IB Geography D.1.2 Volcanic Characteristics and Hazards Notes

Types of Volcanoes and Associated Risks

1. Volcanoes are fascinating yet formidable natural features, each with unique characteristics and hazards.
2. Understanding these differences is essential for assessing the risks they pose to human life and the environment.
3. Volcanic activity is located along tectonic plate boundaries (near subduction zones, along oceanic ridges, in proximity of rift valleys) and in hotspots (intraplate volcanoes).

Shield Volcanoes: Broad and Gentle Giants

1. Shield volcanoes are characterized by their broad, gently sloping profiles, resembling a warrior's shield lying on the ground.
2. They form from low-viscosity basaltic lava that can flow over long distances before solidifying.

Key Characteristics

1. Low Viscosity Lava: The lava is hot and runny, allowing it to travel far from the vent.
2. Gentle Slopes: Slopes are typically less than 10°, creating a wide base.
3. Non-Explosive Eruptions: Eruptions are usually less violent due to the easy escape of gases.

Associated Hazards

1. Lava Flows: Although slow-moving, lava can destroy infrastructure and agricultural land.
2. Gas Emissions: Gases like sulfur dioxide can impact air quality and human health.

Composite Volcanoes (Stratovolcanoes): Steep and Explosive

1. Composite volcanoes, also known as stratovolcanoes, are steep-sided,characterized by andesitic lava of viscous nature (high degree of friction), and formed by alternating layers of lava and pyroclastic material (ash, rocks, and volcanic bombs).

Example

Mount St. Helens in the USA and Mount Fuji in Japan are well-known examples as stratovolcanoes are associated with destructive (convergent) plate margins.

Key Characteristics

1. High Viscosity Lava: The lava is thicker and cooler, leading to steeper slopes.
2. Steep Slopes: Slopes can reach up to 30° near the summit.
3. Explosive Eruptions: Trapped gases in viscous magma lead to violent eruptions.

Associated Hazards

1. Pyroclastic Flows: Fast-moving, hot clouds of gas and volcanic material that can devastate everything in their path.
2. Ashfall: Ash can blanket large areas, disrupting transportation and damaging crops.