Which natural event can occur either over a few weeks or over a few million years?

A formation of a volcano

Explanation:

A natural event that can occur either over a few weeks or over a few million years is a formation of a volcano. Volcanoes are accumulated when magma from inside the Earth's uppermost mantle acts its approach to the surface. Near the covering, that explodes to form lava flows as well as ash sediments. Extra time as the volcano remains to emit, it will become more prominent.