#210 What is 'Shirasu' in the Shirasu Plateau?

Kagoshima Prefecture is home to the Shirasu Plateau, which is covered in volcanic ejecta.
The etymology of 'Shirasu' comes from the Kagoshima dialect words 'shirasuna' (white sand) or 'shirasu' (white sandbar/beach), and because the Shirasu Plateau is a technical term, it is written in katakana rather than kanji or hiragana.

When people think of volcanoes in Kagoshima Prefecture, they think of Sakurajima, so it is often assumed that the Shirasu Plateau was formed by volcanic ash falling from Sakurajima's eruptions, but this is actually incorrect.

In Kagoshima, the bay surrounded by the Satsuma and Osumi Peninsulas is called Kinko Bay. The inner sea beyond Sakurajima in Kinko Bay looks like an ordinary sea, but it is actually a massive caldera called the Aira Caldera, which is the site of an eruption that occurred approximately 29,000 years ago.
The scale of the eruption was one million times that of current Sakurajima eruptions, and the amount of magma ejected was enough to cover Kagoshima Prefecture to a depth of 60 meters, forming the current Shirasu Plateau.
Incidentally, there are two other massive calderas in the middle and near the entrance of Kinko Bay called the Ata Caldera.

Because the Shirasu Plateau has good drainage, it is not suitable for rice cultivation. Furthermore, because landslides occur easily, areas with Shirasu slopes are said to have a high risk of disaster.

However, the people living on the Shirasu Plateau have utilized Shirasu to develop various industries.
In addition to sweet potatoes, which can be called synonymous with Kagoshima Prefecture, as well as the dairy farming and shochu production that utilize them, a material called Shirasu Balloon made from Shirasu is used in facial cleansers, detergents, and paints.
In recent years, it has also gained attention as a material for sidewalk blocks and greening foundations (the material under lawns), and is being used in urban development.

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