The style and dynamics of volcanic eruptions control the level and type of hazards posed for local populations and can have a temporary long-range impact on climate if eruptions are extremely energetic. The purpose of this study is to provide a statistical approach to ash morphometrics in order to provide a means by which to evaluate diverse eruption styles and mechanisms of fragmentation. The methodology presented can be applied to tephra deposits worldwide and may aid volcanic hazard mitigation by better defining a volcano's history of explosive behavior. Ash-sized grains were collected from tephra deposits on Mount Erebus, Antarctica (99% of the total data variance, is interpreted to represent a continuum between fragmentations involving water-magma interaction ("wet") to grains that were formed predominately by magmatic ("dry") fragmentation mechanisms. The Taupo Hatepe ash, which was deposited from a phreatoplinian eruption column, has the highest factor values in the array, which signifies, in part, more rectangular/blocky morphologies with smooth grain edges. Factor values for the 2009 Redoubt eruption (events 2-4) are nearly as high as Hatepe ash and based on this we suggest that it was produced, in part, by phreatomagmatic fragmentation. This is supported by field observations that document melting and eruption through glacial ice during the early phases of the 2009 activity. Redoubt ash grains from later stages of the same eruption (events 9-18) show a significant shift to lower values in factor space (more irregular/vesiculated grains) and are interpreted to be a consequence of 'dryer' conditions. Coarse ash data from Mount Erebus are completely separated from Taupo and Redoubt grains in factor space due primarily to the difference in mean gray value, which is a proxy for vesicle density and size. The vesicle characteristics (larger and deeper) are consistent with documented strombolian-style activity and the scatter in grain shape data support fragmentation by a mixture of wet and dry processes as has previously been proposed based on deposit characteristics and resemblance to tephra produced by current activity. (C) 2017 Elsevier B.V. All rights reserved.