Topic
Shield volcano
About: Shield volcano is a research topic. Over the lifetime, 740 publications have been published within this topic receiving 25492 citations.
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TL;DR: The Ethiopian plateau is made up of several distinct volcanic centres of different ages and magmatic affinities as discussed by the authors, and the three main types of magma have very different major and trace element characteristics ranging from compositions low in incompatible elements in the tholeiites [e.g. 10 ppm La at 7 wt % MgO (=La7), La/εb = 4.2], moderate in the alkali basalts (La7 = 24, La/β = 9.2), and very high in the magnesian alkaline magmas (
Abstract: The Ethiopian plateau is made up of several distinct volcanic centres of different ages and magmatic affinities. In the NE, a thick sequence of 30 Ma flood basalts is overlain by the 30 Ma Simien shield volcano. The flood basalts and most of this shield volcano, except for a thin veneer of alkali basalt, are tholeiitic. In the centre of the province, a far thinner sequence of flood basalt is overlain by the 22 Ma Choke and Guguflu shield volcanoes. Like the underlying flood basalts, these shields are composed of alkaline lavas. A third type of magma, which also erupted at 30 Ma, is more magnesian, alkaline and strongly enriched in incompatible trace elements. Eruption of this magma was confined to the NE of the province, a region where the lava flows are steeply tilted as a result of deformation contemporaneous with their emplacement. Younger shields (e.g. Mt Guna, 10·7 Ma) are composed of Si-undersaturated lavas. The three main types of magma have very different major and trace element characteristics ranging from compositions low in incompatible elements in the tholeiites [e.g. 10 ppm La at 7 wt % MgO (=La7), La/Υb = 4.2], moderate in the alkali basalts (La7 = 24, La/Υb = 9.2), and very high in the magnesian alkaline magmas (La7 = 43, La/Υb = 17). Although their Nd and Sr isotope compositions are similar, Pb isotopic compositions vary considerably; 206Pb/204Pb varies in the range of ∼17·9-18·6 in the tholeiites and ∼19·0-19·6 in the 22 Ma shields. A conventional model of melting in a mantle plume, or series of plumes, cannot explain the synchronous eruption of incompatible-element-poor tholeiites and incompatible-element-rich alkali lavas, the large range of Pb isotope compositions and the broad transition from tholeiitic to alkali magmatism during a period of continental rifting. The lithospheric mantle played only a passive role in the volcanism and does not represent a major source of magma. The mantle source of the Ethiopian volcanism can be compared with the broad region of mantle upwelling in the South Pacific that gave rise to the volcanic islands of French Polynesia. Melting in large hotter-than-average parts of the Ethiopian superswell produced the flood basalts; melting in small compositionally distinct regions produced the magmas that fed the shield volcanoes. © Oxford University Press 2004; all rights reserved.
462 citations
TL;DR: The rifts of the 14 basaltic shield volcanoes that extend from Kauai to Hawaii are composed of thousands of dykes that were fed laterally by periodic leakages from central volcanic con-duits.
Abstract: The rifts of the 14 basaltic shield volcanoes that extend from Kauai to Hawaii are composed of thousands of dykes that were fed laterally by periodic leakages from central volcanic conduits. Individual dykes are believed to be thin, steeply dipping blades, several kilometres from top to bottom, that extend horizontally outward for as much as 120 km. The dykes are contained largely within the volcanic edifices, and, because of such shallow emplacement, the direction of dyke propagation is interpreted to be strongly influenced by the gravitational stresses within these edifices. Simple isolated shields, such as Kauai and West Molokai, had nearly symmetrical stress fields, influenced only slightly by regional stresses, and the dykes injected into these volcanoes had little or no tendency to cluster into well-defined rifts. Other volcanoes, such as Koolau and Kilauea, pierced the thick, sloping apron of pre-existing neighbour volcanoes. The dykes that propagated from these centres were strongly influenced by the gravitational stress fields of the sloping aprons in which they grew. Accordingly, they clustered into well-defined rifts oriented roughly perpendicular to the downslope direction of these aprons. With only minor exceptions, 8 of the 14 volcanoes forming the southeast part of the Hawaiian chain conformed to this pattern of growth; the influence of regional Pacific structure on rift orientation is suspected in only 6 volcanoes that grew as simple, isolated shields, away from the influence of gravitational stresses of any neighbour volcano.
399 citations
TL;DR: The Michoacan-Guanajuato Volcanic Field (MGVF) contains over 1000 late Quaternary volcanic centers, of which approximately 90% are cinder cones.
329 citations
TL;DR: In this article, the authors review physical aspects of continental basaltic eruptions and identify key problems where additional research will help to advance our overall understanding of this important type of volcanism.
312 citations
TL;DR: Tumuli are positive topographic features that are common on Hawaiian pahoehoe lava flow fields, particularly on shallow slopes, and 75 measured examples are presented here to document the size range.
Abstract: Tumuli are positive topographic features that are common on Hawaiian pahoehoe lava flow fields, particularly on shallow slopes, and 75 measured examples are presented here to document the size range. Tumuli form by up-tilting of crustal plates, without any crustal shortening, and are thus distinguished from pressure ridges which are up-buckled by laterally directed pressure. The axial or star-like systems of deep clefts that characterize tumuli are defined here as “lava-inflation clefts”; their tips advanced into red-hot lava and they widened as uplift proceeded and while the lava crust was thickening. Flat-surfaced uplifts, formed like tumuli by injection of lava under a surface crust, were previously called pressure plateaus, but “lava rise” is proposed instead. The pits that abound among lava rises, previously attributed to collapse or subsidence, are generally formed because the lava around them rose, and the name “lava-rise pit” is proposed. Unique examples of tumuli and lava rises, from which lava drained out under a surface crust 1.5 to 2.5 m thick, are described from Kilauea caldera. These examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava, and is able to do so because of its higher vesicle content: the fluid lava loses many of its gas bubbles during residence beneath the crust. The bulk densities of samples from tumuli show a general downward increase. The form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust, suggesting that the lava was stably density-stratified. It is inferred that stable stratification was regulated by out-flows of the more vesicular lava fractions, loss of bubbles through the lava-inflation clefts, and entry of injected lava at its level of neutral buoyancy. Below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava.
305 citations
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| Year | Papers |
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| 2025 | 2 |
| 2024 | 1 |
| 2023 | 15 |
| 2022 | 13 |
| 2021 | 18 |
| 2020 | 26 |