...PHILIP E. LONG; BERNARD J. WOOD Abstract Flood basalt flows of the Columbia River Basalt Group commonly exhibit well-developed colonnade and entablature structures formed during cooling of individual flows. The colonnade refers to the well-defined columnar structure of many flows, which appears...

...Fig. 1. (a) Exceptionally well-developed chisel marks on joint columns forming the colonnade of the Garni intracanyon lava flow, Armenia, a basaltic trachyandesite of mid-Pleistocene age (Neill et al. 2015 ). Geologist is Davit Manucharyan. (b) Colonnade and overlying entablature in a dipping...

...Figure 10. Average column-bounding fracture spacing within flow A ( Fig. 3A ). Spacing is least at the top surface of the flow and increases from both the upper and lower boundaries toward the central entablature. Entablatures prevent trailing column-bounding fractures of the upper and lower...

... in the best observations. The foreshortening may also be worse than ideal. Columns and possibly multiple tiers of columns and/or entablature are visible. Many of the craters exposing columnar jointing formed in regions with histories of extensive volcanic activity. For example, Elysium Planitia...

...-columnar parts of the lava (the entablature) shows textural signs of quenching, compared with the lower more regular columnar zone (the colonnade). These common field and petrographic features confirm the model of multi-tiered flow formation by modification of the cooling regime in the upper part...

... layer located at the contact of the colonnade with the overlying entablature; and type 3, very thick (up to 96 m) lens-shaped accumulations within thickened portions of the flow. No single mechanism is capable of generating all three types. Our evidence indicates that most type 1 segregations were...