Mafic magma

Definition

Mafic magma is a type of molten rock that is rich in magnesium and iron, characterized by its darker color and higher density compared to other types of magma. This composition influences the physical and chemical properties of volcanic eruptions, particularly how explosive or effusive they are. Mafic magma plays a crucial role in shaping the geology of the Earth, particularly at divergent and hotspot boundaries where it is commonly generated.

5 Must Know Facts For Your Next Test

1. Mafic magma has a lower viscosity than felsic magma, allowing it to flow more easily and lead to non-explosive eruptions.
2. The cooling rate of mafic magma can influence the formation of basalt, which often results from rapid cooling during eruptions.
3. Mafic eruptions are typically associated with shield volcanoes, which produce broad, gently sloping structures due to the fluid nature of the lava.
4. In contrast to explosive eruptions seen with more viscous magmas, mafic eruptions tend to be characterized by lava fountains and lava flows.
5. The generation of mafic magma usually occurs at tectonic plate boundaries or mantle plumes, significantly influencing geological activity in those regions.

Review Questions

• How does the composition of mafic magma affect the style of volcanic eruptions?
  • Mafic magma's high magnesium and iron content results in lower viscosity compared to other types of magma. This lower viscosity allows the magma to flow more freely, leading to effusive eruptions rather than explosive ones. As a result, volcanoes that erupt mafic magma often produce extensive lava flows and shield structures rather than violent explosive activity.
• Compare and contrast shield volcanoes and stratovolcanoes in relation to their eruptive styles and associated magma types.
  • Shield volcanoes primarily erupt mafic magma, which is low in viscosity and promotes gentle lava flows. This leads to broad, gently sloping shapes. In contrast, stratovolcanoes typically erupt more viscous felsic magma, resulting in steeper profiles due to explosive eruptions that generate ash and pyroclastic flows. The differences in magma composition directly influence the structure and eruptive behavior of these two types of volcanoes.
• Evaluate the geological significance of mafic magma generation at divergent plate boundaries and hotspot regions.
  • Mafic magma generation at divergent plate boundaries and hotspot regions plays a vital role in reshaping the Earth's crust. At divergent boundaries, tectonic plates pull apart, allowing mantle material to rise and partially melt, creating mafic magma that contributes to seafloor spreading. Similarly, hotspot volcanism produces mafic magma that can form large volcanic islands like those in Hawaii. The continuous generation and eruption of mafic magma not only alter landscapes but also contribute to new crust formation and mineral resources.

Related terms

Basalt: A common type of mafic rock that forms when mafic magma cools rapidly at the Earth's surface, characterized by its fine-grained texture.

Volcanic eruption: The explosive release of magma, gas, and ash from a volcano, which can vary in intensity based on the composition of the magma.

Shield volcano: A type of volcano built primarily from low-viscosity mafic lava flows that result in broad, gently sloping sides.