There still remains to be considered the volcanic region of the Santorin group of the Grecian Archipelago. The island of Santorin or Thera, is the southernmost of the Cyclades. It is an exceedingly curious island, being a submerged volcano, with most of the top of the crater remaining above the waters, so that the entire island has the shape of an irregular circle or crescent broken at several points. Its formation is, probably, due to the gradual sinking of a volcanic mountain until its crater has been almost completely submerged, only the higher parts of the edges of the crater being left above the surface of the waters. Suppose, for example, a mountain like Vesuvius at the time the crater Somma existed, was sunk below the level of the Mediterranean until only the highest parts of the crater remained above the waters. If, now, one or more volcanic eruptions occurred, producing craters or volcanic islands inside the submerged rim, you would have a condition of affairs seen in the island of Santorin.
[CHAPTER VII]
ORIZABA, POPOCATEPETL, IXTACCIHUATL, AND OTHER VOLCANOES OF MEXICO
While some of the volcanoes of Mexico are still in an active condition, most of them are either only slightly active or are dormant or extinct. Humboldt, the celebrated traveller and geographer, states that there are only four active volcanic mountains in Mexico; namely, Popocatepetl, Tuxtula, Colima, and Jorullo. But there are many others, among which may be mentioned Orizaba, Ixtaccihuatl, Xinantecatl, Tuxtula, Cofre de Perote, and Colima.
Of course, you can understand that, since extinct volcanoes may at any time become active, in parts of the world where communication with the interior is not good, many volcanic mountains that have been regarded as extinct may have broken out temporarily, during historical times, without their eruptions having been recorded.
It was at one time thought that Popocatepetl was the highest mountain in North America. More recent measurements, however, have shown that there are at least three other mountains in this part of the world, that are much higher. One of these is the active volcano of Orizaba that we will now briefly describe.
