🌋 Earthquakes and Volcanoes

🔑 Key Definitions

• Earthquake: Sudden shaking of the Earth’s crust caused by movement of tectonic plates
• Volcano: An opening in the Earth’s crust through which magma, ash, and gases erupt
• Magma: Molten rock beneath the Earth’s surface
• Lava: Magma that reaches the surface

🌍 Structure of the Earth

• Crust (outer layer)
• Mantle (semi-molten rock)
• Core (very hot, mostly metal)

👉 The crust is broken into tectonic plates

🌐 Plate Tectonics

🔄 Types of Plate Boundaries

1. ➡️ Constructive (Divergent)

• Plates move apart
• Magma rises → forms new crust

👉 Results:

• Shield volcanoes
• Gentle eruptions

👉 Example:

• Mid-Atlantic Ridge

2. ⬅️➡️ Destructive (Convergent)

• Plates move towards each other
• One plate subducts (goes under another)

👉 Results:

• Explosive volcanoes
• Strong earthquakes

👉 Example:

• Pacific Ring of Fire

3. 🔀 Conservative (Transform)

• Plates slide past each other
• No magma involved

👉 Results:

• Earthquakes only

🌋 Volcanoes

🧱 Features of a Volcano

• Crater: Opening at the top
• Vent: Channel through which magma rises
• Magma chamber: Underground storage of magma

🌋 Types of Volcanoes

1. 🌄 Composite Volcano (Strato-volcano)

📍 Characteristics:

• Steep sides
• Layers of ash and lava
• Explosive eruptions

👉 Example:

• Mount Fuji

2. 🛡️ Shield Volcano

📍 Characteristics:

• Gentle slopes
• Runny lava
• Less explosive eruptions

👉 Example:

• Mauna Loa

🌋 Causes of Volcanic Eruptions

• Heat in mantle melts rock → magma forms
• Pressure builds → magma rises
• Eruption occurs when pressure is released

🌋 Effects of Volcanoes

❗ Negative Effects (Hazards)

• Lava flows destroy buildings
• Ash clouds → breathing problems, air travel disruption
• Pyroclastic flows (hot gas + ash) → very dangerous
• Loss of life and property

✅ Positive Effects (Opportunities)

• Fertile soils (good for farming)
• Tourism (e.g. volcano visits)
• Geothermal energy
• Mineral resources

🌎 Earthquakes

📍 Features of an Earthquake

• Focus (hypocentre): Point where earthquake starts underground
• Epicentre: Point directly above focus on surface
• Magnitude: Strength of earthquake (measured on Richter scale)

🌍 Causes of Earthquakes

• Plates move → stress builds
• Sudden release of energy → seismic waves → shaking

👉 Common at:

• Plate boundaries (especially conservative and destructive)

🌍 Distribution of Earthquakes & Volcanoes

• Found mainly along plate boundaries
• Major zones:
  • Pacific Ring of Fire
  • Mid-ocean ridges
  • Fault lines

👉 Few occur in plate interiors

⚠️ Effects of Earthquakes

❗ Primary Effects (Immediate)

• Buildings collapse
• Deaths and injuries
• Roads and bridges destroyed

❗ Secondary Effects (After)

• Fires
• Landslides
• Tsunamis
• Disease due to poor sanitation

🛠️ Reducing Impacts (Management Strategies)

🌋 Volcanoes

• Monitoring (seismic activity, gas levels)
• Evacuation plans
• Exclusion zones

🌍 Earthquakes

• Earthquake-resistant buildings
• Emergency drills
• Education and awareness
• Early warning systems

📍 Case Study 1: Earthquake

🇯🇵 2011 Tōhoku Earthquake

📊 Key Facts

• Magnitude: 9.0
• Location: Japan
• Caused a tsunami

❗ Effects

Primary:

• Thousands killed
• Buildings destroyed

Secondary:

• Tsunami → flooding
• Nuclear disaster (Fukushima)

🛠️ Responses

• Advanced warning systems
• Strong building design reduced damage
• Emergency services deployed quickly

📍 Case Study 2: Volcano

🇺🇸 Mount St. Helens eruption 1980

📊 Key Facts

• Location: USA
• Explosive eruption

❗ Effects

• Forests destroyed
• Ash spread over large area
• Loss of wildlife and some lives

✅ Benefits

• Fertile soil after eruption
• Tourism

📝 Exam Tips

💡 For “Describe distribution”

• Mention:
  • Plate boundaries
  • Specific zones (e.g. Ring of Fire)

💡 For “Explain causes”

• Link to plate movement
• Use correct terms (subduction, pressure, magma)

💡 For “Effects”

• Separate:
  • Primary
  • Secondary

💡 For “Volcano opportunities”

• Always include:
  • Farming
  • Tourism
  • Energy

💡 For case studies:

• Include:
  • Name
  • Location
  • Causes
  • Effects
  • Responses

❗ Common mistakes

• Confusing focus vs epicentre
• Not linking earthquakes to plate movement
• Forgetting positive impacts of volcanoes

📌 Quick Summary

• Earthquakes and volcanoes occur at plate boundaries
• Types of volcanoes:
  • Composite (explosive)
  • Shield (gentle)
• Earthquakes caused by sudden energy release
• Impacts can be destructive but manageable
• Volcanoes provide both hazards and benefits