The United States Geological Survey took pictures of the beaches in the Caribbean, the Florida Keys and the northern Gulf coast before and after hurricane Georges hit. As you can gather from Rosa and Clara's experiences, the beaches are in a constant state of flux. Assaults on the beach can be sudden and fast, as in a storm or hurricane. The changing seasons also leave their signature on the beaches as they bring different patterns of wind and rain. Every few years an El Nino or La Nina event brings unexpected floods and droughts which also affect beach shape.
Beaches also change on much longer time scales.
During the last ice age, for instance, the sea level was much lower than it is today, so all of those beaches are now underwater. And perhaps most importantly, we know that the agents of change can be human. Building beachfront hotels, seawalls and groins, while often attractive options in the short run, can dramatically alter the natural shape of the shoreline in the long run.