Sue, my husband, oldest son and his fiancee all think that the volcano pool at the Polynesian has a depth of around 4.5 feet at its deepest. In talking further with my DH, he says that it is graduated so some parts are probably only around 3 feet (besides the obvious slope of zero entry). The deepest areas are near the waterfall. The "quiet" pool at the Polynesian is still perhaps six feet deep at the South end with a graduated depth. That pool is not zero entry though.
The quiet pool at the GF he remembers as rather shallow throughout. The zero entry pool he thinks is pretty much like the Polynesian although when I first asked him his overall impression was around 3 feet. We've only had three stays at the GF though and two of them were in very cold weather.
Although I don't swim so much these days, I spend a fair amount of time watching DS2 in the Polynesian volcano pool. He is 5 feet tall and in the center area of the pool that he seems to prefer, the water is about up to his chest.