Whether it conjures up the letter S, a lightning bolt, or perhaps an asymmetrical butterfly, the shape of Japan’s Sado Island is somewhat peculiar. The tripartite geography features two parallel mountain ranges of volcanic origin offset by an alluvial plain. In the hills, volcanic activity formed gold and silver deposits that people mined for centuries, while on the plains, traditional rice cultivation coexists with ecological conservation efforts.
The OLI (Operational Land Imager) on Landsat 8 acquired this image of Sado Island on April 22, 2024. Japan’s sixth largest island, it lies approximately 35 kilometers (22 miles) off the west coast of Honshu, the country’s main island. The volcanic activity that formed the rocks of Sado’s mountains and its gold and silver deposits occurred around 20 million years ago.
During that period of volcanism, magma-heated water containing gold and silver traveled up toward the surface through cracks in the rock. The metals precipitated out in the fractures, forming the deposits that humans would later exploit.
Mining looked different in the southern mountains versus the north. In the south, erosional and tectonic processes left gold deposits in granular form, known as placer gold, on or near the surface. In the northern range, minerals remained locked in veins running deep into the mountains and sometimes exposed at the surface.
Panning for gold in the Nishimikawa Placer Gold Mine may have begun as early as the 12th century, while the Aikawa-Tsurushi Gold and Silver Mine, with its intricate network of tunnels, was developed in the late 1500s. The Sado mines were the leading producer of gold in the world for part of the Edo period (1603–1868), when approximately 40 tons of gold and 1,800 tons of silver were extracted. These sites, along with archaeological remains of the unmechanized mining methods used there, comprise a 2024 addition to the list of UNESCO World Heritage sites.
In the lowlands, Lake Kamo is a large brackish water body known for its farmed oysters. Across the center of the island, a network of rivers cuts through a patchwork of fields. People have cultivated rice on the plains of Sado for centuries, expanding into the hills and creating terraced paddies during the height of gold mining.
Over the past 15 years, Sado rice farmers have endeavored to balance agriculture with biodiversity by nurturing feeding habitat for the endangered crested ibis (Nipponia nippon) in their paddies. The wading birds became extinct in Japan in 2003, but according to news reports, reintroduction efforts and modified farming practices have resulted in ibis numbers exceeding 500 on Sado Island in 2022.
NASA Earth Observatory image by Wanmei Liang, using Landsat data from the U.S. Geological Survey. Story by Lindsey Doermann.
