Fig. 9

a Schematic diagram of the model domain simulating the cooling of a tuff emplacement on the ground. Thicknesses of the tuffs (domain 1) and ground (domain 2) are assumed to be 250 and 700 m, respectively. Lateral walls of domains 1 and 2 are insulated, reflecting the fact that the horizontal length of the model domain is much longer than the vertical length of the domain. b Locations of the 900 °C isotherm (line) and corresponding Peclet numbers (dashed line) every 5 years. The triangle and circle represent the growth rate of the columnar joints and the corresponding Peclet number, respectively. The unfilled and filled symbols represent the upper and lower colonnades, respectively. The growth rate (mm) of columnar joints and the Peclet number were evaluated using the depth of the isotherm. Isotherms from the upper and lower colonnades meet at a depth of approximately 140 m, which is consistent with Grossenbacher and McDuffie (1995)