Yakushima is one of the southwest islands of Japan, which is situated approximately 60 km from the southern most tip of Cape Sata-misaki in Kyushu. Most of the land is made of uplifted granite, and the island is about 504 km² and 132 km in perimeter. Tall mountains, such as Mt. Miyanoura (1,936 m) of the highest peak in Kyushu region, Mt. Kuromi, Mt. Nagata, Mt. Kurio and three other mountains that exceed 1,800 meters dominate the central part of the circular island. Most of the mountains that surround the center exceed at least 1,000 meters, giving the name “Alps on the Ocean.” The population is roughly 13,500, and people live on plain grounds around the coastal area since the mountains are steep. In the administrative section, Yakushima and Kuchinoerabujima islands belong to Yakushima-cho, Kumage-gun, and as well as Kagoshima prefecture.

The rocks lying as the foundation of Yakushima are sedimentary rocks made of sand or mud. They were piled up as a trench approximately 40 million years ago along with landslides that occurred due to tectonic plate movements. Most areas of the mountains that people climb are made of granite created by the result of intrusion of hardened magma (by a cooling process) that developed about 15 million years ago. Because the granite is much lighter than other rocks, it had caused the stratum to be pushed up at several millimeters per year at a considerably fast rate. The outer surface that encompasses the granite are metamorphic rocks (hornfels) made of sedimentary rocks burnt from the heat of magma. Metamorphic rocks are hard and highly resistant to erosion which have allowed many cliffs and waterfalls to be produced. The red volcanic ashes of stratum can be observed especially in the northwestern part of Yakushima. This was a caused by a large eruption of Kikai Caldera that occurred 73 million years ago. Yakushima continues to rise at the rate of 13 cm in 1,000 years.

The climate and weather in Yakushima is greatly influenced by the Kuroshio Current. The moisture-rich air caused by the warm current fills the mountaintops. Because of the cool temperature at the high peaks, however, it produces rain clouds that create a large quantity of rain each year. This is one of the reasons why Yakushima is also known as the “Island of Water.” The rich water in Yakushima is the life of all living things, and it has produced magnificent scenes and untouched cedar forests. There are various ways that it rains which are different by seasons and areas. As a result, the characteristic of the weather in Yakushima can be quite unpredictable and wild. Although a tiny island, it could be raining heavily one minute in the southern part when it is completely sunny on the other side.

The annual mean temperature at the lower altitude level plains where most islanders live is approximately 20 ℃. Because of the mountains in Yakushima, the village areas are considered to be subtropical with warm temperatures, whereas the mountaintop is considered to be the cold zone. It is as if you had placed various climate zones that extend the Japanese mainland perpendicularly on top of this tiny island.