Introduction
The Pacific Northwest is home to some of the most beautiful coastlines and vibrant communities in the U.S. But with environmental changes on the horizon, the region faces a growing risk: flooding. This isn’t just because of rising sea levels. Earthquake-driven subsidence—land sinking after an earthquake—is adding another layer of danger. In this post, we’ll explore how these two forces are increasing flood risks in the Pacific Northwest and why action is needed.
These insights come from a 2025 study titled “Increased flood exposure in the Pacific Northwest following earthquake-driven subsidence and sea-level rise,” published in the journal Proceedings of the National Academy of Sciences (PNAS). The research models how much more flood-prone the region becomes when both land sinking from a major earthquake and sea-level rise are taken into account.
In this post, we break down what the study found — and why it matters for communities across Washington, Oregon, and Northern California.
What is Earthquake-Driven Subsidence?
Subsidence sounds like a big word, but it simply means that the ground sinks. During earthquakes, the earth’s surface can shift, and some parts of the land may drop lower than they were before. Imagine you’re standing on a trampoline, and someone jumps on it. The areas where the weight lands dip down. For the Pacific Northwest, if major earthquakes hit, this could mean that parts of the land near the coast sink lower, making it easier for the ocean water to flood inland.
Sea-Level Rise: A Growing Threat
In addition to earthquakes, sea levels are rising. The water in our oceans is slowly getting higher due to climate change, which causes ice caps to melt and warmer water to expand. Rising sea levels have already caused problems for many coastal areas around the world. The Pacific Northwest is no exception. As sea levels creep higher, areas that were once safe from flooding may start to experience more frequent or severe floods.
How These Two Forces Combine
When we combine earthquake-driven subsidence with rising sea levels, the risk of flooding becomes even greater. In places where the land is sinking, the rising sea can more easily overwhelm the land, leading to higher flood risks. It’s like trying to fill a cup with water while the cup is slowly being pushed deeper into the ground.
The combination of these two forces is making it harder for the Pacific Northwest to protect its communities and natural environments from flood damage. This problem will likely worsen in the coming decades as both earthquakes and sea levels continue to change.
Why This Matters
These changes could affect everything from homes and businesses to wildlife and infrastructure. Communities along the coast need to understand the risks they face and begin planning for the future. This includes considering how to protect homes, roads, and essential services from floods. It also means thinking about how the local ecosystem might change and what needs to be done to preserve it.
