Felsic magma

Definition

Felsic magma is a type of molten rock that is rich in silica (SiO₂) and contains a high proportion of lighter elements like aluminum, potassium, and sodium. This composition leads to its lighter color and lower density compared to other types of magma, such as mafic magma. Felsic magma is primarily associated with explosive volcanic eruptions and forms the basis for rocks like granite and rhyolite.

5 Must Know Facts For Your Next Test

1. Felsic magma typically has a silica content of over 65%, which contributes to its thick, viscous nature.
2. The high viscosity of felsic magma leads to the buildup of pressure in volcanic systems, often resulting in explosive eruptions.
3. Felsic magma can crystallize to form light-colored igneous rocks such as granite when cooled slowly beneath the surface.
4. During volcanic eruptions, felsic lava can produce ash clouds, pyroclastic flows, and dome formations due to its tendency to trap gas.
5. Felsic magma is commonly found at convergent plate boundaries, where oceanic plates subduct beneath continental plates.

Review Questions

• How does the composition of felsic magma influence its behavior during volcanic eruptions?
  • The composition of felsic magma, which is high in silica content, makes it highly viscous. This viscosity inhibits gas escape, resulting in increased pressure within the magma chamber. When the pressure exceeds the strength of surrounding rocks, it can lead to explosive eruptions, ejecting volcanic ash and pyroclastic materials into the atmosphere.
• Compare and contrast felsic magma with mafic magma in terms of their chemical composition and associated volcanic activity.
  • Felsic magma is rich in silica and lighter elements like aluminum, leading to its lighter color and higher viscosity. In contrast, mafic magma has lower silica content and is richer in iron and magnesium, giving it a darker appearance and lower viscosity. While felsic eruptions are often explosive due to gas buildup, mafic eruptions tend to be less explosive and produce more fluid lava flows.
• Evaluate the environmental impacts of felsic volcanic eruptions on surrounding ecosystems and human settlements.
  • Felsic volcanic eruptions can have significant environmental impacts due to their explosive nature. Ash clouds can disrupt air travel and affect air quality, while pyroclastic flows can devastate local ecosystems and human settlements through intense heat and rapid movement. The long-term effects may include changes in landforms, soil fertility due to ash deposition, and alterations in local water systems. Communities near active felsic volcanoes must be prepared for these hazards, emphasizing the importance of monitoring volcanic activity.

Related terms

Mafic magma: A type of magma that contains lower silica content and is richer in iron and magnesium, resulting in a darker color and higher density compared to felsic magma.

Volcanism: The process through which magma from beneath the Earth's crust escapes to the surface, leading to the formation of volcanoes and related geological features.

Rhyolite: An igneous rock that is the extrusive equivalent of granite, formed from the rapid cooling of felsic magma at or near the Earth's surface.