holocene fault scarps near tacoma washington usa airborne laser mapping confirms that holocene active faults traverse the puget sound metropolitan area northwestern continental united states the mapping which detects forest floor relief of as little as 15 cm reveals scarps along geophysical lineaments that separate areas of holocene uplift and subsidence along one such line of scarps we found that a fault warped the ground surface between a d 770 and 1160 this reverse fault which projects through tacoma washington bounds the southern and western sides of the seattle uplift the northern flank of the seattle uplift is bounded by a reverse fault beneath seattle that broke in a d 900 930 observations of tectonic scarps along the tacoma fault demonstrate that active faulting with associated surface rupture and ground motions pose a significant hazard in the puget sound region

upper crustal structure in puget lowland washington results from the 1998 seismic hazards investigation in puget sound a new three dimensional 3 d model shows seismic velocities beneath the puget lowland to a depth of 11 kin the model is based on a tomographic inversion of nearly one million first arrival travel times recorded during the 1998 seismic hazards investigation in puget sound ships allowing higher resolution mapping of subsurface structures than previously possible the model allows us to refine the subsurface geometry of previously proposed faults e g seattle hood canal southern whidbey island and devils mountain fault zones as well as to identify structures tacoma lofall and sequim fault zones that warrant additional study the largest and most important of these newly identified structures lies along the northern boundary of the tacoma basin we informally refer to this structure here as the tacoma fault zone although tomography cannot provide information on the recency of motion on any structure holocene earthquake activity on the tacoma fault zone is suggested by seismicity along it and paleoseismic evidence for abrupt uplift of tidal marsh deposits to its north the tomography reveals four large west to northwest trending low velocity basins tacoma seattle everett and port townsend separated by regions of higher velocity ridges that are coincident with fault bounded uplifts of eocene crescent formation basalt and pre tertiary basement the shapes of the basins and uplifts are similar to those observed in gravity data gravity anomalies calculated from the 3 d tomography model are in close agreement with the observed anomalies in velocity cross sections the tacoma and seattle basins are asymmetric the basin floor dips gently toward a steep boundary with the adjacent high velocity uplift locally with a velocity overhang that suggests a basin vetgent thrust fault boundary crustal fault zones grow from minor folds into much larger structures along strike inferred structural relief across the tacoma fault zone increases by several kilometers westward along the fault zone to lynch cove where we interpret it as a zone of south vergent faulting overthrusting tacoma basin in contrast structural relief along the seattle fault zone decreases west of seattle which we interpret as evidence that the n s directed compression is being accommodated by slip transfer between the seattle and tacoma fault zones together the tacoma and seattle fault zones raise the seattle uplift one of a series of east west trending pop up structures underlying puget lowland from the black hills to the san juan islands

palaeotsunamis along canada s pacific coast abstract to fully understand tsunami hazards along canada s pacific coast we must consider all potential sources including local and region wide earthquakes volcanic activity slope failure events and bolide impacts furthermore as climate changes future extreme meteorological conditions will exacerbate slope failures on steep and over steepened slopes and potentially augment the magnitude and frequency of earthquake generated tsunamis there have been numerous reviews of the geological records of palaeotsunamis along the cascadia margin but as yet there has been no attempt made to pull together all data related to palaeotsunamis along the pacific coast of canada we summarise all geological data related to palaeotsunamis reported in the region all relevant non geological data and other information concerning potential tsunamigenic sources evidence for between 10 and 22 palaeotsunamis prior to european arrival have been documented with the cascadia subduction zone y event ad1700 being the most widely recognised geological archaeological and anthropological data all indicate a complex multi sourced prehistory of seismic tsunami activity that is poorly understood a clustering of potential activity off the se coast of vancouver island suggests that we should also attempt to better understand locally generated events along canada s pacific coast

out of sequence thrusting in experimental coulomb wedges implications for the structural development of mega splay faults and forearc basins 1 we have investigated how an arc ward increase in bulk mechanical strength in an experimental accretionary prism influences the development timing and duration of slip on out of sequence thrusts we have monitored the structural development and kinematics in side view during the development of a frontally accreting coulomb wedge growing out in front of a critically tapered and mechanically stronger inner wedge the inner wedge initially behaved as classic backstop to deformation with the most actively slipping thrust occurring near the deformation front on the forward most thrust structures with continued growth however significant out of sequence slip on reactivated fore thrusts occurred in conjunction with slip on newly formed back thrusts in the inner wedge this out of sequence deformation resulted in punctuated rapid uplift of the model forearc basin and a noticeable break in topographic slope in the outer pro wedge cyclical out of sequence fore and back thrusting driven by ongoing frontal thrust imbrication continued with periodic recovery of taper and was followed by additional out of sequence faulting and associated basin uplift

the excavation of hayonim terrace an examination of terminal pleistocene climatic and adaptive changes abstract the investigation of the epipalaeolithic site of hayonim terrace contributes new evidence relative to our understanding of the series of adaptive changes which took place among populations of palestine during the terminal pleistocene and early holocene the study defines a cultural continuity between the geometric kebaran a and natufian archaeological complexes against a changing environmental background a succession of environmental oscillations which occurred between c 12 500 and 10 000 bp is identified and discussed in regard to changes in epipalaeolithic economic and adaptive patterns an episode of climatic amelioration c 12 000 11 000 bp apparently contributed to the expansion of cereals into the mediterranean hill zone and the abandonment of palaeolithic hunting and gathering strategy by natufian cereal collectors subsequent environmental deterioration associated with the onset of drier conditions c 11 000 bp prompted natufian populations to attempt to maintain their habitable territory artificially through the cultivation of cereals

evidence for earthquake triggering of large landslides in coastal oregon usa abstract landslides are ubiquitous along the oregon coast many are large deep slides in sedimentary rock and are dormant or active only during the rainy season morphology observed movement rates and total movement suggest that many are at least several hundreds of years old the offshore cascadia subduction zone produces great earthquakes every 300 500 years that generate tsunami that inundate the coast within minutes many slides and slide prone areas underlie tsunami evacuation and emergency response routes we evaluated the likelihood of existing and future large rockslides being triggered by pore water pressure increase or earthquake induced ground motion using field observations and modeling of three typical slides monitoring for 2 9 years indicated that the rockslides reactivate when pore pressures exceed readily identifiable levels measurements of total movement and observed movement rates suggest that two of the rockslides are 296 336 years old the third could not be dated the most recent great cascadia earthquake was m 9 0 and occurred during january 1700 while regional climatological conditions have been stable for at least the past 600 years hence the estimated ages of the slides support earthquake ground motion as their triggering mechanism limit equilibrium slope stability modeling suggests that increased pore water pressures could not trigger formation of the observed slides even when accompanied by progressive strength loss modeling suggests that ground accelerations comparable to those recorded at geologically similar sites during the m 9 0 11 march 2011 japan trench subduction zone earthquake would trigger formation of the rockslides displacement modeling following the newmark approach suggests that the rockslides would move only centimeters upon coseismic formation however coseismic reactivation of existing rockslides would involve meters of displacement our findings provide better understanding of the dynamic coastal bluff environment and hazards from future subduction zone earthquakes

reconstructing 4000 years of mass movement and tsunami history in a deep peri alpine lake lake geneva france switzerland the study of mass movements in lake sediments provides insights into past natural hazards at historic and prehistoric timescales sediments from the deep basin of lake geneva reveal a succession of six large scale volumes of 22 x 10 6 to 250 x 10 6 m 3 mass transport deposits associated with five mass movement events within 2600 years 4000 cal bp to 563 ad the mass transport deposits result from i lateral slope failures mass transport deposit b at 3895 225 cal bp and mass transport deposits a and c at 3683 128 cal bp and ii rhone delta collapses mass transport deposits d to g dated at 2650 150 cal bp 2185 85 cal bp 1920 120 cal bp and 563 ad respectively mass transport deposits a and c were most probably triggered by an earthquake whereas the rhone delta collapses were likely to be due to sediment overload with a rockfall as the external trigger mass transport deposit g the tauredunum event in 563 ad known from historical records an earthquake mass transport deposit e or unknown external triggers mass transport deposits d and f independent of their origin and trigger mechanisms numerical simulations show that all of these recorded mass transport deposits are large enough to have generated at least metre scale tsunamis during mass movement initiation since the tauredunum event in 563 ad two small scale volumes of 1 to 2x10 6 m 3 mass transport deposits h and i are present in the seismic record both of which are associated with small lateral slope failures mass transport deposits h and i might be related to earthquakes in lausanne geneva possibly 1322 ad and aigle 1584 ad respectively the sedimentary record of the deep basin of lake geneva in combination with the historical record show that during the past 3695 years at least six tsunamis were generated by mass movements indicating that the tsunami hazard in the lake geneva region should not be neglected although such events are not frequent with a recurrence time of 0 0016 yr 1

carnivore diversity in the late quaternary of israel abstract during the past 70 000 years israeli carnivore faunas have varied only slightly in richness number of species but widely in diversity including the relative abundances of the different species human population growth sedentism and the beginning of agriculture are often considered to have caused habitat destruction toward the end of the pleistocene that may have affected animal populations however patterns of changing carnivore diversities from three sites in the mediterranean region of israel correlate well with changes in precipitation species diversity is higher during more humid phases and lower during drier phases the environmental effect of sedentism may have accelerated the later drop in carnivore diversity but cannot account for fluctuations in diversity preceding it

the potential hazard from tsunami and seiche waves generated by large earthquakes within lake tahoe california nevada we investigate the potential of local earthquakes to generate tsunamis and seiches within lake tahoe we calculated the long wavelength oscillations generated by 3 hypothetical m w 7 earthquake scenarios for faults with normal slip directly under and outside the lake basin the scenarios involving fault slip under the lake are the north tahoe incline village and west tahoe dollar point scenarios the genoa scenario involves a fault that crops out 10 km east of the lake faulting beneath the lake generates a tsunami followed by a seiche that continues for hours with waves as large as 3 to 10 m the seiche potentially threatens low lying lakeside communities and lifelines we also compare the spectral characteristics of synthetic tide gauge records with wind swell observations the fundamental mode calculated for a seiche is consistent with the wind swell observations

reconstruction of a debris slide initiated flood in the southern kenai mountains alaska abstract a flood initiated by a slide of 84 million m 3 of rock and debris swept the forefeild of grewingk glacier during the fall of 1967 we used high water marks bedforms and scours to estimate flow competence and to reconstruct the flood an estimate of flow competence was obtained by graphing the intermediate clast axis of 34 boulders showing no evidence of transport by the flood against the length of sediment shadows and the depth of flood scour upstream from the boulders projection of the best fit lines of these relationships onto the grain size axis identified the largest clast that had no sediment shadow or associated scour and thus is itself assumed to have been transported the representative clast was 35 cm in diameter this in turn was utilized in a selective entrainment equation derived from a data set of grain sizes encompassing the critical clast size a shear stress of 1100 dyn cm 2 and a flow velocity of 2 4 m s 1 3 km downvalley from the slide were estimated from this equation

prehistoric earthquake history revealed by lacustrine slump deposits five strong paleoseismic events were recorded in the past 15 k y in a series of slump deposits in the subsurface of lake lucerne central switzerland revealing for the first time the paleoseismic history of one of the most seismically active areas in central europe although many slump deposits in marine and lacustrine environments were previously attributed to historic earthquakes the lack of detailed three dimensional stratigraphic correlation in combination with accurate dating hampered the use of multiple slump deposits as paleoseismic indicators this study investigated the fingerprint of the well described a d 1601 earthquake i vii viii mw 6 2 in the sediments of lake lucerne the earthquake triggered numerous synchronous slumps and megaturbidites within different subbasins of the lake producing a characteristic pattern that can be used to assign a seismic triggering mechanism to prehistoric slump events for each seismic event horizon the slump synchronicity was established by seismic stratigraphic correlation between individual slump deposits through a quasi three dimensional high resolution seismic survey grid four prehistoric events dated by accelerator mass spectrometry 14c measurements and tephrochronology on a series of long gravity cores occurred at 2420 9770 13 910 and 14 560 calendar yr ago these recurrence times are essential factors for assessing seismic hazard in the area the seismic hazard for lakeshore communities is additionally amplified by slump induced tsunami and seiche waves numerical modeling of such tsunami waves revealed wave heights to 3 m indicating tsunami risk in lacustrine environments

new kinematic models for pacific north america motion from 3 ma to present i evidence for steady motion and biases in the nuvel 1a model we use velocities derived from 2 4 5 years of continuous gps observations at 21 sites on the pacific and north american plates along with a subset of the nuvel 1a data to examine the steadiness of pacific north america motion since 3 16 ma the transfer of baja california to the pacific plate and the magnitude of biases in the nuvel 1a estimate of pacific north america motion we find that pacific north america motion has remained steady since 3 16 ma but at rates significantly faster than predicted by nuvel 1a in the vicinity of baja california our gps derived model and recent seafloor spreading rates in the southern gulf of california both indicate that the nuvel 1a model underestimates pacific north america rates by 4 2 mm yr 1 steady pacific north america motion since 3 16 myr and increasing seafloor spreading rates since 3 58 myr in the gulf of california imply that pacific north america motion was partitioned between seafloor spreading in the gulf of california and decelerating slip along faults in or offshore from the baja peninsula

lake sediments as natural seismographs a compiled record of late quaternary earthquakes in central switzerland and its implication for alpine deformation central switzerland lies tectonically in an intraplate area and recurrence rates of strong earthquakes exceed the time span covered by historic chronicles however many lakes are present in the area that act as natural seismographs their continuous datable and high resolution sediment succession allows extension of the earthquake catalogue to pre historic times this study reviews and compiles available data sets and results from more than 10 years of lacustrine palaeoseismological research in lakes of northern and central switzerland the concept of using lacustrine mass movement event stratigraphy to identify palaeo earthquakes is showcased by presenting new data and results from lake zurich the late glacial to holocene mass movement units in this lake document a complex history of varying tectonic and environmental impacts results include sedimentary evidence of three major and three minor simultaneously triggered basin wide lateral slope failure events interpreted as the fingerprints of palaeoseismic activity a refined earthquake catalogue which includes results from previous lake studies reveals a non uniform temporal distribution of earthquakes in northern and central switzerland a higher frequency of earthquakes in the late glacial and late holocene period documents two different phases of neotectonic activity they are interpreted to be related to isostatic post glacial rebound and relatively recent re activation of seismogenic zones respectively magnitudes and epicentre reconstructions for the largest identified earthquakes provide evidence for two possible earthquake sources i a source area in the region of the alpine or sub alpine front due to release of accumulated north west south east compressional stress related to an active basal thrust beneath the aar massif and ii a source area beneath the alpine foreland due to reactivation of deep seated strike slip faults such activity has been repeatedly observed instrumentally for example during the most recent magnitude 4 2 and 3 5 earthquakes of february 2012 near zug the combined lacustrine record from northern and central switzerland indicates that at least one of these potential sources has been capable of producing magnitude 6 2 to 6 7 events in the past

lacustrine turbidites produced by surficial slope sediment remobilization a mechanism for continuous and sensitive turbidite paleoseismic records turbidite records along ocean margins and in lake basins are increasingly used as paleoseismic proxies however the slope remobilization processes that formed the earthquake related turbidity currents are poorly understood and therefore it is difficult to assess the consistency of turbidite paleoseismic records we analyzed the sedimentary imprint of the giant ad 1960 mw 9 5 chile earthquake in four south central chilean lakes mass transport deposits and turbidites were compared by interpreting reflection seismic profiles sedimentary facies volume balances and proxies for turbidite composition i e grain size radionuclides sediment color organic matter sediment lightness was used as a proxy for organic matter content comparison of lightness of turbidites and the underlying sediments shows that earthquake triggered turbidites in the four lakes result from remobilization of a thin veneer on average about 5 cm of slope sediments and do not result from disintegration of subaquatic landslides statistical analysis of 34 turbidites in a new 5200 year sedimentary record does not show any correlation between inter event time and turbidite thickness and thus volume this means that inter event slope recharging is not a dominant factor governing turbidite recurrence and that initiation of turbidity currents by remobilization of surficial sediments is different to slope failure related to subaquatic landslides we conclude that surficial slope sediment remobilization forms a valid mechanism that explains why turbidite paleoseismic records can be of excellent continuity and high sensitivity moreover based on correlations between seismic intensity turbidite volume and stratigraphic remobilization depth we propose that surficial slope sediment remobilization allows for turbidite records containing information about paleo earthquake intensity

paleoseismic potential of sublacustrine landslide records in a high seismicity setting south central alaska abstract sublacustrine landslide stratigraphy is considered useful for quantitative paleoseismology in low seismicity settings however as the recharging of underwater slopes with sediments is one of the factors that governs the recurrence of slope failures it is not clear if landslide deposits can provide continuous paleoseismic records in settings of frequent strong shaking to test this we selected three lakes in south central alaska that experienced a strong historical megathrust earthquake the 1964 m w 9 2 great alaska earthquake and exhibit high sedimentation rates in their main basins 0 2 cm yr 1 1 0 cm yr 1 we present high resolution reflection seismic data 3 5 khz and radionuclide data from sediment cores in order to investigate factors that control the establishment of a reliable landslide record seismic stratigraphy analysis reveals the presence of several landslide deposits in the lacustrine sedimentary infill most of these landslide deposits can be attributed to specific landslide events as multiple landslide deposits sourced from different lacustrine slopes occur on a single stratigraphic horizon we identify numerous events in the lakes eklutna lake proximal basin 14 events eklutna lake distal basin 8 events skilak lake 7 events and kenai lake 7 events the most recent event in each basin corresponds to the historic 1964 megathrust earthquake all events are characterized by multiple landslide deposits which hints at a regional trigger mechanism such as an earthquake the synchronicity criterion this means that the landslide record in each basin represents a record of past seismic events based on extrapolation of sedimentation rates derived from radionuclide dating we roughly estimate a mean recurrence interval in the eklutna lake proximal basin eklutna lake distal basin skilak lake and kenai lake at 250 yrs 450 yrs 900 yrs and 450 yrs respectively this distinct difference in recording can be explained by variations in preconditioning factors like slope angle slope recharging sedimentation rate and the sediment source area faster slope recharging and a predominance of delta and alluvial fan failures increase the sensitivity and lower the intensity threshold for slope instability also the seismotectonic setting of the lakes has to be taken into account this study demonstrates that sublacustrine landslides in several alaskan lakes can be used as reliable recorders of strong earthquake shaking when a multi lake approach is used and can enhance the temporal and spatial resolution of the paleoseismic record of south central alaska

influence of syntectonic sedimentation on thrust wedges in analogue models scaled analogue sandbox models have been used to simulate the growth of coulomb thrust wedges that include syntectonic sedimentation during thrusting increases in the syncontractional sedimentation rate dramatically change the shape of the coulomb thrust wedge decreasing the number of thrust slices the internal shortening and the critical taper of the wedge thrust trajectories change from ramp flat to sigmoidal with increased syncontractional sedimentation the analogue models show many similarities to thrust fault geometries in accretionary prisms and foreland fold and thrust belts in which thrust slices prograded into basins with active sedimentation

megaturbidite deposits in the holocene basin fill of lake como southern alps italy abstract for the first time limnogeological investigations have been carried out in lake como the deepest lake of the alps combining a bathymetric survey multibeam simrad 3000 with a high resolution seismic reflection study single channel 3 5 khz sub bottom profiler and a coring campaign gravity corer this data set enables detailed characterization of the sedimentary subsurface in the western branch of the lake the como branch which has a typical fjord morphology this paper focuses on the deepest part of the como branch argegno basin in which up to 3 5 m thick turbidite deposits are identified the basin fill of the como branch is characterized by well layered draping and onlapping pelagic sediments that are locally affected by creeping and that are intercalated with mass wasting deposits in particular with two large debris flow deposits evolving into megaturbidites in the deepest part of the basin the multibeam data together with the acoustic facies distributions and the volumes of these two major sedimentary deposits mt1 3 106 m3 and mt2 10 5 106 m3 indicate that they resulted from large slides at the northern tip of the como branch along the steep slopes of a sub lacustrine plateau the estimated ages of these events around the mid 12th mt1 and early 6th mt2 centuries are extrapolated from mean sedimentation rates based on radiocarbon 14c and radionuclide 137cs analyses from short cores in the argegno basin possible trigger mechanisms leading to these catastrophic events in the como branch include a combination of steep slope overloading with significant lake level fluctuations related to holocene climate change and or earthquake shaking the tentative age assignment places the age of both major mass movements near two other events mt1 near the occurrence of a major earthquake in the po plain in 1222 ad intensity ix mcs macroseismically derived magnitude 6 2 and mt2 near a megaturbidite triggered in 700 ad in a proglacial lake in southeastern switzerland blass a anselmetti f grosjean m sturm m 2005 the last 1300 years of environmental history in the sediments of lake sils engadine switzerland eclogae geologicae helvetiae 98 319 332 since dangerous tsunami like waves seiches can be generated by large sub aqueous landslides leading to such megaturbidites in this fjord like basin future studies are required 1 to constrain the age of these catastrophic events 2 to document the stabilities of the steep slopes in the como branch 3 to assess the expected frequency of such catastrophic events and 4 to model the propagation of large waves in the como branch and their potential damage along the highly populated lake shore

active shortening of the cascadia forearc and implications for seismic hazards of the puget lowland 1 margin parallel shortening of the cascadia forearc is a consequence of oblique subduction of the juan de fuca plate beneath north america strike slip thrust and oblique crustal faults beneath the densely populated puget lowland accommodate much of this north south compression resulting in large crustal earthquakes to better understand this forearc deformation and improve earthquake hazard assessment we here use seismic reflection surveys coastal exposures of pleistocene strata potential field data and airborne laser swath mapping to document and interpret a significant structural boundary near the city of tacoma this boundary is a complex structural zone characterized by two distinct segments the northwest trending eastern segment extending from tacoma to carr inlet is formed by the broad 11 5 km southwest dipping 11 20 rosedale monocline this monocline raises crescent formation basement about 2 5 km resulting in a moderate gravity gradient we interpret the rosedale monocline as a fault bend fold forming above a deep thrust fault within the rosedale monocline inferred quaternary strata thin northward and form a growth triangle that is 4 1 to 6 6 km wide at its base suggesting 2 3 mm yr of slip on the underlying thrust the western section of the 40 km long north dipping tacoma fault extending from hood canal to carr inlet forms the western segment of the tacoma basin margin structural relief on this portion of the basin margin may be several kilometers resulting in steep gravity and aeromagnetic anomalies quaternary structural relief along the tacoma fault is as much as 350 400 m indicating a minimum slip rate of about 0 2 mm yr the inferred eastern section of the tacoma fault east of carr inlet crosses the southern part of the seattle uplift has variable geometry along strike and diminished structural relief the tacoma fault is regarded as a north dipping backthrust to the seattle fault so that slip on a master thrust fault at depth could result in movement on the seattle fault the tacoma fault or both

evolution of tectono sedimentary systems in the kumano basin nankai trough forearc abstract sedimentary deposits in the distal kumano forearc basin of the nankai accretionary margin off kii peninsula japan have been imaged using three dimensional 3d seismic data the seismic data along with logging and core data from the integrated ocean drilling program iodp show that the unconformity between the accretionary prism and overlying forearc sediments is time transgressive the unconformity at site c0002 separates 5 ma prism rocks from 3 65 ma basin deposits at site c0009 it separates 5 6 ma prism from 3 8 ma basin sediments acoustic reflections in the basal deposits are sub parallel to the underlying accretionary prism the acoustic facies varies in thickness from 50 to 750 m the mudstone deposits and laterally equivalent turbidites are interpreted as lower trench slope deposits the condensed slope sediment ss section decreases in age from 3 5 to 1 5 ma at site c0002 to 1 5 0 9 ma at c0009 acoustic sequences within the lower forearc basin lfb contain higher proportions of silt and sand turbidites and progressively onlap the ss unit along a low angle discontinuity kl in a landward direction because of the landward onlap of the lfb unit the oldest lfb strata at c0002 are older than 1 67 ma whereas those at c0009 are younger than 0 9 ma thus the amount of time missing or characterized by condensed sedimentation across the kl unconformity decreases in duration in the landward direction the landward onlapping sequences tilt progressively landward in response to regional uplift along an out of sequence thrust oost mega splay fault regional tilting shifted the basin s depocenter progressively landward expanding that part of the basin from 10 km in width to 30 km the onset of sand silt turbidite deposition in the distal basin began after more accommodation space was created by the uplift of the outer ridge along the splay fault at 1 9 ma conversely turbidites of the upper forearc basin ufb progressively onlap lfb in a seaward direction furthermore the respective thicknesses of the lfb and ufb units switch from the seaward side of the basin c0002 farther landward c0009 the lfb unit is 800 m thick in the seaward region whereas it is only 200 300 m thick in the landward region the ufb unit is

the 1946 mount colonel foster rock avalanche and associated displacement wave vancouver island british columbia the 1946 vancouver island earthquake m 7 2 triggered a rock avalanche from the north face of mount colonel foster central vancouver island british columbia approximately 1 5 106 m3 of triassic volcaniclastic rocks detached from between el 1965 m and el 1600 m although just over half of this volume was deposited in the upper part of the track above el 1080 m approximately 0 7 106 m3 descended the lower part of the track and entered the waters of landslide lake at el 890 m the resultant displacement wave ran up a maximum vertical distance of 51 m on the opposite shore and the wave crest was about 29 m high when it spilled over the lip of the lake water displaced during the event destroyed forest in the upper reaches of the elk river valley up to 3 km from landslide lake the wave at landslide lake is comparable to other waves generated by similar magnitude rock avalanches in peru and norway and it is the largest recorded in the canadian cordillera the case history illustrates the conditi

a comparison of the sedimentary records of the 1960 and 2010 great chilean earthquakes in 17 lakes implications for quantitative lacustrine palaeoseismology seismically induced event deposits embedded in the sedimentary infill of lacustrine basins are highly useful for palaeoseismic reconstructions recent well documented great megathrust earthquakes provide an ideal opportunity to calibrate seismically induced event deposits for lakes with different characteristics and located in different settings this study used 107 short sediment cores to investigate the sedimentary impact of the 1960 mw 9 5 valdivia and the 2010 mw 8 8 maule earthquakes in 17 lakes in south central chile i e lakes negra lo encanado aculeo vichuquen laja villarrica calafquen pullinque pellaifa panguipulli neltume rinihue ranco maihue puyehue rupanco and llanquihue a combination of image analysis magnetic susceptibility and grain size analysis allows identification of five types of seismically induced event deposits i mass transport deposits ii in situ deformations iii lacustrine turbidites with a composition similar to the hemipelagic background sediments lacustrine turbidites type 1 iv lacustrine turbidites with a composition different from the background sediments lacustrine turbidites type 2 and v megaturbidites these seismically induced event deposits were compared to local seismic intensities of the causative earthquakes eyewitness reports post earthquake observations and vegetation and geomorphology of the catchment and the lake megaturbidites occur where lake seiches took place lacustrine turbidites type 2 can be the result of i local near shore mass wasting ii delta collapse iii onshore landslides iv debris flows or mudflows or v fluvial reworking of landslide debris on the contrary lacustrine turbidites type 1 are the result of shallow mass wasting on sublacustrine slopes covered by hemipelagic sediments due to their more constrained origin lacustrine turbidites type 1 are the most reliable type of seismically induced event deposits in quantitative palaeoseismology because they are almost exclusively triggered by earthquake shaking moreover they most sensitively record varying seismic shaking intensities the number of lacustrine turbidites type 1 linearly increases with increasing seismic intensity starting with no lacustrine turbidites type 1 at intensities between v and vi and reaching 100 when intensities are higher than vii combining different types of seismically induced event deposits allows the reconstruction of the complete impact of an earthquake

effect of increased shear stress along a plate boundary fault on the formation of an out of sequence thrust and a break in surface slope within an accretionary wedge based on numerical simulations abstract we investigated the effect on accretionary wedge structure of increased shear stress which describes the frictional sliding resistance along a decollement arising from an increase in material friction or reduction in pore pressure to clarify the nature of the effect we performed numerical simulations using two models a stable friction model and an increased friction model the stable friction model produced a low angle smooth surface slope and an in sequence thrust whereas the increased friction model produced a break in surface slope scarp and an out of sequence thrust ost that cuts through the thrust sheet the ost formed via the connection of segments of two adjacent thrusts and its formation resulted in a change in the thickening mode of the wedge from thrust sheet rotation and back thrust activity to underplating this contrast in thickening mode between the landward high friction zone and seaward low friction zone resulted in the formation of a clear break in slope as the landward zone is steeper than the seaward zone consistent with critical taper theory the subduction of a basement slice or seamount can produce similar structures arising from an increase in resistance to basal shear sliding however the distinctive structures arising in an accretionary wedge as a result of increased shear sliding resistance include a flat basal plane and absence of slope failure sediments beneath the ost these structural features are observed in accretionary wedges of the nankai trough off muroto japan the sunda strait and the barbados ridge

backstop geometry and accretionary mechanics of the sunda margin the convergent sunda margin off indonesia displays all geological features characteristic of an accretion dominated subduction zone a combined interpretation of prestack depth migrated seismic reflection data and velocity information gained from refraction studies is supplemented by high resolution bathymetric data and for the first time allows the exact mapping of backstop regimes initially the outer high evolved as material was pushed against a static rigid arc framework backstop underlying a forearc basin increasing material strength of the outer high due to lithification formed a dynamic backstop which controls accretion today an out of sequence thrust marks the transition from the recent active frontal accretionary prism to the outer high and may be traced in the seismic and bathymetric data over the whole extent of the study area the existence of a static as well as a dynamic backstop controls the forearc geometry and is associated with the segmentation of the forearc which is observed in regimes of frontal as well as of oblique subduction mass balance calculations which account for porosity changes and metamorphism indicate a subduction history dominated by accretionary processes since the late eocene accretion is associated with the low values of basal friction inferred for the sunda margin structural investigations of conjugate fault planes indicate a very weak basal detachment effective stress analyses reveal that intrinsically weak material causes the high strength ratio of the detachment to the overlying sediments whereas overpressuring within the frontal accretionary prism is negligible

structural evolution of backthrusting in the mentawai fault zone offshore sumatran forearc 1 we present the interpretation of newly acquired high quality industry standard deep seismic reflection and swath bathymetry data to provide insight into the structural style and evolution of the mentawai fault zone mfz the mfz lies along the boundary between the accretionary wedge and the proposed continental backstop this zone exhibits arcuate ridges on the seafloor convex toward the east beneath these ridges the structures developed as landward vergent imbricated backthrusts in the inner part of the accretionary wedge and higher angle backthrusts that deformed the forearc basin sediments in the forearc high anticlines were developed due to the seaward vergent forearc high thrusts originating in the accretionary wedge the imbricated backthrusts may have initiated during the early middle miocene contemporaneously with the slide and back rotation of forearc high thrusts in the late miocene the higher angle backthrusts were initiated continuous contraction induced the frontal higher angle backthrusts and formed a fold thrust belt toward the east during the pliocene the folds and thrusts were disturbed by diapirs and mud volcanoes backthrusting and fold thrust belts developed in the mfz may explain the compressional features observed at the boundary between the accretionary wedge and continental backstop along the southern sumatra margin the backthrusts along the mfz are waning in activity and hence the risk of a large earthquake and associated tsunami at the present time should be small

a high precision age estimate of the holocene plinian eruption of mount mazama oregon usa the climactic eruption of mount mazama in oregon north america resulted in the deposition of the most widespread holocene tephra deposit in the conterminous united states and south western canada the tephra forms an isochronous marker horizon for palaeoenvironmental sedimentary and archaeological reconstructions despite the current lack of a precise age estimate for the source eruption previous radiocarbon age estimates for the eruption have varied and greenland ice core ages are in disagreement for the mazama tephra to be fully utilised in tephrochronology and palaeoenvironmental research a refined precise and accurate age for the eruption is required here we apply a meta analysis of all previously published radiocarbon age estimations n 81 and perform bayesian statistical modelling to this data set to provide a refined age of 7682 7584 cal yr bp 95 4 probability range although the depositional histories of the published ages vary this estimate is consistent with that estimated from the gisp2 ice core of 7627 150 yr bp zdanowicz et al 1999

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

continuous pollen diagrams for the last 3 5 m y from israel vegetation climate and correlation with the oxygen isotope record abstract several continuous pollen diagrams have been obtained from boreholes penetrating the entire quaternary sequences of the hula and dead sea lakes in the jordan rift valley israel the dead sea served as a terminal base level through this period thus ensuring a complete continuous deposition volcanic intercalations within the hula lake sediments permit some control of the absolute datings a paleoclimatic model for the last 150 k y based on better dated sequences serves as a basis for correlating the israeli sections with the oxygen isotope records known from the oceans and the mediterranean the glacial phases are manifested in israel by periods of somewhat lower temperatures and higher rainfall some in summertime the interglacials are hot and dry with saharan conditions prevailing the interstadials are of the present day character of a short rainy winter and a dry hot long summer the first major cooling of the quaternary in israel took place some 2 4 2 6 m y ago followed by a series of alternating wetter and drier phases corresponding quite well to changes in the global ice volume expressed by the oxygen isotope curves it seems however that some successions of the glacial phases are grouped in israel into longer wetter periods with the interglacials manifested as interstadials a similar case is seen for some of the interglacials successions with glacial phases as interstadials a possible explanation for the difference between the continental and the ocean records may lie in the distribution of the global ice volume differences in the accumulations of ice at the arctic and antarctic regions during some of the glacial phases could explain the extent of a glacial period on land while not being apparent from the oxygen isotope records and vice versa for the interglacials thus a well developed ice cap on antarctica may cause only a minor glaciation in the northern hemisphere but be recorded as a full glacial in the oceans

identification of the static backstop and its influence on the evolution of the accretionary prism in the nankai trough abstract to reveal the origin of a backstop and its influence on the evolution of the accretionary prism we analyzed reflection seismic data acquired in the nankai trough off the kii peninsula the deformation features of the forearc basin sequence show that the landward accretionary prism close to the coast was not deformed after the development of the forearc basin about 2 4 ma the surface of the landward prism can be identified as strong amplitude reflector indicating that the landward prism has higher seismic velocity therefore the landward accretionary prism inferred to be of higher strength constitutes a static backstop based on seismic and geologic observations we interpret that the backstop was generated due to the large age differences of accreted material resulting from an inferred hiatus in subduction between 13 and 6 ma the time dependent processes such as the igneous activity in middle miocene further contribute to the development of the backstop a ridge structure beneath the forearc basin located trenchward of this backstop and running roughly parallel to it appears to reflect activity on an ancient splay fault the strike of the ancient splay fault runs parallel to the backstop identified in this study and oblique to the current trench this geometry suggests that location and mechanical behavior of this splay fault system is influenced by the backstop and its distribution could be related to the coseismic rupture area

the spatial and temporal distribution of grain size breaks in turbidites grain size breaks are surfaces where abrupt changes in grain size occur vertically within deposits grain size breaks are common features in turbidites around the world including ancient and modern systems despite their widespread occurrence grain size breaks have been regarded as exceptional and not included within idealized models of turbidity current deposition this study uses ca 100 shallow sediment cores from the moroccan turbidite system to map out five turbidite beds for distances in excess of 2000 km the vertical and spatial distributions of grain size breaks within these beds are examined five different types of grain size break are found type i in proximal areas between coarse sand and finer grained structureless sand type ii in proximal areas between inversely graded sand overlain by finer sand type iii in proximal areas between sand overlain by ripple cross laminated finer sand type iv throughout the system between clean sand and mud and type v in distal areas between mud rich debrite sand and mud this article interprets types i and v as being generated by sharp vertical concentration boundaries controlled by sediment and clay concentrations within the flows whilst types ii and iii are interpreted as products of spatial temporal fluctuations in flow capacity type iv are interpreted as the product of fluid mud layers which hinder the settling of non cohesive grains and bypasses them down slope decelerating suspensions with sufficient clay will always form cohesive layers near to bed promoting the generation of type iv grain size breaks this may explain why type iv grain size breaks are widespread in all five turbidites examined and are commonplace within turbidite sequences studied elsewhere therefore type iv grain size breaks should be understood as the norm not the exception and regarded as a typical feature within turbidite beds

a study of pleistocene and holocene hyaena coprolites abstract hyaena coprolites from a diachronic series of archaeological sites in israel were examined and compared with recent faecal material from striped hyaena dens and zoos three methods were applied in the analysis of all samples gross morphometrical attributes x ray diffraction and petrological thin sections this last method is an innovation in the field of coprolite studies and facilitates the long term preservation of the original textural characteristics and fabric of sections of the coprolite the combination of these three approaches facilitated among other things the assessment of hyaena diet in the past as well as in the present and determination of local environmental factors affecting the composition of the coprolite we also obtained some indication of changes related to ageing of the material

lacustrine turbidites as a tool for quantitative earthquake reconstruction new evidence for a variable rupture mode in south central chile understanding the long term earthquake recurrence pattern at subduction zones requires continuous paleoseismic records with excellent temporal and spatial resolution and stable threshold conditions south central chilean lakes are typically characterized by laminated sediments providing a quasi annual resolution our sedimentary data show that lacustrine turbidite sequences accurately reflect the historical record of large interplate earthquakes among others the 2010 and 1960 events furthermore we found that a turbidite s spatial extent and thickness are a function of the local seismic intensity and can be used for reconstructing paleo intensities consequently our multilake turbidite record aids in pinpointing magnitudes rupture locations and extent of past subduction earthquakes in south central chile comparison of the lacustrine turbidite records with historical reports a paleotsunami subsidence record and a marine megaturbidite record demonstrates that the valdivia segment is characterized by a variable rupture mode over the last 900 years including i full ruptures mw 9 5 1960 1575 1319 9 1127 44 ii ruptures covering half of the valdivia segment mw 9 1837 and iii partial ruptures of much smaller coseismic slip and extent mw 7 5 8 1737 1466 4 also distant or smaller local earthquakes can leave a specific sedimentary imprint which may resolve subtle differences in seismic intensity values for instance the 2010 event at the maule segment produced higher seismic intensities toward southeastern localities compared to previous megathrust ruptures of similar size and extent near concepci n

landslide erosion controlled by hillslope material landslide erosion is a primary control of landscape relief a wide ranging analysis of landslide geometry shows that soil based landslides are generally less voluminous than landslides that involve the failure of bedrock and provides refined metrics for estimating the volume of a landslide from the area of the failure

steady rotation of the cascade arc displacement of the miocene cascade volcanic arc northwestern north america from the active arc is in the same sense and at nearly the same rate as the present clockwise block motions calculated from gps velocities in a north american reference frame migration of the ancestral arc over the past 16 m y can be explained by clockwise rotation of upper plate blocks at 1 0 m y over a linear melting source moving westward 1 4 5 km m y due to slab rollback block motion and slab rollback are in opposite directions in the northern arc but both are westerly in the southern extensional arc where rollback may be enhanced by proximity to the edge of the juan de fuca slab similarities between post 16 ma arc migration paleomagnetic rotation and modern gps block motions indicate that the secular block motions from decadal gps can be used to calculate long term strain rates and earthquake hazards northwest directed basin and range extension of 140 km is predicted behind the southern arc since 16 ma and 70 km of shortening is predicted in the northern arc the gps rotation poles overlie a high velocity slab of the siletzia terrane dangling into the mantle beneath idaho united states which may provide an anchor for the rotations

signatures of slope failures and river delta collapses in a perialpine lake lake lucerne switzerland historical reports from the 17th century document two destructive tsunamis with runups exceeding 5 m affecting proximal basins of lake lucerne switzerland one event in ad 1601 is coeval with a strong nearby earthquake mw ca 5 9 which caused extensive slope failures in many parts of the lake the second event in ad 1687 is associated with an apparently spontaneous partial collapse of the muota river delta this study combines high resolution bathymetry reflection seismic and lithological data in order to document the sedimentary and morphological signatures of the two subaqueous mass movements that probably generated the observed tsunamis such mass movements are significant as a common sedimentation process and as natural hazard in fjord type lakes and similar environments the deposits covering large parts of the basins with thicknesses reaching 10 m consist of two subunits a lower massflow deposit contains variably deformed sediments from the source areas its emplacement affected pre existing sediments incorporating thin sediment slices into the deposit and increasing its volume deep reaching deformation near this is an accepted article that has been peer reviewed and approved for publication in the sedimentology but has yet to undergo copy editing and proof correction

lituya bay landslide impact generated mega tsunami 50th anniversary on july 10 1958 an earthquake mw 8 3 along the fairweather fault triggered a major subaerial landslide into gilbert inlet at the head of lituya bay on the southern coast of alaska the landslide impacted the water at high speed generating a giant tsunami and the highest wave runup in recorded history the mega tsunami runup to an elevation of 524 m caused total forest destruction and erosion down to bedrock on a spur ridge in direct prolongation of the slide axis a cross section of gilbert inlet was rebuilt at 1 675 scale in a two dimensional physical laboratory model based on the generalized froude similarity a pneumatic landslide tsunami generator was used to generate a high speed granular slide with controlled impact characteristics state of the art laser measurement techniques such as particle image velocimetry piv and laser distance sensors lds were applied to the decisive initial phase with landslide impact and wave generation as well as the runup on the headland piv provided instantaneous velocity vector fields in a large area of interest and gave insight into kinematics of wave generation and runup the entire process of a high speed granular landslide impact may be subdivided into two main stages a landslide impact and penetration with flow separation cavity formation and wave generation and b air cavity collapse with landslide run out and debris detrainment causing massive phase mixing formation of a large air cavity similar to an asteroid impact in the back of the landslide is highlighted a three dimenional pneumatic landslide tsunami generator was designed constructed and successfully deployed in the tsunami wave basin at osu the lituya bay landslide was reproduced in a three dimensional physical model at 1 400 scale the landslide surface velocities distribution was measured with piv the measured tsunami amplitude and runup heights serve as benchmark for analytical and numerical models

paleoseismic evidence for late holocene tectonic deformation along the saddle mountain fault zone southeastern olympic peninsula washington abstract trench and wetland coring studies show that northeast striking strands of the saddle mountain fault zone ruptured the ground about 1000 years ago generating prominent scarps three conspicuous subparallel fault scarps can be traced for 15 km on light detection and ranging lidar imagery traversing the foothills of the southeast olympic mountains the saddle mountain east fault the saddle mountain west fault and the newly identified sund creek fault uplift of the saddle mountain east fault scarp impounded stream flow forming price lake and submerging an existing forest thereby leaving drowned stumps still rooted in place stratigraphy mapped in two trenches one across the saddle mountain east fault and the other across the sund creek fault records one and two earthquakes respectively as faulting juxtaposed miocene age bedrock against glacial and postglacial deposits although the stratigraphy demonstrates that reverse motion generated the scarps slip indicators measured on fault surfaces suggest a component of left lateral slip from trench exposures we estimate the postglacial slip rate to be 0 2 mm yr and between 0 7 and 3 2 mm yr during the past 3000 years integrating radiocarbon data from this study with earlier saddle mountain fault studies into an oxcal bayesian statistical chronology model constrains the most recent paleoearthquake age of rupture across all three saddle mountain faults to 1170 970 calibrated years cal b p which overlaps with the nearby m w 7 5 1050 1020 cal b p seattle fault earthquake an earlier earthquake recorded in the sund creek trench exposure dates to around 3500 cal b p the geometry of the saddle mountain faults and their near synchronous rupture to nearby faults 1000 years ago suggest that the saddle mountain fault zone forms a western boundary fault along which the fore arc blocks migrate northward in response to margin parallel shortening across the puget lowland

geophysical evidence for dewatering and deformation processes in the odp leg 170 area offshore costa rica abstract we use a combination of borehole data from ocean drilling program odp leg 170 and multichannel seismic reflection mcs data to quantify thickness changes in underthrust sediments away from the boreholes sediments thrust beneath the upper plate at convergent margins may be more rapidly loaded than in any other environment depending on the porosity and permeability of the available fluid pathways these sediments can compact and dewater very rapidly as observed in this area offshore the nicoya peninsula costa rica rapid thinning and dewatering was previously interpreted in this area from mcs data but the lack of velocity data in this deep water environment caused ambiguity in the estimates of thickness change we employ a non linear inversion technique using detailed density data primarily logs and some laboratory measurements and coincident mcs data to create 1d synthetic seismograms and detailed velocity functions at three odp drill sites because only a small part of one hole was logged with a sonic tool and the laboratory measurements significantly underestimate in situ velocities these results provide the most accurate estimate of the velocity profiles we used these velocity functions to depth migrate seven mcs lines in the vicinity of the trench and lower slope spanning a distance of 9 km along strike analysis of the depth migrated images shows that there is significant variation along strike in how the underthrust section compacts which appears to be related to the distribution of normal faults on the cocos plate we interpret that preferentially rapid dewatering in the upper part of the underthrust section may lead to deformation below the original decollement and detachments at deeper stratigraphic levels

palaeosols and late pleistocene rainfall fluctuations in the negev desert the existence of a series of palaeosols in the present day desert region of southern israel the northern negev desert 1 2 indicates recurring periods of wetter climate in the past up to seven well developed palaeosols occur within a section and each has a horizon containing soft calcium carbonate nodules 3 15 mm in diameter the palaeosols are developed within loess or fluvially redeposited loess consisting of silty clay or clayey silt the 14c ages of the uppermost three calcic horizons average 13 000 yr bp calcic horizon ch i 28 000 yr bp ch ii and 37 000 yr bp ch iii drier phases occurred between these periods of pedogenesis especially during the last glacial maximum centred at 18 000 yr bp when extensive erosion occurred analysis of the 13c content of nodule carbonates points to the occurrence of strong north south rainfall gradients during each period of calcic horizon formation which excludes the possibility of monsoonal rains contributing to the increased rainfall during these periods the palaeosols correspond to global warm phases of the last glacial period

time dependent recurrence of strong earthquake shaking near plate boundaries a lake sediment perspective abstract accurate probabilistic seismic hazard analysis requires a good knowledge of the recurrence parameters of the strongest earthquakes in a region due to the typical short temporal span of instrumental and historical data it is often unclear whether one should adopt a time dependent or time independent poissonian recurrence model the choice of which has large repercussions on the probability estimates for new strong events the rapidly growing discipline of lacustrine paleoseismology aims at producing long continuous records of strong seismic shaking which integrate the activity of all significant seismic sources in a region and allow a reliable determination of recurrence patterns the typical continuous sedimentation regime in lakes can lead to complete sensitive paleoseismic records and a reduced temporal uncertainty in recurrence intervals here i present a worldwide compilation of published long lacustrine paleoseismic records grouped per tectonic domain and statistically explore the variability of their recurrence intervals expressed by the coefficient of variation cov a cov 1 indicates a time independent process whereas cov 1 may be related to changes in the sensitivity of the lacustrine paleoseismograph or to real earthquake clustering due to e g stress transfer between neighboring faults the most useful lacustrine paleoseismic records can be retrieved in high seismicity settings where many paleoseismic events can be recorded in a relatively short time span i e

landslide and tsunami hazard at yate volcano chile as an example of edifice destruction on strike slip fault zones the edifice of yate volcano a dissected stratocone in the andean southern volcanic zone has experienced multiple summit collapses throughout postglacial time restricted to sectors ne and sw of the summit the largest such historic event occurred on 19th february 1965 when 6 1 10 106 m3 of rock and ice detached from 2 000 m elevation to the sw of the summit and transformed into a debris flow in the upper part of the flow path velocities are estimated to have reached 40 m s 1 after travelling 7 500 m and descending 1 490 m the flow entered an intermontane lake lago cabrera a wavemaker of estimated volume 9 3 106 m3 generated a tsunami with an estimated amplitude of 25 m and a run up of 60 m at the west end of the lake where a settlement disappeared with the loss of 27 lives the landslide followed 15 days of unusually heavy summer rain which may have caused failure by increasing pore water pressure in rock mechanically weathered through glacial action the preferential collapse directions at yate result from the volcano s construction on the dextral strike slip liquine ofqui fault zone movement on the fault during the lifetime of the volcano is thought to have generated internal instabilities in the observed failure orientations at 10 to the fault zone in the riedel shear direction this mechanically weakened rock may have led to preferentially orientated glacial valleys generating a feedback mechanism with collapse followed by rapid glacial erosion accelerating the rate of incision into the edifice through repeated landslides debris flows with magnitudes similar to the 1965 event are likely to recur at yate with repeat times of the order of 102 years with a warming climate increased glacial meltwater due to snowline retreat and increasing rain at the expense of snow may accelerate rates of edifice collapse with implications for landslide hazard and risk at glaciated volcanoes in particular those in strike slip tectonic settings where orientated structural instabilities may exist

vegetation response to glacial interglacial climate variability near lake malawi in the southern african tropics abstract pollen records from lake malawi africa spanning the last 135 kyr show substantial and abrupt vegetation response to multiple episodes of extreme aridity between 135 and 75 ka peaks in both the relative abundance and total production of podocarpus pollen define the first two of these drought episodes from 135 to 127 and again from 117 to 105 kyr bp podocarpus percentages remain above 16 with peak values as high as 38 indicating a period marked by a cool climate resulting in expansion of montane forest taxa to lower elevations marine palynological records from the angola margin and congo fan show similar peak podocarpus percentages at this time oxygen isotope stage 5d indicating a similar climate across the african continent at this latitude from 105 to 90 ka continuing drought resulted in total pollen accumulation rates in lake malawi to fall to less than 300 grains cm2 yr of predominately grass pollen this episode in african history was severe enough to cause the disappearance of pteridophytes and forest taxa such as uapaca and brachystegia as well as montane taxa podocarpus olea spp and ericaceae within the pollen source area of lake malawi these taxa all remain nearly absent from the surrounding vegetation for the next 18 000 years the resultant semi desert vegetation would have been inhospitable for early humans living within or traveling through the lake malawi region increasing moisture following these arid intervals allowed expansion creation and maintenance of a more diverse landscape vegetation mosaic around lake malawi including zambezian miombo woodland humid evergreen woodland and afromontane forests the relative abundance of each fluctuated in response to either cooling i e afromontane expansion from 60 to 56 ka or moisture balance i e increasing humid evergreen woodland between 75 and 65 ka notably there was no significant change in vegetation composition during the last glacial maximum lgm 30 15 ka as compared to the previous 20 000 years