system
Given the following post, respond as if you're commenting on Reddit:
human
How do islands, created entirely from volcanic activity, eventually become fertile? How does the volcanic glass deteriorate into fertile soil?
gpt
So I’m guessing you’re picturing something along the lines of Hawaii, which has fertile soil that’s great for farming. In that case the magma/lava forming the island is generally basaltic and rich in a number of nutrients (e.g. iron, phosphorus, etc.). This type of rock can form a quite fertile soil once adequately weathered. 

Also, “volcanic glass” in the case of a basalt refers more to the structure of the rock (mineral grain size) rather than composition, so basaltic glass can still have plenty of iron, etc. in it.