1. Volcanic Eruptions Notes By: Mrs. Hudson

2. Objectives: Distinguish between non-explosive and explosive volcanic eruptions. Identify the features of a volcano. Explain how the composition of magma affects the type of volcanic eruption that will occur. Describe four types of lava and four types of pryoclastic material.

3. Vocabulary Words: 1.Volcano: are areas of Earth’s surface through which magma and volcanic gases pass. 2.Magma: molten rock 3.Lava: molten rock that flows onto the Earth’s surface 4.Vent: an opening at the surface of the Earth through which volcanic material passes. 5.Magma chamber: the body of molten rock that feeds a volcano. 6.Ash : dust sized particles

4. Volcanic Eruptions Explosive pressure of a volcanic eruption can turn an entire mountain into a billowing cloud of ash and rock in a matter of seconds. Eruptions are also creative forces – they help form fertile farmland During an eruption, molten rock, or magma, is forced to the Earth’s surface. Magma that flows onto the Earth’s surface is called lava.

5. Non-explosive Eruptions Most common type of eruption Produces relatively calm flows of lava Can release huge amounts of lava Huge amounts of the sea floor and the Northwest region of the United States, are covered with lava from these types of explosions.

6. Explosive Eruptions Much rarer than non-explosive eruptions Incredibly destructive Clouds of hot debris, ash, and gas rapidly shoot out from a volcano Causes molten rock to be blown into tiny particles that harden in the air Blast millions of tons of lava and rock Can demolish an entire mountainside

7. Diagram of a Volcano

8. What is inside a Volcano? Magma chamber is a body of molten rock deep underground that feeds a volcano. Vents is where magma rises from the magma chamber through cracks in the Earth’s crust to openings

9. What Makes up Magma? The composition of the magma affects how explosive a volcanic eruption is Key to whether an eruption will be explosive lies in the silica, water, and gas content of magma.

10. Water and Magma are an Explosive Combination Water content of magma is high, an explosive eruption is more likely Magma underground, it is under intense pressure and water stays dissolved in the magma Magma quickly moves to the surface, the pressure suddenly decreases and the water and other compounds, such as carbon dioxide, become gases. Gases expand rapidly and explosion can result.

11. Silica-Rich Magma Traps Explosive Gases Magma that has a high silica content also tends to cause explosive eruptions Has a stiff consistency Flows slowly and tends to harden in a volcano’s vents (plugs vents) The more the magma pushes up from below the more pressure increases and an explosive eruption takes place

12. Stiff magma also prevents water vapor and other gases from easily escaping Magma that contains less silica has a more fluid, runnier consistency. Because gases escape this type of magma more easily, explosive eruptions are less likely to occur.

13. What Erupts from a Volcano? Magama erupts as either lava or pyroclastic material Pyroclastic material forms when magma is blasted into the air and hardents Non-explosive eruptions produce mostly lava Explosive eruptions produce mostly pyroclastic Volcano’s eruptions may alternate between lava and pyroclastic eruptions

14. Types of lava The viscosity of lava, or how lava flows, varies qreatly Lava that have high viscosity is stiff Lava that have low viscosity is more fluid Four types: Aa (ah ah), Pahoehoe (puh Hoy Hoy) Pilow lava, Blocky lava

15. Aa: is so named because of the painful experience of walking barefoot across its jagged surface. This lava pours out quickly and forms a brittle crust. The crust is torn into jagged pieces as molten lava continues to flow underneath.

16. Pahoehoe: lava flows slowly, like wax dripping from a candle. Its glassy surface has rounded wrinkles.

17. Pillow lava: forms when lava erupts underwater. This lava forms rounded lumps that are shape of pillows.

18. Blocky lava: is cool, stiff lava that does not travel far from the erupting vent. Usually oozes from a volcano and forms jumbled heaps of sharp-edged chunks

19. Types of Pyroclastic Material Forms when magma explodes from a volcano and solidifies in the air Also forms when powerful eruptions shatter existing rock The size of the material ranges from boulders that are the size of houses to tiny particles that can remain suspend in the atmosphere for years

20. Pyroclastic Flows Dangerous type of volcanic flow Produced when enormous amounts of hot ash, dust, and gases are ejected from a volcano Can race downhill at speeds of more than 200km/h – faster than most hurricane-forces winds Temperature in the center can exceed 700 degrees Celsius

21. Four types of Pyroclastic Material Volcanic bombs: are large blobs of magma that harden in the air. The shape of this bomb was caused by the magma spinning through the air as it cooled.

22. Volcanic blocks: the largest pieces of pyroclastic material, are pieces of solid rock erupted from a volcano

23. Lapilli: which means “little stones” in Italian, are pebble-like bits of magma that hardened before they hit the ground

24. Volcanic ash: forms when the gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny, glasslike silvers. Makes up most of the pyroclastic material in an eruption