Aggradational

Aggradational is an adjective used in geology and geomorphology to describe processes, surfaces, or deposits characterized by net sediment accumulation that raises the elevation of land surfaces relative to a base level. It is the opposite of degradational or erosional processes, which remove material and lower the surface.

In fluvial systems, aggradation occurs when sediment supply and accommodation space exceed the rate of incision or removal. This leads to vertical build-up of the river bed and floodplain, sometimes accompanied by lateral channel shifts. Over time, rivers may develop aggraded terraces where successive layers of deposited sediment record periods of reduced erosion and sustained deposition. Aggradation can also promote aggradational channel morphologies, such as braided or wide meander belts, depending on sediment load and water flow.

In stratigraphy and sedimentology, aggradational sequences are vertical stacks of deposits formed during relatively steady, long-term sedimentation with limited truncation by erosion. Such sequences often indicate a stable base level or rising accommodation space, which may result from sea-level rise, subsidence, or continued sediment supply.

Coastal and deltaic settings frequently exhibit aggradation when sediment supplied by rivers progrades the shoreline or delta front outward and upward faster than relative sea level can submerge it. Recognizing aggradational deposits helps reconstruct past environmental conditions, sediment supply regimes, and base-level changes.