Felsic magma

Definition

Felsic magma is a type of magma that is rich in silica and characterized by a high viscosity. This composition leads to the formation of explosive volcanic eruptions and the creation of light-colored igneous rocks such as granite and rhyolite. The silica content and viscosity influence how the magma behaves, particularly in relation to volcanic landforms created in different tectonic settings.

5 Must Know Facts For Your Next Test

1. Felsic magma typically contains over 65% silica, making it more viscous than other types of magma.
2. Because of its high viscosity, felsic magma can trap gases, leading to more explosive volcanic eruptions compared to mafic magma.
3. Common minerals found in felsic magma include quartz, feldspar, and biotite, contributing to the light color of the resulting volcanic rocks.
4. Felsic magma is often associated with continental crust and can form large volcanic landforms like stratovolcanoes.
5. In subduction zones, the interaction between oceanic and continental plates can lead to the melting of sediments and rocks that produce felsic magma.

Review Questions

• How does the composition of felsic magma influence volcanic activity in various tectonic settings?
  • The composition of felsic magma, with its high silica content and viscosity, significantly affects volcanic activity. In subduction zones, where oceanic plates are forced beneath continental plates, this type of magma often forms. The high viscosity prevents gases from escaping easily, resulting in explosive eruptions that can create prominent stratovolcanoes. In contrast, mafic magma in divergent settings tends to produce less explosive eruptions due to its lower viscosity.
• Discuss how felsic magma contributes to the formation of specific volcanic landforms and their characteristics.
  • Felsic magma contributes primarily to the formation of stratovolcanoes or composite volcanoes. These landforms are characterized by steep profiles and explosive eruptions due to the thick nature of felsic lava, which can pile up in layers. Additionally, as these eruptions occur frequently over time, they create a layered structure with alternating deposits of lava flows and pyroclastic materials. The light-colored rocks formed from felsic lava are also significant in understanding volcanic geology.
• Evaluate the environmental impacts associated with eruptions driven by felsic magma and their implications for surrounding ecosystems.
  • Eruptions driven by felsic magma can have profound environmental impacts due to their explosive nature. These eruptions often release ash clouds that can travel long distances, affecting air quality and climate. The deposition of ash can alter soil properties and affect water quality in surrounding ecosystems. Additionally, pyroclastic flows generated by these eruptions can devastate local habitats and pose significant risks to human settlements. Understanding these impacts is essential for assessing volcanic hazards in areas with potential for felsic activity.

Related terms

Mafic Magma: Mafic magma has lower silica content and is less viscous than felsic magma, leading to less explosive eruptions and the formation of darker igneous rocks like basalt.

Volcanic Eruption:

A volcanic eruption is the release of magma, gas, and other materials from a volcano, which can be influenced by the composition of the magma present.

Subduction Zone:

A subduction zone is a tectonic setting where one plate moves under another, often leading to the generation of felsic magma due to the melting of the overriding plate.