Geology 101 Quiz 5

Question 1

in both volcanoes and carbonated beverages

Answer 1

gas is dissolved under pressure; when the pressure is released, gases expand and carry part of the liquid out the top with the escaping gas

Question 2

in a volcano, rising magma does what to overlying rock?

Answer 2

stresses, which eventually creates fractures that reach the surface

Question 3

as gases expand, what gets carried up through the fractures along with the expanding gases?

Answer 3

magma

Question 4

Mt. St. Helens in Washington had a ? eruption in what year?

Answer 4

explosive; 1980 - the entire side of the volcano was blasted away

Question 5

are all volcanic eruptions explosive?

Answer 5

no

Question 6

the explosiveness of a volcano depends on two criteria

Answer 6

gas content & magma composition

Question 7

most of the gas in volcanoes is

Answer 7

simple water and carbon dioxide

Question 8

some of the gases come from ?

Answer 8

subducted plates that carry seawater along with the descending crust

Question 9

if the gas content of the magma is (low/high), the potential for an explosive eruption is much higher

Answer 9

high

Question 10

the composition of magma is important because it affects ?

Answer 10

viscosity

Question 11

viscosity

Answer 11

the resistance to flow

Question 12

something with a (low/high) viscosity does not flow easily (like molasses)

Answer 12

high

Question 13

something with a (low/high) viscosity flows easily (like water)

Answer 13

low

Question 14

if a magma has a low viscosity,

Answer 14

gases coming out of the magma can easily rise to the surface and vent

Question 15

if a magma has a high viscosity,

Answer 15

gases will tend to remain trapped within the magma; magma cannot get out of the way easily when gases are rapidly expanding so lots of it will get carried out with the escaping gases

Question 16

(felsic/mafic) magmas have a higher silica content and thus are (less/more) viscous

Answer 16

felsic; more

Question 17

(felsic/mafic) magmas tend to make more explosive eruptions

Answer 17

felsic

Question 18

Mt. St. Helens if fromed from andesitic lavas/tephra (?)

Answer 18

felsic

Question 19

Kilauea is formed from basaltic lavas (?)

Answer 19

mafic

Question 20

felsic (rhyolitic)

Answer 20

higher silica content, more viscous, lower melting temperature

Question 21

mafic (basaltic)

Answer 21

lower silica content, less viscous, higher melting temperature

Question 22

a lower melting temperature means that

Answer 22

felsic magmas can exist when it is not hot enough for mafic rocks to melt

Question 23

Felsic magma will still be more viscous than mafic magma, however, even if ?

Answer 23

the gas content is high

Question 24

very high explosiveness

Answer 24

felsic + high gas content + high viscosity

Question 25

low explosiveness

Answer 25

felsic + low gas content + very high viscosity

Question 26

intermediate explosiveness

Answer 26

mafic + high gas content + very low viscosity

Question 27

very low explosiveness

Answer 27

mafic + low gas content + low viscosity

Question 28

eruptions will not be explosive without

Answer 28

dissolved gas

Question 29

80% of volcanoes on Earth are

Answer 29

basaltic (most oceanic volcanoes)

Question 30

10% of volcanoes on Earth are ? and the other 10% are ?

Answer 30

andesitic & rhyolitic (most continental volcanoes)

Question 31

extrusive igneous rocks are divided into two categories

Answer 31

lava and pyroclastic material (tephra)

Question 32

pyroclastic material

Answer 32

if magma and solidified fragments spend part of their journey from the volcano hurled through the air

Question 33

pyroclastic material is divided into three categories based on size

Answer 33

ash, laphilli, bombs

Question 34

ash

Answer 34

dust size tephra up through the size of a BB (< 2 mm)

Question 35

laphilli

Answer 35

BB to baseball size (2-64 mm)

Question 36

bombs

Answer 36

larger than a baseball (>64 mm)

Question 37

lava

Answer 37

magma that flows over the surface of the ground

Question 38

pahoehoe

Answer 38

smooth, ropey lava formed from high gas content, low viscosity lava

Question 39

aa

Answer 39

rough, jagged lava formed from low gas content, high viscosity lava

Question 40

lava tubes

Answer 40

tunnels that lava travels through; form when the upper surface of a lava flow hardens, but the lava beneath continues to flow

Question 41

three different types of volcanoes that result from various combinations of lava and pyroclastic material

Answer 41

shield volcano, stratovolcano, cinder cone (or tephra cone)

Question 42

shield volcano

Answer 42

formed from lava flows; successive flows builds up a wide, gently sloping volcano with a shield shape

Question 43

examples of shield volcanoes

Answer 43

Mauna Loa and Mauna Kea, Hawaii

Question 44

stratovolcano

Answer 44

formed from lava and pyroclastic material; forms a more traditionally recognized, steeply sided volcano

Question 45

example of stratovolcano

Answer 45

Mt. Fuji, Japan

Question 46

cinder cone (or tephra cone)

Answer 46

formed from pyroclastic material; similar shape as stratovolcanoes, but tends to be smaller

Question 47

example of cinder cone (tephra cone) volcano

Answer 47

Cerro Negro, Nicaragua

Question 48

caldera

Answer 48

large crater formed when a volcano collapses into a massive, partially emptied underlying magma chamber

Question 49

example of a caldera

Answer 49

Crater Lake, Oregon

Question 50

when a large crater is left behind after an eruption,

Answer 50

the volcano has collapsed into the magma chamber (not blasted away)

Question 51

volcanic hazards

Answer 51

lava flows, explosive eruptions, lahars, tsunami, dangerous gas release

Question 52

lava flows

Answer 52

mostly a hazard to property since most flows are slow enough, or channeled enough to give time to get out of the way

Question 53

explosive eruptions

Answer 53

the primary danger in an explosive eruption is the formation of a pyroclastic flow

Question 54

pyroclastic flow

Answer 54

a dense cloud of super-heated tephra and air that flows at high speed down the side of a volcano; these events are also referred to as incandescent avalanches

Question 55

two stories of historic pyroclastic flows

Answer 55

Mt. Pelee in Martinique (1902) and Mt. Vesuvius in Italy (79 AD)

Question 56

Martinique is one of the islands in a volcanic arc formed by

Answer 56

the convergence of two oceanic plates

Question 57

Mt. Vesuviius is associated with a

Answer 57

subduction zone

Question 58

iahars

Answer 58

mudflow of tephra and water; similar to flowing, wet cement; they flow with great force down slopes and in stream channels, knocking over structures in their path and burying lowlands in thick deposits of debris

Question 59

tsunami

Answer 59

a huge wave caused by a sudden displacement of water in a large body of water (used to be called a “tidal wave”)

Question 60

If a volcano erupts violently under water in the ocean or other large water body, it will displace a large volume of water above it that will trigger

Answer 60

a tsunami

Question 61

dangerous gas release

Answer 61

volcanic emissions do include noxious sulfur gases, but the most deadly release in recorded history was simply carbon dioxide

Question 62

If a volcano tends to erupt every so many years, this ? may be used to estimate the next time the volcano will erupt, though the estimate is rarely precise

Answer 62

recurrence interval

Question 63

early warning signs

Answer 63

seismic monitoring, ground deformation (tilt & expansion), water or ground temperature changes, changes in gas emissions (such as SO2 or HCl)

Question 64

seismic monitoring

Answer 64

watching for increased number or intensity of earthquakes

Question 65

ground deformation, tilt & expansion

Answer 65

as magma rises, the volcano expands and the slope angle increases

Question 66

as signs of volcanic activity increased, the ? got smaller and smaller until it was down to a few days

Answer 66

prediction window