Is Japan's airport sinking? All about the uncertain future of Kansai International Airport

When Kansai International Airport first opened its runways to the world in 1994, it stood as a symbol of Japan’s engineering ambition, a man-made island rising from the depths of Osaka Bay, built to ease congestion on land and accommodate a growing international travel demand. Three decades later, that symbol is slowly sinking. While Kansai remains a vital gateway connecting Japan to over 90 global cities, the very seabed it rests upon is shifting beneath its foundations. Faced with accelerating subsidence, typhoon damage, and rising climate and seismic threats, the airport’s long-term survival is now in question, turning one of the world’s most celebrated transport hubs into a high-stakes test of infrastructure versus nature.

Kansai is Japan’s third-busiest airport and a hub for nearly 70 passenger and 20 cargo airlines. The seabed beneath Kansai consists of loose clay and silt. Engineers anticipated settlement, using 2.2 million vertical pipe drains and 200 million cubic metres of landfill to speed up the process. Still, subsidence rates exceeded expectations. The first island sank 12.5 feet, while the second, added later, has dropped 57 feet since construction began. In 2023, 21 centimetres of subsidence was recorded at 54 points on the newer island.

In 2018, Typhoon Jebi, the strongest to hit Japan in 25 years,forced a complete shutdown of Kansai. Storm surges overwhelmed the sea walls, flooded the basement-level disaster response centre and left 5,000 people stranded. The airport lost power, and operations were paralysed for days. The incident highlighted the vulnerability of placing critical infrastructure on a sinking offshore island.

To combat the sinking, over $150 million has been spent reinforcing the sea walls and installing hydraulic jacks beneath terminal buildings, says The New Indian Express. These jacks lift the structure in stages using iron plates, but adjustments are costly and must be repeated every few years. While the subsidence rate has slowed from 19 inches annually in 1994 to 2.3 inches in 2023, the uneven nature of the sinking creates further maintenance challenges.

Several factors contribute to ongoing settlement. The clay beneath the airport remains unconsolidated. The weight of 69.5 square miles of artificial fill continues to compress the seabed. The initial construction began before the seabed had stabilised, and early estimates underestimated long-term settlement rates. Engineers expect parts of the airport to drop below sea level as early as 2056.

Japan’s vulnerability to natural disasters adds to Kansai’s troubles. Rising sea levels and more frequent extreme weather events due to climate change increase the risk of future storm surges. The region is also earthquake-prone, posing a serious threat to an already fragile island structure. Seismic activity could accelerate subsidence or damage critical infrastructure, making future operations more precarious.Despite the challenges, Kansai Airport continues to operate as a major international hub. Passenger traffic is rebounding post-pandemic, with 25.9 million travellers in 2023. However, maintaining its structural integrity will require continued investment and innovation. While the sinking has slowed, the long-term viability of such offshore infrastructure in a seismically active and climate-vulnerable region remains uncertain.