"The historical record says that the initial wave of molasses moved at 35 miles per hour," Ms. Sharp said, "which sounds outrageously fast."

"At the time people thought there must have been an explosion in the tank, initially, to cause the molasses to move that fast," she added. But after the team ran the experiments, she said, it discovered that the molasses could, indeed, move at that speed.

"It's an interesting result," Ms. Sharp said, "and it's something that wasn't possible back then. Nobody had worked out those actual equations until decades after the accident."

If the tank had burst in warmer weather, it would have "flowed farther, but also thinner," Mr. Rubinstein said.

In the winter, however, after the initial burst — which lasted between 30 seconds and a few minutes, Ms. Sharp said — the cooler temperature of the outside air raised the viscosity of the molasses, essentially trapping people who had not been able to escape the wave.