On the Power Point Escape from Pompeii Teaching Slides back on this week's page are examples of sentences with a fronted adverbial. A fronted adverbial goes at the front of the sentence and tells the reader where, how or when. The fronted adverbial has a comma to separate it from the main part (clause) of the sentence e.g. At the top of the mountain, an ash cloud is pluming. If you remove the fronted adverbial, the sentence still makes sense on its own e.g. An ash cloud is pluming.