What signs show that a coastal dune is active?

Coastal dunes are typically stabilized by various types of vegetation, such as grasses and vines, which help hold the sand in place. When a dune lacks this vegetative cover, it is generally considered active and will display clear signs of sand mobility.12

Key indicators that a coastal dune is active include:

• Surface Ripples: The presence of nearly ubiquitous ripples across the dune surface is a primary sign of sand movement.1
• Sand Migration: Active dunes may exhibit large lobes of sand or movement of the entire dune structure as wind blows across it.1
• Cross Stratification: This activity often results in the formation of large, sweeping patterns of wedge-shaped packages of sand within the dune structure.1

In contrast, stable dunes are characterized by the presence of root systems—such as those from marram grass—that create an underground web to anchor the sand and prevent it from shifting.2