Which event is known to cause primary succession?

Primary succession occurs in environments that have been rendered lifeless, where no soil or organic matter exists initially. This process begins when bare rock is exposed, allowing life to gradually establish itself.

Glacier movement is a prominent event known to cause primary succession because when glaciers move, they scrape away existing landscapes, leaving behind bare rock and a lack of soil. As glaciers retreat, they reveal these uncolonized surfaces, which are prime candidates for primary succession.

In the absence of soil, pioneer species, such as lichens and mosses, can colonize the rock surface first. Over time, as these organisms die and decompose, they contribute organic material that helps develop soil, paving the way for more complex plant communities to establish. This gradual development from barren rocks to a fully functioning ecosystem epitomizes primary succession.

The other events mentioned can also lead to ecological changes, but they typically occur in areas where soil exists, thus initiating secondary succession instead. For instance, forest fires and flooding may destroy existing vegetation and soil structure but do not create the same blank slate condition required for primary succession. Volcanic eruptions, while they can also create new land, often deposit layers of lava and ash that can lead to secondary succession as well.