Chapter 6: Volcanoes

1. Chapter 6: Volcanoes

2. 6.1: Volcanoes and Plate tectonics • Where are volcanoes found on Earth’s surface? • A volcano is a mountain that forms in Earth’s crust when molten material, or magma reaches the surface. • Magma is a molten mixture of rock forming substances, gases, and water from the mantle. • When magma reaches the surface, its called lava • Volcanoes are not found randomly on earth. The Ring of Fire The Ring of Fire is a belt of volcanoes that circles the Pacific Ocean. As with most of Earth’s volcanoes, these volcanoes form along boundaries of tectonic plates.

3. Diverging Boundaries/Converging Boundaries Volcanoes form along the mid ocean ridges where two plates move apart. Along the rift valley, lava pours out onto the cracks into the ocean floor. This process gradually builds new mountains Many volcanoes form near converging plate boundaries, where two oceanic plates collide. The volcanoes that are made create a string of islands called an island arc Volcanoes and Converging Boundaries Volcanoes often form where two plates collide.

4. Hot Spots Not all volcanoes form along plate boundaries Some volcanoes are the result of “hot spots” in Earth’s mantle A hot spot is an area where material from deep within Earth’s mantle rises through the crust and melts to form magma A volcano forms above a hot spot when magma erupts through the crust and reaches the surface Hot Spot The Hawaiian Islands have formed one by one as the Pacific plate drifts slowly over a hot spot. This process has taken millions of years.

5. 6.2: Volcanic Eruptions • What happens when a volcano erupts ? • Inside a volcano is a system of passageways through which magma moves Inside a Volcano A volcano is made up of many different parts

6. Inside a Volcano • Magma Chamber: all volcanoes have a pocket of magma beneath the surface. Beneath a volcano, magma collects in a magma chamber • Pipe: magma move upwards through a pipe, a long tube that extends from earth’s crust up through the top of the volcano connecting the magma chamber to the surface • Vent: molten rock and gas leave the volcano through an opening called a vent • Lava flow: a lava flow is the spread of lava as it pours out of the vent • Crater: a crater is a bowl shaped area that may form at the top of the volcano around the central vent

7. Two types of volcanic eruptions When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent Silica is a material found in magma that forms from elements oxygen and silicon. Geologist classify volcanic eruptions as quiet or explosive Magma Composition Magma varies in composition. It is classified according to the amount of silica it contains. The less silica that the magma contains, the more easily it flows.

8. Type of Eruptions Quiet Eruptions: A volcano erupts quietly if its magma is hot or low in silica. The gases in the magma bubble out gently. Quiet eruptions can produce different types of lava harden into different into different types of rocks Explosive eruptions: a volcano erupts explosively if its magma is high in silica. This type of magma is thick and sticky.

9. Volcano Hazards • Both quiet and explosive eruptions can cause damage far from a crater’s rim. • A quiet eruption can cover large areas with a thick layer of lava • An explosive eruption belches out a mixture of dangerous material such as hot rock and ash. This mixture of materials can form a fast moving cloud that rushes down the sides of the volcano. This mixture is called a pyroclastic flow.

10. What are the stages of Volcanic Activity? The activity of a volcano may last from less than a decade to more than a million years Geologist often use the term active, dormant, or extinct to describe a volcano’s stage of activity Active or live volcano is one that has erupted and shows signs that it will erupt again A dormant or sleeping volcano is a volcano that will be active in the future An extinct or dead volcano is a volcano that will not erupt in again

11. 6.3: Volcanic Landforms • What Landforms do Lava and Ash create? • Volcanic eruptions create landforms made of lava, ash, and other materials. These landforms include shield volcanoes, cinder cone volcanoes, composite volcanoes, and lava plateaus. Other landforms include calderas, which is one of the huge holes left by collapse of volcanoes.

12. Landforms Cinder Cone Volcanoes: If the volcano magma has high silicone content, it will be thick and sticky. The volcano can erupt explosively and create a small mountain called cinder cone.

13. Composite Volcanoes: Sometimes the silica content can vary. So the eruptions of lava flow alternate, this can result in composite volcanoes. Composite volcanoes are tall cone shaped mountains with layers of lava alternate with layers of ash

14. Shield Volcanoes: At some spots on earth, thin layers of lava pour out of a vent and harden on top of a previous layer, this creates a shield volcano Lava Plateaus: Lava can flow out of several long cracks in an area. The thin lava floods the area and travels far before cooling and solidifying. His forms high levels of plateaus

15. What Landforms does Magma Create? • Volcanic Necks: forms when magma hardens in a volcano’s pipe and the surrounding rock later wears away • Dikes and Sills: Magma that forces itself across rock layers hardens into a dike. Magma that squeezes between horizontal rock layers hardens to form a sill. • Dome Mountains: created by bodies of harden magma • Batholiths: is a mass of rock formed when a large body of magma cools inside the crust.

16. Volcanic Necks, Dikes, and Sills Magma that cools and hardens into rock before reaching the surface forms volcanic necks, dikes, and sills. Batholiths Batholiths are common in the western United States.