That’s the caldera of Santorini Volcano behind this beautiful little poser.
Now put on your hard hats — it’s time for a little chemistry.
In fact, just this: “What do you get when you remove the oxygen (chemical symbol O) from H2O?”
Okay, so there’s really no need for special gear (unless you want to follow a working geologist out into the field to collect and study some of the world’s oldest rocks).
You get H2 — hydrogen — of course.
Believe it or not, this answer is closely tied to the origin of life on Earth. So is volcanism: source of the heat energy powering that and other chemical reactions necessary for emerging life.