The Topography of Tokachi Shikaoi Geopark and Its Formation
Discover the events that led to the formation of the Tokachi region and the landforms of Tokachi Shikaoi Geopark.
The story begins around one million years ago with the massive eruption of a supervolcano in the northern part of the Tokachi region.
The eruption produced multiple pyroclastic flows. These inundated the area that would become the Tokachi Plain with volcanic matter. In certain areas, volcanic debris accumulated up to 30 meters.
At the time of the eruption, pockets of sea covered what is now the Tokachi Plain. The debris from the pyroclastic flows made these pockets shallower.
Gradually wetlands formed. Rivers transported volcanic debris and sediment from the mountains, and the wind carried in volcanic ash from eruptions across Hokkaido. These wetlands subsequently became the Tokachi Plain as it is today.
The Tokachi Shikaoi Geopark Visitor Center is built on land that was formed in this way.
Further changes occurred around 40,000 years ago, when large quantities of ash from an eruption in western Hokkaido fell over the southern part of the Tokachi region. The resulting thick layers of ash created a desert-like landscape.
Around the same time, lava domes formed in northern Shikaoi.
These formed gradually around vents in Earth’s crust, emitting sticky, high-silica lava. Instead of flowing away, the viscous lava piled up to form domes.
Continued volcanic activity dammed the Shikaribetsu River, which in turn created Lake Shikaribetsu.
The lake was much larger than it is today and likely extended further north and west.
Over time, the river began to flow again. As it carved itself a new path and transported and deposited sediment downstream, it changed course many times, gradually shaping the plains of Shikaoi.
Displays here in the visitor center introduce these geological processes in more detail.
