Rheometry data on ash from Mt Meager, British Columbia, Canada. All measurements that generated these data were performed using an Anton Paar MCR302 rotational rheometer with an Anton Paar powder flow cell attached. The rotating measuring geometry is 24.16 mm in diameter and contains 20 evenly spaced depressions of 1.75 mm that extend the entire length of the measuring cylinder. The profiled nature of this geometry prevents particle slip during rotation. Shear rate sweeps were performed to characterise the rheological behaviour of our pyroclast-gas mixtures. ~50 g of sample (ash from Mt Meager, British Columbia, Canada) was loaded into the powder flow cell with the measuring geometry inserted. Then for a constant gas flux applied to the base of the powder flow cell, the measuring geometry was rotated to apply a range of shear rates starting at 0.1 s-1 ramping up to 328 s-1 with approximately 20 data points generated per decade. These shear rate sweeps were performed for monodisperse grain sizes from 500 µm to 63 µm at a range of volumetric gas flow rates. Specifically for the 500 µm sample the rheology experiments were performed at 0, 15, 30, 45, 50, 55, 60, 65, and 70 L min-1. For the 250 µm sample the rheology experiments were performed at 0, 15, 20, 25, 30, 35, and 40 L min-1. For the 125 µm sample the rheology experiments were performed at 0, 1, 2, 3, 4, 5, 7, 8, 9, and 10 L min-1. For the 63 µm sample the rheology experiments were performed at 0, 0.25, 0.5, 1, 1.5, 2, 3, 4, and 5 L min-1.