decadal scale change of infiltration characteristics of a tephra mantled hillslope at mount st helens washington the cataclysmic 1980 eruption of mount st helens radically reduced the infiltration characteristics of 60 000 ha of rugged terrain and dramatically altered landscape hydrology two decades of erosional biogenic cryogenic and anthropogenic activity have modified the infiltration characteristics of much of that devastated landscape and modulated the hydrological impact of the eruption we assessed infiltration and runoff characteristics of a segment of hillslope thickly mantled with tephra but now revegetated primarily with grasses and other plants to evaluate hydrological modifications due to erosion and natural turbation eruptive disturbance reduced infiltration capacity of the hillslope by as much as 50 fold between 1980 and 2000 apparent infiltration capacities of plots on the hillslope increased as much as ten fold but remain approximately three to five times less than the probable pre eruption capacities common regional rainfall intensities and snowmelt rates presently produce little surface runoff however high magnitude low frequency storms and unusually rapid snowmelt can still induce broad infiltration excess overland flow after 20 years erosion and natural mechanical turbation have modulated but not effaced the hydrological perturbation caused by the cataclysmic eruption copyright 2005 john wiley sons ltd

sedimentology and clast orientations of the 18 may 1980 southwest flank lahars mount st helens washington abstract three lahars that resulted from the flow transformation of an milled pyroclastic surge caused by ejected lithic debris and hydrothermal water during the cataclysmic mount st helena eruption of 18 may 1980 deposited about 1 106 m3 of massive poorly sorted poorly graded volcaniclastic sediment on the southwest flank swf mean peak flow velocities over a 5 km radius ranged from more than 30 m s in the proximal area mean slope angle of 13 to about 5 m s in the distal area mean slope angle of 4 9 the lahars rapidly decelerated as deposition occurred on forested slopes average yield strength of the swf lahars ranged from 9 000 to 12 000 dn cm2 bingham viscosity ranged from 2 8 103 to 50 103 poises average flow density of the swf lahars was about 2 0 g cm3 to determine the grain size distribution of the swf lahars spot sampling of deposit matrix from vertical exposures was supplemented with point count sampling of larger particles results from these analyses indicate that downflow changes in mean gram size and sorting occur only in the coarse fraction of the deposits larger than a critical diameter of about 4 mm and occur only in the basal portion of the deposits both mean grain size and sorting coefficient increase slightly with distance the deposits show weak inverse grading with respect to mean grain size and exhibit a weak trend of upwardly poorer sorting fabric analyses of clast long axes indicate strong planar orientations parallel to flow surfaces an eigenvalue analysis demonstrates the occurrence of both flow parallel long axis orientations with upstream dips and flow transverse orientations similar clast fabric results were obtained for deposits of the north fork toutle river lahar however the mean clast long axis dip in the swf lahars is significantly shallower than the mean clast long axis dip in the north fork toutle lahar and is more like clast long axis dips reported for tills and other sediment flows the data from the swf lahars indicate that lahar clast fabric may be more complex and variable than previously suggested

radar observations of a 3 day kelvin wave in the equatorial mesosphere mesospheric radars are used to investigate the characteristics of a kelvin wave from two equatorial sites jakarta indonesia in the western pacific and christmas island in the central pacific our study focuses on the time span from mid january through mid october 1993 a kelvin wave with a period near 3 days was detected throughout this 9 month duration although it underwent deep amplitude modulations on a 20 day timescale a fitting procedure is applied to study the phase amplitude behavior of the wave the vertical wavenumber was measured by the radars and found to be small wandering around zero with only a weak bias toward downward phase progression the long vertical wavelength suggests that the wave was predominantly zonal wavenumber 1 the amplitude of the wave measured by the jakarta meteor scatter radar was much larger than the amplitude measured by the mf partial reflection radar at christmas island the smaller wave amplitude at christmas island could at least partially be due to a measurement bias associated with mf radars the radar at jakarta is a vhf meteor scatter radar and is not susceptible to this bias however the mean velocities and the amplitudes of the tidal and quasi 2 day wave components were in good agreement at the two sites the estimated 9 month averaged zonal acceleration was 0 67 ms 1 day 1 over jakarta at 94 98 km and only about half as large over christmas island the magnitude of the zonal acceleration occasionally showed large enhancements which suggest the importance of refractive effects associated with vertical and temporal variations in the mean winds the larger 3 day wave amplitudes and inferred acceleration at jakarta may reflect its location in the western pacific a region of high convection and hence an excitation region for equatorial waves the relative phase of the wave between the two radar sites gradually shifted over a timescale of weeks these smooth variations in relative phase are suggestive of a superposition of waves with different zonal wavenumbers perhaps radiating preferentially from one longitude the phase of the wave as a function of altitude and time was much more disordered at jakarta than at christmas island the conjecture can be made that the more chaotic phase structure observed over jakarta is due to higher order zonal wavenumber components which weaken as they propagate eastward

erosion of tephra from the 1980 eruption of mount st helens erosion of tephra on hillslopes north of mount st helens was measured at intervals of several months between 1980 and 1983 using large arrays of stakes rill erosion was initially greater than sheetwash but its importance decreased comparatively quickly both rill erosion and sheetwash decreased by one to two orders of magnitude over the three year period because a stable rill network developed and more permeable and less erodible substrates were created or exposed the decrease occurred prior to recovery of plants the causes for the rapid decline in erosion at mount st helens explain patterns of erosion following several other recent tephra eruptions basin wide annual rates of erosion were computed by mapping the surface cover the hillslope gradient and the texture and thickness of tephra and by using statistical relations developed between them and erosion rates annual erosion decreased from 26 mm between may 1980 and may 1981 to 1 8 mm between may 1982 and may 1983 projecting this rate of decline into the future indicated that only about one sixth of the tephra on hillslopes will be removed by water erosion before soil creep and other forms of mass wasting again dominate hillslope evolution

rainfall runoff properties of tephra simulated effects of grain size and antecedent rainfall abstract rain triggered lahars rtls are a significant and often persistent secondary volcanic hazard at many volcanoes around the world rainfall on unconsolidated volcaniclastic material is the primary initiation mechanism of rtls the resultant flows have the potential for large runout distances 100 km and present a substantial hazard to downstream infrastructure and communities rtls are frequently anticipated in the aftermath of eruptions but the pattern timing and scale of lahars varies on an eruption by eruption and even catchment by catchment basis this variability is driven by a set of local factors including the grain size distribution thickness stratigraphy and spatial distribution of source material in addition to topography vegetation coverage and rainfall conditions these factors are often qualitatively discussed in rtl studies based on post eruption lahar observations or instrumental detections conversely this study aims to move towards a quantitative assessment of rtl hazard in order to facilitate rtl predictions and forecasts based on constrained rainfall grain size distribution and isopach data calibrated simulated rainfall and laboratory constructed tephra beds are used within a repeatable experimental set up to isolate the effects of individual parameters and to examine runoff and infiltration processes from analogous rtl source conditions laboratory experiments show that increased antecedent rainfall and finer grained surface tephra individually increase runoff rates and decrease runoff lag times while a combination of these factors produces a compound effect these impacts are driven by increased residual moisture content and decreased permeability due to surface sealing and have previously been inferred from downstream observations of lahars but not identified at source water and sediment transport mechanisms differ based on surface grain size distribution a fine grained surface layer displayed airborne remobilisation accretionary pellet formation rapid surface sealing and infiltration excess overland flow generation whilst a coarse surface layer demonstrated exclusively rainsplash driven particle detachment throughout the rainfall simulations this experimental protocol has the potential to quantitatively examine the effects of a variety of individual parameters in rtl initiation under controlled conditions

interrelations among pyroclastic surge pyroclastic flow and lahars in smith creek valley during first minutes of 18 may 1980 eruption of mount st helens usa a devastating pyroclastic surge and resultant lahars at mount st helens on 18 may 1980 produced several catastrophic flowages into tributaries on the northeast volcano flank the tributaries channeled the flows to smith creek valley which lies within the area devastated by the surge but was unaffected by the great debris avalanche on the north flank stratigraphy shows that the pyroclastic surge preceded the lahars there is no notable wet character to the surge deposits therefore the lahars must have originated as snowmelt not as ejected water saturated debris that segregated from the pyroclastic surge as has been inferred for other flanks of the volcano in stratigraphic order the smith creek valley floor materials comprise 1 a complex valley bottom facies of the pyroclastic surge and a related pyroclastic flow 2 an unusual hummocky diamict caused by complex mixing of lahars with the dry pyroclastic debris and 3 deposits of secondary pyroclastic flows these units are capped by silt containing accretionary lapilli which began falling from a rapidly expanding mushroom shaped cloud 20 minutes after the eruption s onset the smith creek valley bottom pyroclastic facies consists of a a weakly graded basal bed of fines poor granular sand the deposit of a low concentration lithic pyroclastic surge and b a bed of very poorly sorted pebble to cobble gravel inversely graded near its base the deposit of a high concentration lithic pyroclastic flow the surge apparently segregated while crossing the steep headwater tributaries of smith creek large fragments that settled from the turbulent surge formed a dense pyroclastic flow along the valley floor that lagged behind the front of the overland surge the unusual hummocky diamict as thick as 15 m contains large lithic clasts supported by a tough brown muddy sand matrix like that of lahar deposits upvalley this unit contains irregular friable lenses and pods meters in diameter blocks incorporated from the underlying dry and hot pyroclastic material that had been deposited only moments earlier the hummocky unit is the deposit of a high viscosity debris flow which formed when lahars mingled with the pyroclastic materials on smith creek valley floor overlying the debris flow are voluminous pyroclastic deposits of pebbly sand cut by fines poor gas escape pipes and containing charred wood the deposits are thickest in topographic lows along margins of the hummocky diamict emplaced several minutes after the hot surge had passed this is the deposit of numerous secondary pyroclastic flows derived from surge material deposited unstably on steep valley sides

seismic scattering and absorption mapping of debris flows feeding paths and tectonic units at mount st helens volcano abstract frequency dependent peak delay times and coda quality factors have been used jointly to separate seismic absorption from scattering quantitatively in earth media at regional and continental scale to this end we measure and map these two quantities at mount st helens volcano the results show that we can locate and characterize volcanic and geological structures using their unique contribution to seismic attenuation at 3 hz a single high scattering and high absorption anomaly outlines the debris flows that followed the 1980 explosive eruption as deduced by comparison with remote sensing imagery the flows overlay a nnw sse interface separating rocks of significant varying properties down to 2 4 km and coinciding with the st helens seismic zone high scattering and high absorption anomalies corresponding to known locations of magma emplacement follow this signature under the volcano showing the important interconnections between its feeding systems and the regional tectonic boundaries with frequency increasing from 6 to 18 hz the nnw sse tectonic feeding trends rotate around an axis centered on the volcano in the direction of the regional scale magmatic arc sw ne while the aseismic high scattering region wsw of the volcano shows no evidence of high absorption the regions of highest scattering and absorption are consistently located at all frequencies under either the eastern or the south eastern flank of the volcanic edifice from the comparison with the available geological and geophysical information we infer that these anomalies mark both the location and the trend of the main feeding systems at depths greater than 4 km

normal fault rupture interaction with strip foundations observations after earthquakes where surface fault ruptures crossed engineering facilities reveal that some structures survived the rupture almost unscathed in some cases the rupture path appears to divert avoiding the structure such observations point to an interaction between the propagating rupture the soil and the foundation this paper i develops a two step nonlinear finite element methodology to study rupture propagation and its interaction with strip foundations ii provides validation through successful class a predictions of centrifuge model tests and iii conducts a parameter study on the interaction of strip foundations with normal fault ruptures it is shown that a heavily loaded foundation can substantially divert the rupture path which may avoid outcropping underneath the foundation the latter undergoes rigid body rotation often detaching from the soil its distress arises mainly from the ensuing loss of support that takes place either at the edges or around its center the average pressure q on the foundation largely dictates the width of such unsupported spans increasing q decreases the unsupported width reducing foundation distress the role of q is dual 1 it compresses the soil flattening fault induced surface anomalies and 2 it changes the stress field underneath the foundation facilitating rupture diversion however even if the rupture is diverted the foundation may undergo significant stressing depending on its position relative to the fault outcrop

interaction of piled foundation with a rupturing normal fault post seismic observations in the 1999 kocaeli earthquake in turkey have indicated that piled foundations may be less suitable than stiff mat foundations in defending a structure against a major nor

impacts of explosive volcanism on distal alluvial sedimentation examples from the pliocene holocene volcaniclastic successions of japan abstract volcanic activities can create cataclysmic hazards to surrounding environments and human life not only during the eruption but also by hydrologic remobilisation lahar processes after the cessation of eruptive activity although there are many studies dealing with the assessment and mitigation of volcanic hazards these are mostly concentrated on primary eruptive processes in areas proximal to active volcanoes however the influence of volcaniclastic resedimentation may surpass the impacts of primary eruptive activity in terms of both extent and persistence and can ultimately result in severe hazards in downstream areas examination of the volcaniclastic successions of non marine pliocene holocene sedimentary basins in japan has revealed hydrological volcaniclastic sedimentation in fluvial and lacustrine environments hundreds of kilometres from the inferred source volcano impacts on these distal and often spatially separated basins included drastic changes in depositional systems caused by sudden massive influxes of remobilised pyroclastic material typical volcaniclastic beds comprise centimetre to decimetre thick primary pyroclastic fall deposits overlain by metre to 10s of metres thick resedimented volcaniclastic deposits intercalated in sedimentary successions of non volcanic provenance the relatively low component of primary pyroclastic fall deposits in the volcaniclastic beds suggests that 1 potential volcanic hazards would be underestimated on the basis of primary pyroclastic fall events alone and 2 the majority of resedimented material was likely derived from erosion of non welded pyroclastic flow deposits in catchment areas rather than remobilisation of local fallout deposits from surrounding hillslopes the nature distribution and sequence of facies developed by distal volcaniclastic sediments reflect the influence of 1 proximity to ignimbrite but not directly with the distance to the eruptive centre 2 ignimbrite nature non welded or welded and volume 3 temporal changes in sediment flux from the source area 4 the physiography and drainage patterns of the source area and the receiving basin and any intervening areas and 5 the formation of ephemeral dam lakes and intra caldera lakes whose potential catastrophic failure can impact distal areas models of the styles and timing of distal volcaniclastic resedimentation are thus more complicated than those developed for proximal settings of stratovolcanoes and their volcaniclastic aprons and hence present different challenges for hazard assessment and mitigation

rheological properties of mudflows associated with the spring 1980 eruptions of mount st helens volcano washington rheological properties of three recent mudflows at mount st helens were estimated using techniques developed for determining the properties of debris flows based on the geometry of their deposits calculated yield strengths of 1100 1000 and 400 pa maximum flow velocities of 10 to 31 m s volumetric flow rates of 300 to 3400 m s and plastic viscosities of 20 to 320 pa s all compare favorably with measured and estimated values cited in the literature a method for determining likely sites of future mudflow initiation based on these data is outlined

centrifuge modeling of fault propagation through alluvial soils the behavior of alluvial deposits subjected to fault movements in the underlying bedrock is of major concern for critical structures located within fault zones an understanding of fault propagation through soils would assist in design of such structures but could also be utilized in geological interpretation of fault displacement history on the premise that alluvial fault morphology contains shear patterns characteristic of modes and rates of fault displacements a study was undertaken involving centrifugal and numerical models of reverse faulting this paper describes the centrifuge model testing performed to backup simultaneous numerical studies geognosis report 1980 which will be described elsewhere a comprehensive model test series under earth gravity conditions 1g involving reverse and normal faulting under different angles has recently been undertaken by cole 1979 however model tests performed under 1g conditions are limited to rather thin soil layers because of their inability to simulate realistic gravity stress conditions furthermore it is not possible to simulate faulting fast enough to include inertial effects with such models

hillslope runoff processes and models abstract hillslope hydrology is concerned with the partition of precipitation as it passes through the vegetation and soil between overland flow and subsurface flow flow follows routes which attenuate and delay the flow to different extents so that a knowledge of the relevant mechanisms is important in the 1960s and 1970s hillslope hydrology developed as a distinct topic through the application of new field observations to develop a generation of physically based forecasting models in its short history theory has continually been overturned by field observation thus the current tendency particularly among temperate zone hydrologists to dismiss all hortonian overland flow as a myth is now being corrected by a number of significant field studies which reveal the great range in both climatic and hillslope conditions some recent models have generally attempted to simplify the processes acting for example including only vertical unsaturated flow and lateral saturated flows others explicitly forecast partial or contributing areas with hindsight the most complete and distributed models have generally shown little forecasting advantage over simpler approaches perhaps trending towards reliable models which can run on desk top microcomputers the variety now being recognised in hillslope hydrological responses should also lead to models which take account of more complex interactions even if initially with a less secure physical and mathematical basis than the richards equation in particular there is a need to respond to the variety of climatic responses and to spatial variability on and beneath the surface including the role of seepage macropores and pipes which call into question whether the hillside can be treated as a darcian flow system

experimental investigation of reverse fault rupture propagation through wet granular soil abstract surface fault rupture has been previously investigated in dry cohesionless soil however wet granular soil has not been investigated in detail however apparent cohesion induced by intergranular water causes granular soil to behave differently than dry cohesionless soil field evidence shows that all soil that has been wetted will experience some degree of cohesion in the present study eight experimental faulting tests were conducted on sand in which the water content varied from 0 dry to 15 and the soil layer height ranged from 25 to 35 cm to determine the behavior of the wet sand a series of direct shear tests were carried out at low confining stress corresponds to stresses at different depth of the physical model the results showed that the shear band zone decreased in the wet specimens creating a sharp scarp at the surface the required normalized fault displacement for outcropping decreased significantly in these specimens and reached a minimum value at about a 5 water content the direct shear test results showed that the failure strain of the wet sand can be used for prediction of h0 h surface tension cracks at the hanging wall widened in the zone of distortion at the surface in the wet specimens other aspects of fault rupture also are discussed

quasi biennial variation of the 5 day wave in the stratosphere 1 interannual variability of the 5 day wave in the stratosphere is examined by the use of national center for environmental prediction reanalysis data quasi biennial variation of the 5 day wave amplitude is clearly seen in the stratosphere this quasi biennial variation is closely related to the zonal wind variation associated with the equatorial quasi biennial oscillation in the stratosphere we give a short description of the mechanism bringing about the relationship

fluvial sediment transport and deposition following the 1991 eruption of mount pinatubo the 1991 eruption of mount pinatubo generated extreme sediment yields from watersheds heavily impacted by pyroclastic flows bedload sampling in the pasig potrero river one of the most heavily impacted rivers revealed negligible critical shear stress and very high transport rates that reflected an essentially unlimited sediment supply and the enhanced mobility of particles moving over a smooth fine grained bed dimensionless bedload transport rates in the pasig potrero river differed substantially from those previously reported for rivers in temperate regions for the same dimensionless shear stress but were similar to rates identified in rivers on other volcanoes and ephemeral streams in arid environments the similarity between volcanically disturbed and arid rivers appears to arise from the lack of an armored bed surface due to very high relative sediment supply in arid rivers this is attributed to a flashy hydrograph whereas volcanically disturbed rivers lack armoring due to sustained high rates of sediment delivery this work suggests that the increases in sediment supply accompanying massive disturbance induce morphologic and hydrologic changes that temporarily enhance transport efficiency until the watershed recovers and sediment supply is reduced d 2002 elsevier science b v all rights reserved

swift snowmelt and floods lahars caused by great pyroclastic surge at mount st helens volcano washington 18 may 1980 the initial explosions at mount st helens washington on the moring of 18 may 1980 developed into a huge pyroclastic surge that generated catastrophic floods off the east and west flanks of the volcano near source surge deposits on the east and west were lithic sorted lacking in accretionary lapilli and vesiculated ash not plastered against upright obstacles and hot enough to char wood all attributes of dry pyroclastic surge material deposited at the surge base on steep slopes near the volcano transformed into high concentration lithic pyroclastic flows whose deposits contain charred wood and other features indicating that these flows were hot and dry stratigraphy shows that even the tail of the surge had passed the east and west volcano flanks before the geomorphically distinct floods lahars arrived this field evidence undermines hypotheses that the turbulent surge was itself wet and that its heavy components segregated out to transform directly into lahars nor is there evidence that meters thick snow slab avalanches intimately mixed with the surge to form the floods the floods must have instead originated by swift snowmelt at the base of a hot and relatively dry turbulent surge impacting hot pyroclasts probably transferred downslope momentum to the snow surface and churned snow grains into the surge base melting snow and accumulating hot surge debris may have moved initially as thousands of small thin slushflows as these flows removed the surface snow and pyroclasts newly uncovered snow was partly melted by the turbulent surge base this and accumulating hot surge debris in turn began flowing a self sustaining process feeding the initial flows the flows thus grew swiftly over tens of seconds and united downslope into great slushy ejecta laden sheetfloods gravity accelerated the floods to more than 100 km h as they swept down and off the volcano flanks while the snow component melted to form great debris rich floods lahars channeled into valleys

a 6 5 day westward propagating planetary wave origin and characteristics a large 10 30 m s 1 6 7 day period westward propagating planetary wave was seen in both ground radar and satellite data within the 80 100 km height regime during august and september 1993 previous analyses of these data argue that it was most likely a manifestation of the 1 2 rossby planetary wave commonly referred to as the 5 day wave perhaps shifted to longer periods by interaction with the mean zonal winds in this study the global scale wave model gswm hagan et al 1993 is used to analyze the characteristics of this westward propagating wave we propose that the observed wave is not a doppler shifted 5 day wave but rather an unstable mode drawing energy from unstable regions in the upper mesosphere whose realization is global in scale the concept of atmospheric instability is used to determine a likely source region and the model is used determine the characteristic period growth rate and perturbation fields of the instability driven wave

effects of coarse woody debris and its removal on a channel affected by the 1980 eruption of mount st helens washington during the may 18 1980 eruption of mount st helens washington a pyroclastic surge introduced large volumes of coarse woody debris cwd and fine grained sediment to clearwater creek approximately 15 km northeast of the summit effects of controlled cwd removal on sediment storage substrate and pool frequency and volume were measured in four reaches each with three 200 m segments from 1982 to 1990 in each reach the upstream segment served as a control with no debris removal and cwd was totally and selectively removed from the other two segments unique among similar experiments are the large size and volume of cwd and the large inputs of fine grained sediment except for segments of two reaches that received debris torrents the clearwater channel thalweg scoured until 1985 in three reaches total debris removal caused additional scour and coarsening of the bed surface compared to segments with no or partial debris removal pools contracted from 1982 to 1985 and expanded afterward especially in control segments total debris removal apparently caused pools to become shallower and in segments of low sinuosity decreased the frequency of major pools habitat complexity decreased after total debris removal as indicated by a decrease in the standard deviation of residual depth and an increase in the size of substrate patches

river responses to the 2010 major eruption of the merapi volcano central java indonesia abstract this study examines the fluvial readjustment of a javanese river impacted by the major eruption of the merapi volcano indonesia in october and november 2010 the basin of the opak river located on the southern flank of the merapi was subject to substantial sediment input related to massive pyroclastic deposits that were remobilized by numerous lahars during the year after the eruption two study sites were equipped in order to evaluate the morphodynamic evolution of the riverbed of the opak river topographic surveys bedload particle marking and suspended sediment sampling revealed an important sediment mobilization during efficient flash floods surprisingly no bed aggradation related to the progradation of a sediment wave was observed two years after the eruptive event marked bed incision was observed the opak river readjustment differs from that of other fluvial systems affected by massive eruptions in two ways firstly local population extracted the sand and blocks injected by the eruption as they represent a valuable economic resource secondly several dams trapped the major part of the sediment load remobilized by lahars

sediment yield following severe volcanic disturbance a two decade perspective from mount st helens explosive volcanic eruptions perturb water and sediment fluxes in watersheds consequently posteruption sediment yields can exceed preeruption yields by several orders of magnitude annual suspended sediment yields following the catastrophic 1980 mount st helens eruption were as much as 500 times greater than typical background level and they generally declined nonlinearly for more than a decade although sediment yields responded primarily to type and degree of disturbance streamflow fluctuations significantly affected sediment yield trends consecutive years 1995 1999 of above average discharge reversed the nonlinear decline and rejuvenated yields to average values measured within a few years of the eruption after 20 yr the average annual suspended sediment yield from the 1980 debris avalanche deposit remains 100 times 10 4 mg megagrams km 2 above typical background level 10 2 mg km 2 within five years of the eruption annual yields from valleys coated by lahar deposits roughly plateaued and average yields remain about 10 times 10 3 mg km 2 above background level yield from a basin devastated solely by a blast pyroclastic current diminished to background level within five years these data demonstrate longterm instability of eruption generated detritus and show that effective mitigation measures must remain functional for decades

a morphometric analysis of gullies scoured by post fire progressively bulked debris flows in southwest montana usa in the fall of 2001 an intense thunderstorm in southwest montana triggered many debris flows in the burned area of sleeping child creek in most instances the debris flows cut deep gullies into previously unchannelized colluvial hollows and deposited large volumes of sediment onto the valley floor the presence of rill networks above the gullies as well as the absence of landslide features indicate that the gullies were scoured by progressively bulked debris flows a process in which dilute surface runoff becomes increasingly more laden with sediment until it transforms into a debris flow in this contribution we present a morphometric analysis of six of the gullies to better understand this relatively understudied process we find that the locations of the rill heads and gully heads conform to slope area thresholds that are characteristic of erosion by overland flow our data also suggest that the volumes of the debris flows increase exponentially with normalized drainage area thus lending support to an assumption used in a recently proposed debris flow incision law finally the debris flow fans have been relatively unaltered since deposition suggesting that the valley may be currently aggrading while the hillslopes are being denuded

extraordinary sediment delivery and rapid geomorphic response following the 2008 2009 eruption of chaiten volcano chile u s geological survey volcano science center sernageomin s programa de riesgos volcanicos conicyt fondecyt grants 1110609 1141064 11130671 conicyt fondap 15090013 vamos research centre

effects of forest land management on erosion and revegetation after the eruption of mount st helens the 1980 eruption of mount st helens covered soils with a tephra blanket and killed the forest tree cover in a 550 km2 area after the eruption rates of sheetwash and rill erosion and plant cover were measured on tephra covered hillslopes which had been subject to three land management practices grass seeding scarification and salvage logging on rapidly eroding hillslopes subject to grass seeding limited plant covers were established only after erosion had declined sharply logging of trees downed by the eruption and scarification of previously logged surfaces slowed erosion although the effect was small because erosion rates had already slowed substantially by the time these two practices were implemented the factors controlling erosion revegetation and their relative timing at mount st helens are similar to those following explosive volcanic eruptions elsewhere suggesting that grass seeding is not likely to be effective at slowing erosion following most tephra eruptions and that early mechanical disturbance could be an effective erosion control measure the results also indicate that even without deliberate conservation measures processes which mechanically disturb a surface layer of low hydraulic conductivity such as frost action or trampling can radically reduce runoff and erosion before revegetation has an important effect

land use floods and channel changes upper middle fork willamette river oregon 1936 1980 flow trends and channel characteristics from 1936 to 1980 were evaluated for the middle fork willamette river which drains a 668 km2 forested watershed in the cascade mountains of western oregon an inventory of aerial photographs from 1959 to 1972 shows that landslides associated with roads and in clearcuts were 27 and 23 times more frequent respectively than in forested areas numerous landslides unloaded sediments directly into the drainage system most landslides appear to have been initiated during a large flood return period greater than or equal to 100 years of december 22 1964 analysis of precipitation and peak flows greater than 100m3 s 1 from 1958 to 1980 by means of power function models suggests a trend of increasing flows as timber harvesting and road building expanded in the basin changes in channel pattern documented from aerial photographs show major increases in channel width from 1959 to 1967 and a trend of decreasing width from 1967 to 1980 during summer low flows in 1979 and 1980 65 cross sections of the channel were surveyed to provide detailed measurements of existing channel conditions channel widths of 62 of the aggraded reaches were significantly greater 0 05 than those for nonaggraded reaches

observations of the 6 5 day wave in the mesosphere and lower thermosphere previous observations of atmospheric oscillations with zonal wave number 1 have consistently located waves of periods between 5 and 7 days this study presents a global and seasonal analysis of the 6 5 day wave in high resolution doppler imager daytime mesosphere and lower thermosphere horizontal winds temperatures and nighttime atomic oxygen at 95 km the horizontal structures of all these atmospheric variables are similar to the gravest symmetric wave number 1 rossby wave i e the 1 1 mode the seasonal and spatial analysis displays possible modification by the zonal mean wind finally the observed vertical structures of the 6 5 day wave indicate that it is an internal rossby wave not an external or lamb wave

acute sedimentation response to rainfall following the explosive phase of the 2008 2009 eruption of chaiten volcano chile the 10 day explosive phase at the start of the 2008 2009 eruption of chaiten volcano in southern chile 42 83 s 72 65 w blanketed the steep rain forest cloaked 77 km2 chaiten river drainage basin with 3 to 100 cm of tephra predominantly fine to extremely fine rhyolitic ash fell during the latter half of the explosive phase rain falling on this ash blanket within days of cessation of major explosive activity generated a hyperconcentrated flow lahar followed closely by a complex multi day muddy flood streamflow bordering on dilute hyperconcentrated flow sediment mobilized in this lahar flood event filled the chaiten river channel with up to 7 m of sediment buried the town of chaiten 10 km downstream of the volcano in up to 3 m of sediment and caused the lower 3 km of the channel to avulse through the town although neither the nature nor rate of the sedimentation response is unprecedented they are unusual in several ways 1 nearly 70 percent of the aggradation almost 5 m in the 50 70 m wide chaiten river channel was caused by a lahar triggered by an estimated 20 mm of rainfall over a span of about 24 h an additional 2 m of aggradation occurred in the next 24 36 h 2 direct damage to the town was accomplished by the sediment laden water flood phase of the lahar flood event not the lahar phase 3 the volume of sediment eroded from hillslopes and delivered to the chaiten river channel was at least 3 8 106 m3 roughly 15 40 of the minimum tephra volume that mantled the chaiten river drainage basin 4 the acute sedimentation response to rainfall appears to have been due to the thickness and fineness of the ash blanket inhibiting infiltration of rain and the steepness of the basin s hillslopes other possible factors such as the prior formation of an ash crust development of a hydrophobic surface layer or large scale destruction of rain intercepting vegetation did not play a role

observations of the quasi 2 day wave from the high resolution doppler imager on uars a strong westward traveling oscillation with a period of 2 days and zonal wave number 3 is observed in the mesospheric and lower thermospheric winds from the high resolution doppler imager on the upper atmosphere research satellite the important events happen in january july and september october of which the occurrence in january is the strongest with an amplitude over 60ms 1 detailed analyses for the periods of january 1992 and january 1993 reveal a cause and effect relationship in the wave developing process at 95km the global structures of the wave amplitude and phase are also presented

evolution of coarse gravel bed forms field measurements at flood stage field measurements to investigate the origin and growth of mesoscale gravel bed forms in deep flows were made in the north fork toutle river washington sonar observations of the gravel streambed at a stationary point were recorded during two storm flows in december 1989 and january 1990 with concurrent bed load sampling and continuous velocity measurements mean diameter of bed load was about 3 cm flow depths were 1 4 2 4 m and bed shear stresses were 2 5 times the critical stress of mean bed load diameter as computed from the depth slope product these records document the hydrodynamic conditions under which dunelike coarse gravel bed forms were observed coarse gravel dunes height 20 cm length 6 15 m evolved more than 24 hours after peak stage primarily by accretion as inferred from bed form changes revealed in dual sonar records dune heights increased to 40 cm as mean trough elevation rose about 50 cm over several hours smaller dunes wavelength 1 3 m transitional from bed load sheets migrated on the backs of the large dunes the superposed dunes finally became indistinguishable from the large dunes which diminished in height by increasing the mean level of troughs gravel deposition occurred at the observation point in conjunction with migration of gravel dunes the direct comparison of known bed form regimes and gravel bar facies provides alternative interpretations of gravelly deposits

channel bed mobility response to extreme sediment loading at mount pinatubo since the 1991 eruption of mount pinatubo the specific sediment yields from watersheds draining its slopes have been the highest ever recorded in spite of this overwhelming sediment load rivers inundated by pyroclastic flow deposits delivered almost half of the initial deposits to downslope alluvial and or debris fans by 1996 although most of this transport occurred by hyperconcentrated flows and debris flows lahars very high sediment transport rates also characterize low flow measured flow velocities and depths channel properties and the size of both mobile and stable clasts in the sacobia and pasig potrero rivers indicate median bed surface grain sizes of 2 to 8 mm grain size independent dimensionless critical shear stresses c of 0 016 to 0 041 and manning s n values of 0 017 to 0 024 values well below those previously reported for steep mountain channels the dramatic bed surface fining bed mobility and selective transport in these extremely sediment rich channels indicate that changes in grain size c values and bed roughness can increase transport capacity in response to high sediment supply our observations also suggest viewing the apparently contradictory concepts of an equal threshold of bed mobility and grain size dependent selective transport as end member concepts that apply to channels with low or intermittent and high or continuous sediment supply respectively

soil deformation measurement using particle image velocimetry piv and photogrammetry a deformation measurement system based on particle image velocimetry piv and close range photogrammetry has been developed for use in geotechnical testing in this paper the theory underlying this system is described and the performance is validated digital photography is used to capture images of planar soil deformation using piv the movement of a fine mesh of soil patches is measured to a high precision since piv operates on the image texture intrusive target markers need not be installed in the observed soil the resulting displacement vectors are converted from image space to object space using a photogrammetric transformation a series of validation experiments are reported these demonstrate that the precision accuracy and resolution of the system are an order of magnitude higher than previous image based deformation methods and are comparable to local instrumentation used in element testing this performance is achieved concurrent with an order of magnitude increase in the number of meas

morphological evolution of the north fork toutle river following the eruption of mount st helens washington abstract the north fork toutle river nftr has undergone extensive morphological changes following the catastrophic eruption of mount st helens washington in 1980 especially the upper reaches affected by a 2 5 km3 debris avalanche deposit caused by the eruption this paper reports analysis and interpretation of vertical adjustments to the thalweg long profile at some 33 km river reaches redeveloped on the debris avalanche deposit during the 30 year period since the eruption the results confirm that adjustments in the upper part of the study reaches have generally been led by degradation while that in the lower reaches have been led by aggradation with the middle reaches acting as a hinge zone trends of change in the thalweg long profile and bedslope reveal that channel gradients have decreased nonlinearly through time and with distance downstream from the volcano values of stream power have decreased with time commensurately owing to reductions in slope and channel widening while the bed has coarsened so that rates of erosion of the debris avalanche deposit in the upper nftr have slowed to the point that the long profile now perched and slightly steeper is relaxing toward a new equilibrium or graded condition thirty year relaxation paths for thalweg elevation were simulated at seven key cross sections using newly developed comprehensive rate law models based on nonlinear decay in rates of morphological response to perturbation the results indicate that both single and multistep rate law models can simulate the observed records consequently the rate law approach provides an effective method for studying and simulating morphological response of the fluvial system to a major instantaneous disturbance such as a volcanic eruption

coupled fluid dynamics sediment transport modelling of a crater lake break out lahar mt ruapehu new zealand summary lahars and other sudden onset floods are highly dynamic with temporally and spatially evolving sediment loads numerical models of sudden onset flood behaviour particularly those applied to real world events have tended to neglect sediment transport processes this is a serious though perhaps understandable shortcoming given a lack of field measurements on flow bed interactions the extra computational complexity required and the problem of iteratively updating plastic channel boundaries this paper applies a fluid dynamics model with suspended sediment and bedload transport to calculate flow conditions and rapid landscape change due to an initially dilute lahar from mt ruapehu new zealand we take advantage of an unprecedented dataset of net topographic changes determined from pre and post lahar airborne lidar surveys and time series of hydrological measurements to run and validate the model a sensitivity analysis of key controls on water surface elevation and final sediment thickness illustrates how the flow was supply limited in the upper reaches it was capable of transporting a greater volume and calibre of material than that available modelled patterns of net erosion and deposition can replicate those observed r 2 0 79 and are dominantly controlled by channel gradient and topographic

the 6 5 day wave and its seasonal variability in the middle and upper atmosphere 1 the zonal wave number 1 planetary wave of period near 6 5 days is a robust feature in the mesosphere and lower thermosphere mlt region with prominent seasonal variability as revealed by ground based and satellite observations this wave and its seasonal variability are well reproduced in a recent one model year run of the national center for atmospheric research thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm with its lower boundary specified according to the national centers for environmental prediction analysis year 1993 wavelet analysis of the model output shows that in the mlt region the wave maximizes before and after the equinoxes and minimizes at solstices the wave amplitudes at the equinoxes are smaller than the peaks before and after but are still larger than the wave amplitudes at solstices however at the lower boundary near 30 km the wave peaks are predominantly between fall and the following spring by examining the episodes of maximum and minimum wave amplitude and by conducting additional control experiments using the time gcm the structure of this planetary wave and the factors determining the wave characteristics and seasonal variability are studied in detail it is found that the wave source mean wind structure instability and the critical layers of the wave can all affect the wave response in the mlt region and can have a strong seasonal dependence before and after equinox the wave follows the waveguide and propagates from the stratosphere to the summer mesosphere mesopause where it may amplify due to baroclinic barotropic instability such instability is usually absent from the equinoctial atmosphere so that there is no wave amplification at equinox at solstice the wave decays significantly when propagating away from its winter source due to the strong eastward winter stratospheric jet in the summer side the westward jet is also strong and the meridional and vertical extension of the critical layer of the wave is large enough to enclose the instability in the summer mesosphere mesopause at middle to high latitudes the wave is thus reflected away and prevented from reaching and amplifying at the unstable region the seasonal variation of the quasi two day wave which has zonal phase speed similar to the 6 5 day wave is also studied using similar diagnostics it is further shown that within certain seasonal window periods the variability in the mlt especially the summer mlt may closely track the lower atmospheric variability associated with these waves

centrifuge modeling of pile sand interaction induced by normal faulting abstractmany forensic studies conducted after catastrophic earthquakes revealed severe damages to pile foundations caused by bedrock fault movement the mechanism behind these pile foundation failures is not yet fully understood in this study two centrifuge model tests are carried out on a single pile and on a group of three piles in sand subjected to normal faulting the surface settlement profile and additional internal forces of the piles are measured the surface settlement profile in sand could be well fitted and predicted with a profile function error function the single pile which is located in a differential settlement zone is displaced and the pile top rotates toward the hanging wall inducing an additional bending moment along the pile the pile group is then forced to rotate toward the hanging wall because the three piles are well connected to the pile cap driven by the movement of the two additional piles and a pile cap in place the pile on the footwall side experiences greater displ

caisson foundations subjected to reverse fault rupture centrifuge testing and numerical analysis recent large magnitude m 7 earthquakes have caused numerous failures induced by surface faulting demonstrating the need to account for tectonic deformation in seismic design thanks to their usually high rigidity embedded e g caisson foundations may divert the fault rupture and lead to favorable performance whereas surface or piled foundations may fail we present a series of centrifuge model tests to investigate the response of caisson foundations embedded in a cohesionless soil stratum the base of which is subjected to reverse faulting we elucidate the interplay between the propagating fault rupture and the caisson focusing on the role of the location of the outcropping rupture relative to the caisson the rigid body of the caisson causes diversion and or bifurcation of the shear localization which is forced to develop preferentially around the edges of the caisson the observed failure pattern and the consequent caisson response depend strongly on the exact caisson position relative to the

flow resistance under conditions of intense gravel transport a study of flow resistance was undertaken in a channelized reach of the north fork toutle river downstream of mount st helens washington hydraulic and sediment transport data were collected in flows with velocities up to 3 m s and shear stresses up to 7 times the critical value needed for bed load transport details of the flow structure as revealed in vertical velocity profiles indicate that weak bed load transport over a plane gravel bed has little effect on flow resistance the plane gravel bed persists up to stresses 3 times critical at which point irregular bed forms appear bed forms greatly increase flow resistance and cause velocity profiles to become distorted the latter arises as an effect of flows becoming depth limited as bed form amplitude increases at very high rates of bed load transport an upper stage plane bed appeared velocity profiles measured in these flows match the law of the wall closely with the equivalent roughness being well represented by ks 3d84 of the bed load the effects noted here will be important in very large floods or in rivers that are not free to widen such as those cut into bedrock

environmental impact of the 1 8 ka taupo eruption new zealand landscape responses to a large scale explosive rhyolite eruption abstract large scale ignimbrite eruptions from rhyolitic caldera volcanoes can trigger geologically instantaneous changes in sedimentary systems over huge areas by either burying existing environments or overloading them with vast quantities of unconsolidated particulate material the post eruption readjustment of the landscape to such perturbations is one of the most dramatic processes in physical sedimentology exemplified here by the 1 8 ka taupo eruption in the central north island of new zealand this eruption generated voluminous fall deposits then climaxed with emplacement of a c 30 km 3 non welded ignimbrite over a near circular area of c 20 000 km 2 approximately 90 of the area but the headwaters of many of the north island s largest rivers were impacted by both the primary pyroclastic fall and flow material large scale post eruption remobilisation of this material coupled with the re establishment of fluvial systems occurred in a distinct sequence as recorded by the evolution of sedimentary facies in different sub environments following an initial period dominated by mass flows re establishment of fluvial systems began with the headward erosion of box canyons through the ponded ignimbrite deposits a process often associated with the break out of temporary lakes aggradational streams developed in these channels rapidly evolved from shallow ephemeral sediment laden outbursts associated with flash flood events to deeper permanent braided rivers before declining sediment yields led to retrenchment of single thread rivers and a return to pre eruption gradients and bedloads years to decades later typically the modern profile of many streams and rivers follow closely their pre eruption profiles and incision and erosion is overwhelmingly confined to the deposits of the eruption itself although the general remobilisation pattern is similar for all impacted river systems detailed studies of the waikato rangitaiki mohaka ngaruroro and whanganui catchments show that the relative timing and scale of each eruption response phase differs between each catchment these reflect differences in catchment physiography and hydrology and the volume and type of pyroclastic material deposited in each ultimately the landscape response reflects the relative spatial distributions of and the volumetric ratios between the volumes of pyroclastic debris water and accommodation space in the basin cf kataoka and manville this volume

centrifuge modeling of geotechnical mitigation measures for shallow foundations subjected to reverse faulting surface fault ruptures are particularly damaging to buildings lifelines and bridges located across or adjacent to active faults these structures should be designed in consideration of surface fa

long term elevated post eruption sedimentation at mount pinatubo philippines post eruption sedimentation rates from two basins draining mount pinatubo philippines are compiled and extended through a d 2009 to compare short term predictions with long term yields the pasig potrero and sacobia rivers were covered by 1 km 3 of thick pyroclastic flow deposits during the 1991 eruption of mount pinatubo blanketing 30 of each basin with highly erodible sediments erosion of these deposits led to some of the highest sediment yields ever recorded yields peaked in 1991 and declined exponentially for the first decade following the eruption deposition on the aggrading alluvial fan shows that sedimentation rates from 2001 to 2009 were almost twice as high as an exponential decay model would predict with rates that have leveled off and are no longer declining exponentially patterns of long term sedimentation are similar to those of the north fork toutle river washington state united states at mount st helens with two phases of erosion and sediment export in the first erosion of hillslope tephra and carving of the initial valley network lead to high sediment yields that decline exponentially over 5 10 yr in the second phase continued valley widening and fluvial instability maintain high sediment yields for at least two decades a comparison of post eruption deposition with pre eruption yields indicates that century to millennial scale sedimentation is dominated by sediment associated with discrete eruptive events

crustal channel flows 2 numerical models with implications for metamorphism in the himalayan tibetan orogen 1 results from a thermal mechanical model ht1 that includes midcrustal channel flow are compatible with many features of the himalayan tibetan system radioactive self heating and rheological weakening of thickened model orogenic crust lead to the formation of a hot low viscosity midcrustal channel and a broad plateau channel material corresponding to the greater himalayan sequence ghs flows outward from beneath the plateau in response to topographically induced differential pressure at the plateau flank it is exhumed by focused surface denudation and juxtaposed with cooler newly accreted material corresponding to the lesser himalayan sequence lhs the model channel is bounded by coeval thrust and normal sense ductile shear zones interpreted to represent the main central thrust mct zone and south tibetan detachment system respectively inverted metamorphism associated with the model mct zone results from distributed ductile shear along the mct and extrusion of the hot channel a variety of model p t t path styles resembling those observed in the ghs and lhs are produced for points traveling through contrasting tectonic regimes that coexist in different parts of the model predicted times of peak metamorphism cooling and erosion of metamorphic facies are generally compatible with observations although model ghs cooling ages are too young the times of m1 and m2 metamorphic events observed in the ghs correspond to model times of maximum burial and maximum heating respectively the results highlight the need to integrate tectonics and metamorphism in continental collision models and demonstrate the importance of lateral transport of both heat and material in large hot orogens

observations of the 5 day wave in the mesosphere and lower thermosphere the 5 day planetary wave has been detected in the winds measured by the high resolution doppler imager hrdi on the upper atmosphere research satellite uars in the mesosphere and lower thermosphere 50 110 kin the appearances of the 5 day wave are transient with a lifetime of 10 20 days in the two year data set the structures of selected 5 day wave events are in generally good agreement with the 1 1 rossby normal mode for both zonal and meridional components a climatology of the 5 day wave is presented for an altitude of 95 km and latitudes mainly between 40os and 40on

sediment charged flash floods on montserrat the influence of synchronous tephra fall and varying extent of vegetation damage on 20th may 2006 the soufriere hills volcano on the caribbean island of montserrat experienced a large dome collapse and intense rainfall generated flash floods the floods had very high loads of volcanic debris derived both from this and previous eruptions and can thus be classified as lahars the floods reached unusually high water levels and caused substantial geomorphic change in the belham valley detailed rainfall and geomorphological data coupled with the precise timing of events and yewitness accounts have facilitated an assessment of the relative importance of rainfall volume and intensity older volcanic debris pre and syn flood tephra fall and the extent of pre flood vegetation damage for the behavior of this and subsequent sediment laden floods in this setting the change in runoff behavior was controlled by preexisting vegetation damage and synchronous tephra fall and this was critically important in controlling the impact of these flash floods although rainfall intensity and volume have some control on flood occurrence they are not the critical control on flash flood impact on the geomorphology in the belham valley a significant conclusion of this study is that the extreme nature of the flash floods was not caused by extreme rainfall as is commonly believed to be the primary cause of flash floods but rather it was the result of changed runoff behaviour caused by the widespread syn flood tephra deposition and importantly the widespread vegetation damage by volcanic associated acid rain in the preceding weeks

interaction of shallow foundations with reverse faults a series of centrifuge model tests is reported that investigated the effects of foundation position on the interaction of reverse dip slip faults with shallow foundations resting on sand the model tests have allowed careful examination of both the soil and foundation deformation as a shear localization fault propagates through a 15 m thick sand layer for fault throws up to 5 m by comparing results of the tests with foundations present with those from a free field test the effect of the foundation on the faulting pattern has been observed directly the response of the foundation is very sensitive to the exact position of the fault and even when the fault emerged remotely from the foundation it sometimes caused significant foundation movements detailed results are presented for the tests and it is suggested that these results are used as 1 indications of likely foundation soil fault interaction mechanisms and 2 to allow future validation of numerical models for similar problems finally fou

eruption triggered avalanche flood and lahar at mount st helens effects of winter snowpack an explosive eruption of mount st helens on 19 march 1982 had substantial impact beyond the vent because hot eruption products interacted with a thick snowpack a blast of hot pumice dome rocks and gas dislodged crater wall snow that avalanched through the crater and down the north flank snow in the crater swiftly melted to form a transient lake from which a destructive flood and lahar swept down the north flank and the north fork toutle river

spatial and temporal patterns in fluvial recovery following volcanic eruptions channel response to basin wide sediment loading at mount pinatubo philippines the june 1991 eruption of mount pinatubo philippines was one of the largest volcanic eruptions of the twentieth century emplacing 5 6 km 3 of pyroclastic fl ow material on the fl anks of the volcano the combination of abundant relatively fi ne grained easily erodible material and intense tropical rainfall led to numerous lahars immediately following the eruption even after major lahars ended sediment yields in some basins remained orders of magnitude above pre eruption levels using data collected from 1996 through 2003 we investigated fi ve basins that experienced varying amounts of sediment loading in the 1991 eruption from 1 to 33 of the basin area covered by valley fi lling pyroclasticfl ow deposits from measurements of fl ow and bed characteristics made through time we developed a general conceptual model for channel recovery following basin wide sediment loading initially fi ner grained sediment and pumice are mobilized preferentially through selective transport once the bed is coarse enough for gravel size clasts to interact with one another clast structures develop increasing form roughness and critical shear stress and inhibiting initial clast mobility as sediment inputs continue to decline the channel incises into valley bottom sediments progressively armoring through winnowing at pinatubo incision and armoring occur fi rst as dry season phenomena due to reduced sediment inputs eventually moving to year round low fl ow bed stability observed timing of the onset of in channel biological recovery suggests that reestablishment of channel stability helps catalyze aquatic ecosystem recovery

effect of el nino southern oscillation on the dynamical thermal and chemical structure of the middle atmosphere 1 a simulation of the middle atmosphere is presented using a general circulation model gcm forced with observed sea surface temperature for the period 1950 2000 the gcm extends to the lower thermosphere and reproduces realistic dynamical and temperature distributions the period contains several el nino and la nina events which are identified using the nino3 index composite anomalies of relevant meteorological fields are obtained by stratifying the northern winter season according to the nino3 index these anomalies have the structure of vertically propagating planetary waves extending from the troposphere to the mesosphere circulation anomalies in the middle atmosphere are accompanied by large temperature anomalies that are of opposite sign in the stratosphere and mesosphere the former being warmer and the latter colder during el nino events near the summer mesopause changes in momentum deposition by parameterized gravity waves results in warming during el nino detailed statistical analysis is used to determine the significance of these anomalies a chemical transport simulation is carried out using output from the gcm it shows that when the lower stratosphere is colder as during la nina events some ozone depletion takes place conversely when the lower stratosphere is warmer and more disturbed as is the case during el nino events heterogeneous chemical processes are inhibited

initiation and flow behavior of the 1980 pine creek and muddy river lahars mount st helens washington two large high velocity lahars volcanic debris flows were triggered by a pyroclastic surge during the first few minutes of the may 18 1980 eruption of mount st helens the initial surge cloud evolved progressively by gravity segregation from a gas mobilized highly inflated density flow to a dense water mobilized basal debris flow lahar and accompanying ash cloud as it flowed down the east flank of the volcano the main source of the water for the lahars was probably from eroded snow and ice incorporated into the flow by turbulent mixing but ground water expelled together with the rock debris by the initiating volcanic explosions also may have contributed peak lahar discharge from the pine muddy fan upper smith creek and ape canyon probably exceeded 250 000 m 3 s initially but decreased exponentially in the downstream direction total volume of the lahars was in excess of 1 4 10 7 m 3 initial peak flow velocities in excess of 30 m s also decreased markedly downstream where flow was not impeded velocity was strongly related to the depth slope term r 2 3 s 1 2 from the manning uniform flow equation as a power law function during much of the route traveled lahar flow appears to have been supercritical deposits left in channels were generally thin relative to flow depth 0 to 2 5 m particles up to small boulder size were randomly distributed in the poorly sorted nonstratified matrix indicating complete suspension in a fully developed debris flow slurry however much larger clasts were transported as bed load computed sediment concentrations of matrix slurry samples ranged from 84 to 91 solids by weight and were similar for the two lahars two indirect methods for computing peak flow velocity previously only tentatively applied to debris flows were tested for accuracy by comparing computed lahar arrival times with recorded arrival times at swift reservoir the computed velocities appear to be 15 slower than the recorded velocities which is consistent with the restriction that the velocity formulas produce only minimum values

hyperbolic spiral model for predicting reverse fault ruptures in sand based on centrifuge tests fault deformation can cause severe damage to structures located within the fault zones a logarithmic spiral model was developed by d a cole and p v lade in 1984 to predict the shapes and locat

a numerical simulation of the two day wave near the stratopause abstract the middle atmosphere version of the national center for atmospheric research community climate model 2 maccm2 mechanistic model is used to simulate several aspects of the observed two day wave near the stratopause and its possible connection with inertial instability model experiments show that for a prescribed initial wind condition with strong horizontal wind variation in the tropics inertial instability can trigger the two day wave an increase in horizontal wind curvature fostered by inertial instability circulation barotropically destabilizes the easterly jet in low summer latitudes and allows first the growth of the wavenumber 4 and then the wavenumber 3 component of the two day wave near the stratopause the two day wave eliassen palm flux is directed equatorward away from the wave s critical line source and westerly momentum is transported into the easterly jet core by the wave while much of the wavenumber 4 energy is confined near the stratopause the wavenumber 3 energy can prop

peak flow responses to landscape disturbances caused by the cataclysmic 1980 eruption of mount st helens washington years of discharge measurements that precede and follow the cataclysmic 1980 eruption of mount st helens washington provide an exceptional opportunity to examine the responses of peak fl ows to abrupt widespread devastating landscape disturbance multiple basins surrounding mount st helens 300 1300 km 2 drainage areas were variously disturbed by 1 a debris avalanche that buried 60 km 2 of valley 2 a lateral volcanic blast and associated pyroclastic fl ow that destroyed 550 km 2 of mature forest and blanketed the landscape with silt capped lithic tephra 3 debris fl ows that reamed riparian corridors and deposited tens to hundreds of centimeters of gravelly sand on valley fl oors and 4 a plinian tephra fall that blanketed areas proximal to the volcano with up to tens of centimeters of pumiceous silt sand and gravel the spatially complex disturbances produced a variety of potentially compensating effects that interacted with and infl uenced hydrological responses changes to water transfer on hillslopes and to fl storage and routing along channels both enhanced and retarded runoff rapid posteruption modifi cations of hillslope surface textures adjustments of channel networks and vegetation recovery in conjunction with the complex nature of the eruptive impacts and strong seasonal variability in regional climate hindered a consistent or persistent shift in peak discharges overall we detected a short lived 5 10 yr increase in the magnitudes of autumn and winter peak fl ows in general peak fl ows were larger and moderate to large fl ows q 2 yr were more substantively affected than predicted by early modeling efforts proportional increases in the magnitudes of both small and large fl ows in basins subject to severe channel disturbances but not in basins subject solely to hillslope disturbances suggest that eruptioninduced modifi cations to fleffi ciency along alluvial channels that have very mobile beds differentially affected fl ows of various magnitudes and likely played a prominent and additional role affecting the nature of the hydrological response

posteruption suspended sediment transport at mount st helens decadal scale relationships with landscape adjustments and river discharges received 11 december 2002 revised 30 september 2003 accepted 18 november 2003 published 17 january 2004 1 widespread landscape disturbance by the cataclysmic 1980 eruption of mount st helens abruptly increased sediment supply in surrounding watersheds the magnitude and duration of the redistribution of sediment deposited by the eruption as well as decades to centuries old sediment remobilized from storage have varied chiefly with the style of disturbance posteruption suspended sediment transport has been greater and more persistent from zones of channel disturbance than from zones of hillslope disturbance despite the severe landscape disturbances caused by the eruption relationships between discharge magnitudes and frequencies and suspended sediment transport have been remarkably consistent discharges smaller than mean annual flows generally have transported 5 but locally 15 of the annual suspended sediment loads and infrequent p 0 01 large floods have transported as much as 50 of the annual suspended sediment loads in a single day however moderate magnitude discharges those greater than mean annual flows but less than 2 year floods have transported the greatest amounts of sediment from all disturbance zones such discharges have transported on average 60 to 95 of the annual suspended sediment loads usually within cumulative periods of 1 3 weeks each year although small magnitude and largemagnitude discharges have locally and episodically transported considerable amounts of suspended sediment there has not been any notable change in the overall nature of the effective discharges moderate magnitude flows have been the predominant discharges responsible for transporting the majority of suspended sediment during 20 years of posteruption landscape adjustment index terms 1824 hydrology geomorphology 1625 1815 hydrology erosion and sedimentation 1860 hydrology runoff and streamflow keywords sediment yield suspended sediment transport mount st helens erosion volcano geomorphology

magnitude and timing of downstream channel aggradation and degradation in response to a dome building eruption at mount hood oregon a dome building eruption at mount hood oregon starting in a d 1780 and lasting until ca 1793 produced dome collapse lithic pyroclastic flows that triggered lahars and intermittently fed 10 8 m 3 of coarse volcaniclastic sediment to sediment reservoirs in headwater canyons of the sandy river mobilization of dominantly sandy sediment from these reservoirs by lahars and seasonal floods initiated downstream migration of a sediment wave that resulted in a profound cycle of aggradation and degradation in the lowermost reach of the river depositional reach 61 87 km from the source stratigraphic and sedimentologic relations in the alluvial fill together with dendrochronologic dating of degradation terraces demonstrate that 1 channel aggradation in response to sediment loading in the headwater canyons raised the river bed in this reach at least 23 m in a decade or less 2 the transition from aggradation to degradation in the upper part of this reach roughly coincided with the end of the dome building eruption 3 fluvial sediment transport and deposition augmented by one lahar achieved a minimum average aggradation rate of 2 m yr 4 the degradation phase of the cycle was more prolonged than the aggradation phase requiring more than half a century for the river to reach its present bed elevation and 5 the present longitudinal profile of the sandy river in this reach is at least 3 m above the pre eruption profile the pattern and rate of channel response and recovery in the sandy river following heavy sediment loading resemble those of other rivers similarly subjected to very large sediment inputs the magnitude of channel aggradation in the lower sandy river greater than that achieved at other volcanoes following much larger eruptions was likely enhanced by lateral confinement of the channel within a narrow incised valley a combination of at least one lahar and winter floods from frequent moderate magnitude rainstorms and infrequent very large storms was responsible for flushing large volumes of sediment to the depositional reach these conditions permitted a sedimentation response in the sandy river that approached the magnitude of channel aggradation resulting elsewhere from large explosive eruptions and high intensity rainfall regimes despite the fact that the sandy river aggradation was in response to an unremarkable dome building eruption in a climate dominated by low to moderate rainfall intensities

erosion and aggradation on persistently active volcanoes a case study from semeru volcano indonesia erosion processes on active volcanoes in humid climates result in some of the highest sediment yields on earth episodic sediment yields after large eruptions have been evaluated but not the long term and continuous patterns on persistently active volcanoes we have used high spatial resolution satellite imagery and dems dsms along with field based geologic mapping to assess accurately sediment budgets for the active semeru volcano in java indonesia patterns of aggradation and degradation on semeru differ from that of other active volcanoes because 1 both episodic pyroclastic density currents pdc and continuous supplies of tephra generate pulses of sediment 2 sediment is transferred via cycles of aggradation and degradation that continue for 15 years in river channels after each pdc producing eruption and 3 rain triggered lahars remove much greater material than fluvial transport during long intense rainfall events the geomorphic response of two of semeru s rivers to volcanic sediment migration indicates that 1 each river experiences alternating aggradation and degradation cycles following pdc producing eruptions and 2 spatial patterns of sediment transfer are governed by geomorphic characteristics of the river reaches usually high degradation in the steep source reach is followed by a long bypassing middle reach aggradation predominates in the depositional reaches further down valley on the ring plain average sediment yields 103 105 t km2 year at persistently active volcanoes are two to three orders of magnitude lower than sediment yields after large and infrequent eruptions but the continuous and steady sediment transfer in rivers removes more sediment on a mid term 10 years to long term 30 years basis in contrast to the trend observed on composite cones after large and infrequent eruptions decay of sediment yields is not exponential and river channels do not fully recover at steadily active volcanoes as episodic inputs from baf eruptions superimposed on the background remobilization of daily tephra have a greater cumulative effect

the 6 5 day wave in the tropical stratosphere and mesosphere 1 the 6 5 day wave is a westward propagating zonal wave number 1 s 1 planetary wave that is prominent near equinox the spatial temporal structure of the 6 5 day wave seen in the united kingdom meteorological office ukmo data in the stratosphere is found to be consistent with that obtained from upper atmosphere research satellite high resolution doppler imager hrdi measurements of horizontal winds and temperatures in the mesosphere lower thermosphere mlt two wave events are commonly observed before and after equinox at low latitudes in both ukmo and hrdi data this paper focuses on a pair of such events in late 1994 the amplitude growth and phase decrease with altitude of the zonal wind 6 5 day wave appear to be continuous between the two data sets for the period analyzed both wave events appear to grow from the stratosphere to the upper atmosphere at a rate consistent with the suggested vertical phase velocity such consistency between the two data sets establishes that the wave previously observed in the mlt is propagating from the stratosphere further analyses of the ukmo data shows the presence of the 10 day s 1 and 4 day s 2 waves that appear to be either nonlinearly coupled with the 6 5 day wave or related through a common sourcing mechanism