The concept of the “first” volcanic eruption is somewhat complex, as volcanoes have been erupting for millions of years, well before recorded history. However, one of the earliest known eruptions occurred around approximately 79 AD with the eruption of Mount Vesuvius in Italy. This catastrophic event famously buried the cities of Pompeii and Herculaneum under ash and pumice, preserving them for centuries.
That said, volcanic activity predates Vesuvius by thousands of years. Scientists estimate that the Earth has been home to volcanic eruptions since its formation, but these early events are not well-documented. The oldest known evidence of volcanic activity comes from rocks that are around 4 billion years old.