Question

The 1980 volcanic explosion of Mt. St. Helens in the United States devasted the north side of the mountain and it's forests. The forests were demolished and replaced with volcanic debris that formed the new soil, free of any remnants of the previous ecosystem (such as seeds stored in the soil). Such an event would lead to which one of the following processes? A. Primary succession B. Secondary succession C. Tertiary succession D. Quaternary succession E. Pioneering succession

Short answer

A. Primary succession

Step-by-step solution

Identify the Key Information

The key information here is that the volcanic explosion destroyed the pre-existing ecosystem, leaving behind new soil devoid of any remnants such as seeds.

Understand Succession Types

Primary succession occurs in lifeless areas where there are no existing seeds or soil, such as new volcanic soil. Secondary succession occurs in areas where a disturbance has not completely destroyed the soil and seeds, like after a forest fire.

Apply the Definition to the Scenario

Given the description of the volcanic explosion resulting in an area with new soil free from remnants of the previous ecosystem, the correct process that describes this situation is primary succession.

Eliminate Incorrect Options

The other types given (secondary, tertiary, quaternary, and pioneering) do not fit the scenario as they involve varying degrees of pre-existing soil or remnants of previous ecosystems.

Key concepts

Volcanic Explosion

A volcanic explosion is a powerful and sudden release of energy from inside a volcano. During an eruption, magma, gases, and ash burst out from the volcano. The 1980 eruption of Mt. St. Helens is a famous example. This explosion devastated the north side of the mountain by not only destroying forests but also scattering volcanic debris over a wide area. This debris is initially hostile to life but provides a starting point for new soil formation.

Importantly, volcanic explosions can create entirely new environments. These environments lack any pre-existing soil, plants, or seeds, meaning life must start anew from scratch. This situation sets the stage for primary succession, a type of ecological recovery starting from bare rock or fresh volcanic soil.

New Soil Formation

After a volcanic explosion, the land is covered with volcanic debris. Over time, this debris starts to break down and forms new soil. This initial soil formation is crucial for the recovery of the ecosystem. The process is slow and involves several stages:

• Lichens and mosses first colonize the bare rocks and ash.
• As these organisms die, they add organic material, gradually forming a thin layer of soil.
• Small plants like grasses then establish themselves, followed by larger plants.

This gradual build-up of soil is fundamental for the next stages of ecological recovery. Because the soil is starting from scratch, without any remnants of the previous ecosystem, it sets the stage for primary succession.

Ecosystem Recovery

Ecosystem recovery following a volcanic explosion is a process driven by primary succession. In primary succession, life starts from bare rock or soil and gradually builds a complex ecosystem. The stages of recovery include:

• Pioneer species such as lichens and mosses that can survive without soil.
• Grasses and small plants that further enrich the soil.
• Shrubs and small trees that provide shade and habitats for animals.
• Eventually, a mature forest ecosystem with diverse species and complex interactions.

Each stage paves the way for the next, creating a self-sustaining community of plants and animals. This process can take hundreds or thousands of years, depending on various factors like climate, the speed of soil formation, and the types of pioneer species.

Succession Types

Succession refers to the process by which ecosystems recover after a disturbance. There are different types of succession based on the starting conditions:

• Primary Succession: Takes place in lifeless areas without soil, such as after a volcanic eruption. Life starts anew from bare rock or new soil.
• Secondary Succession: Occurs in areas where the existing ecosystem has been disturbed but soil and seeds remain, such as after a wildfire or hurricane.
• Tertiary Succession: Not commonly discussed, as ecological studies typically focus on primary and secondary succession.
• Quaternary Succession: Similar to tertiary, it is rarely referenced in ecological terms.

Understanding these kinds of succession helps ecologists predict how ecosystems will recover from different types of disturbances. Primary succession, like that occurring at Mt. St. Helens, shows how life can start anew even in the most challenging conditions.