1. Earth Science Notes Volcanic Eruptions

2. Our Objectives Today are… I can … Explain the Factors that affect Volcanic Eruptions Describe the Features of Volcanic Activity –Intrusive Igneous Rocks (CH 5) Describe the destructiveness of Volcanoes The Circle of Life

3. Factors Affecting Eruptions Trapped Gases Carbon dioxide and water vapor get trapped in magma and escape when pressure decreases Gases that build up a lot of pressure cause explosive eruptions

4. Factors Affecting Eruptions Gases build up more pressure in thicker (more viscous) magma. What type of magma would cause the greatest explosion. Recall: Unit 3 Viscosity means RESISTANCE TO FLOW

5. Factors Affecting Eruptions Silica Content Silica is a compound composed of silicon and oxygen Magma that is silica-rich (i.e. Granitic) produces explosive eruptions –Has a high viscosity (THICK) –TRAPS more gasses –RECALL: silica-rich magma formed granitic (felsic) rocks

6. Factors Affecting Eruptions Silica Content Silica is a compound composed of silicon and oxygen Magma that is silica-poor (i.e. Basaltic) produces quiet explosions –Has a LOW viscosity (Thin) –Forms nonexplosive eruptions –RECALL: silica-poor magma formed basaltic (mafic) rocks Hawaiian Volcano

7. Basaltic  Andesitic  Granitic (Rhyolitic)

8. Factors Affecting Eruptions Low Viscosity (Basaltic) Magma –https://www.youtube.com/watch?v=qTTLYx4X o2khttps://www.youtube.com/watch?v=qTTLYx4X o2k Higher Viscosity (Granitic) Magma –https://www.youtube.com/watch?v=e4PUOBI wEv0https://www.youtube.com/watch?v=e4PUOBI wEv0

9. Volcanic Eruption Types Volcanic eruptions are characterized by expolosivity and height of plume. Please Note: as with classification scheme, there are several forms and eruptions may be difficult to distinguish at times

10. Volcanic Eruption Types Four Main categories of volcanic eruptions (see EN: Kinds of Eruptions) Hawaiian –weakest Strombolian – weak Vulcanian –kind of explosive Pelean – massive explosions

11. Volcanic Eruption Types Hawaiian Eruptions https://www.youtube.com/watch?v=CSu_n etRm8E

12. Volcanic Eruption Types Strombolian Eruptions https://www.youtube.com/watch?v=w- S57sd7j9Y

13. Volcanic Eruption Types Vulcanian Eruptions https://www.youtube.com/watc h?v=YF7ib5ToVs4

14. Volcanic Eruption Types Pelean Eruptions

15. Volcanic Eruption Types Even Larger than a Pelean Eruption are Plinian Eruptions https://www.youtube.com/watch?v=IETUa_ nOk1g

16. Volcanoes Destructiveness Mount Vesuvius - 79 AD

17. Volcanoes Destructiveness Mount St. Helen - Washington

18. Volcanoes Destructiveness

19. Features Of Volcanic Activity Limnic Eruptions: Lake Nyos

20. Lake Nyos is a deep lake high on the flank of an inactive volcano in Cameroon. A pocket of magma lies beneath the lake, charging the water with an estimated 90 million tonnes of carbon dioxide (CO2). In 1986, a limnic eruption at Lake Nyos triggered the sudden release of about 1.6 million tonnes of CO2 that rushed down nearby valleys, displacing all the air and suffocating approximately 1,700 people within 20 km of the lake.

21. Features Of Volcanic Activity Limnic Eruptions: Lake Nyos Elements for a Limnic Eruption Very deep volcanic lake. Lake has to be over a slow source of volcanic gas. Lake has to be very, very still.

22. Features Of Volcanic Activity Limnic Eruptions: Lake Nyos

23. Volcanoes Destructiveness

25. This Diagram shows range of potential destruction A super-eruption has the potential to cover the United States in 3 feet of ash from a plume. Pyroclastic flow would engulf the greater part of three states, and there is evidence that the last major 'super' eruption plunged the world into a freezing, volcanic winter that lasted a decade. An eruption would devastate world agriculture, severely effect the distribution of food and cause mass famine.

26. After the Aftermath

27. Features Of Volcanic Activity Batholiths – formed when magma cools underground

28. Features Of Volcanic Activity Volcanic Neck – magma inside volcano cools and outside is eroded away

29. Features Of Volcanic Activity Dike – magma that cools in vertical cracks

30. Features Of Volcanic Activity Sill – magma that cools in horizontal cracks

31. Features Of Volcanic Activity Caldera – top of volcano collapses on emptied magma chamber Photograph by M. Williams, National Park Service, 1977

32. Features Of Volcanic Activity

34. Our Objectives Today were… Can I … Explain the Factors that affect Volcanic Eruptions Describe the Features of Volcanic Activity –Intrusive Igneous Rocks (CH 5) Describe the destructiveness of Volcanoes The Circle of Life