Final answer:
The spread of ash fallout from the Mount Pinatubo eruptions in 1991 is described under the geographic theme of movement.
Step-by-step explanation:
The spread of ash fallout worldwide from the Mount Pinatubo eruptions in 1991 in the Philippines is described under the principal geographic theme of movement. This is true. The eruption of Mount Pinatubo caused massive amounts of ash and smoke to be released into the atmosphere. These ash particles were carried by wind currents and spread to different parts of the world, affecting the movement of these volcanic materials.