Acid lava, also commonly referred to as felsic lava, is a type of molten rock material expelled from a volcanic vent that is distinguished by its high silica content and high viscosity. Unlike fluid, runny lavas, acid lava is thick and sticky, which significantly impacts its flow behavior and the types of volcanic structures it forms.
Key Characteristics of Acid Lava
Acid lava possesses several defining characteristics that differentiate it from other types of lava:
- High Silica Content: Acid lava is rich in silicates, typically containing more than 63% silicon dioxide (SiO₂). This high concentration of silica molecules is the primary reason for its distinct properties. Common examples include rhyolite, dacite, and andesite lavas.
- High Viscosity: Due to its high silica content, acid lava is extremely viscous. Viscosity is a measure of a fluid's resistance to flow; the higher the viscosity, the thicker and stickier the material. This characteristic means it flows very slowly and tends to pile up.
- Limited Flow Distance: Because of its high viscosity, acid lava does not flow far from its source. Instead of spreading out into vast sheets, it accumulates around the volcanic vent, forming steep-sided structures.
- Explosive Eruptions: The thick, viscous nature of acid lava often traps gases beneath the Earth's surface. As pressure builds, these trapped gases can lead to highly explosive and dangerous eruptions, ejecting ash, rock fragments, and pyroclastic flows.
- Volcano Formation: Acid lava is predominantly associated with the formation of stratovolcanoes (also known as composite volcanoes) or lava domes. These volcanoes are characterized by their conical shape, steep slopes, and alternating layers of hardened lava, volcanic ash, and other pyroclastic material.
Acid Lava vs. Basic Lava
To better understand acid lava, it's helpful to compare its properties with those of basic lava (also known as mafic lava), such as basalt.
| Characteristic | Acid Lava (Felsic) | Basic Lava (Mafic) |
|---|---|---|
| Silica Content | High (typically >63% SiO₂) | Low (typically <52% SiO₂) |
| Viscosity | Very High (thick, sticky) | Low (fluid, runny) |
| Flow Behavior | Flows slowly, accumulates near vent, doesn't travel far | Flows quickly, spreads widely, travels long distances |
| Eruption Style | Often explosive, prone to pyroclastic flows | Usually effusive (gentle, steady flow) |
| Volcano Type | Stratovolcanoes, Lava Domes | Shield Volcanoes |
| Common Examples | Rhyolite, Dacite, Andesite | Basalt |
| Appearance | Lighter in color (e.g., grey, pink, red) | Darker in color (e.g., black) |
Understanding the properties of acid lava is crucial for predicting volcanic behavior and assessing potential hazards. Its viscous nature and tendency to trap gases make eruptions involving acid lava particularly powerful and destructive.
