Junior Cert Revision - Plate Tectonics

1. Plate Tectonics
Junior Cert Revision

2. Layers of the earth
• Crust (Outer) – Solid Rock, 60km under continents, 10 km under
oceans
• Mantle (Middle) – Molten Magma, 4,000O C
• Core (2 Layers) – outer core: nickel & iron; inner core: molten, solid
from pressure, 5,000O C

3. Crustal Plates
• Crust is broken into pieces: plates, edges/plate boundaries
• Convection currents cause plates to move, continental drift, 7 major
plates

4. Constructive plate boundary
• Fissure/crack is created, magma rises up & a new crust formed
• Results: volcanic mountains, volcanic islands & mid-ocean ridges

5. Destructive plate boundary
• Heavier plate is pulled under – melts
• Land above plate forced upwards
• Results: earthquakes and fold mountains

6. Conservative plate boundary
• Pressure builds up & is released suddenly
• Results: earthquake

7. Pacific Ring of Fire
• World’s most active earthquake & volcano zone

8. Volcanic Activity
• Takes place mostly along plate boundaries
• Can result in volcanic mountains, mid-ocean ridges & volcanic islands
• Magma reservoir, vent crater, lava ash, volcanic cone
• 3 types: active, dormant, extinct

9. Mount St. Helens
• Volcano, Rocky Mountains, USA
• Pacific Ring of Fire
• Erupted in 1980 after being dormant for 120 years
• Massive eruption – due to build-up of pressure
• Mountain height reduced by 400m – large crater
• 60 died, 250 homes destroyed
• Disaster tourists, hot spring, fertile soil

10. Mid-ocean ridge
• A mountain range that forms under the ocean
• 2 plates pull apart; Mid-Atlantic Ridge

11. Volcanic Island
• Formed when a volcanic mountain on the ocean floor builds up until
it reaches the surface of the ocean; Iceland

12. Earthquakes
• At plate boundaries, plates collide/slide past each other
• Pressure builds up until one moves suddenly
• Focus, epicentre, tremors, aftershock
• Seismograph – records & measures strength
• Richter Scale compares magnitude 1 with 10

13. Earthquake in Philippines, 2013
• 15 October 2013 – Island of Bohol
• 7.2 on Richter Scale
• Area: Pacific Ring of Fire
• 222 died, 8 missing, 976 injured
• Damaged historic buildings
• Earthquake-proof buildings introduced

14. Japanese tsunami, 2011
• Earthquake under ocean – massive wave
• Tsunami, 40m high
• 16,000 died, 25,000 injured, 3,000 missing
• 200,000 buildings damaged/destroyed
• Explosion – Fukushima Daiichi nuclear power plant

15. Folding
• Plates push together – land buckles upwards = folds
• Alpine fold mountains 30-35m years ago – Alps
• Armorican fold mountains – 250m years ago
• Caledonian fold mountains – 400m years ago – Blue Stack Mountains