The series of articles about sacred forests had an interesting instalment in the February 14th issue of Jinja Shinpō — interesting because it isn’t about forests. It does have something of a connection to jinja, however. It is about artificial hills found around ports and coasts in many areas of Japan.
Many of these are called “good weather mountain” (biyoriyama), although they are usually quite small as mountains normally go. These hills were used by fishermen and other sailors to get a good view of the sky, and judge whether it was a good time to go out to sea. They might also be used for watching for ships, or as landmarks for coming into port. Some ports, of course, had natural hills in a suitable location to serve these purposes, but when they didn’t, it was not uncommon to create an artificial hill in a suitable location.
Sometimes, these hills were called “life mountain”, and one of their explicit purposes was to provide a refuge in case of a tsunami or other flooding. A group of such hills in Shizuoka Prefecture has been well-studied, and in this area it was common to build a jinja on top of the hill, at which people would pray for the safety of the area.
Similar examples exist elsewhere. An example that became quite famous is Biyorigaoka in Ishinomaki City, Miyagi Prefecture. This hill overlooks the port, and is the site of Kasuga Miko Jinja. (The “miko” here means “honourable child”, not “miko”.) I have been to this one, and the main flight of steps up to the jinja goes straight down to the low-lying port. On the day of the tsunami, a lot of people came up to the jinja to safety.
Unfortunately, this did not always work. In Yuriagë, in Natori City, also Miyagi, there was a Biyoriyama near the coast, which served as the site of Tominushihimë Jinja. However, this jinja was washed away in the tsunami, because the artificial mountain was only 6.3 m tall, and the tsunami overtopped it by about 2.1 m. (There were marks on surviving trees.)
After the tsunami, the importance of such evacuation sites became obvious again, and more have been built in vulnerable areas. However, because many of them are being built by the state, there are, to the best of my knowledge, no jinja on them.