some unique surface patterns on ignimbrites on earth a bird s eye view as a guide for planetary mappers abstract observations of terrestrial analogs are critical to aiding planetary mappers in interpreting surface lithologies on other planets for instance the presence of ignimbrites on mars has been debated for over three decades and is supported by analogy with deposits on earth critical evidence includes the geomorphic and surface expression of the deposits and those in the central andes of south america are amongst the most cited analogs herein we describe some prominent surface textures and patterns seen in ignimbrites on the scale of high resolution remotely sensed data 10 1 m per pixel these include pervasive joints and fractures that contribute to yardang form and development as well as prominent mounds fissures and fracture networks spiders bugs boxworks on ignimbrite surfaces while all these features are related to intrinsic cooling and degassing processes the involvement of external water buried by hot pyroclastic flows enhances fumarolic activity advective cooling and joint development observations of these geomorphic expressions using remote sensing are only possible with the highest resolution data and limited surface erosion for mars where similarly high resolution datasets are available for example the high resolution imaging sensor experiment or hirise extensive dust cover may limit the recognition of similar features there however significant relief on some of these features on earth indicate they might still be detectable on mars

erosion by pyroclastic flows on lascar volcano chile pyroclastic flows generated in the 19 20 april 1993 eruption of lascar volcano chile produced spectacular erosion features scree and talus were stripped from the channels and steep slopes on the flanks of the volcano exposed bedrock and boulders suffered severe abrasion producing smoothed surfaces on coarse breccias and striations and percussion marks on bedrock and large boulders erosional furrows developed with wavelengths of 0 5 2 m and depths of 0 1 0 3 m furrows commonly nucleated downstream of large boulders or blocks which are striated on the upstream side and thereby produced crag and tail structures erosive features were produced where flows accelerated through topographic restrictions or where they moved over steep slopes the pyroclastic flows are inferred to have segregated during movement into lithic rich and pumice rich parts lithic rich deposits occur on slopes up to 14 whereas pumice rich deposits occur only on slopes less than 4 and mainly at the margins and distal parts of the 1993 fan the lithic rich deposits contain large up to 1 m lithic clasts eroded from the substrate and transported from the vent whereas pumice rich deposits contain only small typically 2 cm lithic clasts these observations suggest that lithic clasts segregated to the base of the flows and were responsible for much of the erosive phenomena the erosive features distribution of lithic clasts and deposit morphology indicate that the 1993 flows were highly concentrated avalanches dominated by particle interactions in some places the flows slid over the bedrock causing abrasion and long striations which imply that large blocks were locked in fixed positions for periods of about 1 s however shorter striae at different angles impact marks segregation of the deposits into pumice and lithic rich parts and mixing of bedrock derived lithic clasts throughout the deposits indicate that clasts often had some freedom of movement and that jostling of particles allowed internal mixing and density segregation to occur within the flows

erosion of tephra from the 1980 eruption of mount st helens erosion of tephra on hillslopes north of mount st helens was measured at intervals of several months between 1980 and 1983 using large arrays of stakes rill erosion was initially greater than sheetwash but its importance decreased comparatively quickly both rill erosion and sheetwash decreased by one to two orders of magnitude over the three year period because a stable rill network developed and more permeable and less erodible substrates were created or exposed the decrease occurred prior to recovery of plants the causes for the rapid decline in erosion at mount st helens explain patterns of erosion following several other recent tephra eruptions basin wide annual rates of erosion were computed by mapping the surface cover the hillslope gradient and the texture and thickness of tephra and by using statistical relations developed between them and erosion rates annual erosion decreased from 26 mm between may 1980 and may 1981 to 1 8 mm between may 1982 and may 1983 projecting this rate of decline into the future indicated that only about one sixth of the tephra on hillslopes will be removed by water erosion before soil creep and other forms of mass wasting again dominate hillslope evolution

erosional furrows formed during the lateral blast at mount st helens may 18 1980 nearly horizontal quasi periodic erosional features of 7 m average transverse wavelength and of order 100 m length occur in scattered locations from 3 5 to 9 km from the crater at mount st helens under deposits of the lateral blast of may 18 1980 we attribute the erosional features to scouring by longitudinal vortices resulting from flow instabilities induced by complex topography namely by streamline curvature in regions of reattachment downstream of sheltered regions and by the cross flow component of flow subparallel to ridge crests the diameter of the vortices and their transverse spacing inferred from the distance between furrows are taken to be of the order of the boundary layer thickness the inferred boundary layer thickness 14 m at 9 km from the source of the blast is consistent with the running length from the mountain to the furrow locations by using knowledge of ablation patterns on bodies and lofting of dust in high speed flow we are able to infer some features of the flow field within the blast within the furrows the erosion rate was of the order of 9 kg m 2 s 1 about 4 times greater than that expected from laboratory data obtained in flow free of longitudinal vortices the orientation of furrows induced by the cross flow instability can be used to measure the upwash angle and estimate the flow mach number at the central ridge of spirit lake the mach number is inferred to have been about 2 5 and the flow velocity approximately 235 m s the similarities and differences between the furrows reported here and channels observed at other volcanoes are discussed

longitudinal ridges in mass movement deposits prominent longitudinal features are often reported on the surfaces of mass movement deposits however the genesis and implications of these have not hitherto been considered and herein we present preliminary observations of their occurrence both in the field and in the laboratory elongated ridges are often oriented sub parallel to the flow direction and aligned radially from the source due to debris spreading they are particularly prominent in large 106m3 rock avalanches emplaced onto deformable substrates and are also found in the proximal reaches of volcanic debris avalanches flowbands which are longer and thinner expressions of longitudinal ridges are continuous along the entire flow length and are observed in rock avalanches emplaced onto glaciers in snow and some ice avalanches in pyroclastic flows and some block and ash flows in ejecta sheets in extraterrestrial landslides and in some volcanic debris avalanches other volcanic debris avalanches and the distal areas of rock avalanches often display hummocks that are aligned radially from the source we propose that these aligned hummocks are remnants of longitudinal ridges the formation of elongate ridges and their expressions as flowbands aligned hummocks or distal lobes and digits in qualitatively similar fashion in both laboratory and field environments suggests they represent an intrinsic tendency of granular flows in a wide range of situations

the significance of heat transport by shallow fluid flow at an active plate boundary the southern alps new zealand fluid flow can influence fault behavior here we quantify the role of groundwater heat advection in establishing the thermal structure of the alpine fault a major tectonic boundary in southern new zealand that accommodates most of the motion between the australian and pacific plates convergence on the alpine fault has rapidly uplifted the southern alps resulting in high geothermal gradients and a thin seismogenic zone a new equilibrium temperature profile from the 818 m deep deep fault drilling project 2b dfdp 2b borehole has been interrogated using one dimensional analytical models of fluid and rock advection models indicate a total heat flux of 720 mw m 2 results from groundwater flow with darcy velocities approximating to 7 8 10 10 m s 1 groundwaters advect significantly more heat than rock advection in the shallow orogen 6 km depth and are the major control on the subsurface temperature field

lithic breccia and ignimbrite erupted during the collapse of crater lake caldera oregon abstract the climactic eruption of mount mazama 6845 y b p vented a total of 50 km3 of compositionally zoned rhyodacitic to basaltic magma from a a single vent as a plinian pumice fall deposit and the overlying wineglass welded tuff and b ring vents as ignimbrite and coignimbrite lithic breccia accompanying the collapse of crater lake caldera new field and grain size data for the ring vent products are presented in this report the coarse grained poorly bedded clast supported lithic breccia extends as far as 18 km from the caldera center like the associated ignimbrite the breccia is compositionally zoned both radially and vertically and silicic mixed and mafic types can be recognized based on the proportion of rhyodacitic pumice matrix fractions in silicic breccias are depleted of fines and are lithic and crystal enriched relative to silicic ignimbrite due to vigorous gas sorting during emplacement ignimbrite occurs as a proximal veneer deposit overlying the breccia a medial 8 to 25 km from the caldera center compositionally zoned valley fill as much as 110 m thick and an unzoned distal 20 km facies which extends as far as 55 km from the caldera breccia within 9 km of the caldera center is interpreted as a coignimbrite lag breccia formed within the deflation zone of the collapsing ring vent eruption columns expanded pyroclastic flows of the deflation zone were probably vertically graded in both size and concentration of blocks as recently postulated for some turbidity currents an inflection in the rate of falloff of lithic clast size within the lithic breccia at 9 km may mark the outer edge of the deflation zone or may be an artifact of incomplete exposure the onset of ring vent activity at mt mazama was accompanied by a marked increase in eruptive discharge pyroclastic flows were emplaced as a semicontinuous stream as few ignimbrite flow unit boundaries are evident as eruption from the ring vents progressed flow runout distance and the extent of breccia deposition decreased due to a greater internal flow friction and b decreasing eruption column heights effect b probably resulted from a progressive decrease in magmatic gas content and discharge rate waning discharge may have been promoted by the tapping of more viscous crystal rich magma collapse of conduit walls and declining caldera collapse rate

evolution of the caldera forming eruption at crater lake oregon indicated by component analysis of lithic fragments crater lake caldera 8 10 km formed 6845 years b p 14c age during the climactic eruption of the volcanic edifice known as mount mazama is intermediate in size between small calderas associated with central vent eruptions and large calderas that have ring fracture vent systems our quantitative study of lithic fragments in the ejecta confirms the existing model of changes in vent configuration during the climactic eruption of mount mazama initial activity was from a single vent that produced a rhyodacite pumice fall from a plinian column altered preexisting volcanic rocks are the predominant lithic type in the plinian deposit and their extensive hydrothermal alteration is considered as evidence of their relatively deep origin the wineglass welded tuff lies atop the plinian deposit and contains a higher proportion of fresh volcanic rocks suggesting enlargement of the single vent by slumping of its walls this same vent enlargement caused the plinian eruption column to collapse and feed valley hugging pyroclastic flows that deposited the wineglass welded tuff when enough material was erupted from the shallow magma chamber that its roof was no longer adequately supported mount mazama collapsed to form the caldera while highly energetic pyroclastic flows produced the climactic ignimbrite a lag breccia that represents the proximal facies of the compositionally zoned climactic ignimbrite lies atop the wineglass welded tuff and contains predominantly altered volcanic rocks of deeper origin accompanied by minor granitoids from the magma chamber walls azimuthal differences in lithic component proportions in the lag breccia correlate well with the geology of the caldera walls indicating that the climactic ignimbrite was ejected by multiple vents along a ring fracture system systematic lithic component changes within the lag breccia suggest different quarrying levels that reflect waxing and waning of the discharge rate during the caldera collapse phase of the climactic eruption our lithic component analysis demonstrates that calderas that may be too small to experience structural resurgence such as crater lake nevertheless may form by syneruptive subsidence along ring fractures

crosshole lithotectonic correlation in high grade metamorphic rocks central southern connecticut well logs acquired in two scientific drill holes in central southern connecticut near moodus township and gillette casue state park measured the electrical sonic and natural radioactive properties of the rocks within and adjacent to the honey hill fault zone a crosshole correlation was made with logs of these physical properties which shows distinct similarities between the metamorphic rocks encountered in each hole even though they are separated by 8 mi 13 km this log based correlation indicates that an anomalous interval associated with the honey hill fault contact maintains a 7 ft 2 m thickness and an apparent dip of 2 3 between the two holes the overlying interval consisting mainly of the tatnic hill and hebron formations thins by about 150 ft 50 m between moodus and gillette castie and the log responses which remain similar in character indicate that tectonic compaction of this interval has taken place log anomalies below the fault in the avalon complex rocks are attributed to regional fracturing and brecciation and also correlate between the holes differences between the holes in fine scale variation and absolute value of the logs are generally attributed to intrinsic mineralogy and or localized structure these log data enable the deformed rocks of the tatnic hill and hebron formations and avalon complex rocks including the honey hill fault zone to be correlated crosshole detailing the lithotectonic stratigraphy as a function of depth

a conceptual model for block and ash flow basal avalanche transport and deposition based on deposit architecture of 1998 and 1994 merapi flows the 1998 block and ash flow baf deposits on the western flanks of merapi were described both immediately following emplacement and after one and two wet seasons of erosion this afforded a unique combination of data on deposit morphology and internal structure from proximal to distal reaches the deposits of the basal avalanches from individual baf events were classified into three major and two minor facies in channelised reaches primarily resulting from effects of channel confinement and slope termination reaches were classified into three facies related to preevent topography the deposit facies architecture was interpreted to understand particle transport and deposition within the framework of granular flow systematics the transport model we propose for these basal avalanches involves unsteady flow conditions generated by pulses of collapse as the source and or by development of kinetic waves during the granular flow the coarsest clasts along with low density material migrated to the wave pulse fronts within these flows whereas in bulk flow grain dispersive pressures and kinetic sieving result in coarsest clasts being buoyed to the flow top with this tendency being greatest on higher slopes greater kinetic energy and with greater flow confinement maximising particle collisions deposition begins as the flow reaches near its full extent an initial pulse or flow wave freezes rapidly from its base upward and its rear forward as it looses kinetic energy and dispersive pressure such that an upper higher energy part of the flow is still able to move downstream over the frozen base later waves or pulses then accrete progressively horizontally upslope banking up onto or overtopping earlier deposited sediment hence the overall flow freezes from its front to its tail at termination reaches in unconfined areas the overflowing upper part of flow gradually deposits from its base upward resulting in a slightly tapering sheet formed deposit marked by a front made up of wood fragments and large boulders on sudden slope breaks in termination areas piling up of sediment occurs in flat reaches producing whaleback type forms as the flows rapidly lost competence one implication of this model is that each kinetic wave or flow pulse crest developed within the basal avalanche represents a portion of greater flow depth or stage height hence development of these crests control the ability of parts of the basal avalanche to escape from confined channels and generate unexpected hazards

three decades of geochronologic studies in the new england appalachians over the past 30 years both isotope geochronology and plate tectonics grew from infancy into authoritative disciplines in the geological sciences previously mountain systems like the appalachians had been viewed almost entirely in the context of the classical geosyncline implying a gradualism in stratigraphic and structural change throughout the orogen age control determined largely from distant fossiliferous strata was unabashedly carried to high grade metamorphic rocks based only on lithological correlations with the new concepts in tectonics came the realization that abrupt breaks in stratigraphy and structure occur in many cases at the boundaries of lithotectonic zones fortunately the new techniques of isotope geochronology could be brought to bear directly on the rocks of the immediate study area this paper chronicles some of the major contributions to the geology of the new england appalachians that resulted from these efforts during the past three decades in tracing the history of geochronologic research one encounters an increasingly sophisticated approach to the analytical and interpretive aspects of the discipline today the geochronologist can under optimum conditions constrain the age of stratigraphic units igneous activity deformation and metamorphism with accuracy that is capable of resolving fine structure within individual orogenic pulses he participates in full partnership with other colleagues of the science in unravelling the mysteries of mountain building several of the topical problems of new england geology in which geochronology played a key role include 1 the recognition and delineation of avalonia as a late proterozoic eastern basement distinct from more western terranes 2 the dating of the white mountain plutonic volcanic suite a mesozoic igneous event spanning 100 m y and 3 the temporal and spatial separation of structural and metamorphic features imprinted by the taconic and acadian orogenies the existing geochronology is summarized into a map and table emphasizing the temporal construction of the new england appalachians by using lithotectonic zones as the building blocks of the orogen seven such zones are defined in terms of pre syn and post assembly geologic history from west to east these lithotectonic zones are 1 berkshire green mountain 2 rowe hawley 3 connecticut valley 4 bronson hill 5 kearsarge central maine 6 tatnic hill nashoba and 7 avalonia avalonia is further divided into three subzones hope valley esmond dedham and penobscot bay which themselves may have had distinct origins and assembly histories the boundaries between these zones are faults in most cases some of which may have had recurring movement to further complicate any plate tectonic scenario a delineation of underlying grenvillian chain lakes and avalonian basement is also attempted which now can make use of isotopes in igneous rocks as petrogenetic indicators to supplement the rare occurrences of basement outcrop within mobile zones of the orogen the belt of permian thermal disturbance within the kearsarge central maine zone is hypothesized to reflect rapid rebound following compressional thickening of underlying avalonian basement during the alleghanian orogeny

origin of giant martian polygons extensive areas of the martian northern plains in utopia and acidalia planitiae are characterized by polygonal terrane polygonal terrane consists of material cut by complex troughs defining a pattern resembling mudcracks columnar joints or frost wedge polygons on earth however the martian polygons are orders of magnitude larger than these potential earth analogues leading to severe mechanical difficulties for genetic models based on simple analogy arguments plate bending and finite element models indicate that shrinkage of desiccating sediment or cooling volcanics accompanied by differential compaction over buried topography can account for the stresses responsible for polygon troughs as well as the large size of the polygons although trough widths and depths relate primarily to shrinkage the large scale of the polygonal pattern relates to the spacing between topographic elevations on the surface buried beneath polygonal terrane material geological relationships favor a sedimentary origin for polygonal terrane material but our model is not dependent on the specific genesis our analysis also suggests that the polygons must have formed at a geologically rapid rate

surface morphology of caldera forming eruption deposits revealed by lidar mapping of crater lake national park oregon implications for deposition and surface modification abstract large explosive eruptions of silicic magma can produce widespread pumice fall extensive ignimbrite sheets and collapse calderas the surfaces of voluminous ignimbrites are rarely preserved or documented because most terrestrial examples are heavily vegetated or severely modified by post depositional processes much research addresses the internal sedimentary characteristics flow processes and depositional mechanisms of ignimbrites however surface features of ignimbrites are less well documented and understood except for comparatively small volume deposits of historical eruptions the 7700 calendar year b p climactic eruption of mount manama usa vented 50 km 3 of magma deposited first as rhyodacite pumice fall and then as a zoned rhyodacite to andesite ignimbrite as crater lake caldera collapsed lidar collected during summer 2010 reveals the remarkably well preserved surface of the manama ignimbrite and related deposits surrounding crater lake caldera in unprecedented detail despite forest cover the 1 m lateral and 4 cm vertical resolution lidar allows surface morphologies to be classified surface morphologies are created by internal depositional processes and can point to the processes at work when pyroclastic flows come to rest we describe nine surface features including furrow ridge sets and wedge shaped mounds in pumice fall eroded by high energy pyroclastic surges flow parallel ridges that record the passage of multiple pyroclastic flows perched benches of marginal deposits stranded by more mobile pyroclastic flow cores hummocks of dense clasts interpreted as lag deposit transverse ridges that mark the compression and imbrication of flows as they came to rest scarps indicating ignimbrite remobilization fields of closely spaced pits caused by phreatic explosions fractures and cracks due to extensional processes resulting from ignimbrite volume loss and stream channels eroded in the newly formed surface the nine morphologies presented here illustrate a dynamic depositional environment that varied spatially and with time during the eruption and show that multiple processes modified the ignimbrite after deposition both during and after the eruption

secondary hydroeruptions in pyroclastic flow deposits examples from mount st helens abstract secondary hydroeruptions occur in pyroclastic flow deposits when water or ice is trapped beneath hot pyroclastic debris and rapidly heated to steam these eruptions display various styles of activity including fumarolic degassing tephra fountaining and explosive cratering the deposits which occupy the layer 3 stratigraphic position on the top of pyroclastic flow units can be distinguished from ash cloud material by lateral thickness variation clast composition and other sedimentary features the ejecta of secondary hydroeruptions comprise a subset of hydrovolcanic pyroclastic deposits a small secondary hydroeruption observed on the mount st helens pumice plain in 1981 produced tephra that was emplaced ballistically by deposition from base surges and by fallout from an eruption column stratigraphic descriptions and grain size analysis of the ejecta from several secondary craters on the pumice plain demonstrate that the bedforms produced by a hydroeruption change with crater diameter in particular craters of small diameter are surrounded by interbedded ripple laminated ash horizons and nonstratified fines depleted units large craters have ejecta ramparts comprised of coarse dunes and antidunes these bedform changes are related to a progressive increase in eruptive energy which produces base surges of greater power and eruptive columns of greater height we suggest that the style of activity displayed during a secondary hydroeruption is controlled by both the total thermal energy of the system and the permeability of the pyroclastic overburden

fine grained linings of leveed channels facilitate runout of granular flows abstract catastrophic dense granular flows such as occur in rock avalanches debris flows and pyroclastic flows move as fully shearing mixtures that have approximately 60 vol solids and tend to segregate to form coarse grained fronts and leveed channels levees restrict spreading of unconfined flows and form as coarse particles that become concentrated in the top of the flow are transported to the front and then advect to the sides in the flow head channels from which most material has drained away down slope are commonly lined with fine grained deposit widely thought to remain from the tail of the waning flow we show how segregation in experimental dense flows of carborundum or sand 300 425 m mixed with spherical fine ballotini 150 250 m on rough slopes of 27 29 produces fine grained channel linings that are deposited with the levees into which they grade laterally maximum runout distance is attained with mixtures containing 30 40 sand just sufficient to segregate and form levees that are adequately robust to restrict the spreading attributable to the low friction fines resin impregnation and serial sectioning of deliberately arrested experimental flows shows how fines lined levees form from the flow head the flows create their own stable conduit entirely from the front which in a geophysical context can play an important mechanistic role in facilitating runout the flow self organization ensures that low friction fines at the base of the segregated channel flow shear over fine grained substrate in the channel thus reducing frictional energy losses we propose that in pyroclastic flows and debris flows which have considerable mobility attributable to pore fluid pressures such fine grained flow contact zones form similarly and not only reduce frictional energy losses but also reduce flow substrate permeability so as to enhance pore fluid pressure retention thus the granular flow self organization that produces fine grained channel linings can be an important factor in facilitating long runout of catastrophic geophysical flows on the low slopes few degrees of depositional fans and aprons around mountains and volcanoes

pulsating flow dynamics of sustained forced pyroclastic density currents insights from a facies analysis of the campo de la piedra pomez ignimbrite southern puna argentina the quaternary campo de la piedra pomez ignimbrite cppi is a superbly exposed partially indurated rhyolitic ignimbrite emplaced on the southern puna of argentina it is characterized by a variety of facies that record in unprecedented detail the flow dynamics of the parent pyroclastic density currents pdcs detailed facies analysis and internal architecture defined using a sequential stratigraphy approach reveal that cppi was formed by sustained pdcs generated from a low fountain eruptive style boiling over the pdcs had overall flow conditions characterized by high particle concentration and limited capability to surmount topographic obstacles the mobility of the pdcs was largely controlled by high pore pressure and the continuous supply at the source sustained forced convection dominated pdcs the successive forestepping backstepping stacking patterns identified in the cppi reflect a marked unsteadiness of its parent pdcs due to a pulsating discharge rate at the source the lateral facies variations in the cppi record the non uniform character of its parent pdcs as they flowed outward from the base of the collapsing fountain proximal medial areas characterized by steady aggradation rates pass through to distal braided thalwegs with highly variable aggradation rates to frontal edges characterized by the step aggradations of secondary decoupled pumice rich lobes collectively the facies variations in the cppi record the complex dynamics of sustained pdcs that include pulsating discharge rate at the source progressive modification of the original topography and lateral flow transformations

characteristics and origin of polygonal terrain in southern utopia planitia mars results from mars orbiter laser altimeter and mars orbiter camera data giant polygons on mars with several kilometers in diameter were first observed in mariner 9 and viking orbiter images and their origin formation and evolution have remained enigmatic since that time new data obtained by the mars orbiter laser altimeter mola and the mars orbiter camera moc on board the mars global surveyor spacecraft now permit analysis of topography and morphology of the polygonal terrain in unprecedented detail mola data show that 1 giant polygonal terrain in utopia is located at the lower slopes of a basin structure that is the utopia basin 2 the onset of polygonal terrain in utopia is close to the same elevation in several profiles and lies at about the same elevation as a terrace which was interpreted as a shore line of an ancient body of standing water within the utopia basin proper 3 polygonal terrain occurs over a wide range of elevations on regional slopes of 0 1 4 the depths of the troughs range from 5 m to 115 m averaging about 30 m and tend to be greater toward the center of the utopia basin 5 the mean width of polygonal troughs is of the order of 2 km ranging from 0 5 to 7 5 km data from the mars orbiter camera moc indicate that 1 the troughs are generally broad graben like features with varying morphologies i e terraces and lobateness and dimensions widths and depths 2 trough morphology has been modified by aeolian processes 3 polygonal troughs are weakly interconnected at moc resolutions and there are no smaller polygons observed within the giant polygons 4 circular depressions which are probably related to subsurface collapse sometimes occur at the bottoms of polygonal troughs 5 small scale polygonal terrain on the ejecta blankets of young craters with fluidized ejecta in the investigated area exhibits different characteristics i e smaller size presence of rims greater degree of interconnections than giant polygons in the viking images we see that 1 old impact craters are increasingly buried with younger materials toward the basin center and that 2 a large number of superposed impact craters on polygonal terrain exhibit distinctive ejecta morphologies such as rampart ejecta blankets and single and double lobate ejecta blankets mola and moc observations are consistent with the formation of polygonal terrain in the area of a former standing body of water but polygon size seems too large to be readily accounted for by desiccation or freezing processes alone on the basis of the observed characteristics we propose that the giant polygons are primarily of tectonic origin being caused by uplift of the floor of the utopia basin there are several candidates for the cause of uplift 1 the removal of the load representing former standing bodies of water water thickness estimated for the utopia basin is about 1 km in this scenario removal of this load comparable to loads placed on terrestrial continental lithosphere by the laurentide and scandinavian ice sheets by loss of the water or ice could cause uplift of the floor and polygon formation 2 the freezing and expansion of residual water buried by sediments or in the near subsurface or 3 a combination of these from the discussion of alternative models in the light of the mola and moc data we conclude that formation of giant polygons by tectonic uplift of the basin floor is most likely and deserves further investigation

the distribution style and intensity of alleghanian metamorphism in south central new england petrologic evidence from the pelham and willimantic domes abstract alleghanian metamorphism in south central new england is characterized by late pennsylvanian documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm kyanite mathrm muscovite mathrm staurolite end document grade heterogeneous reconstitution of migmatitic documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepack

post depositional fracturing and subsidence of pumice flow deposits lascar volcano chile unconsolidated pyroclastic flow deposits of the 1993 eruption of lascar volcano chile have with time become increasingly dissected by a network of deeply penetrating fractures the fracture network comprises orthogonal sets of decimeter wide linear voids that form a pseudo polygonal grid visible on the deposit surface in this work we combine shallow surface geophysical imaging tools with remote sensing observations and direct field measurements of the deposit to investigate these fractures and their underlying causal mechanisms based on ground penetrating radar images the fractures are observed to have propagated to depths of up to 10 m in addition orbiting radar interferometry shows that deposit subsidence of up to 1 cm year 1 occurred between 1993 and 1996 with continued subsidence occurring at a slower rate thereafter in situ measurements show that 1 m below the surface the 1993 deposits remain 5 c to 15 c hotter 18 years after emplacement than adjacent deposits based on the observed subsidence as well as estimated cooling rates the fractures are inferred to be the combined result of deaeration thermal contraction and sedimentary compaction in the months to years following deposition significant environmental factors including regional earthquakes in 1995 and 2007 accelerated settling at punctuated moments in time the spatially variable fracture pattern relates to surface slope and lithofacies variations as well as substrate lithology similar fractures have been reported in other ignimbrites but are generally exposed only in cross section and are often attributed to formation by external forces here we suggest that such interpretations should be invoked with caution and deformation including post emplacement subsidence and fracturing of loosely packed ash rich deposits in the months to years post emplacement is a process inherent in the settling of pyroclastic material

lidar derived surface roughness signatures of basaltic lava types at the muliwai a pele lava channel mauna ulu hawai i we used light detection and ranging lidar data to calculate roughness patterns homogeneity mean roughness and entropy for five lava types at two different resolutions 1 5 and 0 1 m pixel we found that end member types a and p hoehoe are separable with 95 confidence at both scales indicating that roughness patterns are well suited for analyzing types of lava intermediate lavas were also explored and we found that slabby p hoehoe is separable from the other end members using 1 5 m pixel data but not in the 0 1 m pixel analysis this suggests that the conversion from p hoehoe to slabby p hoehoe is a meter scale process and the finer roughness characteristics of p hoehoe such as ropes and toes are not significantly affected furthermore we introduce the ratio frac ent hom derived from lava roughness as a proxy for assessing local lava flow rate from topographic data high entropy and low homogeneity regions correlate with high flow rate while low entropy and high homogeneity regions correlate with low flow rate we suggest that this relationship is not directional rather it is apparent through roughness differences of the associated lava type emplaced at the high and low rates respectively

dip domain method applied to the mesozoic connecticut valley rift basins this paper presents a new approach to structural analysis of u s east coast mesozoic basins a contoured compilation of numerical values of dip data for the connecticut valley rift basins reveals distinct domains related to their broader tectonic development additional more standard geologic constraints are then used to interpret the dip domain patterns most of the tilt deformation involved and hence postdated early jurassic basaltic flow units and overlying jurassic thick alluvial deposits normal drag characterizes the attitude of mesozoic strata along the western border fault of the main hartford basin whereas reverse drag is common along its larger listric eastern border fault strata within the basin mostly along its eastern margin include several subgrabens and or strongly tilted zones associated with early subbasins marked by local changes in strike of the early border fault the meriden cross graben may be a similar structure that extended much farther southwestward across the basin within the hartford basin linear domains of steeper dips are interpreted as surface expressions of the edges of a 5 to 15 km wide late stage central graben that trends n15 e diagonally across the basin possibly a reflection of very late strike slip stress systems

postglacial vegetation fire and climate history of the siskiyou mountains oregon usa the forests of the siskiyou mountains are among the most diverse in north america yet the long term relationship among climate diversity and natural disturbance is not well known pollen plant macrofossils and high resolution charcoal data from bolan lake oregon were analyzed to reconstruct a 17 000 yr long environmental history of high elevation forests in the region in the late glacial period the presence of a subalpine parkland of artemisia poaceae pinus and tsuga with infrequent fires suggests cool dry conditions after 14 500 cal yr b p a closed forest of abies pseudotsuga tsuga and alnus rubra with more frequent fires developed which indicates more mesic conditions than before an open woodland of pinus quercus and cupressaceae with higher fire activity than before characterized the early holocene and implies warmer and drier conditions than at present in the late holocene abies and picea were more prevalent in the forest suggesting a return to cool wet conditions although fire episode frequency remained relatively high the modern forest of abies and pseudotsuga and the present day fire regime developed ca 2100 cal yr b p and indicates that conditions had become slightly drier than before sub millennial scale fluctuations in vegetation and fire activity suggest climatic variations during the younger dryas interval and within the early holocene period the timing of vegetation changes in the bolan lake record is similar to that of other sites in the pacific northwest and klamath region and indicates that local vegetation communities were responding to regional scale climate changes the record implies that climate driven millennial to centennial scale vegetation and fire change should be considered when explaining the high floristic diversity observed at present in the siskiyou mountains d 2005 university of washington all rights reserved

field observations and surface characteristics of pristine block and ash flow deposits from the 2006 eruption of merapi volcano java indonesia abstract a series of pristine block and ash flow deposits from the may june 2006 eruption of merapi represent an exceptional record of small volume pyroclastic flows generated by gravitational lava dome collapses over a period of about two months the deposits form nine overlapping lobes reaching 7 km from the summit in the gendol river valley on the volcano s southern flank which were produced by successive flows generated during and after the major dome collapse event on june 14 both single pulse post june 14 events and multiple pulse pyroclastic flows generated by sustained dome collapses on june 14 are recognised and three types of deposits spread over an area of 4 7 km are distinguished totalling 13 3 10 6 m 3 1 valley confined basal avalanche deposits 11 7 10 6 m 3 in the gendol river valley 2 overbank pyroclastic flow and associated surge deposits 1 4 10 6 m 3 where parts of the basal avalanche spread laterally onto interfluves and were subsequently channeled into the surrounding river valleys and 3 dilute ash cloud surge deposits 0 2 10 6 m 3 along valley margins variations in the distribution surface morphology and lithology of the deposits are related to the source materials involved in individual pyroclastic flow forming events and varying modes of transport and deposition of the different flows inferred flow velocities of the largest block and ash flows generated on june 14 vary from 43 8 13 5 m s for the basal avalanche and from 62 6 24 2 m s for the ash cloud surge the minimum temperatures range from 400 c for the basal avalanche to 165 c for the overlying ash cloud due to the potential of being re channeled into adjacent river valleys and flowing laterally away from the main river channel the overbank pyroclastic flows are considered the most hazardous part of the block and ash flow system the conditions that lead to their development during flow transport and deposition must be taken into account when assessing future pyroclastic flow hazards at merapi and similar volcanoes elsewhere

depositional processes in large scale debris flow experiments this study examines the depositional process and characteristics of deposits of large scale experimental debris flows to 15 m3 composed of mixtures of gravel to 32 mm sand and mud the experiments were performed using a 95 m long 2 m wide debris flow flume that slopes 31 following release experimental debris flows invariably developed numerous shallow 10 cm deep surges sediment transported by surges accumulated abruptly on a 3 runout slope at the mouth of the flume deposits developed in a complex manner through a combination of shoving forward and shouldering aside previously deposited debris and through progressive vertical accretion progressive accretion by the experimental flows is contrary to commonly assumed en masse sedimentation by debris flows despite progressive sediment emplacement deposits were composed of unstratified accumulations of generally unsorted debris hence massively textured poorly sorted debris flow deposits are not emplaced uniquely en masse the depositional

deformation of the wineglass welded tuff and the timing of caldera collapse at crater lake oregon abstract four types of deformation occur in the wineglass welded tuff on the northeast caldera rim of crater lake a vertical tension fractures b ooze outs of fiamme c squeeze outs of fiamme and d horizontal pull apart structures the three types of plastic deformation b d developed in the lower part of the wineglass welded tuff where degree of welding and density are maximum deformation originated from concentric normal faulting and landsliding as the caldera collapsed the degree of deformation of the wineglass welded tuff increases toward the northeast part of the caldera where plastic deformation occurred more easily because of a higher emplacement temperature probably due to proximity to the vent the probable glass transition temperature of the wineglass welded tuff suggests that its emplacement temperature was 750 c where the tuff is densely welded calculation of the conductive cooling history of the wineglass welded tuff and the preclimactic cleetwood lava flow under assumptions of a initially isothermal sheet and uniform properties suggests that a caldera collapse occurred a maximum of 9 days after emplacement of the wineglass welded tuff and that b the period between effusion of the cleetwood lava flow and onset of the climactic eruption was

the taupo eruption new zealand i general aspects the ca a d 186 taupo eruption was the latest eruption at the taupo volcanic centre occurring from a vent at horomatangi reefs now submerged beneath lake taupo in the central north island of new zealand minor initial phreatomagmatic activity was followed by the dry vent 6 km 3 hatepe plinian outburst large amounts of water then entered the vent during the 2 5 km 3 hatepe phreatoplinian ash phase eventually stopping the eruption though large amounts of water continued to be ejected from the vent area causing gullying of the ash deposits after a break of several hours to weeks phreatoplinian activity resumed generating the 1 3 km 3 rotongaio ash notable for its fine grainsize and for containing significant quantities of non or poorly vesicular juvenile material the vent area then became dry again and eruption rates and power markedly increased into the 23 km 3 taupo ultraplinian phase which is the most powerful plinian outburst yet documented synchronous with this ultraplinian activity lesser volumes of non to partially welded ignimbrite were generated by diversion of ejecta from or partial collapse of the eruption column the rapid rate of magma withdraw al during this phase removed support from the vent area to trigger local vent collapse and initiate the catastrophic eruption of the ca 30 km 3 taupo ignimbrite finally after some years lava was extruded on to the floor of the reformed lake taupo and floating fragments derived from the lava carapace were driven ashore the known eruption volume is more than 65 km 3 while additional volumes are represented by primary material now beneath lake taupo and layer 3 to the ignim brite phases a total volume of more than 105 km 3 is likely equivalent to more than 35 km 3 of magma plus more than 3 km 3 of lithic debris airfall deposits more than 10 cm thick blanketed 30000 km 2 of land east of the vent while ignimbrite covers a near circular area of 20000 km 2 widespread and locally severe ground shaking occurred during but mostly after the eruption associated with subsidence in the lake taupo basin secondary deposits are abundant above and extending beyond the taupo ignimbrite consisting of the products of surface water interacting with the still hot ignimbrite and subsequent water reworking of the light pumiceous materials the complexity and size of this eruption preclude accurate forecasting of the size nature and return period of the inevitable next eruption from the taupo volcanic centre

eruptive history and geochronology of mount mazama and the crater lake region oregon geologic mapping k ar and 40 ar 39 ar age determinations supplemented by paleomagnetic measurements and geochemical data are used to quantify the quaternary volcanic history of the crater lake region in order to define processes and conditions that led to voluminous explosive eruptions the cascade arc volcano known as mount mazama collapsed during its climactic eruption of 50 km 3 of mainly rhyodacitic magma 7700 yr ago to form crater lake caldera the mazama edifice was constructed on a pleistocene silicic lava field amidst monogenetic and shield volcanoes ranging from basalt to andesite similar to parental magmas for mount mazama between 420 ka and 35 ka mazama produced medium k andesite and dacite in 2 1 proportion the edifice was built in many episodes some of the more voluminous occurred approximately coeval with volcanic pulses in the surrounding region and some were possibly related to deglaciation following marine oxygen isotope stages mis 12 10 8 6 5 2 and 2 magmas as evolved as dacite erupted many times commonly associated with or following voluminous andesite effusion establishment of the climactic magma chamber was under way when the first preclimactic rhyodacites vented ca 27 ka the silicic melt volume then grew incrementally at an average rate of 2 5 km 3 k y 1 for nearly 20 k y the climactic eruption exhausted the rhyodacitic magma and brought up crystal rich andesitic magma mafic cumulate mush and wall rock granodiorite postcaldera volcanism produced 4 km 3 of andesite during the first 200 500 yr after collapse followed at ca 4800 yr b p by 0 07 km 3 of rhyodacite the average eruption rate for all mazama products was 0 4 km 3 k y 1 but major edifice construction episodes had rates of 0 8 km 3 k y 1 the long term eruption rate for regional monogenetic and shield volcanoes was d 0 07 km 3 k y 1 but only 0 02 km 3 k y 1 when the two major shields are excluded plutonic xenoliths and evidence for crystallization differentiation imply that the amount of magma intruded beneath mount mazama is several times that which has been erupted the eruptive and intrusive history reflects competition between 1 crystallization driven by degassing and hydrothermal cooling and 2 thermal input from a regional magma flux focused at mazama before ca 30 ka relatively small volumes of nonerupted derivative magma crystallized to form a composite pluton because the upper crust had not been heated sufficiently to sustain voluminous convecting crystal poor melt subsequently and perhaps not coincidentally during mis 2 a large volume of eruptible silicic magma accumulated in the climactic chamber probably because of heating associated with mantle input to the roots of the system as suggested by eruption of unusually primitive magnesian basaltic andesite and tholeiite west of mazama