VOLCANOES (ALL TOPICS)

CAUSES OF VOLCANOES - LINK TO PLATE BOUNDARIES

1. Convergent boundaries (destructive)

  • Plates move towards each other and one is forced under the other (subduction).

  • The subducted plate melts, forming magma.

  • Magma rises to the surface → volcanic eruptions.

  • Common around the Pacific Ring of Fire.

2. Divergent boundaries (constructive)

  • Plates move apart.

  • Magma rises to fill the gap and solidifies → forms volcanoes.

  • Usually produces frequent, less explosive eruptions.

3. Hotspots (not at plate boundaries)

  • Occur above mantle plumes where magma rises through the crust.

  • Volcanoes form even in the middle of plates.

  • Example: Hawaii

Volcanoes mainly form where magma can reach the surface—especially at plate boundaries where plates move apart or collide.

TYPES OF VOLCANOS

1. Shield volcano

  • Broad, gently sloping sides

  • Formed by runny lava that flows easily

  • Eruptions are frequent but not very explosive

  • Example: Mauna Loa

2. Composite volcano (stratovolcano)

  • Tall, steep-sided cones

  • Made of layers of lava and ash

  • Eruptions are infrequent but very explosive

  • Example: Mount Fuji

3. Cinder cone volcano

  • Small, steep-sided

  • Built from ash and rock fragments

  • Eruptions are short-lived and moderately explosive

VOLCANIC HAZARDS

Volcanic hazards are the dangerous effects of a volcanic eruption.

Primary hazards:

  • Lava flows – destroy buildings, roads, and farmland

  • Ash clouds (tephra) – can cause breathing problems and damage roofs

  • Pyroclastic flows – fast-moving clouds of hot gas and ash (very dangerous)

Secondary hazards:

  • Lahars – mudflows made of ash and water

  • Flooding – from melted ice or heavy ash blocking rivers

  • Climate effects – ash in the atmosphere can cool temperatures

The most dangerous hazards are fast and unpredictable, especially pyroclastic flows, which can cause the most deaths.

WHAT FACTORS CAN INCREASES THE LEVEL OF DAMAGE CAUSED BY AN EARTHQUAKE?

  • Magnitude – larger earthquakes release more energy

  • Distance from the epicentre – closer = stronger shaking

  • Depth of focus – shallow earthquakes cause more damage

  • Population density – more people and buildings at risk

  • Building quality – weak structures collapse more easily

  • Level of preparedness – poor planning increases impacts

  • Secondary hazards – tsunamis, landslides, and fires worsen damage (common in areas like the Pacific Ring of Fire)

Key idea: Damage depends on both the earthquake’s strength and how prepared the area is.

MANAGEMENT AND PREPAREDNESS FOR A VOLCANO (E.G. BEFORE,DURIMG AND AFTER)

Before:

  • Monitoring using seismometers and gas measurements

  • Hazard maps and exclusion zones

  • Evacuation plans, drills, and education

During:

  • Evacuate when told

  • Wear masks/goggles to protect from ash

  • Stay indoors and away from danger zones

After:

  • Provide aid (food, water, shelter)

  • Clear ash and repair infrastructure

  • Rebuild and improve monitoring systems