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Natural Disasters > Lecture 4 > Flashcards

Lecture 4 Flashcards

1
Q

Where are most volcanoes found?

A
  • located near plate boundaries
  • 2/3 of all volcanoes are found on 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

What is magma?

A

-it is found deep within the crust and upper mantle

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3
Q

What are cinder cone volcanoes?

A
  • these are relatively small volcanoes composed of small pieces of tephra
  • they are around to oval-shaped and typically contain a crater at the top
  • these volcanoes are found in Mexico
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4
Q

What is lava?

A
  • it is found flowing from an erupting volcano
  • lava is magma on the Earth’s surface
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5
Q

What are the components of magma?

A
  • the most abundant elements in magma are silicon and oxygen; when combined they are referred to as silica
  • volcanic rocks are named based on the amount of silica present
  • types of volcanic rocks: basalt, andesite, dacite, rhyolite (low silica–> high silica)
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6
Q

What is magma viscosity determined by?

A
  • contains small amounts of gases (water vapour and CO2)
  • volcanoes have different shapes based on the chemistry and viscosity of their magma
  • magma viscosity is determined by silica content and temperature
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7
Q

What are characteristics of magma with high silica content?

A
  • cooler
  • more viscous
  • more gases
  • produce the most explosive eruptions
  • as magma approaches the surface the pressure lowers allowing gases to bubble up and escape
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8
Q

What are characteristics of magma with low silica content?

A
  • hotter
  • less viscous
  • fewer gases
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9
Q

What kind of eruptions do rhyolitic and dacitic magma produce?

A

-explosive eruptions

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10
Q

What kind of eruptions do basaltic and andesitic magmas produce?

A

-eruptions that tend to flow rather than explode

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11
Q

What is a shield volcano?

A
  • largest volcanoes on Earth and are shaped as broad arcs built from lava
  • they are associated with basaltic magma
  • eruptions are non-explosive and consist of gentle flows
  • some eruptions contain tephra
  • accumulations of tephra are referred to as pyroclastic deposits; if compacted together these deposits are called pyroclastic rock
  • common in Hawaii, Iceland, and around Indian Ocean
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12
Q

What are composite volcanoes?

A
  • cone-shaped and are built from a combination of lava flows and pyroclastic deposits
  • also called stratovolcanoes; comes from layers of lava and deposits
  • eruptions are more dangerous and explosive but less frequent than shield volcanoes
  • common along west coast from Alaska to Oregon
  • Mt.Rainier and Mt. St. Helens are the most well known composite volcanoes in NA
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13
Q

What are volcanic domes?

A
  • contain highly viscous rhyolite magma
  • steep-sided mounts that form around vents
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14
Q

What are maars?

A
  • circular volcanic crater produced by an explosive eruption and filled with water
  • they are caused by groundwater coming in contact with magma creating an explosion
  • Maar derives from Latin “mare” meaning sea and resembles a large lake
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15
Q

What are ice-contact volcanoes?

A
  • some volcanoes erupt beneath or against 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 BC
  • evidence of the Mt. Garibaldi eruption 12000 years ago in BC is preserved in currently exposed rock
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16
Q

What is a crater?

A

-a depression formed by the explosion of a volcano top; they can be up to 2km in diameter

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17
Q

What is a volcanic vent?

A
  • an opening on the surface through which lava and pyroclastic debris erupt
  • most vents are circular but some are elongated cracks called fissures
18
Q

What is a caldera?

A
  • a circular to oval depression formed during the collapse of a volcano
  • they can be up to 25km in diameter
  • eruptions that form caldera are the largest and most deadly eruptions on Earth
19
Q

How do calderas form?

A

-collapse of a magma chamber below a composite volcano during an explosive eruption

20
Q

What is a hot spring? What is a geyser?

A

hot spring: heated groundwater can discharge at the surface as a hot spring

geyser: groundwater that boils in an underground chamber to periodically produce a release of stream or water
- approx 1000 geysers on Earth and nearly half are located in Yellowstone National Park

21
Q

What is Old Faithful?

A
  • most famous geyser in the world
  • erupts to a height up to 50m with eruptions lasting for 2-3 minutes
  • the average interval between eruptions is 70 minutes
22
Q

What are super eruptions?

A
  • products of supervolcanoes and are extremely rare events
  • supervolcano: a volcano capable of producing an eruption with ejected material covering thousands of square km with a lot of ash, can wipe out cities, crop land
  • occur when a large volume of magma rises to shallow depths in the continental crust over a hot spot
  • the magma is unable to break through the crust; pressure builds until the crust can no longer contain it
23
Q

Describe the Yellowstone Supervolcano

A
  • 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
  • super eruptions occurred 2.2 million years ago, 1.3 million years ago, and 640 000 years ago
  • super eruption could last for weeks and spread ash over half of the US- would be over 1000 times the ash fall released by Mt St Helens
  • millions would die from ash suffocation and US agriculture would be destroyed
24
Q

What is the dominant volcanic rock and where does it originate?

A
  • andesite that originates from a melting tectonic plate
  • composite volcanoes are found at these locations
  • over 80% of volcanic eruptions are above subduction zones (ex: cascade mountains)
25
Q

Where are shield volcanoes found (in terms of plate tectonics)?

A
  • mid ocean ridges
  • these are composed of basaltic magma that originates in the athenosphere
  • shield volcanoes are found at these locations
    ex: Iceland
26
Q

What results from hot spots beneath oceans?

A
  • chains of shield volcanoes containing basaltic magma form as a plate moves over a hot spot
  • ex: Hawaiian Islands
  • island of Hawaii is still near the hot spot and contains active volcanoes
  • volcanoes on Oahu and Maui are no longer active
27
Q

What do hot spots beneath continents result in?

A
  • produce explosive eruptions composed of rhyolitic and dacitic magma
  • eruptions often result in the formation of calderas
  • ex: Yellowstone National park
28
Q

Where are volcanoes in Canada?

A
  • generally restricted to BC and southern Yukon
  • Mt Baker in Washington State provides the greatest actual risk to Canada
29
Q

What are primary effects of volcanoes?

A

-lava flows, lateral blasts, pyroclastic flows, ash fall, poisonous gases, sector collapse

30
Q

What are secondary effects of volcanoes?

A

-landslides, floods, fires, tsunamis, and lahars

31
Q

How are volcanic eruptions measured?

A
  • Volcanic Explosivity Index (VEI)
  • scale ranges from 0-8 and is based on tephra ejected
  • logarithmic scale
  • no VEI 8 eruption has likely occurred in the last 10 000 years
  • Yellowstone was VEI 8 and Mt St Helens was VEI 5
32
Q

How can volcanoes affect climate?

A
  • powerful eruptions can impact global climate
  • ash and gases reflect solar radiation causing a cooling
  • notable eruptions impacting climate:

Mt Tambora (1815) Indonesia- 1816 is known worldwide as the year without summer

Mt Pinatubo (1991) Philippines- 1992 is one of the coolest years worldwide in the 20th century

33
Q

What are lava flows? What are the types of lava?

A
  • these occur when magma flows out of a central crater or a fissure on the side of a volcano
  • pahoehoe basaltic lava: low viscosity (a few km/hr), high temperature, when hardened it has a smooth texture
  • aa basaltic lava: high viscosity (few metres per day), low temperature, when hardened it has a blocky texture

Found in Hawaii

34
Q

What are lateral blasts?

A
  • an eruption directed away from a volcano where materials are blown parallel to the surface
  • ex: a lateral blast from Mt St Helens flattened forests for over 20km
35
Q

What are pyroclastic flows?

A
  • pyroclastic flows are avalanches of ash, gas, and rock fragments that travel down the slopes of a volcano during an explosive eruption
  • speeds can reach 150km/h and the flow can travel up to 30km from the source
  • most people have been killed by pyroclastic flows than any other volcanic phenomenon
36
Q

What is ash fall? What are hazards of ash fall?

A
  • particles of ash can be carried downwind hundreds of kms from an eruption site
  • destroys vegetation, contaminates surface water, health hazards to people and animals, causes aircraft engine failure
37
Q

What is sector collapse?

A
  • the flank of a volcano can collapse at any time
  • as magma travels up the channel, the volcano can inflate and its slopes can become steepened
38
Q

What are lahars?

A
  • large amounts of material that become saturated with water and move downslope
  • also referred to as mudflows
  • explosive eruptions can destroy nearby vegetation therefore enhancing the risk from lahars
39
Q

What occurred at the beginning of Mt St Helens eruption?

A
  • before its eruption, the volcano had been dormant for 120 years
  • in march 1980 small explosions were evident due to groundwater contacting magma
  • a bulge began growing on the flank of the mountain
40
Q

What triggered Mt St Helens eruption?

A
  • M 5.1 earthquake on May 18 1980 caused the area of the bulge to break off and fall downslope
  • a lateral blast occurred from the area of the formed bulge and the entire north slope was destroyed
  • ash was ejected from the central crater, reached heights of 19km, and travelled around the world
  • did not affect climate
  • killed 57 people mainly from pyroclastic flows
  • left behind barren landscape that is slowly reforesting naturally
41
Q

What are natural service functions of volcanoes?

A
  • ancient volcanoes provided the gases that now form the atmosphere and sustain life on Earth
  • internal heat from volcanoes can produce renewable geothermal energy
  • volcanic soils can be good for agriculture since they are porous, well-drained, and contain nutrients
  • volcanic landscapes attract tourism and recreation
  • eruptions have created new land (Hawaii, Iceland)
42
Q

What is usually the first sign of an impending volcanic eruption?

A

-small earthquakes

Natural Disasters (11 decks)

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