Final answer:
The Plinian phase of the 79 eruption of Mount Vesuvius refers to a stage characterized by violent explosions, high-altitude ash columns, and pyroclastic flows.
Step-by-step explanation:
The Plinian phase of the 79 eruption refers to a specific stage of the eruption of Mount Vesuvius in Pompeii, Italy. This phase is named after Pliny the Younger, who witnessed the eruption and recorded it in a letter. During the Plinian phase, there was a violent explosion that ejected a high-altitude column of ash, which eventually fell over the area, covering it. Pyroclastic flows, rapid-moving and dense flows of volcanic materials, also occurred during this phase, causing significant destruction in the vicinity of the volcano.