Here's why:
* Viscosity: Silica content is the primary factor determining a magma's viscosity, which is its resistance to flow.
* High silica content: Magma with high silica content is more viscous, similar to thick honey. This makes it harder for the magma to flow, and it often results in explosive eruptions.
* Low silica content: Magma with low silica content is less viscous, similar to thin syrup. This allows it to flow more easily, leading to effusive eruptions with flowing lava.
Other factors:
While silica is the most important factor, other factors can also influence magma thickness:
* Temperature: Hotter magma is less viscous than colder magma.
* Dissolved gases: Magma with a higher concentration of dissolved gases (like water vapor) tends to be less viscous.
* Crystal content: As magma cools and crystallizes, its viscosity increases.
Examples:
* Rhyolite: A very viscous magma with high silica content. It often forms explosive eruptions.
* Basalt: A less viscous magma with low silica content. It often forms effusive eruptions with flowing lava.
So, while other factors play a role, silica is the key mineral that significantly impacts the thickness (viscosity) of magma.
