Freatikus

Freatikus is an adjective used in geology and related fields to describe phenomena or features related to groundwater. In many languages, including Indonesian and several European languages, the term corresponds to the English word phreatic. It is derived from terms for wells and groundwater and is used to distinguish groundwater-driven processes from those driven by meteoric water or magmatic activity.

In volcanology, a freatikus eruption, more commonly called a phreatic eruption, occurs when groundwater or saturated rock is heated by magma or hot rock, causing rapid steam generation and an explosion. The eruption typically ejects steam, ash, and rock fragments but does not involve fresh magma reaching the surface. Phreatic eruptions can be sudden and may occur with little warning, often accompanied by seismicity and gas emissions, and they can alter a volcanic conduit without new lava.

In hydrogeology, the term relates to the phreatic, or saturated, zone of an aquifer where all pore spaces are filled with groundwater. The water table marks the upper surface of the phreatic zone, and groundwater flow within it is driven by hydraulic gradients. Structures or features interacting with this groundwater, such as wells, springs, and fissures, are described using freatikus terminology when referring to processes tied to groundwater.

Overall, freatikus functions as a language-variant descriptor for groundwater-related phenomena and, in a volcanological context, to distinguish steam-driven phreatic activity from magma-driven activity.