Tuyas: a descriptive genetic classification

Abstract

a b s t r a c tWe present a descriptive genetic classification scheme and accompanying nomenclature for glaciovolcanic edifices herein defined as tuyas: positive-relief volcanoes having a morphology resulting from ice confinement during eruption and comprising a set of lithofacies reflecting direct interaction between magma and ice/melt water. The combinations of lithofacies within tuyas record the interplay between volcanic eruption and the attending glaciohydraulic conditions. Although tuyas can range in composition from basaltic to rhyolitic, many of the characteristics diagnostic of glaciovolcanic environments are largely independent of lava composition (e.g., edifice morphology, columnar jointing patterns, glass distributions, pyroclast shapes). Our classification consolidates the diverse nomenclature resulting from early, isolated contributions of geoscientists working mainly in Iceland and Canada and the nomenclature that has developed subsequently over the past 30 years. Tuya subtypes are first recognized on the basis of variations in edifice-scale morphologies (e.g., flat-topped tuya) then, on the proportions of the essential lithofacies (e.g., lava-dominated flat-topped tuya), and lastly on magma composition (e.g., basaltic, lavadominated, flat-topped tuya). These descriptive modifiers potentially supply additional genetic information and we show how the combination of edifice morphologies and lithofacies can be directly linked to general glaciohydraulic conditions. We identify nine distinct glaciovolcanic model edifices that potentially result from the interplay between volcanism and glaciohydrology. Detailed studies of tuya types are critical for recovering paleo-environmental information through geological time, including: ice sheet locations, extents, thicknesses, and glaciohydraulics. Such paleo-environmental information represents a new, innovative, underutilized resource for constraining global paleoclimate models.

Glaciovolcanism at Volcán Sollipulli, southern Chile: Lithofacies analysis and interpretation

“…The largest stacks of lavas (on the southern caldera rim; Fig. 10a) are morphologically very similar to lava-dominated flat-topped or conical tuyas (Russell et al, 2014), at least on their caldera-facing sides.…”

“…Glaciovolcanism, the interaction between erupting magma and ice (in any form) and the resulting meltwater, is a widespread phenomenon on Earth and Mars (Smellie and Chapman, 2002), the significance of which is increasingly being recognised (Russell et al, 2014). For example, such activity can generate or exacerbate certain volcanic hazards (Tuffen, 2010), such as lahars and floods (e.g., Major and Newhall, 1989), edifice collapse (e.g., Huggel, 2009), and secondary phreatomagmatic explosions (e.g., Belousov et al, 2011).…”

“…The responses of these hazards and rates of volcanism to past glacial cycles and future climate change are poorly constrained (Tuffen, 2010;Watt et al, 2013). Furthermore, volcano-ice interactions create a distinctive and wideranging suite of landforms (e.g., Smellie, 2009Smellie, , 2013Russell et al, 2014) and lithofacies (e.g., Smellie et al, 1993;Loughlin, 2002;Skilling, 2009), which are an invaluable source of terrestrial palaeoenvironmental information (e.g., palaeoice distribution, thickness, and thermal regime: e.g., Smellie, 2009;Tuffen et al, 2010;Smellie et al, 2014), especially prior to the last glaciation (e.g., McGarvie et al, 2007;Smellie et al, 2011Smellie et al, , 2014) and on Mars (e.g., Smellie, 2009). Detailed characterisation of the products of glaciovolcanism in each particular setting is necessary to understand their formation processes and the associated hazards, as well as their palaeoenvironmental significance.…”

“…Tuyas (as defined by Russell et al, 2014), lava-fed deltas (e.g., Skilling, 2002;Smellie et al, 2013Smellie et al, , 2014, and sheet-like sequences (e.g., Smellie et al, 1993;Smellie, 2008) are the most common glaciovolcanic landforms in these regions (Smellie, 2009(Smellie, , 2013, except parts of western North America (e.g., Lescinsky and Fink, 2000;Kelman et al, 2002). Glaciovolcanism at stratovolcanoes in continental arcs and/or at temperate latitudes may be distinct, as coherent lavas with fracture patterns and/or morphologies indicative of contact with and confinement by ice (e.g., Lescinsky and Fink, 2000) appear to be more typical than these landforms and fragmental glaciovolcanic lithofacies.…”

Geology of Tindfjallajökull volcano, Iceland

“…Where lava flows from the shallow-dipping top into the ice-dammed lake, a lava delta is formed, and the change in lithofacies at this water level is called a passage zone. The level of the passage zone from subaerial to subaqueous lava emplacement can be used to estimate the thickness of the surrounding ice body (Russell, Edwards, Porritt, & Ryane, 2014;Skilling, 2009). The subsidence pits on Bláfell tuya may have been formed through the draining of subsurface magma or meltwater.…”