What is the result of a vast pressure difference combined with a small opening?

Let's say you have a barrier. On both sides of the barrier, there is an extremely large (infinite would probably make for easier modeling) chamber filled with a fluid. There is a great pressure difference -- say on one side there's air at 1 bar (~100 kPa) and on the other is the equivalent of the bottom of the Mariana Trench (100 MPa, 1000 bar).

Now suppose you open an aperture in the barrier, say, two square meters. How do you calculate the speed with which the high-pressure fluid passes through the opening? I think I learned this in high school, but I've forgotten. T_T