rate of dune reddening in a humid tropical climate the formation of red beds has long interested geologists and pedologists1 3 it has been suggested that the nature and degree of reddening in dune sands can be a useful indicator of the relative age and environmental history of the sands several authors have concluded that dune sands undergo progressive reddening with time4 7 and james and stanley8 considered that coastal dunes might actually be mapped on the basis of colour however quantitative data regarding the rate of reddening in different environmental conditions are generally lacking i present here radiocarbon evidence from north east australia which suggests that red weathering profiles have developed in stabilized dunes of holocene age in humid tropical conditions within the past 7 500 yr

magmatic evolution of a volcano studied by 230th 238u disequilibrium and trace elements systematics the etna case age determinations of several lava flows from etna through 230th 238u disequilibrium internal isochrons yield a precise chronology of the volcano s history for the last 200 000 years and emphasize the main episodes in the formation of this huge complex strato volcano study of 230th232th 0 initial ratios of lavas together with their trace element compositions yields a consistent model of magmatic evolution implying the existence for 200 000 years of a deep reservoir of alkalic magma periodically mixed with magmas of tholeiitic affinity these short periods of mixing appear to be related to the formation of the large calderas of etna in addition to these processes affecting the deep reservoir fractional crystallization also occurred in more superficial levels of the volcanic edifice thereby yielding several series of differentiation of relatively short duration as for its geochemistry etna s volcanism is of oceanic type but with its own characteristics and in a peculiar geodynamic context at the edge of the african plate

palaeoenvironmental change recorded in the palaeodunefields of the western murray basin south australia new data from single grain osl dating this study is concerned with the reconstruction of the palaeoenvironmental history of southeastern australia for the last 300 ka by establishing a luminescence chronology of dune sand deposition in the western murray basin south australia in the study area vast fields of palaeodunes stabilised by vegetation provide evidence of past environmental change in total 98 samples were collected from dune sand layers at 13 different dune sections the time of their deposition was determined using optically stimulated luminescence dating of single quartz grains accounting for the impact of post depositional mixing by the use of a finite mixture model the oldest depositional phase demonstrates that dune sand layers of great antiquity are preserved in the western murray basin ranging up to at least 380 ka phases of substantial dune sand deposition were identified for the periods 18 38 ka and 63 72 ka older depositional phases also exist but are poorly resolved due to relatively large errors of the luminescence ages aeolian deposition during the last termination and the holocene is relatively limited with a slight clustering of ages at the time of the antarctic cold reversal and from 5 8 ka two modern ages give evidence of very recent dune sand deposition comparison with other palaeoclimate records from the region suggests that phases with high aeolian sedimentation coincide with more arid conditions and breaks in the dune record with more humid phases thus although dune records are often discontinuous and their interpretation in palaeoclimatic terms is not always straightforward the palaeodunes of the western murray basin show a good preservation of phases of aeolian activity and provide useful information for palaeoenvironmental reconstruction

the evolution of periglacial patterned ground in east anglia uk during the late pleistocene east anglia experienced multiple cycles of periglacial activity this research investigates whether chalkland patterned ground infilled with coversand developed during one or more glacial cycles or only during the last period of intensive periglacial activity to affect lowland britain single grain luminescence ages from polygons and stripes at six sites in east anglia suggest that the patterns experienced multiple phases of activity during the last 90 10 ka but do not date back to earlier glacial cycles this activity is attributed to four main phases 1 55 60 ka 2 31 35 ka 3 20 22 ka and 4 11 12 ka most sites show some activity around the greenland stadial 2a and the younger dryas stadial but polygons show a longer more temporally and spatially varied record than stripes interpreted phases of activity mostly coincide with stadials within the last glacial interglacial cycle possibly at the end of climatic cold phases

sublimates obtained during fusion of volcanic glasses abstract during fusion of volcanic glasses under vacuum in a gas analysis system sublimates condense out on the walls of the silica sample tube these sublimates were analyzed using x r d and energy dispersive x ray analysis coupled to a s e m successive mineral zones characterized by different compounds condense out in the following order from high to low temperatures 1 cristobalite 2 villiaumite and 3 halite and sylvite in addition there is strong evidence for the presence of digenite between zones 1 and 2 and sphalerite interspersed with the alkali halides these zones are very similar to recently described natural examples and those collected in sample tubes from high temperature fumaroles under reducing conditions because the laboratory examples can be linked to melt and gas compositions under controlled thermal conditions they may prove useful in relating natural sublimate types to the coexisting phases and the prevailing conditions during volcanic emission

the sedimentary structure of linear sand dunes linear sand dunes dunes that extend parallel to each other rather than in star like or crescentic forms are the most abundant type of desert sand dune1 but because their development and their internal structure are poorly understood they are rarely recognized in the rock record2 models of linear dune development2 3 4 5 6 have not been able to take into account the sub surface structure of existing dunes but have relied instead either on the extrapolation of short term measurements of winds and sediment transport or on observations of near surface internal sedimentary structures from such studies it has not been clear if linear dunes can migrate laterally2 7 8 here we present images produced by ground penetrating radar showing the three dimensional sedimentary structure of a linear dune in the namib sand sea where some of the world s largest linear dunes are situated these profiles show clear evidence for lateral migration in a linear dune moreover the migration of a sinuous crest line along the dune produces divergent sets of cross stratification which can become stacked as the dune height increases and large linear dunes can support superimposed dunes that produce stacked sets of trough cross stratification these clear structural signatures of linear dunes should facilitate their recognition in geological records

dip and depth extent of density boundaries using horizontal derivatives of upward continued gravity data a new computer method was developed to derive values of dip and vertical extent as well as location for the truncated face of a horizontal plate model the method is based on lateral offsets of the zero crossover point of the second horizontal derivative of an upward continued gravity profile application requires that the distance to the upper surface of the model be known numerical tests indicate useful results are obtained when both the length of the gravity profile and the finite strike length of a model are at least three times the maximum depth extent of the model gaussian noise with a standard deviation of 1 mgal can be tolerated given an anomaly amplitude of 70 mgal an example from the trans hudson orogen of central manitoba canada indicates that the kisseynew metasedimentary gneisses extend over a vertical distance of 16 18 km and are separated from the baldock batholith to the north by a near vertical boundary

elongation and migration of sand dunes two distinct processes are known to act on dynamic dunes the process of migration by erosion on the windward side and deposition on the lee side typical for transverse dunes and the process of elongation typical for linear dunes these two processes are determined by wind direction relative to the dune alignment this article reviews the assertion that linear dunes experience lateral displacement in addition to elongation fieldwork on vegetated linear dunes vlds and gis work on seif dunes indicates no lateral migration for these dunes linear dunes can shift laterally only when a slip face formed on the lee side reaches the plinth of the dune the winds from both sides of the seif dune are never symmetric usually winds from one direction are more dominant and effective the outcome is the formation of peaks and saddles along the dune the strongest winds create a slip face on the lee side of the peak segments of the dune oblique to the dune alignment which reaches the base of the dune and displaces the peak downwind along the dune alignment the internal structure of the seif dune is formed mostly by this dominant wind direction and gives the impression that the dune has shifted laterally on the other hand there are cases in which the wind directions relative to dune alignment fall between those of transverse and seif dunes in such cases both processes act on the dune which subsequently experiences migration as well as elongation

biogeomorphic model of dunefield activation and stabilization on the northern great plains abstract a conceptual model is proposed for the activity of sand dune systems on the northern great plains that incorporates vegetation growth theory and geomorphic system theory dunefield activity is modeled as a cyclic phenomenon alternating between active and stable states with the latter as the system state attractor the model is divided into two constituent parts an activation model and a stabilization model the activation model is qualitative and describes the transition from stable to active dunes as the result of a climatic perturbation such as drought that decreases vegetation cover the intensity and duration of the climatic perturbation determines the rate of decline of vegetation cover the stabilization model is quantitative and describes the transition from active to stable dunes using a logistic model of vegetation growth small perturbations during stabilization can prolong the duration of recovery enabling dunes to remain active well after the initial perturbation despite the geographic focus of this study the model appears applicable to a variety of environments where dune activity is limited in part by vegetation cover

modelling vegetated dune landscapes this letter presents a self organising cellular automaton model capable of simulating the evolution of vegetated dunes with multiple types of plant response in the environment it can successfully replicate hairpin or long walled parabolic dunes with trailing ridges as well as nebkha dunes with distinctive deposition tails quantification of simulated landscapes with eco geomorphic state variables and subsequent cluster analysis and pca yields a phase diagram of different types of coastal dunes developing from blow outs as a function of vegetation vitality this diagram indicates the potential sensitivity of dormant dune fields to reactivation under declining vegetation vitality e g due to climatic changes nebkha simulations with different grid resolutions demonstrate that the interaction between the abiotic geomorphic processes and the biological vegetation component life introduces a characteristic length scale on the resultant landforms that breaks the typical self similar scaling of un vegetated bare sand dunes

etude geochimique des elements condenses au cours du refroidissement de la phase gazeuse volcanique etna 1976 des sublimes ont ete recoltes a l etna en 1976 le long d un tube en silice la mesure de la temperature du depot et l analyse elementaire par activation neutronique permettent de mieux comprendre des mecanismes magmatologiques metallogeniques et volcanologiques

last glacial maximum dune activity in the kalahari desert of southern africa observations and simulations abstract it has long been understood that as ephemeral landscape features sand dunes are highly sensitive to environmental change and thus their distribution and the timing of their development may provide clues to past climate dynamics the relationship between climate and dune activity however is neither simple nor straightforward with a range of controls affecting the balance between erodibility the availability of sediment for deflation and erosivity the potential for sediment transport to explore such complex systems over large spatial and temporal scales a number of dune activity indices dai have been created that incorporate wind speed and moisture balances to calculate the potential for and degree of dune mobilisation using modern weather station data these indices have generally been shown to provide reasonable indications of dune activity potential until recently however the detailed quantitative data required to inform these equations has not been available for past climate scenarios and attempts to determine the relative importance of the various controls of dune activity have relied on rough estimations of climatic parameters this paper combines data from monthly general circulation model gcm outputs from the coupled ocean atmosphere gcms for 21 ka with the most detailed dai equation presently available to calculate the potential for dune reactivation in southern africa during the last glacial maximum lgm 18 24 ka based on these data and calculations it is indicated that there was significantly less potential for dune activity across southern africa at 21 ka when compared to the aeolian sediment records from the region this study poses serious and fundamental questions about 1 the reliability of the model outputs 2 the degree to which dais are able to account for the complexity and dynamics of aeolian systems and or 3 the interpretation of dune records as palaeoclimatic proxies at millennial time scales

landscape dynamics and human environment interactions in the northern foothills of cho oyu and mount everest southern tibet during the late pleistocene and holocene abstract here we present an integrated earth surface process and paleoenvironmental study from the tingri graben and the archaeological site of su re located on the southern rim of the tibetan plateau spanning the past ca 30 ka the study area is characterized by cold climate earth surface processes and aridity due to its altitude and location in the rain shadow of the mount everest cho oyu massif and is thus sensitive to climatic and anthropogenic perturbations in this highly dynamic geomorphic environment paired cosmogenic nuclide results from boulders on a massive hummocky moraine in the southern tingri graben reveal complex exposure histories that limit our capability of directly dating the corresponding glacial advance and shed a note of caution on previously published single nuclide based exposure ages along the northern himalaya based on geomorphic considerations however the moraine clearly represents the local last glacial maximum and likely coincided with a 344 109 m drepression of discontinuous permafrost zone relative to today during the global last glacial maximum glgm this greatly intensified permafrost and periglacial hillslope processes and led to fluvial aggradation of the valley floors of 12 m we observe formation of a thick 50 cm pedo complex starting at ca 6 7 ka before present bp and erosional truncation at ca 3 9 ka bp widespread landscape instability and erosion characterize the region subsequent to 3 9 ka and intensifies in the 15th century ad several lines of geo archaeological evidence including the presence of pottery sherds sling shot projectiles and hammer stones within the sedimentary record indicate human presence at su re since ca 3 9 ka bp our data suggest that in the su re tingri area climatic conditions were warm and moist enough to allow vegetation expansion and soil formation only from ca 6 7 3 9 ka followed by weakening of the indian summer monsoon ism strength between ca 4 2 and 3 9 ka which is a prominent climatic event in the wider asian monsoon region and reflected in the investigation area by the 3 9 ka erosional boundary merging our holocene landscape reconstruction with the geoarchaeological evidence we speculate that the combined effect of little ice age lia cooling and an anthropogenic overuse of the landscape led to climatically induced landscape degradation and ultimately to an anthropogenically triggered ecological collapse in the 15th century such a scenario is in line with regional historical data on declining monastery construction and migration of the ethnic group of the sherpas from an earth surface dynamics perspective we find that transient landscape processes on the southern rim of the tibetan plateau are strongly linked to millennial scale changes in the ism intensity and duration we identify three types of unidirectional non linear ism landscape interactions given that the tibetan plateau is the largest high altitude landmass on our planet and our limited understanding of several of the key earth surface processes on the plateau we pinpoint the need for more long term quaternary scale empirical data particularly on permafrost and periglacial processes and human environment interactions

late holocene inland dune activity in the uk a case study from breckland east anglia inland dune fields found in breckland east anglia uk have previously been correlated with the widespread late devensian coversands of the region and a seventeenth century sandflood which is known to have inundated the village of santon downham a programme of optically stimulated luminescence and radiocarbon dating undertaken on the dunes at wangford warren and santon downham reveals that episodic aeolian activity has taken place during the last 7000 years five sand depositional phases on breckland dunes are identified c 6500 c 1600 1100 c 500 c 400 335 and from c 200 30 years before present between c 2120 1840 years ago and within the period 1100 300 years ago quiescent periods allowed the development of fen peat and soils local controlling factors on aeolian activity in breckland appear to be related to anthropogenic activities and livestock sheep and rabbits reducing vegetation cover and decreased precipitation and sea levels which led to lowering of water tables breckland aeolian activity when compared to the national and sub continental holocene aeolian activity record shows a high level of concordance the underlying forcing factor for late holocene dune activity in the uk and elsewhere in europe appears to be climatic instability in the north atlantic associated with both the little ice age and previous similar events which led to increased storminess climatic variability and lower temperatures

dynamic processes acting on a longitudinal seif sand dune abstract field measurements were made on a longitudinal dune in the sinai desert in order to understand its morphology and dynamics the field measurements contradicted the wind structure indicated by the helicoidal flow theory rather it was found that winds coming from two basically different directions at different times and striking the dune obliquely were responsible for sand transport and erosion or deposition along the lee flank the essence of this mechanism is the deflection of the wind airflow on the lee flank of the dune to a direction parallel to the crest line the occurrence of erosion or deposition depends upon the angle of incidence between the wind and the crest line when this angle is 40 the velocity of the deflected wind drops and deposition takes place on the lee flank the angle of incidence in each wind storm is changed intermittently between 30 and 100 along the dune because the dune meanders and because of the sinuous outline of the crest line in this manner sand transport and erosion or deposition occurs along the lee flank depending on the angle of incidence between the wind and the crest line as a result of the deflection of the wind the dune elongates at an average rate of more than 1 m per month peaks and saddles along the crest line advance at an average rate of 0 7 m per month the lack of uniformity in the effects of the wind on both sides of the dune creates a lack of uniformity in the rate of erosion and deposition this can explain the formation of peaks along the crest line of the dune

petrological notes on the 1983 lavas at mount etna sicily with reference to their ree and sr nd isotope composition the 1983 hawaiite of mount etna was sampled and analyzed for groundmass and mineral compositions rare earth element concentrations and sr nd isotope ratios microprobe data for coexisting mineral phases and glass show crystallization temperatures of around 1100 c from a rather differentiated hawaiite magma at rather highfo2 10 8 at 1100 c well above the qfm buffer the hawaiites are characterized by a marked enrichment in the light ree similar to other alkaline magmas the ce n yb n is greater than 10 a feature these hawaiites have in common with alkaline magmas erupted earlier on mount etna since the ce yb ratio cannot be affected by fractionation of clinopyroxene and plagioclase it is taken as an accurate reflection of the lree enriched nature of the hawaiites from this point of view the etnean hawaiites are identical to within plate alkaline magmas erupted on the hawaiian islands this similarity extends to the nd sr isotope features two hawaiites have87sr 86sr 0 70346 and 0 70352 and143nd 144nd 0 51286 and 0 51284 these data indicate a source similar to oceanic island basalts a source depleted in rb sr and nd sm for some period of time the sr isotope data are identical to that previously reported for mount etna extraction of hawaiites from depleted source regions requires either recent enrichment events mixing of asthenospheric and lithospheric melts or variable degrees of melting at present the data do not allow a clear decision the peculiar tectonic setting of mount etna between the relatively undeformed african foreland and the active aeolian volcanic islands may suggest contributions to the source region from subduction and within plate processes etnean lavas have a geochemical imprint of subduction related enrichment processes and they also share petrological and chemical features identical to oceanic island basalts whose source region has been affected by within palte enrichment processes

a 10 000 year record of dune activity dust storms and severe drought in the central great plains dune fi elds and loess deposits of the great plains of north america contain stratigraphic records of eolian activity that can be used to extend the short observational record of drought we present a 10 000 yr reconstruction of dune activity and dust production in the central great plains region based on 95 optically stimulated luminescence ages the integration of data from both eolian sand and loess is an important new aspect of this record clusters of ages defi ne episodes of extensive eolian activity which we interpret as a response to frequent severe drought at 1 0 0 7 ka and 2 3 4 5 ka with peaks centered on 2 5 and 3 8 ka sustained eolian activity occurred from 9 6 to 6 5 ka parts of this record may be consistent with hypotheses linking holocene drought to sea surface temperature anomalies in the pacifi c or atlantic oceans or to the el nino southern oscillation phenomenon but the record as a whole is diffi cult to reconcile with any of these hypotheses

history and mechanisms for the expansion of the badain jaran desert northern china since 20 ka geological and luminescence chronological evidence desert landscapes are widely distributed in the arid northern china the badain jaran desert bjd is located north west of the tengger desert td and ulan buh desert ubd with the yabrai and ba

a twenty one year record of surface change on a namib linear dune repeated surveying of two sites on a namib linear dune between 1980 and 2001 provides a 21 year record of dune surface change the surveys con rm the view that the dunes are not inactive relics but are responding to the present day wind regime they also provide no evidence that the dunes are migrating laterally examination of wind data for the survey period provides some evidence that the form of the crest of the dunes is actively responding to the natural year by year climate variability such that an increase in the frequency of easterly winds leads to the development of a double crested form while fewer easterly winds lead to a single crested form copyright 2003 john wiley sons ltd

blame it on the goats desertification in the near east during the holocene the degree to which desertification during the holocene resulted from climatic deterioration or alternatively from overgrazing has puzzled quaternary scientists in many arid regions of the world i

lateral migration thermoluminescence chronology and colour variation of longitudinal dunes near birdsville in the simpson desert central australia the longitudinal dunes of the simpson desert in the vicinity of birdsville have been reworked largely during the holocene from dunes deposited up to 80000 years ago or earlier the widespread asymmetry of these roughly northward trending dunes with steeper eastern faces and more gentle western faces supports wind rose data showing sand transporting winds from the southwest obliquely intersecting the dunes while this suggests a change in the wind pattern since the dune field was oriented it does not indicate that the dunes are necessarily shifting leeward eastward as a consequence it is hypothesized that the direction of migration is controlled by the extent to which the dunes are vegetated relatively well vegetated dunes can accrete sand on their gentle stoss slopes and erode on their lee slopes causing them to shift westward and hence obliquely into the wind a condition that probably prevails in wetter regions and during episodes of relatively humid climate in contrast in very dry areas or during arid phases sand can move unimpeded up a sparsely vegetated stoss face and over the crest to form an avalanche or slip face on the lee side thereby causing the dunes to shift eastward despite evidence that longitudinal dune crests can shift laterally to some extent the dunes in the western part of the simpson desert have not migrated either westward or eastward more than 100m or so from their pleistocene cores aeolian transport and partial or complete removal of iron cutans from around quartz grains results in dunes of widely varying colour yet of similar age

the 1989 1990 activity of etna magma mingling and ascent of h2oclsrich basaltic magma evidence from melt inclusions abstract the melt inclusions in olivine phenocrysts from basaltic tephra erupted by etna volcano during the 1989 1990 eruptive period were investigated for major elements cl and s by electron microprobe fluorine by pigme particule induced gamma ray emission and h 2 o by sims the results indicate the ascent of basaltic magmas with different k 2 o concentrations possibly related to different feeding dykes lk basaltic melt inclusions rich in cl s and h 2 o are trapped in olivine fo 84 from the 1990 tephra and represent the early crystallization stage their composition in major elements is quite similar to those of most of the historic and even pre etnean alkali basalts but significantly lower in k 2 o compared with the 1989 1990 lavas only scarce hk basaltic melt inclusions were observed in the outer rim fo 79 6 of reversely zoned olivine phenocrysts and correspond to late crystallization stage at low pressure high sulfur concentration s 0 3 wt is a general characteristic of the etnean basaltic magmas with h 2 o s ratio as high as 7 the volatile abundances of the etna primitive basalts were computed at 1 45 wt for h 2 o 0 17 wt for cl and 0 047 wt for f with a high cl f ratio close to 3 6 the 1989 lava samples with cl at 660 90 ppm and f at 770 30 ppm have suffered a significant cl loss the possible behaviour of the volatile phase as co 2 h 2 o even cl is discussed with h 2 o and chlorine late degassing and an active role of h 2 o during the lava fountaining activity

combining ground penetrating radar surveys and optical dating to determine dune migration in namibia ground penetrating radar gpr profiles across a complex linear dune in the namib sand sea have been used to image sets of cross stratification and their bounding surfaces a combination of radar facies analysis and radar stratigraphy has been used to interpret the radar profiles and define a relative chronology thick sets of cross stratification indicate when the dune was most active whereas thin sets of cross stratification are interpreted to indicate the increased prevalence of wind reversals and lower rates of dune migration with bounding surfaces formed during periods of stabilization non deposition or erosion a drilling and dating campaign was designed on the basis of the dune stratigraphy as defined by the gpr survey sampling was targeted at large sets of cross stratification formed when the dunes were most active and avoiding bounding surfaces formed when the dune was stable or even eroded the results from optical dating give ages between 0 34 0 02 ka and 1 57 0 07 ka indicating a time averaged dune migration rate of 0 12 m a 1 over the past 1600 years

the etnean lavas 1977 1983 petrology and mineralogy the products emitted by mount etna in the 1977 1983 period are porphyric sodic trachybasalts etnaites that though substantially higher in k2o resemble most of the historic lavas

the timing of linear dune activity in the strzelecki and tirari deserts australia abstract linear dunes occupy more than one third of the australian continent but the timing of their formation is poorly understood in this study we collected 82 samples from 26 sites across the strzelecki and tirari deserts in the driest part of central australia to provide an optically stimulated luminescence chronology for these dunefields the dunes preserve up to four stratigraphic horizons bounded by palaeosols which represent evidence for multiple periods of reactivation punctuated by episodes of increased environmental stability dune activity took place in episodes around 73 66 35 32 22 18 and 14 10 ka intermittent partial mobilisation persisted at other times throughout the last 75 ka and dune activity appears to have intensified during the late holocene dune construction occurred when sediment was available for aeolian transport in the strzelecki and tirari deserts this coincided with cold arid conditions during marine isotope stage mis 4 late mis 3 and mis 2 and the warm dry climates of the late pleistocene holocene transition period and late holocene localised influxes of sediment on active floodplains and lake floors during the relatively more humid periods of mis 5 also resulted in dune formation the timing of widespread dune reactivation coincided with glaciation in southeastern australia along with cooler temperatures in the adjacent oceans and antarctica

fluorine geochemistry of basaltic rocks from continental and oceanic regions and petrogenetic application fluorine contents in about 300 samples of various types of basalts and related rocks from continental southwestern u s a zaire deccan and south africa and oceanic regions hawaii and mid atlantic ridge between 23 n and 40 n were determined by a selective ion electrode method

chlorine isotope composition of volcanic gases and rocks at mount etna italy and inferences on the local mantle source abstract we present the first chlorine isotope compositional data for gases and lavas from mount etna italy and to our knowledge of active mediterranean volcanism we investigated lavas erupted and gases discharged during 2008 2011 from a high temperature fumarole ht 300 c and plume gases from both north east and central craters most of the samples vary in a narrow range of chlorine isotope composition 37 cl values 0 0 7 with gases partially overlapping with rocks only ht gases sampled in 2009 have been clearly affected by secondary processes 37 cl values 15 9 resulting in partial removal of chlorine and isotopic fractionation producing a 37 cl enrichment in the residual gaseous hcl these secondary processes also affect although to a lesser extent plume gases from north east crater nec although post magmatic processes are able to modify the chlorine isotope composition 37 cl values are not affected by magma degassing for residual fractions 0 3 in the melt or any effect is within our data variability finally 37 cl values and cl k ratios of magmatic chlorine constrain the etnean source to be compatible with depleted mantle dmm contaminated by altered oceanic crust aoc in agreement with indications from more common isotopic tracers of mantle processes

reproducibility and utility of dune luminescence chronologies abstract optically stimulated luminescence osl dating of dune deposits has increasingly been used as a tool to investigate the response of aeolian systems to environmental change amalgamation of individual dune accumulation chronologies has been employed in order to distinguish regional from local geomorphic responses to change however advances in dating have produced chronologies of increasing complexity in particular questions regarding the interpretation of dune ages have been raised including over the most appropriate method to evaluate the significance of suites of osl ages when local noisy and discontinuous records are combined in this paper these issues are reviewed and the reproducibility of dune chronologies is assessed osl ages from two cores sampled from the same dune in the northeast rub al khali united arab emirates are presented and compared alongside an analysis of previously published dune ages dated to within the last 30 ka distinct periods of aeolian activity and preservation are identified which can be tied to regional climatic and environmental changes this case study is used to address fundamental questions that are persistently asked of dune dating studies including the appropriate spatial scale over which to infer environmental and climatic change based on dune chronologies whether chronological hiatuses can be interpreted how to most appropriately combine and display datasets and the relationship between geomorphic and palaeoclimatic signals chronological profiles reflect localised responses to environmental variability and climatic forcing and amalgamation of datasets with consideration of sampling resolution is required otherwise local factors are always likely to dominate using net accumulation rates to display ages may provide an informative approach of analysing and presenting dune osl chronologies less susceptible to biases resulting from insufficient sampling resolution

chronologies for late quaternary barchan dune reactivation in the southeastern arabian peninsula abstract the liwa region of the united arab emirates contains some of the largest and most areally extensive megabarchanoid sand dunes on a global scale here we present optical dating results on samples of aeolian sediment from deep drill cores extracted from the largest dune field of the liwa area optical dating of these core sediments using the single aliquot regeneration protocol indicates mid late holocene phases of rapid dune deposition the most recent period of reactivation began at ca 2 8 ka this event was preceded by a period of deposition at ca 5 ka these results suggest that the dune systems of the southeastern arabian peninsula are closely linked to changes in late quaternary global climate particularly linked to the intensity and spatial extent of palaeomonsoon rainfall since the last precessional maxima at ca 9 ka at which time a peak in monsoonal rainfall has been recognised a significant environmental transition to widespread desert conditions occurred in an apparently abrupt fashion during the initial period of aridification large quantities of sand were transported and deposited in the form of large and very large up to 160 m high scale aeolian bedforms following the initial phase of aeolian accumulation the system appears to have remained in stasis

fluorine speciation in topsoils of three active volcanoes of sicily italy fluorine is one of the many environmental harmful elements released by volcanic activity the content of total oxalate extractable and water extractable fluorine was determined in 96 topsoils of three active volcanic systems of southern italy mt etna stromboli and vulcano total fluorine f content f tot ranges from 112 to 7 430 mg kg 1 f extracted with oxalate f ox ranges from 16 to 2 320 mg kg 1 2 93 of f tot and f extracted with distilled water f text h text 2 text o ranges from 1 7 to 159 mg kg 1 0 2 40 of f tot fluorine in the sampled topsoils derives both from the weathering of volcanic rocks and ashes and from the enhanced deposition due to volcanic gas emissions either from open conduit passive degassing mt etna and stromboli or from a fumarolic field vulcano fluorine accumulation in the studied soils does not generally present particular environmental issues except for a few anomalous sites at vulcano where measured contents could be dangerous both for vegetation and for grazing animals

ftir remote sensing of fractional magma degassing at mount etna sicily abstract the chemical composition of volcanic gas emissions from each of the four summit craters of mount etna was measured remotely in may 2001 using a fourier transform infrared ftir spectrometer operated on the upper flanks of the volcano the results reveal constant hci hf ratio but distinct so2 hc1 and so2 hf ratios in the emitted gases which in the light of melt inclusion data for etna basalts can be interpreted in terms of escape of gases from partially and variably degassed magma at different depths beneath the summit gases released from the three main summit craters bocca nuova voragine and northeast had an identical composition controlled by bulk degassing of a single magma body that had previously lost c 25 0 of its original sulphur the similar gas composition at all three main craters suggests that these are connected to a central conduit system that branches at relatively shallow depth measurements of the bulk volcanic plume on the same day c 7 km downwind show that degassing from these craters dominated the total gas output of the volcano and that no significant chemical evolution occurred within the plume over a time scale of c 12 min weaker gas emissions from the southeast crater were comparatively depleted in so2 so2 hc1 and so2 hf ratios a factor of two lower implying that this crater is fed either by a separate conduit or by a branch of the central conduit whose geometry favours solubility controlled volatile fractionation still lower so2 hc1 and so2 hf ratios measured for residual degassing of a lava flow erupted from the southeast crater verify the lower solubility and earlier escape of sulphur compared to halogens at etna fractional magma degassing is also implied by strong chemical contrasts between the bulk volcanic plume and fissure gas emissions measured during the july august 2001 flank eruption these results highlight the ability of ftir spectrometry to detect fine spatial and temporal variations in magma degassing processes and thereby constrain models of shallow plumbing systems introduction magmas contain dissolved volatiles h20 co2 s c1 f etc with differing solubility behaviom which gradually reach a saturation pressure and exsolve into a separate gas phase bubbles during magma ascent and crystallization this volatile phase plays a central role in magmatic and volcanic processes e g anderson 1975 and its chemical composition changes from depth to the surface according to the pressure controlled solubility behaviour of each volatile species but also as a function of the dynamics of magma supply and ascent sparks 2003 this volume in fact gas bubbles may rise with either the same velocity as surrounding magma allowing continuous gas melt equilibration and single step bulk gas emission at the surface or with a higher velocity thereby reaching the surface independently of the parental magma batch e g sparks 1978 vergniolle jaupart 1986 in the latter case chemical equilibrium between gas and magma may be inhibited sustained high gas fluxes in excess of lava production on basaltic volcanoes such as etna and stromboli typically require a separated bubble flow and in the long term convective renewal of volatile rich magma from depth francis

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

crustal suture preserved in the paleoproterozoic trans hudson orogen canada lithoprobe seismic reflection data acquired in 1994 within the trans hudson orogen include a 180 km profile that crosses the boundary between a collapsed marginal basin kisseynew domain and an older volcanic plutonic arc terrane lynn lake belt the seismic data image a prominent band of northeast dipping anastomosing reflections that extend to 10 s two way traveltime from the surface location of a geological boundary where interpreted oceanic crust is preserved and separate thick crust 16 s of the kisseynew domain from the abruptly thinner crust 12 s of the lynn lake belt highly reflective lower crust 10 16 s of the kisseynew domain dips gently northward and extends laterally for at least 40 km beneath the adjacent lynn lake belt in a manner reminiscent of the western alps complementary gravity modeling shows that the thickness of metasedimentary rocks within the kisseynew domain is 20 3 km the seismic image is interpreted as portraying a crustal scale collisional suture that formed as the end result of northward subduction of backarc basin crust ancestral kisseynew basin floor and subsequent contraction and thrusting of the remnant kisseynew basin fill under the margin of the lynn lake belt

modelling potential field sources in the gelibolu peninsula western turkey using a markov random field approach in this study a markov random field mrf approach is used to locate source boundary positions which are difficult to identify from bouguer gravity and magnetic maps as a generalized form of markov chains the mrf approach is an unsupervised statistical model based algorithm and is applied to the analysis of images particularly in the detection of visual patterns or textures here we present a dynamic programming based on the mrf approach for boundary detection of noisy and super positioned potential anomalies which are produced by various geological structures in the mrf method gravity and magnetic maps are considered as two dimensional 2 d images with a matrix composed of n1 n2 pixels each pixel value of the matrix is optimized in real time with no a priori processing by using two parameter sets average steering vector and quantization level m they carry information about the correlation of neighboring pixels and the locality of their connections we have chosen mrf as a processing approach for geophysical data since it is an unsupervised efficient model for image enhancement border detection and separation of 2 d potential anomalies the main benefit of mrf is that an average steering vector and a quantization level are enough in evaluation of the potential anomaly maps we have compared the mrf method to noise implemented synthetic potential field anomalies after satisfactory results were found the method has been applied to gravity and magnetic anomaly maps of gelibolu peninsula in western turkey here we have observed anafartalar thrust fault and another parallel fault northwest of anafartalar thrust fault we have modeled a geological structure including a lateral fault which results in a higher susceptibility and anomaly amplitude increment we have shown that the mrf method is effective to detect the broad scale geological structures in the gelibolu peninsula and thus to delineate the complex tectonic structure of gelibolu peninsula

geophysical transect across a paleoproterozoic continent continent collision zone the trans hudson orogen a summary and comparison of geophysical data and models for the trans hudson orogen in northern manitoba and saskatchewan are presented magnetic total field and bouguer gravity maps are used to define the along strike extension of geological domains of the orogen exposed on the canadian shield and a two dimensional density model is produced which accounts for the observed variations of the bouguer gravity field across the orogen an 800 km long crustal section across the entire continent continent collision zone including the edges of the bounding cratonic blocks is presented it incorporates seismic reflectivity seismic velocities resistivity and density models key results include 1 evidence for west vergent crustal stacking and exhumation in the eastern trans hudson orogen in the form of preserved moho topography and the presence of higher grade higher velocity rocks in the hanging wall of an east dipping crustal stack 2 definition of the eastward extent of the archean sask craton in the

why deposits of longitudinal dunes are rarely recognized in the geologic record dunes that are morphologically of linear type many of which are probably of longitudinal type in a morphodynamic sense are common in modern deserts but their deposits are rarely identified in aeolian sandstones one reason for non recognition of such dunes is that they can migrate laterally when they are not exactly parallel to the long term sand transport direction thereby depositing cross strata that have unimodal cross bed dip directions and consequently resemble deposits of transverse dunes dune parallel components of sand transport can be recognized in ancient aeolian sands by examining compound crossbedding formed by small dunes that migrated across the lee slopes of large dunes and documenting that the small dunes migrated with a component in a preferred along crest direction over the large dunes

plume chemistry provides insights into mechanisms of sulfur and halogen degassing in basaltic volcanoes abstract this paper deals with sulfur chlorine and fluorine abundances in the eruptive volcanic plume of the huge october 2002 january 2003 eruption of mount etna aiming at relating the relevant compositional variations observed throughout with changes in eruption dynamics and degassing mechanisms the recurrent sampling of plume acidic volatiles by filter pack methodology revealed that during the study period s cl and cl f ratios ranged from 0 1 6 8 and 0 9 5 6 respectively plume s cl ratios increased by a factor of 10 as volcanic activity drifted from paroxysmal lava fountaining mid and late november to passive degassing and minor effusion early january and then decreased to the low values s cl 0 1 typical of the final stages of the eruption parallel variations in chlorine to fluorine ratios were also observed a theoretical model is proposed for quantitative interpretation of these changes in plume composition the model calculates the composition of a volatile phase exsolving from an ascending etna magma based on knowledge of solubilities and abundances in the undegassed melt of sulfur and halogens t m gerlach eos 72 1991 249 254 255 according to this model degassing of etnean basaltic melt at high pressures and depths 100 mpa 3 km is likely to release a co2 h2o rich vapor phase with s cl molar ratios 1 extensive sulfur and chlorine degassing from the melt would take place at shallower depth p

monitoring surface change on a namib linear dune in tackling the apparently intractable problem of linear dune initiation and maintenance there has been a move away from large scale deductive models to smaller scale field studies of individual dunes this paper reports a study of surface change on a large complex linear dune in the namib desert southern africa the dune surface responds to a markedly seasonal wind regime in summer westerly winds erode sand from the west flank of the dune and deposit it on the easterly lee side of the dune crest in winter this pattern is reversed easterly winds erode sand from the east slope and deposit it on the west slope the crest therefore moves back and forth some 15 m each year returning at the end of a year s cycle to its position at the beginning the position of the base of the dune appears to remain fixed even though sand is moving throughout the dune system the dune does extend northward along some resultant of the westerly and easterly winds despite relatively high levels of activity especially at the dune crest there is no evidence of the breakdown of the linear dune form the conclusion must therefore be that linear dunes can be maintained in bimodal wind regimes and are not necessarily related to unidirectional parallel regimes as others have suggested

late quaternary environmental change in central southern africa new data synthesis issues and prospects much of the interior of central southern africa is a sand sea within which aeolian and lacustrine landforms and sediments of local and regional extent are preserved closed cave sites are restricted to very few locations while fluvial systems traverse the margins of the interior until the early 1990s chronologies of late quaternary environmental and climatic changes developed for this region were based on only a limited number of proxy data sets derived largely from lacustrine deposits and precipitates in particular directly determined ages from aeolian deposits the most extensive suite of features in the region were absent the application of luminescence dating techniques to dune sediments and the development of further detailed chronologies from cave precipitates is now providing a more comprehensive record for the last 50 ka with some chronologies extending back a further 100 ka we present and review these data assess their contribution to enhanced understanding of late quaternary environmental changes in the region and for the first time assess them against corrected radiocarbon ages from lacustrine sites it is concluded that there is now an enhanced understanding of the spatial and temporal complexity of climate changes affecting the region in the last glacial cycle including a complex record of punctuated aridity but that many issues including data set integration and forcing mechanism controls are imperfectly understood

the timing of coversand deposition in northwest norfolk uk a cautionary tale abstract coversand deposits consisting largely of reworked fluvial and glaciofluvial sediments blanket the landscape in discrete areas of northern and eastern england a newly discovered zone of coversand deposits has been found in northwest norfolk which shows stratigraphic evidence of episodic sand accretion the presence of involutions within the coversand at leziate signifies the occurrence of post depositional periglacial activity infra red stimulated luminescence irsl dating of feldspars has been undertaken on five samples from four sites within the new coversand zone three of the samples were insufficiently zeroed at deposition to provide accurate dates for deposition of the sand sheets challenging the assumption that coversands are all well bleached with consequent implications for existing thermoluminescence tl dates on uk coversands an irsl age of 12 825 1910 yr for well bleached sands at leziate shows that sand accretion occurred during the period of rapid climate transition at the end of the last glacial late holocene aeolian activity resulted in sand emplacement at ling common

late quaternary dune accumulation along the western margin of south africa distinguishing forcing mechanisms through the analysis of migratory dune forms abstract the west coast of south africa is situated at a critical location between temperate and subtropical oceanic and atmospheric circulation systems and palaeoenvironmental proxies from this region have the potential to elucidate issues concerning variations within these systems over glacial interglacical cycles while semi arid climates have hindered the preservations of organic proxies a variety of aeolian bedforms have been analysed in an effort to improve our understanding of environmental change in the region optically stimulated luminescence measurements of 51 samples from 15 reticulate dune sites along the west coast have enabled the identification of phases of aeolian activity as well as periods of relative geomorphic stability combined with data derived from previous studies of the region s sediment accumulating deposits and other palaeoenvironmental proxies periods of increased windiness are identified at 16 24 30 33 43 49 and 63 73 ka from approximately 17 12 ka decreasing transport capacity resulted in the stabilisation of the west coast s dune fields during the holocene altithermal 4 8 ka despite reduced wind strength increased aridity resulting from higher temperatures and a reduced influence of moisture bearing westerly systems appears to have trigged widespread remobilisation of the region s dune fields the combination of ages from a variety of dune forms with different development mechanisms and comparisons with a range of proxy data sources have allowed for an enhanced interpretation of the region s aeolian archives moving beyond simple correlations between dune activity and aridity

volatiles in basalts and andesites from the galapagos spreading center 85 to 86 w abstract glasses from submarine lavas recovered by the alvin submersible from the galapagos spreading center gsc near 86 w have been analyzed by electron microprobe for major elements and by high temperature mass spectrometry for volatiles the samples studied range in composition from basalt to andesite and are more evolved than typical morbs previous studies indicate that they are related to normal morb by extensive crystal fractionation in small isolated magma chambers the h 2 o cl and f contents of these lavas are substantially higher than any previously reported for morbs h 2 o cl and f abundances increase linearly with p 2 o 5 content which is used as an indicator of the extent of crystal fractionation the fe 2 o 3 feo fe 2 o 3 ratios measured in the andesite glasses progressively decrease with increasing p 2 o 5 content and are probably related to fractionation of fe tioxides reduced carbon gas species principally ch 4 and co were discovered in these glasses the presence of reduced carbon species in gsc glasses may be indicative of a more reduced oxidation state of the upper mantle than is commonly assumed

variations of cl f and s in mount etna s plume italy between 1992 and 1995 this study investigates data on the cl f and s concentrations of plume filter samples collected between 1992 and 1995 from mount etna the samples were collected during eruptive and noneruptive activity and show fairly constant cl f ratios but wide variation in the cl s ratios the determination of the cl f ratio between 5 and 14 allows an estimate of f degassing to be derived that ranges from 10 to 30 of the initial f content of the magma the variation in the cl s ratio fits an empirical two stage degassing model where gas with high cl s ratio is discharged during quiescient degassing and gas with low cl s ratios is discharged during eruptive degassing the typical permanent degassing occurs from a depth at which chlorine exsolution exceeds sulfur exsolution cl s 1 the opposite of this behavior is observed during eruptive periods when significant sulfur degassing occurs because magma degasses at near atmospheric pressure cl s 0 1 the cl s ratio in the plume characterizing the type of degassing has the potential to be a useful geochemical tool for monitoring the volcano

the onset of dune formation in the strzelecki desert south australia abstract this study is concerned with the late quaternary climatic chronology of the strzelecki desert dunefields in central australia the sand ridges comprise layers of quartz sand some of which include palaeosol horizons with carbonated rootlets providing excellent opportunity for dating of alternations of dune building and stability by using optically stimulated luminescence osl deduced from the osl age of the oldest aeolian layer dated we conclude that the onset of aridity dates back to at least 65 ka older phases of aeolian activity though following a fluvial depositional phase 160 ka ago cannot be excluded although no aeolian layers giving evidence for this have been found in the two dunes dated here unconsolidated dune sands in the upper part of one section with late holocene 4 ka to modern depositional ages indicate a reactivation of the dunefield in recent times from the crosscheck of 14 c ages of the carbonated rootlets with osl results it is concluded that under the given environmental conditions radiocarbon dating of the calcareous rootlets is not able to provide reliable ages for the phase of soil development

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

linear dune accumulation chronologies from the southwest kalahari namibia challenges of reconstructing late quaternary palaeoenvironments from aeolian landforms abstract the linear dunes of the southern kalahari dunefield constitute one of the major palaeoenvironmental proxies in the region the application of optically stimulated luminescence osl dating since the1990s and advancements in the depth of sampling using augering equipment over the past few years have permitted the reconstruction of linear dune accumulation chronostratigraphies for entire dune profiles from base to crest these methods are applied to four dunes in the mariental stampriet region of the southern kalahari dunefield sampled at predominantly 0 5 m intervals individual dunes record multiple phases of dune construction but with only a few phases recorded consistently between two or more of the dunes results from the 48 osl ages produced here extend the aeolian accumulation record for the southern kalahari dunefield through the last three glacial interglacial cycles with two ages from the early part of mis6 a synthesis of all existing luminescence ages for the southern kalahari reveals that the dunefield has been partially active throughout much of the past 120 ka there are no clear clusters of ages within osl age errors this is in contrast to previous syntheses of ages for this region in addition these new data from mariental stampriet dunes show that clusters in grouped dune osl ages can be spuriously produced as a function of reducing the sampling frequency with depth within the dunes from 0 5 to 1 mintervals this has significant implications for previous conclusions regarding discrete phases of aeolian accumulation based on sampling at 1 m intervals and less vertically intensive sampling techniques the total luminescence data set of 136 ages for the southern kalahari implies that this dunefield has been close to the threshold of reactivation throughout much of the late quaternary

complex systems in aeolian geomorphology aeolian geomorphology provides a rich ground for investigating earth surface processes and landforms as complex systems sand transport by wind is a classic dissipative process withnon linear dynamics while dunefield evolution is a prototypical self organisation phenomenon bothofthesebroadareasofaeoliangeomorphologyarediscussedandanalysedinthecontextofcomplexityandasystems approach afeedbackloopanalysisoftheaeolianboundary layer flow sediment transport bedforminteractions basedoncontemporary physicalmodels revealsthatthesystemisfundamentallyunstable oratmostmeta stable andlikelytoexhibitchaoticbehaviour recent field experimental research on aeolian streamers and spatio temporal transport patterns however indicates that sand transport by wind may be wholly controlled by a self similar turbulence cascade in the boundary layer flow and that key aspects of transport event timeseriescanbefullyreproducedfromacombinationof self organised 1 fforcing motionthreshold andsaltationinertia theevolutionof various types of bare sand dunes and dune field patterns have been simulated successfully with self organising cellular automata that incorporateonlysimplifiedphysically basedinteractions rules becauseoftheirundefinedphysicalscale however itnotclearwhether they in fact simulate ripples bedforms or dunes landforms raising fundamental cross cutting questions regarding the difference between aeolian dunes impact ripples and subaqueous current ripples and dunes an extended cellular automaton ca model currently under development incorporates the effects of vegetation in the aeolian environment and is capable of simulating the development of nebkhas blow outs and parabolic coastal dunes preliminary results indicate the potential for establishing phase diagrams and attractor trajectories for vegetated aeolian dunescapes progress is limited however by a serious lack of appropriate concepts for quantifying meaningful state variables at the landscape scale state variables currently used in the bare sand models are far from capturing the rich 3d topography and patterns and are not sufficiently discriminative to distinguish different attractors the vegetationcomponentintheextendedmodel andindeedecogeomorphicsystemsingeneral poseevengraverchallengestoestablishing

high temperature low pressure metamorphism in the kisseynew domain trans hudson orogen crustal anatexis due to tectonic thickening the kisseynew domain within the central trans hudson orogen constitutes a high temperature t and low to medium pressure p metasedimentary belt characterized by uniform peak metamorphic conditions of 750 50 c and 5 6 kbar 1 kbar 100 mpa to investigate the thermal evolution of the kisseynew domain 1 dimensional thermal modelling was conducted for a range of thermal parameters including the effects of exhumation and incorporating current information about the crustal architecture the results show that tectonic thickening of the sedimentary pile to 40 km consistent with present day thickness estimates and erosional levels is capable of producing enough crustal heating to melt the base of the sedimentary pile advect heat to shallower crustal levels and produce the observed p t conditions deep seated mantle heat sources though not excluded are not required

the gravity profile and its role in positioning the edge of a two dimensional faulted structure having an arbitrary vertical variation of density it is shown analytically that as long as there is no lateral variation of density within a two dimensional faulted structure the value of gravity at any point on the upward extension of the fault remains constant consequently this result leads to a direct method of gravity interpretation where it is possible to delineate the edge of such a faulted structure by continuing the surface gravity values upward to different levels and then by using suitable numerical techniques find the desired resulting straight line gravity contour the method has been verified using several theoretical models and applied to two sets of real data to demonstrate its usefulness on a local scale the gloucester fault near ottawa canada appears to be nearly vertical on a larger scale the gravity signature along the southern appalachian cocorp seismic profile can be explained by density jumps across a steeply dipping major crustal discontinuity

etude geochimique et petrogenese des laves de l etna sicile italie an extensive set of samples representative of the evolution of etna since the beginning of its activity in the quaternary has been analyzed for trace element contents by neutron activation on whole rock samples major element data were taken fromtanguy 1980

melt inclusion investigation of the volatile behaviour in historic alkali basaltic magmas of etna crystallization paths of basaltic 1763 eruption and hawaiitic 1865 and 1329 eruptions scoria from etna were deduced from mineralogy and melt inclusion chemistry the volatile behaviour was investigated through the study of melt inclusions trapped in the phenocrysts and those of the whole rocks and the matrix glasses the results from the 1763 eruption point to the early crystallization of olivine fo 81 7 from a water rich alkaline basalt with high cl 1750 2000 ppm and s 2100 2400 ppm concentrations the hawaiitic melt inclusions trapped in olivine fo 74 salite and plagioclase are characterized by a decrease in cl k2o and s k2o ratios in each investigated system there is good correlation between k2o and p2o5 in the whole rocks cl ranges from 980 to 1680 ppm from basaltic to hawaiitic lavas whereas s 110 136 ppm remains low cl and s behaviour in the 1763 magma suggests an early degassing stage of cl and s with co2 and a water rich gaseous phase for a pressure close to 100 mpa consistent with a permanent outgassing at the summit craters of etna during the eruption the sulphur remaining in the hawaiitic liquid is lost and the degassing of chlorine is limited such a degassing model can be extended to the 1865 and 1329a d eruptions

subsurface geology of the ariana region diapir zone northern tunisia by means of gravity analysis gravity data were used to investigate subsurface geology in the ariana region from the diapir zone in tunisia our study area is located in the north eastern part of the maghrebides affected by the alpine orogeny despite the smooth topography and the low density of the quaternary series integrated geological data and gravity responses bouguer anomaly and derivative mapping help decipher the geological heterogeneities beneath the quaternary overburden the interpretation of the gravity data points to alignments of positive anomalies delineating two major orthogonal features that are thought to characterize the subsurface deep structures 1 a lineament striking north west at the emplacement of an actual horst bordered by a buried fault system directed n140 and 2 a second counterpart striking north east and is clearly expressed in the surface outcrops these principal structural features were described as the result of a regional tectonic compressive phase dating the miocene this phase was marked by reactivation and oblique slip displacements of regional faults some of which n070 are reverse and south east vergent further faulting enhanced the ascension of triassic evaporites in diapir structures this tectonic evolution may be integrated in the regional tectonic scheme of alpine orogeny induced by a collision between african and european plates

fluorine in basalts from iceland the fluorine content of icelandic tholeiitic and alkaline basalts matches values found in similar rocks from other areas covariation between fluorine and incompatible minor elements such as potassium or phosphorus is found in evolved tholeiites and alkali basalts lack of such covariation in primitive olivine tholeiites indicates that fluorine and other incompatible minor and trace elements are not controlled by minerals such as amphibole mica or apatite in the mantle residue and that the covariation between these elements in the evolved basalts cannot be inherited from the mantle model calculations on rocks from the langjokull area show that olivine tholeiite suites are if derived by simple fractional crystallization enriched in incompatible elements much in excess of the increase due to crystal removal these observations are taken to indicate that the well documented covariation between fluorine and other incompatible elements is not established until evolution of the basaltic magma has started in crustal holding chambers the constancy of element ratios and enrichment in excess of what can be accounted for by crystal fractionation or incremental addition of new batches of primitive magmas does indicate 1 mineral control involving amphibole mica or apatite and 2 addition of fluorine potassium and phosphorous from an external source it is argued that this source is the crustal envelope of the holding chamber

wetting and drying of australia over the past 300 ka alternately dry and wet climatic episodes across central and eastern australia during the past 300 ka have greatly affected australia9s rivers lakes and dune fields evidence of widespread climate and flow regime changes has been provided by 75 thermoluminescence tl dates and 18 u th dates from alluvial and eolian sediments fluvial conditions dominated part of the last two interglacials stage 5 and 7 resulting in large sand loads in rivers in the present simpson desert and southeastern australia during the last interglacial fluvial activity in central australia peaked at 110 ka stage 5 pluvial probably 5 10 ka behind world temperature and sea level maxima following the last late interglacial wet phase aridity associated with dune building spread from central australia toward its margins achieving greatest intensity during the last glacial maximum a less widespread wet phase identified at about 55 35 ka stage 3 subpluvial is associated with high lake levels and paleochannel activity in southeastern australia this tl record of variable continental aridity in australia correlates well with global changes including the variable eolian dust flux into central china the northern pacific ocean and antarctica

investigating parabolic and nebkha dune formation using a cellular automaton modelling approach vegetation plays an important role in shaping the morphology of aeolian dune landscapes in coastal and semi arid environments where ecogeomorphic interactions are complex and not well quantified we present a discrete ecogeomorphic aeolian landscape model decal capable of simulating realistic looking vegetated dune forms permitting exploration of relationships between ecological and morphological processes at different temporal and spatial scales the cellular automaton algorithm applies three simple rules that lead to self organization of complex dune environments including nebkhas with distinctive deposition tails that form in association with mesquite type shrubs and hairpin long walled parabolic dunes with trailing ridges that evolve from blowouts in association with vegetation succession changing the conditions of simulations produces differing landscapes that conform qualitatively to observations of real world dunes the model mimics the response of the morphology to changes in sediment supply vegetation distribution density and growth characteristics as well as initial disturbances the introduction of vegetation into the model links spatial and temporal scales previously dimensionless in bare sand cellular automata grid resolutions coarser than the representative size of the modelled vegetation elements yield similar morphologies but when cell size is reduced to much smaller dimensions the resultant landscape evolution is dramatically different the model furthermore demonstrates that the relative response characteristics of the multiple vegetation types and their mutual feedback with geomorphological processes impart a significant influence on landscape equilibria suggesting that vegetation induces a characteristic length scale in aeolian environments this simple vegetated dune model illustrates the power and versatility of a cellular automaton approach for exploring the effects of interactions between ecology and geomorphology in complex earth surface systems

evaluating the use of dune sediments as a proxy for palaeo aridity a southern african case study abstract the dominance of dryland environments in the southern hemisphere makes the study of these regions of critical importance for the development of regional hemispheric and global models of environmental change unfortunately the wetting and drying cycles associated with semi hyperarid climates are not conducive to the preservation of traditional organic proxy data sources the last decade however has seen the development of a number of alternative archives including the application of luminescence dating techniques to dunes and other aeolian deposits in continental situations the existence of relict dune fields has long been thought to be evidence of drier conditions during the pleistocene and direct ages from these features have been interpreted almost exclusively as indicating phases of aridity however an increasing number of ages from a broader range of environments are calling into question the assumption that aeolian activity can be simply equated with aridity presented here is a comparison of dune ages that have been obtained from across southern africa with a range of proxies from both terrestrial and marine records taken as a whole three primary phases of activity can be identified at 60 40 35 20 and 17 4 ka the frequent discordance with other terrestrial records indicating coeval increases in humidity and the close correlation of these phases with wind strength proxies suggest that aridity is unlikely to be the sole or even primary forcing mechanism for aeolian activity in the region and the palaeoclimatic significance of these sedimentary archives needs to be reassessed

late quaternary aeolian dunes on the presently humid blue mountains eastern australia abstract sand dunes on the newnes plateau 1000 m a s l west of sydney were active during the last glacial maximum the scattered sand dunes are forested under the modern humid temperate climate regime dune types range from parabolic to transverse lee dunes and sand sheets or patches all point to the presence of conditions marginal for aeolian activity made possible through wind acceleration on windward slopes ready sand supply from the weathered sandstone of the plateau and sparse vegetation cover modern climate envelopes of sand dune activity in australia predict that unrealistically drier conditions are necessary to allow wind transport at this site only additional impediments to plant growth such as lower temperature and lower atmospheric carbon dioxide concentrations appear to allow the necessary conditions for dune formation these observations and conclusions extend our understanding of the extremes of the lgm climate in humid eastern australia confirming that the widespread treeless vegetation was also sparse even in areas that today have annual rainfall above 1000 mm

aeolian dune field self organization implications for the formation of simple versus complex dune field patterns abstract the interpretation of aeolian dune field patterns as self organizing complex systems is a new paradigm in which pattern evolution may be addressed computer simulations supported by field and experimental data indicate that a given wind regime produces a simple dune field pattern dune type and crest orientation are determined by wind regime and pattern ordering occurs through dune dune interactions over time because dunes reorient only at their crest terminations with a change in wind regime the rate of formation of a new pattern of small dunes is typically faster than the rate of reorientation of the existing pattern resulting in the superposition of simple patterns to give rise to complex patterns complex patterns are distinct from spatial changes in a simple pattern and from the type of superposition that characterizes compound complex dunes complex patterns necessarily indicate a rate of pattern formation that is rapid compared to the rate of sediment accumulation on the depositional surface

understanding linear dune chronologies insights from a simple accumulation model abstract dunefields are today often found in regions where environmental conditions are no longer conducive to widespread aeolian transport and deposition and are thus seen as potential archives of palaeoenvironmental information some dune types are more suitable for this purpose than others and linear dunes used here synonymously with longitudinal dunes have been most frequently employed they are commonly found in dryland and dryland marginal regions and they are apparently less migratory than some other dune forms thereby offering the potential for longer environmental histories most recent studies have employed optical osl dating surveys which directly date the emplacement of dune sands to attempt to produce a representative history of aeolian accumulation at a dunefield scale yet such studies have not always given due consideration to the geomorphology of linear dune accumulation although linear dunes do not rework their sand as readily as say barchans dunes it is clear that sand deposited during an aeolian event is likely to have been removed from elsewhere on the dunefield s surface for this reason all dune archives must be assumed to be discontinuous over long timescales the effect of sediment redistribution on dune preservation and thus palaeoenvironmental interpretation is difficult to observe and poorly understood we present a simplified probabilistic model to replicate deposition erosion of sand at a linear dune crest thus simulating the type of profile sampled in many field studies in order to produce a local accumulation history the modelled sand flux incorporates various feedbacks and the simulations are run with varying boundary conditions in which the simulated surface is assumed to be in equilibrium over the multi millennial timescales of the model s duration periodic instabilities in the landscape are generally well recorded by the modelled dune accumulation history particularly when the events involve the system as a whole briefly functioning out of an equilibrium state i e the probabilities of deposition and reworking are not equal however under forcing conditions where the probabilities are unchanged throughout the duration of the model run the results can show apparent structure within the data when sample sizes are low although at large sample sizes the preservation potential decays with burial age according to a power law the model confirms the importance of rigorous sampling strategies for such studies but also suggests that if such precautions are taken the reworking inherent to linear dune aeolian systems does not preclude their use as a quaternary palaeoenvironmental archive of environmental change

environmental impact of magmatic fluorine emission in the mt etna area universita degli studi di palermo italy istituto nazionale di geofisica e vulcanologia sezione di palermo unione europea fondo sociale europeo

variable vegetation cover and episodic sand movement on longitudinal desert sand dunes abstract longitudinal linear sand dunes of the simpson and strzelecki dunefields in eastern central australia present a paradox low levels of activity today stand in contrast to luminescence dating which has repeatedly shown deep deposits of sand on dune crests dating to within the late holocene in order to investigate the nature of dune activity in the simpson strzelecki dunefield vegetation and sand mobility were investigated by detailed vegetation survey and measurement of rippled area and loose sand depth of dunes at three sites along a climatic gradient the response of both vegetation and sand movement to inter annual climate variability was examined by repeat surveys of two sites in drought and non drought conditions projected plant cover and plant crust cover were found to have inverse linear relationships with rippled area and the area of deep loose sand no relationship was found between these measures of sand movement and the plant frontal area index a negative exponential relationship between equivalent mobile sand depth on dune surfaces and both vascular plant cover and vascular crust cover was also found there is no simple threshold of vegetation cover below which sand transport begins dunes with low perennial plant cover may form small dunes with slip faces leading to a positive feedback inhibiting ephemeral plant growth in wet years and accelerating sand transport rates the linear dunefields are largely within the zone in which plant cover is sufficient to enforce low sand transport rates and in which there is a strong response of vegetation and sand transport to inter annual variation in rainfall both ephemeral plants mostly forbs and crust were found to respond rapidly to large 20 mm month rainfall events on millennial time scales the level of dune activity is controlled by vegetation cover and probably not by fluctuations of wind strength land use or extreme decadal time scale drought may destabilise dunes by removing perennial plant cover accelerating wind erosion

age and dynamics of linear dunes in the namib desert bristow c s duller g a t lancaster n 2007 age and dynamics of linear dunes in the namib desert geology 35 6 555 558 sponsorship american chemical society

chlorine and fluorine in tholeiitic and alkaline lavas of etna sicily abstract chlorine and fluorine were measured from whole rock samples from tholeiites 150 000 years old to present day hawaiites the overall range of f content is from 240 to 985 ppm with a slight decrease of f th and f cl ratios from tholeiites to hawaiites chlorine is positively correlated with th cl th 100 as well as k2o and p2o5 as the differentiation progresses and increases from 220 ppm in tholeiites to 2410 ppm in mugearites data obtained from present day hawaiites indicate that cl lost by degassing during eruption is limited however cl contents of some whole rock samples are inconsistent with previous results published for melt inclusions of phenocrysts from the same historic hawaiite samples and suggesting outgassing of cl prior to the eruption this implies that apparent correlation between cl and th can be considered as the result of superimposition of several petrogenetic processes results point out the richness of etnean tholeiites in chlorine compared to m a r basalts such a character could have been inherited from the mantle source or during the mantle source melting

volcanic tremors and shocks associated with eruptions at etna sicily september 1980 abstract three strong ash eruptions superimposed on an otherwise rather quiet state of volcanic activity took place from the northeast crater of etna during september 1980 the eruptions lasted only a few hours and were associated with an increase in the amplitudes of volcanic tremors by a factor of 10 compared with the mean value of the preceding months special emphasis in the tremor analysis was given to the eruption of september 26 1980 the time function of the amplitude envelope of the tremors follows a mathematical function which resembles the behaviour of a mechanical oscillator with a resonant period of about 300 s a detailed spectral analysis of the tremors before during and after the eruption reveals factors which seem to be associated with the ascent and descent of the tremor sources in the magma columns the turbulent eruptive magma flow apparently is concentrated in a few dykes and pipes their eigenvibrations during an eruption are observed as spectral peaks of small bandwidth superimposed on the smoother spectrum without a volcanic eruption an analysis of seismicity shows a maximum in august with epicenters clustering along a nw se direction

aeolian fluvial interaction evidence for late quaternary channel change and wind rift linear dune formation in the northwestern simpson desert australia in central australia the most easterly extent of the macdonnell ranges border the simpson desert dunefield where widely spaced strike ridges intercept and isolate pockets of broad crested linear dunes that reflect regional changes in late quaternary climate flow regime and channel avulsion an energetic todd river reworked the eastern part of camel flat basin from 75 65 ka until the last glacial maximum lgm when it shifted eastwards but with some flows persisting through the basin until about 10 ka resulting desert surfaces of different age facilitate temporal comparisons of linear dune formation fine grained red dunes 75 65 ka in age occur on the western floor of the basin and are ramped against the foot slopes of the range after the lgm and especially during the holocene the river s departure enabled small pale coloured closely spaced coarser textured linear dunes to form on the abandoned floodplain in the eastern basin their orientation 20 farther west than the larger and older red dunes this realignment indicates that the australian wind whorl shifted southwards some 160 km or 1 5 after the lgm linear dunes in the northwestern simpson desert were formed by wind rifting involving vertical accretion of sand from a proximal source not by long distance sand transport with linear extension the blocking ranges have caused negligible downwind sediment accumulation over the past 75 ka

aclas a method to define geologically significant lineaments from potential field data abstractgeologic features such as faults dikes and contacts appear as lineaments in gravity and magnetic data the automated coherent lineament analysis and selection aclas method is a new approach to automatically compare and combine sets of lineaments or edges derived from two or more existing enhancement techniques applied to the same gravity or magnetic data set aclas can be applied to the results of any edge detection algorithms and overcomes discrepancies between techniques to generate a coherent set of detected lineaments which can be more reliably incorporated into geologic interpretation we have determined that the method increases spatial accuracy removes artifacts not related to real edges increases stability and is quick to implement and execute the direction of lower density or susceptibility can also be automatically determined representing for example the downthrown side of a fault we have evaluated aclas on magnetic anomalies calculated from a simple slab model and from a s

dunes in southeastern namibia evidence for holocene environmental changes in the southwestern kalahari based on thermoluminescence data abstract linear dunes in the southwestern kalahari provide evidence of the nature of paleoclimates they have special significance because their alignments indicate a previous circulation pattern with prevailing northwesterly winds at present the bases of the dunes are fixed by vegetation and only the dune crests are active in contrast to previous suggestions final dune stabilization took place before about 9 8 ka this corresponds to reduced wind velocities accompanied by more humid conditions this seems to be the last important environmental change recorded by significant landforms in the southwestern kalahari since about 8 ka the region remained more or less semi arid the long distance to seasonal south shifting humid tropic air masses innertropical convergence zone itcz and the climatic barrier of the namib and the karas mountains against atlantic influences allowed only minor fluctuations the holocene is a period of reduced pan development the pans are partly buried by the early holocene linear dunes as well as by young sand fields at pan 1073 southeast of grootpan intra pan dunes have formed during the last 1000 years

wind energy variations in the southwestern kalahari desert and implications for linear dunefield activity the southwestern kalahari linear dunefield which displays marked morphological variability possesses a partial but temporally and spatially variable vegetation cover and has frequently been described as a palaeodunefield palaeo status has been ascribed on the basis of several criteria including the presence of vegetation but also because dunes are thought to be out of alignment with modern resultant potential sand moving wind directions and because present day wind energy is regarded as low for the period 1960 1992 wind data from eight dunefield meteorological stations are analysed in detail to examine these assertions potential sand transport directions including spatial and temporal variations and potential drift directions for the windiest three month periods are calculated and explained it is concluded that the present day potential sand transport environment is markedly variable from year to year and from place to place while periods of low sand transport energy do occur it is also noted that the 1980s possessed considerable potential for sand transport in the dunefield directional variability is also relatively high perhaps exceeding that under which linear dunes can be expected to form because linear dune aeolian activity has a number of states however the present day wind environment may allow dune surface aeolian activity to occur which does not alter the overall pattern of the dunes

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

degradation of linear dunes in northwest ngamiland botswana and the implications for luminescence dating of periods of aridity the long morphodynamic history of the linear dune system of northwest ngamiland comprises both construction and degradation processes here we describe features resulting from the latter crest lowering during wet periods is associated with lateral transfer of sand into the straats weathering and leaching have mobilised iron to the base of the dune profiles and have corroded the quartz grains satellite image interpretation indicates that dune sand has been diluted by bioturbation which transferred damaran saprolite from below the dunes to the surface flooding and waterlogging have modified and in places completely destroyed the original crisply linear morphology small linear collapse features across the linear dunes are associated with open fractures or faults where water infiltration is facilitated the implications for luminescence dating of dune sands to identify periods of aridity are discussed the dunes cannot simply be regarded as providing a stacked record of such periods they are very old and much of the record is missing as a result of crest lowering the chronostratigraphy includes degradational components which must be distinguished from those of construction bioturbation cannot be disregarded as a complication which overprints the luminescence signals

dune mobility and vegetation cover in the southwest kalahari desert as part of a wider project investigating the palaeoenvironmental significance of partially vegetated linear dunes in the southwest kalahari data collected in the latter part of 1992 concerning dune movement and vegetation cover suggest that sediment transport is occurring on some dune surfaces and that the majority of surface activity occurs on the crests and upper slopes of the dunes the data suggest that the limiting variables on surface sediment movement vary on different parts of a dune on interdunes and lower dune slopes the primary limiting variable is available wind energy while on dune crests and upper slopes it is vegetation cover ground cover by litter has much greater importance in protecting the surface sediment from erosion than rooted vegetation from individual data points no evidence is found to support a threshold vegetation cover below which sediment movement occurs rather a gradient of activity is suggested whereby a reduction in vegetation cover increases the potential for sediment movement and surface change however dunes with differing amounts of mean vegetation cover display differing degrees of surface activity and at this scale a vegetation cover threshold in the region of 14 per cent may be recognized

late holocene landscape instability in the breckland england drift sands abstract this research investigates the landscape instability associated with the drift sands which are widespread across north western europe it focuses on breckland uk using new sites along with existing geomorphic archaeological and historical data this shows landscape instability of drift sands occurred at 5240 1040 years bce 600 100 1150 50 1600 and 1790 ce comparison of these phases to climate records show no clear patterns with drifting occurring during dry wet as well as cold warm periods additionally similar climatic shifts lead to diverging reactions of landscapes in different regions throughout europe at the regional scale land usage and population pressures also may not be the direct cause of sand drifting suggesting that complex responses or different triggers at different times were responsible within this society s unawareness of the inherent landscape instability and the threat posed by the sand hazard may have been important as it affected whether mitigation measures were or could be implemented in breckland initial instability may have been due to the establishment of the open field system on virgin soil later changes in land ownership and associated power within the society led to an inability of communities to implement mitigation measures and large land owners abstaining from tackling the sand hazard whilst the widespread coversands and climatic extremes provide the underlying susceptibility to sand drifting it would appear that drift sands of the last 2000 years may provide less of a sedimentary archive of late holocene climatic changes and more a record of land management changes

thermoluminescence dating of the british coversand deposits abstract coversand deposits thought to be of lateglacial age are found in britain in north lincolnshire south west lancashire and central east anglia a comprehensive dating study of them using thermoluminescence tl techniques is currently underway in an attempt to link the british coversand deposits to the european coversand chronology initial results from four of the british coversand sites sampled are presented the 26 tl dates from 14 samples show that in lincolnshire aeolian deposition took place from 12 5 ka to i1 ka cessation of the initial sand deposition was synchronous with this in lancashire but sand deposition occurred significantly earlier in east anglia the upper layers of aeolian sand in lancashire are much younger and are attributed to holocene reworking on the basis of these dates lincolnshire and lancashire coversand deposition occurred at a similar time to the younger coversand ii whilst east anglian coversand deposition coincided with the younger coversand i phase in the european coversand chronology

evolution of the etna volcano information from the southern wall of the valle del bove caldera abstract the greater part of etna can be regarded as a complex strato shield volcano constructed from the overlapping products of several centres of trachy basaltic activity the valle del bove is a horse shoe shaped caldera 8 km long and 5 km wide cut into the eastern flanks of etna the caldera is one of the few areas on the volcano where historic eruptions have not obscured the products of pre historic centres of activity and these are well exposed in the cliff walls surrounding the caldera examination of these older volcanics provides important information on the eruptive style and internal plumbing of the etna volcano during pre historic times and suggests that both were significantly different from the present day much of the southern wall of the valle del bove represents a surviving portion of the trifoglietto ii volcano the largest pre historic centre of activity a stratigraphy is constructed for the southern wall the trifoglietto ii lavas and pyroclastics rest unconformably upon the eroded remnants of an older centre and are themselves overlain by the products of younger centres all the lavas exposed in the southern wall are of alkalic affinity and comprise a trachybasaltic suite ranging from hawaiite to benmoreite variation in the chemistry of the lavas can be explained by their differentiation at high levels in the crust from a more basic magma of alkali olivine basalt hawaiite composition an anomalous trend in the tio 2 content of the trifoglietto ii lavas may be explained by the fractionation of kaersutite ti rich amphibole a study has been made of the numerous dykes exposed in the walls of the valle del bove the alignments of which parallel trends which are important on etna at the present time it is proposed that the initial opening of the valle del bove occurred sometime between 20 000 and 10 000 y b p as a result of a phreatic or phreato magmatic explosion near the base of the eastern flank of trifoglietto ii this is visualised as triggering a slope failure and resulting in the destruction of much of the centre by a catastrophic landslide this mechanism has much in common with the explosive eruptions which produced both the bandai san japan caldera in 1888 and the mount st helens caldera in may 1980