Volcanic Eruptions: Causes, Effects & Responses

Volcanic eruptions are dramatic tectonic hazards that can have devastating impacts on people, infrastructure, and the environment. This lesson covers how volcanoes form, the different types of eruption, and the effects and responses using a detailed case study — Eyjafjallajokull, Iceland (2010).

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How Volcanoes Form

Volcanoes form where magma (molten rock beneath the surface) finds a way to escape to the surface. This most commonly occurs at plate boundaries.

At Constructive Boundaries

• Plates move apart, creating a gap.
• Magma rises to fill the gap and solidifies, forming new crust.
• Eruptions are usually gentle with runny basaltic lava that flows long distances.
• Example: volcanoes along the Mid-Atlantic Ridge (e.g. Iceland).

At Destructive Boundaries

• The denser oceanic plate is subducted beneath the continental plate.
• The oceanic plate melts in the intense heat of the mantle, forming magma.
• This magma is thick, viscous, and gas-rich, so pressure builds up.
• Eruptions are explosive and violent.
• Example: Mount St Helens (1980), Cascades Range, USA.

At Hotspots