Minshuku Boukai, Nanki-shirahama Onsen

Why is a hot spring hot?

If it is in volcanic areas, you may imagine that the magma body heats underground water.

However, it cannot explain scalding hot water gushing in the area where there are no active volcanos nearby.

In fact, movements of plates of the earth create some hot springs.

Beach Resort near Metropolis

It is surprising that only two hours’ drive from Osaka will take you to such beautiful beach.

Shirahama Beach

Photo by Henry Burrows – Shirahama Beach (2007) / CC BY-SA 2.0

The hot springs in this beach resort have a long history, so that Nanki-shirahama Onsen is counted among Three Ancient Springs.

There are several sources of springs in this spa city, and I like “Kanro No Yu” the best.


Only a few inns including the place I will visit today provide the spring.

The inn is apart from the sea, but sits on the hill where you have a view of the coastline.

View from Windows

On one hand you can have a big dinner with food from the sea, on the other hand the bathrooms are so rustic.

There are just two gender-separated indoor baths.

The tubs are filled with extremely hot water (187 degrees F) with silky-smooth texture, which is low in salt in comparison with other sources nearby.

Indoor Bath

The earth is breathing

It has been veiled in mystery for a long time that such scalding hot water is gushing in the peninsula that has no active volcanos.

Indeed, the center of the earth is hot, so the temperature will generally increase in 1.6 degrees per 100 feet when you go underground.

However, the water in Nanki-shirahama is so hot that the water must be over two miles (you need to consider cooling during the ascension) from the ground on that assumption; it seems incomprehensible.

Water Outlet

In the 2000s, some researchers found out that movements of plates of the earth create the hot springs.

That is, in the Pacific Ocean near Japan, the Philippine Sea Plate is getting into under the Eurasian Plate at the speed of approximately one inch per a year.

Then the movement makes sea water seep underground.

Finally the elevated pressure and temperature due to the friction of plates causes dehydrating action; so that the hot water escapes into the ground.

Here is the evidence that earth is breathing.

Mishuku Boukai, Nanki-shitrahama Onsen, Wakayama, Japan
Official WebsiteYES

Related hot springs

The most popular hot spring in Nanki-shirahama would be here.


Sakinoyu, Nanki-shirahama Onsen, Wakayama, Japan

The location right in front of the Pacific Ocean is awesome, and you may find too many tourists are bathing in holidays.

Hot Springs in Kinki Region

Hot Springs in Japan

Leave a Reply