Such an interesting question! Such thought-provoking remarks in the comments beneath the question!
Such comments make me wonder, what is the best way to answer such a query? Maybe a few things need to be addressed first, such as:
- What is the meaning of such?
- How is it used in conversation and such?
- What is grammatical, and what sounds natural?
A good online dictionary, such as Wordnik, might help. There, we can find such a great number of meanings and examples, that it will become readily apparent that such a question is not so easily answered. English can be such a hard thing to fully grasp, particularly when dealing with such words – words that can be used in such a myriad of ways! After all, many words, though but one word, can be used as different parts of speech: adjectives, adverbs, pronouns and such; such is one such word.
Really, Ivan, you should go visit such a website, and behold the diverse ways such a simple word can be used. Such a curious man is bound to learn something from such a great smattering of examples!
which is to say, there's no EASY way to tell when to use "such", and when to use "such a" - the word is simply too flexible to nail down in such a fashion...
I consider it awkward in the context of "Japan has a high number of active volcanoes", but it's frequently used that way in biomedical articles. Saying "a large number of" or "many", in this case, is much better style, IMHO, but it's not ungrammatical.
Style is rarely judged as "correct" or "incorrect", except in contests for which a certain style has been prescribed and others have been proscribed. Writing style is usually judged on a sliding scale that runs from Godawful! (-100) to Sublime! (+100), depending upon one's taste. OTOH, style manuals may deal with this kind of structure: that's case by case.
I always change "a high number" to something more appropriate when the quantity or amount is what's important rather than the size of the number: Sometimes a great number?.
Best Answer
Actually the most common phrasing I've personally seen is:
The number of calories can be thought of as either a number (number of) or aggregate (amount of). Other answers/comments have indicated that there's debate over which is more common/appropriate, but what one you use influences which adjective you pick.
Per this NGram: