Intermediate

Definition

In geology, the term 'intermediate' refers to a specific category of magma composition that lies between mafic and felsic types. This classification indicates a balanced presence of silica and other minerals, resulting in unique characteristics that affect the behavior of the magma as well as the types of volcanic rocks formed from it. Intermediate magmas typically produce andesitic rocks, which have implications for volcanic activity and the nature of eruptions.

5 Must Know Facts For Your Next Test

1. Intermediate magmas generally have a silica content ranging from 53% to 65%, making them more viscous than mafic but less viscous than felsic magmas.
2. The formation of intermediate magma often occurs at subduction zones where oceanic crust melts, mixing with continental crust materials.
3. Eruptions from intermediate magma can be explosive due to its higher viscosity, leading to the accumulation of volcanic ash and pyroclastic flows.
4. Common volcanic landforms associated with intermediate magma include stratovolcanoes, which are characterized by their steep profiles and layered structure.
5. Intermediate magmas can evolve from mafic magmas through processes like fractional crystallization, where certain minerals crystallize out, changing the composition of the remaining liquid.

Review Questions

• How does the viscosity of intermediate magma compare to mafic and felsic magmas, and what implications does this have for volcanic eruptions?
  • Intermediate magma has a viscosity that falls between that of mafic and felsic magmas. This means it flows less easily than mafic magma but more readily than felsic magma. The higher viscosity of intermediate magma can lead to more explosive volcanic eruptions, as gas bubbles become trapped and pressure builds up until it is released violently. This results in significant volcanic activity such as ash plumes and pyroclastic flows.
• Discuss the geological processes that lead to the formation of intermediate magma, particularly in relation to tectonic settings.
  • Intermediate magma commonly forms at subduction zones where an oceanic plate descends beneath a continental plate. As the oceanic plate sinks, it undergoes partial melting due to increased temperatures and pressures. This melting can create a mixture of basaltic material from the oceanic crust and sedimentary materials from the continental crust. The result is intermediate magma, which incorporates diverse elements leading to its unique composition.
• Evaluate the role of intermediate magma in shaping volcanic landscapes and its impact on surrounding ecosystems.
  • Intermediate magma plays a crucial role in shaping volcanic landscapes through its tendency to form stratovolcanoes, which create iconic mountain profiles. These volcanoes can have significant impacts on surrounding ecosystems due to their explosive nature, leading to pyroclastic flows and ash fall that can devastate local flora and fauna. However, the nutrients released from volcanic eruptions can also enrich soil over time, creating fertile environments for regrowth. Understanding these dynamics is essential for predicting future volcanic activity and managing land use around such areas.

Related terms

Mafic: Mafic magma has low silica content and is rich in iron and magnesium, leading to darker colored rocks like basalt.

Felsic: Felsic magma has high silica content and is rich in lighter minerals, resulting in lighter colored rocks such as granite.

Andesite: Andesite is an igneous rock formed from intermediate magma, typically characterized by a composition that falls between basalt and rhyolite.