Exam 2 Flashcards
(21 cards)
What are the two types of crust? How are they different in terms of thickness, composition, and density?
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)
How do we know the structure of the deep Earth?
Changes in Seismic Velocity
What is the Moho, and what is its significance?
crust/mantle boundary, sudden increase.
What is the Low Velocity Zone, and what is its significance?
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.
How does pressure vary with depth inside the Earth?
pressure increases the closer you get to Earths core
What is the Geothermal Gradient? the rate of change in temperature with depth What is it’s average value?
about 25 degrees centigrade (77 degrees Fahrenheit) for every kilometer of depth
What is a solidus?
The temperature during solidification of an alloy at which the last of the liquid phase solidifies
What is a liquidus?
he lowest temperature at which all the components of a material have melted and transformed into liquid
Why is the mantle usually solid?
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.
What is the difference between the lithosphere and asthenosphere?
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.
What tectonic environment is the most volcanically active?
divergent
Where and what are the Cascade Mountains? What is the tectonic setting? What type of volcanoes dominate the Cascades?
Volcanic Mountain Range, Convergant
What was the most recent eruption in the Cascades?
Mt. Saint Helens in 1980
What is a lahar?
destructive mudflow on the slopes of a volcano.
What type of volcano is Crater Lake? How did it form?
caldera that formed by the collapse of Mount Mazama during an enormous eruption around 7,700 years ago.
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?
Volcanic Mountain Range, Convergant
Where and what are the Galapagos Islands? What is the tectonic setting? What type of volcano dominates the Galapagos?
Volcanic Island, Intraplate
What is the tectonic setting of East Africa? What is the most common type of volcano?
Where the African Plate is splitting in half, Somali Plate and the Nubian.Divergent
What are the differences between Stratocone, Shield, Scoria cone, and Caldera volcanoes?
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
What are the “three Vs” that control volcanism?
viscosity, volatity, volume
What is the VEI?
Volcanic Explosivity Index measure of the explosiveness of volcanic eruptions
