The January 12th (yes, this article has been sitting in the “to-post” queue for a while) issue of Jinja Shinpō included another article in the series of Shinto records and historical relics. It was about the items excavated from Izumihama (Izumi Beach) on Izu Ōshima island, which is east of the Izu Peninsula and used to be part of Izu Province, but is now part of Tokyo Metropolitan Prefecture.
“Izumi” is written with the characters “和泉”, which are used for Izumi Province, near Osaka. However, “mi” also means “see”, so this can be read as “beach from which you can see Izu”, and that is exactly what it is — on the northwest coast of the island, it has a good view of the peninsula (weather permitting). At this site, offerings and vessels used in matsuri in the late seventh century AD have been discovered in archaeological excavations. This includes shards of deliberately broken ceramic vessels, small gold and silver ingots, and iron weapons and personal adornments.
This is very reminiscent of the lists of things offered to the kami by the central government, through the Jingikan (神祇官), the Bureau of Kami. By the late seventh century, many jinja had storehouses in which these offerings could be kept, but in some cases they were still buried, as was common in an earlier period. The gold and silver ingots resemble other offerings from the seventh and eighth centuries, and they seem to have had high status, suggesting that this was an important matsuri.
The reason for the matsuri is, of course, unclear, but we can speculate with considerable confidence. The Nihonshoki records a major earthquake in this area in 684 AD, accompanied by extensive volcanic activity in and around the Izu islands. Thus, it seems quite likely that this matsuri was performed shortly after the earthquake, in order to pacify the kami of the area, and ask them not to cause further damage. (We do not consider the possibility that the matsuri was performed slightly before the earthquake in order to cause it, both because that would be unethical and because nobody seems to really believe that that would work.)
This seems to have been a one-off matsuri. The site did not develop into a jinja, but the continuing volcanic activity in and around the Izu islands and peninsula did lead to veneration of “Izu Mishima-no-Kami”, or “Mishima Daimyōjin”, who is still revered at Mishima Taisha. His wives and children are also venerated in jinja across the area, and this archaeological site gives us some concrete information about the very early stages of this veneration.