Intraglacial Volcanoes of the Laugarvatn Region, Southwest Iceland, II
TL;DR: The constituents and structure of two basaltic volcanoes which grew in meltwater ponds in an ice sheet are described in this paper, where Pillow lava and para-pillow lava, a newly denned variety of subaqueous lava flow, appear to have fabrics and fabric relationships similar to that of pahoehoe and aa.
Abstract: The constituents and structure of two basaltic volcanoes which grew in meltwater ponds in an ice sheet are described. Pillow lava and para-pillow lava, a newly denned variety of subaqueous lava flow, appear to have fabrics and fabric relationships similar to that of pahoehoe and aa, and are inferred to have similar modes of emplacement. Pillow breccias are attributed to gravitational collapse of pillow lava in varying states of cooling and crystallization. Flow-foot breccias are attributed to the flow into water of lava erupted in air. Vitric tuffs are inferred to be the product of explosive activity coinciding with emergence of the volcanoes from their meltwater ponds. The emergent explosive phase, which followed effusion of lava in water (pillow lava) and preceded effusion in air (sheet lava/flow-foot breccia), is attributed to explosive evolution of steam from water sucked into the conduit by rapidly rising lava. The onset of explosive activity at depths of less than about 200 m is related to increasin...
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TL;DR: In this paper, the authors identified 205 eruptions in historical time by detailed mapping and dating of events along with extensive research on documentation of volcanic activity in historical chronicles and classified them into three categories: effusive, effusive and mixed.
571 citations
Cites background from "Intraglacial Volcanoes of the Lauga..."
...…now are present as distinctive Quaternary landforms in the ice-free parts of the volcanic zones as well as structures within and beneath the current glaciers (e.g. Kjartansson, 1966a, 1966b; Jones, 1969, 1970; Björnsson and Einarsson, 1990; Smellie, 2000; Gudmundsson et al., 2002; Skilling, 2002)....
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TL;DR: In the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of (1) explosive release of magmatic volatiles; (2) explosive expansion and collapse of steam formed at magma-water contact surfaces; (3) exploding expansion of steam following enclosure of water in magma, or entrapment of water close to magma; and (4) cooling-contraction as discussed by the authors.
Abstract: In the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of (1) explosive release of magmatic volatiles; (2) explosive expansion and collapse of steam formed at magma-water contact surfaces; (3) explosive expansion of steam following enclosure of water in magma, or entrapment of water close to magma; and (4) cooling-contraction These processes, named respectivelymagmatic explosivity, contact-surface steam explosivity, bulk interaction steam explosivity, andcooling-contraction granulation, can be enhanced by mutual interaction and feedback The first three (explosive) processes are limited at certain water depths (hydrostatic pressures) and become increasingly vigorous at shallower levels The depth of onset of magmatic explosivity depends largely on juvenile volatile content; it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas At the depth where formation of clastic deposits becomes predominant over effusion of lavas, magmatic explosivity is subordinate to steam explosivity as a clast-forming process The upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it Contact-surface explosivity commonly requires initiation by a vigorous impact between magma and water and, although no certain depth limit is known, likelihood of such explosivity decreases rapidly with depth Clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water, which in sea water is at about 3 km Cooling-contraction granulation can occur in any depth of water, but at shallow levels may be replaced by contact-surface explosivity During continuous eruption under water, tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur Emergent volcanoes are characterized by distinctive steam-explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material, water, and steam The water gets into the vent by flooding across or through the top of the tephra pile, and violent explosions cease when this access is sealed The eruptions during emergence of Surtsey and Capelinhos typify the distinctive explosive activity, the style and controls of which are different from those of maar volcanoes
490 citations
Cites background from "Intraglacial Volcanoes of the Lauga..."
...For example, Jones (1970) , Allen (1980), Moore and Fiske (1969), and Moore and Schilling (1973) show that for tholeiitic basalt magmas, with water contents of up to about 0.5 %, the upward transition to fragmental deposits generally occurs at water depths no greater than 100-200 m and is commonly shallower....
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TL;DR: In the case of Surtseyan volcano, there is no evidence of the fuel-coolant interaction mechanism as discussed by the authors, which is the widely accepted fuel cooling mechanism in the literature.
Abstract: During eruption, the vent of a Surtseyan volcano is occupied by a highly mobile slurry of tephra, hyaloclastite and water. As magma ascends rapidly through the slurry, mixing occurs due to velocity shear, acceleration of the fluid-fluid contacts and mass incorporation. Consequent expansion of the admixed water causes the jetting and continuous up-rush activity that characterizes Surtseyan volcanism. There is no evidence of the widely accepted fuel-coolant interaction mechanism.
213 citations
TL;DR: In this paper, the authors divided density currents fed directly from subaqueous eruptions into three groups based on modes of fragmentation and transport: (i) explosive fragmentation, with deposition from a gas-supported current; (ii) explosive fragmentation, and (iii) fragmentation of flowing lava.
192 citations
Cites background from "Intraglacial Volcanoes of the Lauga..."
...Additional detail is not presented for this transitionally-subaqueous case here, but extensive studies of lacustrine, glacial and modern settings are available (Fuller, 1931; Swanson, 1967; Jones, 1969; Moore et al., 1973; Skilling, 1994; Werner et al., 1996; Smellie and Hole, 1997)....
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TL;DR: Water contents have been measured in basaltic glasses from submarine and subglacial eruption sites along the Reykjanes Ridge and Iceland, respectively, in order to evaluate the hypothesis of Schilling et al. as mentioned in this paper that hot spots are also wet spots.
172 citations
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TL;DR: In this article, the authors collected from the submarine part of the east rift zone of Kilauea Volcano consist of glassy, tholeiitic pillow basalts containing vesicles whose volume and size decrease systematically with depth.
Abstract: Dredge samples collected from the submarine part of the east rift zone of Kilauea Volcano consist of glassy, tholeiitic pillow basalts containing vesicles whose volume and size decrease systematically with depth. Basalt dredged from seamounts near the Island of Hawaii is weathered, and the large volume of vesicles indicates that the seamounts have submerged as much as 1,700 m since their lava was extruded. Close chemical similarity between the glassy crust of submarine pillows and subaerial lava of the same rift zone indicates that exchange does not take place between sea water and deep sea basalt at the time of eruption. There is no evidence that spilite forms at the time of eruption.
298 citations
TL;DR: In this article, the volumetric expansion of vesiculating water vapor at temperatures and pressure corresponding to those of basaltic and rhyolitic magmas erupting under various depths of sea water indicates that explosive ash formation is unlikely at depths greater than 500 meters.
Abstract: Examination of the volumetric expansion of vesiculating water vapor at temperatures and pressure corresponding to those of basaltic and rhyolitic magmas erupting under various depths of sea water indicates that explosive ash formation is unlikely at depths greater than 500 meters. Rhyolitic magmas could produce ash at greater depths, but only if the water content were greatly enriched.
241 citations
145 citations
TL;DR: In this article, ocean-bottom photographs from 18 stations and dredge hauls from 35 stations adjacent to the Island of Hawaii indicate that basaltic pillow lava and pillow fragments are the dominant rock type on the crest and flanks of the submarine rift zone ridges, whereas glassy basalt sand and scoria are dominant on the submarine flanks.
Abstract: Ocean-bottom photographs from 18 stations and dredge hauls from 35 stations adjacent to the Island of Hawaii indicate that basaltic pillow lava and pillow fragments are the dominant rock type on the crest and flanks of the submarine rift zone ridges, whereas glassy basalt sand and scoria are the dominant type on the submarine flanks of the volcanoes directly downslope from land. These relations indicate that three major rock units comprise different levels of the volcanoes depending on the site of eruption: (1) pillow lavas and pillow fragments are dominant below sea level and are erupted from deep-water vents; (2) hyaloclastite rocks (vitric explosion debris, littoral cone ash, and flow-foot breccias) mantle the pillowed base of the volcano, and are erupted from shallow-water vents, subaerial vents in water-soaked ground, or are produced where subaerial lava flows cross the shoreline; and (3) thin subaerial lava flows make up the visible, subaerial shield volcano, are built atop the clastic layer, and are erupted from subaerial vents. This three-fold structure is similar to the table mountains of Iceland that are built by eruption beneath glacial ice. Large-scale slumping in the clastic layer may modify the submarine slopes of the volcanoes as well as produce faulting and downslope movement of parts of the overlying shield volcano. The slope change produced where the gentler shield meets the steeper pillowed pile can be recognized beneath sea level in the older volcanoes, where it has been submerged by regional subsidence.
140 citations
TL;DR: When basalt lava flows from air into water it leaves a distinctive record of the water level of the time in the form of lava sheets overlying and passing down into vitric breccia and/or pillow lava as discussed by the authors.
Abstract: When basalt lava flows from air into water it leaves a distinctive record of the waterlevel of the time in the form of lava sheets overlying and passing down into vitric breccia and/or pillow lava. Relative movements of waterlevel and a volcanic pile or terrain over a period of time may be readily deciphered from such records.
114 citations