Which environmental changes occur fastest? Volcanic eruption, pond succession, decomposition of a tree, or regrowth of a forest after a volcanic eruption.

The environmental change that occurs fastest among the given options is a volcanic eruption. A volcanic eruption is a geological event where molten rock (lava), volcanic ash, and gases are expelled from a volcano. This process is typically very rapid and can happen over the course of just a few hours or days.

Comparatively, pond succession, the decomposition of a tree, and the regrowth of a forest after a volcanic eruption take much longer. Pond succession, or the gradual change of a pond ecosystem to a terrestrial one, can take hundreds to thousands of years. Decomposition of a tree is a biological process that can take anywhere from a few years to several decades, depending on the tree size, species, and environmental conditions. Regrowth of a forest after a volcanic eruption is also a slow process, which can take decades to centuries, as plants and wildlife gradually repopulate the devastated area.