Jernlag

Jernlag is a term used in geology and soil science to describe a distinct layer or stratum within the soil profile that is rich in iron. This iron enrichment is typically a result of various pedogenic processes, meaning the processes of soil formation. The iron can be present in different forms, including iron oxides, iron hydroxides, and sometimes iron carbonates, depending on the soil's redox conditions (the balance between oxidation and reduction).

The presence of a jernlag can indicate specific environmental conditions that have prevailed over time. For instance, fluctuating water tables, where periods of saturation alternate with periods of drainage, can lead to the mobilization and subsequent precipitation of iron, forming a concentrated layer. This process is often associated with gleying, a soil condition characterized by a lack of oxygen. In some cases, a jernlag can be a result of the downward movement of iron-bearing solutions from upper soil horizons, which then accumulate in a less permeable layer below. The color of a jernlag is often reddish-brown or yellowish-brown due to the presence of oxidized iron compounds. The thickness and consistency of a jernlag can vary significantly, from thin, discontinuous patches to thick, continuous horizons.