Pyroclastic passage zones in glaciovolcanic sequences

Abstract

Volcanoes are increasingly recognized as agents and recorders of global climate variability, although deciphering the linkages between planetary climate and volcanism is still in its infancy. The growth and emergence of subaqueous volcanoes produce passage zones, which are stratigraphic surfaces marking major transitions in depositional environments. In glaciovolcanic settings, they record the elevations of syn-eruptive englacial lakes. Thus, they allow for forensic recovery of minimum ice thicknesses. Here we present the first description of a passage zone preserved entirely within pyroclastic deposits, marking the growth of a tephra cone above the englacial lake level. Our discovery requires extension of the passage-zone concept to accommodate explosive volcanism and guides future studies of hundreds of glaciovolcanic edifices on Earth and Mars. Our recognition of pyroclastic passage zones increases the potential for recovering transient paleolake levels, improving estimates of paleoice thicknesses and providing new constraints on paleoclimate models that consider the extents and timing of planetary glaciations.

A tuff cone erupted under frozen-bed ice (northern Victoria Land, Antarctica): linking glaciovolcanic and cosmogenic nuclide data for ice sheet reconstructions

“…It is the most distinctive feature of the tephra outcrop and contrasts with both subaerial and subaqueous tuff cones, which are characteristically well stratified (e.g. Sohn 1996;White 1996;Cole et al 2001;Smellie 2001;Schopka et al 2006;Solgevik et al 2007;Brand and Clarke 2009;Sohn et al 2012;Russell et al 2013; Table 4). Poorly sorted massive deposits in pyroclastic cones occur in beds deposited from granular fluidbased currents (Branney and Kokelaar 2002).…”

“…Eruption through an overlying ice sheet is capable of creating ample meltwater to drive hydrovolcanic activity, as described in models derived for other glaciovolcanic tuff cones (Smellie 2001;Schopka et al 2006;Russell et al 2013;Hungerford et al 2014;Smellie and Edwards 2016). The locus of the eruption, on the saddle of a narrow-crested basement ridge, is also consistent with a subglacial eruption, where an overlying cavity or vault melted in an ice cover is required to confine the water, with heat released by the volcanic products responsible for melting the cavity.…”

Tuyas: a descriptive genetic classification

“…Jones and Nelson, 1970). Passage zone surfaces are now one of the signature tools that allow glaciovolcanic deposits to be used as paleoclimate proxies (e.g., Skilling, 2009;Smellie, 2000Smellie, , 2001Smellie, , 2006Smellie, , 2007Edwards et al, 2011Edwards et al, , 2009bRussell et al, 2013).…”

“…In particular they advocated a specific geometric criteria (>2:1 length to width ratio) Table 1). (A) View of Kima'Kho tuya looking to the west (Ryane et al, 2011;Russell et al, 2013). (B) Modified cross-sectional view of Kima'Kho tuya after Mathews (1947), highlighting the essential components to the tuya including: (i) a tephra cone formed early on in an englacial lake, (ii) lava-fed pillow breccia delta, and iii) capping subaerial lava flows.…”

“…Likewise, Kima 'Kho tuya in north central British Columbia (cf. Kawdy Mountain; Mathews, 1947), comprises a cone on its southern end abutted by a flat, lava plateau (Ryane et al, 2011;Russell et al, 2013). The edifice results from a protracted and diverse eruptive history that includes an explosive, conebuilding onset followed by lava effusion producing a series of pillow lava deltas, and followed by construction of a 'flat-topped' lava plateau.…”