Volcanic activity – how, why and where it occurs

1. 3The Geography of Volcanoes Volcanic activity – how, why and where it occurs How volcanoes and their effects may be predicted Volcanic activity and its effects on the Irish landscape and worldwide

2. Chapter 3: The Geography of Volcanoes What is a volcano? A feature with the following: • Magma chamber from which molten magma moves • Vent • Crater • Volcanic cone

4. Write down the location of each volcano

6. Chapter 3: The Geography of Volcanoes Where does volcanic activity occur? • Where plates separate (constructive plate boundaries) • Where plates collide (destructive plate boundaries) • At hotspots

7. Chapter 3: The Geography of Volcanoes Three stages in the ‘lifecycle’ of a volcano • Active • Dormant • Extinct

8. Chapter 3: The Geography of Volcanoes Causes of a volcanic eruption • Rock of subducted plates melts and forms molten magma • Molten magma pushes towards the surface and builds up in a magma chamber • Gases dissolved in magma expand • Causes the magma to rise • Magma forces its way up through cracks/fissures in the volcano • Reaches the surface, pressure is released and a volcanic eruption occurs

9. Chapter 3: The Geography of Volcanoes Will the volcanic eruption will be violent or not? • Silica • Silica produces thick lava which traps gases • The more silica present in magma, the greater the likelihood that a violent eruption will occur

10. Chapter 3: The Geography of Volcanoes Volcanic materials ejected during volcanic activity • Volcanic ash • Rock particles known as pyroclasts • Dust • Gases • Lava

11. Chapter 3: The Geography of Volcanoes Lava There are two types of lava: • Acid lava • Basic lava

12. Chapter 3: The Geography of Volcanoes Acid lava • High in silica content • Tends to be thick • Doesn’t flow too far • Gases become trapped • Violent eruptions • Volcano will have steep sides/cones

13. Chapter 3: The Geography of Volcanoes Basic lava • Low in silica content • Tends to be runny • Flows greater distances • Gases escape • Eruptions gentler • Volcano will have gently sloping sides/cones

14. Chapter 3: The Geography of Volcanoes There are three main types of lava flow: • Pahoehoe lava • Aa lava • Pillow lava

15. Memory time

16. Chapter 3: The Geography of Volcanoes Intrusive and extrusive structures • Rocks formed within the Earth are called plutonic/intrusive rocks, e.g. granite • Extrusive structures are those formed on the surface of the Earth • Magma erupts through a crack/fissure/volcano to form extrusive rocks

17. Chapter 3: The Geography of Volcanoes Intrusive structures • Batholith • Sills • Dykes • Laccolith • Lopolith

18. sills batholith laccolith dykes Were intrusive…now?

19. Intrusive volcanic features Intrusive features: Sills: magma cools and hardens in a horizontal direction between two layers of rock in the crust. Dykes: Magma cools and hardens vertically in the crust. Batholith: a large dome of magma that forced its way up through the crust. Laccolith: a small, upturned mound of magma that cooled in the crust. Lopolith: a small, downturned mound of magma that cooled in the crust. Intrusive rock: Granite

20. Chapter 3: The Geography of Volcanoes Extrusive structures • Volcanoes • Island chains • Hot spots • Fissure eruptions

21. Chapter 3: The Geography of Volcanoes Different shapes of volcanoes • Shield volcanoes • Volcanic domes • Composite volcanoes • Cinder volcanoes

23. Chapter 3: The Geography of Volcanoes • Hydrothermal areas • Areas where volcanic activity once occurred • Moisture has collected and is heated by magma & then reaches the surface. Types: • Geysers • Hot springs • Black smokers

24. Chapter 3: The Geography of Volcanoes • How volcanic activity and its effects can be predicted • Geologists forecast volcanic eruptions • The type and date of materials and distribution of deposits can give insight into volcanic activity • Tiltmeters identify bulging in the side of a volcano • If a bulge is evident it may indicate that an eruption is imminent • Seismographs measure earthquake activity – they are positioned around the sides of a volcano

25. Chapter 3: The Geography of Volcanoes • How volcanic activity and its effects can be predicted - (continued) • When magma begins to move it creates great heat, rocks begin to crack and break and this leads to vibrations of the Earth’s crust which can be a clear indication of a volcanic eruption being imminent • Gases emitted from a volcano may suggest that an eruption will soon follow • Steam coming out of vents, the appearance of geysers and of hot springs also indicate possible volcanic activity

26. Chapter 3: The Geography of Volcanoes • Positive effects of volcanic activity • Fertile soils • Tourism • Geothermal energy • Creation of new land • Building materials

27. Chapter 3: The Geography of Volcanoes • Negative effects of volcanic activity • Lahars • Nuée ardente • Loss of life • Destruction by fire • Damage to property • Effect on the environment

28. Chapter 3: The Geography of Volcanoes Mt St Helens case study • Earthquake 18 May, 1980 at 8.32 am • Measured 5.1 on the Richter scale • Occurred directly below the northern slope of Mt St Helens • Triggered a landslide, the largest in recorded history • Travelled at speeds of 175 to 250 km/hr

29. Chapter 3: The Geography of Volcanoes Mt St Helens case study • Gigantic clouds of ash hovered some 16 miles above the mountain • 57 human fatalities • 7000 deer, elk and bear died. Birds and other small mammals were also killed. • Elevation of the summit before the eruption was 2,950 m (9,677 feet) • Reduced by 400 m (1,314 feet) to its post-eruption elevation of 2,549 m (8,363 feet)