When this substance mixes with precipitation, it forms andosols, and this substance can be classified by point of origin as scoria-fall or pumice-fall.
Models for the dispersal of this substance include advection-diffusion models like HAZMAP and FALL3D and particle-tracking models like CANERM and VAFTAD. Turney's density-separation method led to the discovery of the "crypto" type of this substance. Sigurdur Thorarinsson showed that this substance can form a "horizon" with a unique chemical signature, which can in turn work as a (*) chronological marker. When this substance mixes with precipitation, it forms andosols, and this substance can be classified by point of origin as scoria-fall or pumice-fall. If this substance is sufficiently hot, it can fuse into tuff. This substance is divided by size into bombs, ash, or lapilli, the latter of which can form glassy round fragments called Pele's tears. For 10 points, name this substance, a catch-all term from the fragments ejected from a volcano.
Models for the dispersal of this substance include advection-diffusion models like HAZMAP and FALL3D and particle-tracking models like CANERM and VAFTAD.
tephra [anti-prompt on “ash” or “volcanic ash”; accept pyroclastic deposits or pyroclasts; prompt on “volcanic ejecta”, “the stuff ejected from volcanoes” or similar answers]