Re: Can rocky islands be electric after vulcanic eruptions

Santorini (Thira) is a Greek island in the Aegean. It is steep and crescent 
shaped, being part of the crater rim from an explosive eruption that 
destroyed an earlier island in the same site. The eruption is historically 
famous and important. It dumped a lot of ash on the nearby island of Crete, 
causing major devastation, and has been linked with the very rapid demise 
of the Minoan civilization based around that island. It has also been 
connected with the Atlantis legend.

Can electricity from three or four thousand years ago still be stored in 
rocks near an eruption site? That is quite possible; some rocks are good 
enough electrical insulators, and we are talking about quite a large 
thickness of rock. But if that electricity has been leaking out enough to 
give islanders and tourists 'forceful electric shocks' throughout that 
period, it would surely be completely discharged by now.

So I think it much more likely that there is some modern source for the 
electrical phenomena. On thinking about the geographical and geological 
environment at Folegandros, I can come up with three possibilities. 

Two of them are connected with the fact that the Aegean is still a 
seismically very active region. Large bodies of rock are still slipping and 
sliding and straining deep underground. This can lead to electricity 
generation in two ways: triboelectricity from the friction of the actual 
sliding contact of the rocks, or piezoelectricity from the straining of 
some minerals -- particularly, but not exclusively, quartz crystal or 
tourmaline.

The third possibility is a different sort of triboelectricity. In the 
Aegean islands there are sometimes long periods when the wind blows from 
the South. Hot, dry and dust-laden air from the Sahara sweeps through the 
area, and there is often a brown dust-haze that restricts visibility. In 
these circumstances, friction of air-borne dust particles on local rock 
features of rather different composition can also generate static 
electricity. Phenomena like this are well known in many desert regions of 
the world -- most notably in the clear-sky electrical storms that occur in 
Arizona USA. The Aegean might be sufficiently desert-like in the summer 
months to produce similar phenomena.