Final answer:
During an explosive eruption, a volcano ejects a mixture of ash, gas, and rock fragments into the air. These materials quickly collapse and descend down the slopes of the volcano due to gravity, forming a pyroclastic flow. The flow is composed of superheated gas and rock fragments that can reach temperatures of several hundred degrees Celsius.
Step-by-step explanation:
A pyroclastic flow is a fast-moving current of hot gas and volcanic matter that moves along the ground. It is one of the most dangerous aspects of explosive volcanic eruptions. During an explosive eruption, the volcano ejects a mixture of ash, gas, and rock fragments into the air. These materials quickly collapse and descend down the slopes of the volcano due to gravity, forming a pyroclastic flow.
The flow is composed of superheated gas and rock fragments that can reach temperatures of several hundred degrees Celsius. It moves downhill at high speeds, often reaching velocities of over 100 km/h. The destructive power of a pyroclastic flow comes from its high temperature and density. It can flatten or destroy anything in its path, including buildings and vegetation.
An example of a destructive pyroclastic flow is the eruption of Mount Vesuvius in 79 AD, which buried the cities of Pompeii and Herculaneum under layers of ash and pyroclastic material.