Acidic Lava - Characteristics of Lava - Geography Notes
Acidic lava is molten material streaming from a volcanic vent. Acid lava is silicate-rich, viscous, and does not flow far. It forms a steep-sided dome. Acidic Lava may be erupted at a volcano or through a fracture in the crust, on land, or undersea. Usually, the temperatures range from 800 to 1200 °C (1470 to 2190 °F). The volcanic rock resulting from subsequent cooling is also often called lava. In this article, we will discuss Acidic Lava which will help in UPSC/IAS exam.
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Table of Contents |
What is Acidic Lava?
- The quick solidification of lava in the vent obstructs the outpouring of lava's flow, resulting in loud explosions and the release of numerous volcanic bombs or pyroclasts.
- Acidic lavas are highly Viscous.
- Viscosity is the resistance of a fluid to gradual deformation by shear or tensile stress is characterized as viscosity. In other terms, viscosity refers to the reluctance of a fluid to flow.
- Lava can be so viscous that it forms a lava plug in the crater, as seen at Mt. Pelée in Martinique (an island in the Lesser Antilles, Caribbean Islands).
- The majority of andesitic lava flows occur along destructive boundaries (convergent boundaries).
- They're light-colored, low-density, and have a high silica content.
- They move slowly and because of that they rarely travel a long distance before hardening.
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| Active Volcanoes | Dormant Volcanoes |
| Extinct Volcanoes | Volcanic Materials |
| Basic Lava | Types of Volcanoes |
Why are Acidic Lava Viscous?
- Acid lava flows are viscous and have a high melting point as compared to basic lava.
- Because of high silica content, they are generally more viscous.
- As a result, the resulting volcanic cone is stratified and steep-sided (hence the name stratovolcano).
Acidic Lava vs Basic Lava
| Basic Lava | Acidic Lava |
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Conclusion
Due to their potential for explosive eruptions, volcanoes emitting acidic lava can be particularly hazardous. Pyroclastic flows, which are fast-moving avalanches of hot ash, rock fragments, and gas, are a common and deadly hazard associated with explosive eruptions from acidic lava.
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| Geography Notes | Physical Geography |
| Geomorphic Processes | Geomorphology |
| Distribution of Oceans and Continents Basins | Minerals and Rocks |
| Endogenic Processes | Exogenic Processes |
FAQs
Question: What is acidic lava?
Answer: Acidic lava, also known as felsic lava, is a type of volcanic lava that is high in silica content (typically over 63%). This lava is viscous, flows slowly, and tends to form steep-sided volcanic structures such as lava domes and stratovolcanoes. Due to its high viscosity, acidic lava can trap gases, leading to explosive volcanic eruptions.
Question: How does acidic lava differ from basic lava?
Answer: Acidic lava is high in silica content and has a high viscosity, causing it to flow slowly and form steep volcanic structures. In contrast, basic lava (also known as mafic lava) has lower silica content, is less viscous, and flows more easily, forming broad, gently sloping shield volcanoes. Basic lava also tends to produce less explosive eruptions compared to acidic lava.
Question: What type of volcanic structures are formed by acidic lava?
Answer: Acidic lava forms steep-sided volcanic structures such as lava domes, stratovolcanoes, and volcanic spines. Due to its high viscosity, it does not spread over large areas but builds up around the vent, forming these distinctive volcanic landforms.
Question: Why are eruptions of acidic lava more explosive?
Answer: The high viscosity of acidic lava traps gases within the magma. As pressure builds up inside the volcano, these trapped gases eventually escape explosively, resulting in violent eruptions. The thick lava also solidifies quickly, blocking the volcanic vent and contributing to the build-up of pressure.
Question: Can acidic lava be found in any specific type of volcanic setting?
Answer: Acidic lava is commonly found in subduction zone settings, where one tectonic plate is forced beneath another. These settings lead to the melting of continental crust, which produces magma that is high in silica content, resulting in acidic lava. Examples include the Andes and the Cascades mountain ranges, which are characterized by explosive volcanic activity.
MCQs
1. What is the primary characteristic of acidic lava?
A) High viscosity
B) Low silica content
C) Rapid flow
D) Formation of shield volcanoes
Answer: A See the Explanation
Explanation: Acidic lava has high viscosity due to its high silica content. This makes it flow slowly and form steep-sided volcanic structures.
2. Which type of volcanic structure is typically formed by acidic lava?
A) Shield volcanoes
B) Stratovolcanoes
C) Flood basalts
D) Mid-ocean ridges
Answer: B See the Explanation
Explanation: Acidic lava forms steep-sided volcanic structures like stratovolcanoes due to its high viscosity, which prevents it from flowing over large distances.
3. What causes acidic lava to produce more explosive eruptions?
A) Low gas content
B) Low viscosity
C) High gas content and high viscosity
D) High flow rate
Answer: C See the Explanation
Explanation: The high viscosity of acidic lava traps gases within the magma, leading to pressure build-up. When these gases are released, the eruption is highly explosive.
4. In which tectonic setting is acidic lava most commonly found?
A) Mid-ocean ridges
B) Hotspots
C) Subduction zones
D) Rift valleys
Answer: C See the Explanation
Explanation: Acidic lava is commonly found in subduction zones, where one tectonic plate is forced beneath another, leading to the formation of silica-rich magma.
5. Which of the following is NOT a feature associated with acidic lava?
A) Lava domes
B) Stratovolcanoes
C) Fluid flow
D) Volcanic spines
Answer: C See the Explanation
Explanation: Acidic lava is known for its thick and viscous nature, which results in slow flow and steep volcanic structures. Fluid flow is characteristic of basic lava, which has low viscosity.
GS Mains Questions and Answers
Q1: Explain the differences between acidic and basic lava, and discuss the impact of these differences on volcanic landforms.
Answer: Acidic and basic lavas differ in their silica content, viscosity, and the types of volcanic landforms they produce. Acidic lava, which has high silica content (over 63%), is highly viscous and flows slowly. As a result, it tends to form steep-sided volcanic structures like stratovolcanoes, lava domes, and volcanic spines. The viscosity also traps gases, leading to explosive eruptions. Acidic lava is commonly found in subduction zones, where tectonic activity melts silica-rich continental crust.
In contrast, basic lava, also known as mafic lava, has lower silica content and lower viscosity, allowing it to flow more easily and cover larger areas. This type of lava forms broad, gently sloping landforms such as shield volcanoes. Basic lava is typically associated with hotspots and mid-ocean ridges, where tectonic activity creates magma from the mantle, which is less rich in silica.
Overall, the differences in viscosity and flow between acidic and basic lavas lead to very distinct volcanic landforms, with acidic lava forming steep, explosive volcanoes and basic lava forming more fluid and expansive volcanic structures.
Q2: Analyze the role of silica content in determining the behavior of volcanic eruptions.
Answer: The silica content of magma plays a critical role in determining the behavior of volcanic eruptions. Silica increases the viscosity of magma, making it thicker and less able to flow freely. High-silica magma, or acidic magma, has a high viscosity, which prevents gases from escaping easily. As a result, pressure builds up inside the magma chamber, and when the gases are eventually released, the eruption is explosive.
In contrast, low-silica magma, or basic magma, has a low viscosity, allowing gases to escape more easily. This leads to less explosive eruptions and more fluid lava flows. The lower viscosity also allows the lava to cover larger areas, forming gently sloping landforms like shield volcanoes. Thus, silica content is a key factor in the explosiveness of eruptions and the types of volcanic landforms created.
Q3: Discuss the environmental and human impacts of volcanic eruptions involving acidic lava.
Answer: Volcanic eruptions involving acidic lava are often highly explosive due to the lava's high viscosity and gas-trapping properties. These eruptions can have severe environmental and human impacts. The explosive nature of these eruptions can result in pyroclastic flows, which are fast-moving currents of hot gas and volcanic material that can devastate nearby areas. Ashfall from such eruptions can affect large regions, disrupting agriculture, air travel, and causing respiratory issues for people.
Acidic lava flows, though slow-moving, can destroy infrastructure and homes in their path. Additionally, volcanic gases released during eruptions, such as sulfur dioxide, can lead to acid rain and have long-term effects on ecosystems. The human impacts are significant, with loss of life, displacement of communities, and economic damage. Managing volcanic risks in areas prone to acidic lava eruptions involves careful monitoring and evacuation plans to mitigate these effects.
Previous Year Questions on Acidic Lava
1. UPSC CSE Prelims 2020:
Question: Which of the following is a feature of acidic lava?
A) Low silica content
B) High viscosity
C) Formation of shield volcanoes
D) Fast flow
Answer: B
Explanation: Acidic lava is characterized by its high viscosity, which results from its high silica content. This leads to slow flow and the formation of steep-sided volcanic structures.
2. UPSC CSE Mains 2019 (GS Paper 1):
Question: "The nature of volcanic eruptions is influenced by the chemical composition of magma." Discuss with reference to acidic and basic lava.
Answer: The chemical composition of magma, particularly its silica content, significantly influences the nature of volcanic eruptions. Acidic lava, which has high silica content, is highly viscous and traps gases, leading to explosive eruptions. These eruptions are characterized by pyroclastic flows, ashfalls, and the formation of steep-sided volcanic landforms such as stratovolcanoes and lava domes. On the other hand, basic lava, with lower silica content, is less viscous, allowing gases to escape more easily. This results in less explosive eruptions and the formation of broad, gently sloping shield volcanoes. The chemical composition of magma is thus a key determinant of the behavior of volcanic eruptions and the types of volcanic landforms created.
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