Exam 2

Question 1

What are the two types of crust? How are they different in terms of thickness, composition, and density?

Answer 1

Continental- 20 to 80 km thick (40 km avg)
"Felsic" composition
Lower density (2.7 g/cm3)
Oceanic- 5 to 15 km thick (10 km avg)
"Mafic" composition
Higher density (2.9 g/cm3)

Question 2

How do we know the structure of the deep Earth?

Answer 2

Changes in Seismic Velocity

Question 3

What is the Moho, and what is its significance?

Answer 3

crust/mantle boundary, sudden increase.

Question 4

What is the Low Velocity Zone, and what is its significance?

Answer 4

zone close to the boundary between the lithosphere and the asthenosphere in the upper mantle. It is characterized by unusually low seismic shear wave velocity compared to the surrounding depth intervals.

Question 5

How does pressure vary with depth inside the Earth?

Answer 5

pressure increases the closer you get to Earths core

Question 6

What is the Geothermal Gradient? the rate of change in temperature with depth What is it’s average value?

Answer 6

about 25 degrees centigrade (77 degrees Fahrenheit) for every kilometer of depth

Question 7

What is a solidus?

Answer 7

The temperature during solidification of an alloy at which the last of the liquid phase solidifies

Question 8

What is a liquidus?

Answer 8

he lowest temperature at which all the components of a material have melted and transformed into liquid

Question 9

Why is the mantle usually solid?

Answer 9

because of the relative melting points of the different layers (nickel-iron core, silicate crust and mantle) and the increase in temperature and pressure as depth increases.

Question 10

What is the difference between the lithosphere and asthenosphere?

Answer 10

The lithosphere (crust/upper mantle) is the strong upper layer of the earth. The asthenosphere (mantle) is the weak and easily deformed layer of the earth that acts as a lubricant for the earths plates to slide over.

Question 11

What tectonic environment is the most volcanically active?

Answer 11

divergent

Question 12

Where and what are the Cascade Mountains? What is the tectonic setting? What type of volcanoes dominate the Cascades?

Answer 12

Volcanic Mountain Range, Convergant

Question 13

What was the most recent eruption in the Cascades?

Answer 13

Mt. Saint Helens in 1980

Question 14

What is a lahar?

Answer 14

destructive mudflow on the slopes of a volcano.

Question 15

What type of volcano is Crater Lake? How did it form?

Answer 15

caldera that formed by the collapse of Mount Mazama during an enormous eruption around 7,700 years ago.

Question 16

Where are what are the Andes Mountains? What is the tectonic setting? What type of volcano dominates the Andes? What rock is named for the Andes Mountains? Where else would you expect to find this type of rock?

Answer 16

Volcanic Mountain Range, Convergant

Question 17

Where and what are the Galapagos Islands? What is the tectonic setting? What type of volcano dominates the Galapagos?

Answer 17

Volcanic Island, Intraplate

Question 18

What is the tectonic setting of East Africa? What is the most common type of volcano?

Answer 18

Where the African Plate is splitting in half, Somali Plate and the Nubian.Divergent

Question 19

What are the differences between Stratocone, Shield, Scoria cone, and Caldera volcanoes?

Answer 19

Stratocone- conical volcano built up by many layers of hardened lava, tephra, pumice, and volcano ash also called a composite volcano.
Shield- a broad, domed volcano with gently sloping sides, characteristic of the eruption of fluid, basaltic lava.
Scoria- most common type. These are characterized by steep slopes on both sides of the edifice. Unlike stratovolcanoes, Scoria con volcanoes consist of only one eruption vent.
Caldera- composite volcano whose top collapses into the magma chamber

Question 20

What are the “three Vs” that control volcanism?

Answer 20

viscosity, volatity, volume

Question 21

What is the VEI?

Answer 21

Volcanic Explosivity Index measure of the explosiveness of volcanic eruptions