Entablature: fracture types and mechanisms

Forbes, Anne; Blake, Stephen; Tuffen, Hugh

doi:10.1007/s00445-014-0820-z

Cited by 38 publications

(21 citation statements)

References 39 publications

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“…Kubbaberg is an Icelandic term meaning cube-jointed lava or entablature (e.g. Saemundsson 1970;Williams 1995;Forbes et al 2014). Kubbaberg jointing occurs exclusively in very glassy zones within the lateral, upper or basal margins of lava flows on Ruapehu.…”

Section: Kubbaberg Jointsmentioning

confidence: 98%

Lava-ice interaction on a large composite volcano: a case study from Ruapehu, New Zealand

et al. 2015

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Ice exerts a first-order control over the distribution and preservation of eruptive products on glaciated volcanoes. Defining the temporal and spatial distributions of ice-marginal lava flows provides valuable constraints on past glacial extents and is crucial for understanding the eruptive histories of such settings. Ice-marginal lava flows are well displayed on Ruapehu, a glaciated andesite-dacite composite cone in the southern Taupo Volcanic Zone, New Zealand. Flow morphology, fracture characteristics and 40 Ar/ 39 Ar geochronological data indicate that lavas erupted between~51 and 15 ka interacted with large valley glaciers on Ruapehu. Icemarginal lava flows exhibit grossly overthickened margins adjacent to glaciated valleys, are intercalated with glacial deposits, display fine-scale fracture networks indicative of chilling against ice, and are commonly ridge-capping due to their exclusion from valleys by glaciers. New and existing 40 Ar/ 39 Ar eruption ages for ice-marginal lava flows indicate that glaciers descending to 1300 m above sea level were present on Ruapehu between~51-41 and~27-15 ka. Younger lava flows located within valleys are characterised by blocky flow morphologies and fracture networks indicative of only localised and minor interaction with ice and/or snow, mainly in their upper reaches at elevations of~2600-2400 m. An 40 Ar/ 39 Ar eruption age of 9±3 ka (2σ error) determined for a valley-filling flow on the northern flank of Ruapehu indicates that glaciers had retreated to near-historical extents by the time of emplacement for this lava flow. The applicability of 40 Ar/ 39 Ar dating to ice-marginal flows on glaciated andesitedacite composite volcanoes makes this technique an additional proxy for paleoclimate reconstructions.

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Section: Kubbaberg Jointsmentioning

confidence: 98%

Lava-ice interaction on a large composite volcano: a case study from Ruapehu, New Zealand

et al. 2015

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“…The formation of a permeable fracture network then increases the infiltration and transport potential of fluids in the cooling body, contributing to the development of entablature 22 . It has previously been proposed that stress build-up and fracturing takes place during rapid cooling beyond the glass transition of the melt inside crystallising lavas (that is, at super-solidus temperatures where lava is still partially molten) 5 , 22 – 24 . Semi-circular petrographic structures, present in some columnar joints, are interpreted to result from melt segregation driven by contraction and fracturing triggered during crystallisation 1 , 25 .…”

Section: Introductionmentioning

confidence: 99%

Disclosing the temperature of columnar jointing in lavas

et al. 2018

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Columnar joints form by cracking during cooling-induced contraction of lava, allowing hydrothermal fluid circulation. A lack of direct observations of their formation has led to ambiguity about the temperature window of jointing and its impact on fluid flow. Here we develop a novel thermo-mechanical experiment to disclose the temperature of columnar jointing in lavas. Using basalts from Eyjafjallajökull volcano (Iceland) we show that contraction during cooling induces stress build-up below the solidus temperature (980 °C), resulting in localised macroscopic failure between 890 and 840 °C. This temperature window for incipient columnar jointing is supported by modelling informed by mechanical testing and thermal expansivity measurements. We demonstrate that columnar jointing takes place well within the solid state of volcanic rocks, and is followed by a nonlinear increase in system permeability of <9 orders of magnitude during cooling. Columnar jointing may promote advective cooling in magmatic-hydrothermal environments and fluid loss during geothermal drilling and thermal stimulation.

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“…Well-formed, narrow (15-30 cm) columns in much of the host lava suggest that it cooled rapidly, probably aided by substantial amounts of water (Long and Wood, 1986;Forbes et al, 2014). Narrow columns in the dikes also suggest rapid cooling, but this may, in part, result from the large surface area-to-volume ratio as dikes are typically b 2 m wide.…”

Section: Field Observations Of the Odessa Cratersmentioning

confidence: 95%

A field investigation of the basaltic ring structures of the Channeled Scabland and the relevance to Mars

Keszthelyi

2015

Geomorphology

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Entablature: fracture types and mechanisms

Cited by 38 publications

References 39 publications

Lava-ice interaction on a large composite volcano: a case study from Ruapehu, New Zealand

Lava-ice interaction on a large composite volcano: a case study from Ruapehu, New Zealand

Disclosing the temperature of columnar jointing in lavas

A field investigation of the basaltic ring structures of the Channeled Scabland and the relevance to Mars

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