Test 2: Chapter 6

Question 1

Define magma and lava:

Answer 1

• magma molten rock below the surface

- lava molten rock at the surface

Question 2

What is viscosity and how is it changed:

Answer 2

• resistance to flow:
  - thick and slow is high
  - smooth and flowy is low
• depends upon:
  - magma composition
  - temperature

Question 3

What causes a volcanic eruption:

Answer 3

-escaping gasses cause eruptions

Question 4

What is “silica” and how does it relate to viscosity:

Answer 4

• a combination of oxygen and silicon that combines with other elements to form minerals
• less silica = lower viscosity
• more silica = higher viscosity

Question 5

What are the 3 kinds of rock we need to be familiar with:

Answer 5

• basalt = low viscosity rank (low silica)
• andesite = medium viscosity rank (medium silica)
• rhyolite = high viscosity rank (high silica)

Question 6

How does viscosity effect eruptions and why:

Answer 6

• the higher the viscosity, the more violent the eruption

- harder for gasses to escape, larger build up of pressure

Question 7

Why are the cascade mountains significant:

Answer 7

• it is a volcanic arc in the pacific northwest

- major cities are close to the arc

Question 8

What is tephra:

Answer 8

-particles blasted into the air by eruption

Question 9

What is a pyroclastic flow:

Answer 9

-dense cloud of tephra and volcanic gas

Question 10

What are lahars:

Answer 10

-mudflows made of volcanic debris and water

Question 11

Name and explain the 3 types of volcanoes and provide an example as well as how they are formed:

Answer 11

• shield = broad, gentle slopes, hawaii, many low viscosity eruptions
• strato = most common, steeper, mt. fuji, alternating layers of tephra and medium viscosity lava
• cinder cone = smallest, sunset crator, higher viscosity tephra

Question 12

How does density effect continental crust:

Answer 12

-the higher the crust is, the thicker the crust has to be to “float” in the mantle

Question 13

What is Isostasy:

Answer 13

-balance between the topography and thickness and density of underground rocks