Explosive eruption

Definition

An explosive eruption is a volcanic event characterized by the violent release of gas, ash, and magma into the atmosphere. These eruptions occur when pressure builds up in a volcano due to the accumulation of volcanic gases, which can result in the rapid fragmentation of magma and the ejection of pyroclastic materials. The explosive nature of these eruptions can significantly impact the surrounding environment and climate.

5 Must Know Facts For Your Next Test

1. Explosive eruptions are often associated with stratovolcanoes, which have steep profiles and a composition that tends to trap gases more effectively than shield volcanoes.
2. The intensity of an explosive eruption is measured using the Volcanic Explosivity Index (VEI), which ranges from 0 (effusive) to 8 (mega-colossal).
3. Explosive eruptions can lead to significant climate effects by injecting ash and sulfur dioxide into the stratosphere, which can cool global temperatures for extended periods.
4. The gases released during explosive eruptions, including water vapor, carbon dioxide, and sulfur dioxide, play a crucial role in the formation of acid rain and contribute to atmospheric changes.
5. Notable examples of explosive eruptions include Mount St. Helens in 1980, Krakatoa in 1883, and Mount Pinatubo in 1991, each demonstrating different impacts on local and global scales.

Review Questions

• How do volcanic gases contribute to the explosive nature of certain eruptions?
  • Volcanic gases contribute to explosive eruptions by increasing pressure within the magma chamber as they accumulate. When this pressure exceeds the strength of the overlying rock, it can lead to a violent release of gas and magma. The composition of the magma also plays a role; more viscous magmas trap gases more effectively, leading to more powerful explosive events when they finally erupt.
• Discuss the environmental impacts of explosive eruptions compared to effusive eruptions.
  • Explosive eruptions have more immediate and widespread environmental impacts than effusive eruptions. The violent expulsion of ash and gas can blanket large areas with tephra, disrupt air travel, and pose health risks due to ash inhalation. Additionally, the injection of volcanic gases into the atmosphere can lead to temporary climate changes, while effusive eruptions generally result in lava flows that are slower and more localized in their effects.
• Evaluate the role of magma viscosity in determining whether a volcanic eruption will be explosive or effusive, using examples to support your analysis.
  • Magma viscosity is a critical factor in determining the nature of volcanic eruptions. High-viscosity magmas, often rich in silica, tend to trap gases effectively, leading to increased pressure and resulting in explosive eruptions. For instance, the explosive eruption of Mount St. Helens involved highly viscous dacitic magma. In contrast, low-viscosity basaltic magmas allow gases to escape easily, resulting in effusive eruptions like those seen at shield volcanoes such as Mauna Loa. This contrast illustrates how magma composition directly influences eruption dynamics.

Related terms

pyroclastic flow: A fast-moving current of hot gas and volcanic matter that flows down the slopes of a volcano during an explosive eruption.

magma viscosity: The resistance of magma to flow, which influences whether an eruption will be explosive or effusive based on its composition and temperature.

tephra: Fragmented material produced by a volcanic eruption, including ash, pumice, and volcanic rock, that can be propelled into the air during explosive eruptions.