seabeam depth changes associated with recent lava flows coaxial segment juan de fuca ridge evidence for multiple eruptions between 1981 1993 after a swarm of earthquakes was detected on the coaxial segment of the juan de fuca ridge in june july 1993 the area was resurveyed with seabeam multibeam sonar to search for depth changes associated with a submarine volcanic eruption quantitative comparison of the 1993 seabeam survey with surveys in 1981 82 and 1991 shows one area of seafloor depth change up to 29 m between 1991 93 exactly where a pristine lava flow was discovered in addition two other depth anomalies up to 37 m and 20 m are identified between 1981 91 evidence that other recent eruptions have occurred along this spreading ridge segment

coquitlam drift a pre vashon fraser glacial formation in the fraser lowland british columbia coquitlam drift is formally defined and stratotypes established for it in the coquitlam port moody area b c it is a pleistocene formation consisting of till glaciofluvial ice contact and glaciomarine sediments deposited between 21 700 and 18 700 years bp during the fraser glaciation late wisconsin and prior to the main vashon glacial maximum at about 14 500 years bp the drift was deposited in short pulses by valley and piedmont glaciers fluctuating into the fraser lowland from the coast mountains to the north and cascade mountains to the east

theoretical limitations to englacial velocity calculations to study the dynamics of ice sheets and glaciers velocities at the bed of a glacier must be measured directly or calculated using data gathered from boreholes and surface surveys boreholes to the bed are expensive and time consuming to drill so the determination of basal velocity is almost exclusively by numerical inversion of velocities observed at the surface for non linearly viscous glaciers a perturbation analysis demonstrates that inversions for englacial velocities will magnify measurement errors at an exponential rate with depth the rate at which calculation errors grow is proportional to a lyapunov exponent a measure of information loss which is shown to be a simple linear function of spatial frequency with a coefficient depending on glen s flow law exponent n the coefficient decreases with increasing non linearity demonstrating that inversions with non linearly viscous ice have smaller calculation errors than inversions with linearly viscous ice in both the linear and nonlinear cases the lyapunov exponent and rate of error growth increases with decreasing wavelength which limits velocity calculations at the bed to wavelengths on the order of one ice thickness or greater this limitation is theoretical and cannot be countered by more accurate survey data or special numerical techniques

the pattern of circumferential and radial eruptive fissures on the volcanoes of fernandina and isabela islands galapagos maps of the eruptive vents on the active shield volcanoes of fernandina and isabela islands galapagos made from aerial photographs display a distinctive pattern that consists of circumferential eruptive fissures around the summit calderas and radial fissures lower on the flanks on some volcano flanks either circumferential or radial eruptions have been dominant in recent time the location of circumferential vents outside the calderas is independent of caldera related normal faults the eruptive fissures are the surface expression of dike emplacement and the dike orientations are interpreted to be controlled by the state of stress in the volcano very few subaerial volcanoes display a pattern of fissures similar to that of the galapagos volcanoes some seamounts and shield volcanoes on mars morphologically resemble the galapagos volcanoes but more specific evidence is needed to determine if they also share common structure and eruptive style

palaeoenvironmental reconstruction of the port moody interstade a nonglacial interval in southwestern british columbia at about 18 000 14c years bp new palynological data from peaty sediments deposited during the port moody interstade at about 18 000 14c years indicate that the environment in the western fraser lowland of british columbia consisted of subalpine forest and parkland with abundant fir and spruce that grew under a temperate and moist climate similar to the wetter subzones of the present day engelmann spruce subalpine fir biogeoclimatic zone the moist conditions interpreted for the port moody interstade are consistent with recent computer modelling and earlier palynological data from unglaciated western washington state but appear to contradict regional cooperative holocene mapping project cohmap reconstructions and some earlier palaeoenvironmental studies that support dry conditions strong seasonality is suggested as part of the explanation with pacific storms in summer following the southern margin of the last cordilleran ice sheet bringing abundant moisture to the study area during the growing season but probably not in wi

eruption fed particle plumes and volcaniclastic deposits at a submarine volcano nw rota 1 mariana arc 1 nw rota 1 is an active submarine volcano in the mariana arc with a summit depth of 517 m and an explosively erupting volcanic vent southwest of the summit at a depth of 530 560 m during a period of ongoing explosive eruptions particle plumes surrounded the volcano and at least 3 3 107 m3 of volcaniclastic material was deposited on the southern flank particle plumes over the summit were magmatic hydrothermal in origin characterized by 3he enrichment hydrothermal precipitates and low ph values plumes at multiple depths below the summit surrounded the volcano and were composed overwhelmingly of fresh glassy shards of basalt rare anhydrite particles were present but there was a complete absence of other hydrothermal components in the deep plume samples these short lived anhydrite particles indicate the source of the deep plumes is from within or very near the eruptive vent and the mechanism for transport down the flanks of the volcano must be far faster than settling of individual particles the deep plumes most likely originated from sediment gravity flows generated by explosive eruptions or slope failure and landslides of unstable materials that had accumulated near the eruptive vent suspended sediments detach from the volcano slopes at multiple depths and are transported laterally up to tens of kilometers where they contribute to fall out deposits in distal sediments these observations link mechanisms for the transport of volcanic ash in the submarine environment to the types of deposits common in volcaniclastic aprons and fine ash layers in distal sediments

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

physical volcanology of the submarine mariana and volcano arcs narrow beam maps selected dredge samplings and surveys of the mariana and volcano arcs identify 42 submarine volcanos observed activity and sample characteristics indicate 22 of these to be active or dormant edifices in the volcano arc are larger than most of the mariana arc edifices more irregularly shaped with numerous subsidiary cones and regularly spaced at 50 70 km volcanos in the mariana arc tend to be simple cones sets of individual cones and volcanic ridges are elongate parallel to the trend of the arc or at 110 counterclockwise from that trend suggesting a strong fault control on the distribution of arc magmas volcanos in the mariana arc are generally developed west of the frontal arc ridge on rifted frontal arc crust or new back arc basin crust volcanos in the central mariana arc are usually subaerial large 500 km3 and spaced about 50 70 km apart those in the northern and southern marianas are largely submarine closer together and generally less than 500 km3 in volume there is a shoaling of the arc basement around iwo jima accompanied by the appearance of incompatible element enriched lavas with alkalic affinities the larger volcanic edifices must reflect either a higher magma supply rate or a greater age for the larger volcanos if the magma supply estimated at 10 20 km3 km of arc per million years at 18 n has been relatively constant along the mariana arc we can infer a possible evolutionary sequence for arc volcanos from small irregularly spaced edifices to large over 1000 km3 edifices spaced at 50 70 km the volcano distribution and basal depths are consistent with the hypothesis of back arc propagation into the volcano arc

vashon drift definition of the formation in the georgia depression southwest british columbia vashon drift was deposited during the fraser glaciation late wisconsinan at the time of maximum expansion of the southwestern part of the cordilleran ice sheet when it filled the georgia depression about 14 500 years ago the drift is present throughout the depression and comprises till and glaciofluvial and glaciolacustrine sediments derived from source areas surrounding the coastal trough it is overlain by capilano sediments and underlain by quadra sand also of fraser age drift deposition was diachronous and complex probably caused by alpine glaciers coalescing in the trough with the ice margin repeatedly grounding and floating in seawater studies of bedrock striae till fabrics and clast provenance reveal that vashon ice movement was generally southward although locally controlled by topography a time space diagram is presented that confirms the long held hypothesis that advance and decay of vashon ice were rapid

lava flows from a mid 1980s submarine eruption on the cleft segment juan de fuca ridge a series of lava flows with a total volume of 0 05 km3 were erupted in the mid 1980s along 17 km of the northern cleft segment of the juan de fuca ridge observations from camera tows and submersible dives show that the new flows are all similar in appearance and consist entirely of pillow lava with a mixture of smooth and striated surface textures suggesting a relatively uniform eruption rate approaching 1 m3 s at point source vents the flows vary in size from small patches to large steep sided ridges and were probably erupted from a dike intruded along the ridge axis because they are aligned along a linear fissure graben system observations at north cleft show that the physical appearance of new flows changes more rapidly than previously realized and that earlier qualitative dating of young lavas based on sediment cover and glassy surface texture were probably overestimates by an order of magnitude sediment accumulation on the lavas is quite variable and locally surprisingly substantial mainly due to hydrothermal deposits that formed while the lava flows were cooling biological vent communities photographed on the new flows in 1989 show that vent animals can colonize new vent sites rapidly but that warm water was still venting only in a few places nonvent animals are much slower to colonize the new flows and rates of colonization observed at north cleft may be useful for making improved age estimates of young 10 years lava flows elsewhere the north cleft eruption represents about 2 of the estimated average annual volcanic output along the global mid ocean ridge implying that many other submarine eruptions are occurring undetected

condor seamount azores ne atlantic a morpho tectonic interpretation abstract high resolution datasets collected by multibeam and acoustic backscatter surveys were used to produce fine scale seafloor nature and morpho tectonic interpretations of the condor seamount condor constitutes an elongated volcanic ridge that extends for 39 km and rises more than 1800 m from the surrounding seafloor constructive morphologies include i linear eruptive centres ii volcanic cones with or without summit depressions iii lava flows and iv hummocky sectors eruptive type is interpreted to vary with depth on the deeper seamount extremities the predominance of highly acoustically backscattering volcanic cones and hummocky terrain is interpreted to result from effusive eruptions not yet covered by sediment deposits in contrast the smoother relief of the central seamount flanks is interpreted as draping and infilling of the underlying effusive relief by i primary volcaniclastic deposits produced by explosive eruptions on the shallowest parts of the ridge together with ii secondary volcanigenic sediments resulting from truncation of the seamount top by swell erosion and iii sediments resulting from biogenic production a set of wnw ese to nw se trending volcano tectonic structures are shown to control most of the fissural volcanism that formed the ridge a network of nnw sse trending faults is identified on the sea floor around condor but they show little relation with the distribution of volcanic edifices or with post emplacement dismantling of the seamount these fault sets are related to the transtensional regime acting on the azorean segment of the eurasia nubia plate boundary erosional features include i palaeo wave cut platforms on the seamount summit ii landslide scars produced by lateral collapses of the ne and sw facing flanks iii gullies and turbidity current channels and iv mass wasting deposits iceberg drag and bump marks are also identified on the seamount upper flanks representing the first reference to such features in the azores and an additional low latitude record given the lack of major erosional and tectonic dismantling condor is suggested to be a relatively young seamount a revised factoring of eustatic erosional and isostatic processes does not exclude that the summit may have been eroded as late as the last glacial maximum

lag of the fraser glacial maximum in the pacific northwest pollen and macrofossil evidence from western fraser lowland british columbia pollen and macrofossil evidence from two sites in northwestern fraser lowland reveals that abies lasiocarpa picea cf engelmannii forest and parkland grew there about 18 000 years ago under cold humid continental conditions taxus brevifolia was also a significant constituent of this forest this plant assemblage resembles the essf biogeoclimatic zone of subalpine elevations in the northern interior of british columbia 900 2250 m climate was probably cold with low to moderate rainfall and characterized by long cold wet winters and very short probably dry frost free summers mean annual temperature was depressed about 8 c and the tree line was probably 1200 1500 m lower than today fraser lowland was probably removed from pacific oceanic influence because the land sea interface was located on the continental shelf to the west of vancouver island and washington about the time of the last global glacial maximum global depression of sea level and quadra sand aggradation in the pacific northwest lo

evolution of backarc rifting mariana trough 20 24 n the mariana trough is an actively opening backarc basin in the western pacific the trough formed by extension which longitudinally split an earlier arc massif creating a crescent shaped basin between the remnant west mariana ridge and eastern active volcanoes of the mariana arc opening increases southward from the volcano islands near 24 n where the two arcs join at 18 n in the central mariana trough the basin is widest and may be opening primarily by seafloor spreading we present a synthesis of closely spaced shipboard gravity magnetic and bathymetry measurements from the northern basin 20 24 n an area that undergoes a significant progressive southward increase in extension we have identified three stages in the evolution of rifting in this area 1 asymmetric rifting from 24 n to 22 15 n where faulting and magmatism have migrated laterally to remain near the active volcanic arc side of the basin 2 a localization of rifting from 22 15 n to 21 n where the primary zone of rifting separates from the active volcanic arc and 3 a further concentration of rifting from 21 n to 20 n leading to the formation of deep tectonic grabens near the center of the basin this last stage may be a precursor to or incipient seafloor spreading we describe a new type of magnetic lineation resolved in a three dimensional seafloor magnetization inversion of the trough between 20 and 24 n the detailed character of these lineations their association with tectonic structures and other geophysical observations indicate that they are not seafloor spreading lineations but rather result from magnetic intrusions and volcanism emplaced within preexisting less magnetic rifted arc crust the development of these well defined magnetization bands indicates that the zone of magmatism remains relatively narrow at any one time throughout the opening of the trough although tectonic deformation appears to be more widely distributed in addition the geometry of the magnetization bands with respect to the remnant arc border faults indicates that rifting propagated rapidly northward

facies architecture of the upper oligocene submarine smrekovec stratovolcano northern slovenia abstract the upper oligocene smrekovec volcanic complex svc represents the remains of a submarine stratovolcano which underwent early miocene tectonic dissection and large scale displacement along the periadriatic line according to the lithofacies architecture abundance and spatial distribution central medial and distal zones of the former volcano edifice have been recognized the zones extend at a distance of 0 2 km 2 5 km and 5 20 km south of the periadriatic line respectively lavas shallow intrusive bodies autobreccia peperite and hyaloclastite deposits occur mainly in the central zone which is extensively altered under hydrothermal conditions characterised by the development of zeolites mainly laumontite prehnite chlorite albite and epidote explosive volcanic activity intensified with the evolution of magma from basaltic andesitic to dacitic gas and water supported eruption fed density flows are assumed their deposits show lithofacies organisation in pyroclastic depositional units pdus similar to either volcaniclastic turbidites type 1 or thin subaqueous ignimbrites type 2 volcaniclastic debris flow deposits are developed as volcaniclastic breccia and sandy debris flow deposits the former occurs in the central and medial zones and the latter occurs in the medial zone only the most widespread lithofacies in the svc are volcaniclastic turbidite deposits three types of sedimentary unit tsu have been distinguished type 1 is 2 5 m thick and dominated by the massive division it mainly occurs in the central zone type 2 is 0 7 3 5 m thick and occurs in the central and medial zones it comprises the massive division bedded fining and thinning upward division and a horizontally wavy and cross laminated division topped by massive fine grained tuff type 3 is 0 1 1 5 m thick and mainly occurs in the distal zone the massive division is absent and thinly bedded and laminated divisions are topped by massive fine grained tuff volcaniclastic turbidites were settled from low density turbidity currents and related suspension clouds mixed volcaniclastic siliciclastic deposits are subordinate in occurrence and restricted to the distal zone they are commonly reworked by bottom currents

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

the sisters creek formation pleistocene sediments representing a nonglacial interval in southwestern british columbia at about 18 ka sisters creek formation is formally defined stratotypes are established for it and the time space chart is updated for the fraser lowland southwestern british columbia the sisters creek is a pleistocene formation comprising in situ and reworked organic rich sediments and nonorganic silt sand and gravel the formation was deposited during the port moody interstade within the late wisconsinan fraser glaciation 18o stage 2 between the coquitlam stade early fraser glaciation and the main vashon stadial maximum that occurred about 14 5 ka the sisters creek formation represents a glacial recession in southwestern british columbia that generally coincided with the timing of the last global glacial maximum the new time space chart implies that in fraser lowland the fraser glaciation represents the rapid advances and retreats of glacial lobes issuing from surrounding mountains which remained ice covered during interstades

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

the submarine flanks of anatahan volcano commonwealth of the northern mariana islands abstract the submarine flanks of anatahan volcano were surveyed comprehensively for the first time in 2003 and 2004 with multibeam and sidescan sonar systems a geologic map based on the new bathymetry and backscatter data shows that 67 of the volcano s submarine flanks are covered with volcaniclastic debris and 26 is lava flows cones and bedrock outcrops the island of anatahan is only 1 of the volume of the entire volcano which has a height from its submarine base of 3700 m and an average diameter of 35 km ne anatahan is a prominent satellite volcano located 10 km ne of the island but it is only 6 of anatahan s volume 40 km 3 vs 620 km 3 seventy eight submarine eruptive vents are mapped associated with lava flows and cones between depths of 350 and 2950 m and 80 of these vents are located in a cluster on the east flank of the volcano the distribution of cones and lava flows vs depth suggests a possible change in eruptive style from explosive to effusive between 1500 and 2000 m eruptive vents below 2000 m have produced mostly lava flows there is no evidence of major landslides on the submarine flanks of anatahan volcano in contrast to many basaltic islands and seamounts suggesting that mass wasting at felsic oceanic arc volcanoes may be characterized by sediment flows of unconsolidated volcaniclastic debris instead of mass movements of relatively large intact blocks

optical dating studies of quaternary organic rich sediments from southwestern british columbia and northwestern washington state the suitability of optical dating using 1 4 ev infrared excitation for determining the time of deposition or compaction of organic rich sediments and peat is assessed with measurements on seven samples from six different lithostratigraphic units one is of zero age two have associated 14c ages three are known to have been deposited during an interglaciation and one is 1 ma old the samples yield satisfactory optical ages ranging from 0 to over 100 ka we conclude that the muir point formation southern vancouver island and the whidbey formation northwestern washington state were both deposited during 18o stage 5 as previously deduced from other evidence the age obtained from the 1 ma sample was significantly too low the optical dating method is simpler and more precise than thermoluminescence dating and is recommended for future work

the 2003 eruption of anatahan volcano commonwealth of the northern mariana islands chronology volcanology and deformation abstract the first historical eruption on anatahan island occurred on 10 may 2003 from the east crater of the volcano the eruption was preceded by several hours of seismicity two and a half hours before the outbreak the number of earthquakes surged to more than 100 events per hour at 0730 utc the washington volcanic ash advisory center issued an ash advisory although the eruption lasted for 3 months the majority of erupted material was expelled during the first 2 weeks the opening episode of the eruption resulted in a deposit of juvenile scoria and lithic clasts the latter derived from geothermally altered colluvial fill from the vent area the opening episode was followed by crater enlargement and deepening which produced deposits of coarse reddish brown ash containing a mixture of juvenile and lithic clasts the third episode of the eruption produced coarse ash and lapilli comprised of juvenile scoria and minor amounts of lithics plume heights were 4500 to 13 000 m for the initial three phases the fourth episode from about may 18 through early august was characterized by smaller plume heights of 900 to 2400 m and steam was the dominant component minor amounts of coarse ash and accretionary lapilli ash comprise most of the deposits of the fourth episode although ballistic blocks and bombs of andesite lava are also locally present these andesite blocks were emplaced by an explosion on 14 june which destroyed a small lava dome extruded during the first week of june activity waned as the summer progressed and subsequent ash deposits accumulated in july and early august by which time the eruption had effectively ended in september and october degassing and geothermal activity continued characterized by small geysers boiling water and jetting steam noteworthy deviations from this activity were a surge event in late may early june and the destruction of the lava dome on 14 june we calculated on land tephra fall deposits to have a bulk volume of about 27 5 10 6 m 3 covering an area of 40 6 km 2 we determined the juvenile to lithic content of the deposits and corrected the bulk volume to a juvenile volume of 24 0 10 6 m 3 we use a volume corrected density of 1 32 g cm 3 to convert the juvenile volume of 24 0 10 6 m 3 to a magma volume of 13 2 10 6 m 3 using the methods of fierstein and nathenson 1992 fierstein j nathenson m 1992 another look at the calculation of fallout tephra volumes bull volcanology 54 156 167 we computed the total eruption volume at 45 4 10 6 m 3 deformation surveys recorded large changes surrounding the east crater the modeled volumetric change based on the surveys was 0 82 10 6 m 3 of magma which we estimate corresponds to a minimum intrusion of 10 10 6 m 3 of magma which is in good agreement with our calculated on land magma volume

submarine silicic volcanism of the healy caldera southern kermadec arc sw pacific i volcanology and eruption mechanisms the submarine healy volcano southern kermadec arc with a 2 2 5 km wide caldera is pervasively mantled with highly vesicular silicic pumice within a water depth of 1 150 1 800 m pumices comprise type 1 white light grey pumice with 30 mm vesicles and weak moderate foliation type 2 grey pumice with millimetre scale laminae flow banded foliation including stretched vesicles 55 mm in length and a minor finely vesicular type 3 pumice all types are sparsely porphyritic with undevitrified glassy groundmass 68 70 sio2 which is microlite and lithic free coexisting pyroxenes yield magma temperatures of 950 c pumice density is 0 5 g cm 3 and vesicularity is 78 83 vesicle size distributions for types 1 and 2 pumice range from 20 m to 20 mm with a strong power law relation with d 2 5 0 4 for vesicles 9 mpa will limit vesicularity to less than the observed 78 83 whereas pressure 6 mpa require a more shallower reconstruction of the edifice and larger volume syn eruptive collapse uniformly high vesicularity is interpreted as evidence of insulation within an eruption column comprising steam and hot pyroclasts most pyroclasts cool condensing and ingesting water into steam inflated vesicles and then sink progression into pyroclastic mode would expand the eruption column displace ambient water reduce the hydrostatic load and further promote vesiculation and fragmentation pyroclasts within the column would quench at these reduced pressures we argue that healy eruptions deeper than 1 000 m cannot be pyroclastic volumes for the lower and upper bounds of edifice size are 2 36 and 3 58 km3 respectively but do not account for intra caldera pumice fill these volumes are considered to be predominantly primary eruption output as shown by a dearth of accessory lithics in all pumice yielding at an average 81 vesicularity eruptive pumice volumes of between 10 and 15 km3 some pyroclasts may have risen to the sea surface and be a correlative of the sea rafted loisels pumice the latter occurs in some new zealand holocene beach sequences and has a estimated age of 590 80 calendar years

mechanical modeling of circumferential and radial dike intrusion on galapagos volcanoes a distinctive and unusual pattern of eruptive fissures is observed on the active volcanoes of the galapagos islands reflecting circumferential dike intrusion near the calderas and radial dike intrusion on the volcano flanks elastic finite element models were used to investigate how a stress field could be produced and maintained to promote both circumferential and radial dike emplacement modeling results show that magma reservoirs of galapagos volcanoes are probably diapiric because this shape promotes both circumferential and radial intrusions but magma pressure alone cannot create the observed pattern of dikes loading by volcano growth and magma reservoir pressure could produce a stress field of suitable orientation but insufficient magnitude the intrusion of circumferential dikes could alter the stress field in a way that promotes future radial diking and vice versa faulting or slumping within the calderas or on the volcano flanks in response to repeated intrusions could also create a stress field conducive to continued intrusion

dynamic basis of volcanic spreading the established models of the structure and dynamics of a typical hawaiian volcano lead inevitably to a paradox finite element viscoelastic calculations using tecton melosh and raefsky 1980 1981 predict that a compressional stress field should characterize their upper flanks instead extension is observed the paradox is solved by postulating that volcanic evolution is determined by feedback processes related to growth and spreading of the volcanic edifice many examples of the process of spreading are documented in the geologic literature on volcanoes of a very broad size range and very different geologic settings the process is similar across many orders of magnitude in size the deformation of the substratum related to magma intrusion during lava dome building events is at the lower end of the scale the spreading of seafloor at oceanic ridges is at the higher end of the scale volcanoes may evolve from small constructs into huge shield volcanoes and perhaps into ocean plates key elements for volcanic spreading are 1 the existence of a weak basal layer and 2 a sufficiently high mass and magma influx to drive the process as the mass of a volcano grows it passes through five phases which may overlap repeat or be omitted building compressing thrusting intruding and spreading during the building phase the mass of a volcano does not significantly affect the stress field of the substratum primitive magmas are likely to be erupted as the mass increases the volcano subsides and becomes characterized by a compressional stress field which inhibits any further intrusion of magma into the volcanic edifice magma may differentiate in the crust allowing for large caldera forming eruptions to occur in the next phase thrusting begins on a decollement usually located at the foot of the edifice while the stress field on the upper slopes of the volcano remains compressional the stress at the base close to the center becomes extensional allowing the magma to intrude and differentiate at the base of the edifice a basal intrusive complex begins to grow explosive eruptions may be expected finally spreading of this complex creates an extensional stress field on the upper flanks of the volcano confining compression to the lower slopes of the edifice the extension allows primitive magma to erupt again at the summit the process of spreading seems to have a fundamental influence on the structural and magmatic evolution of volcanoes at every scale this process results from coupling and feedback between the gravitational and thermal fields thus studying this process may improve our understanding of the relation between structural dynamics and magma evolution and of the origin and evolution of volcanic seismicity and eruptions

anatahan northern mariana islands reconnaissance geological observations during and after the volcanic crisis of spring 1990 and monitoring prior to the may 2003 eruption abstract anatahan island is 9 5 km east west by 3 5 km north south and truncated by an elongate caldera 5 km east west by 2 5 km north south a steep walled pit crater 1 km across and 200 m deep occupies the eastern part of the caldera the island is the summit region of a mostly submarine stratovolcano the oldest subaerial rocks stage 1 are exposed low on the outer flanks and in the caldera walls these include thick 10 m and thin 2 3 m lava flows well indurated tuffs and scoria units that make up the bulk of the island rock compositions range from basaltic andesite to dacite and most are plagioclase phyric on the steep north and south flanks of the volcano these rocks are cut by numerous east west oriented few hundred m long lineaments of undetermined origin indurated breccias unconformably overlie scarps cut into stage 1 units low on the south flank intermediate age eruptive units stage 2 include caldera filling lava flows and pyroclastic deposits and on the outer flanks vents and valley filling lava flows the youngest pre 2003 volcanic unit on anatahan stage 3 is a hydromagmatic surge and fall deposit rich in accretionary lapilli prior to 2003 this unit was found over almost the entire island and in many places original depositional surfaces and outcrops could be found in high energy environments along the coast indicating a young but undetermined age during reconnaissance visits in 1990 1992 1994 and 2001 geothermal activity fumaroles as well as pits with boiling sediment laden pools was observed in the southern part of the pit crater in march and april 1990 increased local seismicity a large regional earthquake and reported increased fumarolic activity in the pit crater prompted evacuation of anatahan village at the west end of the island our first field investigation took place in late april 1990 to assess the level of volcanic unrest conduct reconnaissance geological observations collect rock and geothermal water samples and set up a geophysical monitoring network results at this time were inconclusive with respect to determining whether the activity was anomalous water in some of the geothermal pits within the pit crater was boiling and ph values as low as 0 7 were recorded in the field an electronic distance measurement edm network was installed and over a 1 week period up to 9 cm of extension occurred across some lines but not others seismicity was characterized by intermittent local earthquakes but no sustained swarms or tremor a brief visit in june 1990 revealed that the shallow lake near the boiling pits was gone but activity in the pits themselves was similar to that of april 1990 only minor extension had occurred along a single edm line since the previous visit and no earthquakes m2 5 occurred during the visit subsequent 1 to 2 day visits occurred in october 1990 may 1992 may 1994 and june 2001 activity within the geothermal pits was relatively constant during every visit although during this 11 year period the level of the water in each pit decreased in june 2001 a 50 m wide region of mud pots and steaming ground in the central part of the geothermal area had developed no geologic evidence however suggested that an eruption would occur

morpho sedimentary characteristics of the volcaniclastic apron around stromboli volcano italy abstract submarine portions of stromboli volcano account for about 98 of the whole extent of the volcanic edifice and are mostly covered by volcaniclastic sediments that made up a modern volcaniclastic apron the architecture and main sedimentary processes acting within the apron are depicted through the integration of geophysical evidence multibeam long range side scan sonar and seismic data and seafloor sampling the apron shows on the whole a large variability both across and along slope of morphologies and deposits related to mass wasting and reworking processes passing into areas covered by hemipelagic sedimentation a large spectrum of erosive depositional features was recognized on the surface of the apron on shallower areas i e submerged shelves shore platforms and depositional terraces submarine features related to wave action and sea level fluctuations are present they mainly act as temporary storing and reworking areas for volcaniclastic material derived from subaerial portions unconfined cohesionless inertial flows commonly dominate the upper slope where gradients are very high up to 35 and grain to grain and grain to bed collisions are favoured within the flows these flows tend to evolve into turbidity currents on the lower slope in response to a marked decrease of slope gradients below 8 generating various erosive depositional features such as erosive furrows troughs channel levee features and coarse grained sediment waves the most active area of the apron lies offshore sciara del fuoco on the nw flank where a large amount of coarse grained volcaniclastic material derived by the persistent strombolian activity is collected and deposited by means of high and low density turbidity currents on the lower slope down to 2600 m bsl more than 20 km far from the island conversely other areas are mostly dominated by deposition via settling of suspended sediments related both to hemipelagic sedimentation and to the dispersion of fine tephras by the prevailing wind and marine currents such processes interfinger and overlie in space and time giving rise to a very complex morpho sedimentary facies distribution however the structural bilateral symmetry of stromboli volcano allows defining distinct morpho sedimentary zones where one or more type of processes dominates and related different stratal architecture of the apron the unbuttressed portions of the island nw and se are characterized by the emplacement of wide and thick debris avalanche deposits volume in the order of 1 2 km 3 for each event related to large scale sector collapses representing the most important and efficient mass wasting processes making up the apron such deposits are embedded within different volcaniclastic sequences and can be eroded or exhumed by successive gravity flows the result is a highly complex both spatially and vertically succession of facies where it is often difficult to depict an arranged series of processes conversely on buttressed flanks sw and ne a more ordered evolution of processes and deposits making up the apron is observed giving rise to a less complex apron architecture

waterways ice permeability at depth and water pressures at glacier d argentiere french alps pour eclaircir les changements survenus a la prise d eau sous glaciaire du glacier d argentiere une etude approfondie a ete realisee en 1979 80 avec 31 forages et un carottage jusqu au fond 240m juste en amont de la prise dans une zone surcreusee on observe que la glace en dessous d environ 100 m de profondeur est legerement permeable on a mesure la pression interstitielle de l eau dans la glace profonde le gradient piezometrique entre les trous de forage et le dephasage entre les fluctuations du niveau d eau qui augmente lorsqu on s eloigne de la rive droite il n y a pas de torrent sous glaciaire au fond du surcreusement sauf a son extremite amont la plupart de l eau de fonte doit s ecouler entre glace et rocher le long de la rive droite sa surface libre s elevant d environ 150 m au moment de l engorgement de juin on n a pas trouve de correlation nette entre la pression de l eau interstitielle profonde et la temperature de l air ou le debit a la prise sous glaciaire en aval

deep submarine pyroclastic eruptions theory and predicted landforms and deposits submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows however that significant pyroclastic activity can occur even at depths in excess of 3000 m in order to document and illustrate the full range of submarine eruption styles we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions 1 no gas exsolution 2 gas exsolution but no magma disruption 3 gas exsolution magma disruption and hawaiian style fountaining 4 volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse 5 magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity and 6 volatile content builds up in the top of a dike leading to vulcanian eruptions we also examine the role of bulk interaction steam explosivity and contact surface steam explosivity as processes contributing to volcaniclastic formation in these environments we concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities the most likely circumstance is the quiet effusion of magma with minor gas exsolution and the production of somewhat vesicular pillow lavas or sheet flows depending on effusion rate the amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption the most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity due to the localized concentration of volatiles in magma that has a low rise rate magmatic gas collects by bubble coalescence and ascends in large isolated bubbles which disrupt the magma surface in the vent producing localized blocks bombs and pyroclastic deposits another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions these deposits being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater should be easily distinguishable from strombolian and hawaiian eruptions however we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles in this case a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian style activity the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile induced hawaiian eruption specifically typical pyroclast sizes might be smaller fountain heights may exceed those expected for the purely magmatic hawaiian case cooling of descending pyroclasts would be more efficient leading to different types of proximal deposits and runout distances for density flows would be greater potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer in addition flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles and thus extremely poor in vesicles relative to typical flows associated with hawaiian style eruptions in the primary magmatic gas case we examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid ocean ridges furthermore the latter stages of development of volcanic edifices seamounts formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth but also to 1 the presence of a summit magma reservoir which favors the buildup of magmatic foams enhancing hawaiian style activity and episodic dike emplacement which favors strombolian style eruptions and 2 the common occurrence of alkalic basalts the co2 contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts these models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles

olympia interstadial vegetation landscape history and paleoclimatic implications of a mid wisconsinan mis3 nonglacial sequence from southwest british columbia canada lithostratigraphic 14c and palynologic analyses of peat and silty peat at three nearby sites reveal a 25 000 year vegetation and climate history of the olympia interstade for the fraser lowland british columbia 300 km within the southern limit of the cordilleran ice sheet at lynn valley polypodiaceae fern spores and nonarboreal pollen dominate 47 8 14c ka bp reflecting unstable and cold landscapes a pinus poaceae zone follows representing pine parkland and cool dry climate fluctuating values of picea and tsuga mertensiana pollen at lynn and seymour valleys and port moody characterize most of the olympia interstade during local peat deposition in cyperaceae and myrica wetlands until about 26 7 14c ka bp under a cool and moist climate a brief pinus tsuga heterophylla zone at lynn valley 44 39 14c ka bp suggests a climatic optimum a poaceae artemisia assemblage and deposition of silty sand after 26 7 14c ka bp reflect cooling and drying after which a unique lycopodium assemblage at lynn valley

late pleistocene stratigraphy and chronology of lower seymour valley southwestern british columbia a detailed study of the surficial sediments and landforms in the lower seymour valley has provided a complete record of the last glacial cycle this study shows that the valley was slowly aggrading before 29 ka and rapidly aggrading after 29 ka ice of the fraser glaciation reached the mouth of the valley about 22 ka and retreated before 18 5 ka the valley was subsequently vegetated ice once again advanced and occupied seymour valley after about 17 ka before 11 5 ka ice in seymour valley retreated a final time and the valley once again became vegetated

late pleistocene stratigraphy and chronology of lower chehalis river valley southwestern british columbia evidence for a restricted coquitlam stade sediments in lower chehalis valley span middle wisconsin olympia nonglacial interval to holocene time sediments are divided into six units with chronological control provided by 14 new radiocarbon ages fluvial gravel spans the transition from the late olympia nonglacial interval to the early fraser glaciation glaciolacustrine sedimentation represents the first definitive glacial activity in the valley and indicates that vashon ice in the fraser lowland blocked the mouth of the chehalis valley at ca 18 17 ka bp ice then flowed down the chehalis valley the chehalis valley deglaciated while ice persisted in the fraser lowland forming another lake after this lake drained terraces and fans formed this style of glaciation deglaciation is typical of many watersheds peripheral to the fraser lowland in that local valley ice was slightly out of phase with ice in the lowland this resulted in glacial lakes forming during both advance and retreat phases however in contrast to watersheds in the northwestern fraser lowland no definitive evidence of a coquitlam ice advance was found within the chehalis valley although glaciers in the area were likely active and advancing data from the chehalis valley indicates that they were not as extensive as previously thought since ice source areas in the northeastern fraser lowland are in the leeward area of the coast mountains it is suggested that lower precipitation resulted in limited glacier activity there during the coquitlam stade

glacier volume estimation as an ill posed inversion estimating a glacier s volume by inferring properties at depth e g bed topography or basal slip from properties observed at the surface e g area and slope creates a calculation instability that grows exponentially with the size of the glacier random errors from this inversion instability can overwhelm all other sources of error and can corrupt thickness and volume calculations unless problematic short spatial wavelengths are specifically excluded volume area scaling inherently filters these short wavelengths and automatically eliminates the instability while numerical inversions can also give stable solutions by filtering the correct wavelengths explicitly as is frequently done when regularizing a model each of the scaling and numerical techniques has applications to which it is better suited and there are trade offs in resolution and accuracy but when calculating volume neither the modeling nor the scaling approach offers a fundamental advantage over the other both are significantly limited by the inherently ill posed inversion and even though both provide stable volume solutions neither can give unique solutions

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

an iterative scheme for determining glacier velocities and stresses there are no direct methods to measure the boundary condition at the base of a glacier here we propose a method that works by iteratively changing boundary conditions until a satisfactory fit to surface observations is obtained the method is an accelerated version of one known as kozlov maz ya iteration we apply it to the problem of ice flow through a transverse cross section and show it to be effective by solving the inverse problem for a sequence of synthetic data we also apply the method to two real glaciers athabasca and perito moreno one of which has a known basal velocity distribution

lava bubble wall fragments formed by submarine hydrovolcanic explosions on lō ihi seamount and kīlauea volcano glassy bubble wall fragments morphologically similar to littoral limu o pele have been found in volcanic sands erupted on l ihi seamount and along the submarine east rift zone of k lauea volcano the limu o pele fragments are undegassed with respect to h2o and s and formed by mild steam explosions angular glass sand fragments apparently form at similar and greater depths by cooling contraction granulation the limu o pele fragments from l ihi seamount are dominantly tholeiitic basalt containing 6 25 7 25 mgo none of the limu o pele samples from l ihi seamount contains less than 5 57 mgo suggesting that higher viscosity magmas do not form lava bubbles the dissolved co2 and h2o contents of 7 of the limu o pele fragments indicate eruption at 1200 300 m depth 120 30 bar these pressures exceed that generally thought to limit steam explosions we conclude that hydrovolcanic eruptions are possible with appropriate pre mixing conditions at pressures as great as 120 bar