GA review (see here for what the criteria are, and here for what they are not)
It is reasonably well written.
a. (prose, spelling, and grammar):
Buncha disambiguations that need to be disambiguated. "sub-region of Micronesia in the Pacific Ocean" is an odd formulation. "during periods of volcanic activity" - not "after"? "which is" - repetition. Composition paragraph is quite short - lots of choppy paragraphs in fact. "Volcanic activity on Daikoku has been continuing for the last two decades, since the discovery of the sulfur pond in the summit crater" can probably be reformulated.
"The volcano has many hydrothermal vents, which can host various animal species including the one which makes this seamount widely known, the tonguefish Symphurus thermophilus." needs a source. Where does #2 refer to Daikoku? #3 does not say "slightly" or "rivulets". #6 does not mention Daikoku again.
Some of the file pages have links directly to the source filepage, which can be hard to fix if they break. Is it possible to replace them with links to gallery pages instead? Also, the "Activity" section on my screen is WP:SANDWICHed between the images.