Geology Day

What Is Geology Day?

Every May 10th is "Geology Day" (地質の日, Chishitsu no Hi) in Japan. On May 10, 1876 (Meiji 9), American geologist Benjamin Smith Lyman and his team produced the "Outline Geological Map of Yezo, Japan" (日本蝦夷地質要略之図) at a scale of 1:2,000,000 -- Japan's first wide-area geological map. In addition, on this day in 1878 (Meiji 11), a Geology Section was set up within the Geography Bureau of the Home Ministry as an organization to carry out geological surveys. The day was established in 2007 by geology-related organizations and societies, including the Geological Society of Japan and the Geological Survey of Japan (AIST). It is a day to deepen understanding of the "geology" beneath our feet and to think about the land from two sides: its gifts, such as resources and hot springs, and its hazards, such as earthquakes, eruptions, and landslides.

The History of Geology in Japan

In Meiji-era Japan, geological surveys were carried out with experts invited from overseas, in search of the resources needed for modernization.

• Lyman and the map of Hokkaido: Invited by the Meiji government's Hokkaido Development Commission, Lyman surveyed Hokkaido's coal and other resources. The result was the "Outline Geological Map of Yezo."
• Naumann and the Fossa Magna: German geologist Edmund Naumann, also invited by the Meiji government, proposed the "Fossa Magna," a great trough-like zone running north-south across central Honshu. The extinct Naumann's elephant is named after him.
• The role of geological maps: In the Meiji era, geological maps were essential for finding resources such as coal and metals. Today they are widely used for disaster prevention, construction, and groundwater use.

How the Japanese Archipelago Was Formed

Learning about geology means reading a history that the land has recorded over vast stretches of time.

• Where four plates meet: Four plates converge around Japan: the Pacific, Philippine Sea, North American, and Eurasian plates. This blesses Japan with hot springs and volcanic scenery, but also makes it a land of frequent earthquakes and volcanic activity.
• Accretionary complexes: Much of the Japanese archipelago is said to be made of "accretionary complexes" -- rock formed when seafloor sediments were scraped off and pressed onto the land side as oceanic plates sank beneath it.

Interesting Facts About Geology

• Rocks as time capsules: Rocks and strata hold the shells of ancient plankton, volcanic ash, and more. Researchers use these records to estimate what Earth's environment was like in the past.
• The "Chibanian": Strata in Ichihara, Chiba Prefecture, were chosen as the international reference site because they clearly preserve evidence of the last reversal of Earth's magnetic field about 770,000 years ago. In 2020, the geological age "Chibanian" was born -- the first time a Japanese place name was used for a geological time period.
• Overturned strata: Normally, older layers lie below newer ones, but in some places major crustal movements have left older strata lying on top of younger ones.
• Geology in everyday life: Many building materials that support our lives, such as the limestone and gravel used to make concrete, come from underground resources.
• Strata and water: As rainwater slowly seeps through the ground, it picks up minerals and becomes spring water and groundwater. Local geology is one reason water tastes different from place to place.

Tips for Geology Day

• Check the hazard map for your area. Knowing whether the ground under your home or workplace was once a river or the sea is a first step in disaster preparedness.
• Look at stones by the roadside or at exposed strata (outcrops) in parks and along hiking trails. Their stripes and colors may be records of ancient seafloors or volcanic eruptions.
• Visit a museum or a geopark. Every year around May 10th, museums, universities, and research institutions across Japan hold Geology Day events.
• Notice the shapes of mountains and rivers on your commute or travels, and look up how those landforms came to be.

The Ground Beneath Us Is a Record Built Up Over Ages

May 10th is a day to reflect on how long it took for the land we stand on to take shape. Strata endure crustal movements, wind, and rain, passing on the events of the past to the present. Our daily experiences, too, may build up little by little like strata, eventually becoming a foundation that supports us. Today, why not look down at your feet and get a sense of how the land around you was formed?