Tuyas: a descriptive genetic classification

We 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, lava-dominated, 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.