Learn French: Il est probable que l'éruption du volcan aura lieu demain. - It is probable that the volcano's eruption will happen tomorrow.

This is a major trap! Because il est probable que indicates a high likelihood, it is treated as a near-certainty in French and takes the indicative. You would only use the subjunctive to express doubt, such as with il est peu probable que (it is unlikely that) or il est possible que (it is possible that).

How does aura lieu mean 'will happen'?

The phrase avoir lieu is a fixed idiom meaning 'to take place' or 'to happen'. Here, avoir is conjugated in the future tense (aura) because the event is predicted for demain.

Could I use C'est probable que instead of Il est probable que?

In everyday spoken French, you will absolutely hear c'est probable que. However, standard grammatical rules state that impersonal expressions followed by an adjective and que must use the dummy subject il, making il est probable que the strictly correct formal choice.

Why does the sentence say du volcan instead of just de volcan?

It literally translates to 'the eruption of the volcano'. Since volcan is a masculine noun, the preposition de (of) and the definite article le (the) must combine into the mandatory contraction du.