Download Volcanic Processes and Igneous Rocks

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Unit III: The Lithosphere –Volcanic Processes Test 2 - KEY
Volcanic Processes and Igneous Rocks
Eruption Processes and Types of Volcanoes
1. What is the key ingredient required to make a volcano erupt?
large amounts of dissolved gasses in the magma increase the
pressure and lower the density
2. Compare a shield volcano (A) to a stratovolcano (B):
shield volcano (A)
stratovolcano (B)
Magma Type
and Viscosity
Mafic- very low viscosity
Felsic- high viscosity, very sticky lava.
Shape and slope
of the volcano:
Very low slope, broad sides and rounded
top.
Slope is much steeper; the top of the
mountain makes a tall peak.
Describe what a
typical eruption
is like.
Typical eruptions are somewhat calm, made
of fire fountains and lava flows.
Often produces violent eruptions that are
very explosive and produces pyroclasitic
flows and large ash clouds.
Name an
example of one
somewhere in
the world.
Kilauea in Hawaii
Mt. St. Helens in Washington state.
Magma Types and Viscosity
3. How is viscosity of a substance different than its density?
Viscosity is the thickness or ease of pouring/running of a liquid material. Density is how much room the matter
takes up compared to its amount of matter. Thick liquids tend to have low densities and visa versa.
4. How does the viscosity of magma affect the way a volcano will erupt?
Thick, felsic lava will build up pressure until the volcano explodes.
Thinner mafic lava will produce a calmer eruption.
5. Label and define each of the features shown in the diagram to the
right- (A and B are liquid, C and D are solid rock)
A. Magma- molten (melted) rock found under the surface
B. Lava- molten rock found on the surface
C. Intrusive rock- igneous rocks made of slowly cooled magma
underground.
D. Extrusive rock- igneous rocks made of rapidly cooled magma
out on the surface.
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Volcanic Processes Test 2 Study Guide
Name:
Unit III: The Lithosphere –Volcanic Processes Test 2 - KEY
6. Compare the characteristics of the three magma types based on what you have learned in the lab:
Mafic
Magma Type:
Felsic
Intermediate
Color:
Lighter colored
Darker grey color or
black and white.
Darker colored
Name 2 minerals
it’s made of:
Feldspar and quartz
Feldspar and
hornblende
Hornblende and olivine
Viscosity:
High- very thick
In the middle
Low- very thin
Crust type:
Continental
Where oceanic and
continental mix
Oceanic
Density:
Lower
Middle
Higher
Name several rocks
made of this type:
Granite, rhyolite, pumice,
obsidian
Andesite porphyry and
diorite
Basalt
Igneous Rocks and Their Formation
7. What is a rock made of?
A mixture of minerals and organic materials
8. What is an igneous rock?
Rock that formed by the cooling, crystallizing, and hardening of molten rock (magma below the surface or lava
on the surface depending on the location)
9. What observable characteristics of an igneous rock allow you to infer its cooling rate?
The size of the mineral grains – large cooled slowly and small, glass, or vesicular cooled fast
10. Intermediate rocks are formed at subduction zones forming trenches where continental crust compresses and
melts on oceanic crust.
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Volcanic Processes Test 2 Study Guide
Name:
Unit III: The Lithosphere –Volcanic Processes Test 2 - KEY
11. Use this table to explain how the cooling rate of magma impacts its observable characteristics:
Location where cooling
occurred
(Intrusive/Extrusive)
Intrusive- deep
underground
Extrusive- at or very close
to the surface
Both- starts deep
underground and then gets
erupted to the surface.
Type of Texture: Describe its
cooling rate.
Mineral crystal size
Name an example rock:
Coarse: slow cooling
large crystals
Granite or diorite
Fine: rapid cooling
small crystals
Rhyolite or basalt
no crystals
Obsidian
no crystals with gas
bubbles
Pumice
both large and small
crystals
Andesite porphyry
Glassy: very rapid cooling
Vesicular: very rapid cooling
with dissolved gases forming
bubbles in the rock.
Porphyritic: -cooling begins
slowly and then finishes quickly
12. While walking around a nearby volcano you notice an igneous rock that is a mixture of light and dark grey
colored visible crystals. Based on these characteristics, complete the table below with the correct info:
Magma Type:
Viscosity:
Environment:
What type of volcano
would this rock form?
Stratovolcano – trench
where oceanic and
continental crust meet
13. Describe the viscosity, magma type, and type of volcano if an observed lava flow was fine-grained, dark-colored
basalt that was located several kilometers from the cone of a volcano?
What type of volcano
Magma Type:
Viscosity:
Environment:
would this rock form?
Intermediate
In between
Intrusive – cooled slowly
inside
Mafic
Thin
Extrusive – cooled quickly
close to the surface
Shield
Hazard and Risk Management of Volcanoes – Case Study
14. What does VEI stand for?
Volcano Explosivity Index
What is the scale used for?
Rates the amount of destruction caused by a volcano
What range does the scale cover?
0 (no to low impact) to 8 (indescribable and global effects)
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Volcanic Processes Test 2 Study Guide
Name:
Unit III: The Lithosphere –Volcanic Processes Test 2 - KEY
15. What is the difference between a dormant, active, and extinct volcano?
Dormant – not currently erupting, but can in the future
Active – currently erupting
Extinct – erupted in the past but will not erupt again
16. True or False: Earthquakes are a clue that a volcano is about to erupt
17. Name the volcano that erupted in 1980 and caused damage to Washington and Oregon State
Mt. St. Helens
18. Define the following Volcanic Hazards and on the line, state if they are related to Shield or Stratovolcanoes:
Stratovolcano Debris – Charred items that are air born and effect a small area
Shield
Lava Fountain – A spectacular display of molten rock being sprayed in the air
Stratovolcano Lahar – Melting snow and rain mixes with mud and ash to create rivers
Stratovolcano Landslide – Large amounts of pressure cause serious movement and destruction of the cone.
Shield
Lava Flow - Liquid molten rock that easily pours down the side of the volcano during an eruption.
Shield
Lava Tube – Underground pipe-like structures that carry lava far from vent.
Stratovolcano Plume – Huge amounts of pressure cause the eruption to throw ash several miles into atmosphere
Stratovolcano Pyroclastic Flow – A mass of very hot gas and rock that rush down the sides of a volcano
Natural Disasters
19. Describe how an earthquake occurs. Be sure base your thoughts around energy.
Plates are in constant motion and driven by convection currents in the mantle – Kinetic Energy.
That energy is transferred and stored as potential energy when friction causes the plates to stick.
Eventually, an old fault will slip or a new one will form, releasing all of the stored energy at once, as
Seismic Waves, in the form of kinetic energy.
20. What is the difference between a focus and an epicenter?
The focus is the location in the crust where all of the seismic energy is released from. The epicenter is
the location on the Earth’s surface and gives us coordinates and direction of where the center of the
earthquake is located.
21. Describe how triangulation is used to locate the epicenter of an earthquake.
As a seismic wave radiates from the epicenter, the energy reaches different locations at different times
and is recorded on a seismograph. These readings show the arrival of the P and S waves. Knowing the
time difference between the arrival of the waves allows us to find the distance the station is from the
epicenter, but not the direction. So a circle is draw around three different seismograph cities. Where
they intersect is the location of the epicenter – where the fault slipped and the energy radiated from.
22. What is the relationship between the S-P travel time and the distance from the epicenter?
The further a city is located from the epicenter, the longer the distance between the P and S Waves.
23. What is the relationship between the S-wave amplitude and the distance from the epicenter?
The further a city is located from the epicenter, the lower (less shaking) the amplitude is.
24. What does the Richter scale measure?
The amount of energy released from the epicenter.
25. How do you create a tsunami?
Displace oceanic crust (underwater) with any type of fault.
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Volcanic Processes Test 2 Study Guide