Introduction to Sado Island

Sado is the largest isolated island in the Sea of Japan. Once was a gold production place, representing the golden country "Jipangu", this island also affected the international community. Workers and merchants from the whole country flocked to Aikawa, an almost deserted village, where gold veins were discovered. This village then grew to become one of the largest cities in the country. The prosperity of this gold rush spread to the entire island and sparkled the development of unique performing arts and culture, and they are still practiced today, many generations later.

The formation of Sado and of the gold and silver mines dates back to about 30 million years ago. At that time, Japan was still part of the Eurasian Continent. The earth’s mantle rising from deep underground broke off a chunk of the continent and moved it into the well-known bow shaped archipelago that is Japan today. The volcanic activities, which lasted about 13 million years around Sado Island, formed several gold and silver veins. This island raised further by uplift from the seabed and grew to a beautiful island with mountains of altitude above 1,000 meters.

The topography and natural environment of Sado Island

Sado is the largest island in the Sea of Japan and the only one with mines. The two mountain ranges – Osado mountains and Kosado hills – extend from the northeast to the southwest. Between them, the Kuninaka plain, a [fertile] green zone. On the north side of the Osado is the Sado ridge, and on the west side, the Toyama trough. Passing across the west side of Sado Island is the Sea of Japan’s Eastern Margin Zone, also known as “the region with many earthquakes”. The Sea of Japan’s Eastern Margin Zone follows the Itoigawa–Shizuoka tectonic line to the vicinity of Okushiri Island in Hokkaido.

Due to the influence of warm ocean current, Tsushima, the summer in Sado Island is cooler than the mainland, and winter is quite warm. Given the privileged natural environment, there is a diversity of plants and marine organisms. Large areas on the island are designated either as National Park, or Prefectural Natural Park. Among the Osado mountains, on Mt. Kimpoku, lies the mysterious Otowaike Pond, where Japan's largest marshy island floats.

Sado Island’s National parks, natural monuments and other points of interest

National parkYahiko-Sado-Yoneyama Quasi-national Park (1950)
National designated natural monument
National designated historic site
Sado Ogi Coast (1934)
National designated scenic spotSado Kaifu Coast (1934)
National designated natural monumentWave erosion potholes at Hiranezaki (1940), Gosho zakura, imperial cherry tree at Ogi (1928)
National designated historic siteSado gold and silver mines (underwent name change in 2011)
National designated special natural monumentToki (the Japanese crested ibises) (1952)
Japan’s top 100 geological placesSado gold mine (2007), Sado Ogi Coast (2007)
Prefectural natural parkKosado prefectural natural park (1959)
Prefecture designated natural environment conservation areaUe no daira natural environment conservation area (1989)
Prefecture designated natural monumentFloating island and plant communities of Otowaike (1963); Sugiike pond · autumn leaves forest (1965); Gold ore from the Sado deposit (1958), etc.
Prefecture designated natural monument
Prefecture designated scenic spot
Daigahana (1973)
Prefecture designated scenic spotRuins of Tamatsukuri in Niibo (1952); Tomb of Shizume ichizaemon (1958); Iwayasan Cave (1972), etc.
City designated natural monumentKaidate Sawane formaton (2004); kagami iwa rock at Seki (2004)
City designated scenic spot
City designated natural monument
Sawane cliff (2004)

Sado Island as a Geopark (Park of Earth)

Through the topography and the geology of Sado Island, we can understand the history of the Sea of Japan.

Era of the ancient sea

A few hundred million years ago, Sado was located on the deep ocean floor around the Eurasian Continent. It is possible to see, in various parts of the island, gravels of limestone and calcareous rocks where we can find fusulinids fossils. There are also shales, containing the radiolarians fossils, dating back to approximately 200 million years ago, and granodiorite and granitic rocks, which magma solidified deep underground.

The era of terrestrial volcanic activities and the formation of gold and silver bearing quartz veins.

Volcanic rocks showing the time period from around 30 million years ago to 17 million years ago are widely distributed in the beneath the surface of Sado Island. The geo-thermal fluids of high temperature and pressure were formed around the magma which seeped in this era at that time, and useful metals such as gold and silver melted in there. This geo-thermal fluids rose along the fault and precipitated by the decline of its temperature and pressure, and then it became a deposit of gold and silver. Sado gold and silver mine is the largest scale of mine in Japan and the traces of its excavations are still well preserved.

From the opening of the Sea of Japan to its transformation into the deep sea

Approximately 16 500 000 years ago, the geo-unconformity, which is a shallow marine sediment that overlapped previous volcanic rocks, was formed in various parts of the Japanese archipelago. The outcrop where this phenomenon can be observed is situated on Sado Island. The Sea of Japan deepens from 15 million years ago to 10 million years ago, and so the stratum of diatomite deposited at this period can also be observed. Underwater volcanic rocks such as pillow lava are also present in these strata.

Birth and growth of Sado Island

About 3 million years ago the ocean floor began to rise, and Sado Island was formed. This uplifting process which has reached over 1,000 meters above sea level still continues. It is possible to trace the plain’s history in detail: underneath its surface, marine deposits and terraced sediments which indicate the period of about 3 million years ago after the Pliocene era still remain.

What is a geopark?

The word "geopark" is a coined word that combines geo (planet and earth) and park. It is required to preserve and protect rich nature, and to use it as a regional resource for the development of the region. In the Geopark, our efforts to elicit more public interest in nature continue. We also put lots of efforts into promoting activities geared towards learning and education purposes, as well as increasing tourism and revitalizing a regional sustainable development.

In Japan there is the "Japan Geopark " accredited by the Japan Geopark Committee (JGC), and there is the "Global Geopark" certified by the Global Geopark Network (GGN) in the world. Every region qualified as a Geopark is regularly examined for its aptitude and its activities every four years, and requires the maintenance and the improvement of its activities.

There are seven areas that are certified as a "Global Geopark" in Japan, such as Itoigawa (Niigata Prefecture) and Toyako Usuzan (Hokkaido). Another 39 areas including Sado Island are certified as a "Japan Geopark" (as of September 2015). Additionally, there are more than 50 regions in Japan, which have started their application for Geopark status.

For more information, please visit the website of the Japan geopark network.

Sado, certified a "Japan Geopark" member in the fall of 2013, is now pursuing diverse efforts to be accepted as a member of the "Global Geopark" network.