ESCI 111 Chapter 5 flashcards |

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1. What factors affect the viscosity of magmas?

Temperature (hotter is less viscous). Coposition. High silica is felsic/high viscosity.

2. Why do some volcanoes erupt violently while others erupt "gently"?

Lava can be Pahoehoe which is hotter and more fluid (Hawaii) or Aa which resemble jagged blocks which are cooler and thicker with bubbles formed inside by the gasses. The gasses are generally water vapor and carbon dioxide. Pyroclastic materials such as ash, dust, pumice, walnut sized lapilli and pea sized cinders are also released during an eruption.

3. Name and briefly describe the materials extruded during an eruption. (lava, gases and pyroclastic materials) (see pp. 160-163)

Lava can be Pahoehoe which is hotter and more fluid (Hawaii) or Aa which resemble jagged blocks which are cooler and thicker with bubbles formed inside by the gasses. The gasses are generally water vapor and carbon dioxide. Pyroclastic materials such as ash, dust, pumice, walnut sized lapilli and pea sized cinders are also released during an eruption.

4. Contrast a shield volcano and a stratovolcano. You can use a picture as part of your explanation. Explain how they are different. Give an example of each.

A shield volcano is large and gradually sloping. It is broad with a slight dome. They produce basaltic lava and can be found in places such as Hawaii. Stratovolcanoes such as Mt. St. Helens are large in size. They are very violent and produce a large pyroclastic flow upon eruption. They are generally much steeper than shield volcanos.

5. What is a lahar? What two types sources of water can lead to lahars?

A mudlike volcanic debris flow. Rain or melting snow can lead to lahars.

6. What is a caldera? How does it form? What are the three types of calderas?

A caldera is a large crater that is circular with steep sides. Crater Lake types are formed when a stratovolcano collapses after an erruption. Hawaiian type calderas are formed when magma is drained from underneath a shield volcano. Yellowstone type calderas are collapses resulting from a large discharge of pyroclastic flow.

7. What is a pyroclastic flow?

Ash and pumice fragments propelled from vents at a high speed, typically felsic magma.

8. Be able to describe the basic steps in the eruption of Mt. Saint Helens. (in-class video).

1. The northern mountain collapsed and created a landslide.
2. A blast came out of the collapsed area and along with the landslide destroyed the environment.
3. The landslide then met with nearby lakes to create a dam and formed a lahar that further destroyed the environment.
4. Ash from the volcano clouded the sky and disrupted weather around the planet.

9. Describe how and where (the type of plate boundary or plate location and the process) the following types of volcanic landforms occur and give an example for each (Name a place). (You can draw a picture as part of your answer if you like.)
1. volcanic island arcs
2. continental volcanic arcs
3. continental rift volcanoes

1. Volcanic island arcs result from the subduction of one oceanic plate under another oceanic plate. The pressure caused by this forces the formation of magma which then ascends to creates an arc of volcanic island. The Mariana Islands in the pacific ocean are an example of this.
2. Continental arcs result from the subduction of an oceanic plate under continental crust. This creates and arc shaped mountain belt. The Cascade Volcanoes in the northwestern US are an example of this.
3. When continental crust extends outward magma rises to fill the empty space. This magma forms continental rift volcanoes. The East African Rift that goes through countries such as Mozambique is an example of this.
4. In intra plate volcanoes high temperature mantle plumes extend upward to form volcanoes that are not necessarily near plate boundaries. Yellowstone is an example of this.

What is the Ring of Fire? Where is it?

The ring of fire is an area in the pacific ocean with a large amount of geographic activity. This results in volcanoes, earthquakes and tsunamis.

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