(MODULE 7.2) GEOLOGICAL HAZARDS - VOLCANIC ERUPTIONS

Question 1

a mountain that forms when molten rock (magma) reaches the surface of the earth

Answer 1

volcano

Question 2

volcanoes are formed when ___.

Answer 2

magma forces its way through a crack in the earth’s crust.

Question 3

a volcano is classified as ___ if it erupts lava, rock, gas, or ash, or if it shows seismic activity.

Answer 3

active

Question 4

a volcano is ___ if it hasn’t erupted for a long time (less than 1 million years) but could erupt again one day.

Answer 4

dormant

Question 5

an ___ volcano will never erupt again.

Answer 5

extinct

Question 6

indicate the parts of a volcano

Answer 6

1. crater
2. vent
3. cone
4. conduit
5. magma chamber

Question 7

the opening from which lava flows. dust, ash, and rock particles can also be thrown out of it.

Answer 7

vent

Question 8

the pile of lava, dust, ashes, and rock around the vent; can be found in different shapes

Answer 8

cone

Question 9

the top of the volcano; it is a funnel shaped pit formed when the material explodes out of the vent.

Answer 9

crater

Question 10

some volcanoes have very large circular depressions called ___, that have diameters greater than 1 kilometer.

Answer 10

calderas

Question 11

a passageway followed by magma in a volcano.

Answer 11

conduit

Question 12

the subterranean cavity containing the gas-rich liquid magma which feeds a volcano

Answer 12

magma chamber

Question 13

volcanoes are classified by ___.

Answer 13

how they are formed

Question 14

this type of volcano is wide and somewhat flat, between 2 to 10 degrees.

Answer 14

shield volcano

Question 15

what are the characteristics of a shield volcano?
1.
2.
3.
4.

Answer 15

1. it is wide and flat
2. it is constructed of solidified lava flows
3. it forms from a quiet eruption
4. lava flows out quietly and for great distances because the shield volcano doesn’t have a long conduit

Question 16

this type of volcano has a tall, very sleep slope

Answer 16

cinder cone volcano

Question 17

what are the characteristics of a cinder cone volcano?
1.
2.
3.
4.

Answer 17

1. it has a tall, very steep slope
2. it is constructed of ejected pyroclastic fragments
3. it has explosive eruptions due to its long conduit
4. eruptions from cinder cone volcanoes produce a lot of cinder and ash

Question 18

this volcano is of intermediate steepness and constructed of alternating layers of pyroclastic fragments and solidified lava flows

Answer 18

composite volcano

Question 19

what are the characteristics of a composite volcano?
1.
2.
3.

Answer 19

1. it is constructed of alternating layers of pyroclastic fragments and solidified lava flows
2. it is built over long spans of time because eruption is intermittent
3. it has intermediate steepness; slope is less than 33 degrees

Question 20

why does a volcano erupt?

Answer 20

a volcano erupts when magma and gases find a way to escape and burst to the surface through a vent.

since magma is buoyant, it rises up through the curst to erupt on the surface.

Question 21

there are two factors that determine eruption patterns:
1.
2.

Answer 21

1. the amount of gas in the lava or magma
2. the ease or difficulty with which the gas can escape into the atmosphere (viscosity)

Question 22

___ is how thick and gloopy a material is. an example of such material is honey in room temperature.

Answer 22

viscosity

Question 23

the ___ viscous the lava and the ___ the volume of gas trying to escape, the ___ the eruption.

Answer 23

1. more
2. greater
3. more violent

Question 24

the three factors that influence viscosity of lava or magma are:
1.
2.
3.

Answer 24

1. the silica content
2. the temperature
3. gas dissolved in magma

Question 25

the silica content of lava ranges from ___ to ___ by weight.

Answer 25

45% to 75%

Question 26

___ rocks are silica-rich (>65% silica)

Answer 26

felsic

Question 27

___ rocks are silica-deficient (~50%)

Answer 27

mafic

Question 28

mafic lavas which are silica-deficient tend to ___.

Answer 28

flow easily

Question 29

felsic lavas which are silica-rich are ___ and tend to ___.

Answer 29

much more viscous; flow sluggishly

Question 30

temperatures at which lavas solidify range from about ___ for felsic rocks to ___ for mafic rocks.

Answer 30

1. 700 C 2. 1,200 C

Question 31

if the lava being extruded is considerably hotter than its solidification temperature, the lava is ___ than when its temperature is near its solidification point.

Answer 31

less viscous (more fluid)

Question 32

water vapor dissolved in magma tends to increase fluidity because ___.

Answer 32

it reduces formation of long silicate chains by breaking silicon-oxygen (silicate) bonds.

Question 33

the loss of gases renders magma ___.

Answer 33

more viscous

Question 34

there are two types of eruption patterns, namely: 1. 2.

Answer 34

1. explosive eruption 2. effusive eruption

Question 35

caused by large amounts of gas and high viscosity magma, this is the most violent eruption of all due to the gases and magma trapped in the volcano.

Answer 35

explosive eruption

Question 36

this eruption pattern is characterized by outpourings of lava onto the ground. described as quiet and gentle, the eruptions contain small amounts of gas and/or low viscosity magma. the lava is very runny and can move fast.

Answer 36

effusive eruption

Question 37

most of the gas released during eruptions is ___, which condenses as steam.

Answer 37

water vapor

Question 38

collectively regarded as extrusive igneous rock or surface rock resulting from volcanic activity.

Answer 38

tephra

Question 39

when magma solidified quickly as it was blasted explosively by gases into the air, it produces rock fragments known as ___.

Answer 39

pyroclasts

Question 40

types of volcanic hazards: 1. 2. 3. 4.

Answer 40

1. pyroclastic fall 2. pyroclastic flow 3. volcanic mudflows 4. volcanic lightning

Question 41

the fallout of rock, debris and ash from an explosive eruption column

Answer 41

pyroclastic fall

Question 42

most of the deaths due to pyroclastic fall are caused by ___ or ___.

Answer 42

1. collapse of ash-covered roof 2. being hit by falling rock fragments

Question 43

a mixture of hot gas and pyroclastic debris that rapidly flows down a volcano's flanks

Answer 43

pyroclastic flow

Question 44

characteristics of pyroclastic flows 1. 2. 3.

Answer 44

1. they can reach over 100 km distances from a volcano 2. they can travel 100 km/h 3. temperature is > 400C

Question 45

pyroclastic flows can happen ___ or ___ the eruption

Answer 45

before or after

Question 46

a flowing mixture of soil, fine pyroclastic debris, and water from heavy rains

Answer 46

volcanic mudflows or lahars

Question 47

this volcanic hazard is generated by tiny particles of rocks thrown out by the volcano. the ash causes friction that generates an electrical charge.

Answer 47

volcanic lightning