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Geo of Hazards > Lecture #8 -Volcanoes > Flashcards

Lecture #8 -Volcanoes Flashcards

1
Q

Where are most volcanoes occur?

A

Located near plate boundaries

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2
Q

What is Magma?

A

liquid rock found deep within the crust and upper mantle

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3
Q

What is Lava?

A

Liquid rock found drown for and erupting volcano (basically magma the reaches earths surface)

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4
Q

What are the most abundant elements in magma?

A

Silica and Oxygen

-together they form silica

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5
Q

What is the order of rocks from lowest to highest

A

Basalt
Andesite
Dacite
Rhyolite

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6
Q

What does a higher silica content produce?

A

a bigger explosion

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7
Q

What determines the shapes of volcanoes?

A

Chemistry and viscosity of magma

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8
Q

What are characteristics of magma with a high silica content?

A

Cooler
More viscous
More gases
explosive eruption

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9
Q

What are characteristics of magma with a low silica content?

A

Hotter
less viscous
Fewer gases
not as explosive

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10
Q

What are the 4 types of Volcanoes?

A
  1. Shield
  2. Composite
  3. Volcanic Domes
  4. Cinder Cones
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11
Q

Characteristics of Sheild Volcanoes

A

Form from lava(erupts, cools hardens)
basaltic magma
Not really explosive

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12
Q

What is Tephra?

A

A general term for fragmented material ejected during an explosion

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13
Q

Characteristic of Shield Volcanoes?

A

Form from lava flow and pyroclastic deposits
Andesitic or Dacitic
Eruptions more explosive but less frequent

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14
Q

Characteristics of Volcanic Domes?

A

Highly viscous rhyolitic magma

Steep sided mounts that form around vents

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15
Q

Characteristics of Cinder Cone volcanoes

A

smaller volcanoes made from small pieces of tephra
Round–> oval Shape
Contain a crater at the top of the volcanoe

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16
Q

What is a Maars?

A

Circular volcanic craters produced by an explosive eruption and fill with water

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17
Q

What Causes Maars?

A

When groundwater comes into contact with magma which creates an explosion

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18
Q

What are Ice Volcanoes?

A

When volcanoes erupt beneath or against glaciers

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19
Q

What do Ice volcanoes produce?

A

jökuhloups

-when magma melts large quantities of ice and produce floods

20
Q

What is a crater?

A

Depression formed by the explosion or collapse of a volcano top.
-up to 2km in diamerter

21
Q

What is a volcanic vent?

A

An opening on the surface through which lava and pyroclastic debris erupt.

22
Q

Does lava always erupt out of the top?

A

No, can erupt from fissures in the side

23
Q

what is a Caldera

A

Circular to oval depression formed during the collapse of a volcano.
-Up to 25km in diameter

24
Q

How do calderas form?

A

The collapse of a magma chamber below a composite volcano during an explosive eruption. The chamber become empty and pressures decreases so it doesn’t have the support and therefore collapses

25
Q

What is a hot spring?

A

Heated groundwater that discharges at the surface

26
Q

What is a geyser?

A

ground water that boils in an underground chamber and periodically produce a release of steam or water

27
Q

When does Old faithful erupt?

A

Found in Yellowstone National Park
Erupts for 2-3 mins
every 70 mins
50m high

28
Q

what are Super eruptions

A

Are the products of super volcanoes and are hella rare

-occur when a high volume of magma rises and is unable to break though the crust until enough pressure builds up

29
Q

Subduction Zone volcanoe characteristics

A

Andesite

Composite volcanoes found here

30
Q

Mid ocean ridge volcano characteristics

A

Basaltic

Shield volcanoes

31
Q

Characteristics of volcanoes at hot spots beneath the ocean

A

Basaltic
Chains of Shield Volcanoes
-Islands

32
Q

Characteristics of volcanoes at hotspots beneath continental crust

A

Rhyolitic
Explosive eruptions
Commonly forms Claderas
Ex: Yellowstone

33
Q

Why arent death tolls higher for volcanoes?

A

They occur in high mountain ranges and not a lot of people live there

34
Q

What are some primary effects of volcanoes

A

Lava flows
pyroclastic flow
Ash falls
lateral blasts

35
Q

What are some secondary effects of volcanoes?

A 
Landslides
Floods
Fires 
Tsunamis
Lahars
36
Q

What is Pahoehoe lava?

A

low viscosity
Really hot
When hardened has a smooth texture

37
Q

What is AA lava?

A

High viscosity
lower temperatures
When hardened has a blocky texture

38
Q

What is a Pyroclastic Flow?

A

Avalanches of ash, gas and rock fragments that travel down the slope of a volcano during an explosive eruption
- more people have actually died form these than an actual explosion

39
Q

What is an Ash fall?

A

particles of ash can be carried downwind hindered of km form the eruption site

40
Q

What is a Sector Collapse?

A

Flank of volcanoes can collapse at any time

-as magma travels up the channel, it can inflate and its slopes can be oversteepened

41
Q

What is a Lahar?

A

Large amount of material that become saturated with water and moves downslope

42
Q

Characteristics of Mt St Helen?

A

March 1980

  • small explosions were evident due to ground water contacting magma
  • Bulge began to grown on the flank of the mountain
  • M 5.1 quake caused the bulge to break off
  • Lateral blast occurred
  • 57 people died mainly because of pyroclastic flows
  • left behind a barren landscape
43
Q

What other hazards can volcanoes cause?

A
  • Lava can catch things on fire
  • Earthquakes
  • Landslide
  • Jökulhaups
44
Q

What are natural service functions of volcanoes?

A

Provided gases that sustain the atmosphere
Geothermal energy and heat
Attract tourism and recreation
Creates new land

45
Q

How do we minimize Volcanic hazards?

A
  1. Monitoring seismic activity
  2. Thermal and hydraulic monitoring
  3. Land Surface monitoring
  4. Monitoring volcanic gas emissions
  5. understanding local and geologic history
46
Q

What are the 3 methods in attempting to divert lava flows?

A
  1. Bombing- forcing channel to an alternate rout
  2. Hydraulic Chilling- water used to chill and cool lava
  3. wall Construction- Wall redirecting

Geo of Hazards (12 decks)

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