Hawaii rose from the ocean, born of ancient volcanic fire. But now, in a twist few expected, it’s sinking back down. A new study from the University of Hawai‘i at Mānoa has revealed that parts of Oʻahu, the state’s most populated island, are sinking far faster than previously thought.
But this isn’t just a geological curiosity. No, the researchers say it’s a warning signal for flood risk that’s closer than many realize. The data comes from a new study that focused on subsidence—the gradual sinking of land. The study found that most of Oʻahu is dropping at 0.6 millimeters per year.
Worse, certain areas of the Hawaiian island—like the industrial zone of Mapunapuna—are subsiding at a staggering 25 millimeters per year. That means parts of Hawaii are sinking over 40 times faster than the island-wide average and far outpacing global sea level rise.
So why the dramatic difference? Well, not all land is created equal. The researchers explain that areas built on soft sediment or artificial fill, like Mapunapuna, are more prone to compaction. Over time, this causes the ground to cave in faster, compounding the threat from rising seas. This could mean 50 percent more land at risk of flooding by 2050 in some places.
Flood maps typically focus on sea level rise alone, but the reality of parts of Hawaii sinking this quickly means those maps might be missing half the story. When you combine rising waters with a shrinking landmass, the urgency to act becomes crystal clear.
Fortunately, Oʻahu is already laying the groundwork for climate resilience through initiatives like Climate Ready O‘ahu, which is focused on restoring wetlands, reinforcing dune systems, and protecting shorelines. However, the study’s authors say any effective strategy must now factor in subsidence rates to stay ahead of the threat.
As lead author Kyle Murray said, “In rapidly subsiding areas, sea level rise impacts will be felt much sooner than previously estimated.” And that means decisions about urban planning, infrastructure, and emergency preparedness can’t wait for tomorrow.
