growth and collapse of the reunion island volcanoes this work presents the first exhaustive study of the entire surface of the reunion island volcanic system the focus is on the submarine part for which a compilation of all multibeam data collected during the last 20 years has been made different types of submarine features have been identified a coastal shelf debris avalanches and sedimentary deposits erosion canyons volcanic constructions near the coast and seamounts offshore criteria have been defined to differentiate the types of surfaces and to establish their relative chronology where possible debris avalanche deposits are by far the most extensive and voluminous formations in the submarine domain they have built four huge submarine bulges to the east north west and south of the island they form fans 20 30 km wide at the coastline and 100 150 km wide at their ends 70 80 km offshore they were built gradually by the superimposition and or juxtaposition of products moved during landslide episodes involving up to several hundred cubic kilometers of material about 50 individual events deposits can be recognized at the surface the landslides have recurrently dismantled piton des neiges les alizes and piton de la fournaise volcanoes since 2 ma about one third are interpreted as secondary landslides affecting previously emplaced debris avalanche deposits on land landslide deposits are observed in the extensively eroded central area of piton des neiges and in its coastal areas analysis of the present day topography and of geology allows us to identify presumed faults and scars of previous large landslides the submarine bulges are dissected and bound by canyons up to 200 m deep and 40 km long filled with coarse grained sediments and generally connected to streams onshore a large zone of sedimentary accumulation exists to the north east of the island it covers a zone 20 km in width extending up to 15 km offshore volcanic constructions are observed near the coast on both piton des neiges and piton de la fournaise volcanoes and are continuations of subaerial structures individual seamounts are present on the submarine flanks and the surrounding ocean floor a few seem to be young volcanoes but the majority are probably old eroded seamounts this study suggests a larger scale and frequency of mass wasting events on reunion island compared to similar islands the virtual absence of downward flexure of the lithosphere beneath the island probably contributes to this feature the increased number of known flank failure events has to be taken into consideration when assessing hazards from future landslides in particular the probability of landslide generated tsunamis

volcano destabilization by magma injections in a detachment we report the discovery of a detachment fault within reach of structural investigation in a shield volcano piton des neiges la reunion hotspot the detachment exposed by erosion is located between the top of an extinct gabbroic magma chamber and a cover of debris avalanche deposits the fault simultaneously concentrated ductile and brittle deformation toward the sea hydrothermal alteration in the greenschist facies and repeated sill injections of basic magmas our study of this exceptional detachment exposure suggests that two mechanisms participate in volcano flank failure hydrothermal alteration likely sustained by the heat of cooling sills induces slow inter intrusion deformation whereas sill injections in the fault may trigger rapid cointrusive slip this twofold process of destabilization might currently occur on some active volcanoes such as piton de la fournaise

deposits related to degradation processes on piton des neiges volcano reunion island overview and geological hazard abstract piton des neiges pn volcano on reunion island offers a rare opportunity to study deposits related to degradation processes in a deeply eroded oceanic shield volcano both the inner parts and flanks reveal a large amount of resedimented volcaniclastic material including extensive debris avalanche deposits pn litho structural units first studied by upton and wadsworth 1965 philos trans r soc lond a 271 pp 105 130 are re examined this review highlights the importance of long volcanic repose periods and erosion processes during pn history volcaniclastic deposits have been studied in the field in order to evaluate the spatial and temporal distribution of the three main types of pn degradation processes the deposits of these processes have been classified into 1 talus 2 mudflow and debris flow and 3 debris avalanche lithology frequency and estimated volumes of each deposit type imply that the structural evolution of pn can be considered in terms of the competition between the volcanic productivity and the degradation and erosion processes the occurrence of huge catastrophic avalanches produced by flank failure is convincingly linked to the basaltic activity of pn which implies a very low risk at present on the contrary mudflows and debris flows pose an important risk due to the high population density focussed around the basin outlets moreover if smaller debris avalanches can occur in the cirques of pn another major risk must be evaluated

age and nature of deposits on the submarine flanks of piton de la fournaise reunion island abstract debris avalanche deposits are by far the most extensive and voluminous formations in the submarine domain around reunion island 21 sites sampled offshore of piton de la fournaise were studied all the dredged rocks have a volcanic origin and often consist of blocks buried in a finer grained matrix both massive and vesiculated samples were found but only rare fragments of pillow lavas were encountered all the lavas are basalts with variable amounts of olivine a few plagioclase bearing basalts were also found these lithologies are known among piton de la fournaise subaerial lavas a set of fresh samples representing the various rock types was further studied the microscopic characteristics of these lavas confirm their great similarity with lavas from the subaerial volcano major elements show that all the submarine lavas are transitional basalts with compositions very similar to those of piton de la fournaise subaerial lavas the petrological and geochemical similarity of the dredged samples with piton de la fournaise subaerial lavas indicates that they belong to this volcano the sulfur contents of the dredged samples and of various subaerial lavas from piton de la fournaise were determined on whole rocks the results suggest that massive or slightly vesiculated dredged lavas 0 005 0 010 wt s probably correspond to the internal parts of slowly cooled and subaerially degassed lava flows the dredged pillow lavas display sulfur contents 0 013 0 020 wt s similar to those of the external parts of recent subaerial lavas this indicates that they were primarily degassed in the atmosphere as also suggested by noble gases data or in shallow water only one dredged sample has a relatively high s content 0 034 wt suggesting that it may have been an early lava of a subaerial eruption or a lava directly emplaced under water though at shallow depth thus both the nature of the dredged samples and their sulfur contents indicate that these lavas were subaerially emitted these results thus give strong evidence for landslide deposits having their source areas on land k ar and 230 th 238 u dating were also performed on some samples the dredged lavas involved in the landslides of the volcanic edifice are mostly in the range of 110 ka to

geomagnetic field intensity between 70 000 and 130 000 years b p from a volcanic sequence on la reunion indian ocean abstract a detailed paleointensity study was made of a sequence of 70 successive lava flows of the piton des neiges volcano on the island of la reunion indian ocean radiometric dating brackets the age of this sequence between 130 3 ka and 72 3 ka rock magnetic investigations show that titanomagnetites in the pseudo single domain range are the main magnetic carrier of the natural remanent magnetisation nrm over 350 samples were used for paleointensity determinations carried out with the thellier method in vacuum or in an argon atmosphere of these 89 samples yielded reliable results with within flow scatter often lower than 20 these results indicate that the geomagnetic field intensity has varied at la reunion between 13 and 65 t during the period of time explored the average value 42 t is higher than the present field at la reunion 35 t the results from the upper part of the section are consistent with previous results obtained for the 82 98 ka period also at la reunion 1 and document a broad low around 95 ka not associated with large directional changes on a larger geographic scale the paleointensity values from la reunion are significantly higher than those obtained from mount etna 2 precise comparison is however difficult because of the lack of detail in the etna results in the lower part of the section a marked intensity low coinciding with significant deviation from the dipole field direction is observed at 115 ka and could correspond to the end of the blake event

the eruptive history of morne jacob volcano martinique island french west indies geochronology geomorphology and geochemistry of the earliest volcanism in the recent lesser antilles arc martinique is the lesser antilles island where the most complete volcanic history of the arc can be found from the oligocene to the present time in this study we focused on the construction of morne jacob shield volcano in martinique which is the largest volcano of the lesser antilles we have dated twenty representative samples from the morne jacob by k ar based on the cassignol gillot technique used geochemical data and obtained morphological constraints that have helped us to reconstruct better the volcanic history of this shield volcano our results and the lack of reliable ages on other plio pleistocene islands show that the morne jacob is the oldest volcano of the aerial recent arc that has been dated so far it has a longer history than previously inferred with different stages ranging between 5 2 and 1 5 ma a large basaltic to andesitic shield volcano was first built between 5 2 and 4 0 ma j1 with tholeiitic lavas characterized by an increase of sio2 content through time after 800 kyr of repose calc alkaline andesites erupted over the first shield from 3 2 to 2 2 ma j2a the accumulation of lavas over a hyaloclastitic basement provoked spreading and northeast creeping of the northern flank of the volcano the mass movement induced regressive erosion particularly at the centre of the edifice then between 2 1 and 1 5 ma j2b calc alkaline lavas which show a decrease of the sio2 content through time erupted at the central vent and from peripheral fissures over the previous shield and down to the caribbean coast eruptive volumes were reconstructed permitting estimates of minimum output rates for the volcano s history minimum volume erupted during the first stage is 112 20 km3 and 33 25 km3 during the whole second stage yielding rates of about 0 107 km3 kyr and 0 019 km3 kyr respectively considering the entire history of morne jacob shield volcano between 5 14 0 07 and 1 54 0 03 ma we obtain a total volume of 145 32 km3 above the sea level and a time averaged construction rate of 0 040 0 008 km3 kyr with comparison between the reconstructed paleotopographies and the dem of present topography we have calculated an eroded volume of 18 km3 over the outcropping 210 km2 that have occurred during the last 1 5 myr finally our set of twenty k ar ages obtained on groundmass separates allow us to revise the eruptive chronology of morne jacob volcano and to date the earliest subaerial volcanic activity so far identified for the recent lesser antilles arc

three dimensional structure of the submarine flanks of la reunion inferred from geophysical data 1 la reunion indian ocean constitutes a huge volcanic oceanic system of which most of the volume is submerged we present a study of its submarine part based on the interpretation of magnetic and gravity data compiled from old and recent surveys a model of the submarine internal structure is derived from 3 d and 2 d models using constraints from previous geological and geophysical studies two large scale previously unknown buried volcanic construction zones are discovered in continuation of the island s construction to the east the alizes submarine zone is interpreted as the remnants of les alizes volcano eastward flank whose center is marked by a large hypovolcanic intrusion complex to the southwest the etang sale submarine zone is interpreted as an extension of piton des neiges probably fed by a volcanic rift zone over a large extent they were predominantly built during the matuyama period and thus probably belong to early volcanism a correlation exists between their top and seismic horizons recognized in previous studies and interpreted as the base of the volcanic edifice their morphology suggested a lithospheric bulging beneath la reunion not required to explain our data since the seismic interfaces match the top of our volcanic constructions the coastal shelf coincides with a negative bouguer anomaly belt often associated with magnetic anomalies suggesting a shelf built by hyaloclastites a detailed analysis of the offshore continuation of la montagne massif to the north confirms this hypothesis the gravity analysis confirms that the bathymetric bulges forming the northern eastern southern and western submarine flanks are predominantly built by debris avalanche deposits at the surface

ore genesis of the late cretaceous larong porphyry w mo deposit eastern tibet evidence from in situ trace elemental and s pb isotopic compositions abstract the late cretaceous ca 92 ma larong porphyry w mo deposit 39 44 mt wo3 0 1541 a newly discovered deposit in the easternmost bangong nujiang metallogenic belt bnmb is located in eastern tibet the w mo mineralization occurs as veins and stock works hosted in monzogranite porphyry granodiorite porphyry and surrounding quartz schist and can be divided into two main paragenetic stages the w mineralization stage stage i consists of various k feldspar quartz scheelite veins and the quartz sulfide stage stage ii is dominated by molybdenite and pyrite of which the latter can be further subdivided into three sub stages here we present la icpms in situ trace elements and s pb isotopes of sulfides from the larong deposit in order to constrain the sources of ore forming elements and the processes of mineralization our study shows that pyrite is rich in co and as molybdenite is rich in w pb and bi and chalcopyrite has high sn contents these results are consistent with the mineralization characteristics of the larong deposit where the main metallogenic elements are w and mo accompanied by bi sn and cu overall sulfides from the larong deposit have calculated 34svcdt values ranging from 0 25 to 6 37 suggesting a predominantly magmatic origin for sulfur from stage ii 1 to stage ii 2 to stage ii 3 the average 34svcdt values of pyrite change from 0 33 to 1 88 to 5 34 showing a progressive and gradual change in redox and temperature conditions molybdenite has high pb isotopic ratios 208pb 204pb 39 356 39 908 207pb 204pb 15 747 15 928 206pb 204pb 18 843 20 120 but low re contents and pyrite has low ni contents implying that the ore forming materials were mainly derived from the crust we propose that the w mo mineralization is genetically related to the late cretaceous monzogranite porphyry with the mineralization of w and mo occurring as a result of decreases in temperature and oxygen fugacity of the ore forming fluid exsolved from the magma in combination with previous studies our study led to the identification of three w dominated polymetallic metallogenic events and mineralization potential of igneous rocks in the bnmb

erosional valleys in the thaumasia region of mars hydrothermal and seismic origins analysis of erosional valleys geologic materials and features and topography through time in the thaumasia region of mars using co registered digital spatial data sets reveals significant associations that relate to valley origin valleys tend to originate 1 on noachian to early hesperian stages 1 and 2 large volcanoes 2 within 50 100 km of stages 1 and 2 rift systems and 3 within 100 km of noachian stage 1 impact craters 50 km in diameter these geologic preferences explain observations of higher valley source densities vsds in areas of higher elevations and regional slopes 1 because the volcanoes rifts and craters form high steep topography or occur in terrain of high relief other stage 1 and stage 2 high steep terrains however do not show high vsds the tendency for valleys to concentrate near geologic features and the overall low drainage densities in thaumasia compared to terrestrial surfaces rule out widespread precipitation as a major factor in valley formation as is proposed in wann wet climate scenarios except perhaps during the early noachian for which much of the geologic record has been obliterated instead volcanoes and rifts may indicate the presence of shallow crustal intrusions that could lead to local hydrothermal circulation melting of ground ice and snow and groundwater sapping however impact crater melt would provide a heat source at the surface that might drive away water fonning valleys in the process post stage 1 craters mostly have low nearby vsds which for valleys incised in older rocks suggests burial by ejecta and for younger valleys may indicate desiccation of near surface water and deepening of the cryosphere later hesperian and amazonian stages 3 and 4 valleys originate within 100 200 km of three young large impact craters and near rifts systems at warrego valles and the southern part of coprates rise these valleys likely developed when the cryosphere was a couple kilometers or more thick inhibiting valley development by hydrothermal circulation however eruption of groundwater may have occurred from impact induced fracturing and lateral and perhaps minor upward transport of water due to seismic pumping the two smaller craters formed along the plateau margin where the highest potential hydraulic head would occur in aquifers beneath the plateau in the case of the larger crater lowell 200 km in diameter potential aquifers would likely be at depths of kilometers below the cryosphere seismic energy generated by the lowell impactor would have been much greater pumping both groundwater and perhaps fluidized slurry to the surface from beneath the cryosphere to form the young valleys and flow deposit along the margin of thaumasia tectonic pressurization of groundwater also may have contributed to valley formation dissection of rim materials of the argyre impact may relate to tectonic activity and the unconsolidated state of basin ejecta

orographic precipitation in valley network headwaters constraints on the ancient martian atmosphere 1 we examine the martian valley networks in the framework of topographic influences on precipitation we use an analytical model and the laboratoire de meteorologie dynamique lmd early mars global circulation model gcm to explore the local scale distribution of orographically forced precipitation as a function of atmospheric pressure in simulations with 500 mbar and 1 bar co2 atmospheres orographic lifting results in enhanced snowfall upslope of the observed valley network tributaries our framework also suggests that a 2 bar atmosphere cannot create the observed valley pattern at the highest relief valley network warrego valles as in previous work the gcm does not generate temperatures warm enough for rain or significant snowmelt in the highlands with co2 greenhouse warming alone thus while transient periods of unusual warming are still required to melt the deposits and carve the valleys our model predicts snow deposition in the correct locations

the off shore continuation of an active basaltic volcano piton de la fournaise reunion island indian ocean structural and geomorphological interpretation from sea beam mapping abstract in 1984 a sea beam survey of the submarine east flank of piton de la fournaise was performed with r v jean charcot three main types of volcanic or volcano tectonic features have been identified 1 1 the subaerial ne and se volcanic rift zones of piton de la fournaise do not extend more than about five kilometers offshore unlike typical hawaiian rift zones which form narrow 2 4 km ridges extending tens of kilometers from the summit the active rift zones of piton de la fournaise widen downslope attaining more than 10 km at their front 2 2 the submarine extension of the grand brule slide is larger than the subaerial portion the entire slide forms a 7 24 km scar bounded by two ramparts to the north and south the slumped material may have moved as a debris flow forming a large talus downslope of the slide however the submarine counterpart of the south area of the grand brule seems to be composed by a slumped block whose structure is apparently not disturbed 3 3 another prominent feature is a conspicuous topographic high that occupies nearly all the center of the surveyed zone this cast flank submarine plateau cannot be associated with any active structure of piton de la fournaise its surface generally dips gently 2 3 and its northern and southern flanks are extensively cut by landslides cones of variable dimensions are observed on the plateau and farther to the east three hypotheses are examined to account for the origin of this morphology a remnant flank of an ancestral fournaise volcano associated with a large buried intrusion found by drilling beneath the grand brule b distinct volcanic massif or c material of a huge and ancient landslide the geophysical data show that the western part of this submarine plateau is reversely magnetized and associated with a moderate positive gravity anomaly this confirms that as suggested by the bathymetric analysis this part of the plateau is relatively coherent conversely the eastern portion of the plateau appears to be poorly magnetized and composed of low density material probably chaotic materials derived from landslides the reversed magnetization of the western part shows that the whole structure is older than 0 7 ma these results show that the volcanic history of piton de la fournaise is more complex than previously thought

fractal analysis of drainage basins on mars 1 we used statistical properties of drainage networks on mars as a measure of martian landscape morphology and an indicator of landscape evolution processes we utilize the mars orbiter laser altimeter mola data to construct digital elevation maps dems of several mostly ancient martian terrains drainage basins and channel networks are computationally extracted from dems and their structures are analyzed and compared to drainage networks extracted from terrestrial and lunar dems we show that martian networks are self affine statistical fractals with planar properties similar to terrestrial networks but vertical properties similar to lunar networks the uniformity of martian drainage density is between those for terrestrial and lunar landscapes our results are consistent with the roughening of ancient martian terrains by combination of rainfall fed erosion and impacts although roughening by other fluvial processes cannot be excluded the notion of sustained rainfall in recent mars history is inconsistent with our findings

dem based reconstruction of southern basse terre volcanoes guadeloupe archipelago fwi contribution to the lesser antilles arc construction rates and magma production abstract we combine radiometric ages and geomorphologic investigations to quantify the relief creation of well preserved volcanic surfaces applied to the volcanoes of southern basse terre guadeloupe lesser antilles arc the last 650 ka volcanic evolution of this island has been modeled using ten main stages constrained by k ar ages previously obtained on lava flows and domes from the volcanic massifs of the axial chain 1000 435 ka and from the grande decouverte volcanic complex 250 ka present based on the construction of a 250 000 point database inferred from the analysis of the guadeloupe digital elevation model 3d reconstructions of the successive volcanic stage landforms were calculated and the correlated geochronological maps drawn using arcgis software volumes and rates of construction were computed for each time span separating these ten stages the average construction rates calculated here are 2 4 0 3 10 4 km 3 yr for the last million years 0 9 0 3 10 4 km 3 yr for the last 100 ka and 0 9 0 2 10 4 km 3 yr for the last 15 ka although basse terre volcanism is characterized by a marked dominance of effusive products our estimates should be considered as minimum values because the material that went into the sea during explosive events was not taken into account however we note that a relatively high construction rate of 4 5 1 3 10 4 km 3 yr has been obtained for the icaques volcano which was emplaced during the 630 600 ka time interval within the depression formed by the first large scale flank collapse having affected southern basse terre the sudden release of the lithostatic load induced by this mass wasting event could explain this value which is significantly higher than the average value of 0 8 0 1 10 4 km 3 yr obtained for the last 650 ka finally the comparison with other analogous volcanic massifs from islands and continental arcs points to a relatively low magmatic production for southern basse terre which could be tentatively related to the relatively slow subduction rate of the atlantic plate

geomorphic evolution of the piton des neiges volcano reunion island indian ocean competition between volcanic construction and erosion since 1 4 ma abstract reunion island indian ocean is a volcanic complex whose eruptive history was dominated by the activity of two main edifices piton des neiges pn and piton de la fournaise pf volcanoes the tropical climate induces erosion processes that permanently compete with volcanic constructional processes exposed to the trade winds and associated heavy rainfalls the northeastern part of the island exhibits the most complex morphological evolution geomorphological analysis performed on a 50 m dem and associated to new k ar ages has clarified the overall history of pn volcano each massif is assigned to one of the main building stages of the edifice in addition the arrangement of these different massifs reveals that the eruptive phases have led to successive relief inversions and successive excavations of large central depressions in the proximal area as a result the younger massifs are always located in more proximal parts of the volcano the youngest being close to the edifice center in distal areas early lava flows were channeled into valleys incised along the massif boundaries leading to a more complex geochronological organization quantitative study of the dissection of pn volcano allows us to propose a minimum eroded volume of 101 44 and 105 41 km3 for the mafate and cilaos cirques depressions respectively during the last 180 kyr and a minimum average long term erosion rate of 1 2 0 4 km3 ka this leads us to estimate the removed volume during the whole history of pn volcano 1000 km3 as equivalent to the volume of the deposits identified on the submarine flanks of piton des neiges volcano therefore as regressive erosion appears to be the prevailing geomorphic process during the whole pn history it questions the presence of major flank collapses younger than 1 4 ma on this volcano erosion processes have largely been neglected in recent models but our study emphasizes them as a key component of landscape development and a major process in the morphological evolution of reunion island that has to be fully integrated in future studies

new 230th 238u and 14c age determinations from piton des neiges volcano reunion a revised chronology for the differentiated series 230th 238u age measurements were carried out on 18 samples of lava from piton des neiges these lavas range from basalts to trachytes the ages extend from 270 000 to 12 000 a b p and cover most of the period in which differentiated series magmas were erupted new 14c ages on charcoal sampled in young pyroclastic deposits are also presented the late stage evolution of the volcano is discussed in the light of these new ages and a chronology of the explosive activity is given the oldest pyroclastic flow ste suzanne is more than 220 000 a other pyroclastic units were emitted between 220 000 and 110 000 a there were at least two episodes of caldera formation the first episode is inferred to have occurred about 190 000 a ago the last occurred between 190 000 and 110 000 a although the most recent lava activity was mainly concentrated on the eastern flank of the volcano and around the summit area it also occurred about 70 000 a ago in the southwestern part of the massif the youngest explosive activity about 50 000 to 20 000 a on the eastern flank of the volcano has now been dated by three different methods 14c and th u ages on block and ash flow tuffs k ar ages on associated domes youthful explosive activity about 35 000 to 12 000 a on the western flank of the volcano is also demonstrated by 14c dating on charcoal and by a th u age of 12 000 a on a trachytic nuee ardente deposit this last age indicates that activity may have persisted later than previously supposed and implies a high rate of erosion for the cirque de mafate

topographic influences on development of martian valley networks 1 some morphometric differences between terrestrial and martian valley networks may reflect the precursor topography on mars particularly impact basins or tectonic slopes to evaluate these possible influences we mapped highland watersheds in nine study areas that sample a range of geographic and topographic settings we collected data including latitude longitude watershed length divide and terminal elevations watershed relief and slope slope orientation and qualitative descriptors including whether a drainage basin was open or closed the longest valley networks and most overflowed basins occur on preexisting intercrater slopes of 0 1 1 particularly on north facing slopes associated with the crustal dichotomy the control of watershed length by earlier noachian topographic features which the relict networks did not significantly modify suggests that the early to middle noachian geomorphic environment was nominally much drier than the later noachian to hesperian transition the distribution of fluvial valleys and likely orographic effects created by the crustal dichotomy suggest that evaporation from the northern lowlands was an important source of atmospheric humidity over short time scales much of the highland plateau consists of smaller enclosed watersheds which along with cooler temperatures detained surface water at high elevations lengthening or impeding the global water cycle ponding and evaporation may have partly offset a continentality effect of the highland landmass prolonged modification of the intercrater geomorphic surface prior to incision of valley networks included substantial weathering reduction of relief and gravity driven sediment transport indicating a long term role for surface water in a transport limited arid to hyperarid noachian paleoclimate

topography of small martian valleys abstract small valleys are common in the ancient highlands of mars valley widths are typically a few kilometers and are independent of length for valleys longer than about 50 km topographic profiles across several representative small valleys produced using one dimensional photoclinometry have smoothly curved shapes and valley side slopes of 10 20 profiles of unusual valleys from maumee valles the flanks of alba patera and softened terrain also have slopes of 10 20 but the profiles of maumee valles are more v shaped than those of the typical small valleys while the profiles of the softened valley have proportionately longer upslope convexities depths from 15 to 800 m are measured for the small martian valleys and most valleys have depths between 20 and 250 m the mean depth to width ratio from 135 measurements of 45 different valleys is 0 08 standard deviation 0 04 when valley profiles with uneven rims are excluded the mean depth to width ratio is 0 07 standard deviation 0 03 applying the lower ratio to the widths of a larger sample of small valleys yields depths that are almost all between 40 and 300 m the majority of the small valleys we have studied are probably the result of groundwater sapping and in this context the measured valley depths imply that liquid water was often less than a few hundred meters below the surface in the vicinity of these valleys at the time early in martian history when the valleys formed

gravity structure of piton de la fournaise volcano and inferred mass transfer during the 2007 crisis abstract the structure and mass transfers at piton de la fournaise volcano are investigated using new on land and offshore measurements the structures are defined using 2 and 3d modelling short wavelength positive anomalies to the w and nw of the central area are interpreted as shallow piles of thick dense lava flows which have filled volcano tectonic depressions several hundreds of meters deep this finding provides a new insight into the evolution of the volcano conversely the currently active central zone is associated with a negative short wavelength anomaly explained by the presence of thin highly vesiculated and fractured lava flows building the central cone low density formations underlying the rivieres des remparts and langevin areas are tentatively interpreted as breccias related to erosion and or to southward directed mass wasting topographic offshore highs in the continuation of the se and ne rift zones of piton de la fournaise are characterized by negative gravity anomalies and reversed magnetic anomalies their interpretation as hyaloclastites and pillow lavas provides a coherent explanation for both types of signals if we admit that they were primarily constructed during the alizes stage two main deeper dense structures are also found the grand brule complex and a complex beneath the plaine des sables and the enclos fouque both are identified as hypovolcanic intrusive complexes the grand brule complex 10 18 km in plan view shows a marked ns elongated geometry unlike the other comparable complexes on the island the plaine des sables enclos fouque complex a more or less circular structure 5 km in diameter is attributed to the ancient shield stage it is centered on the enclos fault suggesting that the paleo center of the ancient shield was located about 1 5 km eastward of the previously proposed location an apparent contradiction was noted between the seismic and gravity images of the internal structure in particular a high velocity cylinder beneath the summit was not detected in the gravity models this contradiction was resolved by considering the relative sensitivity of each method finally the gravity dataset has allowed us to explore the gravity changes that accompanied the major eruptive and volcano tectonic crisis of april 2007 350 m collapse of the summit and emission of 120 106 m3 of lava the change in the mass distribution of the edifice was large enough to be detected in the survey data collected in the central area before and after the crisis however the accuracy was too low for the precise assessment of the mass transfers

structure of reunion island indian ocean inferred from the interpretation of gravity anomalies abstract reunion is a volcanic edifice whose origin is related to a hot spot in the indian ocean only 3 of its volume is emergent many geological and geophysical studies were carried out on reunion island during the 1980 s but few of them allow study of the internal structure of the edifice several gravity surveys have been carried out on the island since 1976 and we have compiled the available data set the lack of data on the western side of the island led us to conduct a regional survey in 1993 to obtain a more homogeneous distribution of the stations computation of bouguer anomalies for different correction densities accounts for the variable density of the rocks constituting the edifice and provides a distribution of gravity anomalies interpreted as dense bodies of intrusive rocks inside the edifice two very large intrusive complexes can be unambiguously recognised one beneath piton des neiges and one beneath the grand brule area both have been penetrated by geothermal exploration drill holes and the first is also known from outcrop observations 2 5d simple models were constructed to reveal the geometry and extent of the buried intrusives they are deeply rooted extending several kilometres below sea level and extensive 20 25 km long and 10 13 km wide for the piton des neiges complex 12 15 km long and some kilometres wide for the grand brule complex the development of such complexes implies that the activity of the two volcanic centres was long lasting and remained stable while the volcanoes were growing the grand brule complex has been interpreted as relics of an old volcano named alizes volcano the interpretation of the gravity maps suggests the presence of a ridge of dense rocks to the north of the axis joining the centres of piton des neiges and piton de la fournaise volcanoes by analogy with the other structures 2 5d models show that this structure would culminate between 0 and 1 km below sea level and be 15 km wide this complex induces a maximum anomaly in takamaka valley and we thus propose to name it takamaka volcano no geological evidence of the nature of these dense rocks is available but the ridge coincides with structures revealed by magnetic and seismic data interpretation of the bouguer anomaly maps suggests that the inner gravity structure of piton de la fournaise is not characterised by the presence of a voluminous dense body but probably by more restricted concentrations of dense rocks some structures can be recognised along the present ne and se rift zones and in the previous central part of piton de la fournaise to the west of the present summit the recent eastward migration of the centre of activity of piton de la fournaise accounts for the lack of a large positive anomaly beneath the active craters

late alluvial fan formation in southern margaritifer terra mars 1 crater statistics indicate alluvial fans crater floor and fill mantling deposits within impact craters 50 km in diameter in southern margaritifer terra were likely emplaced during multiple epochs fans formed during the amazonian or near the amazonian hesperian boundary crater floor deposits are likely hesperian in age and most fill mantling deposits are amazonian the regional distribution of fans points to a late period of widespread water driven degradation two of the final candidate landing sites for the 2011 mars science laboratory mission would land on or near some of these fans which appear younger than previously considered

outflow channels with deltaic deposits in ismenius lacus mars abstract a connected series of outflow channels in the ismenius lacus quadrangle are identified for the first time and characterized using high resolution stereo camera images of mars express the context camera images of mars reconnaissance orbiter and the topography of the mars observer laser altimeter these channels named okavango valles which stretch over 400 km south to north and join the northern plains were identified from braided channels scour groove marks poorly sinuous valleys and depositional landforms discharge rates were estimated to 0 1 5 10 6 m 3 s 1 from analysis of the topography of scour marks pathways of channels segments were extracted from topography showing a unique source at a breached crater rim suggesting overflow from ponded depressions a series of delta fans are observed inside depressions along the channel pathways the presence of these deltas formed in former bodies of water is a compelling argument for formation of this outflow channel system by fluvial flows the similarity of these flows with other outflow channels on mars proves that volcanically related outflows cannot explain all such features in addition this study also shows that catastrophic floods are able to create fan deltas in transient lakes this example has to be taken into account in the interpretation of late stage fans associated with poorly branched valleys and single channels

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

gold mineralization in gaize area tibet gaize area is located in the western part of bangongcuo nujiang plate suture zone in tibet where original gold mineralization was poorly explored and studied and therefore the prospecting orientation was not clear based on the study of the metallogenic background characteristics and ages this paper discusses the model of gold mineralization in gaize area for the purpose of finding out some clues to gold prospecting studies show that gold deposits are mainly distributed in jurassic yanshiping group and mugagangri group both of which are typical epimetamorphic volcano sedimentary formations the yanshiping group occurs in tiegeshan area on the southern margin of qiangtang plate chip whereas the mugagangri group is present in dacha area and belongs to mugagangri block within the suture zone it is clearly known from tectonic and geochemical studies that the yanshiping group and mugagangri group were jurassic metastable flysch sedimentary rocks formed in the continental rift valley and marginal sea along the suture zone the formation of the strata was accompanied by large scale ophiolite and basic volcanic eruption as well as hydrothermal fluid activities on the ocean floor these processes concentrated such mantle derived materials as au and cu in the strata and hence the strata became the primary source bed of the gold ore deposits in the process of collision and amalgamation between the gangdise block and the qiangtang block at the late stage of early cretaceous the i type intermediate acidic magma rich in mantle derived components such as au and cu moved upward and heated the downward infiltrated marine water this caused the marine water to mix with the magmatic water thus forming the effective media such media extracted au from the primary source bed ophiolite basic and intermediate acidic magmatic rocks and carried au through various cracks in the rocks to form gold orebodies of transitional type between the altered rock type and the quartz vein type in late cretaceous the ocean basin came to a closure and the differential orogenic uplift took place as a result the top part of the original deposit was eroded resulting in the rebirth of the gold deposit and the formation of placers

40k 40ar dating of the main deccan large igneous province further evidence of ktb age and short duration most mass extinctions coincide in time with outpourings of continental flood basalts cfb some 20 years ago it was shown courtillot v besse j vandamme d montigny r jaeger j j cappetta h 1986 deccan flood basalts at the cretaceous tertiary boundary earth planet sci lett 80 361 374 courtillot v feraud g maluski h vandamme d moreau m g besse j 1988 deccan flood basalts and the cretaceous tertiary boundary nature 333 843 846 duncan r a pyle d g 1988 rapid eruption of the deccan flood basalts at the cretaceous tertiary boundary nature 333 841 843 that the age of the deccan traps was close to the cretaceous tertiary kt boundary and its duration under 1 myr we have undertaken a new geochronological study using the unconventional 40k 40ar cassignol gillot technique which is particularly well suited to the potassium poor deccan lavas the mean of 4 determinations from the topmost ambenali and mahabaleshwar formations is 64 5 0 6 ma they straddle the c29r c29n reversal boundary for which they provide a new constraint the mean age of 3 determinations from the oldest jawhar formation is 64 8 0 6 ma the difference in age between top and bottom of a 3500 m composite section probably comprising 80 of the total deccan volume is statistically insignificant with the overall mean age being 64 7 0 6 ma n 7 our results are consistent with the most recent 40ar 39ar determinations knight k b renne p r halkett a white n 2003 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps earth planet sci lett 208 85 99 knight k b renne p r baker j waight t white n 2005 reply to 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps discussion by a k baksi earth planet sci lett 239 374 382 confirming that there should be no systematic difference between the two methods when they are used in an optimal way an earlier smaller but significant pulse of volcanism between 68 and 67 ma extending over at least 500 km in latitude in the northern part of the deccan cfb has also been identified after 2 to 3 ma of quiescence the second major phase of volcanism occurred near 65 ma expanding over most of the area covered by the first pulse and another 500 km to the south consistent with drift of india by 300 to 450 km at not vert similar 150 mm yr during the quiescence period new paleontological data from the remote rajahmundry section keller g adatte t gardin s bartolini a bajpai s humler e in prep the cretaceous tertiary boundary in deccan traps of the krishna godavari basin of southeastern india epsl to be submitted suggest that this second pulse can itself be divided into two major pulses one starting in c29r and ending at the kt boundary the second starting in the upper part of c29r and ending within c29n

extraction of martian valley networks from digital topography 1 we have developed a novel method for delineating valley networks on mars the valleys are inferred from digital topography by an autonomous computer algorithm as drainage networks instead of being manually mapped from images individual drainage basins are precisely defined and reconstructed to restore flow continuity disrupted by craters drainage networks are extracted from their underlying basins using the contributing area threshold method we demonstrate that such drainage networks coincide with mapped valley networks verifying that valley networks are indeed drainage systems our procedure is capable of delineating and analyzing valley networks with unparalleled speed and consistency we have applied this method to 28 noachian locations on mars exhibiting prominent valley networks all extracted networks have a planar morphology similar to that of terrestrial river networks they are characterized by a drainage density of 0 1 km 1 low in comparison to the drainage density of terrestrial river networks slopes of streams in martian valley networks decrease downstream at a slower rate than slopes of streams in terrestrial river networks this analysis based on a sizable data set of valley networks reveals that although valley networks have some features pointing to their origin by precipitation fed runoff erosion their quantitative characteristics suggest that precipitation intensity and or longevity of past pluvial climate were inadequate to develop mature drainage basins on mars

the grand brule exploration drilling new data on the deep framework of the piton de la fournaise volcano part 1 lithostratigraphic units and volcanostructural implications abstract the sinking of a deep drill hole 3003 5 m for geothermal exploration in the eastern part of the piton de la fournaise volcano on reunion island has revealed the underlying lithostratigraphy six principal sequences have been distinguished a 0 440 m subaerial basaltic flows b 440 556 m a transitional series characterized by an alternation of subaerial basalts and submarine deposits vitric basalt and hyaloclastic breccia c 556 616 m submarine basalts lavas and hyaloclastites d 616 890 m subaerial basalts e 890 1010 m submarine basaltic deposits with abundant argillized hyaloclastites f 1010 3003 5 m a layered intrusive complex comprising 1010 1129 m sheets of gabbro injected into the lavas and hyaloclastites 1129 1920 m a zoned intrusion of olivine gabbro and dolerite 1920 3003 5 m stratified cumulate gabbro wehrlite dunite the occurrence of the first submarine deposits at 440 m 268 m below present sea level and the intercalation with them of subaerial basalts down to 890 m 728 m below present sea level tend to support a hypothesis of sliding into the sea during subsidence of the eastern flank of the fournaise massif the intrusive complex intersected from 1010 m down is regarded as a former shallow magma chamber a large positive gravimetric anomaly 40 50 mgal centered over grand brule and attributed to the intrusive complex indicates that its roof forms an ellipse 3 20 km elongated n s stratigraphic and morphological structural evidence on land and on the sea floor and the results of the mineralogical study of this very large magma chamber suggest that it belongs to an ancient edifice proto fournaise whose activity preceded the construction of the present fournaise and ended at about 0 6 ma on land the evidence for this earlier edifice is to be found in the zeolitised basalts and differentiated lavas hawaiites forming the basement to the phase 1 lava flows certain subsidence structures on the present fournaise are interpreted as resulting from settling of the proto fournaise volcano the destabilization of the east flank grand brule area of the currently active volcano and the location of the ne and se rift zones could be attributed to the same phenomenon

crossover analysis of mars orbiter laser altimeter data in its first 15 months of continuous operation the mars orbiter laser altimeter mola instrument aboard mars global surveyor ranged to mars over 330 million times generating more than 5000 orbital profiles with a ranging precision of 0 4 m over smooth terrain the accuracy of the profiles depends on knowledge of the spacecraft position orientation and observation time which are subject to errors we model these errors via the analysis of over 24 million altimetric crossovers a quasiperiodic once per revolution adjustment of the ground tracks as a function of time in three locally orthogonal directions minimizes the altimetric residuals via least squares using a sparse matrix technique computational effort scales linearly with the number of crossovers and only marginally with the number of parameters orbital errors mainly result from poor modeling of spacecraft thrusting events in the absence of tracking seasonal effects likely due to changing thermal environment as well as residual miscalibrations are evident in the pointing solutions incorporating multiple parameters per revolution significantly improves crossover residuals and resolves pointing aberrations during orbital transitions from night to day altimetry from the adjusted tracks generates a topographic model whose accuracy is typically better than 1 m vertically with respect to the center of mass of mars the centroid position of each mola shot is typically accurate to 100 m horizontally terrain models from accurately located lidar data can be gradient shaded to illuminate geological structures with 1 in 1000 slopes that are invisible to cameras temporal changes in elevation e g frost deposition ablation at decimeter levels may also be assessed using crossovers but results must be interpreted with caution due to uncertainties in range walk correction

reunion hotspot activitity through tertiary time initial results from the ocean drilling program leg 115 abstract leg 115 of the ocean drilling program recovered basaltic rocks from four sites along the ancient trail of the reunion hotspot the age of volcanism determined from biostratigraphic data at the four sites increases to the north and records the motion of india away from the reunion hotspot through tertiary time hotspot activity began with the eruption of the deccan flood basalt flows at the time of the cretaceous tertiary boundary the reunion hotspot has been stationary with respect to other hotspots in the atlantic and indian ocean basins through tertiary time the geochemical compositions of the drilled basalts differ according to the relative contributions of magmas from hotspot and morb mantle sources

a new model for the evolution of the volcanic island of reunion indian ocean the island of reunion has been studied using data from airborne and shipborne magnetic surveys the subaerial history of reunion spans the last 2 1 million years the brunhes matuyama geomagnetic reversal enables differentiation of volcanic rocks older and younger than 0 78 ma the lower submarine flanks are poorly magnetized and are interpreted as landslide deposits the core of the island is composed of highly magnetized rocks piton des neiges volcano is composed mostly of rocks older than 0 78 ma only its western flank and central area include thick piles of younger rocks piton de la fournaise is a highly and normally magnetized edifice but its northern and eastern flanks are underlain at shallow depth by reversely magnetized formations the latter are regarded as remnants of les alizes volcano associated with the grand brule hypovolcanic complex at the matuyama brunhes transition the island was composed of at least two main volcanoes piton des neiges and les alizes and perhaps also of a third old volcano takamaka at the center north of the island piton de la fournaise grows on the flank of les alizes and is a relatively young focus of volcanism these volcanoes have had successive phases of construction and destruction the analysis of magnetic anomalies over reunion was decisive in defining a new coherent model for the evolution of the island

kar chronology of the ultimate activity of piton des neiges volcano reunion island indian ocean abstract potassium argon measurements were made on 17 samples from the ultimate stage of activity of the piton des neiges volcano which corresponds to a differentiated series with lavas varying from basalt to quartz trachyte samples were selected as a function of their stratigraphic position and their representativity of magmatic evolution the technology used to date young volcanic rocks pleistocene by k ar is described and discussed because of its reliability in the analysis of modern lavas and because of the agreement of the results with the available stratigraphic control the data together with those previously obtained by mcdougall yield ages ranging between 330 000 and 30 000 years with two mainly effusive periods separated by a phase of instability of chiefly explosive volcanism around 190 000 to 150 000 years ago a rough correlation between the chemical evolution of the lavas and time is established the kudo and weil geothermometer when cross checked with buddington and lindsley s geothermometer allows us to establish that the lavas of the two effusive periods correspond to two different depths of the magmatic chamber in the oceanic crust 17 and 10 km respectively the phase of instability may correspond to a sudden variation in these magmatic conditions the differentiated series the ultimate stage of activity of the piton des neiges volcano 330 000 and 30 000 years can be explained as the evolution of a magmatic body isolated when the focus of basaltic eruption migrated southeast from piton des neiges to piton de la fournaise

noachian climatic conditions on mars inferred from valley network junction angles abstract valley networks vns on mars offer convincing evidence for its past water activities previous research empirically and theoretically suggested that the geometry properties such as junction angles of streams on earth formed under different climatic conditions are different thus the geometry properties of vns can be used to infer the early mars climatic conditions under which vns were formed the frequency distribution of junction angles is less influenced by the post formational modification processes than valley density and cross section and can be accurately extracted from low resolution data we first analyzed the association between the junction angles and environmental factors on earth the results suggested that the climatic factors are stronger than or on par with the geologic factors in controlling junction angles and that climatic parameters aridity index ai and mean annual precipitation map can be estimated from junction angles we then applied the associations between terrestrial junction angle and climatic conditions to estimate the ai and map of mars considering the different solar radiation of the two planets the spatial analysis of inferred climatic conditions showed that the noachian mars had an active global hydrological cycling and mars was warm during the vns formation period the duration of warm mars is estimated by the ratio between the required water volume to form vns and the runoff discharge derived from map the range of warm period is from 4 4 to 77 million years the results support the hypothesis that mars was episodically warm

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

volcanic geomorphology an overview abstract the review examines the role of geomorphology in analyzing the volcanoes on earth five objectives are stressed first classifications of volcanic landforms should be improved to take care of the complexity in volcanic landform generation as magmatic systems style of eruption and the erupted material all influence the morphology second geomorphology should contribute to the science of volcanology through its capability in reconstructing growth stages in complex volcanoes and also in analyzing the structural factors which contribute to the catastrophic collapse of volcanoes third geomorphology can contribute to physical volcanology by assessing the effects of topography on transport erosion and deposition of volcanogenic flows and identifying the sources and climatic tectonic conditions which govern the emplacement of volcaniclastic deposits fourth volcanic geomorphology a identifies sedimentary facies associations b constructs facies models for dynamic volcano delivery systems and c analyzes the characteristics of sediment gravity flows in order to determine relevant parameters for modelling their behaviour fifth process oriented geomorphology is critical in developing accurate methods for measuring rates of geomorphic processes that shape ephemeral volcanic constructs and for evaluating and comparing geomorphic impacts on disturbed catchments and the related hydrologic response before during and after eruptions this should help to refine parameters for the exponential decay model finally volcanic geomorphology is essential for risk assessment through geomorphic hazard zonation and composite risk zonation such treatments are necessary in order to face the enhanced challenge posed by the combination of natural hazards and the increasing number of people who are at risk around volcanoes

origin of the valley networks on mars a hydrological perspective abstract the geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall globally higher heat flow and localized hydrothermal systems comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin nor are they indicative of formation by an early global uniformly higher heat flow in general valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion with the exception of fluvial valleys on some volcanoes most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology in contrast terrestrial sapping valleys form from and along with runoff valleys the isolated or clustered distribution of valleys suggests localized water sources were important in drainage development persistent groundwater outflow driven by localized but vigorous hydrothermal circulation associated with magmatism volcanism impacts or tectonism is however consistent with valley morphology and distribution snowfall from sublimating ice covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal hydrothermal activity is sufficient to melt accumulated snowpacks

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

k ar dating extended into the last millennium application to the youngest effusive episode of the teide volcano spain less than one thousand years dating of the youngest volcanic episode of the teide volcano canary islands spain has been performed using the k ar cassignol technique analyses of about 20 g of pure alkali feldspar yielded a weighted mean age of 800 300 years stratigraphic historic and archeomagnetic dating validate this age and rule out the hypothesis of the presence of significant excess argon contamination for this flow our result shows that the last effusive activity of the teide volcano took place shortly before european settlement in tenerife island this study confirms that the cassignol technique can be applied with success for historic dating and demonstrates that it can now even be extended to the last millennium

geomorphological study of long term erosion on a tropical volcanic ocean island tahiti nui french polynesia abstract a quantitative geomorphological study has been made on 27 river basins in tahiti nui volcanic island french polynesia to reconstruct the erosional evolution of a young oceanic island subjected to heavy tropical rainfall tahiti nui is composed of a main shield volcano cut by two huge landslides on each side of a main e w rift zone the northern landslide depression was rapidly buried by the construction of a second shield the late activity of which overflowed the crest and then filled the southern landslide depression the island is now volcanically inactive and is deeply dissected by erosion the present geometries of the river basins are first compared using dimensionless parameters derived from a digital elevation model the original volcanic surfaces are then reconstructed to estimate the volumes removed by erosion and determine the average rates of long term erosion the basins developed on the flanks of the main shield are wider shallower and gentler than the basins incising the post landslide second shield indicating a higher degree of evolution rainfall concentration on the windward eastern side of the island also contributed to increase the vertical lowering of the volcanic relief and the enlargement of the valleys the magnitude of erosion however is neither directly linked with the age of the units incised nor with the differential amounts of rainfall erosion rates determined over the last 1 myr range between 10 3 km 3 kyr 1 and 0 25 km 3 kyr 1 the highest values occur in the basins incising the main e w rift zone and or the lateral rims of the northern and southern landslide depressions long term dissection has thus been enhanced along the geological discontinuities of the eruptive system deep erosion was first constrained along the axis of the main e w rift zone where numerous dykes compartmentalize the volcanic structure into large unstable blocks dykes most probably acted as mechanical discontinuities along which shallow gravitational landslides recurrently occurred such mass wasting episodes produced significant amounts of debris partly preserved as highly indurated sedimentary breccias of various ages exposed at various locations subsequent dissection of tahiti nui was enhanced to the north and to the south leading to the rapid evolution of the papenoo and taharuu drainage systems over the last 500 kyr long term dissection on tahiti nui has been responsible for the removal of at least 350 km 3 of volcanic material from the surface and for the partial exhumation of a shallow intrusive complex partly composed of coarse grained plutonic rocks gabbros and syenites in the central part of the eruptive system structurally controlled erosion is thus a key component of landscape evolution on such high relief oceanic tropical islands

explosive activity of the reunion island volcanoes through the past 260 000 years as recorded in deep sea sediments the explosive activity of reunion volcanoes since approximately 260 ka is investigated through detailed sedimentologic isotopic and geochemical analyses of three deep sea marine cores twenty four eruptions from piton des neiges and one from piton de la fournaise are identified the marine stratigraphic record of ash layers is undisturbed whereas corresponding tephra deposits on land may have disappeared or have been disturbed through erosion and volcano tectonic processes consequently the new data presented herein may be regarded as a reference sequence of the main explosive events of reunion in addition the chronology based on 18o stratigraphy offers continuous time constraints with respect to other isotopic methods used for dating lavas explosive events were more frequent during the period 180 150 ka the comparison of major element composition and chronologic data between known explosive deposits on land and marine ash layers allows us to propose correlations between marine and land data however most of the marine ash layers do not yet have a recognized subaerial counterpart for the main explosive events known on land we propose the following succession sainte suzanne formations 257 240 ka dalle soudee formation 218 ka salazie formations two groups at 165 168 ka and 80 102 ka saint gilles formations 175 ka saint louis formations 158 161 ka and saint pierre formations 165 166 ka

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

effects of obliquity and water vapor trace gas greenhouses in the early martian climate 1 we explore possible mechanisms for the generation of warm wet climates on early mars as a result of greenhouse warming by both water vapor and periodic volcanic trace emissions the presence of both water vapor a strong greenhouse gas and other trace greenhouse gases such as so2 in a predominantly co2 atmosphere may act under certain conditions to elevate surface temperatures above the freezing point of liquid water at least episodically variations in obliquity are explored to investigate whether these periodic variations in insolation at mars can broaden the regions or seasons where warm temperatures can exist we use the mars weather research and forecasting general circulation model to perform several simulations of the conditions of the early martian atmosphere containing these gases and find global temperatures to be cooler than the elevated levels suggested by at least one recent study by johnson et al 2008 while achieving temperatures above 273 k globally remains challenging the additional warming by greenhouse gases under certain obliquity states can permit for widespread seasonally warm conditions which can help to explain the presence of fluvial surface features e g valley networks and hydrous minerals of post noachian age a period when alternate methods do not convincingly explain the sustainability of liquid water furthermore we find that global warming can be achieved with the presence of a darker surface globally which is consistent with both widespread exposure of unweathered basaltic bedrock or the presence of a large surface ocean or sea

dielectric map of the martian northern hemisphere and the nature of plain filling materials 1 a number of observations suggest that an extended ocean once covered a significant part of the martian northern hemisphere by probing the physical properties of the subsurface to unprecedented depth the marsis mars express provides new geophysical evidences for the former existence of a late hesperian ocean the vastitas borealis formation located inside a putative shoreline of the ancient ocean has a low dielectric constant compared with that of typical volcanic materials we show that the measured value is only consistent with low density sedimentary deposits massive deposits of ground ice or a combination of the two in contrast radar observations indicate a distribution of shallow ground ice in equilibrium with the atmosphere in the south polar region we conclude that the northern plains are filled with remnants of a late hesperian ocean fed by water and sediments from the outflow channels about 3 gy ago

planetary geomorphology some historical analytical perspectives abstract three broad themes from the history of planetary geomorphology provide lessons in regard to the logic valid reasoning processes for the doing of that science the long controversy over the origin of lunar craters which was dominated for three centuries by the volcanic hypothesis provides examples of reasoning on the basis of authority and a priori presumptions percival lowell s controversy with geologists over the nature of linear markings on the surface of mars illustrates the role of tenacity in regard to the beliefs of some individual scientists finally modern controversies over the role of water in shaping the surface of mars illustrate how the a priori method i e belief produced according to reason can seductively cloud the scientific openness to the importance of brute facts that deviate from a prevailing paradigm

formation of gravel pavements during fluvial erosion as an explanation for persistence of ancient cratered terrain on titan and mars abstract in many terrestrial channels the gravel bed is only transported during rare floods threshold channels and rates of erosion are very slow in this paper we explore how coarse debris delivered to channels on mars and titan from erosion may inhibit further erosion once a coarse gravel channel bed develops portions of the equatorial region of titan are fluvially eroded into banded crenulated terrain some of which contains numerous circular structures that are likely highly degraded large impact craters surviving from the late heavy bombardment no mechanism that can chemically or physically break down ice likely the most important component of titans crust has been unambiguously identified this paper examines a scenario in which fluvial erosion on titan has largely involved erosion into an impact generated megaregolith that contains a modest component of gravel sized debris as the megaregolith is eroded coarse gravel gradually accumulates as a lag pavement on channel beds limiting further erosion and creating a dissected but largely inactive or senescent landscape similar development of gravel pavements occur in ancient mountain belts on earth and partially explain the persistence of appreciable relief after hundreds of millions of years likewise coarse gravel beds may have limited the degree to which erosion could modify the heavily cratered terrains on mars particularly if weathering were largely due to physical rather than chemical weathering processes in a relatively cold and or arid environment

crater size frequency distributions and a revised martian relative chronology a revised martian relative chronology is determined which dates geologic units with respect to the end of the period of heavy bombardment this analysis differs from previous studies by using viking 1 2m photomosaics to map all 25 826 craters 8km diameter which postdate the lithologic units making up the martian surface the relative plotting technique is used because it shows changes in the shape and density of the crater size frequency distribution curves more clearly than cumulative plots the changes in shapes of the distribution curves are interpreted to be due to two different impacting populations one dominating during the heavy bombardment period and the other emplaced during the post heavy bombardment period the 8 km diameter limit was chosen to exclude the majority of secondary craters and to minimize obliteration effects acting over the age of the planet the results obtained are average ages valid for units with typical thicknesses between about 1 and 3 km and extending over an area of about 105 km2 the shapes and densities of the crater distribution curves indicate that approximately 60 of the martian lithologic units in which these craters occur formed during the period of heavy bombardment many of the small volcanoes those generally less than 200 km diameter including most in the tharsis and elysium regions date from this period the hellas and argyre impacts bracket the average age of the intercrater plains in the highlands the ridged plains distribution curves indicate formation during the period of heavy bombardment but their lower crater density indicates that they are the last geologic unit to retain the scars from this population of impactors they therefore likely formed near the end of heavy bombardment the remaining 40 of martian terrain units show distribution curves indicative of emplacement since the end of heavy bombardment the wide range in crater densities among different regions of plains indicate a range in formation ages although the general view of martian geologic evolution does not differ significantly from previous studies the present analysis explicitly states the relationship of numerous geologic units to the period of heavy bombardment and has revised the relative ages of localized regions across mars

evidence from geoid data of a hotspot origin for the southern mascarene plateau and mascarene islands indian ocean a high resolution geoid map of the madagascar and mascarene basins is constructed from geos 3 and seasat satellite altimetric data with an accuracy of 0 7 m large positive anomalies are due to topographic highs and their regional compensation the deflection of the lithosphere under volcanic loads and its effect on the geoid are modeled for the southern mascarene plateau mauritius reunion and rodriguez islands assuming a purely elastic lithospheric model the effective flexural rigidity is estimated for the four zones rigidity varies from 1 10 21 to 2 10 23 n m increasing from north to south the highest rigidity occurs under reunion island and suggests a recent origin for the volcanism 3 5 ma the southern mascarene plateau shows the lowest rigidity suggesting a near ridge origin rodriguez island shows the same trend but in another tectonic framework the topographic and geoid swell is studied as an effect of a thermal mantle plume using a conductive model of lithospheric heating we confirm the assumption of hotspot migration for the origin of the southern mascarene plateau and the mascarene islands

viscous relaxation of impact craters on icy planetary surfaces determination of viscosity variation with depth spacecraft images show that the icy galilean satellites have surfaces with very low topographic relief impact craters on ganymede and callisto are anomalously shallow and are characterized by sharp well defined rims and domed floors these morphological characteristics can be explained by viscous relaxation of topography on an icy crust in which the viscosity is uniform or decreases with depth under these conditions large craters relax more rapidly than small craters therefore explaining a possible underabundance of large craters viscous relaxation on an icy crust that is thin compared to the crater diameter or on a thick icy crust in which viscosity increases with depth could not produce this crater morphology and would result in the more rapid relaxation of small craters rather than large craters the results of this study suggest that more detailed analysis of relaxing impact crater morphology may resolve the rate of viscosity decrease with depth and so provide evidence on the interior thermal evolution of icy planetary bodies

hydrology of early mars valley network incision 1 widespread occurrences of valley networks on mars provide geomorphic evidence for an active hydrologic cycle to constrain the climatic conditions capable of forming the valley networks a hydrological model was used to analyze the valley incision depth and volume of eroded valleys because the absolute magnitudes of precipitation runoff and evaporation are uncertain we have used the ratio of these quantities the x ratio to express climatic conditions the spatial distribution and strength of the correlations between 1 the estimated depth and volume of eroded material and 2 estimated flood magnitude and valley gradients were investigated as a function of the assumed x ratio we also conducted an analysis of conditions required to have appreciable discharge in selected valley networks which provided the most definitive constraint on martian paleoclimate the other methods show a relatively weak dependency of incision depths and volumes upon the assumed x ratio the multiple regression analyses indicate that incision depth is strongly influenced by gradient and weakly related to modeled flood discharge the factors determining relative depth of incision depend partly on the type of channel bed however postflow modification of the valley networks by mass wasting cratering aeolian infilling and ice related processes precludes direct determination of bed morphology our hydrological analyses suggest that climatic conditions on early mars were at least as moist as those that occurred in the great basin region of the u s when large lakes were present during the pleistocene in terms of the balance of runoff and lake evaporation

morphometry of great basin pluvial shore landforms implications for paleolake basins on mars 1 many basins with relict contributing valley networks and outlet valleys in the martian highlands indicate past flowing and ponded water on the surface these likely paleolakes motivate an investigation of pluvial shore landforms in the great basin region of the western united states as confident identification of strandlines on mars would facilitate analyses of its past hydrology and climate the purpose of this study is to characterize the scale of late pleistocene erosional and depositional shore landforms in an endorheic setting determine the preservation potential of similar forms from multiple epochs in early martian history and identify the data products that would be necessary to detect them we use differential global positioning system field surveys to measure the dimensions and elevations of shore landforms compare shore platform widths to theoretical maxima and note the minimum scale of landforms that have survived since the late noachian and early hesperian epochs on mars we find that due to impact gardening and aeolian erosion martian highland paleolakes like those in the pluvial great basin would likely not have well preserved shore landforms unless they were unusually large and formed in the late hesperian or later individual strandlines are often not equally well expressed around an entire basin so correlating shore landforms in plan view imaging and using their consistency in elevation as a hypothesis test for paleolakes can be challenging detection of younger shore landforms like those examined here would require meter resolution imaging and topography such as stereo digital elevation models

dem based morphometry as a tool for reconstructing primary volcanic landforms examples from the borzsony mountains hungary a complex application of digital elevation model dem derivatives is presented for a highly degraded volcanic area the miocene borzsony mountains hungary we propose unconventional geometrical and mathematical transformations of the original dem data in order to enhance the topographic features of the volcanic relief that stem from the primary landforms it is the actual ridges that represent the least degraded surfaces of an original hypothetical volcanic cone therefore the statistical dem properties such as ridge pattern 1 slope angle distribution 2 and higher order slope derivatives 3 should be strongly correlated with the paleosurface automated creation of a ridge pattern image is based on the local histogram of the dem and helps to outline the original surface remnants a local slope angle histogram may point out structurally coherent parts of the original cone for instance tectonic displacements or large scale sector slumping does not affect the slope angle histogram of the original relief evaluating the ridge maps and slope aspect maps of the borzsony mountains allows various cone sectors to be identified and connected to the original volcano structural elements finally the polar coordinate transformed pct image 4 centered on a hypothesized eruptive vent enhances the original radial valley pattern in the case of multiple eruptive centers and or post eruptive tectonic modifications the radial pattern is changed which may be evidenced in the pct image in fact the pct image analysis for the borzsony mountains suggests a complex post eruptive tectonic scenario the presented methods can be recommended to infer the original configuration of highly degraded volcanic structures with poorly known tectonic and erosional history

role of the structural inheritance of the oceanic lithosphere in the magmato tectonic evolution of piton de la fournaise volcano la reunion island la reunion island is located east of madagascar on the eastern rim of the tectonically inactive mascarene basin this island is composed of three shield volcanoes of which only piton de la fournaise is currently active although the magmatic activity is restricted to piton de la fournaise a scattered seismicity occurs on the whole 200 km wide volcanic edifice and in the underlying oceanic crust we carried out a multiscale analysis to understand 1 the origin of the seismicity in the geodynamic context and 2 the role of the oceanic lithosphere in the deformation of piton de la fournaise and la reunion island analysis of the magmatic system suggests that the magma ascent is controlled by large n25 30 and n125 130 fracture zones located below the enclos depression we also show that the orientation difference between the eruptive fissures and the related dykes result from a rotation of the main principal stress s 1 from vertical to downslope through the surface combining a digital elevation model dem analysis field observations and the geophysical data reveals that the volcano is affected by large fault zones the fault distribution indicates the predominance of a main n70 80 trend magnetic data show the same n80 orientation characterizing the remnant part of the alizes volcano such parallel alignment suggests a control exerted by the underlying alizes volcano on piton de la fournaise furthermore the alignment between the crustal orientations and the structures determined on the island suggests a control of the crustal structures in la reunion s volcano tectonic activity contrary to several volcanic islands such as hawaii and tenerife la reunion volcanoes lie on an upbending crust then we interpret the reactivation of the crustal faults as resulting from a crustal uplift related to the thermal erosion of the base of the lithosphere and or to strong underplating the upward deformation may prevent the spreading of the volcanoes as no evidence of such a mechanism is observed in the bathymetry and the seismic data around the island

small martian valleys pristine and degraded morphology the equatorial heavily cratered uplands of mars are dissected by two classes of small valleys that are intimately associated in compound networks pristine valleys with steep valley walls preferentially occupy downstream portions of compound basins degraded valleys with eroded walls are laterally more extensive and have higher drainage densities than pristine valleys morphometric and crater counting studies indicate that relatively dense drainage networks were emplaced on mars during the heavy bombardment about 4 0 b y ago over a period of approximately 10 sup 8 years these networks were degraded and subsequently invaded by headwardly extending pristine valleys the pristine valleys locally reactivated the compound networks probably through sapping processes dependent upon high water tables fluvial activity in the heavily cratered uplands generally ceased approximately 3 8 3 9 b y ago coincident with the rapid decline in cratering rates the relict compound valleys on mars are morphometrically distinct from most terrestrial drainage systems the differences might be caused by a martian valley formation episode characterized by hyperaridity by inadequate time for network growth by very permeable rock types or by a combination of factors

calderas landslides and paleo canyons on piton de la fournaise volcano la reunion island indian ocean based upon a re interpretation of previous data and a new field campaign a structural evolution is proposed for the early history of piton de la fournaise volcano from 500 000 to 50 000 years conceptually it is shown that the formation of a caldera in which lava flows are contained inside the caldera depression gives time for erosion to excavate deep canyons on the external slopes of the volcano for example the riviere des remparts the riviere langevin and the riviere de l est canyons on piton de la fournaise volcano these canyons are infilled when lavas filling the caldera and overflowing its rim are able again to flow on the external slopes of the volcano in the past this excavating infilling process has occurred twice following the formation of the riviere des remparts and morne langevin calderas the formation of the third caldera the plaine des sables caldera was followed by the excavation of the current canyons in addition to this process two large landslides have been documented in the field the first which happened about 300 000 years ago is apparently the first episode of the break up of piton de la fournaise volcano predating the formation of the four large calderas the second landslide which occurred 150 000 years ago and is considered to be less extensive has carried away the entire southern flank of the riviere des remparts caldera

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

petrology geochemistry and zircon u pb and lu hf isotopes of the cretaceous dykes in the central north china craton implications for magma genesis and gold metallogeny abstract the trans north china orogen tnco a paleoproterozoic suture that amalgamates the western and eastern blocks of the north china craton ncc witnessed extensive magmatism and metallogeny during mesozoic associated with intraplate tectonics and differential destruction of the cratonic lithosphere here we investigate a suite of porphyry dykes surrounding the mapeng batholith in the fuping complex within the tnco in relation to the mesozoic gold and molybdenum mineralization the major element chemistry of these dykes show a range of sio 2 57 92 to 69 47 wt na 2 o 3 20 to 4 77 wt k 2 o 3 12 to 4 60 wt and mgo 0 51 to 3 67 wt together with high concentration of lree and lile and relatively low contents of hree and hfse the rocks display la yb n 13 53 48 11 negative nb ta th u and zr anomalies and distinctly positive ba k and sm anomalies the mineralogy and geochemistry of the porphyry dykes indicate the rocks to be high k calc alkaline and i type with adakitic features similar to those of the adjacent mapeng batholith the source magma for these rocks was derived from a mixture of reworked ancient continent crust and juvenile mantle materials the zircon u pb data from these rocks show ages in the range of 124 to 129 ma broadly coinciding with the emplacement age of the mapeng intrusion the inherited zircons of ca 2 5 2 0 and 1 8 ga in the dykes represent capture from the basement rocks during melting the zircon lu hf isotopic compositions show negative e hf t values varying from 27 8 to 11 3 with hf depleted model ages t dm ranging from 1228 ma to 1918 ma and hf crustal model ages t dm c of 1905 ma to 2938 ma suggesting that the mesozoic magmatism and associated metallogeny involved substantial recycling of ancient basement rocks of the ncc we present an integrated model to evaluate the genesis of the porphyry systems and their relation to mineralization we envisage that these dykes probably acted as stoppers impermeable barriers that prevented the leakage and run off of the ore bearing fluids and played a key role in concentrating the gold and molybdenum mineralization

comparative study between rivers in tarim basin in northwest china and evros vallis on mars abstract the morphometric characteristics of the kaidu river and keriya river in the extremely arid tarim basin and the evros vallis on mars were compared to study the formation of the dendritic evros vallis which has great significance for exploring ancient climate of mars the following results were obtained a the average sinuosities of kaidu river keriya river and evros vallis are 1 17 1 35 and 1 32 respectively b the average bifurcation ratios are 3 84 4 73 and 3 43 respectively c the average stream length ratios are 2 21 3 86 and 2 08 respectively d the stream frequencies are 0 017 0 028 and 0 002 respectively e the drainage densities are 0 195 km 1 and 0 217 km 1 and 0 048 km 1 respectively f the stream gradients are 3 74 7 03 and 1 63 respectively g the stream fractal dimensions are 1 70 1 0 and 1 68 respectively paleodischarge estimations at different stream segments of evros vallis support the hypothesis that the v bend area that joints the eastern and western segments possibly has a tectonic origin geomorphological evidence e g tributaries from high resolution images and stream morphometric parameters from a comparative analysis e g concave upward longitudinal profile and stream fractal dimension support previous hypothesis that evros vallis is a mature drainage system formed by precipitation driven surface runoff this drainage process occurred either in a continuously warm wet climate that lasted long enough on early mars or in regional hydrologic cycles consisting of precipitation and occasionally returned runoff in intermittently clement climates

drainage network development in the keanakāko i tephra kīlauea volcano hawai i implications for fluvial erosion and valley network formation on early mars 1 a number of studies have attempted to characterize martian valley and channel networks to date however little attention has been paid to the role of lithology which could influence the rate of incision morphology and hydrology as well as the characteristics of transported materials here we present an analysis of the physical and hydrologic characteristics of drainage networks gullies and channels that have incised the keanak ko i tephra a basaltic pyroclastic deposit that occurs mainly in the summit area of k lauea volcano and in the adjoining ka desert hawai i the keanak ko i tephra is up to 10 m meters thick and largely devoid of vegetation making it a good analog for the martian surface although the scales are different the keanak ko i drainage networks suggest that several typical morphologic characteristics of martian valley networks may be controlled by lithology in combination with ephemeral flood characteristics many gully headwalls and knickpoints within the drainage networks are amphitheater shaped which results from strong over weak stratigraphy beds of fine ash commonly bearing accretionary lapilli pisolites are more resistant to erosion than the interbedded coarser weakly consolidated and friable tephra layers because the banks of the gullies and channels are easily eroded widths vary downslope similar to martian valley networks that have been characterized as degraded the floors of the gullies and channels tend to be low relief with few prominent bed forms reflecting the large proportion of sediment transported as bed load in high energy but short lived flood events we calculate that the average flow velocities within the drainage networks are typically 1 m 24 h given some recent modeling of the early martian climate our observations imply that rainfall on early mars could also be associated with large intense events and that martian valley network formation may be related to similar cyclonic storms

the morphology of the submarine flanks of volcanic ocean islands a comparative study of the canary and hawaiian hotspot islands the submarine flanks of volcanic islands are shaped by volcanic constructional processes landslides erosion sediment deposition and tectonic movements we use a newly acquired multibeam sonar dataset from the westerly canary islands el hierro la palma and tenerife to develop a comparison with the hawaiian islands which suggests differences in the processes constructing and modifying their flanks landslides affect the flanks of both island groups debris avalanches fast moving shallow landslides have left smooth chutes and blocky deposits in both cases but blocks within some hawaiian avalanche deposits are markedly larger we attribute the larger block sizes in the hawaiian islands to the fact that their avalanches were relatively unconfined whereas many canary and hawaiian avalanches with small block sizes appear to have been constrained down narrow chutes forcing interactions between blocks within the flows and encouraging disintegration furthermore the hawaiian avalanches with the largest blocks initiated near sea level whereas many of the canary avalanches initiated above sea level so hydraulic resistance of water entering cracks may be an additional factor in resisting block disintegration during flow slow moving deep seated slumps or volcanic spreading have produced submarine benches and tabular escarpments due to thrust faulting adjacent to several hawaiian rift zones but are not well developed in the canaries although volcanic morphology is partly obscured by sedimentation in the canaries we are able to interpret lava terraces around the deep flanks of el hierro which are similar to those found in the hawaiian islands however cones rather than terraces are the most common volcanic forms in the canary islands implying that flank eruptions have involved magma with significant volatile contents assuming that volatile contents dictate whether cones or terraces are formed these differences may ultimately originate from the different building rates of the two island groups for example the lack of evidence for high level magma chambers in the canaries associated with their lower outputs implies that there is less possibility for degassing of magma below the summit before lateral intrusion down rift zones hence cones rather than lava terraces are more commonly observed the apparent lack of slumping or volcano spreading could also reflect a lack of driving pressure from extensive high level magma chambers in the canaries

volcano tectonic and geochemical evolution of an oceanic intra plate volcano tahiti nui french polynesia abstract geological mapping accurate k ar dating and geochemical analyses of lavas allow a detailed reconstruction of the geological history of tahiti nui island french polynesia the exposed volcanic activity is first characterized by the construction of a main shield from 1 4 ma to 870 ka with a maximum aerial eruptive rate around 2 km3 kyr lavas from this early building stage are alkaline slightly silica undersaturated with 87sr 86sr and 143nd 144nd compositions rather constant and close to the enriched mantle ii type vent locations were first concentrated along a main e w rift zone which was responsible for the lateral collapse of the northern and southern flanks of the main shield around 0 87 ma ago the subsequent activity was first restricted to the northern depression corresponding to an eruptive rate of about 5 km3 kyr in the period 850 760 ka significant variations in la sm 87sr 86sr and 143nd 144nd occur in lavas erupted immediately after the main northern landslide indicating a sudden increase in the extent of partial melting likely caused by the decompression subsequent to collapse however the later activity declined and the lavas exhibit a gradual change toward strongly silica undersaturated basanites likely indicating a decreasing extent of partial melting of the upper mantle the evolution of radiogenic isotope ratios over time indicates a change in the source toward more depleted compositions until around 500 ka post erosion volcanic activity following an apparent hiatus of 240 kyr exhibits similar major and trace element and isotope compositions the volcano structural and geochemical evolution of tahiti nui and the overall alkaline character of the lavas from other eruptive complexes of the society alignment suggest a relative weakness low temperature and low eruptive rate of the society plume compared to the hawaiian hot spot

recurrence of major flank landslides during the last 2 ma history of reunion island new detailed swath bathymetry and backscatter data corroborate the existence of four large bulges on the submarine flanks of reunion island these fan shaped promontories are 20 25 km wide at the coastline and 70 150 km across the seafloor 40 50 km offshore their surfaces are characterized by a speckle sonar pattern indicating the presence of large blocks up to several hundred meters across each bulge results from the superposition of multiple landslide deposits whose older ones are dissected and delimited by erosive channels as much as 200 m deep and 20 km long the submarine flanks of reunion island are thus mostly built by accumulation of debris avalanche fans morphologic and geologic evidence define large subaerial source areas for these mass wasting events in particular inferred headwalls of most landslides having affected the piton des neiges massif generally coincide with the boundaries of its cirques mafate salazie and cilaos whereas recurrent landslides have resulted in the formation of large concentric amphitheatre structures through the piton de la fournaise massif thus about 15 slide events accompanied growth of the reunion island shield since 2 ma

computer generated global map of valley networks on mars 1 the presence of valley networks vn on mars suggests that early mars was warmer and wetter than present however detailed geomorphic analyses of individual networks have not led to a consensus regarding their origin an additional line of evidence can be provided by the global pattern of dissection on mars but the currently available global map of vn compiled from viking images is incomplete and outdated we created an updated map of vn by using a computer algorithm that parses topographic data and recognizes valleys by their morphologic signature this computer generated map was visually inspected and edited to produce the final updated map of vn the new map shows an increase in total vn length by a factor of 2 3 a global map of dissection density d derived from the new vn map shows that the most highly dissected region forms a belt located between the equator and mid southern latitudes the most prominent regions of high values of d are the northern terra cimmeria and the margaritifer terra where d reaches the value of 0 12 km 1 over extended areas the average value of d is 0 062 km 1 only 2 6 times lower than the terrestrial value of d as measured in the same fashion these relatively high values of dissection density over extensive regions of the planet point toward precipitation fed runoff erosion as the primary mechanism of valley formation assuming a warm and wet early mars peculiarity of the global pattern of dissection is interpreted in the terms of climate controlling factors influenced by the topographic dichotomy

martian geomorphology from fractal analysis of drainage networks 1 an alternative approach to conventional planetary terrain analysis is proposed martian terrains represented by topography based on the mars orbiter laser altimetry mola data are represented as a series of drainage basins regardless of the historical presence or absence of actual fluid flow a fractal analysis of each drainage network computationally extracted from an underlying terrain yields a network descriptor a list of four numbers that describes the traits of a network network descriptors are used for a quantitative characterization and classification of martian surfaces we have extracted and analyzed 387 drainage networks from 74 martian locations representing all major epochs and geological units to investigate whether their network descriptors are capable of differentiation between different epochs and geological units we have found that our approach can distinguish morphologically different terrains but only in a statistical sense in particular the method could be used to measure the degree of surface cratering and thus the age of the surface in addition for surfaces that are not heavily cratered the method is capable of distinguishing between different geological units we have found no global trends in the character of martian drainage networks their network descriptors show no systematic dependence on location or elevation our analysis reveals that all noachian surfaces grouped in the npld geological unit have very similar network descriptors regardless of prominence and integration of their visible fluvial features the comparison between statistical description of npld and terrestrial drainage networks shows overall similarities but also some marked differences because of these differences the notion of sustained rainfall on mars during the noachian epoch is inconsistent with our findings but a limited rainfall is compatible with our results