Beaches are dynamic, living landscapes. Spend a day on the beach and you see the micro scale — in the grains of sand blown by winds, tumbled by the surf, or carried out in your shoes. Spend a week, and you see sandbars and wading pools arise and disappear. Spend a year, and you see dunes grow, shrink, and migrate. When you look across decades and centuries, you see the landscape evolving on a wider scale, but still one that humans can experience.

The prime example of beach evolution is the coastal barrier. These strips of land are usually long and narrow and run parallel to the mainland. Sometimes they are islands and other times they are connected to land at one end, a feature dubbed a “spit.” Scientists estimate that there are more than 2,100 barrier islands in the world fronting nearly 10 percent of continental shorelines. In the United States, barrier spits and beaches line up along nearly a quarter of the coast, mostly facing the Atlantic Ocean and Gulf of Mexico. Some of the best-known barrier systems include Padre Island in Texas, the Outer Banks of North Carolina and Virginia, the south shore of Long Island, New York, and the Sea Islands of South Carolina and Georgia.

These beaches are not only attractive to human settlers and tourists; they promote the development of critical marsh and wetland habitats. Barrier beaches also protect the mainland from the full force of ocean wind and wave energy. This is particularly important on shorelines prone to hurricanes, typhoons, and nor’easters.

Barrier beaches and spits are constantly raised up, shifted, and torn down by the natural ebb and flow of waves, currents, winds, and tides. Storms can reshape them abruptly and dramatically. Hooks form, inlets open and close, and beaches slowly march across their back bays and lagoons toward the mainland, as if seeking shelter from the full force of the ocean. This process allows them to naturally march upwards as sea levels rise.

On the southeastern elbow of Cape Cod, where the New England coast reaches out into the cold and choppy North Atlantic, this natural progression has been taking place in full view of satellites for more than 30 years. The images above were collected by three generations of Landsat instruments: the Thematic Mapper on Landsat 5, the Enhanced Thematic Mapper Plus on Landsat 7, and the Operational Land Imager on Landsat 8. Each scene shows the shape of the coast off of Chatham, Massachusetts, from June 1984 through August 2020. (Click on the dots to scroll through the images, or hit the play arrow for a slideshow.)

The changes to the Nauset-Monomoy barrier system are sometimes subtle and sometimes dramatic. In 1984, when the image series begins, an unbroken barrier spit shields the Atlantic-facing coast of Chatham and its harbor. South of the mainland, North and South Monomoy Islands stand apart from each other and from the coast. Over the span of 35 years and 22 images, several major breaches open in the system and the barrier islands connect to the coastline and to each other at various times. All the while, sandbars and shoals—which appear as light tan waters just offshore—hint at the underwater movement of sand up and down the coast. (Note that some of the change in individual images may be due to different tidal stages at the time of satellite overpass.)

The first major change appears in September 1987. A nor’easter in January 1987 cut a new inlet through North Beach, forming what the locals called South Beach Island. In the 1990 image, the north end of South Beach Island nearly connects to the mainland; by 1993, the connection is complete and the south end of the spit starts to grow longer and wider. For most of the 1990s and early 2000s, South Beach keeps reaching southward toward South Monomoy. Meanwhile, the waters around North Monomoy grow shallower as sandbars and shoals rise up toward the water line.