Complex sentence: The island is formed from a volcano, which had not known to have been active in recent times, until on June 8 2005 there were reports of "mud and smoke" being ejected from the volcano.
Split into simpler sentences: The island is formed from a volcano, which is not known to have been active in recent times. However on June 8 2005 there were reports of "mud and smoke" being ejected from the volcano.