Question

Describe what kind of eruption is produced when basaltic lava that is low in silica flows from a volcano.

Short answer

Basaltic lava with low silica leads to effusive eruptions, producing lava flows.

Step-by-step solution

Understand Lava Composition

Basaltic lava is characterized by having a low silica content. This means it is typically less viscous and flows more easily compared to lava with higher silica content.

Recognize the Type of Eruption

Due to the low viscosity of basaltic lava, eruptions tend to be less explosive. Instead, they produce lava flows that can travel quite far, spreading out over great distances.

Identify the Specific Eruption Type

The kind of eruption associated with basaltic lava is often referred to as an "effusive eruption." This type of eruption is marked by the steady outpouring of lava onto the ground, in contrast to explosive eruptions that eject ash and pumice into the air intensely.

Conclusion on Eruption Characteristics

Effusive eruptions result in the formation of broad, shield-shaped volcanoes with gentle slopes, such as those seen in Hawaii. They create extensive lava fields rather than towering ash plumes.

Key concepts

Basaltic Lava

Basaltic lava is a type of lava that is extremely important in the world of volcanoes. It forms from basalt, a dark-colored volcanic rock. What's special about basaltic lava is its chemical makeup, which is mostly comprised of compounds rich in iron and magnesium. This gives basaltic lava its characteristic dark appearance.

Basaltic lava flows are generally categorized by their smooth and ropy textures, known as "pahoehoe," or their rough, jagged, and clinkery surfaces, called "a'a." These flows are usually fast-moving due to their lower viscosity. This means they can cover extensive areas quickly as they spread out during an eruption. Because of this, understanding basaltic lava is key to predicting the behavior of certain types of volcanic eruptions.

Low Silica Content

Lava with low silica content behaves quite differently from its high silica counterparts. Silica acts almost like a thickening agent in lava. When a lava has a low silica content, it tends to be more fluid and less sticky. This results in lava that flows more readily.

Silica content in lava is a critical factor in determining how explosive or effusive a volcanic eruption will be. When the silica content is low, the lava has minimal resistance to flow, allowing it to move smoothly down the slopes of a volcano. This easy flow often creates vast, expansive lava fields rather than explosive ash clouds. By contrast, lavas with high silica content are thicker and can trap more gases, leading sometimes to violent eruptions.

Volcano Eruption Types

Volcanoes are fascinating natural structures that display a variety of eruption types, primarily determined by the lava's properties. There are two broad types of volcanic eruptions: explosive and effusive. Explosive eruptions are dramatic and involve the violent ejection of ash, gas, and rock into the atmosphere. These are usually associated with lava that has high silica content.

On the other hand, effusive eruptions are characterized by the gentle flow of lava across the surface of the earth. These are commonly associated with basaltic lava which, as we know, has a low silica content, making it less viscous. Effusive eruptions create wide and gently sloping shield volcanoes. Understanding these eruption types is essential in the field of volcanology, as it helps in predicting future volcanic activities and their potential impacts.

Lava Viscosity

Lava viscosity is an essential term in understanding volcanic eruptions. Viscosity refers to how thick and sticky a fluid is. You can think of it like honey versus water. Honey is much more viscous, meaning it's thicker and flows slowly, while water is less viscous and flows quickly.

For lava, the viscosity is determined by its composition, particularly the amount of silica. Basaltic lava, which has low silica content, is less viscous. This means it flows more smoothly and covers more ground than more viscous types of lava. Low-viscosity lava results in non-explosive eruptions, where lava can spread easily to form extensive areas called lava flows.

• Low viscosity = fast-flowing lava.
• High viscosity = slow-moving, often explosive eruptions.

Understanding viscosity helps predict what a volcanic eruption might look like and what hazards it could pose to the surrounding area.