Question

Magma that is low in silica generally produces what kind of eruptions? A) thick C) quiet B) caldera D) explosive

Short answer

C) quiet

Step-by-step solution

Understand the Relationship between Silica and Viscosity

Silica content in magma affects its viscosity, or thickness. High silica content makes magma more viscous (thicker), while low silica content results in less viscous (thinner) magma.

Identify Eruption Characteristics of Low-Silica Magma

Low-silica magma, which is less viscous, allows gases to escape easily, resulting in less explosive eruptions. This type of magma flow leads to smoother and quieter volcanic eruptions.

Determine the Eruption Type of Low-Silica Magma

Magma that is low in silica generally leads to quiet eruptions. This is because the low viscosity prevents the build-up of pressure that causes explosive eruptions.

Key concepts

Silica Content

Magma, the molten rock beneath the Earth's surface, contains various elements. One of the key components that influence the behavior of magma is silica content. Silica, often found in the form of silicon dioxide, plays a significant role in determining the properties of magma.

High silica content leads to the formation of rhyolitic magma, while low silica content results in basaltic magma. The amount of silica affects the structure formed within the molten rock: high silica magma has complex, interlinked structures; low silica magma has simpler structures. High silica magmas are thicker and tend to trap gases, whereas low silica magmas are more fluid, allowing gases to escape easily.

• High silica content = thicker, more viscous magma
• Low silica content = thinner, less viscous magma

Understanding silica content helps predict the eruption style of a volcano, distinguishing whether an eruption will be explosive or quiet.

Magma Viscosity

Viscosity is a term used to describe the thickness or stickiness of a fluid. In the context of volcanic eruptions, magma viscosity is a crucial factor in dictating how volcanic material flows. Magma with different silica content will vary in viscosity, which affects how it behaves once it reaches the surface.

High-viscosity magma, rich in silica, is thick and flows slowly, leading to the potential for more explosive eruptions. This is because its thicker consistency can trap gases within the magma, building up pressure until it eventually erupts violently.

• High-viscosity magma = slower flow, increased gas retention
• Low-viscosity magma = faster flow, ease of gas escape

Meanwhile, low-viscosity magma, which has a lower silica content, flows more freely. This molten rock allows volcanic gases to escape more easily, preventing pressure from building up, which results in quieter eruptions. Recognizing magma viscosity offers vital insights into the dynamics of volcanic activity.

Quiet Eruptions

A quiet eruption is characterized by the gentle flow of lava rather than explosive ejections of volcanic material. These types of eruptions are commonly associated with low-silica, low-viscosity magma. The critical factor in quiet eruptions is the ability of gases to escape easily from the magma. Low silica content in magma contributes to its fluidity, preventing the pressure buildup that can cause explosive eruptions.

During a quiet eruption:

• Volcanic gases are released steadily, without sudden eruptions
• Lava flows smoothly and can cover large areas

Quiet eruptions usually occur at shield volcanoes, which have gentle slopes due to the fluid nature of the lava flows. These eruptions contrast with explosive eruptions that occur with more viscous, silica-rich magma, which can lead to hazardous volcanic events. Predicting whether a volcano will have a quiet eruption involves assessing the silica content and viscosity of its magma. This understanding helps in mitigating risks and preparing communities that may be affected by volcanic activity.