| Term: | Diachronous |
| Definition: | Of a surface or layer, spanning time. The word diachronous is needed most commonly when the surface or layer did not form instantaneously. The summer surface may be diachronous, forming at different times over a span of days or weeks, but it is assumed to be instantaneous. In a record of a ground-penetrating radartraverse, a marker horizon may be valuable in the determination of mass balance if it is an isochrone, but not if it is diachronous. |