A broad volcano with gently sloping sides

A broad volcano with gently sloping sides

• A. Rift Valley
• B. Rock
• C. Sial
• D. Shield Volcano

Answer: (D)

Magma viscosity controls the shape of a volcano: when lava is low in viscosity, it pours and spreads easily rather than piling up steeply. This horizontal lava spreading builds a broad, low-profile mound around the vent, giving a gently sloping, wide-sided form. That kind of volcano is known as a shield volcano, and it often forms where basaltic magma erupts effusively, such as at hotspots or along divergent plate boundaries. Rift valleys are tectonic features created by crustal extension, not volcanoes. Rock is just a material, not a landform. Sial refers to a silica–aluminium crust composition, not a volcanic structure.

Magma viscosity controls the shape of a volcano: when lava is low in viscosity, it pours and spreads easily rather than piling up steeply. This horizontal lava spreading builds a broad, low-profile mound around the vent, giving a gently sloping, wide-sided form. That kind of volcano is known as a shield volcano, and it often forms where basaltic magma erupts effusively, such as at hotspots or along divergent plate boundaries.

Rift valleys are tectonic features created by crustal extension, not volcanoes. Rock is just a material, not a landform. Sial refers to a silica–aluminium crust composition, not a volcanic structure.