Simultaneous effusive and explosive cinder cone eruptions at Veniaminof Volcano, Alaska

Historical eruptions of Veniaminof Volcano, Alaska have all occurred at a 300-m-high cinder cone within the icefilled caldera that characterizes the volcano. At least six of nineteen historical eruptions involved simultaneous explosive and effusive activity from separate vents. Eruptions in 1944, 1983–1984, 1993–1994, 2013, 2018 and 2021 included periods of explosive ash-producing Strombolian activity from summit vents and simultaneous nonexplosive effusion of lava from flank vents on either the southern or northeast sides of the cone. A T-junction conduit network is proposed to explain the simultaneous eruptive styles and as a mechanism for gas-magma segregation that must occur to produce the observed activity. Historical eruptions with simultaneous summit and flank activity produced slightly higher rising ash clouds compared to historical eruptions where simultaneous activity did not occur. This could be a consequence of the partitioning of more gas-charged magma into the vertical conduit of a T-junction conduit system.

Conduit system, degassing, and flow dynamics of a rhyolite lava: A case study of the Shiroyama lava on Himeshima Island, Japan

This study presents a description of a rhyolite lava-forming eruption, including the conduit system, degassing history during the lava flow dynamics. We examined the Pleistocene Shiroyama rhyolite lava on Himeshima Island, Japan. The lava is mainly characterized by locally developed obsidian. Based on the structural variation, the obsidian lithofacies correspond to the shallow conduit. The geological investigation and FTIR analyses showed that gas removal from the conduit magma proceeded via vesiculation, fracturing, and brecciation, allowing formation of the dense obsidian. Since the lava originally maintained some extent of water, the lava effervesced just after the effusion. This vesiculation resulted in pervasive bubble coalescence and the formation of abundant permeable pathways. The volcanic gasses escaped via those pathways, allowing collapse of the bubbles and deflation of the lava. AMS (anisotropy of magnetic susceptibility) results indicate that the lava spread concentrically.

Silicification and mechanical stratigraphy control on flow pathways and hypogenic karst development in carbonate rocks

<p>Fractured and karstified carbonate rocks are important targets for the hydrocarbon exploration industry as they usually represent very productive reservoirs. Most of the karst features in carbonate reservoirs are the result of rising fluid flow in deeply buried settings (i.e., hypogenic karst), whose origin and solutional efficiency are not connected to surface processes. Hypogenic conduits are often intercepted by drilling during hydrocarbon exploration, and their occurrence is sometimes associated with high-permeability horizons characterized by intense silicification. Silicification is a common diagenetic process in sedimentary basins, in which Si-rich fluids modify textures, mineralogy, and petrophysical properties of the host rock.  </p><p>We present the preliminary results of a multidisciplinary study performed in a cave developed within a mixed carbonate-siliciclastic succession of the Salitre Formation, in Northeastern Brazil (Calixto Cave). This cave offers the opportunity to study an accessible and extensive (more than 1 km long) conduit system associated with silicification. We performed a detailed stratigraphic and structural characterization of the sedimentary sequence in the cave, identifying different SiO<sub>2</sub> facies and textural associations. Furthermore, we described cave geometry and pattern by topographic and morphometric observations using terrestrial laser scanner 3D models. Petrographic observations at the optical microscope were complemented with porosity-permeability analyses on rock plugs, XRD, XRF, and SEM-EDX analyses to highlight composition and petrophysical properties of the different lithostratigraphic units in the cave.</p><p>We found that silicification and mechanical stratigraphy determined the formation of high-permeability and seal units, whose distribution was fundamental for controlling paleo-flow pathways, karstification, and the spatial-morphological organization of the resultant conduit system. Cave morphologies, evidence of silica dissolution, crystalline quartz deposits and their associated paragenesis suggest that the speleogenetic phase contributing to the main karst formation happened in deeply buried hypogenic conditions, involving rising alkaline fluids probably of hydrothermal origin.</p>

DETERMINING 3D SEISMIC CHARACTERISTICS OF CONDUIT SYSTEM OF CHANGCHANG SAG, QIONGDONGNAN BASIN

Although some giant gas fields found in the deep-water area of the Qingdongnan Basin, China, are often associated with mud diapirs and/or gas chimneys, no comprehensive 3D work has been undertaken to characterize them. We conducted 3D seismic investigation using root mean squares (RMS), coherence, and instantaneous frequency attributes to provide better understanding of the conduit systems in the Qiongdongnan Basin. The results show that the conduit system that we investigated can be separated vertically into four zones in the following order. (1) A structurally diapiric weak zone at the base, followed by (2) an injected or reinjected sandstones zone, (3) a gas chimney zone, and (4) a mud volcanic zone at the top. The morphology of the structurally weak zone is elliptical, formed by the intersection of NW–SE– and nearly E–W–trending tectonic faults. We infer that this zone provides pathways for the ascent of the diapiric mud that was probably sourced by the underlying overpressured mudstones. The injected or reinjected sandstones zone is characterized by high amplitude anomalies (HAAs), and was probably fed by the lobes of underlying submarine fans. The gas chimney zone which is characterized by low frequencies and weak amplitudes, is probably composed of a mixture of uprising mud and free gas formed from the underlying overpressured mudstones; whereas, the mud volcano which has a Christmas-tree pattern, and composed of a central crater, the southern flank of which is a mudflow, formed when the uprising mud migrating upward through faults got to the paleo sea floor. Finally, we have proposed schematic illustrations that would aid in understanding the different stages of the formation and internal architecture of this conduit system.

Infectious Diseases and the Lymphoid Extracellular Matrix Remodeling: A Focus on Conduit System

The conduit system was described in lymphoid organs as a tubular and reticular set of structures compounded by collagen, laminin, perlecan, and heparin sulfate proteoglycan wrapped by reticular fibroblasts. This tubular system is capable of rapidly transport small molecules such as viruses, antigens, chemokines, cytokines, and immunoglobulins through lymphoid organs. This structure plays an important role in guiding the cells to their particular niches, therefore participating in cell cooperation, antigen presentation, and cellular activation. The remodeling of conduits has been described in chronic inflammation and infectious diseases to improve the transport of antigens to specific T and B cells in lymphoid tissue. However, malnutrition and infectious agents may induce extracellular matrix remodeling directly or indirectly, leading to the microarchitecture disorganization of secondary lymphoid organs and their conduit system. In this process, the fibers and cells that compound the conduit system may also be altered, which affects the development of a specific immune response. This review aims to discuss the extracellular matrix remodeling during infectious diseases with an emphasis on the alterations of molecules from the conduit system, which damages the cellular and molecular transit in secondary lymphoid organs compromising the immune response.