geothermal control on flow patterns in the last glacial maximum ice sheet of iceland because it is located both on the mid atlantic ridge and on a mantle plume iceland is a region of intense tectonics and volcanism during the last glaciation the island was covered by an ice sheet approximately 1000 m thick a reconstruction of the ice flow lines based on glacial directional features shows that the ice sheet was partly drained through fast flowing streams fast flow of the ice streams has been recorded in megascale lineations and flutes visible on the currently deglaciated bedrock and is confirmed by simple mass balance considerations locations of the major drainage routes correlate with locations of geothermal anomalies suggesting that ice stream activity was favoured by lubrication of the bed by meltwater produced in regions of high geothermal heat flux similar control of ice flow by geothermal activity is expected in ice sheets currently covering tectonically and volcanically active area such as the west antarctic ice sheet copyright 2000 john wiley sons ltd

glacier retreat during the recent eruptive period of popocatepetl volcano mexico popocatepetl 19802 n 98862 w 5424 m is one of the largest active stratovolcanoes in the transmexican volcanic belt a glacier located on the north side has undergone severe ablation since the volcano reinitiated eruptive activity in december 1994 in our study we calculate the extent of the glacier recession and the loss in glacial mass balance during the period of greatest laharic activity 1994 2002 using photogrammetric treatment of 20 pairs of aerial photographs the results indicate that from november 1997 to december 2002 the glacier released approximately 3 967 000 m 3 of water a period of intense glacier melting occurred from 4 november 2000 to 15 march 2001 during which time 717 000 m 3 of water was released much of the melting was attributed to the pyroclastic flow that took place on 22 january 2001 and produced a 14 2 km lahar with 68 000 m 3 of water among the many types of volcanic events pyroclastic flows were the most effective in causing sudden snowmelt although small explosions were also effective since they deposited incandescent material on the glacier the collapse of the plinian columns covered the glacier with pyroclasts and increased its volume the existence of control points for georeferencing and a knowledge of the topography underlying the glacier previous to the eruption would have provided more accurate and useful results for hazard prevention

the 1997 and 2001 lahars of popocatepetl volcano central mexico textural and sedimentological constraints on their origin and hazards abstract popocatepetl volcano is the most active volcano in central mexico and represents a high risk for more than 40 million people including mexico city in 1994 volcanic activity at popocatepetl renewed with the formation of ash rich plumes up to 7 km high in april 1996 lava emissions filled the crater and were accompanied by a series of explosions that produced eruptive columns up to 8 km high associated with explosive events in 1997 and 2001 two major lahars events occurred leaving debris flow deposits along huiloac gorge for as far as 15 km to the town of santiago xalitzinta the 1997 debris flow deposit originated after a prolonged emission of ash which caused glacier melt and a rapid release of water 1 107 m3 the amount of melting water was sufficient to gradually erode the river bed causing a flood that gradually transformed from a debris flow to a hyperconcentrated flow in contrast the 2001 debris flow that originated from a post depositional remobilization of a pumice flow deposit did not experience any flow transformation and carried 25 water at maximum the different behavior of these two lahars has important hazard implications both lahars reached xalitzintla town but at that point the 1997 lahar had already transformed into a sediment loaded stream flow the 2001 lahar by contrast maintained the characteristics of a debris flow being more competent and with greater destructive power what happened with these lahars demonstrates how important it is to take into consideration secondary volcanic phenomena even though they were not large flows they were capable of threatening populated areas even during periods of volcanic quiescence or reduced magmatic activity

isolation basins sea level changes and the holocene history of the greenland ice sheet abstract isolation basins are natural topographic depressions that at various times in their history may be connected to or isolated from the sea by changes in relative sea level rsl they provide a valuable source of data for tracking large scale tens of meters changes in rsl over millennia as well as quiet water depositional environments where abrupt changes caused by tsunami iceberg roll or storms may be recorded in this paper we review isolation basins as sources of rsl data with a particular focus on their use in greenland to constrain the holocene history of the ice sheet a new rsl curve from disko fjord west greenland is presented which shows that local ice free conditions were established at c 11 k cal yr bp after which rsl fell rapidly from a marine limit at c 80 m to reach close to present sea level by c 4 k cal yr bp we compare this record with other isolation basin rsl data from six other sites in disko bugt and note a strong northwest southeast differential rebound across the area during the early and mid holocene that reflects variations in ice load history we compare the disko bugt data with other previously published isolation basin rsl records from sisimiut central west greenland nanortalik south greenland and ammassalik southeast greenland rsl fell below present during the early holocene at nanortalik c 10 k cal yr bp and during the mid to late holocene elsewhere before rising to present these differences reflect variations in the timing and amount of greenland ice load change since the last glacial maximum as well as non greenland processes notably the collapse of the laurentide forebulge and also changes in ice equivalent sea level isolation basin data have relatively small age and height uncertainties compared with other rsl indicators enabling them to resolve between different earth and ice sheet models especially during periods of large ice load and rsl change

late holocene sea level changes in south and southwest iceland reconstructed from littoral molluscan stratigraphy sediments deposited during late holocene rise in sea level have been found in the stokkseyri eyrarbakki floi area of south iceland at stokkseyri marine littoral sediments containing a thermophilic intertidal faunal assemblage mainly consisting of gastropods bivalves and barnacles with a few polychaets bryozoans and echinoids have been encountered behind the present storm beach a short distance from the sea the shell layers are up to 4 m in thickness and reach up to 6 m above the present sea level and 300 m inland during the late holocene sea level rise the sea brought sediments and shell material from the coast into a lagoon behind the ridge where it accumulated on former bog layers during two transgressive tendencies separated by a short regressive tendency the ages of the two transgressive tendencies are apparently 2600 2800 and 2200 2400 c years bp respectively then after the sea retreated a thin soil layer formed on top of the marine series marine sediments of late holocene age cont

interpreting luminescence data from a portable osl reader three case studies in fluvial settings optically stimulated luminescence osl is a technique that has been applied from the mid 1980s mainly for sediment dating the osl technique is based on sample stimulation by light to determine the luminescence signal that is stored in the crystal lattices of sediment grains after deposition burial by later sediment and subsequent exposure to ionizing radiation from radioactive elements in the surrounding sediment in such sediment dating two parameters are required the equivalent dose i e the luminescence signal stored in the grains and the dose rate i e the ionizing energy from and radiation emitted by naturally occurring radioisotopes in the deposit plus the effects of cosmic radiation in this research the osl technique is not used for dating the study goal is to analyse only the luminescence signals the total photon counts in polymineral samples obtained after light stimulation in the blue blsl and infrared irsl wavelengths using a portable osl reader designed and built at the scottish universities environmental research centre suerc three fluvial case studies from cambodia australia and mexico are used to illustrate the geomorphological interpretations possible with the portable osl reader data from sediments resulting from a range of different depositional processes the case studies show that aspects of sediment s transport and depositional processes can be inferred from the portable osl reader data providing valuable insights into geomorphological history copyright 2010 john wiley sons ltd

tephrabase tephrochronology and the development of a centralised european database tephrabase was launched on the world wide web in 1995 as a tool for tephrochro nological research in order to facilitate the identification correlation and dating of tephra deposits this database may be interrogated through multiple routes including by source volcano date location and tephra chemistry datasets include stratigraphy geochemistry chronology and spatial information currently all the european data refer to late quaternary icelandic sourced tephras post 12 k yr bp the sites 62 where the tephra deposits are found include iceland the united kingdom ireland the faroe islands sweden and russia in addition there are also data on tephra layers in central mexico use of tephrabase highlights the importance of selected geochemical data but this has to be used with care as major element characteristics alone do not always produce unique definitions for single tephra deposits for the most accurate results multiple criteria must be used tephrabase can be found at http www tephrabase org copyright 2007 john wiley sons ltd

lateglacial to holocene relative sea level changes in the bjarkarlundur area near reykholar north west iceland this paper presents results from seven isolation basins to investigate the relative sea level history from the lateglacial and the mid to late holocene from the bjarkarlundur area near reykholar on the reykjanes peninsula in north west iceland results presented help to constrain the timing and rate of relative sea level rsl change since deglaciation and also the timing of deglaciation itself in the bjarkarlundur area the marine limit is estimated to be approximately 80 m above sea level based on an isolation basin with sill altitude at 79 1 m the maximum age of this marine limit and hence local deglaciation is estimated at 12 2 14c ka bp relative sea level then fell rapidly during the late bolling early allerod at a rate of approximately 35 mm 14c a 1 to below 50 m by 11 4 14c ka bp after this the rate of rsl fall decreased significantly during the late allerod and younger dryas chronozones averaging 6 mm 14c a 1 between 11 4 and 9 7 14c ka bp based on isolation basins with sill altitudes of 51 1 and 41 1 m our data constrain any possible fluctuation in rsl produced by regrowth of ice during the younger dryas to below 10 m after 9 7 14c ka bp the rate of rsl fall increased significantly to approximately 23 mm 14c a 1 to at least 9 0 14c ka bp if eustatic sea level rise is taken into account and the calibrated timescale is used actual crustal uplift rates are estimated at 56 and 46 mm cal a 1 during lateglacial and early holocene times respectively during the mid to late holocene rsl then rose to at least 1 m above present day levels gradually falling to the present day level from 3 1 14c ka bp these results demonstrate the potential of isolation basin data for investigating the timing and rate of rsl change in iceland this can add important well constrained information on rsl when combined with data from raised beaches copyright 2009 john wiley sons ltd

toward a revised hazard assessment at merapi volcano central java abstract of 1 1 million people living on the flanks of the active merapi volcano 440 000 are at relatively high risk in areas prone to pyroclastic flows surges and lahars for the last two centuries the activity of merapi has alternated regularly between long periods of viscous lava dome extrusion and brief explosive episodes at 8 15 year intervals which generated dome collapse pyroclastic flows and destroyed part of the pre existing domes violent explosive episodes on an average recurrence of 26 54 years have generated pyroclastic flows surges tephra falls and subsequent lahars the 61 reported eruptions since the mid 1500s killed about 7000 people the current hazard zone map of merapi pardyanto et al 1978 portrays three areas termed forbidden zone first danger zone and second danger zone based on successively declining hazards revision of the hazard map is desirable because it lacks details necessary to outline hazard zones with accuracy in particular the valleys likely to be swept by lahars and excludes some areas likely to be devastated by pyroclastic gravity currents such as the 22 november 1994 surge in addition risk maps should be developed to incorporate social technical and economic factors of vulnerability eruptive hazard assessment at merapi is based on reconstructed eruptive history on eruptive behavior and scenarios and on existing models and preliminary numerical modeling firstly the reconstructed eruptive activity in particular for the past 7000 years and from historical accounts of eruptions helps to define the extent and recurrence frequency of the most hazardous phenomena newhall et al 2000 camus et al 2000 pyroclastic flows traveled as far as 9 15 km from the source pyroclastic surges swept the flanks as far as 9 20 km away from the vent thick tephra fall buried temples in the vicinity of yogyakarta 25 km to the south and subsequent lahars spilled down the radial valleys as far as 30 km to the west and south at least one large edifice collapse has occurred in the past 7000 years newhall et al 2000 camus et al 2000 secondly four eruption scenarios are portrayed as hazardous zones on two maps and derived from the past eruptive behavior of merapi and from the most affected areas in the past thirdly simple numerical simulation based on a digital elevation model a stereo pair of spot satellite images and one 2d orthoimage helps to simulate pyroclastic and lahar flowage on the flanks and in radial valley channels and to outline areas likely to be devastated three major threats are identified 1 a collapse of the summit dome in the short to mid term that can release large volume pyroclastic flows and high energy surges towards the south southwest sector of the volcano 2 an explosive eruption much larger than any since 1930 may sweep all the flanks of merapi at least once every century 3 a potential collapse of the summit area involving the fumarolic field of gendol and part of the southern flank which can contribute to moderate scale debris avalanches and debris flows

a gigantic bezymianny type event at the beginning of modern volcan popocatepetl the history of volcan popocatepetl can be divided into two main periods the formation of a large primitive volcano approximatively 30 km wide on which is superimposed a modern cone 6 8 km in diameter and 1700m high a major event of bezymianny type marks the transition between these two dissimilar periods the activity of the primitive volcano was essentially effusive and lasted several hundred thousands of years the total volume of products ejected by the volcano is of the order of 500 600 km3 its last differentiated magmas are dacitic a gigantic debris flow d f spread on the southern side is related to the bezymianny type event which destroyed the summit area of the ancient edifice an elliptical caldera 6 5 11 km wide was formed by the landslide its deposits with a typical hummocky surface cover 300 km2 for a volume of 28 30 km3 numerous outcrops belonging to this debris flow show slabs of more or less fractured and dislocated rocks that come from the primitive volcano these deposits are compared to two studied debris flows of similar extent and volume the mount shasta and colima s d f this eruption takes a major place in the volcanologic and magmatic history of popocatepetl pyroclastic products of surge type with laminites and crude layers ashflows and pumiceous airfall layers are directly related to this event and begin the history of the modern volcano probably less than 50 000 years ago in addition a second andesitic and dacitic phase rose both from the central vent forming the basis of modern popo and from lateral vents the terminal cone is characterized by long periods of construction by lava flows alternating with phases of destruction the duration of these episodes being 1000 to 2000 years the cone is composed of two edifices the first volcan el fraile began with effusive activity and was partly destroyed by three periods of intense explosive activity the first period occurred prior to 10 000 years b p the second from 10 000 to 8000 years b p and the third from 5000 to 3800 years b p each period of destruction shows cycles producing collapsing pyroclastic flows or nuees of the st vincent type related to the opening of large craters plinian air fall deposits and minor lava flows the second edifice the summit popo produced lava flows until 1200 years b p and since that time entered into an explosive period two cataclysmic episodes each including major pyroclastic eruptions occurred 1200 and 900 1000 years ago during the pre hispanic and historic times effusive activity was restricted entirely to the summit area alternating with plinian eruptions nevertheless despite the quiet appearance of the volcano the last period of pyroclastic activity which started 1200 years ago may not have ended and can be very dangerous for the nearby populations

instrumental lahar monitoring at merapi volcano central java indonesia abstract more than 50 volcanic debris flows or lahars were generated around mt merapi during the first rainy season following the nuees ardentes of 22 november 1994 the rainfalls that triggered the lahars were analyzed using such instruments as weather radar and telemetered rain gauges lahar dynamics were also monitored using new non contact detection instrumentation installed on the slopes of the volcano these devices include real time seismic amplitude measurement rsam seismic spectral amplitude measurement ssam and acoustic flow monitoring afm systems calibration of the various systems was accomplished by field measurements of flow velocities and discharge contemporaneously with instrumental monitoring the 1994 1995 lahars were relatively short events their duration in the boyong river commonly ranging between 30 min and 1 h 30 min the great majority 90 of the lahars was recognized at kaliurang village between 13 00 and 17 30 h due to the predominance of afternoon rainfalls the observed mean velocity of lahar fronts ranged between 1 1 and 3 4 m s whereas the peak velocity of the flows varied from 11 to 15 m s under the gardu pandang viewpoint location at kaliurang to 8 10 m s at a section 500 m downstream from this site river slopes vary from 28 to 22 m km at the two sites peak discharges recorded in various events ranged from 33 to 360 m3 s with the maximum value of peak discharge 360 m3 s on 20 may 1995 to improve the lahar warning system along boyong river some instrumental thresholds were proposed large and potentially hazardous lahars may be detected by rsam units exceeding 400 ssam units exceeding 80 on the highest frequency band or afm values greater than 1500 mv on the low gain broad band setting

geochemistry of historical age silicic tephras in iceland the major element chemistry of nine silicic tephras of historical age from iceland is assessed as a key step in the development of the recent tephrochronology of the north atlantic region the tephras include the largest such layers produced by each of the five central volcanoes hekla o raefajokull eyjafjallajokull torfajokull and askja since the ninth century ad h 1104 o1362 e 1821 landnam tephra c 870 a 1875 and four other tephras h 1158 h 1510 h 1947 o1727 the determination of grain discrete major element chemistry of the glass fraction is a fundamental stage in the identification and correlation of tephra and allows links to be made between icelandic source areas with precise dating evidence and distal deposits elsewhere in the north atlantic region although major element data can be used to discriminate between tephra layers produced by the different central volcanoes on its own it cannot be used to identify all the holocene layers produc

empirical models to predict the volumes of debris flows generated by recently burned basins in the western u s abstract recently burned basins frequently produce debris flows in response to moderate to severe rainfall post fire hazard assessments of debris flows are most useful when they predict the volume of material that may flow out of a burned basin this study develops a set of empirically based models that predict potential volumes of wildfire related debris flows in different regions and geologic settings the models were developed using data from 53 recently burned basins in colorado utah and california the volumes of debris flows in these basins were determined by either measuring the volume of material eroded from the channels or by estimating the amount of material removed from debris retention basins for each basin independent variables thought to affect the volume of the debris flow were determined these variables include measures of basin morphology basin areas burned at different severities soil material properties rock type and rainfall amounts and intensities for storms triggering debris flows using these data multiple regression analyses were used to create separate predictive models for volumes of debris flows generated by burned basins in six separate regions or settings including the western u s southern california the rocky mountain region and basins underlain by sedimentary metamorphic and granitic rocks an evaluation of these models indicated that the best model the western u s model explains 83 of the variability in the volumes of the debris flows and includes variables that describe the basin area with slopes greater than or equal to 30 the basin area burned at moderate and high severity and total storm rainfall this model was independently validated by comparing volumes of debris flows reported in the literature to volumes estimated using the model eighty seven percent of the reported volumes were within two residual standard errors of the volumes predicted using the model this model is an improvement over previous models in that it includes a measure of burn severity and an estimate of modeling errors the application of this model in conjunction with models for the probability of debris flows will enable more complete and rapid assessments of debris flow hazards following wildfire

late devensian and holocene relative sealevel changes at loch nan eala near arisaig northwest scotland pollen diatom radiocarbon and lithostratigraphical data from isolation basins in northwest scotland are used to quantify the reference water tide level indicative range and age of differenty types of isolation and connection contacts tendencies of sea level movement and relative sea level changes from the mid lateglacial interstadial 11 8 ka bp to the late holocene are constructed from these data relative sea level fell continuously from 17 8 m od at 11 8 ka bp to ca 5 2 m od at 10 1 ka bp from an unkown minimum between 10 ka and 9 ka bp relative sea level then rose to 6 3 m od at 8 3 ka bp the maximum holocene sea level occurred within the range 6 6 m od to 9 3 m od between 6 6 ka bp and 4 0 ka bp before falling to present isobase age altitude and quantitative rebound models for northwest scotland are tested using these sealevel data but none of the published models shows close agreement with the new results

volcanic mixed avalanches a distinct eruption triggered mass flow process at snow clad volcanoes a generally unrecognized type of pyroclastic deposit was produced by rapid avalanches of intimately mixed snow and hot pyroclastic debris during eruptions at mount st helens nevado del ruiz and redoubt volcano between 1982 and 1989 these mixed avalanches traveled as far as 14 km at velocities up to 27 m s involved as much as 10 7 m 3 of rock and ice and left unmelted deposits of single flow units as thick as 5 m during flow downslope heat transfer from hot rocks to snow produced meltwater that partially saturated the mixtures apparently giving these mixed avalanches mobilities equal to or greater than those of dry debris avalanches of similar volume the avalanches studied for this report began as snow avalanches triggered during explosive phases of the eruptions by ballistic bombardment of snow slopes by hot pyroclastic debris erosion by the avalanches incorporated additional snow fragments of glacier ice and other rock debris mixed avalanche deposits were massive very poorly sorted and ungraded to inversely graded prior to melting although rock debris composed as much as 70 wt of the frozen samples the bulk volumetric content of rock debris was only 9 to 36 snow and ice composed between 36 and 72 of the frozen samples with void space making up the remainder of the volume deformation and consolidation after melting of the ice content reduced the deposits to loose porous layers that were only a fraction of their original thickness and that later gave little hint of their origin after melting and desiccation the deposits are highly susceptible to erosion and unlikely to be well preserved in the stratigraphic record

clast orientations of the 1985 lahars of the nevado del ruiz colombia and implications for depositional processes abstract the eruption of the nevado del ruiz colombia on 13 november 1985 produced lahar flows resulting in extensive deposits the imbrications of flat clasts within the deposits as well as the orientations of large boulders resting on the surface of these deposits were measured the imbrications of the long a axes of the small clasts were found to dip 25 upstream against the lahar flow direction with a dispersion of 30 indicating transport of such clasts by normal stream flow contrary to this the boulders mostly on the surface of the deposits are aligned with their long a axes normally to the lahar flow indicating rolling on the surface both orienting mechanisms occurred in runoff pulses subsequent to the main event which produced only unordered deposits en masse thus the genesis of the emplacement of the lahar deposits in question has been mechanically explained

combining airborne and terrestrial laser scanning for quantifying erosion and deposition by a debris flow event abstract we quantified the sediment volume transported by a major debris flow event in the halltal austrian alps using a combination of terrestrial tls and airborne laser scanning als which has rarely been carried out before a digital terrain model dtm derived from als data pre event surface was combined with a dtm derived from tls data post event surface both datasets were aligned and compared in a cut and fill analysis estimating differential volumes the main focus lay on the evaluation and accuracy assessment of the applied method tie point based registration of both datasets proved to be insufficient additional alignment by multi station adjustment was necessary to minimise the averaged height error between both datasets amounting for a volumetric error of less than 10 which is comparable to pure als campaigns larger errors were estimated for complex terrain with low scanning resolutions a particular problem in data processing was the low and dense shrub vegetation in the study area which required a specifically adapted filter algorithm an insufficient ground representation was observed for the als data overestimating ground heights for averaged 70 cm despite these limitations the approach proved to be suitable for accurate extreme event quantification the starting zones of the debris flows lie at the bedrock debris interface where runoff is concentrated volumes of 5000 to 12 000 m3 were assessed volume estimation worked better for the erosional than for the depositional features this is because the erosional gullies are relatively deep and the calculation is not affected by pre event vegetation while erosion and sedimentation are balanced for one of the three catchments investigated the deposited volumes are higher than the detected eroded volumes for the other two the reasons are not fully understood the magnitude of the flows was determined by catchment size topographical characteristics and deforestation by a major wildfire in 1946

the cohesive naranjo debris flow deposit 10 km3 a dam breakout flow derived from the pleistocene debris avalanche deposit of nevado de colima volcano mexico abstract mass movement processes on volcanic terrains such as landslides and debris avalanches can cause the obstruction of main drainages producing the formation of temporary dams a good example of this occurred 18 5 ka ago when the eastern flank of the nevado de colima volcano collapsed producing a debris avalanche deposit that was previously described as one of the largest in the world the deposit extended from the volcanic summit as far as the pacific coast 120 km away new stratigraphic sedimentological and componentry data suggest that the volcanic collapse of nevado de colima resulted in a debris avalanche that traveled 20 km southeast to the naranjo river there it crashed against a topographic barrier consisting of cretaceous limestones cerro la carbonera and the flow direction was diverted to the south down the naranjo river channel for another 25 km before the avalanche came to a halt the obstruction of the drainage produced a temporary dam that stored ca 1 km3 of water and deposited fluvial and slack water sediments some time after the damming the accumulated water sediment load was able to overtop the obstructing material and to release a breakout flow with a calculated initial flow discharge of 3 5 million m3 s the resulting flood cohesive debris flow followed the channel of the naranjo river and due to the high erodibility of the channel and introduction of substrate material the debris flow progressively increased its volume up to 10 km3 six times its initial volume this study highlights the relevance of evaluating the potential remobilization of debris avalanche deposits to initiate large magnitude cohesive debris flows therefore the hazard and risk analysis of future potential events of this nature must consider the pre eruption conditions and the topography surrounding a volcano

geomorphological evolution of a fluvial channel after primary lahar deposition huiloac gorge popocatepetl volcano mexico abstract popocatepetl volcano 19 02 n 98 62 w 5424 m began its most recent period of volcanic activity in december 1994 the interaction of volcanic and glacier activity triggered the formation of lahars through the huiloac gorge located on the northern flank of the volcano causing significant morphological changes in the channel the most powerful lahars occurred in april 1995 july 1997 and january 2001 and were followed by secondary lahars that formed during the post eruptive period this study interprets the geomorphological evolution of the huiloac gorge after the january 2001 lahar variations in channel morphology at a 520 m long research site located mid way down the gorge were recorded over a 4 year period from february 2002 to march 2005 and depicted in five geomorphological maps scale 1 200 for 14 february and 15 october 2002 27 september 2003 9 february 2004 and 16 march 2006 a gis was used to calculate the surface area for the landforms identified for each map and detected changes and erosion deposition processes of the landforms using the overlay function for different dates findings reveal that secondary lahars and others types of flows like sediment laden or muddy streamflows caused by precipitation rapidly modified the gorge channel following the january 2001 non eruptive lahar a period associated with volcanic inactivity and the disappearance of the glacier once located at the headwall of the gorge field observations also confirmed that secondary flows altered the dynamics and geomorphological development of the channel these flows incised and destroyed the formations generated by the primary lahars 1997 and 2001 causing a widening of the channel that continues today after february 2004 a rain triggered lahar and other flows infilled the channel with materials transported by these flows the deposits on the lateral edges of the channel form terraces a recent lull in lahar activity contrasts with the increasing instability of the edges of the channel and the continuous edification and destruction of recent lahar terraces

the n and w iceland shelf insights into last glacial maximum ice extent and deglaciation based on acoustic stratigraphy and basal radiocarbon ams dates abstract we present 32 ams radiocarbon dates collected from sediments obtained during cruises of css hudson 1993 rv jan mayen 1996 and bjarni saemundsson 1997 the radiocarbon dates were obtained on samples from the basal part of sediment cores collected across an area between 64 and 67 n and 18 29 w core sites were based on 3 5 khz acoustic subbottom surveys the 3 5 khz subbottom profiles indicate that several of the troughs contain 30 m of quaternary sediment at many sites the acoustic surveys suggest the presence of one or more strong reflectors which can be traced over extended areas 100 km of the seafloor these may represent large scale volcanic ash falls such as the vedde ash and its correlatives as well as other regionally significant tephras we report dates from seven areas 1 northern troughs eyjafjardarall hunafloadjup and reykjafjardarall 2 hunafloi area and inner shelf and fjords 3 djupall area 4 isafjardardjup area 5 kolluall 6 western shelf break and slope and 7 jokuldjup the dates range in age from marine isotope stages 3 1 five cores have basal dates 16 ka and thus provide information on the timing and environments during the deglaciation several dates of 12 ka indicate that the inner shelf may have been largely ice free by that time estimates of average sediment accumulation rates vary between 4 and 90 cm kyr with modal estimates of 30 40 cm kyr

late devensian and holocene records of relative sea level changes in northwest scotland and their implications for glacio hydro isostatic modelling raised tidal marshes and isolation basins lakes that were once connected to the sea in northwest scotland record changes in relative sea level following deglaciation during the late devensian to the present the kentra to arisaig area which was covered by relatively thick ice c 900 m at the last glacial maximum lgm shows a regression from a marine limit between 36 5 m od and 40 m od at c 15 9 kyr cal bp range 15 6 16 3 kyr cal bp through to an early holocene minimum a range of sites in the same area record a mid holocene maximum indicative of mean sea level c 6 5 m above present the maximum is not a well developed and short duration highstand as predicted by a number of models but is an extended period 8 0 5 0 kyr cal bp with sea level within c 1 m of the maximum sites to the north in kintail show no late devensian record because much of the area lies within the younger dryas ice limit the altitude of the mid holocene maximum in kintail is not well constrained but occurred 7 9 8 1 kyr cal bp further north sites on the applecross peninsula record a late devensian fall in sea level and a holocene maximum for mean sea level no higher than c 3 0 m above present in coigach the furthest north of the new sites and well outside the younger dryas ice limit there is no evidence recorded of late devensian sea levels above present the holocene maximum here was around c 2 5 m above present these observations of sea level change all standardised to change in mean sea level relative to present constrain the glacio hydroisostatic rebound model parameters earth models comprising three mantle layers with lateral viscosity and elastic parameters give a satisfactory description of rebound the parameters h lithosphere thickness 65 km g 6 upper mantle viscosity 4 1020 pa 14c seconds and g lower mantle viscosity 1022 pa 14c seconds give the best overall agreement but discrepancies between observations and predictions remain an increase of 10 in ice thickness north of the great glen compared to the previous optimum ice model provides good agreement for many sites but important discrepancies remain for the northern sites and indicate inadequacies in the model of the british ice sheet several alternative ice models are examined but the various combinations of earth and ice model illustrate the non uniqueness of the solution a combination of more extensive ice limits especially onto the hebridean shelf and west shetland shelf and some changes to ice thicknesses over the mainland should produce a better agreement but the spatial coverage of observations remains a limitation to producing a unique solution the characteristics of the holocene highstand age duration and amplitude at the di erent sites refutes the assumption that globally deglaciation ceased abruptly 7000 yr ago the observations are consistent with an ice model that includes c 3 m of melting over the last 7000 yr 2000 elsevier science ltd all rights reserved

a gis based method to determine the volume of lahars popocatepetl volcano mexico abstract lahars are flows composed of water and volcanic sediment which are often dangerous for people living near volcanoes therefore a reliable estimation of lahar volume is needed to effectively assess the risk this paper proposes a new method to calculate the volume of lahar sediments found in channels of volcanic landscapes the method requires surveys of several cross sections along a gorge a digital elevation model of the study area and measurements of the thickness of the lahar deposits with these data and a geographical information system gis the volume is calculated for the erosive section where deposit volume is divided into oblique parallelepipeds and the sedimentary section where deposit volume is divided into polyhedrons this new method was applied to the 1997 and 2001 lahars that occurred in the channel of a gorge at popocatepetl volcano mexico the estimated volumes are 1 85 10 5 and 1 6 10 5 m 3 respectively which is about 40 less than those obtained by the traditional method that multiplies lahar flow path length sediment width and sediment depth this observation suggests that the traditional method tends to overestimate volumes

volcanoes and climate the triggering of preboreal jokulhlaups in iceland the early holocene 12 8 2 cal ka deglaciation and pulsed warming was associated in iceland with two major generations of jokulhlaups around the vatna ice cap vatnajokull at ca 11 4 11 2 cal ka and ca 10 4 9 9 cal ka and major tephra emissions from the grimsvotn and bar arbunga subglacial volcanoes the earliest flood events were recorded inland during the middle younger dryas and their deposits were overlain by the early preboreal vedde ash 11 8 cal ka the first holocene flood events ca 11 4 11 2 cal ka are issued from a glacial advance the second and major set of floods was partly driven by the erdalen cold events and advances 10 1 9 7 10be ka initially issued from the bar arbunga 10 4 10 1 9 9 ka and grimsvotn volcanoes saksunarvatn tephra complex ca 10 2 9 9 cal ka these floods were also fed by the residual glacio isostatic depressions below the vatnajokull that enabled the storage of meltwaters in large subglacial lakes or aquifers until ca 9 3 cal ka this storage was enhanced by ice damming and permafrost especially during the twinned erdalen events due to the glacio isostatic rebound the general slope was nearly flat and the valley was partly filled with sediments until ca 10 8 cal ka temporary lacustrine deposits in this valley resulted from the very broad splay of waters as for the ca 11 2 cal ka and ca 10 1 9 9 cal ka flood due to regional permafrost these floods had a potential duration of several months as they were mostly fed by climate driven meltwater the maximal volume evacuated by these events did not greatly exceed 1 106 m3 s 1 from the flood affected transverse profile of the valleys that remain partly filled with sediments

parallel adaptive numerical simulation of dry avalanches over natural terrain high fidelity computational simulation can be an invaluable tool in planning strategies for hazard risk mitigation the accuracy and reliability of the predictions are crucial elements of these tools being successful we present here a new simulation tool for dry granular avalanches using several new techniques to create a highly accurate tool with a combination of good models and numerical methodologies highlights of our methodology are the use of a depth averaged model of the conservation laws and an adaptive grid godunov solver to solve the resulting equations the software is designed to run on distributed memory supercomputers and make use of digital elevation data dynamically i e refine the grid and input data to finer resolutions to better capture flow features as the flow evolves our simulations are validated using quantitative and qualitative comparisons to tabletop experiments and data from field observations our software is freely available and can be used on a range of hardware from inexpensive desktop computers to the largest supercomputers

gis and sda applications in geomorphology abstract this special issue of geomorphology consists mainly of selected papers from the s15 session gis and sda applications in geomorphology at the 6th international conference on geomorphology held in zaragoza spain in september 2005 for this session 53 abstracts from europe asia the americas africa and oceania were submitted and 18 oral communications and 35 posters were presented the session provided an opportunity to overview discuss and evaluate new advances of gis geographical information systems and sda spatial data analysis applications in the field of geomorphology eight of the manuscripts submitted for the publication call for this special issue survived the review process and two other invited contributions together form this special issue with 10 papers

a sph depth integrated model for popocatepetl 2001 lahar mexico sensitivity analysis and runout simulation abstract lahars are debris flows of volcanic origin which can endanger or even destroy communities located near the flanks of volcanoes lahars are not always triggered by eruptions they can form during heavy rainfall or after hydrothermal alteration and volcanic edifice collapse decision makers need lahar hazard maps to devise hazard prevention measures that will prevent casualties so lahar modelling is an important tool for assessing flow behavior and determining inundation areas the depth integrated numerical model used in this study is derived from the velocity pressure of the biot zienkiewicz model and was discretized using the smoothed particle hydrodynamics sph method to simulate a lahar that occurred at popocatepetl volcano in 2001 in order to investigate the convergence of the model we used a range of different sph mesh resolutions once the optimum mesh resolution was bounded we analyzed the model s sensitivity to the initial lahar volume the density of the geomaterial and the rheological parameter of the bingham fluid the results show that the sph depth integrated model produced a highly accurate simulation of the distribution and velocity of the 2001 lahar the study also shows the effects of sph mesh resolution and the relevant influence of rheological parameters

lahar flow simulations using laharz program application for the popocatepetl volcano mexico lahars are a type of catastrophic event that is generated in volcanic environments due to the recent technological advances computer simulated models have become widely used by the scientific community to predict the distribution of catastrophic events such as floods debris avalanches earth landslides or lahars and to mitigate possible damage to populations located in a risk area our study risk area is located in the popocatepetl volcano a large and active stratovolcano in the trans mexican volcanic belt here lahars have been occurring during the last century and some of them have seriously affected nearby towns since one of the main input parameters into a lahar simulation is the digital elevation model dem this paper focuses on studying lahar simulations on popocatepetl using dems obtained from various sources with the aid of a popular package known as laharz the first simulations were performed using a 1 50 000 topographic map with 20 m contours interval the second set of tests used an enhanced dem with profiles measured during fieldwork in the lahar channel in the last set of tests we added lateral artificial barriers to the channel profiles used in the previous enhanced dem our results show that the use of high resolution and detailed dems does not necessarily guarantee a realistic lahar simulation as was previously thought and a detailed explanation as to why the laharz code computation creates ragged edges is offered our results also offer useful information on the level of detail necessary for an input dem into laharz in order to obtain lahar simulations closer to real lahars the minimum resolution for the dem used in simulations must be less than the width of the narrowest cross section of the channel to realistically reproduce the lahars for dems with lower resolution sometimes the modeled lahars are shorter in length and therefore underestimate real hazards to populations also the results show that lateral barriers are sometimes needed to obtain more realistic inundation areas

magnitude of the sediment transport event due to the late pleistocene sector collapse of asama volcano central japan abstract a rapid large scale sediment transport event due to a catastrophic landslide plays an important role in changing drainage basin topography however volumetric evaluation of such events that occurred before the holocene has been limited this study quantitatively examines the volume of sediments derived from the late pleistocene 24 ka sector collapse of asama volcano central japan a sequence of sediments supplied from the sector collapse was identified based on geological and geomorphological field surveys and literature search the total volume of the sediments was estimated from borehole columns to be 4 9 5 4 km3 reconstruction of the morphology of the volcanic edifice before and after the collapse provided an estimated volume of the lost sector of 4 0 km3 the greater estimated volume of the sediments released by the collapse is attributed to the entrainment of fluvial material during the flow of volcanic debris and to dilation of the original volcanic material

intcal13 calibrated ages of the vedde and saksunarvatn ashes and the younger dryas boundaries from krakenes western norway from krakenes lake in western norway there exist 118 accelerator mass spectrometry 14c dates for the time interval 12 000 8000 14c a bp that we earlier calibrated using the intcal09 data set these yielded the most accurate and precise ages available for the younger dryas boundaries and the vedde and saksunarvatn ashes here we present a new calibration using the recently published intcal13 data set all differences between the two sets of calibrated ages are within the 1 error of the original intcal09 results the most significant differences are that the error for the allerod younger dryas boundary decreased that this boundary became slightly older and that the length of the younger dryas increased slightly

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

isolation basin stratigraphy and holocene relative sea level change on arveprinsen ejland disko bugt west greenland this paper presents the results of an investigation into holocene relative sea level rsl change isostatic rebound and ice sheet dynamics in disko bugt west greenland data collected from nine isolation basins on arveprinsen ejland east disko bugt show that mean sea level fell continuously from ca 70 m at 9 9 ka cal yr bp 8 9 ka 14c yr bp to reach a minimum of ca 5 m at 2 8 ka cal yr bp 2 5 ka 14c yr bp before rising to the present day a west east gradient in isostatic uplift across disko bugt is confirmed with reduced rebound observed in east disko bugt however rsl differences up to 20 m at 7 8 ka to 6 8 ka cal yr bp 7 ka to 6 ka 14c yr bp also exist within east disko bugt suggesting a significant north south component to the area s isostatic history the observed magnitude and timing of late holocene rsl rise is not compatible with regional forebulge collapse instead rsl rise began first in the eastern part of the bay as might be expected under a scenario of crustal subsidence caused by neoglacial ice sheet readvance the results of this study demonstrate the potential of isolation basin data for local and regional rsl studies in greenland and the importance of avoiding data compilations from areas where the isobase orientation is uncertain copyright 1999 john wiley sons ltd

contemporary and fossil foraminifera from isolation basins in northwest scotland isolation basins are widely used in sea level reconstructions but contemporary analogues have been poorly studied comparatively recent research has identified isolation basins with extended transitional isolation contacts that pose problems in sea level interpretations this paper presents foraminiferal results from 24 contemporary isolation basins combined with data from two isolation basins with extended isolation contacts foraminiferal associations identified from the contemporary basins show a clear relationship with water salinity and sill altitude that supports interpretation of the extended fossil sequences an association dominated by miliammina fusca mf signifies a basin close to final isolation from marine influence increasing marine inundation of basins is signified by a series of associations dominated by the following foraminifera ja jadammina macrescens and m fusca me m fusca and elphidium williamsoni ew e williamsoni he haynesina germanica and e williamsoni nd nonion depressulus these associations can be used to interpret the sedimentary isolation sequences from loch nan corr and rumach vi a pilot study of the stable isotope signature from the two species h germanica and e williamsoni is reported from rumach vi and loch nan corr the results show the potential of stable isotope analysis for environmental reconstruction from isolation basins in particular using 18o for salinity reconstruction

smoothed particle hydrodynamic modeling of volcanic debris flows application to huiloac gorge lahars popocatepetl volcano mexico abstract lahars are among the most catastrophic volcanic processes and the ability to model them is central to mitigating their effects several lahars recently generated by the popocatepetl volcano mexico moved downstream through the huiloac gorge towards the village of santiago xalitzintla the most dangerous was the 2001 lahar in which the destructive power of the debris flow was maintained throughout the extent of the flow identifying the zone of hazard can be based either on numerical or empirical models but a calibration and validation process is required to ensure hazard map quality the geoflow sph depth integrated numerical model used in this study to reproduce the 2001 lahar was derived from the velocity pressure version of the biot zienkiewicz model and was discretized using the smoothed particle hydrodynamics sph method the results of the calibrated sph model were validated by comparing the simulated deposit depth with the field depth measured at 16 cross sections distributed strategically along the gorge channel moreover the dependency of the results on topographic mesh resolution initial lahar mass shape and dimensions is also investigated the results indicate that to accurately reproduce the 2001 lahar flow dynamics the channel topography needed to be discretized using a mesh having a minimum 5 m resolution and an initial lahar mass shape that adopted the source area morphology field validation of the calibrated model showed that there was a satisfactory relationship between the simulated and field depths the error being less than 20 for 11 of the 16 cross sections this study demonstrates that the geoflow sph model was able to accurately reproduce the lahar path and the extent of the flow but also reproduced other parameters including flow velocity and deposit depth

post glacial rebound of iceland during the holocene abstract the geodynamic context of iceland provides the rare opportunity to analyse the combined effects of a ridge and a hotspot on deformation processes from a digital elevation model field analysis and a compilation of previous work we propose a synthesis of vertical motions of iceland during the holocene with a focus on the post glacial rebound we determined two ancient marine limits one above and one below the present sea level estimated at 10 ka 300 years and 8150 350 years bp respectively we calculated an uplift phase of 40 170 m with a rate of 2 1 9 2 cm a 1 between 10 ka 300 years and 8150 350 years bp corresponding to the post glacial rebound of iceland following the weichselian glaciation spatial variations of the rebound are mainly related to the local glacial dynamics ice load and deglaciation history rather than the geodynamic context however the relaxation time deduced from uplift data is 4167 years in west iceland and 2000 years in ssw iceland we estimated viscosity from relaxation time ranging from 2 1 10 19 pa s to 3 2 10 19 pa s the significant difference in the relaxation time is due to local variation of the lithospheric thickness as a result of rifting rather than because of a variation of the viscosity

lateglacial to holocene relative sea level changes in the stykkisholmur area northern snaefellsnes iceland comparatively little research has been undertaken on relative sea level rsl change in western iceland this paper presents the results of diatom tephrochronological and radiocarbon analyses on six isolation basins and two coastal lowland sediment cores from the stykkisholmur area northern snaefellsnes western iceland the analyses provide a reconstruction of lateglacial to mid holocene rsl changes in the region the marine limit is measured to 65 69 m above sea level asl with formation being estimated at 13 5 cal ka bp rsl fall initially occurred rapidly following marine limit formation until ca 12 6 cal ka bp when the rate of rsl fall decreased rsl fell below present in the stykkisholmur area during the early holocene by ca 10 cal ka bp the rates of rsl change noted in the stykkisholmur area demonstrate lesser ice thicknesses in snaefellsnes than vestfir ir during the younger dryas when viewed in the regional context consequently the data provide an insight into patterns of glacio isostatic adjustment surrounding brei afjor ur a hypothesized major ice stream at the last glacial maximum

postglacial relative sea level changes in northwest iceland evidence from isolation basins coastal lowlands and raised shorelines relative sea level rsl data provide constraints on land uplift associated with former ice loading and can be used to differentiate between contrasting ice unloading scenarios isolation basin coastal lowland and geomorphological evidence is employed to reconstruct rsl changes in northwest nw iceland which may have experienced contrasting uplift patterns under local nw uplift highest rsl would be expected in central vestfir ir whereas highest rsl would be closest to the main ice loading centre under regional central iceland uplift four new rsl records are presented based on 16 sea level index points and 4 limiting ages from sites principally focussed along a transect away from central iceland the new rsl records highlight spatial variability of holocene rsl changes and provide constraints on deglaciation there is an increase in marine limit elevation with proximity to the proposed principal ice loading centre in central iceland highest recorded marine limit shorelines are found in hrutafjor ur heggsta anes southeast the lowest in hlo uvik and rekavik bak latrum north and at an intermediate elevation in reykjanes laugardalur central vestfir ir evidence from brei avik latrar records early rapid deglaciation in brei afjor ur or a complex interplay of multiple uplift centres rsl fell rapidly following deglaciation in several locations as a result of the quick response of the icelandic lithosphere to unloading the rsl data along the transect show an uplift pattern consistent with extensive regional glaciation emanating from central iceland which could have implications for ice sheet configuration and patterns of deglaciation glacio isostatic adjustment modelling and the volume of meltwater input into the north atlantic