VOLCANOES

1. VOLCANOES

2. Volcano Features • Magma chamber: contains the hot, liquid magma • Vents: holes in the crust where the magma rises to the surface • Crater: a funnel shaped pit at the top of a volcano’s central vent • Caldera: a large, circular depression caused by the roof of a volcano collapsing

3. Volcano features

4. Volcano features

5. What Causes Volcanoes? • Scientists use models based on rock samples to “see” what is going on deep inside the Earth • Volcanoes result from the buildup of rock around a vent

6. What Causes Volcanoes? • Magma forms below the Earth’s surface in the lower crust and part of the upper mantle • The temperature of the mantle is hot enough to melt any rock, but why doesn’t the mantle melt? • The weight of the rock above the mantle creates a lot of pressure. This pressure keeps the mantle tightly packed so it remains a solid. • A decrease in pressure causes magma to form

7. What causes volcanoes? • Magma rises toward the surface of the Earth because it is less dense than the surrounding rock • What is density? • Density is how much stuff can fit in a certain space or how compact something is. Remember our density demo with water and the different examples?

8. Where Do Volcanoes form? • The Ring of Fire! https://www.youtube.com/watch?v=IfAcAxX81tk

9. Where do volcanoes form? • A lot of volcanoes lie directly on tectonic plate boundaries • The plate boundaries surrounding the pacific Ocean have so many volcanoes (Ring of Fire) • Volcanoes form at the plate boundaries because this is where the plates collide or separate from one another. It is easier for magma to travel up through the crust.

10. Tectonic Plate Separation • When 2 tectonic plates separate and move away from each other it is a divergent boundary • As they separate a deep crack called a rift forms • Mantle rises to fill the gap, pressure decreases, and the mantle rock melts to become magma • Magma continues to rise up through the rift to create new crust • Usually occurs at the ocean floor

11. Tectonic Plate Collision • When 2 tectonic plates collide it is a convergent boundary • Usually occurs where a continental and oceanic plate collide • The oceanic plate is more dense and moves below the continental crust. The movement of one plate under another is called subduction. • As the oceanic crust moves deeper into the mantle, it gets hotter and pressure increases. Water in the oceanic crust is released and mixes with the mantle rock so it has a lower melting point.

12. How volcanoes are formed

13. Hot SPots • Volcanoes can also form at hot spots. For example, the Hawaiian islands. • Hot spots are places on the Earth’s surface that are directly above columns of rising magma called mantle plumes • A hot spot creates a long chain of volcanoes

14. Volcanic eruptions • There are 2 types of volcanic eruptions: • Non-explosive • Explosive • Scientists compare the amount of water and silica in magma to decide if a volcanic eruption is non-explosive, explosive, or in between

15. Non-Explosive Eruptions • Lava is magma that flows onto the Earth’s surface • Lava flows are rivers of red-hot lava • Some of the largest mountains on Earth were created by repeated lava flows over many years

16. Explosive Eruptions • Clouds of hot debris and gas shoot out from the volcano at very high speeds • Molten is blown into many pieces that harden in the air • Many tons of solid rock can also be blasted away

17. Predicting Volcanic Eruptions • Extinct volcanoes have not erupted in the past and will never erupt again • Dormant volcanoes are not currently erupting, but have erupted at some time in the past • Active volcanoes are in the process of erupting or show signs of erupting in the near future

18. Predicting Volcanic Eruptions • Volcanoes can be predicted by measuring: • Small quakes • Slope • Volcanic gases • Temperature from orbit

19. Small quakes • Active volcanoes produce small earthquakes as the magma moves up to the surface and causes the surrounding rock to move • The number and intensity of the small earthquakes increases right before an eruption and can be measured with a seismograph

20. Slope • Measurements of a volcano’s slope provide clues to predict eruptions • Bugles may form as magma pushes against the inside of the volcano • A tiltmeter is used to detect small changes in the angle of the slope

21. Volcanic Gases • Measurements of the gases coming out of volcano can help predict eruptions • The amount of certain gases is used to predict eruptions. A change in the amount of gases means things are changing in the volcano.

22. Temperature from orbit • Satellite images can help predict eruptions • These images record infrared radiation (IR) to measure changes in temperature over time • Analyzing the images allows scientists to decide if the volcanic site is getter hotter as magma pushes closer to the surface

23. What Erupts from a volcano? • Magma erupts either as lava or pyroclastic material • Lava is produced by non-explosive eruptions. There are different types of lava based on its consistency. What is consistency? • Pyroclastic material are rock fragments crated by explosive volcanic eruptions. • Pyroclastic material is formed: • when magma explodes from a volcano and becomes a solid in the air • when rock is shattered by powerful eruptions

24. Pyroclastic material • There are 4 types of pyroclastic material: • Volcanic bombs • Volcanic blocks • Lapilli • Volcanic ash

25. Pyroclastic Material • Volcanic bombs are large blobs of magma that harden in the air • Volcanic blocks are the largest pieces of pyroclastic material and are solid rock blasted out of the volcano

26. Pyroclastic material • Lapilli means “little stones” and are pebble-like bits of magma that become solid before they hit the ground • Volcanic ash forms when the gases in magma expand very fast and the walls of the gas bubbles explode into tiny glass-like pieces

27. Types of Volcanoes • There are 3 types of volcanoes: • Shield • Cinder cone • Composite

28. Shield Volcano • Built of layers of lava from repeated non-explosive eruptions • Has gentle sloping sides • Spread out over a wide area

29. Cinder cone volcano • Small volcanic cones made of pyroclastic material • Has steep slopes • Spread out over a narrow area • Erupt only for a short time and occur in groups on the sides of shield and composite volcanoes

30. Composite volcano • Also called stratovolcanoes • Most common type of volcano • Form by explosive eruptions of pyroclastic materials followed by non-explosive eruption of lava • The combination of both types of eruptions creates alternating layers of pyroclastic material and lava

31. Volcano activity For the rest of the period you will build your own volcano in lab groups. You will need: • Oak tag and markers • Empty water bottle • Food coloring When you are ready, ask the teacher for: • Vinegar • Baking soda