A paper in press by M.-A. de Lumley and colleagues suggests that the five Lower Pleistocene hominins recovered at Dmanisi, Georgia, entered the paleoanthropological record as the result of a volcanic eruption. Here's the abstract:
"The human remains unearthed at the Lower Pleistocene site of Dmanisi (Georgia), are numerous, well preserved and show no evidence of transportation or predation. They were discovered over a small surface and correspond to at least five Homo georgicus individuals, whose age at death is regularly distributed from the teenager to the elder over 40 years old. These characteristics evoke a family group who died suddenly. Granulometry and chemical analyses of ca. 30 volcanic tephra samples prove its unicity and its primary position. Since this tephra cannot correspond to a nuée ardente, it is probable that the Dmanisi Hominids were surprised and asphyxiated, 1 810 000 years ago, by volcanic ashfalls." (de Lumley et al., in press: 1)Not impossible, I suppose, and it has the advantage of explaining why you find five relatively well-preserved hominins in direct association with volcanic ash. As far as where the eruption itself took place, the authors state, in the abridged English version of the article, that
"The volcanic ashes were sorted during aerial transportation from the emissive point, presumably located ca. 20 km west of Dmanisi (Emliki heights in the Džavacheti Mountains). From such a distance, the ashfall does not burn, but when inhaled, it mixes with naso-bucco-pharyngeal secretions and forms a mixture that provokes suffocation by obstruction of respiratory and digestive tubes...It'd be interesting to see whether the faunal assemblages at the site reflect a similar pattern, and whether the lithic assemblages differ from most contemporary ones by their more or less 'systemic' character (sensu Schiffer 1972). That is to say, whether the stone tools differ from archaeological assemblages comprising purposefully discarded items as opposed to representing an assemblage 'frozen in use' by a volcanic eruption.
"In Dmanisi, the concentration of Hominids in a depression may represent a search for shelter. The ashfall, cold hence non-mortal, could have allowed the Hominids to gather in a natural depression. Tephra inhalation, mixed with natural secretions, may have led to animal and human death by obstruction of respiratory
and digestive tubes." (de Lumley et al., in press: 4)
de Lumley, M.-A., J.-M. Bardintzeff, P. Bienvenu, J.-B. Bilcot, G. Flamenbaum, C. Guy, M. Jullien, H. de Lumley, J.-P. Nabot, C. Perrenoud, O. Provitina, and M. Tourasse. 2008. Impact probable du volcanisme sur le décès des Hominidés de Dmanissi/Probable volcanic impact on the death of the Dmanisi Hominids. Comptes Rendus Palevol: in press; doi:10.1016/j.crpv.2007.09.002
Schiffer, M. B. 1972. Archaeological context and systemic context. American Antiquity 37:156-165.