Dunes are an ever-changing landscape
The Coos Bay dune field is one of ten different sand due sheets spreading across half of the Oregon coast. The Coos Bay dune field, directly across the bay in front of you, is the southern end of a 60-mile-long dunes sheet that runs north to Florence. How and when did these dunes form?
Layers of a Dune “Sandwich”
The Coos Bay dunes consist of layers of ever-changing sand deposits on top of a hard coastal terrace. The bottom layer is the oldest and most stable — deposited more than 80,000 years ago. The next layer consists of dunes developed between 70,000 and 30,000 years ago. The youngest dune on top began about 5,000 years ago. Dunes advance repeatedly as they slowly progress inland. During the last million years, sea levels, climate, ocean currents, wind directions, and locations of the coastline changed many times. The current eastern boundaries of the dunes in the local area are about 3-4 miles (5-6 km) inland.
Starting in the 1930’s, European beachgrass was planted on the dunes to stabilize them so their sand would stop drifting over roads, railroads, and local property. The migration of sand from the dunes could also interfere with navigation and other human development.
The beachgrass successfully stabilized the dunes but created unforeseen problems. It became and invasive species that drove out native vegetation and “starved” areas such as the deflation plains of new sand needed for replenishment. These dunes are dynamic features of the natural landscape; they rely upon natural processes and respond to any change in the environment.