Lesson 4 Flashcards
What are the primary factors of magma that determine the nature/violence of volcanic eruptions?
temperature
composition
amount of dissolved gas
What is viscosity?
A measure of a materials resistance to flow
As viscosity increases, the mobility _____.
decreases
What are the factors that affect viscosity?
temperature
composition
volatiles (dissolved gasses)
If the temperature of the magma is hotter, then it is _____ viscous.
less
If the magma’s composition has a high silica content, the magma will have a _____ viscosity.
high
If the magma’s composition has a low silica content, the magma will have a _____ viscosity because it has more ___..
low
fluid
What is an example of a magma composition with a high silica content?
rhyolitic lava
What is an example of a magma composition with a low silica content?
basaltic lava
What is the most abundant volatile or gas in magma?
water vapor
What are the main gasses in magma?
water vapor
carbon dioxide
What provides the force to extrude lava?
gases expanding near the surface
What is the violence of a eruption related to?
how easy gas escapes form magma
When gases have a hard time to escape, they have a ____silica content, ____viscosity, and _____eruptions
high
high
violent
What is congealing?
solidify by cooling
When gases have an easy escape, they have a ____silica content, ____viscosity, and _____eruptions
low
low
non-violent
What are the materials associated with volcanic eruptions?
lava flows
gases
pyroclastic materials
Are basaltic lavas more or less fluid?
more
What are the types of basaltic lava?
Pahoehoe lava
Aa lava
What does Pahoehoe lava look like?
resembles braids in ropes
What does Aa lava look like?
rough, jagged blocks
Pahoehoe lava is _____ viscous than AA lava.
less
What kind of flows does rhyolitic lava create?
short and thick flows
What kind of flows does basaltic lava create?
fluid flows that travel long before congealing
How much percent of magma by weight is gases?
1-5
What are pyroclastic materials also called?
“fire fragments”
What are the types of pyroclastic materials?
Ash and dust
Pumice
Lapalli
Cinders
Give a description of ash and dust (pyroclastic material).
fine, glassy fragments
Give a description of pumice (pyroclastic material).
from “frothy” lava
Give a description of lapilli (pyroclastic material).
“walnut” size
Give a description of Cinders (pyroclastic material).
“pea-sized”
What are particles larger than lapilli?
blocks
bombs
What are blocks?
hardened lava
What are bombs?
ejected as hot lava
What is pulverized rock and lava fragments blown from the volcanos vent?
pyroclastic material
Successive eruptions of lava from a central vent results in a montainous accumulation of material called a ____
volcano
What is a volcanoes surface opening called?
vent
What is a steep-walled depression located at the summit called?
crater
The vent is connected to the ______ through a pipe.
magma chamber
What is the pipe that carries gas rich magma to the surface?
conduit
What is a caldera?
a crater that is greater than 1 km diameter
What is the cone shaped material formed from volcanic material not part of the central vet of a volcano.
Parasitic cones
What is the opening called where gases emerge?
fumaroles
What are the three types of volcanos?
shield
cinder
composite
What is a shield cone volcano shape?
broad, slightly domed
What are shield cones primarily built of?
fluid- basaltic lava
Shield volcanoes are generally sized ____ and produce a _____ of lava
large
large volume
What is an example of a shield volcano?
Mauna Loa in Hawaii
What type of volcano frequently occurs in groups?
Cinder cones
What is the shape of cinder cone volcanoes?
very steep slopes and rather small
What are cinder cones composed of?
pyroclastic material- ejected lava fragments
What are composite cones built of ?
interbedded lavas
pyroclastic deposits.
Where are most composite cones located?
adjacent to the pacific ocean
What is an example of a composite cone volcano?
Mt Rainer
What is another name for composite cones?
stratovolcanoes
What is the shape of composite cones?
large
nearly symmetrical
What volcano has the most violent type of activity?
composite cone
What do composite volcanoes often produce?
nuea ardente
What is a nuea ardente?
fiery cloud of hot gases infused with incandescent ash
Nuea ardente flows down the side of a volcano at speeds up to ____per hour?
200km (125 miles) per hour
Composite cones may generate mudflow called _____.
lahar
What is lahar?
a type of mudflow
What are most volcanoes are fed by?
conduits or pipes
What are resistant vents left standing after erosion has removed the volcanic cone?
volcanic neck
Volcanic eruptions from a central vent are the most familiar, but the largest amounts of volcanic material are extruded from ______
fissures
The term flood basalts describes the fluid, waterline, basaltic lava flows that cover an extensive region in the northwestern United States known as the __________
Columbia Plateau
When silica-rich magma is extruded, pyroclastic flows consisting largely of _______ fragments.
ash and pumice
How are calderas formed?
by collapse
What is the shape of calderas?
nearly circular
What is fluid basaltic lava extruded from crustal fractures?
fissures
What are short conduits that connect a magma chamber to the surface?
pipes
Example of a volcanic pipe and neck?
Ship Rock, New Mexico
Magma is created from a rock located where?
crust and upper mantle
How can a rocks temperature raise?
from hot mantle plume “ponds” beneath crustal rocks
What can happen when there is a decrease in pressure?
decompression melting
What can volatiles (water) do to a rock to generate magma?
lower a rock’s melting point
What end of the compositional spectrum is the partial melting magma
granitic (felsic) end
What factors influence the generation of magma from solid rock
heat
pressure
volatiles
partial melting
Earth’s natural temperature increases with depth is called a ______
geothermal gradient
What three ways is heat created to melt magma?
Friction in subduction zones
Crustal rocks heated during subduction
Rising, hot mantle rocks
What happens to the temperature if the confining pressure increases?
melting temp increases
What plays an important role in subducting ocean plates?
volatiles
What kind of minerals is partial melting made of?
lowest-melting-temperature minerals
What is different from the low melting temp minerals and original rock?
they have a high silica content
What are most active volcanoes are associated with?
plate boundaries
Plate boundry found along mid-ocean ridges where seafloor spreading is occurring?
divergent plate boundaries
Rising plumes of hot mantle rock are the source of most ______
intraplate volcanism
what are the three plate motions providing help to create magma?
Convergent
Divergent
intraplate igneous activity
Name the plate motion.
- Deep-ocean trenches are generated
- Descending plate partially melts
- Magma slowly rises upward forming a structure
convergent plate boundaries
What two structures can form from convergent plate boundaries?
Volcanic island arcs in an ocean
Continental volcanic arcs
What is the composition of Volcanic island arcs in an ocean?
Basaltic composition
What is the composition of Continental volcanic arcs?
Andesitic or rhyolitic composition
What is an example of a volcanic island arc in an ocean?
the Aleutians
What is an example of continental volcanic arcs?
Andes mountains
Name the plate motion.
a. Activity within a rigid plate
b. Plumes of hot mantle material rise
c. Form localized volcanic regions called hot spots
Intraplate igneous activity
Where is the greatest volume of volcanic rock produced along
the oceanic ridge system
Name the plate motion.
- Lithosphere pulls apart
- Less pressure on underlying rocks
- Partial melting occurs
- Large quantities of fluid basaltic magma are produced
Divergent plate boundaries
Plate boundary in the vicinity of ocean trenches where one plate is being subducted beneath another?
convergent plate boundaries
Plate boundary in the interiors of plates themselves?
intraplate volcanism
