seismicity related to the glacier of cotopaxi volcano ecuador 1 significant seismic activity is generally recorded on volcanoes covered by an icecap this work was carried out in order to quantify the role of the glaciers in the generation of seismicity for cotopaxi volcano we compared the seismic activity registered on the glacier and on the rock near the snout of the north flank glacier we focused on the analysis of low frequency events 5 hz similar to volcanic lp events when recorded on rock base the particle motion analysis helps to estimate source locations which are distributed in crevasses areas high incident angles suggest a superficial origin these events are interpreted as icequakes for which we propose as source mechanism a fluid driven crack model triggered by ice cracking or hydraulic transients the low quality factor values estimated are consistent with the resonance of an ice crack filled with water this work shows that low frequency icequakes can be confusingly taken as volcanic lp events

submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

frequency and initiation of debris flows in grand canyon arizona 1 debris flows from 740 tributaries transport sediment into the colorado river in grand canyon arizona creating rapids that control its longitudinal profile debris flows mostly occur when runoff triggers failures in colluvium by a process termed the fire hose effect debris flows originate from a limited number of geologic strata almost exclusively shales or other clay rich fine grained formations observations from 1984 through 2003 provide a 20 year record of all debris flows that reached the colorado river in grand canyon and repeat photography provides a 100 year record of debris flows from 147 tributaries observed frequencies are 5 1 events year from 1984 to 2003 and historic frequencies are 5 0 events year from 1890 to 1983 logistic regression is used to model historic frequencies based on drainage basin parameters observed to control debris flow initiation and transport from 5 to 7 of the 16 parameters evaluated are statistically significant including drainage area basin relief and the height of and gradient below debris flow source areas variables which reflect transport distance and potential energy the aspect of the river channel which at least partially reflects storm movement within the canyon is also significant model results are used to calculate the probability of debris flow occurrence at the river over a century for all 740 tributaries owing to the variability of underlying geomorphic controls the distribution of this probability is not uniform among tributaries of the colorado river in grand canyon

rapid submarine melting of the calving faces of west greenland glaciers widespread glacier acceleration has been observed in greenland in the past few years oceanographic observations taken in summer 2008 show that ocean waters melted a substantial fraction of ice along the calving fronts of three west greenland glaciers indicating that submarine melting has a profound influence on grounding line stability widespread glacier acceleration has been observed in greenland in the past few years1 2 3 4 associated with the thinning of the lower reaches of the glaciers as they terminate in the ocean5 6 7 these glaciers thin both at the surface from warm air temperatures and along their submerged faces in contact with warm ocean waters8 little is known about the rates of submarine melting9 10 11 and how they may affect glacier dynamics here we present measurements of ocean currents temperature and salinity near the calving fronts of the eqip sermia kangilerngata sermia sermeq kujatdleq and sermeq avangnardleq glaciers in central west greenland as well as ice front bathymetry and geographical positions we calculate water mass and heat budgets that reveal summer submarine melt rates ranging from 0 7 0 2 to 3 9 0 8 m d 1 these rates of submarine melting are two orders of magnitude larger than surface melt rates but comparable to rates of iceberg discharge we conclude that ocean waters melt a considerable but highly variable fraction of the calving fronts of glaciers before they disintegrate into icebergs and suggest that submarine melting must have a profound influence on grounding line stability and ice flow dynamics

structures and facies associated with the flow of subaerial basaltic lava into a deep freshwater lake the sulphur creek lava flow north cascades washington abstract the ca 8800 14c yrs bp sulphur creek lava flowed eastward 12 km from the schriebers meadow cinder cone into the baker river valley on the southeast flank of mount baker volcano the compositionally zoned basaltic to basaltic andesite lava entered crossed and partially filled the 2 km wide and 100 m deep early holocene remnant of glacial lake baker the valley is now submerged beneath a reservoir but seasonal drawdown permits study of the distal entrant lava as a lava volume that may have been as much as 180 106 m3 entered the lake the flow invaded the lacustrine sequence and extended to the opposite east side of the drowned baker river valley the volume and mobility of the lava can be attributed to a high flux rate a prolonged eruption or both basalt exposed below the former level of the remnant glacial lake is glassy or microcrystalline and sparsely vesicular with pervasive hackly or blocky fractures together with pseudopillow fractures these features reflect fracturing normal to penetrative thermal fronts and quenching by water a fine grained hyaloclastite facies was probably formed during quench fragmentation or isolated magma water explosions although the structures closely resemble those developed in lava ice contact environments establishing the depositional environment for lava exhibiting similar intense fracturing should be confirmed by geologic evidence rather than by internal structure alone the lava also invaded the lacustrine sequence forming varieties of peperite including sills that are conformable within the invaded strata and resemble volcaniclastic breccias the peperite is generally fragmental and clast or matrix supported fine grained and rounded fluidal margins occur locally the lava formed a thickened subaqueous plug that as the lake drained in the mid holocene was exposed to erosion the baker river then cut a 52 m deep gorge through the shattered highly erodible basalt

peak discharge of a pleistocene lava dam outburst flood in grand canyon arizona usa abstract the failure of a lava dam 165 000 yr ago produced the largest known flood on the colorado river in grand canyon the hyaloclastite dam was up to 366 m high and geochemical evidence linked this structure to outburst flood deposits that occurred for 32 km downstream using the hyaloclastite outburst flood deposits as paleostage indicators we used dam failure and unsteady flow modeling to estimate a peak discharge and flow hydrograph failure of the hyaloclastite dam released a maximum 11 109 m3 of water in 31 h peak discharges estimated from uncertainty in channel geometry dam height and hydraulic characteristics ranged from 2 3 to 5 3 105 m3 s 1 for the hyaloclastite outburst flood this discharge is an order of magnitude greater than the largest known discharge on the colorado river 1 4 104 m3 s 1 and the largest peak discharge resulting from failure of a constructed dam in the usa 6 5 104 m3 s 1 moreover the hyaloclastite outburst flood is the oldest documented quaternary flood and one of the largest to have occurred in the continental usa the peak discharge for this flood ranks in the top 30 floods 105 m3 s 1 known worldwide and in the top ten largest floods in north america

displacement rates on the toroweap and hurricane faults implications for quaternary downcutting in the grand canyon arizona the toroweap and hurricane faults considered to be the most active in arizona cross the uinkaret volcanic field in the western grand canyon these normal faults are downthrown to the west and the colorado river crosses these faults as it flows west in the grand canyon cosmogenic 3 he 3 he c dates on basalt flows and related landforms are used to calculate vertical displacement rates for these faults the two faults cross unruptured alluvial fans dated as 3 ka toroweap and 8 ka hurricane and 10 other landforms that range in age from 30 to 400 ka are displaced middle and late quaternary displacement rates of the toroweap and hurricane faults are 70 180 and 70 170 m m y respectively on the basis of these rates the combined displacement of 580 m on these faults could have occurred in the past 3 to 5 m y all 3 he c dates are younger than existing k ar dates and are consistent with new 40 ar 39 ar dates and existing thermoluminescence tl dates on basalt flows these different dating techniques may be combined in an analysis of displacement rates downcutting rates for the colorado river in the eastern grand canyon 400 m m y are at least double the downcutting rates west of the faults 70 160 m m y faulting probably increased downcutting in the eastern grand canyon relative to downcutting in the western grand canyon during the late quaternary

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

owyhee river intracanyon lava flows does the river give a dam rivers carved into uplifted plateaus are commonly disrupted by discrete events from the surrounding landscape such as lava flows or large mass movements these disruptions are independent of slope basin area or channel discharge and can dominate aspects of valley morphology and channel behavior for many kilometers we document and assess the effects of one type of disruptive event lava dams on river valley morphology and incision rates at a variety of time scales using examples from the owyhee river in southeastern oregon six sets of basaltic lava flows entered and dammed the river canyon during two periods in the late cenozoic ca 2 ma 780 ka and 250 70 ka the dams are strongly asymmetric with steep blunt escarpments facing up valley and long low slopes down valley none of the dams shows evidence of catastrophic failure all blocked the river and diverted water over or around the dam crest the net effect of the dams was therefore to inhibit rather than promote incision once incision resumed most of the intracanyon flows were incised relatively rapidly and therefore did not exert a lasting impact on the river valley profile over time scales 10 6 yr the net long term incision rate from the time of the oldest documented lava dam the bogus rim lava dam 1 7 ma to present was 0 18 mm yr but incision rates through or around individual lava dams were up to an order of magnitude greater at least three lava dams bogus rim saddle butte and west crater show evidence that incision initiated only after the impounded lakes filled completely with sediment and there was gravel transport across the dams the most recent lava dam formed by the west crater lava flow around 70 ka persisted for at least 25 k y before incision began and the dam was largely removed within another 35 k y the time scale over which the lava dams inhibit incision is therefore directly affected by both the volume of lava forming the dam and the time required for sediment to fill the blocked valley variations in this primary process of incision through the lava dams could be influenced by additional independent factors such as regional uplift drainage integration or climate that affect the relative base level discharge and sediment yield within the watershed by redirecting the river tributaries and subsequent lava flows to different parts of the canyon lava dams create a distinct valley morphology of flat broad basalt shelves capping steep cliffs of tertiary sediment this stratigraphy is conducive to landsliding and extends the effects of intracanyon lava flows on channel geomorphology beyond the lifetime of the dams

k ar ages of pleistocene lava dams in the grand canyon in arizona at least 13 times during the pleistocene epoch lava flowed into the inner gorge of the grand canyon and formed lava dams as high as 600 m that temporarily blocked the flow of the colorado river k ar ages on these lava dams indicate that the seven youngest formed within a short period of time between about 0 6 and 0 4 mega annum ma the physiography of the lava dam remnants within the canyon shows that each dam was destroyed by erosion the colorado river rapidly reaching its pre existing grade level before the next dam was emplaced by new eruptions the total time for emplacement and destruction for an individual lava dam was probably as little as 0 01 0 02 million years the k ar ages of the two oldest dams the lava butte dam 0 577 0 054 ma and the prospect dam 0 684 0 051 ma are somewhat younger than the physiography of their remnants suggest

hydroacoustic signals generated by parked and drifting icebergs in the southern indian and pacific oceans summary we report the detection principally by the french polynesian seismic network of hydroacoustic signals generated inside large icebergs either parked along the wilkes coast of antarctica in the indian ocean or drifting in the southern pacific ocean between latitudes of 55 and 65 s during the years 2002 2004 the signals can be classified into two very broad families based on the nature of their spectra a first group features prominently monochromatic signals whose frequency can however fluctuate with time during a single sequence of emission typically lasting a few to a few tens of minutes such signals are generally reminiscent of those detected in 2000 in the ross sea and are generated principally in the indian ocean iceberg parking lot between longitudes 144 e and 156 e a new family of signals features a much broader spectrum superimposed on a number of preferential frequencies suggesting the background activation of a number of resonators these signals occur both in the parking lot and in the southern pacific further variations in spectra are documented inside each family on the basis of similar in situ observations on ross sea icebergs under project southberg the first family is generally interpreted as expressing a stick and slip process during collisions between large iceberg masses the second family of signals are observed during exceptional episodes of the otherwise silent drift of the icebergs in the deep pacific basin some of which correlate with their passage over the various fronts defining the oceanographic southern convergence zone finally a most recent episode of activity generally similar to the above first family was detected on 2004 december 3 4 at the ocean entry of the dibble ice tongue 600 km west of the parking lot along the coast of antarctica it is interpreted as resulting from collisions between large drifting icebergs and fragments of the ice tongue calved off during its disintegration as documented by satellite imagery

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

a unifying framework for iceberg calving models we propose a general framework for iceberg calving models that can be applied to any calving margin the framework is based on mass continuity the assumption that calving rate and terminus velocity are not independent and the simple idea that terminus thickness following a calving event is larger than terminus thickness at the event onset the theoretical near steady state analysis used to support and analyze the framework indicates that calving rate is governed to first order by ice thickness thickness gradient strain rate mass balance rate and backwards melting of the terminus the analysis furthermore provides a physical explanation for a previously derived empirical relationship for ice shelf calving alley and others 2008 in the calving framework the pre and post calving terminus thicknesses are given by two unknown but related functions the functions can vary independently of changes in glacier flow and geometry and can therefore account for variations in calving behavior due to external forcings and or self sustaining calving processes positive feedbacks although the calving framework does not constitute a complete calving model any thickness based calving criterion can easily be incorporated into the framework the framework should be viewed as a guide for future attempts to parameterize calving

differential incision of the grand canyon related to quaternary faulting constraints from u series and ar ar dating incision of the colorado river in the grand canyon widely thought to have happened between ca 6 and 1 2 ma has continued at variable rates along the canyon over the past 500 k y based on measurements of bedrock incision combined with u series and 40 ar 39 ar ages river incision rates downstream of the toroweap fault in the western grand canyon are about half the 140 m m y incision rate calculated for a distance of at least 200 km upstream of the fault we hypothesize that this differential incision is due to westdown slip on the toroweap fault of 94 6 6 m m y based on measured offset of the newly dated upper prospect basalt flow which is the major middle late quaternary slip evident along the river regional incision has been driven mostly by base level fall related to drainage reversal off the colorado plateau ca 6 ma because local normal faulting is lower in rate than this regional incision and is likely an expression of basin and range extension and subsidence rather than uplift this is a case where active faulting diminishes but does not drive incision quaternary incision rates are insufficient to have carved the grand canyon in 6 m y suggesting either that rates have decreased through time as the original base level signal has attenuated or that some component of the canyon relief we see today existed prior to colorado river integration

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100

landscape evolution modelling of naturally dammed rivers natural damming of upland river systems such as landslide or lava damming occurs worldwide many dams fail shortly after their creation while other dams are long lived and therefore have a long term impact on fluvial and landscape evolution this long term impact is still poorly understood and landscape evolution modelling lem can increase our understanding of different aspects of this response our objective was to simulate fluvial response to damming by monitoring sediment redistribution and river profile evolution for a range of geomorphic settings we used lem lapsus which calculates runoff erosion and deposition and can deal with non spurious sinks such as dam impounded areas because fluvial dynamics under detachment limited and transport limited conditions are different we mimicked these conditions using low and high erodibility settings respectively to compare the relative impact of different dam types we evaluated five scenarios for each landscape condition one scenario without a dam and four scenarios with dams of increasing erodibility results showed that dam related sediment storage persisted at least until 15 000years for all dam scenarios incision and knickpoint retreat occurred faster in the detachment limited landscape than in the transport limited landscape furthermore in the transport limited landscape knickpoint persistence decreased with increasing dam erodibility stream capture occurred only in the transport limited landscape due to a persisting floodplain behind the dam and headward erosion of adjacent channels changes in sediment yield variation due to stream captures did occur but cannot be distinguished from other changes in variation of sediment yield comparison of the model results with field examples indicates that the model reproduces several key phenomena of damming response in both transport limited and detachment limited landscapes we conclude that a damming event which occurred 15 000years ago can influence present day sediment yield profile evolution and stream patterns copyright c 2014 john wiley sons ltd

geochemical discrimination of five pleistocene lava dam outburst flood deposits western grand canyon arizona abstract pleistocene basaltic lava dams and outburst flood deposits in the western grand canyon arizona have been correlated by means of cosmogenic 3he 3hec ages and concentrations of sio2 na2o k2o and rare earth elements these data indicate that basalt clasts and vitroclasts in a given outburst flood deposit came from a common source a lava dam with these data it is possible to distinguish individual dam flood events and improve our understanding of the interrelations of volcanism and river processes at least five lava dams on the colorado river failed catastrophically between 100 and 525 ka subsequent outburst floods emplaced basalt rich deposits preserved on benches as high as 200 m above the current river and up to 53 km downstream of dam sites chemical data also distinguishes individual lava flows that were collectively mapped in the past as large long lasting dam complexes these chemical data in combination with age constraints increase our ability to correlate lava dams and outburs

source mechanics for monochromatic icequakes produced during iceberg calving at columbia glacier ak 1 seismograms recorded during iceberg calving contain information pertaining to source processes during calving events however locally variable material properties may cause signal distortions known as site and path effects which must be eliminated prior to commenting on source mechanics we applied the technique of horizontal vertical spectral ratios to passive seismic data collected at columbia glacier ak and found no dominant site or path effects rather monochromatic waveforms generated by calving appear to result from source processes we hypothesize that a fluid filled crack source model offers a potential mechanism for observed seismograms produced by calving and fracture processes preceding calving

modelling long term 300 ka upland catchment response to multiple lava damming events landscapes respond in complex ways to external drivers such as base level change due to damming events in this study landscape evolution modelling was used to understand and analyse long term catchment response to lava damming events palaeodem reconstruction of a small turkish catchment 45km 2 that endured multiple lava damming events in the past 300ka was used to derive long term net erosion rates these erosion rates were used for parameter calibration and led to a best fit parameter set this optimal parameter set was used to compare net erosion landscape time series of four scenarios i no uplift and no damming events ii no uplift and three damming events iii uplift and no damming events and iv uplift and three damming events spatial evolution of net erosion and sediment storage of scenario iii and iv were compared simulation results demonstrate net erosion differences after 250 000years between scenarios with and without dams initially trunk gullies show less net erosion in the scenario with damming events compared with the scenario without damming events this effect of dampened erosion migrates upstream to smaller gullies and local slopes finally an intrinsic incision pulse in the dam scenario results in a higher net erosion of trunk gullies while decoupled local slopes are still responding to the pre incision landscape conditions sediment storage differences also occur on a 100ka scale these differences behaved in a complex manner owing to different timings of the migration of erosion and sediment waves along the gullies for each scenario although the specific spatial and temporal sequence of erosion and deposition events is sensitive to local parameters this model study shows the manner in which past short lived events like lava dams have long lasting effects on catchment evolution copyright c 2014 john wiley sons ltd

the generation of infrasonic ambient noise in the ocean by nonlinear interactions of ocean surface waves expressions for the spectra of infrasonic ocean noise and microseisms induced by nonlinear wave interaction are derived theoretically for an ocean environment modeled as a water layer overlying a solid half space a series of spectral transfer functions relating the source pressure field induced by the wave action to the underwater acoustic noise field and that of the microseisms this generates in the seabed are defined and calculated the effect of bottom reflections on the transfer function is examined and an estimate of the contribution of the rayleigh wave component of the microseism signal received onshore is also made

submarine melting of the 1985 jakobshavn isbrae floating tongue and the triggering of the current retreat 1 photogrammetric reanalysis of 1985 aerial photos has revealed substantial submarine melting of the floating ice tongue of jakobshavn isbrae west greenland the thickness of the floating tongue determined from hydrostatic equilibrium tapers from 940 m near the grounding zone to 600 m near the terminus feature tracking on orthophotos shows speeds on the july 1985 ice tongue to be nearly constant 18 5 m d 1 indicating negligible dynamic thinning the thinning of the ice tongue is mostly due to submarine melting with average rates of 228 49 m yr 1 0 62 0 13 m d 1 between the summers of 1984 and 1985 the cause of the high melt rate is the circulation of warm seawater thermal forcing of up to 4 2 c beneath the tongue with convection driven by the substantial discharge of subglacial freshwater from the grounding zone we believe that this buoyancy driven convection is responsible for a deep channel incised into the sole of the floating tongue a dramatic thinning retreat and speedup began in 1998 and continues today the timing of the change is coincident with a 1 1 c warming of deep ocean waters entering the fjord after 1997 assuming a linear relationship between thermal forcing and submarine melt rate average melt rates should have increased by 25 57 m yr 1 sufficient to destabilize the ice tongue and initiate the ice thinning and the retreat that followed

the history and dynamics of a welded pyroclastic dam and its failure the 2 360 bp eruption of mount meager british columbia began as an explosive dacitic sub plinian eruption that waned rapidly to a sustained period of vulcanian eruption triggered dome collapse events producing voluminous block and ash flow baf deposits the earliest baf deposits accumulated rapidly enough immediately downslope of the vent to retain heat and weld using the deposit as a paleoviscometer determines an effective viscosity of 109 1010 pa s during welding this prolific production of hot lava and block and ash flows in a steep mountainous terrain created a 110 m high largely impermeable dam capped by permeable non welded baf deposits and unconsolidated avalanche deposits that blocked the flow of the lillooet river and created a temporary lake the welded pyroclastic dam was compromised and overtopped at least once before the peak dam height was reached renewed eruption caused buildup of the dam to a maximum of 780 m above sea level asl and grew the temporary lake to an elevation of 740 m asl and a minimum volume of 0 55 km3 the rise of lake level led to catastrophic failure of the top of the dam generating an outburst flood that carved a canyon through most of the dam and resulted in a voluminous lahar that is traced at least 65 km downstream based on current flow rates of the lillooet river the lake would have overtopped the final dam at a minimum of 39 65 days after its formation the peak deluge lasted approximately 8 h and eroded a 2 5 km long canyon into the still hot dam core before returning to background flow rates

pleistocene volcanic damming of yukon river and the maximum age of the reid glaciation west central yukon stratigraphic paleomagnetic and radioisotope investigations of the selkirk volcanic group have identified a new eruptive period and constrained the age of the reid glaciation the most extensive middle pleistocene cordilleran advance recognized in central yukon downstream from fort selkirk a complex of valley filling compound pahoehoe basalt flows and pillow basalt is exposed for 10 km along the yukon river and is overlain by outwash deposited during the reid glaciation the flows have an 40ar 39ar age of 311 32 ka this age is consistent with the normal magnetization of the flows and their termination below the level of the contemporary yukon river flood plain taken with the ca 190 ka sheep creek tephra which overlies reid drift elsewhere in yukon territory the reid glaciation is constrained to oxygen isotope stage 8 not stage 6 as previously thought the presence of thick foreset bedded pillow breccia units intercalated with the subaerial flows indicates that this eruption caused damming of t

large scale changes in greenland outlet glacier dynamics triggered at the terminus the recent dramatic retreat of many outlet glaciers of the greenland ice sheet has raised concerns over greenland s contribution to future sea level rise simulations with a numerical ice flow model indicate that the recent rates of mass loss in greenland s outlet glaciers are transient and should not be extrapolated into the future

three dimensional lithofacies variations in hyaloclastite deposits analysis of the spatial lithofacies variability within lava fed delta formations in southern iceland has revealed complex three dimensional volcanic architectures in hyaloclastite deposits in non glacial settings two depositional environments are studied a lava entering a marine embayment stori nupur and b lava advancing into a body of water of the flanks of a surtseyan cone hjorleifshof i interaction between environmental factors such as shoreline geomorphology water depth wave energy levels the nature of the lava transport system lava supply rate all affect the resulting lava deltas creating complex lithofacies arrangements and stacking patterns recognised here are two types of hyaloclastite deltas one of syn sedimentary origin hjorleifshof i and one derived from primary fragmentation processes stori nupur syn sedimentary systems are dominated by destabilisation of the hyaloclastite pile leading to reworking downslope and share similarities to alluvial delta systems conversely primary fragmented systems are controlled by waxing and waning cycles in volcanic effusivity whereby the hyaloclastite unit recorded is not the product of one lava flow rather than one eruptive event

cosmogenic 3he age estimates of plio pleistocene alluvial fan surfaces in the lower colorado river corridor arizona usa abstract plio pleistocene deposits of the lower colorado river lcr and tributary alluvial fans emanating from the black mountains near golden shores arizona record six cycles of late cenozoic aggradation and incision of the lcr and its adjacent alluvial fans cosmogenic 3he 3hec ages of basalt boulders on fan terraces yield age ranges of 3 3 2 2 ma 2 2 1 1 ma 1 1 ma to 110 ka

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

paleoflood evidence for a natural upper bound to flood magnitudes in the colorado river basin the existence of an upper limit to the magnitude of floods in a region is a long standing and controversial hypothesis in flood hydrology regional envelope curves encompassing maximum flood magnitudes stabilize with progressive increases in the areal coverage and period of observation wolman and costa 1984 however the short lengths of conventional gaging records limit substantial advances in testing whether this stabilization is evidence of an upper limit in the colorado river basin there are 32 120 station years of gage data but the average period at a gaging station is only 20 years with most stations having less than 70 years of observation paleoflood magnitudes derived from sediments of large prehistoric floods from 25 sites on rivers in arizona and utah provide additional data to extend the records of the largest floods the paleoflood data identify the maximum flood discharges that have occurred on individual rivers over the last several hundred to several thousand years even with this increase in the observational period the largest paleoflood discharges do not exceed the upper bound of maximum peak discharges delineated by the envelope curve derived from the available gaged and historical records this result accords with the hypothesis of an upper physical limit for flood magnitudes and suggests that for the colorado river basin the upper limit can be approximated by existing systematic and historical data for large floods similar relationships also hold when paleofloods and gaged records are presented for the subregion of southern arizona

the impact of glacier meltwater on the underwater noise field in a glacial bay ambient noise oceanography is proving to be an efficient and effective tool for the study of ice ocean interactions in the bays of marine terminating glaciers however obtaining quantitative estimates of ice melting or calving processes from ambient noise requires an understanding of how sound propagation through the bay attenuates and filters the noise spectrum measurements of the vertical structure in sound speed in the vicinity of the hans glacier in hornsund fjord spitsbergen made with o 130 ctd casts between may and november 2015 reveal high gradient upward refracting sound speed profiles created by cold fresh meltwater during summer months simultaneous recordings of underwater ambient noise made at depths of 1 10 and 20 meters in combination with propagation model calculations using the model bellhop illustrate the dominant role these surface ducts play in shaping the underwater soundscape the surface ducts lead to a higher intensity and greater variability of acoustic energy in the near surface layer covered by glacially modified waters relative to deeper waters indicating deeper zones as most appropriate for inter seasonal acoustic monitoring of the glacial melt surface waveguides in hornsund are relatively shallow and trap sound above o 1 khz deeper waveguides observed elsewhere will also trap low frequency sounds such as those generated by calving events for example finally the ambient noise field in hornsund is shown to be strongly dependent on the distribution of ice throughout the bay stressing the importance of performing complementary environmental measurements when interpreting the results of acoustic surveys this article is protected by copyright all rights reserved

underwater acoustic signatures of glacier calving climate driven ice water interactions in the contact zone between marine terminating glaciers and the ocean surface show a dynamic and complex nature tidewater glaciers lose volume through the poorly understood process of calving a detailed description of the mechanisms controlling the course of calving is essential for the reliable estimation and prediction of mass loss from glaciers here we present the potential of hydroacoustic methods to investigate different modes of ice detachments high frequency underwater ambient noise recordings are combined with synchronized high resolution time lapse photography of the hans glacier cliff in hornsund fjord spitsbergen to identify three types of calving events typical subaerial sliding subaerial and submarine a quantitative analysis of the data reveals a robust correlation between ice impact energy and acoustic emission at frequencies below 200 hz for subaerial calving we suggest that relatively inexpensive acoustic methods can be successfully used to provide quantitative descriptions of the various calving types

passive underwater acoustic evolution of a calving event direct measurements of processes occurring at the ice ocean boundary are difficult to acquire because of the dangerous and dynamic nature of the boundary yet these processes are among the least well understood in glaciology because sound travels well through water passive underwater acoustics offers a method to remotely sense activity at this boundary here we present passive acoustic measurements and spectral analysis of the evolution of a subaerial calving event and the subsequent mini tsunami and seiche at meares glacier alaska usa using two hydrophones to record sound from 1 to 40 000 hz we find that each phase of a calving event has distinctive spectral characteristics an event begins with an infrasound rumble 1 20 hz then the ice fractures 20 100 hz falls and impacts the water 200 600 hz high frequency 10 000 hz sound increases in intensity quickly as the iceberg oscillates creating turbulence spray and waves within 10 s the low frequency audible sound dissipates and the mini tsunami and seiche sounds dominate infrasound plus high frequencies and continue for over 10 min the specific frequencies and duration of each phase of a calving event depend on its size and location and the glacier and fjord characteristics

a 4500 year record of large floods on the colorado river in the grand canyon arizona a sequence of flood deposits left by the colorado river in the grand canyon arizona provides evidence of at least 15 floods with peak discharges greater than 5500 m 3 sec 1 over the last 4500 yr ten floods during the last 2000 2300 yr had discharges greater than 6800 m 3 sec 1 one flood 1600 1200 yr ago had a discharge exceeding 14 000 m 3 sec 1 a flow rate more than twice the largest gaged flood this record of flooding is one of the longest for a major u s river and combined with the gaged record of twentieth century floods allows determination of the frequency and history of large floods that have affected key aspects of colorado river geomorphology

cyclic aggradation and downcutting fluvial response to volcanic activity and calibration of soil carbonate stages in the western grand canyon arizona abstract in the western grand canyon fluvial terraces and pediment surfaces both associated with a pleistocene basalt flow document quaternary aggradation and downcutting by the colorado river illuminate the river s response to overload and the end of overload and allow calibration of soil carbonate stages and determination of downcutting rates four downcutting aggradation cycles are present each begins with erosion of older deposits to form a new river channel in which a characteristic suite of deposits is laid down the current cycle i started 700 yr b p the oldest iv includes the 603 000 8000 to 524 000 7000 yr black ledge basalt flow emplaced when the river channel was 30 m higher than it is now the flow is overlain by basalt cobble gravel and basalt sand soils reach the stage v level of carbonate development calibrated ages for soil stages are stage v 525 000 yr stage iv

emplacement conditions of the c 1 600 year bp collier cone lava flow oregon a lidar investigation a long standing question in lava flow studies has been how to infer emplacement conditions from information preserved in solidified flows from a hazards perspective volumetric flux effusion rate is the parameter of most interest for open channel lava flows as the effusion rate is important for estimating the final flow length the rate of flow advance and the eruption duration the relationship between effusion rate flow length and flow advance rate is fairly well constrained for basaltic lava flows where there are abundant recent examples for calibration less is known about flows of intermediate compositions basaltic andesite to andesite which are less frequent and where field measurements are limited by the large block sizes and the topographic relief of the flows here we demonstrate ways in which high resolution digital topography obtained using light detection and ranging lidar systems can provide access to terrains where field measurements are difficult or impossible to collect we map blocky lava flow units using lidar generated bare earth digital terrain models dtms of the collier cone lava flow in the central oregon cascades we also develop methods using geographic information systems to extract and quantify morphologic features such as channel width flow width flow thickness and slope morphometric data are then analyzed to estimate both effusion rates and emplacement times for the lava flow field our data indicate that most of the flow outline which comprises the earliest and most voluminous flow unit can be well explained by an average volumetric flux 14 18 m3 s channel data suggest an average flux 3 m3 s for a later channel filling flow unit when combined with estimates of flow volume these data suggest that the collier cone lava flow was most likely emplaced over a time scale of several months this example illustrates ways in which high resolution dtms can be used to extract and analyze morphologic measurements and how these measurements can be analyzed to estimate emplacement conditions for inaccessible heavily vegetated or extraterrestrial lava flows

cyclicity and basin axis shift in a piggyback basin towards modelling of the eocene tremp ager basin south pyrenees spain

mass balance of glaciers and ice caps consensus estimates for 1961 2004 1 working with comprehensive collections of directly measured data on the annual mass balance of glaciers other than the two ice sheets we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960 mass balance was slightly below zero around 1970 and has been growing more negative since then excluding peripheral ice bodies in greenland and antarctica global average specific balance for 1961 1990 was 219 112 kg m 2 a 1 representing 0 33 0 17 mm sle sea level equivalent a 1 for 2001 2004 the figures are 510 101 kg m 2 a 1 and 0 77 0 15 mm sle a 1 including the smaller greenland and antarctic glaciers global total balance becomes 0 38 0 19 mm sle a 1 for 1961 1990 and 0 98 0 19 mm sle a 1 for 2001 2004 for 1991 2004 the glacier contribution 0 77 0 26 mm sle a 1 is 20 30 of a recent estimate of 3 2 0 4 mm a 1 of total sea level rise for 1993 2005 while our error estimates are not rigorous we believe them to be liberal as far as they go but we also discuss several unquantified biases of which any may prove to be significant

glacier calving observed with time lapse imagery and tsunami waves at glaciar perito moreno patagonia calving plays a key role in the recent rapid retreat of glaciers around the world however many processes related to calving are poorly understood since direct observations are scarce and challenging to obtain when calving occurs at a glacier front surface water waves arise over the ocean or a lake in front of glaciers to study calving processes from these surface waves we performed field observations at glaciar perito moreno patagonia we synchronized time lapse photography and surface waves record to confirm that glacier calving produces distinct waves compared with local noise a total of 1074 calving events were observed over the course of 39 d during austral summer calving occurred twice more frequently than in spring the cumulative distribution of calving interevent time interval followed exponential model implying random occurrence of events in time we further investigated wave properties and found that source to sensor distance can be estimated from wave dispersion within 20 error we also found that waves produced by different calving types showed similar spectra in the same frequency range between 0 05 0 2 hz and that the amplitude of surface waves increased with the size of calving this study demonstrates the potential of surface wave monitoring for understanding calving processes

unusually loud ambient noise in tidewater glacier fjords a signal of ice melt in glacierized fjords the ice ocean boundary is a physically and biologically dynamic environment that is sensitive to both glacier flow and ocean circulation ocean ambient noise offers insight into processes and change at the ice ocean boundary here we characterize fjord ambient noise and show that the average noise levels are louder than nearly all measured natural oceanic environments significantly louder than sea ice and nonglacierized fjords icy bay alaska has an annual average sound pressure level of 120 db referenced to 1 pa with a broad peak between 1000 and 3000 hz bubble formation in the water column as glacier ice melts is the noise source with variability driven by fjord circulation patterns measurements from two additional fjords in alaska and antarctica support that this unusually loud ambient noise in icy bay is representative of glacierized fjords these high noise levels likely alter the behavior of marine mammals

a catastrophic flood caused by drainage of a caldera lake at aniakchak volcano alaska and implications for volcanic hazards assessment aniakchak caldera located on the alaska peninsula of southwest alaska formerly contained a large lake estimated volume 3 7 10 9 m 3 that rapidly drained as a result of failure of the caldera rim sometime after ca 3400 yr b p the peak discharge of the resulting flood was estimated using three methods 1 flow competence equations 2 step backwater modeling and 3 a dam break model the results of the dam break model indicate that the peak discharge at the breach in the caldera rim was at least 7 7 10 4 m 3 s 1 and the maximum possible discharge was 1 1 10 6 m 3 s 1 flow competence estimates of discharge based on the largest boulders transported by the flood indicate that the peak discharge values which were a few kilometers downstream of the breach ranged from 6 4 10 5 to 4 8 10 6 m 3 s 1 similar but less variable results were obtained by step backwater modeling finally discharge estimates based on regression equations relating peak discharge to the volume and depth of the impounded water although limited by constraining assumptions provide results within the range of values determined by the other methods the discovery and documentation of a flood caused by the failure of the caldera rim at aniakchak caldera underscore the significance and associated hydrologic hazards of potential large floods at other lake filled calderas

iceberg calving during transition from grounded to floating ice columbia glacier alaska 1 the terminus of columbia glacier alaska unexpectedly became ungrounded in 2007 during its prolonged retreat visual observations showed that calving changed from a steady release of low volume bergs to episodic flow perpendicular rifting propagation and release of very large icebergs a style reminiscent of calving from ice shelves here we compare passive seismic and photographic observations through this transition to examine changes in calving mechanical changes accompany the visible changes in calving style post flotation generation of seismic energy during calving is substantially reduced we propose this is partly due to changes in source processes

the statistical physics of iceberg calving and the emergence of universal calving laws determining a calving law valid for all glaciological and environmental regimes has proven to be a difficult problem in glaciology for this reason most models of the calving process are semi empirical with little connection to the underlying fracture processes in this study i introduce methods rooted in statistical physics to show how calving laws valid for any glaciological domain can emerge naturally as a large spatial scale long temporal scale limit of an underlying continuous or discrete fracture process an important element of the method developed here is that iceberg calving is treated as a stochastic process and that the probability an iceberg will detach in a given interval of time can be described by a probability distribution function using limiting assumptions about the underlying probability distribution the theory is shown to be able to simulate a range of calving styles including the sporadic detachment of large tabular icebergs from ice tongues and ice shelves and the more steady detachment of smaller sized bergs from tidewater outlet glaciers the method developed has the potential to provide a physical basis to include iceberg calving into numerical ice sheet models that can be used to produce more realistic estimates of the glaciological contribution to sea level rise

basal icequakes during changing subglacial water pressures beneath gornergletscher switzerland using dense networks of three component seismometers installed in direct contact with the ice the seismic activity of gornergletscher switzerland was investigated during the summers of 2004 and 2006 as subglacial water pressures varied drastically these pressure variations are due to the diurnal cycle of meltwater input as well as the subglacial drainage of gornersee a nearby marginal ice dammed lake up to several thousand seismic signals per day were recorded whereas most icequakes are due to surface crevasse openings about 200 events have been reliably located close to the glacier bed these basal events tend to occur in clusters and have signals with impulsive first arrivals at the same time basal water pressures and ice surface velocities were measured to capture the impact of the lake drainage on the subglacial hydrological system and the ice flow dynamics contrary to our expectations we did not observe an increase of basal icequake activity as the lake emptied thereby raising the subglacial water pressures close to the flotation level for several days in fact the basal icequakes were usually recorded during the morning hours when the basal water pressure was either low or decreasing during the high pressure period caused by the drainage of the lake no basal icequakes were observed furthermore gps measurements showed that the glacier surface was lowering during the basal seismic activity these observations lead us to conclude that such icequakes are connected to the diurnal variation in glacier sliding across the glacier bed

time place and mode of propagation of foreland basin systems as recorded by the sedimentary fill examples of the late cretaceous and eocene retro foreland basins of the north eastern pyrenees the relationship between tectonics and sedimentary fill has been studied in two syncontractional basins of the western corbieres eastern north pyrenean retro foreland basin the late cretaceous basin formed during c 10 12 ma as a result of left lateral transpressional deformation and is composed of forward younging sub basins characterized by reworking of the forelimbs of growing fold propagation folds thrust wedge advance and cratonward migration of the platform are recorded by a deepening upward stacking pattern indicating increased regional subsidence with a limited contribution of the submarine orogen tectonic quiescence and erosional unloading lasting 29 30 ma are recorded by a shallowingupward stacking pattern and fluvial sedimentation issued from widespread sources in the emerging inner orogen the early to middle eocene basin formed as a result of pure shortening normal to the range the marine early eocene basin developed during c 2 ma by widening of a single basin provoked by the two step propagation of a basement duplex this is recorded by growth stratal patterns and coarsening upward depositional sequences indicating the increasing contribution of the emerged orogen the middle eocene continental deposits infilled two sub basins working synchronously and were transported by alluvial fans with a provenance in the inner orogen during decreasing thrust wedge advance and increasing erosional unloading

calving of a tidewater glacier driven by melting at the waterline we present a study of the development of a thermo erosional notch at the waterline and its influence on calving of hansbreen a medium sized grounded tidewater glacier in southern svalbard the study is based on the results of undercut notch melt modelling based on measurements of sea water properties repeated terrestrial laser scans and analysis of time lapse camera images there is a strong correlation between observed calving activity and modelled melt rate of the undercut notch measured depths of the undercut reach 4 m and vary greatly over time the calving activity of hansbreen was significantly lower in 2011 than in 2012 due to the persistent presence of the ice pack in hornsund fjord which cooled the sea surface and suppressed the wave action calving on hansbreen is controlled by a local imbalance of forces at the front due to thermo erosional undercutting at the sea waterline calving activity is therefore sensitive to changes in sea water temperature and wave height it may be expected that calving rates will rise with increased advection of warm oceanic water to the arctic

dam break outburst flood propagation and transient hydraulics a geosciences perspective summary dam break outburst floods are sudden short lived and high magnitude discharges of water and sediment propagating over an initially dry terrain both field observations by geoscientists and experimental measurements by engineers have produced understanding of outburst floods but neither approach has satisfactorily supplied data that is directly of use to hazard managers this study draws together those two literature groups and provides new experimental data to test hypotheses concerning the effect of a series of external controls on resultant longitudinal flow propagation and transitory hydraulics these external controls form experimental treatments and are i the height of the lock gate raise as a surrogate for dam breach evolution and initial hydrograph ii bed roughness and iii suspended sediment concentration these control both horizontal and vertical fluid motion the latter of which is a key property for controlling aeration bed shear stress and turbulence intensity the experimental treatments show that outburst floods on horizontal beds can be identified to possess three longitudinal flow regimes firstly there is a short acceleration due to the reservoir pressure level i e the depth of impounded water secondly channel flow quickly converges to an inertial regime the third flow regime is viscous and dominated by channel bed friction flow depth increases in the inertial regime then decreases in the viscous regime experiments herein show that the timing of the peaks at a point down channel of each hydraulic quantity varies most notably peak bed shear stress precedes flow velocity which precedes peak flow depth a point of inflexion occurs with distance down channel that is a manifestation of the transition from accelerating to decelerating flows these external controls and the effects of them on longitudinal and vertical motion are analysed statistically and quantitative relationships are derived to underpin the resultant conceptual model this conceptual model should serve as a platform for future probabilistic and process based modelling of outburst floods

late quaternary spring fed deposits of the grand canyon and their implication for deep lava dammed lakes one of the most intriguing episodes in the quaternary evolution of the grand canyon of the colorado river arizona was the development of vast lakes that are thought to have backed up behind lava erupted into the gorge stratigraphic evidence for these deep lava dammed lakes is expectedly sparse possible lacustrine deposits at six areas in the eastern canyon yielded no compelling evidence for sediment deposited in a deep lake at two of the sites the sediment was associated with late quaternary spring fed pools and marshes water lain silt and sand at lower havasu creek was deposited 3000 cal yr ago the deposit contains an ostracode assemblage similar to that living in the modern travertine dammed pools adjacent to the outcrop the second deposit at lees ferry formed in a spring fed marsh 43 000 cal yr ago as determined by 14 c and amino acid geochronology it contains abundant ostracode and mollusk fossils the richest assemblages reported from the grand canyon to date our interpretation of these sediments as spring fed deposits and their relative youth provides an alternative to the conventional view that deposits like these were formed in deep lava dammed lakes that filled the grand canyon c 2002 university of washington

effects of tributary debris on the longitudinal profile of the colorado river in grand canyon 1 the colorado river in grand canyon has long been known as a rapids and pools river with the rapids owing their existence primarily to tributary debris flows the debris flows deposit subaerial debris fans that constrict the channel laterally and when they enter the river raise the bed elevation the rapids are short wavelength 0 1 to 1 km small amplitude 5 m convexities in the river s longitudinal profile arising from the shallow gradient in the upstream pool and the steep gradient through the rapid itself analysis of the entire longitudinal profile through grand canyon reveals two long wavelength 100 km large amplitude 15 30 m river profile convexities the eastern canyon convexity between river mile rm 30 and rm 80 and the western canyon convexity between rm 150 and rm 250 convexities of intermediate scale are also identified in the longitudinal profile these longer wavelength larger amplitude convexities have strong spatial correlations with high rates of debris flow occurrence high densities of holocene debris fans the largest debris fans along the river and alluvial thicknesses of 10 m or more river profile convexities are unstable and require an active and powerful geologic process to maintain them in this case the abundant frequent and voluminous holocene debris flow activity in grand canyon at all wavelengths the most likely cause for these river profile convexities is holocene aggradation of the riverbed beneath them driven by the coarse particles of tributary debris flows large enough debris flows will slow river flow for kilometers upstream causing it to drop much of its suspended load integrated over time and all of the tributary point source contributions this process will build short wavelength convexities into long wavelength convexities for most if not all of the holocene the colorado river has been dissipating most of its energy in the rapids and expending the remainder in transporting fine sediment through grand canyon with little or no regional incision of bedrock

calving icebergs a source of low frequency seismic signals from columbia glacier alaska low frequency icequakes produced by columbia glacier alaska are caused by large icebergs which break off the glacier terminus into prince william sound occasionally many ice seracs fall in rapid succession producing complex low frequency icequake signals with durations sometimes exceeding 10 min an empirical relationship v 4000 t between the volume v of an iceberg in cubic meters and the duration t of the seismic signal in seconds can be used to estimate the calving rate of columbia glacier from seismological data alone during 1984 and 1985 a period of rapid retreat of the glacier the calculated number of icequakes per month showed seasonal fluctuations that corresponded to variations in calving rate determined by photogrammetry it is likely that most previously reported low frequency icequakes in southern alaska are produced by calving tidewater glaciers

sound channel observations of ice generated tremor in the indian ocean 1 mid to low southern latitude hydrophone stations within the indian ocean have recorded two distinct types of low frequency 100 hz tremor that can be correlated with drifting icebergs and glacial features along the wilkes land coast of eastern antarctica the most common of these signals is a variable harmonic tremor vht with spectral peaks that exhibit frequency fluctuations through time these signals typically display a 4 to 10 hz fundamental frequency and may have as many as ten harmonic bands individual vht signal packets have durations of up to 30 min and occur throughout the year in clusters that continue for hours to days a second less commonly observed signal is characterized by shorter duration 25 to 90 s pulses with a convex upward spectrogram appearance these cusped pulse tremors cpt often exhibit a near uniform pulse spacing with episodes continuing for minutes to hours tremor received levels at hydrophones near 32 s 114 e and 7 s 72 e reach as high as 142 and 133 db re 1 pa peak to peak respectively propagation likely occurs as a sea surface reflected phase at high latitudes and a sound channel phase north of the convergence zone with low frequency transmission loss estimates suggesting maximum acoustic source levels of 245 db re 1 pa at 1 m source locations for a subset of the loudest vht signals correlate with the satellite derived locations of a large iceberg b 15d that migrated westward along the wilkes land shelf region during 2002 and early 2003 most vht sources however cannot be correlated with known iceberg locations suggesting that these signals also may be sourced from smaller unnamed icebergs and or associated with outlet glaciers distributed along the wilkes land coast cpt signals have a more limited spatial distribution originating from five specific regions where ice streams are observed the harmonic nature of both signal types is consistent with the resonance of an ice layer or fluid filled cavity within an ice mass

seismic and hydroacoustic tremor generated by colliding icebergs 1 iceberg harmonic tremor iht emanating from tabular icebergs in the southern ocean and along calving margins of the antarctic ice sheet is a complex evolving signal at frequencies above approximately 0 5 hz iht has been observed as t phases on islands in the equatorial pacific as hydroacoustic signals in the indian ocean and by local and regional antarctic seismic networks to identify the iht source mechanism and to understand its relevance to iceberg calving evolution and breakup we deployed seismometers on a giant 25 by 50 km tabular iceberg called c16 in the ross sea antarctica during a uniquely accessible period austral summer 2003 2004 when it was aground against the northern shore of ross island during the deployment period c16 was in sporadic contact with another giant tabular iceberg b15a that was moving under the influence of local ocean currents this study reveals that the c16 associated iht was a manifestation of extended episodes of discrete repeating stick slip icequakes typically thousands of individual subevents per hour produced when the cliff like edges of the tabular icebergs underwent glancing strike slip collisions the iht signal that we observed is thus not a phenomenon associated with iceberg elastic or fluid resonance modes but is instead the consequence of long sequences of very regularly spaced and similar pulses of seismic radiation from these constituent stick slip subevents iht represents a newly identified glaciogenic source of seismicity that can be used to improve our understanding of iceberg dynamics and possibly of ice shelf disintegration processes

catastrophic partial drainage of pangong tso northern india and tibet abstract catastrophic partial drainage of pangong tso one of the largest lakes in tibet is supported by the geomorphology of the tangtse valley ladakh northern india and cosmogenic 10be nuclide ages of roche moutonnees strath terraces and a flood deposit downstream from the former spillway the former spillway for pangong tso is 20 m high and likely allowed 18 km3 of water to drain catastrophically down the tangtse valley over a period of about 2 days sometime during the latest pleistocene to early holocene the largest flood deposit composed of imbricated granitic boulders up to 4 5 m in length is present 33 km downvalley of the spillway these boulders have a cosmogenic 10be exposure age of 11 1 1 0 ka the age of the outburst flood the minimum calculated discharge was 110 000 m3 s 1 one set of strath terraces upvalley of the flood deposit along the flood s drainage path shows that the rate of fluvial incision 0 3 0 1 mm y 1 during 122 10 5 ka increased to 1 5 0 5 mm y 1 during 10 5 ka to the present the temporal overlap of this increase in the rate of fluvial incision with the main flood deposit suggests that the flood was important in defining the incision along the tangste valley a second set of strath terraces shows little change in incision from 0 6 0 9 to 0 9 1 4 mm y 1 sometime between 18 and 27 ka roche moutonnees upvalley from strath terraces yield a cosmogenic 10be age of 35 8 3 0 ka defining the time when glaciers last occupied the tangtse valley however the lack of glacial sediment along the tangste valley suggests that the flood eroded glacial depositional landforms and sediments resulting in high sediment loads in the floodwater which in turn increased fluvial incision to form strath terraces much of the eroded glacial sediment was subsequently redeposited as the main flood deposit the catastrophic drainage of pangong tso may be the result of breaching of the pangong tangste spillway during very high lake levels in a period of intensified monsoon 10 7 9 6 ka and or possibly the consequence of seismic activity along the karakoram fault that is associated with the initial formation of pangong tso

methods for predicting peak discharge of floods caused by failure of natural and constructed earthen dams floods from failures of natural and constructed dams constitute a widespread hazard to people and property expeditious means of assessing flood hazards are necessary particularly in the case of natural dams which may form suddenly and unexpectedly we revise statistical relations derived from data for past constructed and natural dam failures between peak discharge qp and water volume released v0 or drop in lake level d but assert that such relations even when cast into a dimensionless form are of limited utility because they fail to portray the effect of breach formation rate we then analyze a simple physically based model of dam breach formation to show that the hydrograph at the breach depends primarily on a dimensionless parameter kv0 gl 2d7 2 where k is the mean erosion rate of the breach and g is acceleration due to gravity the functional relationship between qp and takes asymptotically distinct forms depending on whether 1 relatively slow breach formation or small lake volume or 1 relatively fast breach formation or large lake volume theoretical predictions agree well with data from dam failures for which k and thus can be estimated the theory thus provides a rapid means of predicting the plausible range of values of peak discharge at the breach in an earthen dam as long as the impounded water volume and the water depth at the dam face can be estimated