Fig. 5

Conceptual diagram illustrating key differences between (a) high V_FALL/V ratio eruptions, and (b) low V_FALL/V ratio eruptions. For (a), the erupted mass is concentrated into a vertically-ascending, fine-ash enriched plume. This plume facilitates the injection of both fine-ash and volatile gases (e.g., SO₂) into the upper troposphere/stratosphere; the latter driving notable atmospheric disturbance through formation of aerosols, and ozone destruction. The mass erupted during (b) is also enriched in fine-ash particles but concentrated primarily in the thrust region, where materials are partitioned into local pyroclastic density currents via pyroclastic fountaining and plume collapse. Not only would this mitigate the net flux of SO₂ into the stratosphere, but it would also favor exceptionally high (~ 700 °C) temperatures, enabling more effective ‘scrubbing’ of SO₂ prior to atmospheric injection. Arrow tips indicate the direction of transport, and colour denotes the emission type. ‘Volatile gases’ (e.g., SO₂, CO₂, methane) are released from magma during explosive eruptions, with effects on atmospheric chemistry that are known to evoke significant climate disturbance (von Glasow et al. 2009). ‘Tephra’ is used here as an all-encompassing term for the solid products produced during an explosive eruption, including all grain sizes, compositions, and emplacement processes (Lowe 2011). Vertical dashed lines mark proximal, medial, and distal zones of deposition. Note: this figure is schematic and so not drawn to true scale. However, the stratosphere and troposphere are labelled as points of reference, and equate to altitudes of ∼10–50 km, and ∼0–10 km, respectively. No co-ignimbrite plumes are pictured