So. Portland, Me., for his question:

Where are the Mariana Islands?

The vast Pacific Ocean covers almost half the globe. Here and there it is dotted with smallish islands, though you may have to search to find them. The little Mariana Islands were discovered by the famous Portuguese  explorer Ferdinand Magellan way back in 1521. They are on the far side of the Pacific, westward from Central America. Japan is to the north of the little islands, and the Philippine Islands are farther to the west.

There are 15 Mariana Islands, strewn like a string of beads in the far western Pacific. The mid ocean sea bed is very deep. But here there is a chain of underwater mountains. And some of their high peaks poke above the waves. These dots of dry land are the Marianas, built up by underwater volcanoes in underwater mountains. Guam and the other larger islands are at the southern end of the chain. Some of the smallest islands of the northern end still have active volcanoes.