Showa Shinzan

Showa-Shinzan: The Miraculous Mountain Born from a Wheat Field in Wartime Hokkaido

Few places on Earth allow you to witness the raw, ongoing creation of a mountain. Showa-Shinzan, rising 398 meters above the rolling farmland of Sobetsu Town in southern Hokkaido, is one of them. This rust-red lava dome, still steaming and warm to the touch in places, did not exist before December 1943. In just under two years, the gentle wheat fields of a small farming community heaved upward in a series of earthquakes and eruptions to give birth to one of the youngest mountains on the planet. Designated as a Special Natural Monument of Japan, Showa-Shinzan is not only a geological marvel but a window into a wartime story of perseverance, scientific curiosity, and quiet defiance.

What Is Showa-Shinzan?

Showa-Shinzan is an active volcanic lava dome located within Shikotsu-Toya National Park, on the southern shore of Lake Toya in Hokkaido's Iburi region. Its name literally means "the new mountain of the Showa era," referring to the reign of Emperor Hirohito (1926–1989), during which it was formed. The volcano is a parasitic cone of the much larger Mount Usu, which has erupted repeatedly over the past several thousand years.

Unlike most volcanoes, which build their cones gradually through successive lava flows or ash deposits, Showa-Shinzan was created by a process called endogenous doming. A thick, viscous mass of dacitic lava pushed upward from below, lifting the existing ground surface—farmland, forest, and even a section of riverbed—into the sky. Geologists classify it as a tholoid or "upheaval-type" volcano, and it is one of the clearest examples of this phenomenon anywhere in the world. Its surface still reaches temperatures of around 300°C in places, and white plumes of steam rise from its rugged brown flanks even today.

The Birth of a Mountain in the Shadow of War

The story of Showa-Shinzan began on December 28, 1943, when a series of strong tremors began shaking the farms around Mount Usu. Earthquakes continued through the winter and into the spring of 1944, and by June, the wheat fields east of the mountain had begun to swell visibly upward. On June 23, 1944, a powerful phreatic eruption tore open the bulging earth, sending volcanic ash high into the sky. Eruptions and explosions repeated throughout the summer and autumn of 1944.

By November 1944, the eruptions ceased and a thick plug of lava began to push slowly through the swelling—what locals dubbed the "roof mountain" (yane-yama). For nearly a year, this lava dome rose at an astonishing rate, sometimes by more than a meter in a single day. Activity finally settled in September 1945, just as the Second World War ended. The new mountain stood at roughly 407 meters; cooling and gradual erosion have since reduced it to its present 398 meters.

All of this took place during the most desperate years of the Pacific War. The Japanese authorities of the time, fearful that the sudden appearance of a fiery new mountain might be interpreted as an ill omen, quietly suppressed news of the eruption. Aerial photography was forbidden and reporting was discouraged. Without the dedication of one extraordinary local citizen, the world might have lost the chance to study this rare phenomenon as it unfolded.

Mimatsu Masao and the Famous "Mimatsu Diagram"

That citizen was Mimatsu Masao (1888–1977), the postmaster of Sobetsu. Without formal training in geology, he resolved to record the mountain's growth for posterity. Working from his post office window, he stretched horizontal fishing lines across two vertical posts, using them as reference grids against the changing skyline. Day after day, year after year, he sketched the silhouette of the rising mountain on paper, layering each new outline over the previous one.

The result was a remarkable visual record of a volcano being born—an image now known internationally as the Mimatsu Diagram. When his work was presented at the World Volcanological Conference in Oslo in 1948, it stunned professional volcanologists with its precision and clarity. Mimatsu later went on to purchase the land on which the new mountain stood, partly to ensure its protection. To this day, Showa-Shinzan remains private property—a rare distinction for a Special Natural Monument anywhere in the world. The land is now cared for by Mimatsu's descendants.

Why Showa-Shinzan Is Designated a Special Natural Monument

Showa-Shinzan was first designated a Natural Monument of Japan on June 9, 1951, just six years after its formation came to rest. In 1957, its status was elevated to Special Natural Monument, the highest level of protection accorded to a natural site under Japan's cultural property law. This designation reflects several extraordinary qualities.

First, Showa-Shinzan is one of the very few volcanoes in the world whose entire process of formation was observed and documented in real time. Geologists, volcanologists, and educators around the world continue to draw on the Mimatsu Diagram and related records to study how lava domes grow. Second, the mountain is a textbook example of the upheaval-type volcanic dome, a relatively uncommon variety that contrasts with the more familiar cone-shaped stratovolcanoes. Third, the surrounding landscape—including Mount Usu, Lake Toya, and the disrupted riverbeds and forests caused by the uplift—forms an unusually complete record of recent volcanic activity. The whole region has been recognized as part of the Toya-Usu UNESCO Global Geopark since 2009, the first geopark in Japan to receive UNESCO recognition.

Highlights and Things to See

The Mountain Itself

Visitors cannot climb Showa-Shinzan—the slopes are private property and remain volcanically active—but the views from the foot are spectacular. The contrast between the deep green forests around the base and the bare, rust-red flanks of the dome is striking, and steam continues to rise from the rocks. A faint scent of sulfur hangs in the air, a reminder that the earth here is still very much alive. The colors of the mountain shift dramatically with the seasons: vibrant against autumn foliage, austere against winter snow, and gleaming under the summer sun.

Mount Usu Ropeway

A short walk from the parking area at the base, the Mount Usu Ropeway carries visitors up the neighboring stratovolcano in about six minutes. From the upper station and the observation decks beyond, you can look directly across at Showa-Shinzan from above, with sweeping views of Lake Toya, the Pacific Ocean to the south, and Mount Yotei rising in the distance. The ropeway operates year-round.

Mimatsu Masao Memorial Hall

A short walk from the foot of the mountain, this small but absorbing museum tells the personal story of the postmaster who chronicled the mountain's birth. Original sketches, the famous diagram, photographs, and Mimatsu's own observation tools are on display. A bronze statue of Mimatsu, gazing toward the mountain through a surveying instrument, stands nearby.

Showa-Shinzan Bear Park

Adjacent to the visitor area, this park is home to a population of Hokkaido brown bears (Ezo higuma). It has been a fixture of the area for decades and offers a chance to observe these powerful animals up close.

Shinzan-numa Pond

The 1944 uplift dammed a section of the Sobetsu River, creating a small wetland known today as Shinzan-numa. A short trail and observation point allow you to see how the eruption transformed the watershed itself.

Around the Area

Showa-Shinzan is at the heart of one of Hokkaido's most rewarding sightseeing regions. Just a few kilometers away lies Lake Toya, a circular caldera lake famous for its clear water, scenic boat cruises, and nightly summer fireworks. The lakeside Toyako Onsen is among Hokkaido's best-loved hot spring resorts, with public footbaths and accommodations of every price range. The 1977 Volcanic Ruins Park preserves buildings damaged by Mount Usu's most recent major eruptions, offering another vivid look at the geological forces shaping this region. Farther afield, Noboribetsu Onsen with its dramatic Hell Valley, the historic port city of Hakodate, and the Ainu cultural center Upopoy in Shiraoi are all accessible as day trips or overnight excursions.