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

location of the southern edge of the gorda slab and evidence for an adjacent asthenospheric window results from seismic profiling and gravity as the mendocino triple junction migrates northward along the california margin it is widely presumed to leave a slab free or asthenospheric window in its wake a 250 km long south north seismic refraction reflection profile crossing the transition from transform to subduction regimes allows us to compare and contrast crust and upper mantle of the north american margin before and after it is modified by passage of the mendocino triple junction from the seismic data we have determined that 1 the crust is laterally homogeneous in velocity to a depth of 20 km interpreted by us as franciscan complex 2 below 20 km depth the crust is characterized by velocities of 7 0 km s for the southern half of the profile and by velocities of 3 2 g cm 3 is required on the southern end of the profile we interpret these combined results to indicate that our profile crosses the southern edge of the gorda plate and that directly adjacent to this edge is an asthenospheric window with overlying mafic rocks in the crust these mafic rocks and a reforming lithospheric mantle increase in thickness southward

transition from slab to slabless results from the 1993 mendocino triple junction seismic experiment three seismic refraction reflection profiles part of the mendocino triple junction seismicexperiment allowustocompareandcontrastcrustanduppermantleofthenorth american margin before and after it is modified by passage of the mendocino triple junction upper crustal velocity models reveal an asymmetric great valley basin overlying sierran or ophiolitic rocks at the latitude of fort bragg california and overlying sierran or klamath rocks near redding california in addition the upper crustal velocity structure indicates that franciscan rocks underlie the klamath terrane east of eureka california thefranciscancomplexis onaverage laterallyhomogeneousandisthickestinthe triple junction region north of the triple junction the gorda slab can be traced 150 km inboardfromthecascadiasubductionzone southofthetriplejunction strongprecritical reflections indicate partial melt and or metamorphicfluids at the base of the crust or in theuppermantle breaksinthesereflectionsarecorrelatedwiththemaacamaandbartlett springs faults suggesting that these faults extend at least to the mantle we interpret our datatoindicatetectonicthickeningofthefranciscancomplexinresponsetopassageofthe mendocino triple junction and an associated thinning of these rocks south of the triple junction due to assimilation into melt triggered by upwelling asthenosphere the region of thickenedfranciscancomplexoverliesazoneofincreasedscattering intrinsicattenuation or both resulting from mechanical mixing of lithologies and or partial melt beneath the onshore projection of the mendocino fracture zone our data reveal that we have crossed thesouthernedgeofthegordaslabandthatthisedgeand ortheoverlyingnorthamerican crust may have fragmented because of the change in stress presented by the edge

the influence of surface and tectonic processes on landscape evolution of the iberian chain spain quantitative geomorphological analysis and geochronology abstract in tectonically active areas the landscape response to tectonic forcing is described and possibly quantified by regional topographic and hydrographic features as well as by spatial variation in rates of surface processes we investigated the recent landscape evolution of the iberian chain ne spain an intraplate thrust belt formed in cenozoic times and characterized by a dome shaped topography in its central sector the landscape is dominated by low relief surfaces late neogene in age presently standing at an average altitude of 1300 m a recent regional uplift controlled the organization of the present fluvial network and dissection of the landscape in this framework we investigated the geomorphic responses to tectonic forcing by the calculation of morphometric parameters focusing on topography map of local relief swath profiles and hydrography basin hypsometric curve and integral basin asymmetry factor river longitudinal profiles and relative indices and using srtm dem the results of morphometric analysis have been coupled with radiometric uranium series dating of calcareous tufas lying on fluvial strath terraces the obtained ages allow the estimation of incision rate along the high tajo and martin rivers our results indicate that uplift and rock type erodibility are the main factors influencing landscape evolution of the study area the incision rates are very similar throughout the central sector of the range indicating that despite subtle local variation the rivers are responding to a main tectonic input the regional uplift in conclusion the iberian chain landscape is in a transient state in response to a recent dome like uplift indeed the fluvial processes that weakly incised this landscape at a rate of 0 6 mm yr are approaching a radial pattern on the basis of geological and geomorphic constraints we hypothesize that the uplift started around or after 3 ma

evolution and thickness of the lithosphere beneath coastal california many of the tectonic features of the california coast ranges are directly related to the northward migration of the mendocino triple junction along the western edge of north america during the past 20 to 30 m y at the triple junction the western edge of the north american plate slides off the relative northward moving and subducting gorda plate leaving the thin western edge in direct contact with asthenosphere upwelling to fill the space vacated by the underlying gorda plate two dimensional time dependent thermal modeling of this process constrained by teleseismic delay studies is used to construct a map of lithospheric thickness of coastal california among the implications of this map are that 1 the high heat flow in the coast ranges can be almost entirely accounted for by the asthenospheric upwelling associated with the migrating mendocino triple junction 2 the general elevation and the late cenozoic volcanism in the california coast ranges are responses to a zone of unusually thin 20 to 45 km lithosphere that extends southward behind the mendocino triple junction and 3 the course of some segments of the san andreas fault in both central and southern california appear to deviate from a deeper more fundamental transform boundary separating the pacific and north american plates

aminostratigraphy and faunal correlations of late quaternary marine terraces pacific coast usa recent studies using the extent of racemization of amino acids to date fossil mollusc shells in the arctic1 the british isles2 and on the atlantic3 4 and pacific5 13 coasts of north america have relied mainly on theoretical kinetic models of racemization ages generated in this fashion are highly model dependent and require estimates of integrated long term diagenetic temperatures we present here an alternative empirical approach to aminostratigraphy in which we plot amino acid enantiomeric ratios versus latitude for localities along the pacific coast of the united states and generate isochronal correlations by connecting data points of geographically proximal localities that have similar d l ratios and zoogeographic aspect isochrons are calibrated at a few localities by independent radiometric dates the diagenetic temperature effect on racemization is reflected in the slope of the isochrons but the need to quantify temperature is eliminated

rapidly intensifying hurricane guillermo 1997 part i low wavenumber structure and evolution abstract the structure and evolution of rapidly intensifying hurricane guillermo 1997 is examined using airborne doppler radar observations in this first part the low azimuthal wavenumber component of the vortex is presented guillermo s intensification occurred in an environmental flow with 7 8 m s 1 of deep layer vertical shear as a consequence of the persistent vertical shear forcing of the vortex convection was observed primarily in the downshear left quadrant of the storm the greatest intensification during the 6 h doppler observation period coincided with the formation and cyclonic rotation of several particularly strong convective bursts through the left of shear semicircle of the eyewall some of the strongest convective bursts were triggered by azimuthally propagating low wavenumber vorticity asymmetries mesoscale budget analyses of axisymmetric angular momentum and relative vorticity within the eyewall are presented to elucidate the mechanisms contributing to guillermo s structural evol

late pleistocene landscape evolution in south central chile constrained by luminescence and stable cosmogenic nuclide dating landscapes in tectonically active regions develop in response to a complex interplay between rapid tectonic deformation and surface processes in order to understand the evolution of these environments and distinguish between the different factors it is fundamental to identify and quantify geomorphic processes and rates on different time scales the forearc of south central chile provides an ideal setting to elucidate the response of surface processes to climatic and tectonic forcing however in contrast to northern chile this region has attracted little attention due to difficulties in quantifying the age of geomorphic surfaces we use luminescence and stable cosmogenic nuclides 3 he 21 ne on conglomeratic units in the central depression and fluvial valley fills in the coastal cordillera to constrain exposure and burial ages of these units that form major landscape elements in the southern chilean forearc our data indicate that disturbances in the drainage network are controlled by local uplift which may be caused by deformation above an active blind thrust in the coastal cordillera local short term uplift rates reach a minimum of 0 27 mm a 1 and are on the same order as late quaternary minimum incision rates of 0 15 mm a 1 to 0 43 mm a 1 the valley fills in the coastal cordillera have depositional ages of 80 ka and 255 ka respectively exposure ages of the extensive alluvial surfaces in the central depression cluster between 135 ka and 175 ka and between 240 ka and 280 ka hence the deposition of these surfaces broadly coincides with marine isotope stages mis 6 and 8 and appears to be climatically driven

assimilation of geosat altimeter data for the agulhas current using the ensemble kalman filter with a quasigeostrophic model abstract the ring shedding process in the agulhas current is studied using the ensemble kalman filter to assimilate geosat altimeter data into a two layer quasigeostrophic ocean model the properties of the ensemble kalman filter are further explored with focus on the analysis scheme and the use of gridded data the geosat data consist of 10 fields of gridded sea surface height anomalies separated 10 days apart that are added to a climatic mean field this corresponds to a huge number of data values and a data reduction scheme must be applied to increase the efficiency of the analysis procedure further it is illustrated how one can resolve the rank problem occurring when a too large dataset or a small ensemble is used

coupled magma chamber inflation and sector collapse slip observed with synthetic aperture radar interferometry on mt etna volcano 1 volcanoes deform dynamically due to changes in both their magmatic system and instability of their edifice mt etna features vigorous and almost continuous eruptive activity from its summit craters and periodic flank eruptions even though its shape is that of a large stratovolcano its structure features two rift systems and a flank collapse structure similar to hawaiian shield volcanoes we analyze european remote sensing ers satellite differential interferometric synthetic aperture radar insar data 1993 1996 for mt etna spanning its quiescence from 1993 through the initiation of renewed eruptive activity in late 1995 we use synthetic aperture radar sar data from both ascending and descending ers satellite tracks comparison of independent interferograms covering the first 2 years of the inflationary period shows a pattern consistent with inflation of the volcano calculation of the tropospheric path delay based on meteorological data does not change this interpretation interferograms from late summer 1995 1996 show no significant deformation joint inversion of interferograms from ascending and descending satellite tracks require both inflation from a spheroidal magmatic source located beneath the summit at 5 km below sea level and displacement of the east flank of etna along a basal decollement both sources of deformation were contemporaneous within the resolution of our data and suggest that inflation of the central magma chamber acted to trigger slip of etna s eastern flank these results demonstrate that flank instability and recharge of a volcano s magma system must both be considered toward understanding how volcanoes work and in their hazard evaluation

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

satellite analysis and puff simulation of the eruptive cloud generated by the mount etna paroxysm of 22 july 1998 1 we applied the puff algorithm searcy et al 1998 to simulate the space time evolution of the eruptive cloud generated by one of the main paroxysms to have occurred this past century at etna volcano namely the 22 july 1998 explosive event at the voragine summit crater the comparison of puff simulations to satellite images of the ash cloud at different times allowed us to estimate several parameters of the eruptive event such as onset time duration ash cloud height and shape and pyroclast size based on this analysis we concluded that the paroxysm started around 1645 gmt lasted between 20 and 40 min and generated a poissonian shaped ash column nearly 13 km high and composed of particles with a mean diameter md of 10 3 m and size logarithmic standard deviation lsd equal to 1 5 the puff simulations using horizontal and vertical diffusivity values of 5000 and 10 m2 s 1 respectively provided the best agreement to the eruption clouds observed on satellite images the results were compared to the information available in the literature concerning the eruption e g volcanological video camera and volcanic tremor data the analysis showed that the method of simulating the eruptive clouds and comparing simulations to satellite images can give a contribution to the study of paroxysmal events generated by the etna volcano also the degree of accuracy of the cloud simulation leads us to be optimistic about the potential of using this method as a tool for hazard mitigation in the etna region with particular applications to air traffic

tomographic images and 3d earthquake locations of the seismic swarm preceding the 2001 mt etna eruption evidence for a dyke intrusion 1 on july 12 2001 mt etna experienced a sudden increase of seismic activity heralding one of the most intense eruptions of the past 30 years between july 12 and july 18 when the eruption started thousands of small magnitude earthquakes occurred and were recorded by a dense seismic network run by the istituto nazionale di geofisica e vulcanologia sezione di catania ingv ct hypocentral depths of earthquakes were very shallow mostly located above 3 km b s l and clustered near the summit area the high quality seismic dataset gives us the unique opportunity to study the process of magma migration before the eruption in this study we present the three dimensional earthquake locations and the velocity structure obtained by a tomographic inversion the shallowness of seismicity allowed us to enhance the details of the structure beneath the summit craters in a volume poorly defined by previous tomographic studies the presence of a high vp body previously observed at mt etna is confirmed at shallow depth beneath the southeastern part of the summit area the earthquakes preceding the eruption onset concentrated at its western border a low vp vs anomaly is found at 0 1 km depth just at the top of the volume where the magma intruded before the eruption this anomalous zone can be considered as molten material wealthy in gas the relocated seismicity occurs in a cylinder below the vents activated along the fracture system and exhibited an upward migration until the eruption all these results show evidence for the emplacement of a near vertical dyke striking about n s and a few kilometres south of the summit craters

late quaternary uplift rates of marine terraces on the pacific coast of north america southern oregon to baja california sur abstract marine terraces are common landforms along the pacific coast of north america from southern oregon to southern baja california we report 60 new uranium series ages of marine terrace corals hydrocorals and other fossils terraces representing the ca 80 ka and ca 125 ka high stands of sea are the most common along the pacific coast and we have used these ages along with terrace shoreline angle elevations and paleo sea level estimates to calculate late quaternary uplift rates uplift rates in the forearc region of the cascadia subduction zone range from 0 45 1 08 m kyr farther south along most of the coast west of the san andreas fault zone uplift rates range from 0 15 0 35 m kyr but some areas have significantly higher rates of uplift and others have apparently experienced little or no uplift in the last 125 ka in baja california sur west of the east pacific rise little or no uplift has occurred during the late quaternary on average the magnitude of rates of uplift for the tectonic regimes is as follows cascadia subduction zone san andreas fault zone region east pacific rise region

implications of the northwestwardly younger age of the volcanic rocks of west central california erosional remnants of volcanic fields in west central california form a linear northwest trending belt growing younger in age to the northwest major fields within the belt are represented by the neenach volcanics pinnacles volcanic formation quien sabe volcanics volcanic rocks in the berkeley hills tolay volcanics sonoma volcanics and clear lake volcanics dispersion in the age distance relation is reduced by restoration of inferred offsets on transecting right lateral fault systems the offsets include 115 km on the san gregorio hosgri fault 314 km on the san andreas fault 43 km on the hayward rodgers creek fault and 28 km on the carneros franklin sunol calaveras fault on the basis of the age and restored position of the volcanic rocks we judge that the locus of initial active volcanism migrated northwestward 3 75 cm yr from 25 to 12 ma and 1 35 cm yr from 12 ma to the present the volcanic rocks apparently formed south of the northwardly retreating edge of the subducted part of the juan de fuca plate corroborating one corollary of a published model of an expanding hole in the subducted farallon juan de fuca cocos plate the present position of the locus of melting at clear lake california requires substantial overthrusting of the juan de fuca plate by the pacific plate as was postulated on the basis of foreshortening of magnetic anomalies in the gorda basin the change in rate of northwestward migration 12 ma reflects a change in spreading direction of the juan de fuca plate vis a vis the pacific plate previously recognized from changes in orientation of oceanic magnetic anomalies from the migration rates it can be inferred that the relative movement between the pacific plate and the westernmost fringe of the north american plate averaged 3 5 cm yr from 27 m y ago to the present

late neogene and quaternary landscape evolution of the northern california coast ranges evidence for mendocino triple junction tectonics a landscape records the surface response to tectonics at time scales intermediate between short time scale information derived from seismic imaging and global positioning systems and the long term geologic record we link late neogene and quaternary deposits and landforms in the northern california coast ranges to the tectonics of the mendocino triple junction in the northern california coast ranges the mendocino crustal conveyor geodynamic model describes crustal thickening thinning and dynamic topography that produce a double humped pattern of uplift that migrates northward with the mendocino triple junction the tectonics are manifest in the drainage system and elevation pattern of the coast ranges at long wavelengths the elevation pattern closely matches the predicted double peaked shape of mendocino crustal conveyor topography and the high points of uplift control the location of drainage divides presently the divide between the russian and eel rivers and the divide between the eel and van duzen rivers approximately correspond to the peaks of uplift predicted by the mendocino crustal conveyor model as the triple junction migrates northward the double humped pattern of uplift and subsidence migrates and the coast ranges emerge smaller drainages develop and evolve by stream capture and flow reversal and the two main divides migrate in concert with the triple junction in contrast to the systematic development of the small streams the largest trunk streams can maintain grade through regions of high uplift and coastal river mouths remain stationary despite the uplift moving north before ca 2 ma the majority of the coast range drainage flowed to a southern coastal outlet near the present mouth of the russian river at 2 ma facilitated by headwater stream capture at key locations the drainage direction reversed and the majority of coast range rivers now drain into the north flowing eel river the major drainage reorganization at 2 ma highlights the potential for complexity in geomorphic response to tectonics

the volume and shape of the 1991 1993 lava flow field at mount etna sicily the 1991 1993 lava flow is the most voluminous flow erupted at mount etna sicily in over 300 years estimates of the volume obtained by various methods range from 205 106 m3 tanguy 1996 to over 500 106 m3 barberi et al 1993 this paper describes the results of an electronic distance measurement edm based field survey of the upper surface of the 1991 1993 flow field undertaken in 1995 the results were digitised interpolated and converted into a digital elevation model and then compared with a pre eruption digital elevation model constructed from a 1 25 000 contour map of the area based on 1989 aerial photographs our measurements are the most accurate to date and show that the 1991 1993 lava flow occupies a volume of 231 29 106 m3

the july august 2001 eruption of mt etna sicily the july august 2001 eruption of mt etna stimulated widespread public and media interest caused significant damage to tourist facilities and for several days threatened the town of nicolosi on the s flank of the volcano seven eruptive fissures were active five on the s flank between 3 050 and 2 100 m altitude and two on the ne flank between 3 080 and 2 600 m elevation all produced lava flows over various periods during the eruption the most voluminous of which reached a length of 6 9 km mineralogically the 2001 lavas fall into two distinct groups indicating that magma was supplied through two different and largely independent pathways one extending laterally from the central conduit system through radial fissures the other being a vertically ascending eccentric dike furthermore one of the eccentric vents at 2 570 m elevation was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer during both the initial and closing stages of the eruption for 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer permitting powerful explosive and effusive magmatic activity while the eruption was characterized by a highly dynamic evolution complex interactions between some of the eruptive fissures and changing eruptive styles its total volume 25 106 m3 of lava and 5 10 106 m3 of pyroclastics was relatively small in comparison with other recent eruptions of etna effusion rates were calculated on a daily basis and reached peaks of 14 16 m3 s 1 while the average effusion rate at all fissures was about 11 m3 s 1 which is not exceptionally high the eruption showed a number of peculiar features but none of these except the contemporaneous lateral and eccentric activity represented a significant deviation from etna s eruptive behavior in the long term however the 2001 eruption could be but the first in a series of flank eruptions some of which might be more voluminous and hazardous placed in a long term context the eruption confirms a distinct trend initiated during the past 50 years toward higher production rates and more frequent eruptions which might bring etna back to similar levels of activity as during the early to mid seventeenth century

post middle miocene accretion of franciscan rocks northwestern california deformed sedimentary rocks assigned to the franciscan assemblage in the king range south of cape mendocino northern california are dominantly deep water argillite and sandstone occurring as thick to thin bedded locally channelized marine turbidites of arkosic to andesitic volcani clastic composition these rocks structurally overlie late cretaceous coniacian to campanian basaltic pillow flows flow breccias diabase sills and arkosic sandstone turbidites that also are assignable to the franciscan assemblage and are well exposed along the coast at point delgada radiolarians and planktic and benthic foraminifers indicate that the oldest rocks in the king range may be early tertiary and that the youngest rocks are middle miocene or younger the youngest rocks yet reported from the franciscan assemblage partly coeval miocene relizian and luisian to quaternary rocks representing shallower sedimentary facies of the inner shelf to outer continental slope occupy the eel river basin and isolated fault bounded slivers adjacent to the king range on the north and east wide zones of penetrative shearing that may delineate a middle miocene or younger suture separate the deep water franciscan rocks of the king range from less severely deformed neogene rocks of the eel river basin the king range appears to be a displaced terrane of oceanic basement overlain by paleogene and neogene sedimentary and igneous rocks of continental and oceanic derivation this terrane may have been displaced north or eastward and obductively accreted to california 15 m y ago before or perhaps during northward passage of the pacific farallon north american plate junction

deformation in the lower crust of the san andreas fault system in northern california a continuous seismic velocity and reflectivity cross section of the san andreas fault system in northern california shows offsets in the lower crust and the mohorovicic discontinuity near the san andreas and maacama strike slip faults these faults may cut through the crust to the upper mantle in a zone less than 10 kilometers wide the northern california continental margin to the eastern edge of the coast ranges is underlain by a high velocity lowermost crustal layer that may have been emplaced within 2 million years following the removal of the gorda plate slab the rapid emplacement and structure within this layer are difficult to reconcile with existing tectonic models

active thrusting landscape evolution and late pleistocene sector collapse of baru volcano above the cocos nazca slab tear southern central america in this paper stratigraphy geochronology and geologic mapping are used to characterize a sequence of quaternary deposits associated with edifice failure of baru volcano which together with balanced cross sections illustrate the upper plate s response to along strike variations in subduction properties that occur across the tear in the subducting slab located at the panama fracture zone the subducting panama fracture zone is an active transform that separates disparate styles of subduction between the thick rapid and flat subduction of the cocos plate to the west and the thinner more oblique and steeper subduction of the nazca plate to the east we focus on the arc forearc region above the cocos nazca slab tear where both the fila costena inner forearc fold and thrust belt and the exhumed cordillera de talamanca terminate along strike to the southeast the fila costena thrust belt imbricates an eocene late miocene forearc basin sequence with up to 40 km of shortening inboard of cocos plate subduction and crosscuts a sequence of pleistocene and younger volcano sedimentary units on the southwestern flanks of the active baru volcano at its southeastern termination these units constrained in age by radiocarbon dating n 11 soil color and 40 ar 39 ar n 5 data include a sequence of late pleistocene to holocene debris avalanche and lahar deposits landscape morphology the areal distribution of units and new shortening estimates from balanced cross sections collectively suggest that the southeastern termination of the fila costena thrust belt actively propagates to the southeast coeval with migration of the panama triple junction the prevailing map pattern suggests that the forearc s response to southeastward migration of the slab tear varies with distance to the trench in contrast to deformation patterns in the outermost forearc plate boundary tractions associated with shallow subduction and cocos caribbean convergence are more influential in the development of arc forearc deformation than either oblique subduction of the 2 km bathymetric scarp or right lateral shear which both occur astride the subducting panama fracture zone

self stratification of tropical cyclone outflow part i implications for storm structure extant theoretical work on the steady state structure and intensity of idealized axisymmetric tropical cyclones relies on the assumption that isentropic surfaces in the storm outflow match those of the unperturbed environment at large distances from the storm s core these isentropic surfaces generally lie just above the tropopause wheretheverticaltemperaturestructureisapproximatelyisothermal soithas beenassumedthat the absolute temperature of the outflow is nearly constant here it is shown that this assumption is not justified at least when applied to storms simulated by a convection resolving axisymmetric numerical model in whichmuchofthe outflowoccursbelowtheambienttropopauseanddevelopsits ownstratification unrelated to that of the unperturbed environment the authors propose that this stratification is set in the storm s core by the requirement that the richardson number remain near its critical value for the onset of small scale turbulence this ansatz is tested by calculating the richardson number in numerically simulated storms and then showing that the assumption of constant richardson number determines the variation of the outflow temperature with angular momentum or entropy and thereby sets the low level radial structure of the storm outside its radius of maximum surface winds part ii will show that allowing the outflow temperature to vary also allows one to discard an empirical factor that was introduced in previous work on the intensification of tropical cyclones

geodetic constraint on the motion of a slab window implication for the mendocino crustal conveyor model the migration of the slab window in the northern california coast ranges provides a unique setting to study the viscous coupling between crust and asthenosphere flow the mechanisms of these dynamic processes are explained by the mendocino crustal conveyor model which predicts a 2 d double humped surface uplift rate pattern on a 400 km long profile to evaluate the mendocino crustal conveyor mcc model using accurate geodetic measurements we derive the vertical velocity field from 43 continuous gps cgps stations in the coast ranges region and project it onto the profile along three possible orientations of the slab window the cgps measured uplift rates are in good agreement with the mcc prediction when the slab window orientation is parallel to the symmetry axis of the region of thickened crust thus the cgps solutions not only provide a complementary means to diagnose the mcc model but also provide an effective way to constrain the orientation of the slab window

a 1 d mechanistic model for the evolution of earthflow prone hillslopes 1 in mountainous terrain deep seated landslides transport large volumes of material on hillslopes exerting a dominant control on erosion rates and landscape form here we develop a mathematical landscape evolution model to explore interactions between deep seated earthflows soil creep and gully processes at the drainage basin scale over geomorphically relevant 10 3 year timescales in the model sediment flux or incision laws for these three geomorphic processes combine to determine the morphology of actively uplifting and eroding steady state topographic profiles we apply the model to three sites one in the gabilan mesa california with no earthflow activity and two along the eel river california with different lithologies and varying levels of historic earthflow activity representative topographic profiles from these sites are consistent with model predictions in which the magnitude of a dimensionless earthflow number based on a non newtonian flow rheology reflects the magnitude of recent earthflow activity on the different hillslopes the model accurately predicts the behavior of earthflow collection and transport zones observed in the field and estimates long term average sediment fluxes that are due to earthflows in agreement with historical rates at our field sites finally our model predicts that steady state hillslope relief in earthflow prone terrain increases nonlinearly with the tectonic uplift rate suggesting that the mean hillslope angle may record uplift rate in earthflow prone landscapes even at high uplift rates where threshold slope processes normally limit further topographic development

morphology and growth history of delgada fan implications for the neogene evolution of point arena basin and the mendocino triple junction long range side scan gloria sonographs and seismic reflection data acquired during a survey of the western u s exclusive economic zone in 1984 coupled with information from deep sea drilling project sites provide new insights into the growth and evolution of the delgada fan construction of the fan commenced in the latest miocene 6 ma following the filling of the neogene point arena basin the fan presently covers more than 50 103 km2 of the pacific plate and contains approximately 15 103 km3 of predominantly terrigenous detritus the large size of the fan is incompatible with the small present day supply of sediment to the canyon system the gloria data show the delgada fan to be a hybrid type fan exhibiting characteristics of both elongate and radial fans the morphology and volume of the fan along with evidence for a decline in accumulation rates on the lower fan during the quaternary period suggest that the fan experienced an early growth phase latest miocene and pliocene characterized by relatively rapid progradation of elongate fan lobes followed by a period quaternary of slower growth that has featured a shift of depocenters to sites closer to the canyons and a transition to distributary channels bordered by less prominent levees and overbank deposits we examine the growth of delgada fan in relation to the neogene evolution of the north american pacific plate boundary using a series of paleogeographic reconstructions based on recently published time displacement histories of the mendocino triple junction mtj the san andreas fault saf and the pacific plate upon which the fan rests the time displacement curves for the saf and the mtj suggest that the mtj and mendocino fracture zone overtook and passed point arena basin at about 10 ma when the basin lay immediately southwest of the present san francisco bay area we suggest that the mtj joined the saf at approximately that time and location thus making the saf the master fault in the transform system this interpretation is compatible with evidence from seismic reflection profiles over the fan which demonstrate that the fan and the canyon system and therefore point arena basin have moved as a unit since the inception of fan growth 6 7 ma point arena basin lay southwest of the san francisco area at 10 12 ma and the passage of the mtj caused the disruption of the forearc shelf and slope and the development of local uplifted and subsiding blocks in particular uplift of the bay block immediately east of the saf may have provided the source area for the late miocene sediments that filled point arena basin and set the stage for the growth of delgada canyon and fan system the growth rate of the fan has decreased and the style of deposition has changed as the system was tectonically transported to its present location adjacent to the small youthful drainages of the king range

contrasting triggering mechanisms of the 2001 and 2002 2003 eruptions of mount etna italy abstract mount etna produced two significant eruptions in 2001 and 2002 2003 which we have analysed using geological seismic and deformation data these eruptions showed some similarities such as the activating of two magmatic plumbing systems central lateral and eccentric but they differed in their triggering mechanisms while the 2001 eruption was largely the result of the emplacement of a n s eccentric dike independent from the central conduits consistent with e w regional extension the 2002 2003 eruption occurred in response to a major flank slip on the eastern and southeastern sides of the volcano this is demonstrated by the spatial and temporal distribution of seismicity and deformation preceding and accompanying the two eruptions during the months prior to the 2001 eruption most epicenters were concentrated on the southern flank at depths of 5 15 km below sea level during the 4 days before the eruption earthquake hypocenters migrated to shallower levels from 5 km bsl upward indicating the emplacement of the eccentric dike this is confirmed by the patterns of ground fracturing observed in the field and deformation documented by electronic distance measurements edm in contrast the months before the 2002 2003 eruption were characterised by shallower seismicity mainly concentrated along the active faults bordering the slipping flank sector flank slip accelerated in september 2002 and a second more vigorous acceleration of flank slip occurred on 26 27 october 2002 accompanying the opening of eruptive vents the very short 2 h seismic crisis preceding the onset of eruptive activity stands in neat contrast with the 4 days of intense seismicity before the 2001 eruption subsequently flank slip deformation extended all over the eastern and southeastern flanks of the volcano causing serious damage in this sector the events of 2001 2003 can be seen as a continuous chain of intimately interacting processes including regional tectonics magma accumulation and eruption and flank instability in this scenario the 2001 eruption led to increased flank instability that subsequently accelerated and culminated with the massive flank slip which in turn facilitated the 2002 2003 eruption this sequence of events points to a long term feedback mechanism between magmatism and flank instability at etna

controls on sediment distribution in the coastal zone of the central california transform continental margin usa abstract we use 10 000 km of high resolution seismic reflection data together with multibeam bathymetry to document complex and highly variable post last glacial maximum lgm sediment distribution and thickness in the coastal zone 10 m isobath to 5 6 km offshore along a 800 km section of central california s transform continental margin sediment thickness ranges from 0 seafloor bedrock to 64 m with a mean of 8 7 m we delineate 25 coastal zone sediment domains and group them based on common geomorphology and sediment occurrence thickest sediment occurs in mountain front and large river domains which comprise 14 5 and 7 9 of the coastal zone and contain 30 1 and 18 2 of coastal zone sediment respectively in contrast small river domains and sediment poor shelf domains comprise 50 7 and 15 7 of the coastal zone and contain 18 4 and 12 7 of its sediment the distribution and thickness of post lgm sediment in the coastal zone is controlled by a combination of tectonics sediment supply and eustasy sediment is derived from a tectonically controlled coastal landscape of rapidly uplifting mountain fronts more slowly uplifting marine terraces and fault bounded headlands and alluvial estuarine troughs sediment supply is maximized along steep landslide prone mountain fronts and at the mouths of large watersheds and minimized along lower relief terraced coastal landscape drained by smaller rivers and creeks in the offshore coastal zone tectonics generates local uplifts and basins and influences shelf width and gradient as well as the locations of some shelf incised submarine canyons sea level rise raises base level drowns estuaries creates accommodation space on the shelf amount based on gradient and isolates the heads of many submarine canyons at or near the shelfbreak comparison of shelf sediment volumes with estimates of unaltered watershed sediment supply reveals that a relatively small proportion of post lgm sediment supply is preserved on the shelf offshore of some of the largest rivers sediments deposited in shoreline and shelf environments have limited preservation potential and the most complete long term geologic record of the post lgm transgression and highstand is likely represented in slope and submarine fan deposits

influence of the mendocino triple junction on the tectonics of coastal california abstract the migration of the mendocino triple junction through central and northern california over the past 25 30 million years has led to a profound change in plate interactions along coastal california the tectonic consequences of the abrupt change from subduction plate interactions north of the triple junction to the development of the san andreas transform system south of the triple junction can be seen in the geologic record and geophysical observations the primary driver of this tectonism is a coupling among the subducting juan de fuca gorda north american and pacific plates that migrates with the triple junction this coupling leads to ephemeral thickening of the overlying north american crust associated uplift and subsequent subsidence and a distinctive sequence of fault development and volcanism

three dimensional crustal structure of the mendocino triple junction region from local earthquake travel times the large scale three dimensional geometry of the mendocino triple junction at cape mendocino california was investigated by inverting nearly 19 000 p wave arrival times from over 1400 local earthquakes to estimate the three dimensional velocity structure and hypocentral parameters a velocity grid 175 km n s by 125 km e w centered near garberville california was constructed with 25 km horizontal and 5 fan vertical node spacing the model was well resolved near cape mendocino where the earthquakes and stations are concentrated at about 40 6 n latitude a high velocity gradient between 6 5 and 7 5 km s dips gently to the south and east from about 15 km depth near the coast relocated hypocenters concentrate below this high gradient which we interpret as the oceanic crust of the subducted gorda plate therefore the depth to the top of the gorda plate near cape mendocino is interpreted to be 15 km the gorda plate appears intact and dipping 8 eastward due to subduction and flexing downward 6 12 to the south both hypocenters and velocity structure suggest that the southern edge of the plate intersects the coastline at 40 3 n latitude and maintains a linear trend 15 south of east to at least 123 w longitude the top of a large low velocity region at 20 30 km depth extends about 50 km n s and 75 km e w roughly between garberville and covelo and is located above and south of the southern edge of the gorda plate we interpret this low velocity area to be locally thickened crust 8 10 km due to either local compressional forces associated with north south compression caused by the northward impingement of the rigid pacific plate or by underthrusting of the base of the accretionary subduction complex at the southern terminous of the cascadia subduction zone south of cape mendocino and southwest of the garberville fault high velocities indicative of oceanic crust are detected at 15 km depth we interpret this evidence as tectonic underplating of the pacific oceanic crust beneath the coastal franciscan complex similar to the situation seismically imaged in central coastal california page and brocher 1994 this geometry indicates that the westernmost portion of the slab window has been filled by tectonic underplating and crustal thickening while deep seated mantle upwelling is confined to an area centered about 75 km north of clear lake benz et al 1992 zandt et al 1992

the uplift of the adriatic flank of the apennines since the middle pleistocene new insights from the tronto river basin and the acquasanta terme travertine central italy abstract the apennines chain is an active neogene fold and thrust belt resulting from the westward subduction of the adriatic microplate starting from the end of the early pleistocene the chain was affected by an increase in regional uplift recent gps data resolved uplift rates of 1 2 mm yr for the whole apennines whereas in the adriatic flank several studies estimated rates between 0 3 and 0 5 mm yr over the last 1 myr a number of works investigated the evolution of the drainage systems along the periadriatic margin of the apennines providing long term incision rates studies from the northern part of this sector reported uplift rates varying from 0 2 to 1 1 mm yr whereas only few studies concentrated on the central sector of the adriatic flank of the apennines focusing mainly on the evolution of the lower reach of major rivers this work aims to quantify the long term rock uplift and incision rates of the eastern portion of the central apennines through the analysis of the tronto river basin because of its geologic and geomorphological configurations this basin is an ideal test site to investigate the influence of tectonics and climate on the recent topographic evolution of the central apennines the basin extends with a roughly wsw ene direction from the inner sector of the chain to the adriatic coast crossing several tectonic structures such as the amatrice extensional basin and the acquasanta and montagna dei fiori anticlines in particular in the acquasanta terme area the right flank of the tronto river valley is characterized by fluvial and travertine deposits organized and exposed in several levels in this work we investigated the hydrography river longitudinal profiles and topography swath profile slope and local relief of the tronto river basin coupling these data with field observations and geochronological analysis on the continental sediments fluvial deposits and travertines outcropping in the acquasanta terme area to better characterize the nature of travertines we performed geochemical characterization of three travertine forming thermal springs obtaining their physico chemical parameters the percentage of dissolved gases and the isotopes content finally we applied a knickpoint celerity model to chronologically constrain the geomorphological evolution of the whole drainage system the results show the occurrence of a continuous tectonic uplift 0 5 mm yr across the study area since middle pleistocene the uplift together with climate fluctuations drove the incision 0 6 mm yr of the landscape and the delineation of the present drainage network these data are consistent with previous estimates of uplift and incision rates in adjacent areas and provide new constraints on the quaternary evolution of the central apennines this study highlights how the coupling of field surveys with morphometric and topographic analyses of a drainage system is crucial to understand and quantify the influence of tectonic and climate changes in shaping the landscape

revised age of the rockland tephra northern california implications for climate and stratigraphic reconstructionsin the western united states lanphere et al 1999 1 presented new data for the age of the rockland pumice tuff breccia of wilson 1961 2 using the incremental heating 40ar 39ar technique their age 610 ka is 200 ka older than zircon fission track ages obtained on this tuff by meyer et al 1980 3 1991 4

topographic signatures and a general transport law for deep seated landslides in a landscape evolution model a fundamental goal of studying earth surface processes is to disentangle the complex web of interactions among baselevel tectonics climate and rock properties that generate characteristic landforms mechanistic geomorphic transport laws can quantitatively address this goal but no widely accepted law for landslides exists here we propose a transport law for deep seated landslides in weathered bedrock and demonstrate its utility using a two dimensional numerical landscape evolution model informed by study areas in the waipaoa catchment new zealand and the eel river catchment california we define a non dimensional landslide number which is the ratio of the horizontal landslide flux to the vertical tectonic flux that characterizes three distinct landscape types one is dominated by stochastic landsliding whereby discrete landslide events episodically erode material at rates exceeding the long term uplift rate another is characterized by steady landsliding in which the landslide flux at any location remains constant through time and is greatest at the steepest locations in the catchment the third is not significantly affected by landsliding in both the stochastic landsliding and steady landsliding regimes increases in the non dimensional landslide number systematically reduce catchment relief and widen valley spacing producing long low angle hillslopes despite high uplift rates the stochastic landsliding regime captures the frequent observation that deep seated landslides produce large sediment fluxes from small areal extents while being active only a fraction of the time we suggest that this model is adaptable to a wide range of geologic settings and is useful for interpreting climate driven changes in landslide behavior

topographic form of the coast ranges of the cascadia margin in relation to coastal uplift rates and plate subduction the coast ranges of the cascadia margin are overriding the subducted juan de fuca gorda plate we investigate the extent to which the latitudinal trend in average topography of the coast ranges is a function of the latitudinal change in attributes related to the subduction process these attributes include the variable age of the subducted slab that underlies the coast ranges and average vertical crustal velocities of the western margin of the coast ranges for two markedly different time periods the last 45 years and the last 100 kyr these vertical crustal velocities are computed from the resurveying of highway bench marks and from the present elevation of shore platforms that have been uplifted in the late quaternary respectively topography of the coast ranges is in part a function of the age and buoyancy of the underlying subducted plate this is evident in the fact that the two highest topographic elements of the coast ranges the klamath mountains and the olympic mountains are underlain by youngest subducted oceanic crust the subducted blanco fracture zone in southernmost oregon is responsible for an age discontinuity of subducted crust under the klamath mountains the northern terminus of the topographically higher klamaths is offset to the north relative to the position of the underlying blanco fracture zone the offset being in the direction of migration of the fracture zone as dictated by relative plate motions vertical crustal velocities at the coast derived from bench mark surveys are as much as an order of magnitude greater than vertical crustal velocities derived from uplifted shore platforms this uplift rate discrepancy indicates that strain is accumulating on the plate margin to be released during the next interplate earthquake in a latitudinal sense average coast range topography is relatively high where bench mark derived short term vertical crustal velocites are highest because the shore platform vertical crustal velocites reflect longer term permanent uplift we infer that a small percentage of the interseismic strain that accumulates as rapid short term uplift is not recovered by subduction earthquakes but rather contributes to rock uplift of the coast ranges the conjecture that permanent rock uplift is related to interseismic uplift is consistent with the observation that those segments of the subduction zone subject to greater interseismic uplift rates are at approximately the same latitudes as those segments of the coast ranges that have higher magnitudes of rock uplift over the long term

three dimensional geometry of the gorda plate beneath northern california the isostatic residual gravity field over northern california displays a gravity gradient interpreted to reflect the south edge of the gorda plate where it is subducted eastward beneath the north american plate the locus of points of maximum slope defines a line trending s60 e from a coastal point approximately 20 km south of cape mendocino a point where the buried plate boundary is inferred from magnetic and seismicity data southeast from the coast for a distance of 120 km the gravity anomaly parallels the strike of the blanco fracture zone and the present direction of relative motion between the pacific and northern gorda plates calculations from the form of the anomaly yield depth estimates that fit an east southeast plunge of approximately 9 for the top of the gorda south edge the sense of the anomaly higher gravity to the south supports the hypothesis that a window developed in the subducted slab east of the san andreas fault and south of the gorda plate south of the gorda boundary the base of the north american plate is thus in contact with hot material from the asthenosphere that invaded the window because the overlying north american plate has been moving relatively south across the gorda boundary the north american plate beneath the coast ranges east of the san andreas fault in central california may be decoupled from the underlying material at a depth slightly deeper than the depth to the top of the boundary at the time the north american plate passed over it

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

rates and processes of soil evolution on uplifted marine terraces northern california time dependent changes in soil development have been evaluated for two flights of uplifted marine terraces with similar site characteristics and a range in terrace ages 3 9 ka to 330 ka in northern california six pedogenic properties of soils developed in unconsolidated deposits overlying bedrock marine platforms have systematic time dependent trends but each property differs in rate of change and in the time period over which its changes are useful as relative age dating or correlation tools changes in accumulated mass of organic carbon and ph are useful properties only for the youngest soils and probably for soils less than 10 20 ka in this climatic region soils on terraces older than 29 ka have nearly similar amounts of mass of organic carbon with values of about 3 6 by weight for the upper meter of the soil profile soil reaction ph in the top 20 cm of the soil profile decreases at a rapidly declining rate reaching and maintaining a value of 5 by 39 40 ka total mass of accumulated clay is an excellent indicator of relative soil age during all stages of soil development the rate of accumulation of clay is about 0 4 g cm2 soil column per thousand years so that pedons on terraces with inferred ages of about 124 ka have accumulated at least 50 g cm2 soil column of clay systematic and linear increases in accumulated mass of several forms of pedogenic iron make them very useful for chronological purposed for at least 240 ky of soil development crystalline forms of iron enable greater distinction among young soils than amorphous forms which have negligible accumulations until at least 40 ka the rate of accumulation of crystalline forms of iron fed feo is about 0 02 g cm2 soil column per thousand years so that pedons on terraces with inferred ages of about 124 ka have accumulated about 3 g cm2 soil column of crystalline forms of pedogenic iron changes with time in accumulated mass of amorphous forms of pedogenic aluminum alo are negligible within the first 29 ka then reflect a rapid increase in rate of accumulation until at least 124 ka two pedons from the same terrace inferred age 124 ka contain strikingly different amounts of pedogenic alo however and suggest that alo may be an unreliable indicator of the degree of soil development in addition to mass values of different soil substances maximum percent values were calculated soils developed on marine terraces older than 29 ka have at least 10 maximum clay older than 100 ka at least 30 maximum clay and older than 240 ka at least 40 50 maximum clay soils on terraces younger than 29 ka have less than 1 maximum fed and soils older than 240 ka at have at least 4 maximum fed these easily obtained values provide textural and chemical boundaries for separating marine terraces younger or older than about 29 100 and 240 ka in this region but are useful only as very general tools for correlation maximum percent clay is a more reliable indicator of soil age than maximum percent fed as the latter is greatly influenced by local groundwater flux and percent values of fed have a high degree of scatter

geometry and evolution of the san andreas fault zone in northern california the evolution of the san andreas fault system is controlled by thermal mechanical processes associated with the development and evolution of a narrow slabless window formed beneath the western edge of north america this fault zone evolution begins after initiation of transform motion along the plate boundary with the northward migration of the mendocino triple junction as a consequence of initial lithospheric structure and the shallow emplacement of asthenospheric mantle the plate boundary separating the north american and pacific plates follows a complex three dimensional geometry which varies through time seismic velocity structure heat flow seismicity surface deformation uplift and fault development are controlled by the evolving thermal structure in the region after triple junction passage thermal mechanical models have been used to evaluate the fault system s time varying three dimensional dynamical behavior simulating the principal processes involved in the thermal mechanical evolution of the san andreas fault system results from this modeling indicate that the fault system has essentially a three stage history 1 in the vicinity of the mendocino triple junction the san andreas fault maps the eastern edge of the pacific plate with a broad 100 km zone of asthenospheric mantle separating the pacific and north american plates in the 25 to 90 km depth range 2 between 37 n and 39 n the plate boundary within the mantle separating the pacific and north american plates has developed approximately 40 60 km east of the surface trace of the san andreas fault and lies beneath the hayward calaveras faults and associated faults the surface trace of the plate boundary appears to be connected to the mantle segment via a lower crust subhorizontal detachment surface this fault zone orientation produces the surface deformations observed geodetically in the region 3 south of 37 n the surface fault again overlies the deeper plate boundary apparently as a result of an eastward jump in the surface fault

upper plate contraction north of the migrating mendocino triple junction northern california implications for partitioning of strain geologic measurement of permanent contraction across the cascadia subduction margin constrains one component of the tectonic deformation along the convergent plate boundary the component critical for the seismic hazard assessment of crustal faults a comprehensive survey of active faults in onshore subduction margin rocks at the southern end of the cascadia subduction zone indicates that these thrust faults accommodate 10 mm yr of convergence oriented 020 045 seismotectonic models of subduction zones typically assign this upper plate strain to the estimate of aseismic slip on the megathrust geodetic models include this permanent crustal strain within estimates of elastic strain accumulation on the megathrust both types of models underestimate the seismic hazard associated with crustal faults subtracting the observed contraction from the plate convergence rate 40 50 mm yr directed 040 055 leaves 30 40 mm yr of convergence to be partitioned between slip on the megathrust contraction within the southern juan de fuca plate and crustal contraction outside the subduction complex rocks this simple estimate of slip partitioning neglects the discrepancy between the plate convergence and contraction directions in the vicinity of the mendocino triple junction the san andreas and cascadia limbs of the mendocino triple junction are not collinear the eastern edge of the broad san andreas boundary is 85 km east of the cascadia subduction boundary and across this zone the pacific plate converges directly with the north america plate the skewed orientation of crustal structures just north of the leading edge of the pacific plate suggests that they are deforming in a hybrid stress field resulting from both juan de fuca north america motion and pacific north america motion the composite convergence direction 50 mm yr directed 023 is consistent with the compressive stress axis 020 inferred from focal mechanisms of crustal earthquakes in the humboldt region deformation in such a hybrid stress field implies that the crustal faults are being loaded from two major tectonic sources the slip on crustal faults north of the mendocino triple junction may consume 4 5 mm yr of pacific humboldt convergence the remaining 17 18 mm yr of convergence may be consumed as distributed shortening expressed in the high rates of uplift in the cape mendocino region or as northward translation of the continental margin north of the triple junction

erosional response to northward propagating crustal thickening in the coastal ranges of the u s pacific northwest we measured basin scale erosion rates using cosmogenic 10 be concen trations in quartz from fluvial sediment in rivers draining the coastal mountain ranges of the u s pacific northwest between 40 and 47 n apparent erosion rates are 0 1 to 0 2 mm yr 1 throughout the oregon coast ranges north of 43 n and increase to the south to 0 6 to 1 1 mm yr 1 in the northern california coast ranges near 40 n we propose that these observations display the erosional response to northward migrating crustal thickening associated with subduction of the mendocino triple junction north south variations in erosion rate range elevation and metrics of landscape relief and steepness are consistent with the hypotheses that i their primary cause is northward migrating crustal thickening ii erosion rates are strongly controlled by topographic relief and weakly if at all controlled by climate and iii the dependence of erosion on relief is nonlinear and obeys a threshold relief relationship

landslides threshold slopes and the survival of relict terrain in the wake of the mendocino triple junction establishing landscape response to uplift is critical for interpreting sediment fluxes hazard potential and topographic evolution we assess how landslides shape terrain in response to a wave of uplift traversing the northern california coast ranges united states in the wake of the mendocino triple junction we extracted knickpoints landslide erosion rates and topographic metrics across the region modified by mendocino triple junction migration landslide erosion rates mapped from aerial imagery are consistent with modeled uplift and exhumation while hillslope gradient is invariant across the region suggesting that landslides accommodate uplift as predicted by the threshold slope model landslides are concentrated along steepened channel reaches downstream of knickpoints generated by base level fall at channel outlets and limit slope angles and relief we find evidence that landslide derived coarse sediment delivery may suppress catchment wide channel incision and landscape denudation over the time required for the uplift wave to traverse the region we conclude that a landslide cover effect may provide a mechanism for the survival of relict terrain and orogenic relief in the northern californian coast ranges and elsewhere over millennial time scales

sediment yield spatial characteristics and the long term evolution of active earthflows determined from airborne lidar and historical aerial photographs eel river california in mountainous landscapes with weak fine grained rocks earthflows can dominate erosion and landscape evolution by supplying sediment to channels and controlling hillslope morphology to estimate the contribution of earthflows to regional sediment budgets and identify patterns of landslide activity earthflow movement needs to be quantified over significant spatial and temporal scales presently there is a paucity of data that can be used to predict earthflow behavior beyond the seasonal scale or over spatially extensive study areas across 226 km 2 of rapidly eroding franciscan complex rocks of the eel river catchment northern california we used a combination of lidar light detection and ranging and orthorectified historical aerial photographs to objectively map earthflow movement between 1944 and 2006 by tracking the displacement of trees growing on earthflow surfaces we find that 7 3 of the study area experienced movement over this 62 yr interval preferentially in sheared argillaceous lithology this movement is distributed across 122 earthflow features that have intricate elongate planform shapes a preferred south southwesterly aspect and a mean longitudinal slope of 31 the distribution of mapped earthflow areas is well approximated by a lognormal distribution with a median size of 36 500 m 2 approximately 6 of the study area is composed of earthflows that connect to major channels these flows generated an average sediment yield of 19 000 t km 2 yr 1 rock erosion rate of 7 6 mm yr over the 62 yr study period equating to a regional yield of 1100 t km 2 yr 1 0 45 mm yr if distributed across the study area as such a small fraction of the landscape can account for half of the regional denudation rate estimated from suspended sediment records 2200 t km 2 yr 1 or 0 9 mm yr we propose a conceptual model for long term earthflow evolution wherein earthflows experience intermittent activity and long periods of dormancy when limited by the availability of readily mobilized sediment on upper slopes ultimately high order river channels and ephemeral gully networks may serve to destabilize hillslopes controlling the evolution of earthflow prone terrain

determining key model parameters of rapidly intensifying hurricane guillermo 1997 using the ensemble kalman filter abstractin this work the authors determine key model parameters for rapidly intensifying hurricane guillermo 1997 using the ensemble kalman filter enkf the approach is to utilize the enkf as a tool only to estimate the parameter values of the model for a particular dataset the assimilation is performed using dual doppler radar observations obtained during the period of rapid intensification of hurricane guillermo a unique aspect of guillermo was that during the period of radar observations strong convective bursts attributable to wind shear formed primarily within the eastern semicircle of the eyewall to reproduce this observed structure within a hurricane model background wind shear of some magnitude must be specified and turbulence and surface parameters appropriately specified so that the impact of the shear on the simulated hurricane vortex can be realized to identify the complex nonlinear interactions induced by changes in these parameters an ensemble of model simulations have been condu

late neogene geohistory analysis of the humboldt basin and its relationship to convergence of the juan de fuca plate geohistory analysis of neogene humboldt basin strata provides important constraints for hypotheses of the tectonic evolution of the southern cascadia subduction margin leading up to the arrival of the mendocino triple junction this analysis suggests that the tectonic evolution of the humboldt basin area was dominated by coupling between the downgoing juan de fuca plate and the continental margin this coupling is reflected in the timing of major hiatuses within the basin sedimentary sequence and margin uplift and subsidence which occur during periods of tectonic plate adjustment stratigraphic evidence indicates that humboldt basin originated at the base of the continental slope in early miocene time syndepositional uplift of basin strata began in the late pliocene and was both thermal isostatic and tectonic in origin isostatic uplift was a function of an increasingly more buoyant slab being subducted whereas tectonic uplift was due to imbricated thrusting of the accretionary complex and underplating of offscraped sediment during subduction a component of margin uplift is postulated to have been caused by a change in the rate of convergence between the juan de fuca and north american plates coeval with late pliocene uplift documented onshore was a sharp decrease in covergence rate 3 ma a reduction in rate of tectonic uplift observed in the eel river section in early pleistocene time was coeval with a marked increase in relative motion parallel to the continental margin this localized subsidence may have been caused by syndepositional folding

active spreading and regional extension at mount etna imaged by sar interferometry abstract large flank instability has been proposed by most recent authors as a major process in the dynamics of mount etna however several aspects of the models are still disputed such as the boundaries of the moving area and the driving force for the instability in this paper we present synthetic aperture radar interferometric data which allow us to identify two main sectors of active instability where the deformational process differs an eastern sector is bounded to the north by the pernicana provenzana fault to the west by the north rift zone and the south rift zone and to the south by the mascalucia tremestieri trecastagni fault system interferograms provide new data on the activity and extent of the southern boundary which was previously underestimated in this sector the structural features indicate an eastward sliding driven by e w regional extension which can be interpreted as a result of the retreating slab of the ionian subduction a second collapsing sector exists along the southern flank of mount etna where the interferograms show the presence of an active anticlinal ridge this ridge is interpreted as the result of southward gravity spreading over a basal decollement between etna and its plio quaternary basement and the hyblean platform the two sectors first became active in summer 1996 after the beginning of a new cycle of eruptive activity at the summit the activity was ongoing until january 1998 with the deformation rate ranging from 4 6 mm yr for the mascalucia tremestieri trecastagni faults to 12 mm yr for the anticlinal ridge

relationship between tremor and volcanic activity during the southeast crater eruption on mount etna in early 2000 1 the southeast crater of mount etna italy was characterized by a violent eruptive activity between 26 january and 24 june 2000 this activity produced 64 lava fountain episodes with repose periods from 3 hours to 10 days we estimated a volume of about 15 20 106 m3 lava and at least 2 3 106 m3 of tephra we compared the paroxysmal volcanic activity to its associated seismic signature the high number of events highlighted a strict correlation between tremor and volcanic activity seismic and volcanic characteristics such as the frequency of occurrence the duration of lava fountains and the associated tremor energy suggested the subdivision of the studied period into two stages separated by the 20 february event combining volcanic with seismic data we observed some useful relationships among lava fountain height sustained column height and reduced displacement in addition we found that the entire episode was well correlated with the duration of the amplitude increase computing the tremor energy linked to each event the total energy associated with lava fountains episodes results in 76 of the energy released during the whole period finally the different ratios among the overall spectral amplitude of the seismic signals of the stations located at different altitudes suggested to us the elaboration of a simple qualitative model to explain the dynamic behavior of the tremor source during the whole episode

differences in channel and hillslope geometry record a migrating uplift wave at the mendocino triple junction california usa tectonic plate motion and the resulting change in land surface elevation has been shown to have a fundamental impact on landscape morphology changes to uplift rates can drive a response in fluvial channels which then drives changes to hillslopes because hillslopes respond on different time scales than fluvial channels investigating the geometry of channels and hillslopes in concert provides novel opportunities to examine how uplift rates may have changed through time here we perform coupled topographic analysis of channel and hillslope geometry across a series of catchments at the mendocino triple junction mtj in northern california usa these catchments are characterized by an order of magnitude difference in uplift rate from north to south we find that dimensionless hillslope relief closely matches the uplift signal across the area and is positively correlated with channel steepness furthermore the range of uncertainty in hillslope relief is lower than that of channel steepness suggesting that it may be a more reliable recorder of uplift in the mtj region we find that hilltop curvature lags behind relief in its response to uplift which in turn lags behind channel response these combined metrics show the northward migration of the mtj and the corresponding uplift field from topographic data alone

ephemeral crustal thickening at a triple junction the mendocino crustal conveyor as the north american crust interacts with the migrating mendocino triple junction the crust is first significantly thickened and then equivalently thinned over a distance of a few hundred kilometers within a time frame of 5 m y or less this process of ephemeral crustal thickening is proposed to result from viscous coupling between the northward migrating gorda slab and the base of north america south of the triple junction a time dependent thermal mechanical finite element model is developed to test this hypothesis of plate boundary tectonics results of the numerical simulations show patterns of crustal deformation consistent with the mapped sequence of folding and faulting in the area the observed crustal structure and triple junction regional seismicity and localized regions of crustal extension coincident with the position of a hypothesized lower crustal melt zone

transport and storage of bed material in a gravel bed channel during episodes of aggradation and degradation a field and flume study the dynamics of sediment transport capacity in gravel bed rivers is critical to understanding the formation and preservation of fluvial landforms and formulating sediment routing models in drainage systems we examine transport storage relations during cycles of aggradation and degradation by augmenting observations of three events of channel aggradation and degradation in cuneo creek a steep 3 gravel bed channel in northern california with measurements from a series of flume runs modeling those events an armored single thread channel was formed before feed rates were increased in each aggradation run output rates increased as the channel became finer and later widened steepened and braided after feed rates were cut output rates remained high or increased in early stages of degradation as the incising channel remained fine grained and later decreased as armoring intensified if equilibrium was not reached before sediment feed rate was cut then a rapid transition from a braided channel to a single thread channel caused output rates for a given storage volume to be higher during degradation than during aggradation variations in channel morphology and surface bed texture during runs that modeled the three cycles of aggradation and degradation were similar to those observed in cuneo creek and provide confidence in interpretations of the history of change cuneo creek aggraded rapidly as it widened shallowed and braided then degraded rapidly before armoring stabilized the channel such morphology driven changes in transport capacity may explain the formation of flood terraces in proximal channels transport storage relations can be expected to vary between aggradation and degradation and be influenced by channel conditions at the onset of changes in sediment supply published in 2011 this article is a us government work and is in the public domain in the usa

structural features of the july august 2001 mount etna eruption evidence for a complex magma supply system we describe the evolution of the volcanic activity and deformation patterns observed at mount etna during the july august 2001 eruption seismicity started at 3000 m below sea level on 13 july accompanied by moderate ground swelling ground deformation culminated on 16 july with the development of a ne sw graben c 500 m wide and c 1 m deep in the cisternazza area at 2600 2500 m above sea level on the southern slope of the volcano on 17 july the eruption started at the summit of mount etna from the se crater central lateral eruptive system from which two radial c 30 m wide c 3000 m long fracture zones associated with eruptive fissures propagated both southward 17 july and northeastward 20 july on 18 july a new vent formed at 2100 m elevation at the southern base of the montagnola followed on the next day by the opening of a vent further upslope at 2550 m eccentric eruptive system the eruption lasted for 3 weeks approximately 80 of the total lava volume was erupted from the 2100 m and the 2550 m vents the collected structural data suggest that the cisternazza graben developed as a passive local response of the volcanic edifice to the ascent of a north south eccentric dyke which eventually reached the ground surface in the montagnola area 18 19 july in contrast the two narrow fracture zones radiating from the summit are interpreted as the lateral propagation from the conduit of the se crater of north south and ne sw oriented shallow dykes 2 3 m wide the evolution of the fracture pattern together with other volcanological data magma ascent and effusion rate eruptive style petrochemical characteristics of the erupted products and petrology of xenoliths within magma suggest that the eccentric and central lateral eruptions were fed by two distinct magmatic systems examples of eccentric activity accompanied by central lateral events have never been described before at etna

magma chambers modeled as cavities explain the formation of rift zone central volcanoes and their eruption and intrusion statistics the volcanic rift zone in iceland is characterized by elongate volcanic systems consisting of tension fractures normal faults and volcanic fissures where most of the volcanotectonic activity takes place most volcanic systems develop central volcanoes the formation of which is still poorly understood there is great difference in the eruption and intrusion statistics of the volcanic systems inside and outside the central volcanoes in the central volcanoes eruptions are frequent typically one every several hundred years of small volume normally less than 0 1 km3 and fed mainly by thin average thickness of 0 5 m inclined sheets outside central volcanoes the eruptions are rare typically one every several thousand years but of large volume typically more than 1 km3 and fed mainly by thick average thickness of 4 5 m subvertical dikes using the results of a boundary element study of magma chambers modeled as a cavities or holes in a semi infinite plate these empirical relations as well as the formation of specific central volcanoes in the volcanic systems can be explained once a cavity like magma chamber has formed its existence in the rift zone concentrates tensile stress this stress concentration causes the segment containing the magma chamber to rupture much more frequently than the other parts of the volcanic system which partly explains the formation of central volcanoes and their high eruption frequencies this concentration also gives rise to a local stress field that encourages injection of small volume sheets in all directions and at various dips from their source magma chamber the magma chamber acts as a trap for upward propagating dikes from mantle reservoirs and channels magma through inclined sheets toward a limited area at the surface where the central volcano gradually forms the inverse relationship between eruption frequency and eruption volume when the central volcano is compared with other parts of the volcanic system is also partly due to the trap like nature of the magma chamber the chamber is normally much smaller than its source mantle reservoir so that a single magma flow through a dike from the reservoir lasting perhaps many years may trigger tens of magma flows through sheets from the chamber many of which would reach the surface in the central volcano

fission track age 400 000 yr of the rockland tephra based on inclusion of zirco grains lacking fossil fission tracks abstract a zircon fission track age of about 400 000 yr b p has been determined for the rockland tephra a widespread pyroclastic layer in northern california and western nevada new ages of zircon separates from both proximal and distal exposures of this layer range from 370 000 to 460 000 yr ages of the best material provide a narrower range from 370 000 yr for unwelded ash flow tuff to 420 000 yr for distal air fall ash that appears to be uncontaminated by clastic detritus or xenocrysts detrital or xenocrystic grains in the ash flow tuff may have been annealed during emplacement and cooling of the tuff detrital and xenocrystic zircons are identified on the basis of their physical characteristics and distinctly older ages independent stratigraphic and magnetostratigraphic data constrain the age of the rockland tephra between 300 000 and 600 000 yr a range that is compatible with the fission track age zircon grains containing no spontaneous fossil tracks are regarded as part of the normal population of comagmatic grains because maximum ages calculated for these grains form a population that mimics the distribution of ages of individual zircon grains that contain fossil tracks modal ages of both groups fall between 250 000 and 500 000 yr induced fission tracks from grains that lack fossil tracks are included in the age calculations resulting in significantly younger and more coherent dates than would result if these tracks had been omitted especially those of the finer grained distal samples

what does a mean mean the temporal evolution of detrital cosmogenic denudation rates in a transient landscape in equilibrium landscapes 10 be concentrations within detrital quartz grains are expected to quantitatively refl ect basin wide denudation rates in transient landscapes though detrital quartz is derived from both the incising adjusting lowland and the unadjusted relict upland the integrated 10 be concentrations still provide a denudation rate averaged across the two domains because fi eld samples can provide only a snapshot of the current upstream averaged erosion rate we employ a numerical landscape evolution model to explore how 10 be derived denudation rates vary over time and space during transient adjustment model results suggest that the longitudinal pattern of mean denudation rates is generated by the river s progressive dilution of low volume high concentration detritus from relict uplands by the integration of high volume low concentration detritus from adjusting lowlands the proportion of these materials in any detrital sample depends on what fraction of the upstream area remains unadjusted because the boundary of the adjusting part of the landscape changes over time the longitudinal trend in cosmogenic nuclide derived erosion rates changes over time these insights are then used to guide our interpretation of geomorphic and longitudinal cosmogenic nuclide data from the south fork eel river sfer in the california coast range united states the northward propagating crustal thickening and rock uplift associated with the passage of the mendocino triple junction generates a mobile wave of uplift that progressively sweeps longitudinally down the sfer the consequences of this forcing can be both replicated in the model environment and observed in the fi eld the sfer contains transient landforms including knickpoints and river terraces along mainstem and tributary channels that defi ne a clear boundary between an incised adjusting lowland and an unadjusted relict upland we report nine nested basin wide denudation rates in the mainstem of the sfer using terrestrial cosmogenic 10 be in river borne sediment we fi nd that denudation rates increase in the downstream direction from 0 2 mm yr in the upper catchment to 0 5 mm yr at the outlet using comparisons to the modeled landscape we show that this pattern of denudation rates paired with the distribution of relict topography throughout the watershed refl ect the immaturity of the landscape s transient adjustment later in this modeled transient the predicted erosion rates decrease downstream before they become uniform this interpretation of our data has potentially far reaching implications for quantifying the uplift history and response time of transient landscapes using cosmogenic nuclides

formation and growth of normal faults at the divergent plate boundary in iceland the divergent plate boundary in iceland is characterized by 40 80 km long and 5 10 km wide swarms of tension fractures 102 m long and normal faults 103 m long the upper part of the crust is mainly composed of lava flows with abundant columnar joints that are mostly perpendicular to the lava contacts the lava flows are horizontal at the surface of the rift zone but become tilted at the rate of 1 for every 150 m depth in the crust at the surface of the rift zone the joints are vertical and parallel to the vertical principal stress because of tilting of the lava pile the columnar joints become oblique to this stress hence becoming potential shear fractures and form echelon sets at greater depths in the crust theoretical considerations suggest that normal faults start to nucleate on sets of en echelon columnar joints and or large scale tension fractures at crustal depths of 0 5 1 5 km the width depth must be the smallest controlling dimension of many faults nevertheless there is a positive linear relation r 0 91 between maximum throw and length of the holocene faults if the faults grow as self similar structures the throw length relationship can be explained by a similar relation between fault length and width

interpreting quaternary uplift rates at the mendocino triple junction northern california from uplifted marine terraces analysis of the altitudinal spacing of 14 flights of marine terraces indicates a spatial pattern of varying uplift rates that agrees with that determined from previously dated terraces for the past 3 81 ka and temporal changes in uplift rates from 1 m ka to 3 5 m ka that may reflect response to changes in tectonic regime during passage of the mendocino triple junction mtj a possible mechanism for regional uplift is growth of a slab window south of the mtj the region of most rapid uplift is 25 43 km south of the mtj immediately south of the northern boundary of the slab window the coastline is tilted upward to the south in the region directly above the southern edge of the subducted gorda plate at point delgada 55 km south of the present mtj where the northern edge of the slab window passes approximately 300 ka uplift rates have been 1 2 m ka for at least 330 ka more than 1 4 m y after passage of the southern edge of the subducted slab at the mendocino coast uplift rates have been less than 0 4 m ka for at least 330 ka

late neogene and quaternary tectonics associated with northward growth of the san andreas transform fault northern california strain patterns within the forearc at a convergent margin adjacent to a passing fault fault trench triple junction show a systematic evolution we describe late neogene and quaternary deformation in northern coastal california in the last 3 m y associated with the migration of the mendocino triple junction deformation in the north american forearc near humbolt bay consists of a 30 km wide zone of on land contraction with a narrower zone of translation to the east the zone of subaerial contraction is part of the relatively wide southernmost extent of forearc contraction within the cascadia subduction zone net quaternary northeast southwest contraction across forearc thrust faults is at least 7 9 km and minimum fault slip rates on the six major thrust faults are 0 8 2 3 mm yr net right slip within the zone of translation is a minimum of 3 km south of the forearc translation is predominant in the north american plate and is accommodated along two major right lateral fault zones of the san andreas transform boundary the lake mountain and garberville fault zones discontinuous exposures of late neogene sediments along these faults near covelo and garberville respectively indicate that crustal contraction expressed by thrust faults and associated folding predated translational deformation at each site inception of contraction near covelo was related to inception of internal deformation of the gorda plate at 3 ma this contraction due to coupling of the convergent plates migrated northward in the forearc in advance of and at the rate of migration of the triple junction present day deformation near humboldt bay thus reflects contraction associated with subduction of the gorda plate and translation farther east associated with oblique convergence at the plate boundary as the triple junction migrates the strike slip faults of the san andreas transform boundary will extend to the north northwest into the present forearc and forearc strike slip faults will become faults of the san andreas system contractional structures near humboldt bay will then cease to be active and will be preserved in the geologic record in the same way as contractional structures are preserved farther south

instabilities in the summit region of mount etna during the 1999 eruption during the 1999 eruption of mount etna sicily the summit of the volcano changed dramatically lavas erupted from a fissure on the southern flank of se cone formed a large compound flow field that buried a substantial part of the northern wall of valle del bove and the ground between there and se cone hot mass flow deposits formed on the eastern and western flanks of the chasm following a period of intense strombolian activity at the same time a new vent opened on the southern flank of se cone and there was a major rockfall from its summit seven weeks later part of the outer western rim of bocca nuova crater collapsed during another period of intense strombolian activity and lava emerged at a high effusion rate through the breached crater wall following a subsequent collapse of the bocca nuova crater rim a hot avalanche flowed a few hundred metres on top of the previous lava flow field similar deposits have been described on other volcanoes but their importance in the evolution of the summit of etna has not previously been recognised

the role of the pernicana fault system in the spreading of mt etna italy during the 2002 2003 eruption flank instability and collapse are observed at many volcanoes among these mt etna is characterized by the spreading of its eastern and southern flanks the eastern spreading area is bordered to the north by the e w trending pernicana fault system pfs during the 2002 2003 etna eruption ground fracturing along the pfs migrated eastward from the ne rift to as far as the 18 km distant coastline the deformation consisted of dextral en echelon segments with sinistral and normal kinematics both of these components of displacement were one order of magnitude larger 1 m in the western previously known portion of the pfs with respect to the newly surveyed 9 km long eastern section 0 1 m this eastern section is located along a pre existing but previously unknown fault where displaced man made structures give overall slip rates 1 1 9 cm year only slightly lower than those calculated for the western portion 1 4 2 3 cm year after an initial rapid motion during the first days of the 2002 2003 eruption movement of the western portion of the pfs decreased dramatically while parts of the eastern portion continued to move these data suggest a model of spreading of the eastern flank of etna along the pfs characterized by eruptions along the ne rift instantaneous short lived meter scale displacements along the western pfs and more long lived centimeter scale displacements along the eastern pfs the surface deformation then migrated southwards reactivating one after the other the nnw sse trending timpe and trecastagni faults with displacements of 0 1 and 0 04 m respectively these structures along with the pfs mark the boundaries of two adjacent blocks moving at different times and rates the new extent of the pfs and previous activity over its full length indicate that the sliding eastern flank extends well below the ionian sea the clustering of seismic activity above 4 km b s l during the eruption suggests a deep decollement for the moving mass the collected data thus suggests a significant movement volume 1 100 km3 of the eastern flank of etna both on shore and off shore

geomorphology denudation rates and stream channel profiles reveal patterns of mountain building adjacent to the san andreas fault in northern california usa relative horizontal motion along strike slip faults can build mountains when motion is oblique to the trend of the strike slip boundary the resulting contraction and uplift pose off fault seismic hazards which are often difficult to detect because of the poor vertical resolution of satellite geodesy and difficulty of locating offset datable landforms in active mountain ranges sparse geomorphic markers topographic analyses and measurement of denudation allow us to map spatiotemporal patterns of uplift along the northern san andreas fault between jenner and mendocino california emergent marine terraces found southwest of the san andreas fault record late pleistocene uplift rates between 0 20 and 0 45 mm yr 1 along much of the coast however on the northeast side of the san andreas fault a zone of rapid uplift 0 6 1 0 mm yr 1 exists adjacent to the san andreas fault but rates decay northeastward as the coast becomes more distant from the san andreas fault a newly dated 4 5 ma shallow marine deposit located at 500 m above sea level masl adjacent to the san andreas fault is warped down to just 150 masl 15 km northeast of the san andreas fault and it is exposed at just 60 110 masl to the west of the fault landscape denudation rates calculated from abundance of cosmogenic radionuclides in fluvial sediment northeast of and adjacent to the san andreas fault are 0 16 0 29 mm yr 1 but they are only 0 03 0 07 mm yr 1 west of the fault basin average channel steepness and the denudation rates can be used to infer the erosive properties of the underlying bedrock calibrated erosion rates can then be estimated across the entire landscape using the spatial distribution of channel steepness with these erosive properties the lower elevation areas of this landscape that show high channel steepness and hence calibrated erosion rate are distinct from higher elevation areas with systematically lower channel steepness and denudation rates these two areas do not appear to be coincident with lithologic contacts assuming that changes in rock uplift rates are manifest in channel steepness values as an upstream propagating kinematic wave that separates high and low channel steepness values the distance that this transition has migrated vertically provides an estimate of the timing of rock uplift rate increase this analysis suggests that rock uplift rates along the coast changed from 0 3 to 0 75 mm yr 1 between 450 and 350 ka this zone of recent relatively rapid crustal deformation along the plate boundary may be a result of the impingement of relatively strong crust underlying the gualala block into the thinner weaker oceanic crust left at the western margin of the north american plate by the westward migration of the subduction zone prior to establishment of the current transform plate boundary the warped pliocene marine deposits and the presence of a topographic ridge support the patterns indicated by the channel steepness analyses and further indicate that the zone of rapid uplift may herald elevated off fault seismic hazard if this uplift is created by periodic stick slip motion on contractional structures

low level thermodynamic kinematic and reflectivity fields of hurricane guillermo 1997 during rapid intensification abstract from 0600 utc 2 august to 1200 utc 3 august hurricane guillermo 1997 deepened by 54 hpa over the eastern north pacific ocean easily exceeding the thresholds that define rapid intensification ri the noaa wp 3ds observed a portion of this ri with similar two aircraft missions on consecutive days the aircraft jettisoned 70 successful global positioning system gps dropwindsondes or gps sondes which reveal how conditions in the lower troposphere on the octant to quadrant scale evolved within 250 km of the eye reflectivity fields demonstrate that the deepening is correlated with a spiraling in of the northern eyewall that reduces the eye diameter by 10 km this behavior contrasts the more uniform contraction witnessed during eyewall replacement cycles mixing between the lower eye and eyewall as detailed by other investigators appears to have triggered the reduction in the eye diameter after ri the eyewall remains asymmetrical with the tallest echo tops and heaviest rain rates located o

actively growing anticlines beneath catania from the distal motion of mount etna s decollement measured by sar interferometry and gps we used sar interferometry and gps to measure the rise of an anticline beneath the urban area of catania italy which originates from outward thrusting above the basal decollement of etna volcano the anticline grows at a rate of over 0 015 m a 1 of se thrusting and about 0 007 m a 1 of relative uplift by relating this growth to the simultaneous extension measured at the summit of the volcano we demonstrate the occurrence of active volcanic spreading this process may exert a control on eruptions earthquakes sector collapses and landslides

neogene uplift of central eastern patagonia dynamic response to active spreading ridge subduction the chile triple junction ctj episodically migrated northward during the past 14 ma from 54 s to its present day position at 46 30 s as different almost trench parallel spreading segments entered in subduction this migration resulted in the opening of an asthenospheric window below patagonia inducing a disturbance in the regional mantle convection on the overriding plate the middle miocene time corresponds to a major change in the central patagonian basin dynamics with a transition from subsidence to generalized uplift the detailed mapping and the morphological study of post middle miocene terraces evidence regional scale trench parallel tilt histories that differ depending on latitude south of 46 30 s the slopes of the fluvial terraces indicate a change from northward to southward tilt during late miocene terraces younger than the early pliocene do not show any trench parallel tilt north of 46 30 s in contrast only northward tilt active until the pleistocene is recorded we use a semianalytical model of dynamic topography which suggests that the northward migration of the chile triple junction should be accompanied by a dynamic uplift of the central patagonian basin uplift would cause both north directed and south directed tilt north and south of the triple junction respectively with values of 0 1 0 2 500 km east of the trench tilt measured in the southeastern part of the central patagonian basin 0 1 is comparable to values predicted using the semianalytical model the dynamic topography associated to the chile ridge subduction may have exerted a major control on the neogene dynamics of patagonia

integrated geomorphic and geodynamic modeling of a potential blind thrust in the san francisco bay area california abstract geometries and slip budgets of the faults in the san francisco bay area imply previously unrecognized fault linkages including examples of blind thrust structures that appear to connect segments of strike slip faults and accommodate along strike variations in slip rate along these structures displacement along linking faults may be associated with the development of topography and also may serve as earthquake sources in marin county california systematic spatial patterns in landscape topography and geomorphic indices suggest that the region north of mt tamalpais is experiencing differential rock uplift we suggest that a blind thrust underlies the elevated area creating the observed topography and possibly resolving a slip discrepancy between the hayward and san andreas fault in this region we have developed and implemented an integrative approach that combines observations from tectonic deformation and geomorphic properties to identify a potential blind thrust beneath marin county elastic displacement modeling has been tested for compatibility with the blind thrust hypothesis and to assess the sensitivity of observables to fault geometry and orientation from this a set of plausible blind thrust structures are defined we use a range of empirical relationships between channel steepness index and erosion rate to estimate spatial variations in erosion rate along bolinas ridge by coupling these erosion estimates with elastic displacement fault modeling we can use the resulting topographic envelopes to constrain the rate and duration of deformation these constraints along with spatial bounds on the possible fault models are used to calculate potential seismic moment and moment magnitude with an assumed recurrence interval of 100 years such blind thrusts can produce a mw 6 3 earthquake while a longer recurrence time 1000 years results in a maximum mw 7 0 earthquake although such events are not likely to be catastrophic they are large enough to cause significant strong ground motions in the san francisco bay area

mechanisms for ground surface fracturing and incipient slope failure associated with the 2001 eruption of mt etna italy analysis of ephemeral field data abstract during the july august 2001 eruption of mt etna development of extensional fractures faults and grabens accompanied magma intrusion and subsequent volcanic activity during the first days of the eruption we performed an analysis of attitude displacement and propagation of fractures and faults exposed on the ground surface in two sites torre del filosofo and valle del leone located along the same fracture system in the region surrounding the valle del bove depression on the eastern flank of mt etna fractures and faults formed as the consequence of a shallow intruding dyke system that fed the several volcanic centres developed along the fracture system the investigated sites differ in slope attitude and in geometrical relationships between fractures and slopes in particular the fracture system propagated parallel to the gentle slope

changes in plate boundary kinematics punctuated or smoothly varying evidence from the mid cenozoic transition from lithospheric extension to shortening in new zealand abstract the marine magnetic anomaly record and plate kinematics derived from that data provide evidence of numerous cases of significant changes in plate motions and plate interactions however in most cases the temporal resolution provided by the marine record does not discriminate between punctuated abrupt or smooth variations in plate motions during a 10 million year period 30 ma to 20 ma the euler poles stage poles describing australia pacific relative plate motion migrated more than 20 in latitude the new zealand segment of the plate boundary is close to the location of the euler poles and their migration making the tectonics of its plate boundary structures particularly sensitive to the history of plate kinematics based on the rapid southward migration of the euler stage poles from north of new zealand to south of the landmass there is an expected rapid migrating transition from an extensional stage pole north of the site to transpressional stage pole south of the site plate boundary system the geologic signature of this rapid change in plate boundary kinematics is preserved in the stratigraphic record of a suite of basin deposits that span the latitudinal sweep of the migrating euler poles analyses of these deposits indicate that the timing of the transition from extensional to transpressional tectonics shows a continuous and systematic southward sweep indicating that the changes in australia pacific plate motions during the 30 ma 20 ma interval were smoothly continuous and not punctuated

magma ascent and the pressurization of mount etna s volcanic system after a period of deflation during the 1991 1993 flank eruption mount etna underwent a rapid inflation seismicity and ground deformation show that since 1994 a huge volume of magma intruded beneath the volcano producing from 1998 onward a series of eruptions at the summit and on the flank of the volcano the last of these started on 27 october 2002 is still in progress and can be considered one of the most explosive eruptions of the volcano in recent times here we show how geodetic data and seismic deformation between 1994 and 2001 indicate a radial compression around an axial intrusion consistent with a repressurization of mount etna s plumbing system at a depth of 6 to 15 kilometers which triggered most of the seismicity and provoked the dilatation of the volcano and the recent explosive eruptive activity

asynchronous miocene pliocene exhumation of the central venezuelan andes constraining the uplift and exhumation history of the venezuelan andes is critical for understanding the complex geodynamic evolution of northern south america we present new apatite fission track aft data from the sierra nevada de merida in the central venezuelan andes and compare the results with previously published aft data for the sierra la culata el carmen block to the north the aft data are combined with three dimensional thermal modeling to constrain the exhumation and relief history of both blocks which show significant differences the sierra nevada indicates exhumation rates of 1 7 km m y from ca 10 ma until 4 ma decreasing to 0 4 km m y from 4 ma to present the el carmen block in contrast underwent much more rapid recent exhumation with rates of 1 4 km m y since 4 ma the data suggest 4 km of relative rock uplift of the sierra la culata with respect to the sierra nevada since 4 ma and support significant uplift of basement blocks along major preexisting discontinuities during transpression in the northern andes linked to accretion of the panama arc and indentation of the maracaibo block rapid middle late miocene exhumation in the sierra nevada resulted from surface uplift that caused the late miocene deflection of the orinoco river inferred from the neogene sedimentary record

controls on the seasonal deformation of slow moving landslides article history precipitation drives seasonal velocity changes in slow moving landslides by increasing pore water pressure and reducing the effective normal stress along basal shear zones this pressure change is often modeled as a pore water pressure wave that diffuses through the landslide body such that the minimum time required for landslides to respond to rainfall should vary as the square of landslide depth which often approximates the saturated thickness and inversely with hydraulic diffusivity here we assess this model with new observations from the landslide prone eel river catchment northern california using satellite radar interferometry insar time series precipitation data and high resolution topographic data from airborne lidar we quantify the seasonal dynamics of 10 slow moving landslides which share the same lithologic tectonic and mediterranean climate conditions these slope failures have areas ranging from 0 16 to 3 1 km 2

oscillatory motion of drainage divides 1 a simple model of topographic ridge evolution is developed in which mass wasting is treated as a vectorial erosion process channel incision drives backcutting as well as downcutting of the connected hillslope and the result is a mobile drainage divide that exhibits sustained horizontal and vertical motions mediated by asynchronous asymmetric channel incision rates the model resolves a ridge cross section into coupled hillslope and channel links and the model equations are found to form a low dimensional non linear dynamical system for weak forcing of hillslope erosion the system converges to a stable symmetric geometry but for strong forcing a limit cycle arises and the divide oscillates back and forth over time the lessons to draw from this model are that such low dimensional dynamical behavior i may explain the sinuous planform of interfluves ii may form a key constituent of the high dimensional dynamics of landscape evolution as a whole

an exceptional case of endogenous lava dome growth spawning pyroclastic avalanches the 1999 bocca nuova eruption of mt etna italy abstract during an eruption at the bocca nuova one of the summit craters of mt etna in october november 1999 a part of the crater floor near its wnw rim was uplifted to form a dome shaped feature that consisted of older lava and pyroclastics filling the crater this endogenous dome grew rapidly over the crater rim thus being perched precariously over the steep outer slope of the bocca nuova and near continuous collapse of its steep flanks generated swiftly moving pyroclastic avalanches over a period of several hours these avalanches advanced at speeds of 10 20 m s and extended up to 0 7 km from their source on top of lavas emplaced immediately before their deposits were subsequently covered by lava flows that issued from vents below the front of the dome and from the bocca nuova itself growth of the dome was caused by the vertical intrusion of magma in the marginal western part of the crater which deformed and uplifted previously emplaced still hot and plastically deformable eruptive products filling the crater the resulting avalanches had all the characteristics of pyroclastic flows spawned by collapse of unstable flanks of lava domes but in this case the magma involved was of mafic hawaiitic composition and would under normal circumstances have produced fluid lava flows the formation of the dome and the generation of the pyroclastic avalanches owe their occurrence to the rheological properties of the eruptive products filling the crater which were transformed into the dome and to the morphological configuration of the bocca nuova and its surroundings the density contrast between successive erupted products may also have played a role although events of this type are to be considered exceptional at etna their recurrence might represent a serious hazard to visitors to the summit area

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

volumetric observations during paroxysmal eruptions at mount etna pressurized drainage of a shallow chamber or pulsed supply abstract the october 17 to november 5 1999 eruption of mount etna s bocca nuova crater emplaced a 15 10 6 m 3 flow field the eruption was characterized by 11 paroxysmal events during which intense strombolian and lava fountain activity fed vigorous channelized a a flows at eruption rates of up to 120 m 3 s 1 each paroxysm lasted between 75 and 450 min and was separated by periods of less intense strombolian activity and less vigorous 3 s 1 effusion ground based satellite and model derived volumetric data show that the eruption was characterized by two periods during which eruption rates and cumulative volume showed exponential decay this is consistent with a scenario whereby the system was depressurized during the first eruptive period october 17 23 repressurized during an october 24 pause and then depressurized again during the second period october 25 28 the imbalance between the erupted and supplied volumes mean that the two periods involved the collection of 1 5 5 7 10 6 m 3 and 1 2 3 6 10 6 m 3 respectively or an increase in the time averaged supply to 11 6 13 6 m 3 s 1 and 12 5 14 9 m 3 s 1 two models are consistent with the observed episodic fountaining derived volumetric trends and calculated volume imbalance a magma collection model and a pulsed supply model in the former case depressurization of a shallow reservoir cause the observed volumetric trends and foam collapse at the reservoir roof powers fountaining in the pulsing case variations in magma flux account for pressurization depressurization and supply the excess volume increases in rise rate and volatile flux coupled with rapid exsolution during ascent trigger fountaining limiting equations that define critical foam layer volumes and magma rise rates necessary for hawaiian style fountaining favor the latter model

new observations on the middle fork eel river coal bearing beds mendocino county california usa abstract mid 19th century reports of immense coal outcrops in the middle fork eel river mfer drainage near round valley in california s northern coast ranges fueled the early geological interest in this area with mine development the primary focus of many studies it was not until samuel g clark s 1940 geology of the covelo district mendocino county california that the coal was placed in its regional geologic context and assigned to the miocene a determination that relied primarily on a desmostylus hesperus molar found in shale overlying the coal and an associated equivocal though miocene compatible marine molluscan fauna our investigation of the mfer coal bearing beds has provided new data from foraminifera marine mollusks fish remains and the first reported fossil plants which as a whole support clark s miocene age assignment we also present an updated stratigraphy proposing under modern day stratigraphic protocols that the informal name sand bank beds sbb be used in place of the temblor formation to refer to the sbb coal bearing fluvial marine unit analysis of the sbb stratigraphy and sedimentology reveals the presence of a fluvial system that flowed from a distal upland region southward toward the paleocoast of california an abundant diverse palynoflora containing lycophytes ferns conifers and mesic thermophillic herbaceous and woody angiosperms indicates the drainage flowed through a coastal swampy forested bottomland and estuarine environment before emptying into a coastal basin presence of taxodium like wood foliage pollen and other hydrophiles suggests the mfer coal was a local mire buried by the progradation of the sbb fluvial system during a regressive phase an interpretation to be tested with future field work and detailed compositional analysis of the coal

neogene non marine sedimentation and tectonics in small pull apart basins of the san andreas fault system sonoma county california the san andreas fault system in northern california forms an 80 90 km wide zone of right lateral shear extensional tectonism within this broad shear zone is indicated by both neogene silicic volcanic rocks that gradually young in the direction of shear propagation to the north west and by numerous neogene faultbounded structural basins filled with thick non marine sequences the little sulphur creek basins three well exposed 1 5 2 km wide pull apart basins within this shear system have sedimentation patterns analogous to those of much larger pull apart basins they were formed and subsequently deformed by east west extension and by north west to south east orientated right slip concurrently with basin filling palaeocurrent and maximum clast size data indicate both lateral sediment transport from fault bounded basin margins and longitudinal transport down the basin axes the basins are filled primarily with coarse alluvial fan and streamflow deposits derived from a surrounding igneous sedimentary and metamorphic provenance two of the basins contain basin plain type lacustrine turbidites that grade laterally into distal alluvial fan fan delta and sublacustrine delta deposits talus deposits along the south west margin of the basins contain megabreccia indicative of active uplift structures indicative of dewatering liquefaction and slumping suggest penecontemporaneous tectonism

morphometric dating of the fluvial landscape response to a tectonic perturbation 1 despite constant progress in numerical and field studies of landscape evolution time evolution is still poorly constrained in many uplifted areas where low denudation rates prevent the use of low temperature thermochronology especially outside high relief mountainous areas here i show that regional statistics of the landscape metric r involving hypsometric integrals at three nested levels of a catchment are able to isolate the time effect on landscape geometry during the latter s transient response to a tectonic perturbation analysis of 210 catchments from 9 regions of known uplift age worldwide shows that the regionally characteristic r derivedsrindex is in inverse power law relation with the time elapsed since a base level lowering suggesting a response time of 5 my this finding has important implications for quantifying the rate of landform evolution and determining whether a landscape has reached steady state form

kinematics of earthflows in the northern california coast ranges using satellite interferometry abstract slow moving landslides exhibit persistent downslope motion with variations in velocity driven by transient stress perturbations along the sliding surface here we use satellite insar and high resolution topographic data to identify 50 slow moving landslides in the northern california coast ranges and monitor their seasonal kinematics over 4 years these landslides have similar mechanical properties and are subject to the same external forcings which allows us to explore geometrical controls on kinematics to overcome errors associated with large deformation gradients we incorporate a deformation model in the insar processing that enables us to generate deformation time series we test our novel methodology using a synthetic deformation time series confirming our ability to resolve seasonal velocity patterns time series analysis of four representative landslides reveals that seasonal velocity changes are characterized by comparatively rapid acceleration and gradual deceleration each slide displays distinct kinematic zones with different mean velocities although velocity changes appear to occur synchronously along the landslide body over seasonal timescales because these deformation patterns are sensitive to subsurface geometry we employ a commonly used non newtonian viscous flow law to infer slide thickness and find that these slides likely exhibit a highly variable thickness and an irregular i e rough and non planar basal sliding surface our results suggest that slide geometry controls long term motion but does not strongly regulate their response to seasonal stress perturbations