Why did vesuvius erupt sideways?

Answer 1

It didn't. Mount Vesuvius erupted vertically. However, the ash cloud was carried toward Pompeii by the wind. Additionally, clouds of ash and pumice that were too dense to rise formed pyroclastic flows that raced down the sides of the volcano.

Answer 2

Mount Vesuvius did not erupt sideways. Instead, it erupted vertically, releasing a column of ash and volcanic material into the atmosphere. The eruption in 79 AD blanketed nearby cities like Pompeii and Herculaneum, resulting in their destruction.