The Thórólfsfell tuya, South Iceland – A new type of basaltic glaciovolcano

Hodgetts, Alastair G.E.; McGarvie, David W.; Tuffen, Hugh; Simmons, Isla C.

doi:10.1016/j.jvolgeores.2021.107175

Cited by 8 publications

(5 citation statements)

References 61 publications

(94 reference statements)

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“…Radiant heat from the cooling lava would cause the melting of the ice roof, and meltwater would flow freely over the lava surfaces. A similar scenario was proposed by Hodgetts et al (2021) for subglacially emplaced, water-cooled sheet lavas in an unusual tuya in Iceland. The tuya was constructed on a sloping bedrock surface, which promoted efficient subglacial drainage and a wet but not water-filled englacial vault.…”

Section: Megapillow Complexessupporting

confidence: 75%

Controlling influence of water and ice on eruptive style and edifice construction in the Mount Melbourne Volcanic Field (northern Victoria Land, Antarctica)

2023

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The Mount Melbourne Volcanic Field (MMVF) is part of the West Antarctic Rift System, one of Earth’s largest intra-continental rift zones. It contains numerous small, compositionally diverse (alkali basalt–benmoreite) flank and satellite vents of Late Miocene–Pliocene age (≤12.50 Ma; mainly less than 2.5 Ma). They demonstrate a wide range of morphologies and eruptive mechanisms despite overlapping compositions and elevations, and they occur in a relatively small area surrounding the active Mount Melbourne stratovolcano. The volcanic outcrops fall into several main categories based on eruptive style: scoria cones, tuff cones, megapillow complexes, and shield volcanoes. Using the analysis of lithofacies and appraisal of the internal architectures of the outcrops, we have interpreted the likely eruptive setting for each center and examined the links between the environmental conditions and the resulting volcanic edifice types. Previous investigations assumed a glacial setting for most of the centers but without giving supporting evidence. We demonstrate that the local contemporary environmental conditions exerted a dominant control on the resulting volcanic edifices (i.e., the presence or absence of water, including ice or snow). The scoria cones erupted under dry subaerial conditions. Products of highly explosive hydrovolcanic eruptions are represented by tuff cones. The water involved was mainly glacial (meltwater) but may have been marine in a few examples, based on a comparison of the contrasting internal architectures of tuff cones erupted in confined (glacial) and unconfined (marine, lacustrine) settings. One of the glaciovolcanic tuff cones ceased activity shortly after it began transitioning to a tuya. The megapillow complexes are highly distinctive and have not been previously recognized in glaciovolcanic successions. They are subglacial effusive sequences emplaced as interconnected megapillows, lobes, and thick simple sheet lavas. They are believed to have erupted at moderately high discharge and reduced cooling rates in partially drained englacial vaults under ice, probably several hundred meters in thickness. Finally, several overlapping small shield volcanoes crop out mainly in the Cape Washington peninsula area. They are constructed of previously unrecognized multiple ‘a‘ā lava-fed deltas, erupted in association with a thin draping ice cover c. 50–145 m thick. Our study highlights how effectively water in all its forms (e.g., snow, ice, and any meltwater) or its absence exerts a fundamental control on eruption dynamics and volcano construction. When linked to published ages and 40Ar/39Ar dates produced by this study, the new environmental information indicates that the Late Pliocene–Pleistocene landscape was mainly an icefield rather than a persistent topography-drowning ice sheet. Ice thicknesses also generally increased toward the present.

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Section: Megapillow Complexessupporting

confidence: 75%

Controlling influence of water and ice on eruptive style and edifice construction in the Mount Melbourne Volcanic Field (northern Victoria Land, Antarctica)

2023

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“…(b) View from the north shows subtle layering (black arrow) and trough along the ridge crest (white arrow) that we interpret to have formed by slumping. (c) Stacked lava flows ∼7–∼20 m thick at Thórólfsfell, Iceland, formed subglacially but were prevented from autobrecciation into hyaloclastite by rapid drainage of the water generated by lava‐ice interaction (Hodgetts et al., 2021). Photograph provided by Alastair Hodgetts and Dave McGarvie.…”

Section: Northeast Ridges: Observationsmentioning

confidence: 99%

“…One hypothesis we consider, but reject, is that Ridge A formed as an effusion‐dominated tuya like Thórólfsfell in Iceland (Figure 3c). Thórólfsfell (Hodgetts et al., 2021) consists largely of stacked basaltic flows with fine entablature columnar jointing due to cooling by locally generated meltwater; basal drainage along the steep regional bedrock slope prevented meltwater from accumulating at the ice‐lava interface, preventing abundant pillow basalts or hyaloclastite lava deltas from forming as in the “classic” tuya model. However, any liquid water generated by glaciovolcanism at Ridge A is unlikely to have drained efficiently, as it is located on a flat regional slope (<0.05°) and the Pavonis Mons paleoglacier was predominantly cold‐based (Shean et al., 2005).…”

Section: Northeast Ridges: Interpretationmentioning

confidence: 99%

“…Here we describe a population of ridges in the northeastern Pavonis Mons FSD. We interpret these ridges as tephra‐dominated tindar (glaciovolcanic edifices primarily composed of phreatomagmatic tuff, e.g., Russell et al., 2014, whose classification scheme is followed in this work; see also Smellie & Edwards, 2016) based on morphologic comparisons with Icelandic analogs, including the Thórólfsfell tuya (Hodgetts et al., 2021) and the Sveifluháls (Mercurio, 2011) and Helgafell (Schopka et al., 2006) tindar.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for Glaciovolcanic, Phreatomagmatic Tuff Dominated Ridges at Pavonis Mons, Mars

Scanlon,

Garry,

Head

2024

Geophysical Research Letters

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HiRISE images and digital elevation models (DEMs) of outcrops in candidate Martian glaciovolcanoes provide more detailed evidence for glaciovolcanic processes than has previously been available for Mars. A group of ridges in the Pavonis Mons fan‐shaped glacial deposit features pervasive layering, evidence for local collapse and slumping, and steeper faces in the direction of paleoglacier flow inferred from other features in the deposit. After comparison with terrestrial analogs, we conclude that these ridges are excellent candidates for tephra‐dominated tindar, formed in phreatomagmatic subglacial eruptions. The englacial meltwater lakes required for a phreatomagmatic origin represent a rare example of voluminous surface water bodies in the Late Amazonian of Mars.

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“…Impoundment or confinement commonly results in overthickened lavas, which is especially evident for low viscosity lava (i.e., phonolite, basalt, nephelinite, basanite; Harder and Russell, 2007; Figures 6E,F) but also found in intermediate composition glaciovolcanic lavas. The extreme case of ice-confined effusive volcanism leads to the formation of lava-dominated tuyas (Kelmen et al, 2002;Wilson et al, 2019;Hodgetts et al, 2021). The key to interpreting these features as having formed in a cryospheric environment depends on there being no logical present-day physiographic explanation for confinement of the flow of lavas.…”

Section: Cryospheric Impacts On Volcanic Lithofaciesmentioning

confidence: 99%

Cryospheric Impacts on Volcano-Magmatic Systems

2022

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In contrast to water and air, ice is the most dynamic enveloping medium and unique environment for volcanic eruptions. While all three environments influence volcanic activity and eruption products, the cryospheric eruption environment is unique because: 1) it supports rapid changes between those environments (i.e. subglacial, subaqueous, subaerial), 2) it promotes a wide range of eruption styles within a single eruption cycle (explosive, effusive), 3) it creates unique edifice-scale morphologies and deposits, and 4) it can modulate the timing and rates of magmatism. The distinctive products of cryospheric eruptions offer a robust means of tracking paleoclimate changes at the local, regional and global scale. We provide a framework for understanding the influence of the cryosphere on glaciovolcanic systems, landforms and deposits.

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The Thórólfsfell tuya, South Iceland – A new type of basaltic glaciovolcano

Cited by 8 publications

References 61 publications

Controlling influence of water and ice on eruptive style and edifice construction in the Mount Melbourne Volcanic Field (northern Victoria Land, Antarctica)

Controlling influence of water and ice on eruptive style and edifice construction in the Mount Melbourne Volcanic Field (northern Victoria Land, Antarctica)

Evidence for Glaciovolcanic, Phreatomagmatic Tuff Dominated Ridges at Pavonis Mons, Mars

Cryospheric Impacts on Volcano-Magmatic Systems

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