1. Violent Volcanoes - Kaboom!

2. What did Mummy Volcano say to Baby Volcano? - I lava you!

3. Volcanoes (origins…) So, who on Earth came up with the name volcano to describe a smouldering mountain that can explode? Well, there are different stories around the world to explain what causes volcanoes, but you can blame the actual name on the ancient Romans and their hot- tempered fire god, Vulcan… According to legend, Vulcan lived on the island of Vulcano, inside a smouldering mountain.

4. Volcanoes (origins…) All the smouldering, sparks and rumbling noises were caused by Vulcan’s frantic activities. He was blacksmith to the gods… He made weapons for Mars… Armour for Hercules…

5. Volcanoes (origins…) And thunderbolts and lightning for Jupiter. But Vulcan used his skills in other ways too. For no good reason, Vulcan would pick on villagers and terrorise them with fire, lightning, lava flows and explosions! So, which came first, Vulcan or Vulcano? No one knows, but the name, tweaked a bit, stuck.

6. Volcanology (a proper definition) Includes all processes by which solid, liquid or gaseous materials are forced into the Earth’s crust or are ejected onto the surface

7. Lesson Objectives Main features of a volcano – Physical characteristics – Internal forces Processes that create volcanoes Life of volcanoes

8. Main Features of a Volcano – Physical Characteristics Vent: An opening in the Earth’s surface Pipe: A channel which allows the magma to rise to the top of the volcano during an eruption Crater: A bowled-shaped opening at the top of the volcano Cone: The shape of the volcano

9. Main Features of a Volcano – Internal Forces When the temperature beneath the Earth’s surface is so great, magma (molten mantle) is formed Magma that reaches the Earth’s surface is called lava Vulcanicity is the process in which magma and other materials reach the Earth’s surface

10. Volcanoes grow by intrusion and extrusion -An intrusion is magma that moves up into a volcano and then it stops, never erupting  volcano grows on the inside -An extrusion is an eruption  can add layers of lava or ash  volcano grows on the outside  The outpouring of the lava onto the Earth’s surface is called an eruption. Hardened lava from eruptions through a single hole or vent may result in a cone-shaped mountain called a volcano Main Features of a Volcano – Internal Forces

11. Processes that Create Volcanoes Convergent plates – Mantle above subducting plate, below over-riding plate hot but not hot enough to melt rock – Oceanic plate on the ocean floor for tens of millions of years, incorporating a lot of water and buried in sediment – As plate subducts, comes into contact with overlying hot mantle – Causes water and sediment to melt and move into overlying mantle – Lowers melting temperature of mantle enough to generate magma Divergent plates – Accumulation of lava at the surface – Magma mostly originates by melting in the mantle – As hot rock gets closer to the surface the pressure decreases and the rock begins to melt  magma. – Magma more buoyant than the surrounding rock  rises towards surface and may supply a volcano (or solidify before it reaches the surface)

12. Processes that Create Volcanoes Hotspots – Source of heat and/or magma supplied to surface – BUT exact nature of hotspots poorly known – Stationary with respect to the moving lithosphere – Linear chains of volcanoes form on the overlying plates – Volcanoes get older as you look in the direction of plate motion

13. Example of Volcanic Hotspots: The Hawaiian Islands

14. This movement takes it to the northwest compared to the layers below it at a rate of 5 to 10 cm/yr As the plate moves over a fixed spot deeper in the Earth where magma (molten lava) forms, a new volcano can punch through this plate and create an island As the plate moves away, the volcano stops erupting and a new one is formed in its place With time, the volcanoes keep drifting westward and getting older relative to the one active volcano that is over the hot spot As they age, the crust upon which they sit cools and subsides + erosion of the islands once active volcanism stops  shrinking of the islands with age  eventual submergence below the ocean surface

15. Life of Volcanoes Active Dormant Extinct

16. Active – A volcano that has shown eruptive activity within recorded history – Need not be in eruption to be considered active – 600 volcanoes on Earth considered to be active – 50 to 60 of volcanoes actually erupt yearly Life of Volcanoes

17. Extinct – A volcano that has not shown any historic activity – Usually deeply eroded, and shows no signs of recent activity – How old a volcano must be to be considered extinct depends to a large degree on past activity. Yellowstone Caldera: about 600,000 years old and is deeply eroded, but geothermal activity, hot springs, and geysers all point to the fact that magma still exists beneath the surface  not considered extinct Other volcanoes that are deeply eroded, smaller, and much younger than Yellowstone, that show no hydrothermal activity may be considered extinct Life of Volcanoes

18. Dormant (aka sleeping volcano) – Somewhere between active and extinct – Has not shown eruptive activity within recorded history but shows geologic evidence of activity within the geologic recent past – Because the lifetime of a volcano may be on the order of a million years, dormant volcanoes can become active volcanoes all of sudden  perhaps the most dangerous – Examples: Yellowstone Caldera would be considered a dormant volcano. Mount St. Helens was a considered a dormant volcano, having not erupted for 123 years, before its reawakening in 1980. Mount Pinatubo in the Philippines had been dormant for over 400 years before its eruption in 1991. Mount Vesuvius, near Naples, Italy was considered an extinct volcano prior to its devastating eruption of 79 A.D. Life of Volcanoes

19. Dormant (aka sleeping volcano) – Examples: Yellowstone Caldera would be considered a dormant volcano. Mount St. Helens was a considered a dormant volcano, having not erupted for 123 years, before its reawakening in 1980. Mount Pinatubo in the Philippines had been dormant for over 400 years before its eruption in 1991. Mount Vesuvius, near Naples, Italy was considered an extinct volcano prior to its devastating eruption of 79 A.D. Life of Volcanoes