Complex sentence: Vesuvius was thought to be extinct before its famous eruption of AD 79, which destroyed the towns of Herculaneum and Pompeii, more recently, the long-dormant Soufriere Hills volcano on the island of Montserrat was thought to be extinct before activity resumed in 1995.
Split into simpler sentences: Vesuvius was thought to be extinct before its famous eruption of AD 79, which destroyed the towns of Herculaneum and Pompeii. More recently, the long-dormant Soufriere Hills volcano on the island of Montserrat was thought to be extinct before activity resumed in 1995.