Answer
The composition and viscosity of lava flows differ significantly between composite volcanoes and shield volcanoes due to variations in the types of magma erupted and the eruptive processes involved.
Composite Volcanoes:
- Composition: Lava flows associated with composite volcanoes typically consist of intermediate to high silica content magma, such as andesite or dacite. These lavas have a higher viscosity, meaning they are more resistant to flow, and tend to be more viscous and sticky compared to the lavas of shield volcanoes.
- Viscosity: The higher silica content in the magma of composite volcanoes leads to a higher viscosity. As a result, the lava flows from composite volcanoes are slower-moving and more prone to solidifying and building up thickness, forming steep-sided volcanic cones.
Shield Volcanoes:
- Composition: Lava flows associated with shield volcanoes are primarily composed of low silica content magma, such as basalt. Basaltic lavas have a lower viscosity and are more fluid compared to the lavas of composite volcanoes.
- Viscosity: The lower silica content in the magma of shield volcanoes results in a lower viscosity. This allows the lava to flow more easily and spread out in broad, thin sheets, forming the characteristic shield-shaped slopes of these volcanoes.
In summary, composite volcanoes have more viscous and slower-moving lava flows due to their higher silica content magma, while shield volcanoes have less viscous and more fluid lava flows due to their lower silica content magma. These differences in lava composition and viscosity contribute to the contrasting shapes and eruptive behaviors of composite and shield volcanoes.
Work Step by Step
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