basaltic composition dyke with radial divisions from middle Eocene age (rosette).

A dyke of middle Eocene basaltic composition with radial radial divisions (rosette). Probably “Feeder” dyke (Feeder dyke) – a dyke that performs the function of a magma conduit/extraction channel from the magma chamber to the surface.

As thick basaltic (mostly) lava flows begin to cool, they may develop hexagonal fissures/cracks called columnar cleavage.

Columnar separation – immediately after erupting on the surface, lavas of (mostly) basaltic composition begin to cool instantly from the top, bottom and sides towards the center, where the most heat remains. The bottom of the stream cools more slowly because it has underlying rock on which to settle, while the top (roof) of the stream cools more quickly because it is exposed to cooler ambient air, wind and rain, and standing or flowing water.

The difference in the cooling rate is manifested in the formation of two types of structures. In the lower part of the lava flow, where the cooling is slower, large columns of equal-shaped columns are formed, the group of which is called “colonnade” by geologists. The upper part cools relatively quickly and results in thinner and less straight columns. A set of columns of such an irregular shape is called “entablature”.