Blast deposit -- vertical sequence
The generalized succession of material in the blast deposits starts with a distinctive carbon-rich unit derived from ripped up soil and vegetation. Above this is a series of pebbly gravels and sands with a crudely fining upwards character. The basal (A1) section is strongly depleted in fines compared to other material such as lahars. Thickness varies from a feather edge at the end of the blast zone to a meter or so close to the crater. The valley of South Coldwater Creek, behind Johnston Ridge, has a particularly thick accumulation reaching as much as 15 m.
Redrawn from Waitt 1981, fig. 258 - all rights reserved