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Ken Hon - One of the best experts on this subject based on the ideXlab platform.
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lava flow hazard prediction and monitoring with uas a case study from the 2014 2015 pāhoa lava flow crisis hawai i
Journal of Applied Volcanology, 2017Co-Authors: Nicolas R Turner, Ryan L Perroy, Ken HonAbstract:Accurately predicting lava flow path behavior is critical for active crisis management operations. The advance and emplacement of pāhoehoe flows modifies and inverts pre-existing topography, prompting the need for rapid and accurate updates to the topographic models used to forecast flow paths. The evolution and velocity of pāhoehoe flows are dependent on macro and micro topography, the slope of the descent path, effusion rate, and rheology. During the 2014–2015 Pāhoa crisis on the island of Hawai‘i, we used a low-altitude unmanned aerial system (UAS) to quickly and repeatedly image the active front of a slowly advancing pāhoehoe lava flow. This imagery was used to generate a series of 1 m resolution bare-earth digital elevation models (DEMs) and associated paths of steepest descent over the study area. The spatial resolution and timeliness of these UAS-derived models are an improvement over the existing topographic data used by managers during the crisis. Results from a stepwise resampling experiment suggest that the optimum DEM resolution for generating accurate pāhoehoe flow paths through lowland tropical forest environments is between 1 and 3 m. Our updated models show that future flows in this area will likely be deflected by these newly emplaced flows, possibly threatening communities not directly impacted by the original 2014–2015 lava flow. We demonstrate the value of deploying UAS during a dynamic volcanic crisis and suggest that this technology can fill critical monitoring gaps for Kīlauea and other active volcanoes worldwide.
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a new model for the emplacement of columbia river basalts as large inflated Pahoehoe lava flow fields
Geophysical Research Letters, 1996Co-Authors: Stephen Self, George Pl Walker, Ken Hon, Thorvaldur Thordarson, Laszlo P Keszthelyi, M T Murphy, Philip E Long, S FinnemoreAbstract:Extensive flows of the Columbia River Basalt (CRB) Group in Washington, Oregon, and Idaho are dominantly inflated compound Pahoehoe sheet lavas. Early studies recognized that CRB lavas are compound Pahoehoe flows, with textures suggesting low flow velocities, but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks. However, small volume (< 1 km³) compound Pahoehoe flows on Kilauea, Hawai'i, demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger (10–20 km3) Pahoehoe flows in Iceland. The vertical distribution of vesicles and other morphologic features within CRB lava flows indicate that they grew similarly by inflation. Small Pahoehoe lobes at the base and top of many CRB Pahoehoe lava flows indicate emplacement in a gradual, piecemeal manner rather than as a single flood. We propose that each thick CRB sheet flow was active for months to years and that each group of flows produced by a single eruption (a flow field) was emplaced slowly over many years.
Evandro Fernandes De Lima - One of the best experts on this subject based on the ideXlab platform.
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characterization of subaerial volcanic facies using acoustic image logs lithofacies and log facies of a lava flow deposit in the brazilian pre salt deepwater of santos basin
Marine and Petroleum Geology, 2019Co-Authors: Sofia Alves Fornero, Gabriel Medeiros Marins, Janaina Teixeira Lobo, Antonio Fernando Menezes Freire, Evandro Fernandes De LimaAbstract:Abstract Volcanic rock facies characterization in subsurface log data have always being challenging. Even though considerable types of well logs are acquired, the results achieved on facies characterization with the conventional log suits are very limited. Conversely, high-resolution borehole image logs calibrated with side wall core samples can provide the necessary structural and textural information for facies definitions. In this case study, an integration of good quality acoustic image log data, side wall core petrography and geochemical analyses provided a good understanding of volcanic facies and stratigraphic relationships. Additionally, outcrop data from the analogous Serra Geral Formation and other Large Igneous Provinces were used for comparison. In the studied well, from Santos basin, Brazil, it was possible to identify several kinds of subaerial basaltic lava flow units, such as compound Pahoehoe, sheet Pahoehoe and rubbly Pahoehoe lava flows. Vesicles, amygdales, vesicle cylinders, sub-horizontal vesicle sheets, autobreccias and entablature are some of the structures described in this study. As a result, 2 image catalogues of subaerial volcanic rocks were produced characterizing facies and flow units along with a stratigraphic model of the history of this volcanism. This is the first time that Pahoehoe lava flow units could be characterized at an offshore Brazilian basin. The results achieved are important for the understanding of the Cretaceous volcanism events in the pre-salt layer and also provide support for the evaluation and geological modelling of the volcanic rocks in Santos Basin oil fields.
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The role of viscosity in the emplacement of high-temperature acidic flows of Serra Geral Formation in Torres Syncline (Rio Grande do Sul State, Brazil)
2018Co-Authors: Matheus Silva Simões, Evandro Fernandes De Lima, Lucas De Magalhães May Rossetti, Bruno Pinto RibeiroAbstract:The acidic flows from Serra Geral Formation in Torres Syncline, Rio Grande do Sul, Brazil, are on the top of a volcanic sequence composed by a complex facies association of compound, simple and rubbly Pahoehoebasic flows, acidic lava domes, and tabular acidic lava flows. The origin and emplacement conditions of the acidic volcanic rocks are discussed in this paper based on petrology, on calculated apatite saturation thermometry temperatures, and on estimated viscosity data. The liquidus temperatures for metaluminous rhyodacite to rhyolite samples are about 1,067.5 ± 25ºC in average. The viscosity (η) values vary from 105 to 106 Pas for anhydrous conditions, suggesting the emplacement of high-temperature - low-viscosity lava flows and domes. The occurrence of acidic lava domes above simple Pahoehoe flows as flow-banded vitrophyres was under low effusion rates, in spite of their high temperature and low viscosities, which are reflected in their small height. The emplacement of lava domes has continued until the eruption of rubbly Pahoehoe flows and the geometry of these deposits rugged the relief. Presence of tabular acidic lava flows covering the landscape indicates that it was under high effusion rates conditions and such flows had well-insulated cooled surface crusts. The capacity to attain greater distances and overpass relief obstacles is explained not only by high effusion rates, but also by very low viscosities at the time of emplacement.
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geochemical and sr nd pb isotopic insight into the low ti basalts from southern parana igneous province brazil the role of crustal contamination
International Geology Review, 2016Co-Authors: Carla Joana Santos Barreto, Jean Michel Lafon, Evandro Fernandes De Lima, Carlos Augusto SommerAbstract:ABSTRACTThe south hinge of the Torres Syncline in southernmost Brazil hosts a volcanic succession of Pahoehoe and rubbly Gramado-type lavas belonging to the ~132 Ma Parana–Etendeka Igneous Province. We evaluate the geochemical and Sr–Nd–Pb isotopic variations using local-scale stratigraphy in order to discuss the petrogenesis of lava flows in a single magma type and to estimate the role of crustal contamination and the potential contaminants involved. The geochemical and isotopic variations along the lava pile are not systematic, implying that the magma chamber could have undergone successive replenishments of basaltic magma. The process of crustal assimilation explains the high and widespread initial Sr isotopic ratios at 0.707798–0.715751 and the very low eNd at −8.36 to −5.41, with associated Pb isotopic variations (18.42 < 206Pb/204Pb < 18.86; 15.65 < 207Pb/204Pb < 15.71; 38.62 < 208Pb/204Pb < 39.37). The magmatic evolution of the SCSH and LJ lava flows begins with the storage of mafic liquids during ...
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Geochemical and Sr–Nd–Pb isotopic insight into the low-Ti basalts from southern Paraná Igneous Province, Brazil: the role of crustal contamination
2016Co-Authors: Carla Joana Santos Barreto, Jean Michel Lafon, Evandro Fernandes De Lima, Carlos Augusto SommerAbstract:The south hinge of the Torres Syncline in southernmost Brazil hosts a volcanic succession of Pahoehoe and rubbly Gramado-type lavas belonging to the ~132 Ma Paraná–Etendeka Igneous Province. We evaluate the geochemical and Sr–Nd–Pb isotopic variations using local-scale stratigraphy in order to discuss the petrogenesis of lava flows in a single magma type and to estimate the role of crustal contamination and the potential contaminants involved. The geochemical and isotopic variations along the lava pile are not systematic, implying that the magma chamber could have undergone successive replenishments of basaltic magma. The process of crustal assimilation explains the high and widespread initial Sr isotopic ratios at 0.707798–0.715751 and the very low εNd at −8.36 to −5.41, with associated Pb isotopic variations (18.42
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Volcanic succession and feeder systems of acidic lava-domes of Serra Geral Formation in São Marcos-Antônio Prado region, South Brazil
2014Co-Authors: Evandro Fernandes De Lima, Waichel, Breno Leitão, Philipp, Ruy Paulo, Rizzon, Gabriela Cioato, Rossetti, Lucas De Magalhães MayAbstract:Na região entre São Marcos (RS) e Antônio Prado (RS), a Formação Serra Geral expõe na base uma sucessão de basaltos do tipo Pahoehoe sotopostos a derrames ´a´ā. Os primeiros foram gerados por um volume de erupção baixo em um regime de fluxo fechado e colocado em uma paleotopografia plana (< 5° de declividade). A lenta perda de calor deste sistema permite que os fluxos atinjam distâncias da fonte > 100 km. Os tipos ´a´ā foram gerados por descargas dos fluxos superiores às das Pahoehoe e transportados em canais abertos, em que o rápido resfriamento limita o deslocamento dos fluxos por longas distâncias da fonte. Ambos são toleíticos de baixo TiO2 e a morfologia dos derrames não pode ser explicada por variações geoquímicas. Acima destes afloram vulcanitos ácidos quimicamente compatíveis com o Grupo Palmas e Subgrupo Caxias. Recentemente, a extração de rochas ornamentais na região expôs as porções internas dos diques de alimentação deste vulcanismo. Observam-se estruturas magmáticas subverticais e verticais que em superfície abasteceram domos de lavas com características exógenas. Propõe-se um modelo para a geração destes envolvendo a ascensão diapírica de magmas ácidos que se tornam vesiculados, viscosos e estacionários em subsuperfície. Posteriormente, maiores volumes de recargas magmáticas ascendem rapidamente e extraem “pedaços” da fração vesiculada gerando no conduto autobrechas e estruturas verticalizadas que se expandem lateralmente em direção à superfície organizando os domos de lavas com vitrófiros na base e no topo e um núcleo maciço fanerítico fino. A ciclicidade e homogeneidade textural dos domos são típicas de efusivas e a identificação das zonas subvulcânicas de alimentação permite compreender o modo de colocação destes fluxos na Formação Serra Geral.In the São Marcos (RS) and Antonio Prado (RS), the Serra Geral Formation exposes at the base basalts of Pahoehoe type, covered by basalts of the ´a´ā type. The first succession was generated by a low rate of eruption in a closed flow system allowed the flow to reach distances > 100 km of the source.T he ´a´ā lava flow types were generated by higher rates of eruption andt ransported in open channels where rapid cooling prevented long distances from the source to be reached. The two types of basalts are low-TiO2 tholeiitic and the morphology of flows is not related to variations in SiO2 and MgO contents. Above these rock types outcrop acidic volcanic rocks geochemically of Caxias Group (Palmas Subgroup). Dimension stones extraction exposed the inner portions of the acidic feeder dikes with vertical magmatic foliations. The lava domes have exogenous characteristics and horizontal foliations. We propose a model for the generation of domes involving the diapirically rise of acids magmas that become vesicular and more viscous, that stop near the surface. New magmatic pulses extracted “pieces” of the vesicular fraction generating autobreccias in the conduit and vertical structures that extend laterally toward the surface organizing the lava domes with vitrophyres in the base and in the top, with a thin massive phaneritic core. Magmatic textures of the domes are typical of effusive units and the identification of the feeder dykes in the area allows the understanding of the emplacement process of acidic flows in the Serra Geral Formation
Stephen Self - One of the best experts on this subject based on the ideXlab platform.
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chapter 24 large igneous provinces and flood basalt volcanism
The Encyclopedia of Volcanoes (Second Edition), 2015Co-Authors: Stephen Self, Millard F Coffin, Michael R Rampino, John A WolffAbstract:Abstract Large igneous provinces (LIPs) represent huge volumes of erupted and intruded magma and are exceptional volcanic events in Earth history. They were erupted over a brief period of geologic time. The volume of magma emitted during each individual eruption that makes up an LIP (frequently 103 to perhaps 104 km3) is also exceptional, and these form Earth's largest eruptions. LIPs occur on continental crust (flood basalt provinces) and in ocean basins (oceanic plateaus), and at the transition between continents and oceans (“volcanic-”divergent margins). Basaltic LIPs usually form within a geologically brief period of time, especially the climax, or peak, of volcanic output, which may be less than 1 million years in duration. The eruptions that form flood basalt provinces have been proposed as a cause of major environmental perturbations throughout much of Earth history, including mass extinctions. Pāhoehoe-type lavas dominate in flood basalt provinces, and eruptions are thought to have durations of decades to perhaps centuries. The huge flow fields of pāhoehoe lavas are dominated by sheet lobes in many provinces, as well as alternations with flow fields dominated by smaller inflated lava lobes. Vents are poorly known, but some, at least, were long fissure-type systems.
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emplacement of continental flood basalt lava flows
Geophysical monograph, 2013Co-Authors: Stephen Self, Thorvaldur Thordarson, Laszlo P KeszthelyiAbstract:We propose that continental flood basalt (CFB) lavas were predominantly emplaced as inflated compound Pahoehoe flow fields via prolonged, episodic eruptions. Our most detailed observations come from the ∼14,7 Ma Roza flow field of the Columbia River Basalt (CRB) Group. The Roza flow field seems to be typical of many flood basalt lavas. Individual flows show a wide range of Pahoehoe surface features and a three-part internal structure in vesicularity and other textural parameters. This three-fold division into an upper crust, core, and basal crust appears to be diagnostic of the inflation process and is ubiquitous in basaltic lava flows over a remarkable range of sizes. The Pahoehoe surface features and indications of inflation are inconsistent with rapid emplacement of these lava flows. Instead, we interpret the observations to imply that the Roza, and other CFB flows, were emplaced over an extended period of time. From the thickness of the upper crust, which we suggest formed while the flow was actively inflating, and an empirical expression for the rate of crust growth of Hawaiian inflated sheet flows, we estimate that individual Roza flows were emplaced over 5 to 50 months and that the Roza flow field was constructed over a period of 6 to 14 years. However, even with this longer eruption duration, the average lava effusion rate of ∼4000 m 3 /s is similar to that of the highest-effusion-rate eruption in recorded history (the 1783-4 Laki eruption in Iceland). Our observations of lava characteristics in other CRB flows and in the Deccan Traps suggest that this emplacement style is typical of many, if not most, CFB flows. Initial estimates of the volatile release from the Roza eruption indicate that prodigious amounts of S, Cl, and F were injected into the upper troposphere and lowermost stratosphere; thus this single flood basalt eruption could have had a significant effect on the global atmosphere If other flood basalt eruptions produced similar amounts of volatiles, volatile release might provide a link between flood basalt eruptions and mass extinctions.
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a ā lava flows in the deccan volcanic province india and their significance for the nature of continental flood basalt eruptions
Bulletin of Volcanology, 2011Co-Authors: Stephen Blake, Richard J Brown, Ninad R Bondre, Vinit Phadnis, Stephen SelfAbstract:Newly identified ´a´ā lava flows outcrop intermittently over an area of ~110 km2 in the western Deccan Volcanic Province (DVP), India. They occur in the upper Thakurvadi Formation in the region south of Sangamner. The flows, one of which is compound, are 15–25 m thick, and exhibit well-developed basal and flow-top breccias. The lavas have microcrystalline groundmasses and are porphyritic or glomerocrystic and contain phenocrysts of olivine, clinopyroxene or plagioclase feldspar. They are chemically similar to compound pāhoehoe flows at a similar stratigraphic horizon along the Western Ghats. Petrographic and geochemical differences between ´a´ā flows at widely spaced outcrops at the same stratigraphic horizon suggest that they are the product of several eruptions, potentially from different sources. Their presence in the DVP could suggest relative proximity to vents. This discovery is significant because ´a´ā lavas are generally scarce in large continental flood basalt provinces, which typically consist of numerous inflated compound pāhoehoe lobes and sheet lobes. Their scarcity is intriguing, and may relate to either their occurrence only in poorly preserved or exposed proximal areas or to the flat plateau-like topography of flood basalt provinces that may inhibit channelization and ´a´ā formation, or both. In this context, the ´a´ā flow fields described here are inferred to be the products of eruptions that produced unusually high-effusion-rate lavas compared to typical flood basalt eruptions. Whether these phases were transitional to lower intensity, sustained eruptions that fed extensive low effusion rate pāhoehoe flow fields remains unclear.
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gas fluxes from flood basalt eruptions
Elements, 2005Co-Authors: Stephen Self, Thorvaldur Thordarson, Mike WiddowsonAbstract:Subaerial continental flood basalt volcanism is distinguished from all other volcanic activity by the repeated effusion of huge batches of basaltic magma (∼102-103 km3 per eruption) over short periods of geologic time (<1 Myr). Flood basalt provinces are constructed of thick stacks of extensive Pahoehoe-dominated lava flow fields and are the products of hundreds of eruptions. Each huge eruption comes from a dyke-fed fissure tens to hundreds of kilometres long and lasts about a decade or more. Such spatial and temporal patterns of lava production do not occur at any other time in Earth history, and, during eruptions, gas fluxes of ∼1 Gt per year of SO2 and CO2 over periods of a decade or more are possible. Importantly, the atmospheric cooling associated with aerosols generated from the SO2 emissions of just one flood basalt eruption is likely to have been severe and would have persisted for a decade or longer. By contrast, warming due to volcanogenic CO2 released during an eruption is estimated to have been insignificant because the mass of CO2 would have been small compared to that already present in the atmosphere.
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the roza member columbia river basalt group a gigantic Pahoehoe lava flow field formed by endogenous processes
Journal of Geophysical Research, 1998Co-Authors: Thorvaldur Thordarson, Stephen SelfAbstract:We present studies on the physical volcanology of the ∼15 Ma Roza Member of the Wanapum Formation in the Columbia River Basalt Group. The Roza Member represents a compound Pahoehoe flood basalt lava flow field, with an area of ∼40,300 km 2 and a volume of 1300 km 3 . It consists of 4 major lava flows each composed of numerous, decimeter to kilometer long Pahoehoe lobes. Roza lavas feature a wide range of Pahoehoe surface structures, such as lava rise plateaus, tumuli, and surface breakouts, and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas. An integral component of the Roza flow field is the sheet lobe with internal structures identical to those of inflated Pahoehoe sheet lobes from Hawaii and Iceland, both at the same scale and at much larger scales. We identify a three-part division of the sheet lobes into basal crust, lava core, and lava crust, which are interpreted as the equivalent to the bottom crust, the liquid lava core, and the surface crust of an active inflating Pahoehoe lobe. The upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling. This relationship is used to calculate the emplacement time for individual Roza sheet lobes and to derive a first-order estimate on the duration of the Roza eruption. The results indicate that the emplacement of individual Roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years. We propose that the Roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth. As the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of <0.1°C/km and allowed for efficient transport of lava over distances up to 300 km.
Thorvaldur Thordarson - One of the best experts on this subject based on the ideXlab platform.
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lava field evolution and emplacement dynamics of the 2014 2015 basaltic fissure eruption at holuhraun iceland
Journal of Volcanology and Geothermal Research, 2017Co-Authors: Gro Pedersen, Thorvaldur Thordarson, Armann Hoskuldsson, Tobias Durig, Ingibjorg S Jonsdottir, Morten S Riishuus, Birgir V Oskarsson, Stephanie Dumont, Eyjolfur Magnusson, Magnus T GudmundssonAbstract:Abstract The 6-month long eruption at Holuhraun (August 2014–February 2015) in the Barðarbunga-Veiðivotn volcanic system was the largest effusive eruption in Iceland since the 1783–1784 CE Laki eruption. The lava flow field covered ~ 84 km2 and has an estimated bulk (i.e., including vesicles) volume of ~ 1.44 km3. The eruption had an average discharge rate of ~ 90 m3/s making it the longest effusive eruption in modern times to sustain such high average flux. The first phase of the eruption (August 31, 2014 to mid-October 2014) had a discharge rate of ~ 350 to 100 m3/s and was typified by lava transport via open channels and the formation of four lava flows, no. 1–4, which were emplaced side by side. The eruption began on a 1.8 km long fissure, feeding partly incandescent sheets of slabby pāhoehoe up to 500 m wide. By the following day the lava transport got confined to open channels and the dominant lava morphology changed to rubbly pāhoehoe and ‘a’ā. The latter became the dominating morphology of lava flows no. 1–8. The second phase of the eruption (Mid-October to end November) had a discharge of ~ 100–50 m3/s. During this time the lava transport system changed, via the formation of a 19 km2 of the flow field. The primary lava morphology from this phase was spiny pāhoehoe, which superimposed on the ‘a’ā lava flows no. 1–3 and extended the entire length of the flow field (i.e. 17 km). This made the 2014–2015 Holuhraun a paired flow field, where both lava morphologies had similar length. We suggest that the similar length is a consequence of the pāhoehoe is fed from the tube system utilizing the existing ‘a’ā lava channels, and thereby are controlled by the initial length of the ‘a’ā flows.
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emplacement of continental flood basalt lava flows
Geophysical monograph, 2013Co-Authors: Stephen Self, Thorvaldur Thordarson, Laszlo P KeszthelyiAbstract:We propose that continental flood basalt (CFB) lavas were predominantly emplaced as inflated compound Pahoehoe flow fields via prolonged, episodic eruptions. Our most detailed observations come from the ∼14,7 Ma Roza flow field of the Columbia River Basalt (CRB) Group. The Roza flow field seems to be typical of many flood basalt lavas. Individual flows show a wide range of Pahoehoe surface features and a three-part internal structure in vesicularity and other textural parameters. This three-fold division into an upper crust, core, and basal crust appears to be diagnostic of the inflation process and is ubiquitous in basaltic lava flows over a remarkable range of sizes. The Pahoehoe surface features and indications of inflation are inconsistent with rapid emplacement of these lava flows. Instead, we interpret the observations to imply that the Roza, and other CFB flows, were emplaced over an extended period of time. From the thickness of the upper crust, which we suggest formed while the flow was actively inflating, and an empirical expression for the rate of crust growth of Hawaiian inflated sheet flows, we estimate that individual Roza flows were emplaced over 5 to 50 months and that the Roza flow field was constructed over a period of 6 to 14 years. However, even with this longer eruption duration, the average lava effusion rate of ∼4000 m 3 /s is similar to that of the highest-effusion-rate eruption in recorded history (the 1783-4 Laki eruption in Iceland). Our observations of lava characteristics in other CRB flows and in the Deccan Traps suggest that this emplacement style is typical of many, if not most, CFB flows. Initial estimates of the volatile release from the Roza eruption indicate that prodigious amounts of S, Cl, and F were injected into the upper troposphere and lowermost stratosphere; thus this single flood basalt eruption could have had a significant effect on the global atmosphere If other flood basalt eruptions produced similar amounts of volatiles, volatile release might provide a link between flood basalt eruptions and mass extinctions.
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melt segregations in a columbia river basalt lava flow a possible mechanism for the formation of highly evolved mafic magmas
Lithos, 2009Co-Authors: Margaret E Hartley, Thorvaldur ThordarsonAbstract:The Levering lava lies within the Grande Ronde Formation of the Columbia River Basalt Group. At Sentinel Gap it consists of a 14–20 m-thick Pahoehoe sheet lobe featuring the threefold vertical division typical of inflated Pahoehoe lobes into basal zone, lava core and lava crust. Segregation structures such as horizontal vesicle sheets are exceptionally well developed at the lava core to lava crust interface. The lava core contains numerous well-developed vesicle cylinders which extend from the basal zone up through the core and transform into horizontal vesicle sheets at the interface with the upper crust.
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gas fluxes from flood basalt eruptions
Elements, 2005Co-Authors: Stephen Self, Thorvaldur Thordarson, Mike WiddowsonAbstract:Subaerial continental flood basalt volcanism is distinguished from all other volcanic activity by the repeated effusion of huge batches of basaltic magma (∼102-103 km3 per eruption) over short periods of geologic time (<1 Myr). Flood basalt provinces are constructed of thick stacks of extensive Pahoehoe-dominated lava flow fields and are the products of hundreds of eruptions. Each huge eruption comes from a dyke-fed fissure tens to hundreds of kilometres long and lasts about a decade or more. Such spatial and temporal patterns of lava production do not occur at any other time in Earth history, and, during eruptions, gas fluxes of ∼1 Gt per year of SO2 and CO2 over periods of a decade or more are possible. Importantly, the atmospheric cooling associated with aerosols generated from the SO2 emissions of just one flood basalt eruption is likely to have been severe and would have persisted for a decade or longer. By contrast, warming due to volcanogenic CO2 released during an eruption is estimated to have been insignificant because the mass of CO2 would have been small compared to that already present in the atmosphere.
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the roza member columbia river basalt group a gigantic Pahoehoe lava flow field formed by endogenous processes
Journal of Geophysical Research, 1998Co-Authors: Thorvaldur Thordarson, Stephen SelfAbstract:We present studies on the physical volcanology of the ∼15 Ma Roza Member of the Wanapum Formation in the Columbia River Basalt Group. The Roza Member represents a compound Pahoehoe flood basalt lava flow field, with an area of ∼40,300 km 2 and a volume of 1300 km 3 . It consists of 4 major lava flows each composed of numerous, decimeter to kilometer long Pahoehoe lobes. Roza lavas feature a wide range of Pahoehoe surface structures, such as lava rise plateaus, tumuli, and surface breakouts, and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas. An integral component of the Roza flow field is the sheet lobe with internal structures identical to those of inflated Pahoehoe sheet lobes from Hawaii and Iceland, both at the same scale and at much larger scales. We identify a three-part division of the sheet lobes into basal crust, lava core, and lava crust, which are interpreted as the equivalent to the bottom crust, the liquid lava core, and the surface crust of an active inflating Pahoehoe lobe. The upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling. This relationship is used to calculate the emplacement time for individual Roza sheet lobes and to derive a first-order estimate on the duration of the Roza eruption. The results indicate that the emplacement of individual Roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years. We propose that the Roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth. As the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of <0.1°C/km and allowed for efficient transport of lava over distances up to 300 km.
Gevorg Navasardyan - One of the best experts on this subject based on the ideXlab platform.
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intracanyon basalt lavas of the debed river northern armenia part of a pliocene pleistocene continental flood basalt province in the south caucasus
Journal of Volcanology and Geothermal Research, 2015Co-Authors: Hetu Sheth, Khachatur Meliksetian, Hripsime Gevorgyan, Arsen Israyelyan, Gevorg NavasardyanAbstract:Abstract Late Pliocene to Early Pleistocene (~ 3.25–2.05 Ma), 200–400 m thick basalt lavas outcrop in the South Caucasus region, including the Kars–Erzurum Plateau (northeastern Turkey), the Javakheti Plateau (Georgia–Armenia), and the Lori Plateau (northern Armenia). These fissure-fed, rapidly erupted fluid lavas filled pre-existing river valleys over many tens of kilometres. The basalts exposed in the Debed River canyon, northern Armenia, are ~ 200 m thick and of three morphological types: (1) basal pillow basalts and hyaloclastites, overlain by (2) columnar-jointed Pahoehoe sheet flows, in turn overlain by (3) slabby Pahoehoe and rubbly Pahoehoe flows. The lower and middle lavas show evidence for damming of river drainage, like many lavas of the Columbia River flood basalt province, Scotland, Ireland, and Iceland. There is also evidence for syn-volcanic faulting of the early lavas. Related basalts also outcrop in the Gegham Uplands and the Hrazdan River basin in Armenia. This 3.25–2.05 Ma South Caucasus basalt province, covering parts of Turkey, Georgia and Armenia, has an estimated areal extent of ~ 15,000 km2 and volume of ~ 2250 km3. Because its main geological features are remarkably like those of many continental flood basalt (CFB) provinces, we consider it a true, albeit small, CFB province. It is the smallest and youngest CFB in the world. An analogue closely similar in major features is the Late Miocene Altos de Jalisco CFB province in the western Trans-Mexican Volcanic Belt. Both provinces formed during lithospheric pull-apart and transtensional faulting. Their broader significance is in showing flood basalt size distribution to be a continuum without natural breaks, with implications for geodynamic models.
