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Accretionary lava balls record the Pāhoehoe to `A`ā transition

Thomas J. Jones1, Yannick Le Moigne2, James K. Russell3 & Glyn Williams-Jones4

  • Affiliations: 1 Lancaster Environment Centre, Lancaster University, Lancaster, United Kingdom 2 Natural Resources Canada, Geological Survey of Canada, Vancouver, BC, Canada 3 Earth, Ocean & Atmospheric Sciences, The University of British Columbia, Vancouver, BC, Canada 4 Centre for Natural Hazards Research, Department of Earth Sciences, Simon Fraser University, Burnaby, Canada

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 21

  • Programme No: 3.7.28

  • Theme 3 > Session 7

Abstract

Mafic lavas are a widespread product of effusive volcanism. They commonly erupt as pāhoehoe lava and transition to aā as they travel from the vent. Pāhoehoe lavas have a smooth, near continuous surface and are capable of engulfing large areas. While aā lavas have a surface crust that is fragmented and rough; they also can self-channelise, form levees, and overturn structures. These vastly different surface morphologies also give rise to different thermal characteristics, where aā with a disrupted crust exhibits greater heat loss. Thus, determining when different lava flow morphologies form and the physical processes behind morphological transitions is important for hazard mapping and lava flow modelling. Here, we present a series of detailed field observations and laboratory analyses on accretionary lava balls that formed at, or very close to, the pāhoehoe to aā transition. The lava balls were spatially mapped belonging to the most recent effusive products from Tseax (Sii Aks) volcano, British Columbia, Canada. They have a low-density, vesicular core comprised of pieces of pāhoehoe crust and are coated by multiple thin layers of denser, microlite-rich, poorly vesicular lava. We discuss the physics behind their formation and how they can be used during field studies on mafic volcanoes to infer lava flow dynamics, especially the transition between pāhoehoe and aā lava flow morphologies.