Which will you prefer to say; "What happens when a volcano erupts." or "What will happen when a volcano erupts.". Please give your answer from a grammatical prospective and your native sense of English.

Also, when it comes to "What comes out of a volcano when it erupts." or "What will come out a volcano when it erupts.", your answer will be still same?

  • 1
    This is simply a question about when to use the present tense (what happens?), and when to use the future tense (what will happen?). You would appear from your profile to be either Chinese or Japanese. Surely a similar matter must arise in your language too, doesn't it? In any event it is not really a question for EL & U - more one for the sister site "English Language Learners"
    – WS2
    May 19, 2020 at 7:01
  • I thought both were ok, even they have a little bit different meaning. But I do not have confident. And it seems you are right. I know Chinese and Japanese, but both languages do not account "will": the tense of future very important. We usually distinguish possibility and fact in other ways.
    – Ranger
    May 20, 2020 at 7:36

2 Answers 2


What happens when a volcano erupts = What is the usual course of events what an eruption occurs

(scientific/logical implication, rather than a reference to a potential situation)

Zero conditional

What will happen when a volcano erupts = What is going to happen if one of these volcanos erupts

(results of an actual event)

First conditional

PS. RE: The "coming out" - grammatically, the same distinction applies. However, it sounds like in that case you are referring to the lava.

  • So both are grammatically correct, and we can see both speeches depend on the situation and will, right?
    – Ranger
    May 20, 2020 at 7:44
  • @Ranger All the 4 sentences are grammatically correct. However, they will be used in different situations. May 20, 2020 at 8:59

It's just perspective on the situation. They're equivalent in most cases.

It might be at a closer time or at a farther time. It refers possibly more to the real, unknown future-- What will happen next?

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