rift morphology in the early stages of extension toward magma dominated extension during break up the extrapolation of modelling results suggests that a variable rift obliquity contributes to the observed along axis variations in rift architecture and evolutionary stage being oblique rifting conditions controlling the mer evolution since its birth in the late miocene in relation to a constant post ca 11 ma n100 e nubia somalia motion

fault and graben growth along active magmatic divergent plate boundaries in iceland and ethiopia recent studies highlight the importance of annual scale dike induced rifting episodes in developing normal faults and graben along the active axis of magmatic divergent plate boundaries mdpb however the longer term 102 105 years role of diking on the cumulative surface deformation and evolution of mdpb is not yet well understood to better understand the longer term normal faults and graben along the axis of mdpb we analyze fissure swarms in iceland and ethiopia we first focus on the simplest case of immature fissure swarms with single dike fed eruptive fissures these consist of a 1 km wide graben bordered by normal faults with displacement up to a few meters consistent with theoretical models and geodetic data a similar structural pattern is found with asymmetric and multiple graben within wider mature fissure swarms formed by several dike fed eruptive fissures we then consider the lateral termination of normal faults along these grabens to detect their upward or downward propagation most faults terminate as open fractures on flat surface suggesting downward fault propagation this is consistent with recent experiments showing dike induced normal faults propagating downward from the surface however some normal faults also terminate as open fractures on monoclines which resemble fault propagation folds this suggests upward propagation of reactivated buried faults promoted by diking these results suggest that fault growth and graben development as well as the longer term evolution of the axis of mdpb may be explained only through dike emplacement and that any amagmatic faulting is not necessary

active layer dynamics in three topographically distinct lake catchments in byers peninsula livingston island antarctica abstract topography exerts a key role in controlling permafrost distribution in areas where mean annual temperatures are slightly negative one such case is the low altitude environments of maritime antarctica where permafrost is sporadic to discontinuous below 20 40 m asl and continuous at higher areas and active layer dynamics are thus strongly conditioned by geomorphological setting in january 2014 we installed three sites for monitoring active layer temperatures across byers peninsula livingston island south shetland islands at elevations between 45 and 100 m the sites are situated in lake catchments lakes escondido cerro negro and domo that have different geomorphological and topographical conditions our objective was to examine the role of topography and microclimatic conditions in determining the active layer thermal regime in order to identify the factors that control geomorphic processes in these lake catchments at each site a set of loggers was installed to monitor air temperature at snow thickness swt and soil temperature st down to 80 cm depth mean annual air temperatures maat showed similar values in the three sites 2 7 to 2 6 c whereas soil temperatures showed varying active layer thicknesses at the three catchments the ground thermal regime was strongly controlled by soil properties and snow cover thickness and duration which is influenced by local topography geomorphological processes operating at the lake catchment scale control lacustrine sedimentation processes and both are dependent on the combination of topographical and climatic conditions therefore the interpretation of lake sediment records from these three lakes requires that soil thermal regime and snow conditions at each site be taken into account in order to properly isolate the geomorphological environmental and climatic signals preserved in these lake records

fossil contourites a critical review abstract despite three decades of study there is still great controversy over the recognition and interpretation of fossil contourites exposed in ancient series on land in order to best examine this problem we briefly review the evidence from modern systems including the many examples of cenozoic contourites that have been recovered from dsdp odp drilling on major drifts in the present day oceans the range of contourite facies described from both deep water 2000 m and mid water 300 2000 m drifts are mostly fine grained bioturbated and homogeneous often with a distinct bedding cyclicity and with some coarser grained sandy contourites developed under higher energy bottom currents there are also a number of current controlled sediment bodies that have formed in outer shelf upper slope settings 50 300 m under the influence of counter currents underflows and major surface currents these are not considered contourites sensu stricto but may be mistaken as such in ancient examples the most commonly described fossil contourites in the literature have been interpreted by the authors concerned as bottom current reworked turbidites however a critical review suggests that these are the facies most subject to misinterpretation and many of the sediments claimed as fossil contourites are almost certainly fine grained turbidites whereas others were more likely formed under outer shelf upper slope current systems there remain very few ancient examples that are more closely comparable to modern contourites these include the cretaceous talme yafe formation in israel the ordovician jiuxi drift in china and parts of the paleogene lefkara formation cyprus and the neogene misaki formation in japan we present a set of possible criteria for the recognition of fossil contourites and bottom current reworked turbidites

active layer thermal monitoring of a dry valley of the ellsworth mountains continental antarctica abstract the ellsworth mountains are located along the southern edge of the ronne filchner ice shelf and are subdivided by the minnesota glacier into the heritage range to the east and the sentinel range to the west figure 1 the climate of the ellsworth mountains is strongly controlled by proximity to the ronne filchner ice shelf and elevation the entire ice free area is underlain by continuous permafrost of unknown thickness most in the form of dry permafrost active layer depths in drift sheets of the ellsworth mountains range from 15 to 50 cm detailed knowledge on antarctic permafrost is patchy especially at the continent two adjacent active layer monitoring sites were installed at mt dolence ellsworth mountains in the summer of 2012 two dry valley soils at mt dolence area on quartzite drift deposits were studied i a convex slope site exposed to the wind lithic haplorthel 886 m asl 5 cm 10 cm 30 cm and a sheltered concave slope site protected from winds lithic anhyorthel 850 m asl 5 cm 10 cm 30 cm data was recorded at hourly intervals from january 2nd 2012 until december 29th 2013 the soil climate temperature at 5 cm reaches a maximum daily mean in late december reaching a minimum in mid july at both sites active layer thickness reaches a maximum of 48 4 cm at p1 on january 17th 2013 and 47 8 cm at p2 on january 7th 2012 the soil thermal regime at the dry valley of mt dolence ellsworth mountains is characteristic of cold desert affected by dry frozen permafrost although air temperature does not reach elevated positive values variations in soil temperature are intense showing the soil s response to solar radiation the origins of typical surface periglacial features and landform on the widespread ellsworth drifts may be inherited from past events of warmer climates since liquid water is unlikely to play any significant role under the present climate

reconstructing prehistoric settlement models and land use patterns on mt damota sw ethiopia abstract although high altitude mountain habitats are often regarded as unfavorable for human occupation e g aldenderfer 2014 on the other hand tropical highlands in africa are suggested as potential refugia during times of environmental stress e g basell 2008 brandt et al 2012 archaeological investigations on mount damota 2908 m a s l located on the boundary between the southwest ethiopian highlands to the west and the southern main ethiopian rift valley to the east yielded a large number of archaeological sites from the middle stone age period until historical times in this paper we try to reconstruct settlement models for the late pleistocene and holocene occupation in this area and speculate about potential land use patterns such complex topics demand a landscape archaeological approach that includes open air sites and rock shelters the results from our excavations at mochena borago rock shelter and evidence from open air sites that were recorded during intensive surveys on the slopes and plateau of the mountain allow a first reconstruction of the settlement history of the area

environmental changes in a tropical lake lake abiyata ethiopia during recent centuries lake abiyata is a small closed saline alkaline lake located in the central part of the ethiopian rift valley east africa a multi proxy study of a sediment core 116 cm long and with undisturbed mud water interface was performed to test the sensitivity of the lake system and of different proxies to the changes in climate and human activities that occurred in the catchment during the past few centuries the 210pb analyses suggest that the upper 80 cm of the core represent the past 200 years this study complements millennial scale environmental records available in the region the main freshwater climatic and biological features of the modern lake system and their variations over the past decades as known from observations are first summarised results derived from individual proxies analysed along the core are then presented successively major physical and chemical properties of bulk sediments diatoms and pollen uncertainties on the chronological framework are discussed major limnological stages are finally identified based on the multi proxy interpretation of our record our record shows large variations in the lake water and salt balances in the sediment sources and in the vegetation distribution in the basin using our 210pb chronology major changes observed in the core are tentatively compared with environmental events known from instrumental and historical records the upper 41 cm of the core 210pb age 1940 1998 ad reveal several fluctuations in diatom inferred water depth and salinity which seem to be consistent with known changes in water level human impact on vegetation clearly appears since about 30 years the interval 85 41 cm suggests a period of overall water deficit lake abiyata experienced episodes shallower and more saline than over the past decades especially around 68 66 cm 210pb dated at ca 1890 ad this level may coincide with one of the worst droughts known in the ethiopian history during 1888 1892 the lower part of the core includes a stage 108 85 cm of lake level much higher than today and which ended before 1800 ad although its base is undated so far this stage suggests that conditions much wetter than today have prevailed in the region during at least part of the 18th century lake abiyata appears to be a suitable site for a detailed environmental reconstruction over the recent past although further work is needed to reduce the uncertainties on our record as discussed in the conclusions

bayesian noise reduction in arabia somalia and nubia arabia finite rotations since 20 ma implications for nubia somalia relative motion knowledge of nubia somalia relative motion since the early neogene is of particular importance in the earth sciences because it i impacts on inferences on african dynamic topography and ii allows us to link plate kinematics within the indian realm with those within the atlantic basin the contemporary nubia somalia motion is well known from geodetic observations precise estimates of the past 3 2 myr average motion are also available from paleo magnetic observations however little is known of the nubia somalia motion prior to 3 2 ma chiefly because the southwest indian ridge spread slowly posing a challenge to precisely identify magnetic lineations this also makes the few observations available particularly prone to noise here we reconstruct nubia somalia relative motions since 20 ma from the alternative plate circuit nubia arabia somalia we resort to trans dimensional hierarchical bayesian inference which has proved effective in reducing finite rotation noise to unravel the arabia somalia and arabia nubia motions we combine the resulting kinematics to reconstruct the nubia somalia relative motion since 20 ma we verify the validity of the approach by comparing our reconstruction with the available record for the past 3 2 myr obtained through antarctica results indicate that prior to 11 ma the total motion between nubia and somalia was faster than today furthermore it featured a significant strike slip component along the nubia somalia boundary it is only since 11 ma that nubia diverges away from somalia at slower rates comparable to the present day one kinematic changes of some 20 might have occurred in the period leading to the present day but plate motion steadiness is also warranted within the uncertainties

evaluation of frozen ground conditions along a coastal topographic gradient at byers peninsula livingston island antarctica by geophysical and geoecological methods abstract geophysical surveying and geoelectrical methods are effective to study permafrost distribution and conditions in polar environments geoelectrical methods are particularly suited to study the spatial distribution of permafrost because of its high electrical resistivity in comparison with that of soil or rock above 0 c in the south shetland islands permafrost is considered to be discontinuous up to elevations of 20 40 m a s l changing to continuous at higher altitudes there are no specific data about the distribution of permafrost in byers peninsula in livingston island which is the largest ice free area in the south shetland islands with the purpose of better understanding the occurrence of permanent frozen conditions in this area a geophysical survey using an electrical resistivity tomography ert methodology was conducted during the january 2015 field season combined with geomorphological and ecological studies three overlapping electrical resistivity tomographies of 78 m each were done along the same profile which ran from the coast to the highest raised beaches the three electrical resistivity tomographies are combined in an electrical resistivity model which represents the distribution of the electrical resistivity of the ground to depths of about 13 m along 158 m several patches of high electrical resistivity were found and interpreted as patches of sporadic permafrost the lower limits of sporadic to discontinuous permafrost in the area are confirmed by the presence of permafrost related landforms nearby there is a close correspondence between moss patches and permafrost patches along the geoelectrical transect

three dimensional seismic imaging of a protoridge axis in the main ethiopian rift models of continental breakup remain uncertain because of a lack of knowledge of strain accommodation immediately before breakup our new three dimensional seismic velocity model from the main ethiopian rift clearly images mid crustal intrusions in this active transitional rift setting supporting breakup models based on dike intrusion and magma supply the most striking features of our velocity model are anomalously fast elongate bodies velocity v p 6 5 6 8 km s extending along the rift axis interpreted as cooled mafic intrusions these 20 km wide and 50 km long bodies are separated and laterally offset from one another in a right stepping en echelon pattern approximately mimicking surface segmentation of quaternary volcanic centers our crustal velocity model combined with results from geologic studies indicates that below a depth of 7 km extension is controlled by magmatic intrusion in a ductile middle to lower crust whereas normal faulting and dike intrusion in a narrow zone in the center of the rift valley control extension in the brittle upper crust this zone is inferred to be the protoridge axis for future seafloor spreading

permafrost conditions in the mediterranean region since the last glaciation the relatively warm climate conditions prevailing today in the mediterranean region limit cold geomorphological processes only to the highest mountain environments however climate variability during the late pleistocene and holocene has led to significant spatio temporal variations of the glacial and periglacial domain in these mountains including permafrost conditions here we examine the distribution and evolution of permafrost in the mediterranean region considering five time periods last glaciation deglaciation holocene little ice age lia and present day the distribution of inactive permafrost derived features as well as sedimentary records indicates that the elevation limit of permafrost during the last glaciation was between 1000 m and even 2000 m lower than present permafrost was also widespread in non glaciated slopes above the snowline forming rock glaciers and block streams as well as meter sized stone circles in relatively flat summit areas as in most of the northern hemisphere the onset of deglaciation in the mediterranean region started around 19 20 ka the ice free terrain left by retreating glaciers was subject to paraglacial activity and intense periglacial processes under permafrost conditions many rock glaciers protalus lobes and block streams formed in these recently deglaciated environments though most of them became gradually inactive as temperatures kept rising especially those at lower altitudes following the younger dryas glacial advance the early holocene saw the last massive deglaciation in mediterranean mountains accompanied by a progressive shift of permafrost conditions to higher elevations it is unlikely that air temperatures recorded in mediterranean mountains during the holocene favoured the existence of widespread permafrost regimes with the only exception of the highest massifs exceeding 2500 3000 m lia colder climate promoted a minor glacial advance and the spatial expansion of permafrost with the development of new protalus lobes and rock glaciers in the highest massifs finally post lia warming has led to glacial retreat disappearance enhanced paraglacial activity shift of periglacial processes to higher elevations degradation of alpine permafrost along with geoecological changes

structural and geochronological implications of the fentale volcanics at a nascent passive margin of the main ethiopian rift constraints from magnetostratigraphy study at the kereyou lodge ethiopia abstract we sampled twenty four cooling units for magnetostratigraphic study from a 110 m thick early pleistocene volcanic section near kereyou lodge in the main ethiopian rift seven samples were used from each site for analysis of remanent magnetization using thermal and alternating field demagnetization techniques the natural remanent magnetization nrm direction comprises two vector components in most samples the first low stability component is isolated generally by heating to 100 c 250 c or by demagnetization using an alternating field intensity of 10 15 mt after these steps most magnetization directions define straight lines directed towards the origin and record the primary nrm or chrm characteristic remanent magnetization magnetization decay curve analyses show the possible magnetic minerals to be titanomagnetite magnetite titanohematite and hematite paleomagnetic site mean directional analyses revealed that upper 18 flows are of reversed polarity and the bottom 4 flows are normal using available age information the normal interval is correlated to the olduvai subchron on the geomagnetic polarity time scale gpts of cande kent 1995 and the flows at the polarity transition are dated to be 1 77 ma the overall declination and inclination differences calculated d 4 8 4 4 i 0 8 4 2 are consistent with the 7 counterclockwise reported kidane et al 2009 site mean inclinations show a systematic change with flow position inclinations get progressively shallower with depth for the top 17 volcanic flows and progressively steeper for the bottom 4 flows consistent with progressive backward and rift ward block tilting mechanisms respectively

have wet and dry precambrian crust largely governed cenozoic intraplate magmatism from arabia to east africa to explain cenozoic continental volcanism between arabia and east africa the existing model infers that a plume impinged beneath ethiopia between 30 ma and 20 ma and volcanism extruded within a 1000 km radius because relative motion of the afro arabian plate was about northeast in the last 120 ma we infer that at 84 ma a plume originated from the core mantle boundary impinged beneath nubia arabia and is now under the tanzania craton this plume caused uplift afro arabian swell and magma under plating after fyfe s idea 1992 the conceptual model proposed herein suggests that following plume impact there was in nubia arabia only intrusion of mafic dykes because the crust was largely unprocessed wet at about 50 ma the plume was under ethiopia and coeval volcanism extruded because the crust was highly recycled dry in zaire burundi and tanzania volcanism is explained to be coeval with the arrival of the plume because there also the crust is recycled in arabia and yemen ethiopia continental flood basalts younger than 30 ma formed because lithospheric extension along the red sea gulf of aden was the cause of or the result of plume s probably originated from the upper mantle

garba iii melka kunture ethiopia a msa site with archaic homo sapiens remains revisited garba iii in the upper awash valley of ethiopia is one of the many sub sites of melka kunture where the overall archaeological record starts at c 1 8 ma garba iii was excavated over several years in the 1970s under the direction of francis hours who was able to publish only preliminary reports before his untimely death at the base of the sequence acheulean layers were discovered and above then msa layers characterized by ferruginous concretions where three cranial fragments of homo sapiens were also found an age close to 150 ka was suggested for the human remains and associated industry of the upper layers which are the focus of the current re assessment at the time however no clear cut distinction was made between acheulean and msa in 2011 the original site was re located geological trenches were dug the stratigraphic sequence was documented in detail and a geomorphological reconstruction was prepared lithic collections and anthropological remains kept in addis ababa were also re studied new field research highlights complex site formation processes including cyclic phases of erosion and re deposition of pre existing soils and deposits however pedogenetic processes which developed twice also point to prolonged phases of stability in good accordance with the state of preservation of the lithic industry which is neither rolled nor fragmented small sized obsidian pebbles were knapped which were available locally in the alluvium deposits the technological and typological analysis confirms that the lithic industry is early msa a variety of knapping methods were in use including the levallois method well established and mostly recurrent points were produced as well as scrapers denticulates and scaled pieces circumstantial evidence points to an age not later than an early phase of mis 5e the anthropological remains one of which was so far undescribed are fragments of a right parietal bone of a parietal or more likely of a frontal bone and of an occipital bone they contribute to the still scanty fossil record available at the key time of the archaic h sapiens emergence and early spread

effect of improper water and land resource utilization on the central main ethiopian rift lakes the ethiopian rift is characterized by a chain of lakes varying in size hydrological and hydrogeological setting some of the lakes and tributary rivers are used for irrigation soda abstraction commercial fish farming and recreation and they support a wide variety of endemic birds and wild animals few lakes shrunk due to excessive abstraction of water others expanded due to increase in surface runoff and groundwater flux from percolated irrigation water excessive land degradation deforestation and over irrigation resulted in sedimentation in lakes and increase in soil salinity the chemistry of some of the lakes has also been changed dramatically this paper addresses the major environmental changes in the last few decades in the central main ethiopian rift lakes that resulted mainly from anthropogenic factors the methods employed include field hydrogeological mapping supported by aerial photograph and satellite imagery interpretations hydro meteorological data analysis water balance estimation catchment hydrological and groundwater flow modelling and hydrochemical analysis a converging evidence or integrated approach has been adapted to reconstruct the temporal and spatial variations of lake levels and hydrochemistry the result revealed that the major changes in the rift valley are related mainly to recent improper utilization of water and land resources in the lakes catchment and direct lake water abstraction aggravated intermittently by climatic changes the terminal lakes show dramatic reduction in level and increase in salinity these changes appear to have grave environmental consequences on the fragile rift ecosystem which demands extremely urgent integrated basin wide water management practice

the nature of the crust beneath the afar triple junction evidence from receiver functions the afar depression is an ideal locale to study the role of extension and magmatism as rifting progresses to seafloor spreading here we present receiver function results from new and legacy experiments crustal thickness ranges from 45 km beneath the highlands to 16 km beneath an incipient oceanic spreading center in northern afar the crust beneath afar has a thickness of 20 26 km outside the currently active rift segments and thins northward it is bounded by thick crust beneath the highlands of the western plateau 40 km and southeastern plateau 35 km the western plateau shows vp vs ranging between 1 7 1 9 suggesting a mafic altered crust likely associated with cenozoic flood basalts or current magmatism the southeastern plateau shows vp vs more typical of silicic continental crust 1 78 for crustal thicknesses 2 0 can only be explained by significant amounts of magmatic intrusions in the lower crust this suggests that melt emplacement plays an important role in late stage rifting and melt in the lower crust likely feeds magmatic activity the crust between the location of the miocene red sea rift axis and the current rift axis is thinner 2 0 than beneath the eastern part of afar 26 km vp vs 1 9 this suggests that the eastern region contains less partial melt has undergone less stretching extension and has preserved a more continental crustal signature than west of the current rift axis the red sea rift axis appears to have migrated eastward through time to accommodate the migration of the afar triple junction

thermal regimes at the snow ground interface and their implications for permafrost investigation abstract snow cover is a critical factor determining the presence or absence of permafrost in mid latitude high mountain regions this paper discusses the relation between temporal changes in temperature at the snow ground interface and permafrost distribution four fundamental types of temporal change in winter ground surface temperature gst are identified 1 nearly constant at 0 c 2 short term fluctuation 3 gradual increase without short term fluctuation and 4 gradual decrease without short term fluctuation the latter three are favorable for permafrost growth and result from direct cold penetration throughout winter ground cooling before the onset of seasonal snow cover and cold air funneling and concentrating in voids between coarse blocks respectively the fourth thermal effect predominantly contributes to growth of permafrost and thus should be included in the bottom temperature of snow cover bts concept which involves mainly the third effect monitoring gst over a winter provides a new tool for investigating the distribution of permafrost as well as information on the thermal regimes that control permafrost development

scaling of differentially eroded surfaces in the drainage network of the ethiopian plateau differentially eroded regions selected over the ethiopian plateau northeast africa were statistically analyzed using satellite images of various electromagnetic spectrum regions and resolutions landsat tm and ers 1 the power spectrum exponent values for the landsat tm2 visible and ers 1 images over the same surface are associated to the intrinsic properties of the different sensor type and postprocessing of the data differences in the values were observed between eroded area blue nile canyon bnc and relatively noneroded area plateau pla for all data sets these differences are associated to the mechanical erosion of the plateau the remotely sensed data fields show scaling from 35 m to 15 km with no break at 1 5 km and are highly multifractal analyses of the landsat tm bands over each area demonstrated something particular values for bands in the shortwave infrared swir range differed from values for bands in the visible spectrum range in the plateau area by about 0 48 while in the drainage area this difference is around 0 13 landsat tm swir bands are sensitive to spectral signature of clay minerals while data in the visible spectrum range mostly depict topography gradients two concurrent processes are highlighted mechanical erosion and chemical erosion deposition which interact to produce the observed differences in the drainage area where cliffs and steep slopes are present and mechanical erosion intensively occurs the alteration minerals are remobilized quickly whereas in the plateau area mechanical erosion is low and alteration mineral deposition is less disturbed such new statistical highlights of topographic versus chemical surfaces will have to be taken into account in landforming models

chronological and behavioral contexts of the earliest middle stone age in the gademotta formation main ethiopian rift there is a general consensus that our species emerged first in africa currently the best known skeletal evidence for the earliest anatomically modern homo sapiens amhs derives from sites in the rift valley in ethiopia however archaeological evidence from cave sites in southern and northern africa largely dominates discussions on behaviors that characterize the dawn of modern humans later middle pleistocene open air sites in east africa present unparalleled geochronological control and thus a better chance to study hominin behavior here we present results of a multidisciplinary investigation of the archaeology and geochronology of one of the oldest known middle stone age msa occupations from the gademotta formation fm in the main ethiopian rift renewed excavation lithic analysis fracture mechanics and tephrochronological investigations at gademotta provide a better understanding of the chronological and behavioral contexts during the critical period immediately preceding the origin of our species

dispersion of the afar plume implications from the spatiotemporal distribution of the late miocene to recent volcanics southwestern arabian peninsula abstract forty three new k ar dates from the yemen inland volcanic fields amran sana a dhamar rada and marib sirwah field in the southwestern arabian peninsula reveal a progression that can be divided into four stages stage 1 6 4 5 2 ma stage 2 3 6 2 9 ma stage 3 2 2 1 7 ma and stage 4

crustal structure of the main ethiopian rift from gravity data 3 dimensional modeling abstract a three dimensional interpretation of the newly compiled bouguer anomaly map of the main ethiopian rift is presented a high resolution 3 d model constrained with the seismic results reveals a possible crustal thickness and density distribution beneath the graben the bouguer anomalies along the axial portion of the rift floor as deduced from the results of the regional and residual separation are mainly caused by the deep seated structures the inferred zone of intrusion which is the main subject of the present study coincides with the maximum gravity anomaly of the rift floor the intrusion is displaced at several sectors along the east west direction and the two major displacements coincide with the locations of the major rift offsets on the surface because of the asthenospheric uplift the crust under the main ethiopian rift is slightly thinned the zone of crustal thinning 31 km coincides with the location of the intrusion beneath the rift floor and the maximum of which is attained in the northern and central sectors of the graben the trend of the crustal thinning zone which is from south to north is the same as the one obtained in the afar depression the southeastern and western plateaus on the other hand show by far the largest crustal thickness in the region 38 51 km in contrast to the afar depression where the crust is partly oceanized the thickness and density of the crust suggest that the main ethiopian rift is underlain by a purely continental crust the deep and relatively large nature of the intrusion leads to the conclusion that a large scale asthenospheric upwelling might be responsible for the thinning of the crust and subsequent rifting of the graben

contourites associated with pelagic mudrocks and distal delta fed turbidites in the lower proterozoic timeball hill formation epeiric basin transvaal supergroup south africa abstract five genetic facies associations architectural elements are recognised for the epeiric sea deposits preserved in the early proterozoic timeball hill formation south africa basal carbonaceous mudrocks interpreted as anoxic suspension deposits grade up into sheet like laminated graded mudrocks and succeeding sheets of laminated and cross laminated siltstones and fine grained sandstones the latter two architectural elements are compatible with the te td and tc subdivisions of low density turbidity current systems thin interbeds of stromatolitic carbonate within these first three facies associations support photic water depths up to about 100 m laterally extensive sheets of mature cross bedded sandstone disconformably overlie the turbidite deposits and are ascribed to lower tidal flat processes interbedded lenticular immature sandstones and mudrocks comprise the fifth architectural element and are interpreted as medial to upper tidal flat sediments small lenses of coarse siltstone very fine grained sandstone analogous to modern continental rise contourite deposits occur within the suspension and distal turbidite sediments and also form local wedges of inferred contourites at the transition from suspension to lowermost turbidite deposits blanketing and progressive shallowing of the floor of the timeball hill basin by basal suspension deposits greatly reduced wave action thereby promoting preservation of low density turbidity current deposits across the basin under stillstand or highstand conditions a lowstand tidal flat facies tract laid down widespread sandy deposits of the medial klapperkop member within the formation salinity gradients and contemporaneous cold periglacial water masses were probably responsible for formation of the inferred contourites the combination of the depositional systems interpreted for the timeball hill formation may provide a provisional model for early proterozoic epeiric basin settings

sandy contourites of the lower kazusa group in the boso peninsula japan kuroshio current influenced deep sea sedimentation in a plio pleistocene forearc basin abstract bottom current influenced sandy sediments sandy contourites were identified in outer fan and basin plain deposits of the kazusa group the infill of the plio pleistocene kazusa forearc basin in the boso peninsula of japan these are characterized by traction structures such as parallel lamination and ripple cross lamination together with minor inverse grading and wave ripple lamination in particular ripple cross lamination is commonly associated with mud drapes and flaser and lenticular bedding in general sedimentary structures of these sandy contourites do not display any regular vertical sequences such as the bouma sequence in turbidites these lithofacies indicate oscillating traction and suspension deposition in a deep sea environment and are interpreted to document long erm fluctuation in bottom currents additionally internal erosion surfaces in some of the sandy contourites similarly record fluctuations between periods of erosion versus deposition in general paleocurrent directions of sandy contourites are variable compared to those of associated turbidites the latter indicate northeastward to southeastward downslope transport in the kazusa forearc basin in contrast some paleocurrents of sandy contourites fall in a range of directions from north to northwest and other paleocurrents fall in a range of directions from south to southwest these indicate largely alongslope bottom currents although some upslope and downslope directed paleocurrents were also recognized within the sequence stratigraphic framework for the kazusa group no distinct relationship between paleocurrent directions of sandy contourites and associated systems tracts was evident variations in speed and direction of deep water currents under the modern kuroshio current and its associated deep sea environments have been documented off the japanese islands thus analogous processes appear to have been responsible for the deposition of sandy contourites in the kazusa forearc basin during the pliocene through pleistocene

dynamics of magma emplacement in centrifuge models of continental extension with implications for flank volcanism a set of experimental small scale models of continental extension investigated the emplacement of orthogonal and oblique magma chambers initially underplated at the base of the crust the models are driven by a centrifugal body force which simulates the role of gravity in nature the models represent crustal conditions analogous to relatively mature continental rifts and consider both symmetric and asymmetric extension the experimental results suggest that magma emplacement is controlled by the interactions between tectonics and rheology of the crustal layers in particular extension is mainly accommodated by lateral flow and ductile doming in the viscous layer simulating the lower crust and by listric normal faults in the overlying brittle layer associated with the ductile domal uplift stretching of the continental crust induces a reactive migration of viscous layers into the footwall of major normal faults where magma accumulation at the core of the domes takes place this behavior suggests that widespread magmatism is expected to localize in the footwall of major normal faults a situation that is often observed in core complex structures although the models presented here are intended to simulate magma emplacement during extension of a two layer brittle ductile system lateral flow and migration of magma initially underplated at the base of the crust beneath narrow rifts e g the ethiopian rift may also provide a similar mechanism and a possible explanation for the occurrence of important volcanoes on the plateaus flanking the rift zones in the suggested model such volcanoes are related to large basaltic magma reservoirs located at the base of the crust to accommodate the space vacated by lateral flow and thinning of the ductile crust the similarity in structure of the models with natural examples of continental extension modes such as rift systems and core complexes may suggest a close similarity of dynamic processes

the central main ethiopian rift is younger than 8 ma confirmation through apatite fission track thermochronology an isolated block of precambrian basement rocks and mesozoic sediments is exposed at kella along the western margin of the central main ethiopian rift mer surrounded by tertiary to quaternary volcanic rocks apatite fission track thermochronology on two basement samples yielded ages of 7 2 1 0 ma and 6 7 3 0 ma and a long mean track length 14 5 lm rapid late miocene cooling is attributed to denudation related to rifting despite the paucity of data due to the absence of suitable lithologies in the area our data confirm that the central mer is younger than 8 ma as recently proposed on the basis of field evidence and radiometric dating of volcanics this implies that the central mer formed after the northern mer indicating a diachronous development of this third arm of the red sea gulf of aden ethiopian rift system

new age constraints on the timing of volcanism and tectonism in the northern main ethiopian rift southern afar transition zone ethiopia abstract forty new k ar and 40 ar 39 ar isotopic ages from the northern main ethiopian rift mer southern afar transition zone provide insights into the volcano tectonic evolution of this portion of the east african rift system the earliest evidence of volcanic activity in this region is manifest as 24 23 ma pre rift flood basalts transition zone flood basalt activity renewed at approximately 10 ma and preceded the initiation of modern rift margin development bimodal basalt rhyolite volcanism in the southern afar rift floor began at approximately 7 ma and continued into recent times in contrast post subsidence volcanic activity in the northern mer is dominated by mio pliocene silicic products from centers now covered by quaternary volcanic and sedimentary lithologies unlike other parts of the mer mio pliocene silicic volcanism in the mer afar transition zone is closely associated with fissural basaltic products the presence of pliocene age ignimbrites on the plateaus bounding the northern mer whose sources are found in the present rift indicates that subsidence of this region was gradual and that it attained its present physiography with steep escarpments only in the plio pleistocene large 7 5 ma silicic centers along the southern afar and northeastern mer margins apparently formed along an e w oriented regional structural feature parallel to the already established southern escarpment of the afar the addis ababa rift embayment and the growth of 4 5 3 ma silicic centers in the addis ababa area are attributed to the formation of a major cross rift structure and its intersection with the same regional e w structural trend this study illustrates the episodic nature of rift development and volcanic activity in the mer afar transition zone and the link between this activity and regional structural and tectonic features

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

seismicity associated with magmatism faulting and hydrothermal circulation at aluto volcano main ethiopian rift the silicic volcanic centres of the main ethiopian rift mer play a central role in facilitating continental rifting many of these volcanoes host geothermal resources and are located in heavily populated regions insar studies have shown several are deforming but regional seismic networks have detected little seismicity a local network of 12 seismometers was deployed at aluto volcano from 2012 to 2014 and detected 2142 earthquakes within a 24 month period we locate the events using a 1d velocity model that exploits a regional model and information from geothermal boreholes and calculate local magnitudes b values and focal mechanisms event depths generally range from the near surface to 15 km with most of the seismicity clustering in the upper 2 km a significant amount of seismicity follows the artu jawa fault zone which trends in alignment with the wonji fault belt nne ssw and is consistent with previous studies of strain localisation in the mer focal mechanisms are mostly normal in style with the mean t axes congruent to the orientation of extension in the rift at this latitude some show relatively small left lateral strike slip components and are likely associated with the reactivation of ne ene structures at the southern tip of the aluto gedemsa segment events range from 0 40 to 2 98 in magnitude and we calculate an overall b value of 1 40 0 14 this relatively elevated value suggests fluid induced seismicity that is particularly evident in the shallow hydrothermal reservoir and above it subdividing our observations according to depth identifies distinct regions beneath the volcanic edifice a shallow zone 2 0 km of high seismicity and high b values that corresponds to the hydrothermal system and is influenced by a high fluid saturation and circulation a relatively aseismic zone 0 2 km with low b values that is impermeable to ascending volatiles a region of increased fluid induced seismicity 2 9 km that is driven by magmatic intrusion from below and a deeper zone below 9 km that is interpreted as a partially crystalline magmatic mush these observations indicate that both the magmatic and hydrothermal systems of aluto volcano are seismically active and highlight the need for dedicated seismic monitoring at volcanoes in the mer

low frequency earthquakes beneath tullu moye volcano ethiopia reveal fluid pulses from shallow magma chamber abstract the active magmatic processes beneath volcanoes in continental rifts is poorly understood for example until recently in the east african rift ear the majority of the young volcanoes were thought to be inactive more recent studies have shown that numerous volcanoes in the ear are seismically active and deforming rapidly however an unambiguous sign of actively degassing magma hosted in shallow magma bodies has eluded most investigators here we present detailed analysis of the first low frequency lf earthquake swarms to be observed in the main ethiopian rift the earthquakes locate to beneath tullu moye volcano and are directly related to the presence of a shallow magma body with a high fluid content using spectral modelling we show that the lf earthquakes appear to have low stress drops 1 50 kpa which we interpret in terms of low rupture velocities and high pore fluid pressure careful relocation of the lf earthquakes place them approximately 4 km below the surface within one of two possible clusters however analysis of the correlation between earthquake waveforms show that each swarm contains a range of earthquake families and as such a diversity of earthquake source mechanisms to explain these observations we propose the seismicity is induced by h2o co2 fluid pulses from the shallow magma body into a highly fractured region fluid pulses cause high pore fluid pressures which also cause the low rupture velocities

constraining the african pole of rotation abstract in the absence of well defined transform faults in the east african rift system for constraining the plate kinematic reconstruction the pole of relative motion for the african nubian and somalian plates has been determined from residual motion if africa and somalia are to continue to drift apart along the east african rift system which would then evolve into a series of ridges offset by transform faults then incipient transform faults that may reflect the direction of relative motion should already be in place along the east african rift system the incipient transforms along the east african rift system are characterized by shear zones such as the zambezi shear zone in the south and the aswa and hamer shear zones in the north some of these shear zones have been associated with recent strike slip faulting in the nw se direction during periods of earthquakes provided that these consistently nw se oriented strike slip movements in the shear zones give the direction of relative motion of the adjacent plates then they can be used to constrain the position of the africa somalia euler pole due to the fact that identifying transform faults in the east african rift system is difficult and because the genesis of transform faults characterizing a plate boundary at an inception stage is not well known the discussion here is limited to the northern segment of the east african rift system where shear zones are better characterized by the existing geophysical data the characterizing features vary with latitude indicating the complexity of the problem of the genesis of transform faults i believe however that the relatively well defined intra continental transform fault in the northern east african rift system which is characterized by strike slip faulting and earthquakes constrains the pole of relative motion for the african and somalian plates to a position near 1 5 s and 29 0 e

stratigraphy of the kazusa group boso peninsula an expanded and highly resolved marine sedimentary record from the lower and middle pleistocene of central japan major climatic reorganizations including changes in the nature of glacial interglacial cycles through the pleistocene are a key issue for improving the understanding of earth s climate system highly resolved marine sedimentary records are essential to reconstruct the details of these past climatic changes and investigate the mechanisms responsible for them the kazusa group located in the central part of the japanese island chain is well exposed and contains a remarkably continuous and thick deep and shallow water marine sedimentary succession this group also contains well preserved marine microfossils pollen paleomagnetic reversal events geochemical signatures and a large number of tephra beds these features allow us to establish a robust chronological and stratigraphic framework for the kazusa group and provide a rare opportunity to study oceanic and terrestrial climatic and environmental changes at high resolution especially through the lower and lower middle pleistocene in the boso peninsula chiba prefecture the kazusa group is deeply incised yielding spectacular river cut exposures the matuyama brunhes paleomagnetic reversal is observed immediately above the widespread byakubi e byk e tephra in the chiba composite section within the kokumoto formation kazusa group because the matuyama brunhes boundary customarily serves as the primary guide for the lower middle pleistocene subseries boundary the chiba composite section is considered an excellent candidate for its global boundary stratotype section and point gssp this study reviews the published data for the kazusa group hitherto almost exclusively in japanese in order to place the chiba composite section within its broader depositional and chronostratigraphic context

solifluction rates processes and landforms a global review abstract field data on the rates of solifluction and associated parameters are compiled from the literature in an attempt to evaluate factors controlling the spatial variability in solifluction processes and landforms with special attention on the climate solifluction relationship the analyzed data originate from 46 sites over a wide range of periglacial environments from antarctic nunataks to tropical high mountains solifluction broadly defined as slow mass wasting resulting from freeze thaw action in fine textured soils involves several components needle ice creep and diurnal frost creep originating from diurnal freeze thaw action annual frost creep gelifluction and plug like flow originating from annual freeze thaw action and retrograde movement caused by soil cohesion the depth and thickness of ice lenses and freeze thaw frequency are the major controls on the spatial variation in solifluction processes near the warm margin of the solifluction affected environment diurnal freeze thaw action induces shallow but relatively rapid movement of a superficial layer 5 10 cm thick on average often creating the thin stone banked lobes typically seen on tropical high mountains in addition to diurnal movement annual frost creep and gelifluction may occur on slopes with soil climates of seasonal frost to warm permafrost dislocating a soil layer shallower than 60 cm at a rate of centimeters per year and eventually producing medium size solifluction lobes in high arctic cold permafrost regions two sided freezing can induce plug like flow of a soil mass 60 cm or thicker the correlation between process and landform suggests that the riser height of lobes is indicative of the maximum depth of movement and prevailing freeze thaw type climate change may result in new different ground freezing conditions thereby influencing the surface velocity and maximum depth of soil movement soil moisture and topography also control solifluction high moisture availability in the seasonal freezing period enhances diurnal freeze thaw action and subsequent seasonal frost heaving the latter contributes to raising the moisture content of the thawed layer and promotes gelifluction during the thawing period the slope angle defines the upper limit of the surface velocity of solifluction a diagram correlating the potential frost creep with the actual surface velocity permits an inter site comparison of the relative magnitude of solifluction components physically based modelling of periglacial slope evolution requires synthetic and more detailed field monitoring and laboratory simulations of solifluction processes

heterogeneous initial sr isotope compositions of highly evolved volcanic rocks from the main ethiopian rift ethiopia many individual mineral sr isotope studies have revealed the complex evolution of highly evolved rocks in upper crustal magmatic systems casting doubts on the meaning of whole rock sr isotopes in such samples in this paper whole rock sr isotope measurements were replicated three to 13 times on six highly evolved peralkaline rhyolites from the main ethiopian rift mer to appraise their internal heterogeneity and thus the significance of such data these rocks were all fresh samples of pumice obsidian and lava their maximum sr contents and ages were 15 g g and 1 7 ma respectively significant small scale heterogeneities of both sr isotopes and rb and sr contents were observed in most samples although not necessarily associated with petrological characteristics suggesting possible inheritance processes only two almost crystal free obsidian give fairly homogeneous sr isotope ratios these results outline the ambiguity of a single whole rock sr isotope determination on highly evolved peralkaline rocks especially when no simultaneous accurate determination of the rb sr is performed they also suggest that the limitations of sr whole rock analyses are not restricted to phenocryst rich samples as phenocryst poor obsidian and almost aphyric pumices and lava are also concerned these data further underscore that unreplicated whole rock sr isotope measurements should always be used with great caution in the petrogenetic modeling of highly evolved rocks however multiple determinations of whole rock 87sr 86sr in the same samples combined with other geochemical and isotopic data may provide constraints on the shallow level evolution of these magmas it is suggested that selective upper crustal contamination and or interactions with halogen bearing hydrous fluids typical of evolved peralkaline magmas were probably involved in the late magmatic evolution of these mer rhyolites the more pervasive character of fluid interaction processes would probably better account for the small scale association of uncontaminated and contaminated signatures in a single sample thus even fresh samples may have their rb sr isotopic system significantly modified by fluid interactions not as a secondary process but at the late magmatic stage

active layer thermal dynamics at two lithologically different sites on james ross island eastern antarctic peninsula abstract the active layer thermal regime was studied at two sites with different lithological properties located on james ross island eastern antarctic peninsula to assess the main driving factors the abernethy flats site 41 m a s l is located in cretaceous calcareous sandstones and siltstones of the santa marta formation in contrast the berry hill slopes site 56 m is composed of muddy to intermediate diamictites tuffaceous siltstones to fine grained sandstones of the mendel formation the data of air temperature at 2 m and ground temperature at two 75 cm deep profiles were analysed for the period 1 january 2012 to 31 december 2014 small differences were found when comparing mean air temperatures and ground temperatures at 5 50 and 75 cm depths in the period 2012 2014 while the mean air temperatures varied between 7 7 c and 7 0 c the average ground temperatures oscillated between 6 6 c and 6 1 c at 5 cm 6 7 c and 6 0 c at 50 cm and 6 9 c and 6 0 c at 75 cm at abernethy flats and berry hill slopes respectively the increasing difference of ground temperature with depth and a significant difference in active layer thickness 52 to 64 cm at abernethy flats and 85 to 90 cm at berry hill slopes respectively suggests the significant effect of lithology the higher proportion of fine particles and more thermally conductive minerals together with higher water saturation has been found to be fundamental for higher active layer thickness documented at berry hill slopes

a mediterranean perspective on 10be sedimentation and climate around the matuyama brunhes boundary les liaisons dangereuses abstract the 10be 9be ratio is commonly employed as a tool for establishing the stratigraphic position of paleomagnetic excursions and reversals whenever the traditional paleomagnetic approach fails to provide conclusive results in particular it is held that 10be production rates in the atmosphere depend on the strength of the earth s magnetic field and the fallout and deposition of cosmogenic beryllium at the surface happen on a very short time scale however investigations performed on terrestrial and marine successions demonstrate that the 10be record and the paleomagnetic signal are often asynchronous mechanisms that control the conveyance and deposition of cosmogenic 10be to the seafloor are still ambiguous and poorly documented here we discuss the dynamics of 10be in a central mediterranean marginal marine depositional scenario characterized by a pervasive terrigenous influx our data show that a very close correlation exists between 10be concentrations and the local proxy of rainfall rates and regimes pollen indicating that a considerable 10be transport from the mainland may occur in response to the remobilization of terrestrial reservoirs during periods of increased runoff superimposed is a dynamic oceanographic setting that further controls the preservation potential of 10be at the bottom in terms of changing water chemistry and or composition of the sedimentary flux to the seafloor results of our investigation suggest that in particular environmental and depositional settings the interplay between climate terrigenous yield and oceanography may jeopardize the sedimentary depiction of the meteoric 10be contribution thus challenging the use of 10be for tracking the stratigraphic position of geomagnetic reversals

recent shallowing of the thaw depth at crater lake deception island antarctica 2006 2014 abstract the western antarctic peninsula region is one of the hot spots of climate change and one of the most ecologically sensitive regions of antarctica where permafrost is near its climatic limits the research was conducted in deception island an active stratovolcano in the south shetlands archipelago off the northern tip of the antarctic peninsula the climate is polar oceanic with high precipitation and mean annual air temperatures maat close to 3 c the soils are composed by ashes and pyroclasts with high porosity and high water content with ice rich permafrost at 0 8 c at the depth of zero annual amplitude with an active layer of about 30 cm results from thaw depth ground temperature and snow cover monitoring at the crater lake calm s site over the period 2006 to 2014 are analyzed thaw depth td was measured by mechanical probing once per year in the end of january or early february in a 100 100 m with a 10 m spacing grid the results show a trend for decreasing thaw depth from ci 36 cm in 2006 to 23 cm in 2014 while maat as well as ground temperatures at the base of the active layer remained stable however the duration of the snow cover at the calm s site measured through the snow pack factor sf showed an increase from 2006 to 2014 especially with longer lasting snow cover in the spring and early summer the negative correlation between sf and the thaw depth supports the significance of the influence of the increasing snow cover in thaw depth even with no trend in the maat the lack of observed ground cooling in the base of the active layer is probably linked to the high ice water content at the transient layer the pyroclastic soils of deception island with high porosity are key to the shallow active layer depths when compared to other sites in the western antarctic peninsula wap these findings support the lack of linearity between atmospheric warming and permafrost warming and induce an extra complexity to the understanding of the effects of climate change in the ice free areas of the wap especially in scenarios with increased precipitation as snow fall

3 d analysis and interpretation of magnetotelluric data from the aluto langano geothermal field ethiopia the main ethiopian rift valley encompasses a number of volcanoes which are known to be actively deforming with reoccurring periods of uplift and setting one of the regions where temporal changes take place is the aluto volcanic complex it hosts a productive geothermal field and the only currently operating geothermal power plant of ethiopia we carried out magnetotelluric mt measurements in early 2012 in order to identify the source of unrest broad band mt data 0 001 1000 s have been acquired at 46 sites covering the expanse of the aluto volcanic complex with an average site spacing of 1 km based on this mt data it is possible to map the bulk electrical resistivity of the subsurface down to depths of several kilometres resistivity is a crucial geophysical parameter in geothermal exploration as hydrothermal and magmatic reservoirs are typically related to low resistive zones which can be easily sensed by mt thus by mapping the electrical conductivity one can identify and analyse geothermal systems with respect to their temperature extent and potential for production of energy 3 d inversions of the observed mt data from aluto reveal the typical electrical conductivity distribution of a high enthalpy geothermal system which is mainly governed by the hydrothermal alteration mineralogy the recovered 3 d conductivity models provide no evidence for an active deep magmatic system under aluto forward modelling of the tippers rather suggest that occurrence of melt is predominantly at lower crustal depths along an off axis fault zone a few tens of kilometres west of the central rift axis the absence of an active magmatic system implies that the deforming source is most likely situated within the shallow hydrothermal system of the aluto langano geothermal field

morphological comparison of distributed volcanic fields in the main ethiopian rift using high resolution digital elevation models abstract distributed volcanic fields of scoria cones maars tuff cones and lava flows represent a crucial expression of the interplay between magmatism tectonics and surface processes in continental rifts we compare the cone morphology of two fields butajira and east ziway in the main ethiopian rift mer using high resolution digital elevation models dems to investigate volumes surface environment and age of emplacement volumes of individual cones are similar in both fields mean 4 106 m3 and lower than in other distributed volcanic fields located in extensional environments volcanism at butajira has created linear clusters of superimposed cones suggesting a small number of larger 107 108 m3 fissure eruptions compared to the isolated events at east ziway the presence of maars and deep craters within cones at butajira indicates phreatomagmatic activity not seen at east ziway where cones may have been emplaced during a dry climate phase shape parameters including curvature of cone rims and ratios of cone height width and crater depth suggest younger eruption ages at butajira compared to east ziway and the possibility of ongoing activity in this area a broader survey of cone fields across the mer using the aster global digital elevation model fails to identify systematic variation in height width and volume from cone morphology limited by low resolution high resolution topography provides a useful insight into rift environments at the time of emplacement and further surveys across the main ethiopian rift may advance our understanding of distributed volcanism in extensional settings and the hazards they present

the origin of along rift variations in faulting and magmatism in the ethiopian rift the geological record at rifts and margins worldwide often reveals considerable along strike variations in volumes of extruded and intruded igneous rocks these variations may be the result of asthenospheric heterogeneity variations in rate and timing of extension alternatively pre existing plate architecture and or the evolving kinematics of extension during breakup may exert first order control on magmatism the main ethiopian rift mer in east africa provides an excellent opportunity to address this dichotomy it exposes along strike several sectors of asynchronous rift development from continental rifting in the south to incipient oceanic spreading in the north here we perform studies of volcanic cone density and rift obliquity along strike in the mer by synthesizing these new data in light of existing geophysical geochemical and petrological constraints on magma generation and emplacement we are able to discriminate between tectonic and mantle geodynamic controls on the geological record of a newly forming magmatic rifted margin the timing of rift sector development the three dimensional focusing of melt and the ponding of plume material where the rift dramatically narrows each influence igneous intrusion and volcanism along the mer however rifting obliquity plays an important role in localizing intrusion into the crust beneath en echelon volcanic segments along strike variations in volumes and types of igneous rocks found at rifted margins thus likely carry information about the development of strain during rifting as well as the physical state of the convecting mantle at the time of breakup

tephra sources and correlations in ethiopia application of elemental and neodymium isotope data abstract combined elemental and neodymium nd isotope data for proximal and distal pyroclastic deposits from the ethiopian volcanic province illustrate the utility of these parameters for establishing potential source regions for distal tephra and for correlation of widely separated distal deposits in the ethiopian volcanic province nd isotopic compositions and to some extent elemental characteristics of volcanic products from distinct geographic tectonic sub provinces allow first order indentification of geochemical domains these domains are used to target potential source regions for the numerous distal tephra deposits exposed within the fossiliferous sedimentary sequences of the afar and omo turkana basins pliocene distal deposits from the hadar and middle awash regions of afar ethiopia and the omo turkana region of southern ethiopia northern kenya are examined combined elemental and nd isotope data are consistent with derivation of these tephra from sources within or adjacent to the central sector of the main ethiopian rift or within the central to northern afar the data presented in this paper also point to the need for a better understanding of the physical and chemical characteristics of the eruptions giving rise to many of the distal deposits until information regarding the range of chemical and isotopic variability in these magmatic systems is available it is difficult to link a specific set of geochemical characteristics to one particular eruption or vent

the role of aridification in constraining the elevation range of holocene solifluction processes and associated landforms in the periglacial belt of the sierra nevada southern spain climate variability during the mid late holocene has influenced the activity of geomorphic processes in the current periglacial belt of the sierra nevada we studied two types of sedimentary records that reveal a synchronous timing for slope instability in this high semi arid massif solifluction landforms and mountain lake sediments lithological and sedimentological properties of both records have recorded numerous cycles of different magnitude of slope processes in the massif solifluction deposits record seven phases of solifluction activity and soil development during the last 7 ka bp and lake sediments show evidence of eight periods with increased geomorphic activity in the catchments over the last 6 ka bp although present day climate conditions do not promote active solifluction processes in the sierra nevada colder and wetter periods during the holocene triggered solifluction and transported coarse grained sediments into the lakes by contrast warm phases favoured soil formation and spread an incipient vegetation cover over the headwaters of the highest valleys diminishing the grain size of the particles reaching the lakes lake sediments record an aridification trend in the massif intensifying since 4 2 ka bp that has conditioned solifluction activity to shift gradually to higher elevations during major cooler phases such as the little ice age active solifluction was recorded back down to 2500 m altitude copyright 2010 john wiley sons ltd