Kansai International Airport: Japan’s Engineering Marvel That’s Slowly Sinking

When Kansai International Airport opened its doors in 1994, it was hailed as a bold symbol of Japanese innovation—a futuristic airport built entirely on two massive man-made islands in Osaka Bay. Created to overcome a severe land shortage, the airport was celebrated worldwide for its advanced design and engineering resilience against earthquakes and typhoons. Floating atop layers of soft marine clay, Kansai quickly became an icon of modern infrastructure.

But three decades later, the airport’s fame has taken a different turn. Kansai is now equally known for its ongoing struggle against nature: the islands beneath it are sinking into the sea at an alarming rate.

A Sinking Wonder

Engineers had long expected some subsidence due to the clay seabed, but the actual figures have far exceeded predictions. Since it opened, parts of the airport have sunk by as much as 13.6 meters. As of 2024, Island 1 continues to sink around 6 centimeters each year, while Island 2, which was added later, is subsiding even faster—by nearly 21 centimeters annually. The worst-affected areas have seen a drop of about 17.47 meters in total.

Even the central terminal area, where passengers arrive and depart, has already sunk by nearly 3.84 meters—posing major challenges for runways, roads, and airport buildings.

Typhoon Jebi’s Wake-Up Call

The danger of Kansai’s location was dramatically underscored in 2018, when Typhoon Jebi—one of Japan’s strongest storms in a quarter-century—brought a devastating storm surge. Floodwaters swamped parts of the airport, damaged power infrastructure, and left thousands stranded, forcing a temporary shutdown and sparking urgent calls to strengthen defenses.

Engineering Against the Odds

Japan hasn’t abandoned its ambitious airport. Instead, engineers have launched an ongoing fight against nature. Over $150 million has been spent reinforcing seawalls, building new drainage systems, and installing technologies to slow the subsidence. One innovative measure, the Vertical Sand Drain System, helps remove water trapped in the clay below, reducing the ground’s tendency to compress.

Parts of the terminals also use hydraulic jacks to adjust and lift sinking structures—a striking example of real-time engineering adaptation.

Why It Keeps Sinking

The heart of the problem lies beneath the airport itself: thick, soft marine clay that compresses under the enormous weight of runways, terminals, and other facilities. While the islands were expected to settle gradually, they’ve continued sinking faster than anticipated. Rising sea levels and climate change worsen the situation, increasing risks of flooding and damage from future storms.

Still a Busy Gateway

Despite these daunting challenges, Kansai International Airport remains a critical hub. In 2024, it handled over 30 million passengers and offered flights to 91 cities worldwide. That same year, it was even recognized globally for its efficient luggage handling.

Uncertain Future

Engineers remain cautiously optimistic about keeping Kansai operational for the coming decades, but the long-term picture is less certain. The focus has shifted to continuous adaptation rather than permanent stability, requiring constant monitoring, fresh investment, and new engineering solutions.

Kansai International Airport stands today as a unique blend of vision and vulnerability—a remarkable achievement that showcases both the power and the limits of human engineering against the forces of nature.