Chapter 15.2: Volcanoes


Published on

Grade 8 Integrated Science Chapter 15 Lesson 2 on volcanoes. This lesson goes into detail about volcanoes, plate boundaries, lava chemistry, eruption types, and volcano types. The purpose of this lesson is for students to understand where and why volcanoes form and what factors cause differing volcanic features.

Published in: Education
1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Chapter 15.2: Volcanoes

  1. 1. Volcanoes Chapter 15 Lesson 2 Pages 544 - 552
  2. 2. Vocabulary • Volcano – a vent in Earth’s crust through which melted – or molten – rock flows • Magma – Molten rock below Earth’s crust • Lava – Molten rock that erupts onto Earth’s surface • Hot spot – Volcanoes that are not associated with plate boundaries • Shield volcano – common along divergent plate boundaries and ocean hot spots, these volcanoes are large with gentle slopes of basaltic lavas
  3. 3. Vocabulary • Composite Volcano – large, steep-sided volcanoes that result from explosive eruptions of andesitic and rhyolitic lava and ash along convergent plate boundaries • Cinder Cone – small, steep-sided volcanoes that erupt gas-rich, basaltic lava • Volcanic Ash – tiny particles of pulverized volcanic rock and glass • Viscosity – a liquid’s resistance to flow
  4. 4. Famous Volcanoes • Do you know the three famous volcanoes that have erupted with the last 40 years? – Mount St. Helens (WA, USA) – Kilauea (HI, USA) – Mount Pinatubo (Philippines)
  5. 5. What is a volcano? • A volcano is a vent in Earth’s crust through which melted – or molten – rock flows. • Molten rock below Earth’s surface is called magma.
  6. 6. How do volcanoes form? • Volcanic eruptions constantly shape Earth – They can form large mountains, create new crust, and leave a path of destruction behind • They are created and continue to erupt due to tectonic plate movement – Volcanoes form at: • Convergent plate boundaries • Divergent plate boundaries • Hotspots
  7. 7. Convergent Boundaries • Volcanoes form along convergent plate boundaries. – When two plates collide the denser plate sinks, or subducts, into the mantle. – The thermal energy below the surface and fluids driven off the subducting plate melt the mantle and form magma – Magma is less dense than the surrounding mantle and rises through cracks in the crust forming a volcano – Lava is molten rock that erupts onto Earth’s surface
  8. 8. Divergent Boundaries • Volcanoes can happen here too! – Recall that two plates spread apart at divergent plate boundaries. – As the plates separate, magma rises through the vent or opening in Earth’s crust that forms between them – This process commonly occurs at mid-ocean ridges and forms new crust – More than 60% of all volcanic activity occurs along mid-ocean ridges
  9. 9. Hot Spots • Not all volcanoes form on or near plate boundaries – Volcanoes in the Hawaiian Island – Emperor Seamount chain are far from plate boundaries. • Volcanoes that are not associated with plate boundaries are called hot spots. – Geologist hypothesize that hot spots originate above a rising convection current deep within Earth’s mantle.
  10. 10. Hot Spots • They use the word plume to describe these rising currents of hot mantle material. – When the plate moves over the plume, a new volcano forms – When the plate moves away from the plume the volcano becomes dormant, or inactive • Over time, a chain of volcanoes forms as the plate moves. – The oldest volcano will be farthest away from the hot spot.
  11. 11. Where do volcanoes form?
  12. 12. Ring of FIRE!!! • The Ring of Fire represent an area of earthquake and volcanic activity that surrounds the Pacific Ocean. • Volcanoes form mostly along convergent plate boundaries (where plates collide), divergent plate boundaries (where they separate), and over hot spots (like Hawaii)
  13. 13. Volcanoes in the States • There are 60 potentially active volcanoes in the United States – Most of these are part of the ring of fire • In the United States, the United States Geologic Society (USGS) has established three volcano observatories to monitor the potential for future volcanic eruptions • Because of the populated areas surrounding some potentially active volcanoes the USGS has developed a hazard assessment program. – Scientists monitor earthquake activity, changes in shape, gas emissions, and past eruptive history to evaluate the possibility of future eruptions
  14. 14. Types of Volcanoes • Volcanoes are classified based on their shapes and sizes. • Magma composition and eruptive style of the volcano contribute to the shape
  15. 15. Shield Volcanoes • Shield volcanoes are common along divergent plate boundaries and oceanic hot spots • They are large with gentle slopes of basaltic lavas
  16. 16. Composite volcanoes • Composite Volcanoes are large, steep-sides volcanoes that result from explosive eruptions of andesitic and rhyolitic lava and ash along convergent plate boundaries
  17. 17. Cinder Cones • Small, steep-sided volcanoes that erupt gas- rich, basaltic lavas
  18. 18. Supervolcanoes • Some volcanoes are classifies as supervolcanoes – volcanoes that have large and explosive eruptions • Approximately 630,000 years ago, the Yellowstone Caldera in Wyoming, USA ejected more than 1000km^3 of rhyoltic ash and rock in one eruption • This eruption produced nearly 2500 times the volume of material erupted from Mt. St. Helens in 1980.
  19. 19. Volcanic Eruptions • When magma comes to the surface, it might erupt as lava slows flows out. • Other times, magma might erupt explosively, sending volcanic ash – tiny particles of pulverized volcanic rock and glass – high into the atmosphere Quiet Eruption Violent Eruption
  20. 20. Eruption Style • Magma chemistry determines a volcano’s eruptive style. • The explosive behavior of a volcano is affected by the amount of dissolved gases, specifically the amount of water vapor, a magma contains • It is also affected by the silica, SiO2, content of the magma
  21. 21. Magma Chemistry • Silica is the main chemical compound in all magmas. • Differences in the amount of silica affect magma thickness and its viscosity – a liquid’s resistance to flow
  22. 22. • High silica = high viscosity – Flows like sticky tooth paste – This type is magma is formed from melt rocks rich in silica or from the mixture of magma from the mantle and continental crust – Volcanic andesite and rhyolite rocks form when intermediate and high silica magma erupt from subduction zone volcanoes and continental hot spots • Low silica = low viscosity • Flows like warm maple syrup • When the magma erupts, it flows as fluid lava that cools, crystallizes, and forms volcanic basalt. • Erupts along mid-ocean ridges and hot spots
  23. 23. Dissolved Gases • The presence of dissolved gases in magma contributed to how explosive a volcano can be – Like shaking a bottle of soda, the CO2 in the liquid creates the bubbles. When the bottle is opened pressure decreases rapidly. The trapped bubbles increase in size and escape the liquid • All magma contains dissolved gas including water vapor and small amounts of CO2 and sulfur dioxide. • As magma moves towards the surface, the pressure from the weight of the rock above decreases. • As pressure decreases the gases can no longer remain dissolved and bubbles begin to form. • Because gases cannot easily escape from high-viscosity lavas, this results in explosive eruptions
  24. 24. Effects of Volcanic Eruptions • On average, about 60 different volcanoes erupt each year. – the-year-in-volcanic-activity/100645/ • Volcanoes enrich rock and soil with valuable nutrients and help to regulate climate • Unfortunately, they also can be destructive and sometimes even deadly
  25. 25. • Mount Etna is one of the world’s most active volcanoes. People that live near the volcano are accustomed to frequent eruptions of both lava and ash.
  26. 26. Lava Flows • Because lava flows are relatively slow moving, they are rarely deadly • However they can be extremely damaging • Mount Etna in Sicily, Italy, is Europe’s most active volcano. – In May 2008, the volcano began spewing lava and ash in an eruption lasting over 6 months • Although lava is slow moving it threatens nearby communities – People that live on the slopes of Mt. Etna are use to frequent evacuations
  27. 27. Ash Fall • During an explosive eruption, volcanoes can erupt large volumes of volcanic ash – Ash columns can reach heights of more than 40km – The ash is a mixture of pulverized rock and glass • Ash can disrupt traffic and cause airplane engines to stop mid-flight as the ash fuses onto hot engine blades • Ash can also affect air quality and cause serious breathing problems • Large quantities of ash in the atmosphere can also affect climate by blocking out sunlight and cooling the atmosphere
  28. 28. Pyroclastic Flow • Explosive volcanoes can produce fast-moving avalanches of hot gas, ash, and rock called pyroclastic flows. – “pyro” = hot ; “clast” = volcanic particles • Pyroclastic flows travel at speeds of more than 100 km/hr and with temperatures greater than 1000°C. • In 1980, Mount St. Helens produced a pyroclastic flow that killed 58 people and destroyed 1 billion km³ of forest.
  29. 29. Predicting Volcanic Eruptions • Unlike earthquakes, volcanic eruptions can be predicted. • Moving magma can cause ground deformation, a change in shape of the volcano, and a series of earthquakes called an earthquake swarm. • Volcanic emissions can increase. • Ground and surface water near the volcano can become more acidic • Additionally, geologists will study satellite and aerial photographs, to assess volcanic hazards
  30. 30. Volcanic Eruptions and Climate Change • Volcanic eruptions affect climate when volcanic ash in the atmosphere blocks sunlight • High-altitude wind can move ash around the world. • In addition, sulfur dioxide gases released from a volcano form sulfuric acid droplets in the upper atmosphere • These droplets reflect sunlight into space, resulting in lower temperatures as less sunlight reaches Earth’s surface