Global Volcanism Program | Image GVP-02892
The fine-grained gray layer behind the ruler was produced by the 18 May 1980 lateral blast of Mount St. Helens. The deposit is about 50 cm thick at this location, 13 km NE of the volcano. The blast deposit is overlain by airfall pumice that was erupted later on 18 May and underlain by a pumice deposit from an eruption in 1482 CE.
Photo by Lee Siebert, 1982 (Smithsonian Institution).