Felsic magma

Definition

Felsic magma is a type of magma that is rich in silica (SiO2) and contains a high proportion of lighter-colored minerals such as quartz and feldspar. This composition leads to a higher viscosity compared to other types of magma, which affects both the nature of volcanic eruptions and the types of volcanoes that form from it. Felsic magma is primarily associated with explosive eruptions, resulting in the formation of stratovolcanoes or composite volcanoes, which are characterized by their steep profiles and layered structures.

5 Must Know Facts For Your Next Test

1. Felsic magma has a silica content typically greater than 65%, which contributes to its high viscosity and tendency to trap gas bubbles.
2. The explosive nature of eruptions associated with felsic magma can produce pyroclastic flows, ash clouds, and volcanic domes.
3. Common examples of felsic rocks formed from this type of magma include granite and rhyolite.
4. Felsic magma is usually found at convergent plate boundaries where oceanic plates subduct beneath continental plates, leading to melting and the formation of continental crust.
5. Eruptions from felsic magma can significantly impact the environment and climate due to the large amounts of ash and gases released into the atmosphere.

Review Questions

• How does the composition of felsic magma influence its viscosity and eruption style compared to mafic magma?
  • Felsic magma has a higher silica content than mafic magma, leading to increased viscosity. This thicker consistency prevents gas bubbles from escaping easily, which builds pressure within the magma chamber. As a result, when felsic magma erupts, it tends to do so explosively, producing more violent eruptions compared to the more fluid eruptions associated with mafic magma.
• Discuss the environmental impacts of explosive eruptions associated with felsic magma, including potential hazards.
  • Explosive eruptions from felsic magma can have significant environmental impacts. They can produce ash clouds that affect air quality and aviation safety, while pyroclastic flows pose severe hazards to life and infrastructure near volcanoes. Additionally, the release of volcanic gases can lead to climate changes by injecting aerosols into the stratosphere, potentially causing global cooling for months or years following an eruption.
• Evaluate the role of felsic magma in shaping the geological features associated with stratovolcanoes and their eruption history.
  • Felsic magma plays a crucial role in forming stratovolcanoes due to its composition and eruption characteristics. These volcanoes are built up over time through alternating layers of lava flows and tephra resulting from explosive eruptions. The history of these volcanoes often reflects cycles of quiet lava effusion followed by explosive events, leading to complex stratigraphy that tells us about past volcanic activity. Understanding these patterns helps scientists predict future eruptions and assess risks to nearby populations.

Related terms

Mafic Magma: A type of magma that has a lower silica content and is richer in iron and magnesium, typically resulting in darker-colored minerals.

Viscosity:

A measure of a fluid's resistance to flow, with felsic magma having higher viscosity, which can lead to more explosive volcanic activity.

Stratovolcano: A type of volcano characterized by its steep profile and alternating layers of lava flows, ash, and volcanic rocks, commonly formed from eruptions of felsic magma.