duripan

A duripan is a soil horizon in which a substantial portion of the horizon is cemented by silica, resulting in a hard, dense layer that resists penetration. The cementing material is typically microcrystalline silica such as opal, chalcedony, or related forms, which bind mineral grains together and reduce pore space.

Duripans form when silica-bearing solutions move through the soil and precipitate silica within the pore spaces of the horizon. This cementation often occurs in arid and semiarid climates where leaching is limited and groundwater or soil solutions can supply silica. The resulting horizon is usually low in permeability and root penetration is hindered, making the layer a barrier to water movement and plant growth.

In soils, a duripan is considered a diagnostic horizon and is most commonly found within the B horizon, though it can occur at other depths depending on the soil development history. It is distinct from other hard horizons such as caliche (carbonate-cemented) or fragipans (dense horizons not necessarily cemented by silica). The presence of a duripan influences soil water dynamics, aeration, and agronomic potential, and it is a key factor in soil surveys and classifications.

Geographically, duripans occur in many regions with silica-rich parent materials or conditions favorable to silica precipitation, including parts of North America, Australia, Africa, and other arid to semiarid landscapes. Management considerations for areas with duripans focus on deep-rooted vegetation, drainage, and, where possible, disturbance of the horizon to improve subsoil access, though durability often makes natural restoration slow.