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Week 8 Flashcards

1
Q

where are volcanoes generally found?

A

most volcanoes are located near plate boundaries

approximately 65% of all volcanoes are found along the “ring of fire” surrounding the Pacific Ocean

subduction zones and mid-ocean ridges allow molten rock to reach the surface

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2
Q

differentiate between magma and lava

A

magma
—- found deep within the crust and upper mantle

lava
—- found flowing from an erupting volcano

essentially, lava is magma on the Earth’s surface

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3
Q

what is the most abundant element in magma? why is this relevant?

A

silicon and oxygen – when combined, it is referred to as silica

volcanic rocks are named based on the amount of silica present

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4
Q

what are the types of volcanic rocks?

A

note, volcanic rocks are named based on the amount of silica present

in order of silica content, least to greatest

basalt (least silica)

andesite

dacite

rhyolite (greatest amt of silica)

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5
Q

what is viscosity?

A

liquid’s resistance to flow

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6
Q

what determines magma’s viscosity?

A

the silica content and temperature

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7
Q

what gases are found in magma?

A

water vapour

CO2

sulphur dioxide

note, only small amounts of these are found in magma

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8
Q

what determines the shape of volcanoes?

A

it is based on the chemistry and viscosity of their magma

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9
Q

differentiate the characteristics of magma with high silica content and low silica content

A

high silica content
—- cooler, more viscous, more gases
e.g. rhyolite and dacite

low silica content
—- hotter, less viscous, fewer gases
e.g. basalt and andesite

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10
Q

what volcanoes produce the explosive eruptions?

A

the ones with high silica content

as magma approaches the surface, the pressure lowers allowing the gases to bubble up and escapes

rhyolitic and dacitic magmas produce explosive eruptions

basaltic and andesitic magmas produce non-explosive eruptions with lava that flows easily

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11
Q

what are the 4 types of volcanoes?

A

the classification is based on their shape, appearance, and eruption style

shields

composite

volcanic dome

cinder cone

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12
Q

describe shield volcanoes

A

the largest volcanoes on Earth and are shaped as broad arcs (like warrior shields) built from lava

they are associated with basaltic magma

eruptions consist of well-flowing lava

some eruptions can contain tephra which can accumulate into pyroclastic deposits and then compact into pyroclastic rocks

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13
Q

what is a tephra?

A

fragmented material blown out during an eruption

e.g. pieces of rock / ash

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14
Q

what are pyroclastic deposits?

A

accumulations of tephra

eventually, these pyroclastic deposits will compact together into pyroclastic rock

note, tephra are fragmented material blown out during an eruption e.g. pieces of rock, ash

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15
Q

where can shield volcanoes be found?

A

common in Hawaii, Iceland, and around the Indian Ocean

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16
Q

what are composite volcanoes?

A

these volcanoes are cone-shaped and are built from a combination of lava flows and pyroclastic deposits

they are also called stratovolcanoes; this term comes from the stratified layer of lava and deposits

eruptions are more dangerous and explosive but less frequent than shield volcanoes

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17
Q

where are composite volcanoes commonly found?

A

along the west coast from Alaska to Northern California

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18
Q

what are the most well known composite volcanoes in North America?

A

Mt. Rainier, Mt. St. Helens (both in Washington State) and Mt. Adams in Oregon

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19
Q

what are volcanic domes?

A

these volcanoes contain highly viscous rhyolite magma

they are steep-sided mounds that form around vents

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20
Q

what are cinder cone volcanoes?

A

relatively small volcanoes composed of small forms of tephra

they are round to oval-shaped and typically contain a crater at the top

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21
Q

where are cinder cone volcanoes found?

A

in Mexico

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22
Q

what are maars?

A

a circular volcanic crater produced by an explosion and filled with water

they are caused by groundwater encountering magma, creating the explosion

maar is derived from the Latin word, mare, meaning sea, and it resembles a lake

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23
Q

what are ice-contact volcanoes?

A

some volcanoes erupt beneath or alongside glaciers

these eruptions melt huge quantities of ice producing floods known as jokulhlaups

when lava contacts glaciers, it quickly cools to form pyroclastic rock

ice-contact volcanoes are found in Iceland and British Columbia

24
Q

what is an example of an ice-contact volcano?

A

evidence of the Mt Garibaldi eruption 12,000 years ago in British Columbia is preserved in currently exposed rock

25
what are craters?
a depression formed by the explosion of a volcano top. they can be up to 2km in diameter
26
what is a volcanic vent?
an opening on the surface thru which lava pyroclastic debris erupt most vents are circular, but some are elongated cracks called fissures
27
what are fissures?
a volcanic vent that is an elongated crack instead of circular volcanic vent: an opening on the surface thru which lava pyroclastic debris erupt
28
what is a caldera?
a circular to oval depression formed during the collapse of a volcano they can be up to 25 km in diameter eruptions that form calderas are the largest and most deadly eruptions on Earth
29
how are calderas formed?
calderas are formed by the collapse of a magma chamber below a composite volcano during an explosive eruption
30
what is a hotspring?
heated groundwater can discharge at the surface as a hotspring
31
what is a geyser?
where groundwater boils in an underground chamber to periodically produce a release of steam or water
32
where can geysers be found?
there are approximately 1000 geysers on Earth and nearly half are in Yellowstone National Park
33
what is the most famous geyser in the world? describe it
old faithful eruptions lasting for 2-3 minutes up to a height of 50 m average interval between eruptions is 70 minutes, hence the name
34
what are super eruptions?
products of supervolcanoes and are extremely rare events they occur when a large volume of magma rises to shallow depths in the continental crust over a hotspot the magma is originally unable to break thru the crust; pressure continues to build until the crust can no longer contain it can cover vast amounts of land in an ash fall
35
describe the Yellowstone supervolcano
the Yellowstone national park sits on a massive caldera created from the last eruption of the Yellowstone supervolcano the area is located over a continental hot spot the earthquakes in the park are monitored continuously a super eruption could last for weeks and spread ash over half of the US ash fall and millions of people would die from ash suffocation and the US agriculture economy would be destroyed from a super eruption
36
describe the volcanic hazard for Canada
in Canada, volcanoes are found only in BC and southern Yukon Mt. Baker in Washington provides the greatest actual risk to Canada an eruption of Mt. Baker would eject large amounts of ash over a densely populated part of British Columbia it would also cause landslides and melt glaciers, thus causing floods and lahars
37
each year, around how many volcanoes erupt?
50 - 60 volcanoes per year
38
how many human casualties have been caused by volcanoes in the past two centuries?
over 100,000 people have been killed by eruptions
39
what are the climatic effects of volcanoes?
ash and gases reflect solar radiation causing a cooling takes a few months or a year before temperatures are impacts - the disruption also doesn't last long and we bounce back
40
what are some notable eruptions that have caused climatic effects?
Mt. Tambora (Indonesia, 1815) but effects shown in 1816, worldwide, which is called a year without summer Mt. Pinatubo (Philippines, 1991) but effects shown in 1992, and it was one of the coolest years worldwide in the 20th century
41
what is a lava flow? what are the types of lava flows?
when magma flows out of a central crate or a fissure along the side of a volcano pahoehoe basaltic lava aa basaltic lava
42
what is pahoehoe basaltic lava?
a lava flow low viscosity (a few km per hour) and has high temperature when hardened, it has a smooth texture
43
what is aa basaltic lava?
a lava flow has high viscosity (a few meters per day), lower temperature when hardened, it has a block texture
44
what is a lateral blast? give an example of a lateral blast
an eruption directed away from a volcano where materials are blown parallel to the surface a lateral blast from Mt St. Helens flattened forests for over 20km
45
what is a pyroclastic flow? describe its speed
an avalanche of ash, gas, and rock fragments that travels down the slopes of a volcano during an explosive fire speeds can reach 150km/h and the flow can travel up to 30km from the source more people have been killed by pyroclastic flows than any other volcanic phenomenon
46
what volcanic phenomenon is responsible for majority of the human casualties?
pyroclastic flow
47
what is an ash fall?
particles of ash can be carried downward hundreds of kilometres from an eruption site
48
what are the hazards or negative consequences of an ash fall?
destroys vegetation contaminates surface water (ground water) health impacts to people and animals causes aircraft engine failure
49
describe the poisonous effect of volcanoes
volcanoes emit numerous gases at high quantities eruptions containing sulphur dioxide can burn holes in leaves and lead to the formation of acid precipitation a type of smog known as vog can be produce; this can induce asthma attacks and respiratory problems high amounts of CO2 released as once can kill animals and vegetation
50
what is vog?
a type of smog that can be produced by volcanoes / volcanic gases this may induce asthma attacks and respiratory problems
51
what is a sector collapse?
when the flank of a volcano collapses at any time as magma travels up an inner channel, the volcano can form a bulge where its slopes have become over-steepened
52
what is a lahar?
a large amount of material that has become saturated with water and moves downslope lahars are also referred to as mudflows
53
what can be used to determine the recurrence intervals (frequency) of lahars?
knowledge of local topography and the history of past events
54
describe Mt St. Helen's eruption in 1980. how it occurred and its effects
before its eruption, the volcano has been dormant for 120 years in March 1980, small explosions occurred due to groundwater contacting magma a bulge began growing on the flank of the mountain on May 18, 1980, a M5.1 earthquake caused the bulge to break off and fall downslope a lateral blast occurred from the area of the former bulge and the entire north slope was destroyed ash was ejected from the central crater, reached heights of 19km and travelled around the world it killed 57 people, mainly from pyroclastic flow the eruption left behind a barren landscape that is slowly reforesting naturally
55
what are the natural service functions of volcanoes?
ancient volcanoes provided the gases that now form the atmosphere and sustain life on Earth internal heat from volcanoes can produce geothermal energy volcanic landscapes attract tourism and recreation eruptions have created new land (Hawaii, Iceland)
56
how can volcanic hazards be minimized?
via an eruption forecast, a statement containing the probability that a volcano will erupt within a given timespan
57
what information is used for eruption forecasting (volcanoes)?
monitoring of the following... seismic activity ---- shallow earthquakes can precede eruptions ---- but short warning times from this information are concern thermal and hydrologic ---- an accumulation of magma changes properties of the rock and soil ---- increased heat may melt snow or glaciers above land surface ---- involves checking for growth of bulges, swelling, and opening of cracks volcanic gas emissions ---- increases in CO2 or sulphur dioxide may indicate magma is moving towards the surface local geologic histoy ---- mapping of volcanic rocks ---- dating of pyroclastic deposits

GEO (19 decks)

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