Figure 2
From: The first physical evidence of subglacial volcanism under the West Antarctic Ice Sheet
In situ micro-CT sphericity and grain size analysis and SEM images of selected tephra layers from WDC06A. Top row- distribution of tephra particle sphericity based on depth in meters (A–C). Sphericity is a particle shape metric. High sphericity values are more shaped like a sphere (blocky phreatomagmatic particles). Low sphericity values are irregularly shaped particles (more vesiculated and elongated magmatic particles). Black arrows for Tephra A and C represent a change in grain size and sphericity. Middle row- grain size distribution of particles within the ice for Tephra A-C. Vertical white bars equal 1 cm in length. Two layers are considered to be phreatomagmatic (A and C) with reverse grading and several pulses of larger irregular particles and the other layer (B) is magmatic. Bottom row: SEM images of tephra A and C have bimodal particle distribution, large irregular and blocky particles (>100 μm) and small blocky shards (<50 μm). Irregular fluidal particle (yellow arrows) indicative of magmatic eruptions and blocky and mossy (red arrows) particles are typical of phreatomagmatic eruptions. Tephra B contains very large particles (>200 μm) that would be from a large Plinian eruption. White bars are equal to 100 μm.
