scholarly journals Lower Crustal Heterogeneity and Fractional Crystallization Control Evolution of Small-volume Magma Batches at Ocean Island Volcanoes (Ascension Island, South Atlantic)

2019 ◽  
Vol 60 (8) ◽  
pp. 1489-1522 ◽  
Author(s):  
K J Chamberlain ◽  
J Barclay ◽  
K J Preece ◽  
R J Brown ◽  
J P Davidson
Keyword(s):  
Fractional Crystallization ◽  
Lower Crust ◽  
South Atlantic ◽  
Small Scale ◽  
Evolutionary Trend ◽  
Diverse Range ◽  
Ocean Island ◽  
Ascension Island ◽  
Wide Range

Abstract Ocean island volcanoes erupt a wide range of magmatic compositions via a diverse range of eruptive styles. Understanding where and how these melts evolve is thus an essential component in the anticipation of future volcanic activity. Here we examine the role of crustal structure and magmatic flux in controlling the location, evolution and ultimately composition of melts at Ascension Island. Located in the South Atlantic, Ascension Island is an ocean island volcano that has produced a continuum of eruptive compositions from basalt to rhyolite in its 1 Myr subaerial eruptive history. Volcanic rocks broadly follow a silica-undersaturated subalkaline evolutionary trend, and new data presented here show a continuous compositional trend from basalt through trachyte to rhyolite. Detailed petrographic observations are combined with in situ geochemical analyses of crystals and glass, and new whole-rock major and trace element data from mafic and felsic pyroclastic and effusive deposits that span the entire range in eruptive ages and compositions found on Ascension Island. These data show that extensive fractional crystallization is the main driver for the production of felsic melts for Ascension Island, a volcano built on thin, young, oceanic crust. Strong spatial variations in the compositions of erupted magmas reveal the role of a heterogeneous lower crust; differing degrees of interaction with a zone of plutonic rocks are responsible for the range in mafic lava compositions, and for the formation of the central and eastern felsic complexes. A central core of nested, small-scale plutonic, or mush-like, bodies inhibits the ascent of mafic magmas, allowing sequential fractional crystallization within the lower crust, and generating felsic magmas in the core of the island. There is no evidence for magma mixing preserved in any of the studied eruptions, suggesting that magma storage regions are transient, and material is not recycled between eruptions.

scholarly journals The role of Edge-Driven Convection in the generation of volcanism I: a 2D systematic study

2020 ◽  
Author(s):  
Antonio Manjón-Cabeza Córdoba ◽  
Maxim Ballmer
Keyword(s):  
Numerical Models ◽  
High Volume ◽  
Oceanic Lithosphere ◽  
Companion Paper ◽  
Small Scale ◽  
Continental Lithosphere ◽  
Transient Phenomenon ◽  
Mantle Viscosity ◽  
Wide Range

Abstract. The origin of intraplate volcanism is not explained by the plate tectonic theory, and several models have been put forward for explanation. One of these models involves Edge-Driven Convection (EDC), in which cold and thick continental lithosphere is juxtaposed to warm and thin oceanic lithosphere to trigger convective instability. To test whether EDC can produce long-lived high-volume magmatism, we run numerical models of EDC for a wide range of mantle properties and edge (i.e., the oceanic-continental transition) geometries. We find that the most important parameters that govern EDC are the rheological paramaters mantle viscosity η0 and activation energy Ea. However, even the maximum melting volumes found in our models are insufficient to account for island-building volcanism on old seafloor, such as at the Canary Islands and Cape Verde. Also, beneath old seafloor, localized EDC-related melting commonly transitions into widespread melting due to small-scale sublithospheric convection, inconsistent with the distribution of volcanism at these volcanic chains. In turn, EDC is a good candidate to sustain the formation of small seamounts on young seafloor, as it is a highly transient phenomenon that occurs in all our models soon after initiation. In a companion paper, we investigate the implications of interaction of EDC with mantle-plume activity.

scholarly journals The role of edge-driven convection in the generation of volcanism – Part 1: A 2D systematic study

Solid Earth ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 613-632
Author(s):  
Antonio Manjón-Cabeza Córdoba ◽  
Maxim D. Ballmer
Keyword(s):  
Numerical Models ◽  
High Volume ◽  
Oceanic Lithosphere ◽  
Companion Paper ◽  
Rheological Parameters ◽  
Small Scale ◽  
Transient Phenomenon ◽  
Mantle Viscosity ◽  
Wide Range

Abstract. The origin of intraplate volcanism is not explained by plate tectonic theory, and several models have been put forward for explanation. One of these models involves edge-driven convection (EDC), in which cold and thick continental lithosphere is juxtaposed with warm and thin oceanic lithosphere to trigger convective instability. To test whether EDC can produce long-lived high-volume magmatism, we run numerical models of EDC for a wide range of mantle properties and edge (i.e., the oceanic–continental transition) geometries. We find that the most important parameters that govern EDC are the rheological parameters mantle viscosity η0 and activation energy Ea. However, even the maximum melting volumes predicted by our most extreme cases are insufficient to account for island-building volcanism on old seafloor, such as at the Canary Islands and Cabo Verde. Also, beneath old seafloor, localized EDC-related melting commonly transitions into widespread melting due to small-scale sublithospheric convection, inconsistent with the distribution of volcanism at these volcano chains. In turn, EDC is a good candidate to sustain the formation of small seamounts on young seafloor, as it is a highly transient phenomenon that occurs in all our models soon after initiation. In a companion paper, we investigate the implications of interaction of EDC with mantle plume activity (Manjón-Cabeza Córdoba and Ballmer, 2021).

scholarly journals Dynamics of Orographically Triggered Banded Convection in Sheared Moist Orographic Flows

2007 ◽  
Vol 64 (10) ◽  
pp. 3542-3561 ◽  
Author(s):  
Oliver Fuhrer ◽  
Christoph Schär
Keyword(s):  
Small Amplitude ◽  
Three Dimensional ◽  
Horizontal Resolution ◽  
Small Scale ◽  
Mean Flow ◽  
Topographic Roughness ◽  
Wide Range ◽  
Orographic Convection ◽  
Wind Profiles

Abstract Shallow orographic convection embedded in an unstable cap cloud can organize into convective bands. Previous research has highlighted the important role of small-amplitude topographic variations in triggering and organizing banded convection. Here, the underlying dynamical mechanisms are systematically investigated by conducting three-dimensional simulations of moist flows past a two-dimensional mountain ridge using a cloud-resolving numerical model. Most simulations address a sheared environment to account for the observed wind profiles. Results confirm that small-amplitude topographic variations can enhance the development of embedded convection and anchor quasi-stationary convective bands to a fixed location in space. The resulting precipitation patterns exhibit tremendous spatial variability, since regions receiving heavy rainfall can be only kilometers away from regions receiving little or no rain. In addition, the presence of banded convection has important repercussions on the area-mean precipitation amounts. For the experimental setup here, the gravity wave response to small-amplitude topographic variations close to the upstream edge of the cap cloud (which is forced by the larger-scale topography) is found to be the dominant triggering mechanism. Small-scale variations in the underlying topography are found to force the location and spacing of convective bands over a wide range of scales. Further, a self-sufficient mode of unsteady banded convection is investigated that does not dependent on external perturbations and is able to propagate against the mean flow. Finally, the sensitivity of model simulations of banded convection with respect to horizontal computational resolution is investigated. Consistent with predictions from a linear stability analysis, convective bands of increasingly smaller scales are favored as the horizontal resolution is increased. However, small-amplitude topographic roughness is found to trigger banded convection and to control the spacing and location of the resulting bands. Thereby, the robustness of numerical simulations with respect to an increase in horizontal resolution is increased in the presence of topographic variations.

scholarly journals Artistic explorations of Lviv artists of decorative and applied arts in small-scale plastics of the second half of the 20th century: image of a human being

2021 ◽  
Vol IX(258) (47) ◽  
pp. 10-14
Author(s):  
V. Honcharuk
Keyword(s):  
20Th Century ◽  
Art Criticism ◽  
Fine Arts ◽  
Decorative Arts ◽  
Small Scale ◽  
Human Being ◽  
Applied Art ◽  
Wide Range ◽  
Characteristic Features

The present article examines the special characteristics of the development of small-scale sculpture as an independent phenomenon in Lviv fine arts of the second half of the 20th century within the framework of the interpretation of a human being image, since the following problem has not been sufficiently studied in Ukrainian art criticism. In particular, the research focuses on the specific features of artistic experiments of the representatives of decorative and applied art in the field of anthropomorphic sculpture; traces characteristic features of conceptual and modelling solutions; identifies artistic and stylistic features and peculiarities of the representation of a human being image. The author stresses upon the role of Lviv Ceramic and Sculpture Factory that largely set trends in the development of small-scale sculpture. In addition, as based on works of famous representatives of Lviv school of decorative arts, the author identifies the variety of interpretations and wide range of modelling means as well as traces the most vivid anthropomorphic designs.

scholarly journals Building intersectoral networks: the role of health brokers in a community health promotion program

2020 ◽  
Vol 30 (Supplement_5) ◽  
Author(s):  
M de Jong
Keyword(s):  
Health Promotion ◽  
Community Health ◽  
Health Promotion Program ◽  
Small Scale ◽  
Diverse Range ◽  
Community Health Promotion ◽  
Network Building ◽  
City District ◽  
Insight Into

Abstract Background In community health promotion programs (HPP) aiming to improve health and reduce health inequities, health brokers can have a crucial role in building and sustaining intersectoral networks. These networks are pivotal for developing and implementing the HPP. However, the role of health brokers is new and there is little insight into the changes in the networks' size and composition over time and the processes that facilitate brokers' networks. The aim of this study was to map the brokers' network in detail and unravel the barriers and facilitators in network building. Methods To study the brokers' networks in a HPP in a Dutch socioeconomically deprived city district, in October 2017 and November 2019 the Composed Network Analysis (CNA) and the Coordinated Action Checklist (CAC) were used, as part of the action research accompanying the HPP. The CNA provides insight into the size and composition of the network and the CAC explores facilitators and barriers in network building and sustaining. Focus groups with the core network members (n = 6) were held to discuss and interpret results. Results The health brokers' network had expanded from an average of 100 contacts in 2017 to about 140 contacts in 2019. Existing contacts (e.g. social work, welfare work) had been strengthened and new partners, e.g. general practitioners and volunteers joined the network. This resulted in an increased attention for health on the agenda of these organizations and several joint activities as part of the HPP. Facilitators were working on a small scale, informal and formal, and frequent personal contacts. The most important barrier was change of partners. Conclusions The health brokers have been successful in and expanding their networks, putting health on the agenda of network partners and supporting activities. As such, the broker is essential in connecting a diverse range of partners and organizations in an intersectoral network in the city district. Key messages Working on a small scale, and with frequent personal, formal and informal contacts facilitated the health brokers network building and sustaining. A health brokers’ role, being initiator, facilitator and connector is essential for continuation of the community health promotion approach.

scholarly journals A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

Solar Physics ◽  
2021 ◽  
Vol 296 (5) ◽  
Author(s):  
Bart De Pontieu ◽  
Vanessa Polito ◽  
Viggo Hansteen ◽  
Paola Testa ◽  
Katharine K. Reeves ◽  
...  
Keyword(s):  
Solar Atmosphere ◽  
Resonant Absorption ◽  
Interface Region ◽  
Machine Learning Techniques ◽  
Small Scale ◽  
Wide Range ◽  
Field Lines ◽  
Far Ultraviolet ◽  
Imaging Spectrograph

AbstractThe Interface Region Imaging Spectrograph (IRIS) has been obtaining near- and far-ultraviolet images and spectra of the solar atmosphere since July 2013. IRIS is the highest resolution observatory to provide seamless coverage of spectra and images from the photosphere into the low corona. The unique combination of near- and far-ultraviolet spectra and images at sub-arcsecond resolution and high cadence allows the tracing of mass and energy through the critical interface between the surface and the corona or solar wind. IRIS has enabled research into the fundamental physical processes thought to play a role in the low solar atmosphere such as ion–neutral interactions, magnetic reconnection, the generation, propagation, and dissipation of waves, the acceleration of non-thermal particles, and various small-scale instabilities. IRIS has provided insights into a wide range of phenomena including the discovery of non-thermal particles in coronal nano-flares, the formation and impact of spicules and other jets, resonant absorption and dissipation of Alfvénic waves, energy release and jet-like dynamics associated with braiding of magnetic-field lines, the role of turbulence and the tearing-mode instability in reconnection, the contribution of waves, turbulence, and non-thermal particles in the energy deposition during flares and smaller-scale events such as UV bursts, and the role of flux ropes and various other mechanisms in triggering and driving CMEs. IRIS observations have also been used to elucidate the physical mechanisms driving the solar irradiance that impacts Earth’s upper atmosphere, and the connections between solar and stellar physics. Advances in numerical modeling, inversion codes, and machine-learning techniques have played a key role. With the advent of exciting new instrumentation both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST) and the Atacama Large Millimeter/submillimeter Array (ALMA), and space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim to review new insights based on IRIS observations or related modeling, and highlight some of the outstanding challenges.

scholarly journals Volcanoes: Identifying and Evaluating Their Significant Geoheritage Features from the Large to Small Scale

2021 ◽  
Author(s):  
Margaret Brocx ◽  
Vic Semeniuk ◽  
Tom J. Casadevall ◽  
Dan Tormey
Keyword(s):  
Volcanic Rocks ◽  
Structural Features ◽  
Gas Content ◽  
Small Scale ◽  
Diverse Range ◽  
Rock Types ◽  
Wide Range ◽  
Full Complement ◽  
Tectonic Settings ◽  
Geologic Setting

Across the globe, volcanoes and volcanic terrains present one of the most complex geological systems on Earth that, depending on magma type, viscosity, and water and gas content, form a diverse range of products in terms of geomorphology, lithologic suites, structures, and stratigraphy. In broad terms, magmas, with their diagnostic composition, derive from specific tectonic settings, e.g., basalt-dominated oceanic crusts, acidic magma from continental plates, and andesitic convergent-plate margins. In addition to magma composition and volcanic rock types, there is a wide range of volcanic products, manifest at all scales, dependent on how magma interacts with the Earth’s surface, varying, for instance, from lava flows such as vesicular lava beds and flow-banded to flow-laminated lava beds, to breccias, tephra (ejecta) deposits, and bombs, amongst others, each commonly with their diagnostic small-scale lithological/structural features. This wealth of rock types, stratigraphy, and structures linked to geologic setting, potentially has geoheritage significance, and we provide here methods tailored for volcanoes and volcanic rocks of identifying, classifying and evaluating the complex and heterogeneous nature of volcanoes so that the full complement of their geology for a given region can be appreciated and incorporated into thematic geoparks, Nature Reserves and protected areas. For sites of geoheritage significance, we present (1) a globally-applicable Geoheritage Tool-kit to systematically identify volcanic geoheritage sites, (2) a technique to classify/categorise geoheritage sites, and (3) a semi-quantitative method to evaluate the geoheritage significance of volcanic sites.

scholarly journals What Makes a Small Farm Successful? A Review of Success Factors, Needs, and Challenges

2021 ◽  
Author(s):  
Katie Tritsch ◽  
Ken Mix ◽  
Michelle Edwards ◽  
Manuel Piña
Keyword(s):  
Success Factors ◽  
Systematic Approach ◽  
Future Research ◽  
Small Scale ◽  
Small Farms ◽  
Small Farm ◽  
Diverse Range ◽  
Needs Assessments ◽  
Small Scale Farmers

Small-scale farmers face unique challenges. In this review, we conceptualize small farm success by aggregating and categorizing results from recent (post-2000) literature on small farm success factors and producer needs assessments. Our findings suggest that small farm success is multifaceted and not limited to profitability. We find that small farms have a diverse range of needs, though little has been done to rank their importance. We conclude that future research would benefit from increased methodological transparency and a systematic approach to needs evaluation. We consider the role of Extension professionals regarding the continued success of small farms.

Rethinking Economic Structure: Exploring the Role of the Small Firm and Self-Employment in the British Economy

1990 ◽  
Vol 4 (5) ◽  
pp. 125-146 ◽  
Author(s):  
James Curran
Keyword(s):  
Economic Restructuring ◽  
Economic Structure ◽  
Small Scale ◽  
Economic Activities ◽  
Self Employment ◽  
The Social ◽  
Wide Range ◽  
Industrial Societies ◽  
Theoretical Issues

Dominant sociological interpretations of the economic structures of industrial societies have long neglected the role of small scale economic activities. However, current rethinking, stimulated by attempts to explain economic restructuring in the 1980s, appears to offer petty capitalism and self-employment a more important role in the economy. Several versions of economic restructuring theory are examined critically and argued to continue to offer an inadequate account of the role of small scale enterprise in the economy and especially of the social reality of small scale enterprise ownership, organisational patterns and employment. Conceptual and theoretical issues relevant to a more direct focus on small scale economic activities are explored together with a review of studies of a wide range of aspects of such activities. The paper ends by arguing for the continuing importance of small scale economic activities in industrial societies and the need for analyses of economic restructuring and, more fundamentally economic sociology generally, to incorporate a proper recognition of small scale economic activities and self-employment.

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