Table 7.2.

Summary characteristics of the primary PDC and fallout deposits of the 11 February collapse

FaciesUnitDescriptionMdØσØSkLocation
BVStFPBHHaFRVFaTrWBG
FalloutPumice fallAngular pumice clasts lying in upper fine-ash fallXXXXXXXX
Fine ash fallFine ash fall with accretionary lapilliXXXXXXXX
PumiceousScattered pumicePumice boulders up to 2 m, present inside and around buildings, accumulated in standing and downed trees, and scattered across upper deposit surface. Not associated with any fine-grained depositXXXXXX
Pumice-richPumice-rich flow with typical coarse-grained levees of well-rounded pumice. Multiple pulses and anastomosing features1.62.4−0.1XXXXXXX
BrecciaSheetExtensive, massive, matrix-poor deposits up to 9 m thick with boulders up to 15 m on Farrell's PlainXX
HummockSeries of isolated hummocks in the lower reaches of the Farm River Valley, up to 4 m thick with 2–3 m boulders. Single large hummock in Harris−1.42.90.2XX
BlockyBAFCoarse-grained, blocky, typical BAF deposits with decimetre- to metre-scale blocks in coarse lapilli matrix. Symmetrical grading within 1–2 m-thick units. Degassing pipes present−2.91.70.3XXXX
Fine-grainedMassive ash0.5–1 m-thick, pinkish-orange coloured fines-rich unit. Massive with many degassing pipes. Closely associated with hummocky breccias1.72.3−0.1XX
Coarse ashCoarse ash bed separated by a fine, medium ash bed. Strong orangey-brown thermal colouration in the upper layers. 10–30 cm thick1.22.10.1XXXXXX
Medium ashFine grained with a typically grey colour. Generally massive, but with occasional thin lamination3.71.06−0.4XXX
Crystal-richFines-poor, crystal-rich layer, 1–30 cm thickXXXX
  • BV, Belham Valley; St, Streatham; FP, Farrell's Plain; BH, Bugby Hole; Ha, Harris; FR, Farm River; Fa, Farm; Tr, Trants; WB, White's Bottom Ghaut. See Figures 7.1 and 7.6 for the locations of areas.