A long, narrow tank was linearly stratified with an aqueous solution of common salt. A grid of vertical bars was towed through this stratification, starting midway along the tank. The location and shape of the resultant front between turbulent and nonturbulent fluid were monitored photographically, and the time for the beginning of front collapse was determined. The magnitudes of the integral (Lc) and Osmidov (Loc) length scales at this time were calculated from independent measurements. It was found that at the start of collapse, Lc≂2Loc and Ntc≂2.1 or the disturbance Froude number Wc'/NLc≂0.68, where N is the Brunt frequency and tc and Wc' are the time and rms vertical velocity fluctuations at the start of collapse, respectively. Interaction between the growing frontal features resulted in the growth of only the larger ones, so that an average intrusion with a height of about 7Lc finally evolved. At t≂30N1 the original turbulence had collapsed completely, leaving a field of weak internal waves and energetic horizontal eddies constrained by the width of the tank. ¿American Geophysical Union 1987