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

Abstract

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.

The Last Glacial Maximum in the central North Island, New Zealand: palaeoclimate inferences from glacier modelling

“…Only two of the catchments studied here (MPO, WAH) have moraines been directly dated to the LGM Eaves, 2015), while others are inferred from moraine morphostratigrahy and indirect age constraints (e.g. Gamble et al, 2003;Conway et al, 2015;Conway et al, 2016). Moraines representing glacial advances prior to the LGM have been recognised and dated on Tongariro massif ; therefore, it is possible that some of the limits we targeted predate the LGM.…”

“…1; Eaves, 2015). Further constraints on the timing of moraine formation and ice extent at the LGM are provided by the age and distribution of pre-, syn-, and post-LGM lava flow emplacement (Hobden et al, 1996;Gamble et al, 2003;Price et al, 2012;Conway et al, 2015;Conway et al, 2016) and the stratigraphic relationship of these flows to both moraines and glaciated valleys.…”

“…Gamble et al, 2003;Conway et al, 2015;Conway et al, 2016) has allowed a test of the impact that changing topographic boundary conditions have on palaeoclimate estimates for glacier modelling. Using topographic reconstructions, informed by these recent field mapping and radiometric dating campaigns, the temperature forcing required to simulate the inferred LGM glaciers is altered by +0.2 to −0.5 • C. The majority of the imposed topographic changes serve to remove post-glacial lava flows that have built volcanic cones (e.g.…”

Linking distal volcaniclastic sedimentation and stratigraphy with the development of Ruapehu volcano, New Zealand

“…These deposits indicate frequent and ongoing eruptive activity of the stratovolcano during the Mangawhero and Whakapapa cone-building formations, 55-15 and <15 ka, respectively (Gamble et al 2003;Conway et al 2015). The most violent activity of the stratovolcano known during this episode occurred between 14.7 and 11.9 ka and produced the pumiceous tephra sequence of the Bullot Formation as well as pumice-rich syn-eruptive hyperconcentrated flows that spilled into the Tongariro and Whangaehu Rivers (e.g., Donoghue and Neall 2001;Pardo et al 2012).…”

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

“…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. This has been reported to be the case at volcanoes including Hoodoo Mountain (Edwards and Russell, 2002) and some in the Garibaldi Volcanic Belt (Kelman et al, 2002) in British Columbia, Nevados de Chillán in Chile (Mee et al, 2006(Mee et al, , 2009, Ruapehu in New Zealand (Spörli and Rowland, 2006;Conway et al, 2015), and the United States Cascades (e.g., Lescinsky and Sisson, 1998;Lescinsky and Fink, 2000), although hyaloclastite is noted locally at some volcanoes (e.g., Mee et al, 2009;Schmidt and Grunder, 2009). This difference has been attributed to the comparative rarity of considerable interaction with meltwater (e.g., producing pillow lava or hyaloclastic or phreatomagmatic breccia/tuff: e.g., Loughlin, 2002) in the latter case (Lescinsky and Fink, 2000;Kelman et al, 2002).…”