Transgression and Regression: How Coastlines Move

He walks through the mechanics of what happens when sea levels shift, and the terminology tells you everything. When ice melts and sea level rises, coastlines don't hold their ground. They move inland. That movement has a name: transgression. The seas transgress onto the land. When sea level drops, the opposite occurs. Coastlines migrate seaward, and that's called regression. The seas regress, pulling back from the land.

It's a simple concept, but it matters because it describes the physical reality of what happens during glacial and interglacial periods. Coastlines are not fixed features. They respond to the volume of water in the ocean basins. Understanding transgression and regression is foundational to reading the geologic record and recognizing how dramatically landscapes have shifted over the course of the Holocene.