> That increase in volume- which happens nearly instantly- brings with it a massive spike in pressure as well. Meaning a loss of pressure can indeed lead to an essentially explosive increase in pressure.
Except that the secondary pressure is, by necessity, no greater than the initial pressure. Depressurizing a supercritical fluid to make it expand into a larger volume brings it to an equilibrium at that volume. The pressure can only be equal or less, and the temperature now has a larger surface area from which it can dissipate.
The steam will be moving fast, certainly. It will not be moving at high pressure.