The reaction between chlorite and thiourea is excitable and autocatalytic in HOCl. It produces a chemical wave of ClO2 when ClO2- is in stoichiometric excess over thiourea. The chemical wave has been studied in glass tubes of varying diameters. The dynamics of the wave front propagation have been studied as a function of convection, which is known to induce density gradients. The ClO2--thiourea reaction is highly exothermic, and the chemical wave has a positive isothermal density change, In vertical tubes the effect of the exothermicity of the reaction opposes the effect of the isothermal density change, giving an asymmetric and unstable wave front in descending waves. Multicomponent convection and fingering patterns have been observed in descending waves. Ascending waves propagate without structure and are generally slower than descending waves. In starch solutions fingering patterns are observed which propagate downward at greater than 10 times the normal front velocity. These fingers turn into rapidly-rising plumes after they reach the bottom of the tube. Formation of rising plumes is due to the hot interior of the finger which is lighter than the unreacted solution, but when the reacted solution propagates upward into the cold unreacted region, the cooling effect makes the solution heavier, giving a symmetric "mushroom-shaped" plume.