Hi Genghis kush, i lived 6 years in reunion island whzn i was young so i think i can help you a lil' bit.
Reunion is a volcanic island, so the biggest volcano of the place ("piton des neiges" or "Snow Peak" in english, dead volcano btw) is the center of the island, which is very montainous. Around this volcano you can find 3 "cirque" (caldeiras), named Cilaos, Salazie and Mafate.
Mafate is the only cirque thant you can't reach with cars, you have to walk or take a helicopter. that's why it's said by locals that it is probably the only place where you can find pure zamal. that is why it is called Zamal Mafate
Hope it helps!