Father François Richard was a French Jesuit missionary who lived in Santorini between 1644 and 1675 and researched the beliefs and practices of the local islanders. He was present on the island during the volcanic eruption in 1650.
In 1657, he published his account of his experiences in the book with the title starting ‘Relation de ce qui s’est passé de plus remarquable à Sant-Erini, isle de l’Archipel . . .‘ , the full, extended title translating into something like:
Account of what has happened, most remarkably, at Sant-Erini island of the archipelago, since the establishment of the Fathers of the Society of Jesus there. With the declaration of several memorable things touching upon the life and the belief of the Greeks of this time, and touching upon the underground fires, which came from the bottom of the sea in the year 1650 with many wonders.
A facsimile copy of the original French book can be read on Google Books.