Shield volcanoes are typically built from which lava composition?

Shield volcanoes are typically built from which lava composition?

• A. Mafic basaltic composition
• B. Intermediate
• C. Felsic
• D. Ultramafic

Answer: (A)

Shield volcanoes form from low-viscosity lava, which is basaltic (mafic) in composition. Because basaltic lava has relatively low silica, it flows easily and can travel long distances, spreading out to create broad, gentle slopes. Repeated effusive eruptions pile these lava flows into a wide, shield-like shape. In contrast, more viscous magmas, such as intermediate or felsic types, tend to erupt explosively or build steep, cone-shaped volcanoes, not broad shields. Ultramafic magmas are even less common at the surface and don’t typically form the characteristic shield profile. So the lava composition most associated with shield volcanoes is basaltic, mafic lava.

Shield volcanoes form from low-viscosity lava, which is basaltic (mafic) in composition. Because basaltic lava has relatively low silica, it flows easily and can travel long distances, spreading out to create broad, gentle slopes. Repeated effusive eruptions pile these lava flows into a wide, shield-like shape. In contrast, more viscous magmas, such as intermediate or felsic types, tend to erupt explosively or build steep, cone-shaped volcanoes, not broad shields. Ultramafic magmas are even less common at the surface and don’t typically form the characteristic shield profile. So the lava composition most associated with shield volcanoes is basaltic, mafic lava.