Extensive soft-sediment deformation and peperite formation at the base of a rhyolite lava: Owyhee Mountains, SW Idaho, USA (original) (raw)
Related papers
Emplacement and Thermal History of a Rhyolite Lava Flow near Fortymile Canyon, Southern Nevada
Geological Society of America Bulletin, 1966
The rhyolite of Comb Peak is one of a series of related rhyolitic lava flows and domes that postdate formation of the Timber Mountain caldera in southern Nevada. The Comb Peak body consists of bedded rhyolitic tuffs overlain by a rhyolitic lava flow that has a foliated interior with fluidal structure, enveloped by breccia. The vent for the lava flow and the pre-eruption topography have been exposed by erosion and indicate the general conditions and direction of flow. These indications have been corroborated by study of the foliation pattern and by a semiquantitative statistical analysis of flow folds and related features. Geologic relationships indicate that brecciation of the lava flow occurred mainly during periods when the flow was spreading, whereas the body eroded its floor and walls much as does a glacier during periods when the flow was confined.
From volcanoes to sedimentary systems
Geological Society, London, Special Publications
Volcanoes produce probably the most spectacular geological phenomena on Earth. Any of their eruptions can have a strong consequence on the surrounding environment, often captured in great detail in the sedimentary records of volcanically active regions. In addition, flank landslides and background erosive processes affecting volcanic sequences release volcanic particles that circulate within sedimentary environments up to billions of years after their generation. Therefore, exploring volcanically influenced sedimentary environments is an exciting and challenging scientific exercise requiring insights across multiple geological disciplines, drawing upon an increasing varied range of expertise and analytical approaches from across the geoscientific community. This book aims to provide an updated collection of works that illustrate the state-of-the-art in this topic, and to define the future directions of the geological sciences in utilising and interpreting sedimentary records of volc...
Emplacement of the Rocche Rosse rhyolite lava flow (Lipari, Aeolian Islands)
Bulletin of Volcanology, 2018
The Rocche Rosse lava flow marks the most recent rhyolitic extrusion on Lipari island (Italy), and preserves evidence for a multi-stage emplacement history. Due to the viscous nature of the advancing lava (10 8 to 10 10 Pa s), indicators of complex emplacement processes are preserved in the final flow. This study focuses on structural mapping of the flow to highlight the interplay of cooling, crust formation and underlying slope in the development of rhyolitic lavas. The flow is made up of two prominent lobes, small (< 0.2 m) to large (> 0.2 m) scale folding and a channelled geometry. Foliations dip at 2-4°over the flatter topography close to the vent, and up to 30-50°over steeper mid-flow topography. Brittle faults, tension gashes and conjugate fractures are also evident across flow. Heterogeneous deformation is evident through increasing fold asymmetry from the vent due to downflow cooling and stagnation. A steeper underlying topography mid-flow led to development of a channelled morphology, and compression at topographic breaks resulted in fold superimposition in the channel. We propose an emplacement history that involved the evolution through five stages, each associated with the following flow regimes: (1) initial extrusion, crustal development and small scale folding; (2) extensional strain, stretching lineations and channel development over steeper topography; (3) compression at topographic break, autobrecciation, lobe development and medium scale folding; (4) progressive deformation with stagnation, large-scale folding and refolding; and (5) brittle deformation following flow termination. The complex array of structural elements observed within the Rocche Rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at the Chilean volcanoes of Chaitén and Cordón Caulle, offering a fluid dynamic and structural framework within which to evaluate our data.
Emplacing a Cooling-Limited Rhyolite Lava Flow: Similarities with Basaltic Lava Flows
Frontiers in Earth Science, 2017
Accurate forecasts of lava flow length rely on estimates of eruption and magma properties and, potentially more challengingly, on an understanding of the relative influence of characteristics such as the apparent viscosity, the yield strength of the flow core, or the strength of the lava's surface crust. For basaltic lavas, the relatively high frequency of eruptions has resulted in numerous opportunities to test emplacement models on such low silica lava flows. However, the flow of high silica lava is much less well understood due to the paucity of contemporary events and, if observations of flow length change are used to constrain straightforward models of lava advance, remaining uncertainties can limit the insight gained. Here, for the first time, we incorporate morphological observations from during and after flow field evolution to improve model constraints and reduce uncertainties. After demonstrating the approach on a basaltic lava flow (Mt. Etna 2001), we apply it to the 2011-2012 Cordón Caulle rhyolite lava flow, where unprecedented observations and syn-emplacement satellite imagery of an advancing silica-rich lava flow have indicated an important influence from the lava flow's crust on flow emplacement. Our results show that an initial phase of viscosity-controlled advance at Cordón Caulle was followed by later crustal control, accompanied by formation of flow surface folds and large-scale crustal fractures. Where the lava was unconstrained by topography, the cooled crust ultimately halted advance of the main flow and led to the formation of breakouts from the flow front and margins, influencing the footprint of the lava, its advance rate, and the duration of flow advance. Highly similar behavior occurred in the 2001 Etna basaltic lava flow. In our comparison of these two cases, we find close similarities between the processes controlling the advance of a crystal-poor rhyolite and a basaltic lava flow, suggesting common controlling mechanisms that transcend the profound rheological and compositional differences of the lavas.
Intense Shallow Magma Sediment Mingling Within Dikes at Guffey Butte Maar, Idaho
2021
The interactions between magma and shallow unconsolidated sediments on the way to the surface influences the eruption behavior and products. Phreatomagmatic eruptions are a result of the interaction of magma and water or wet sediment and their deposits are evidence of this interaction. The relative influence of internal magmatic and external environmental factors that control magma sediment interaction are not well constrained. This study focuses on exposed dike structures in an eroded Pleistocene basalt maar complex, Guffey Butte, Idaho to investigate extreme sediment magma mingling in a non-explosive environment. Exposed dikes cut through both lake Idaho sands and silts and Guffey Butte pyroclastic deposits. Through a combination of field mapping, microtexture measurements from 36 thin sections, and geochemistry (whole rock major and trace elements using XRF and ICP-MS), the scales of interactions and diversity of mixing styles between the basaltic dikes and host sediments were constrained. The two host materials were characterized for componentry and grain size. Field observations reveal the scales of these interactions range from blocks (< 10 cm) to individual crystals. GB basalts contain less lithics than mixed samples. The intensity of mingling is diverse and the style of mingling over a spatial area is not systematic. Magma penetrated through wet unconsolidated siliciclastic sediment and due iv to their differing densities mixing occurs through Kelvin-Helmholtz Instability. Mingling is separated into three categories: 1) Least Homogenized, 2) Moderate Homogenization, and 3) Homogenized. The different levels of mixing preserve the different stages of Kelvin-Helmholtz instability over a distance of a few cm to meters. In thin section, changes in crystal, sedimentary grain, and basalt fragment sizes occur as well as injections of sediment into basalt and basalt into sediment at the mm scale. Basaltic and siliciclastic mineral preservation suggest mixed dike temperatures to be slight below 900°C-1,000°C. This study expands the observed range of interactions between wet sediments and shallow basaltic intrusions that can occur in a non-explosive environment. v APPROVAL PAGE The faculty listed below, appointed by the Dean of the College of Arts and Sciences, have examined a thesis titled "Intense Shallow Magma Sediment Mingling within Dikes at Guffey Butte Maar, Idaho" presented by Hannah Grachen, candidate for the Master of Science degree, and certify that in their opinion it is worthy of acceptance.
Sedimentary Geology, 2009
Volcaniclastic sediments, broadly defined as clastic deposits derived from the transport, deposition and/or redeposition of the products of volcanic activity, have long been a Cinderella of the geosciences. This status is a function of the inherent complexity of the fragmentation, transport and depositional processes that operate in volcanically-impacted environments and the comparatively recent development of the discipline as a specialist area. Volcaniclastic studies are truly interdisciplinary, drawing on many elements of physical volcanology, fluid dynamics, classical clastic sedimentology, hydrology and geomorphology. In the past 30 years volcaniclastic studies have blossomed, partly in response to a number of catastrophic and high-profile volcanic eruptions, including Mount St. Helens in 1981, Nevado del Ruiz in 1985 and Pinatubo in 1991, and partly due to integration with the maturing science of fluid dynamics and an increased understanding of the behaviour of particulate dispersions and two-phase granular flows. These historical events have demonstrated that the sedimentary repercussions of volcanic eruptions can have more severe, far-reaching, and prolonged impacts than the initial volcanism. In parallel, studies of well-preserved examples from the geological record have extended our understanding of landscape and environmental responses to styles and scales of volcanism that have not been recorded historically, such as the impacts of caldera-forming eruptions from silicic calderas. As a consequence, studies have expanded beyond classical stratigraphic and sedimentological studies of ancient successions in a variety of plate tectonic settings to a more dynamic focus on process. Ultimately, volcaniclastic successions are the product of the interplay between the volcano, in terms of the style, magnitude and explosivity of the eruption, and the environment, as expressed by physiography, hydrology, energy, and accommodation space.
The Canadian Mineralogist, 2001
Although komatiitic lavas have long been depicted as turbulent flows, especially near the vent, field characteristics indicate that many komatiitic lavas did not flow turbulently, or only initially so. The bases of komatiites are commonly conformable with their substrate, including fine pelitic sediments, and the margins of komatiites are overwhelmingly coherent, or marked by local quench-fragmented hyaloclastite breccia. Autobreccias are notably missing. These characteristics are not consistent with turbulent flow, but clearly indicate conditions of laminar flow. If komatiitic flows were turbulent, they should commonly have scoured into substrate sediments through a variety of physical erosion processes, including foundering into underlying seafloor sediments, because of density inversion, and turbulence-induced scouring of sediments. These features are not commonly developed, also indicating that generally komatiites were emplaced under tranquil, laminar-flow conditions. Trough-like structures that commonly host nickel sulfide mineralization have commonly been interpreted to originate by thermal erosion of substrate by the komatiitic lava. The evidence supporting thermal erosion is not strong, and commonly ambiguous. Trough structures at Kambalda, Western Australia, are fault bounded, as noted by several previous investigators. However, there is a common, but not universal, antithetic relationship between trough presence and sediment absence. Removal of sediment from troughs could be explained by physical erosion, with an initial narrow, turbulent flow-head scouring a channel in the underlying sediments. As the lava flows spread laterally, their flow-front velocity decreased, and flow became laminar, so explaining the conformable contacts with substrate and the presence of coherent crusts represented by the random spinifex textural zone. Thermal erosion was rare, and could only have resulted beneath sustained lava tubes, within the flow interior, not from the flow head.
Bulletin of Volcanology, 1993
A model is presented for the emplacement of intermediate volume ignimbrites based on a study of two ∼6 km3 volume ignimbrites on Roccamonfina Volcano, Italy. The model considers that the flows were slow moving, and quickly deflated from turbulent to non-turbulent conditions. Yield strength and density increased whereas fluidisation decreased with time and runout of the pyroclastic flows. In proximal locations, on the caldera rim, heterogeneous exposures including discontinuous lithic breccias, stratified and cross-stratified units interbedded with massive ignimbrite suggest deposition from turbulent flows. In medial locations thick, massive ignimbrite occurs associated with three types of co-ignimbrite lithic breccia which we interpret as being emplaced by non-turbulent flows. Multiple grading of different breccia/lithic concentration types within single flow units indicates that internal shear occurred producing overriding or overlapping of the rear of the flow onto the slower-moving front part. This overriding of different parts of non-turbulent pyroclastic flows could be caused by at least two different mechanisms: (1) changes in flow regime, such as hydraulic jumps that may occur at breaks in slope; and (2) periods of increased discharge rate, possibly associated with caldera collapse, producing fresh pulses of lithic-rich material that sheared onto the slower-moving part of the flow in front. We propose that ground surge deposits enriched in pumice compared with their associated ignimbrite probably formed by a flow separation mechanism from the top and front of the pyroclastic flow. These turbulent clouds moved ahead of the non-turbulent lower part of the flow to form stratified pumice-rich deposits. In distal regions well-developed coarse, often clast-supported, pumice concentrations zones and coarse intra-flow-unit lithic concentrations occur within the massive ignimbrite. We suggest that the flows were non-turbulent, possessed a relatively high yield strength and may have moved by plug flow prior to emplacement.
Journal of volcanology and geothermal research, 1992
. Structures within large volume rhyolite lava flows of the Devonian Comerong Volcanics, southeastern Australia, and the Pleistocene Ngongotaha lava dome, New Zealand. J. Volcanol. Geotherm. Res., Many rhyolitic units within the Late Devonian Comerong Volcanics erupted as lava flows and domes, some up to 18 km long and 350 m thick. The textural and structural characteristics that distinguish the flows and domes as lava rather than rheomorphic ignimbrite include unbroken phenocrysts, zones of autobrecciation, and finely developed flow layering with individual layers continuous for several metres. The flow layering is typically contorted into isoclinal folds with forms suggesting fluidal deformation and is interlayered with and gradational into restricted zones of pumice-rich lapilli tuff and zones of lenticulite breccia. The lenticulite breccia comprises discontinuous, lenticular rhyolite fragments, the long axes of which define a foliation parallel to flow layering. Lenticles in the breccia vary from elongate layers up to 1 m long and several millimetres thick to short fragments less than 10 cm long and several cenlimetres wide. Similar zones of lenticulite breccia consisting of glassy lenticular clasts in a devitrified, spherulitic "'matrix" of cristobalite and albite, exist within the Late Pleistocene Ngongotaha dome near Rotorua, New Zealand. The lenticulite breccia is considered to form by aqueous diffusion and selective devitrification of the rhyolite along anastomosing fluid paths and to be modified by mechanical fracturing of the lava in a zone of high shear stress.
Journal of Volcanology and Geothermal Research, 2015
Activity at Augustine Volcano, Alaska, has been characterized by intermediate composition domes, flows, and tephras during the Holocene. Erosive lahars and pyroclastic flows associated with the 2006 eruption revealed large exposures of voluminous rhyolite pumice fall beneath glacial tills; the massive rhyolite deposit is evidence of anomalously large prehistoric eruptions. The rhyolite is petrologically and mineralogically different from more recent eruptive products, with abundant amphibole (calcic amphiboles and cummingtonite) and quartz. Three texturally and chemically distinct lithologies are present. Fe-Ti oxide equilibria suggest temperatures of ~765°C and oxygen fugacities of NNO+1.5. Melt inclusions indicate that magma representing the stratigraphically lowest lithology was crystallizing at ~260 MPa with a contemporary mixed H 2 O-CO 2 fluid phase becoming progressively more H 2 O-rich. Magma forming the other lithologies crystallized in the presence of this H 2 O-dominated fluid , as demonstrated by the presence of cummingtonite and little to no CO 2 in melt inclusions. Amphibole and quartz-feldspar-melt equilibria models yield results indicating a range of crystallization pressures from ~400 MPa to ~175 MPa. Apatites and melt inclusions have lower chlorine contents than more recently erupted material at Augustine suggesting that the composition of Augustine's volatile phase has changed over time. Reheating textures in melt inclusions and phenocrysts, as well as the presence of xenocrysts of olivine and clinopyroxene containing mafic melt inclusions, signify the likelihood of mixing and/or mingling of magmas as an eruption trigger. The unique qualities of this Pleistocene rhyolite and the potential hazard of a similarly large eruption in modern times indicate that further study is warranted.