May be an impossibly teleological question

[fivemack]

Why is it that volcanic ash makes good fertiliser?

It contains minerals pulled up from the upper mantle and pulverised into conveniently absorbable powder; but is it purely a coincidence that it tends not to contain chromium, cadmium, arsenic and heavy-metal fluorides (fluorides mentioned specifically because volcanic steam does contain non-negligible HF)?

I suppose the volcanoes that erupt great clouds of sulphur tend to be known as sulphur mines, and obviously people won't farm next to volcanoes whose outpourings make plants wither, but it seems unaccountably convenient that they so often work.

Comments

[twoeleven.livejournal.com]

One could go even further and say it supports the "black smoker" hypothesis, that life first evolved around black smokers and other volcanic vents on the sea floor. Volcanic ash is then just a similar environment on land.