1. Volcanoes Liquid Hot Magma. Tungerahua Volcano, Ecuador
Talk about this volcano when it erupted and what it is doing right now.
Volcanoes
Tungerahua Volcano, Ecuador
Picture by Alcinoe Calahorrano
Liquid Hot Magma.

2. Volcano Stats Definition of Volcano Number of active volcanos = ?
Mountain that forms when molten rock (magma) is forced to the Earth’s surface
Number of active volcanos = ?
20 erupting right now (50-60/year) (160/decade)
Number of volcanologists = 1,500
MASS, DENSITY, AND ESCAPE VELOCITY The Earth's mass is about 5.98 x 1024 kg. The Earth has an average density of 5520 kg/m3 (water has a density of 1027 kg/m3). Earth is the densest planet in our Solar System. To escape the Earth's gravitational pull, an object must reach a velocity of 24,840 miles per hour (11,180 m/sec).

3. Volcanoes form around vents that release magma onto the Earth’s surface.
Lava
Magma chamber

4. Nonexplosive Eruptions
Volcanic Eruptions
Lava flow
Lava fountain
Nonexplosive Eruptions
Explosive Eruptions
What is Lava?
-magma that flows onto the Earth’s surface

5. Non-explosive Eruptions
Quiet eruption in which magma flows easily
Usually gas dissolved in magma bubbles out gently
Thin, runny lava oozes quietly from vent
A’a
pahoehoe

6. Non-explosive Eruptions
Lava flows: river of red-hot lava

7. Non-explosive Eruptions
Lava fountains: Sprays of lava, rarely exceeding a few hundred meters in the air.

8. Non-explosive Eruptions
Relatively calm outpourings of lava can release a huge amount of molten rock.
Some of the world’s largest mountains grew from repeated lava flows over hundred of thousands of years.
(EX: Hawaiian Islands)

9. Explosive Eruptions
Thick and sticky magma will not flow out of a volcano. Instead, it plugs then vent like a cork in wine bottle.
Dissolved gasses cannot escape, build up pressure until they explode.

10. Explosive Eruptions
Clouds of hot debris and gasses shoot out from the volcano, often at supersonic speeds.
Molten rock is blown into millions of pieces that harden in the air.
Dust-sized particles can circle the globe for years in the upper atmosphere.
Larger pieces fall closer to the volcano.

11. Explosive Eruptions
Can blast millions of tons of solid rock and, in just a few minutes, can demolish rock formations that took hundred or thousands of years to accumulate.
Volcanoes can actually shrink due to repeated eruptions.

12. Mount St. Helens

13. The Composition of Magma Determines whether it is explosive or not!
High water content
More likely to be !!!
Why?
The effect water has on magma is similar to the effect carbon dioxide gas has on a soft drink.
High Silica content
More likely to be !!!
Silica has a thick, stiff consistency
Flows slowly & tends to harden in the volcano’s vent, plugging it, causing pressure build-up.
Thick magma also prevents water vapor & other gases from easily escaping. (Think of popcorn!)
EXPLOSIVE
EXPLOSIVE
The Earth is made of many different and distinct layers. The deeper layers are composed of heavier materials; they are hotter, denser and under much greater pressure than the outer layers. Core: The Earth has a iron-nickel core that is about 2,100 miles in radius. The inner core may have a temperature up to about 13,000°F (7,200°C = 7,500 K), which is hotter than the surface of the Sun. The inner core (which has a radius of about 750 miles (1,228 km) is solid. The outer core is in a liquid state and is about 1,400 miles (2,260 km) thick.

14. More likely to be NON-Explosive !
Low Silica content
More likely to be NON-Explosive !
Why?
Magma with less silica is thinner and runnier. Gases escape more easily, so less pressure builds.

15. What Erupts from a Volcano?
Block
Lava can be
thick or thin.
Pahoehoe
A’a
Pillow

16. Lava: Block Cooler and stiff Oozes from volcano
Forms jumbled heaps of sharp-edged chunks.
Mexico’s Colima Volcano

17. Lava: Pohoehoe Flows slowly, like wax dripping from a candle.
Forms glassy surface with rounded wrinkles ‘ropey’ appearance.

18. Lava: A’a A’a is slightly stiffer.
Pours out quickly and forms a brittle crust which is torn into jagged pieces as molten lava underneath continues to move.

19. Lava: Pillow Forms when lava erupts underwater
Forms rounded lumps the size and shape of pillows.

20. What Erupts from a Volcano?
Pyroclastic material
Rock fragments created by eruptions
magma explodes from volcano and solidifies in the air
existing rock is shattered by powerful eruptions
EXPLOSIVE
Lapilli
Volcanic bombs
Volcanic blocks
Volcanic ash

21. Pyroclastic Material: Size
Volcanic blocks: solid rock blasted out of volcano
Volcanic bombs: large blobs of magma that harden in air
Lapilli: “little stones” (Italian) – pebble-like bits of magma that become solid before hitting the ground.
Ash: forms when gases in stiff magma expand rapidly & walls of gas bubbles explode into tiny glasslike slivers.

22. Pyroclastic Flow
A ground-hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano at 100 km/hour or more.
Temperature may be greater than 500o C, sufficient to burn and carbonize wood.
Pyroclastic flow, Philippines

23. Where do volcanoes occur?
In three kinds of places:
Divergent boundaries
Convergent boundaries
Hot spots

24. What causes volcanoes? The Formation of Magma
Mantle rock melts when the temperature increases
or the pressure decreases.
There are lots of uncertainties about why volcanoes form, because scientists have to rely on models based on rock samples and other data.

25. What causes volcanoes? Where Volcanoes Form
Tectonic Plate Boundaries!!!
There are lots of uncertainties about why volcanoes form, because scientists have to rely on models based on rock samples and other data.
~75% world’s active volcanoes in Ring of Fire

26. What causes volcanoes?

27. What causes volcanoes?
Hot Spots

28. Types of Volcanoes Shield volcano Cinder cone volcano
Composite volcano

29. Shield Volcanoes Look like a warrior’s shield
Broad, slightly dome-shaped volcanoes are the world’s largest volcanoes.
May erupt many times over a period of more than a million years.
Generally have lava that flows easily and can spread over great distances, building up in layers to form the low, wide mountain.

30. Shield Volcanoes
Shield volcanoes are almost exclusively basalt, a type of lava that is very fluid when erupted. For this reason these volcanoes are not steep. (You can’t pile up a fluid that easily runs downhill.)

32. Cinder Cones
A cinder cone volcano is built up from ashes, cinders, and rocks that burst from Earth during a violent eruption.
The rocks fall back to Earth near the opening, to form a cone. Meanwhile, hot ash covers a larger surrounding area.
Erupt for a short period of time, so most are not taller than 300 m (about 1000 ft)
Occure in clusters or on sides of shield and composite volcanoes.
Erode quickly due to pyroclastic material not being cemented together by lava.

33. Cinder Cone

34. Mount Eta, Italy – Cinder Cone

35. Composite Volcanoes
A composite volcano switches between quiet eruptions of flowing lava and violent eruptions of thick, gas-rich lava (pyroclastic material). This type of volcano has the most powerful eruptions of all.
Composite volcanoes, also called stratovolcanoes, form tall conical mountains.

36. Composite Volcano

37. Mount St Helens – Composite Volcano

38. Craters, Calderas, and Lava Plateau
From explosions of material out of the vent and the collapse of material back into vent
Caldera
Much larger depression that forms when magma chamber empties and its roof collapses
Lava Plateau
Forms when lava erupts from long cracks, or fissures, and spreads out evenly (thousands of km)

39. How do volcanologists predict eruptions?
Measuring Small Quakes
Before eruption, increase in number & intensity
Measuring Slope
Bulges may form with magma (tiltmeter)
Measuring Volcanic Gases
Outflow of volcanic gases
Sulfur dioxide, carbon dioxide
Measuring Temperature from Orbit
Measure changes in temperature over time