Abstract

CALDERON, Camilo E.  and  SANCHEZ, John J.. The geometry and dimensions of columnar jointing structures in volcanic rocks of Colombia. Bol. geol. [online]. 2023, vol.45, n.1, pp.37-51.  Epub Feb 28, 2023. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v45n1-2023002.

Columnar jointing structures in volcanic rocks correspond to the joint pattern that results from the contraction and deformation of materials during post-emplacement cooling. Data of 394 polygons in fourteen outcrops of volcanic rocks with columnar jointing in Colombia were visually inspected, and 349 polygons were defined by image processing with computer scripts. These polygonal geometries, along with the relative variations of the sizes of columns were used to estimate the homogeneity, order, and maturity of the jointing patterns. The relationship between stria size and column width was used to approximate the dominant heat transfer mechanism during the emplacement of lavas and pyroclastic density currents (PDC) deposits. Visual inspection of outcrops reveals that the hexagonal geometry dominates in lavas, whereas in PDC, the dominant geometries are pentagons and tetragons. Computational processing indicates that in general, columnar jointing in Colombia tends to be the optimal hexagonal organization, although other orders are observed. It is found that the Cristales outcrop, located on the southeastern flank of Nevado del Ruiz volcano, in the Cordillera Central, shows the highest degree of maturity; Domo Victoria, a monogenetic volcano in the Cordillera Central, has the most homogeneity, and Los Ataúdes site, on the eastern flank of Cordillera Occidental, is the most ordered. Striae sizes are usually 10-25% of column widths. Values of Péclet number in the range 0.28-0.41 indicate that heat transfer by conduction dominated during lava emplacement, although heat dissipation by joint-aided convection cannot be discarded.

Keywords : Hexagonality index; Maturity; Homogeneity; Ordering; Heat dissipation.

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