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EOSC 114 > Volcanos > Flashcards

Volcanos Flashcards

1
Q

What are volcanos?

A

Magma and gas leaking out from earth’s crust and or mantle

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2
Q

How do volcanos form?

A

magma is melted pre-existing rock below earth’s surface, reaching surface through fractures.
Extrudes as lava
Explodes as pyroclastic material

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3
Q

What are the rocks formed from magam?

A

Basalt: extrusive rock that cools fast in the outside bits
Granite: plutonic/intrusive rock that cools before reaching surface

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4
Q

What are the two types of igneous rocks?

A

Volcanic

Plutonic

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5
Q

What is extrusive vs. intrusive?

A

extrusive: quick cooling, small crystals
intrusive: slow cooling large crystals

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6
Q

What are the 4 parts of the volcanic system?

A

Source region: deep in mantle or crust
Transport region: bring to storage/surface (i.e. the crust)
Storage region
Eruption

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7
Q

Describe the source region. What is the difference in melted mantle rocks?

A

Deep, hot, mantle rocks
Mantle (peridotite 33– kgm3)
this melts into..
Magma (basaltic-granite 2700-2500 kgm3)

when this melts density decreases to form magma which is less dense and therefor RISES

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8
Q

Describe the transport region.

A

magma moves along cracks in earth’s crust forming
DIKES: vertical intrusion that cut through older rock, often basaltic
SILLS: horizontal intrusion of magma

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9
Q

Describe the storage region of the crust?

A

Where magma accumulates in weak crusty bits

- stored in chambers

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10
Q

Describe the eruptive region

A

Active volcano! Explosive or Effusive

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11
Q

Why was the Kilauea volcano in hawaii so damaging?

A

the volume they thought there was going to be was 10x higher because ppl focused on the lake but below there was a huge reservoir
- flowed for 5 months

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12
Q

What are the properties of magma?

A
  1. Density: magma is about 3g/cm3
    crust: 2.7-3.3
    mantle: 3.3-5.7 (we know densities because of earthquakes and velocity of seismic waves are different depending on material that made them)
    Magma is often less dense and will rise to crust
  2. Viscosity: 10-10^15 Pas, resistant to flow, causes eruption style
    dependant on TEMP, GAS, CRYSTAL content
  3. Silica content: high vs. low
    Felsic: high silica
    Mafic: low silica
  4. Magma temp:
    Hot: low viscosity, low silica (mafic)
    Cool: high viscosity, high silica (felsic)
  5. Gas/volitiles: dissolved gas (H20,CO2,SO2)
    When magma rises, there is less pressure and less solubility leading to BUBBLES=explosion
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13
Q

Which lava is more viscous? Rhyolite or andeside?

A

rhyolite

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14
Q

describe mafic and felsic?

A

felsic: light colour, 65-75% silica, k, na, al, si, high viscosity, 4-6% volitiles
i. e. granite/rhyolite

mafic: 45-55% silica, dark, Mg, Fe, low viscosity, 0.1-1% volitiles
i. e. Gabbro, Basalt

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15
Q

How does composition differ through different rock types? (name 4)

A

Basalt, Andesite, Dacite, Rhyolite

Dark, mafic, hot, low viscosity, non explosive
»>
Light, felsic (more silica), cooler, high viscosity, explosive

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16
Q

Why does viscosity matter?

A

Think pahoehoe and a’a, same basalitic composition but different flow!

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17
Q

What determines explosivity?

A

Mafic: low gas content, low viscosity = effusive
felsic: high gas, high viscosity =explosive

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18
Q

Where do volcanos occur?

A

Plate boundaries
- spreading ridges, subduction zones
Hotspots

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19
Q

What are volcanos at mid-oceanic ridges like?

A

Biggest, most volume, not exposed at earth surface (except in iceland because of a hotspot), divergent boundaries

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20
Q

What are the charictaristics of continental volcanic arcs?

how about a oceanic volcanic arc?

A

subduction volcanos, with mafic magma at the bottom, felsic magma in chambers and felsic/intermediate magmas/lavas closest to the top

local: Subduction of juan de fuca under north american plate (cascadia subduction zone, with Mt Baker, mt. st helens, mazama, mt. shasta)

OCEANIC: two oceanic plates converging, mafic magmas at bottom AND the top

  • results in effusive expulsion
    i. e. western aleutian arc, cleveland, pavlof
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21
Q

Describe hot spots

A

Mafic magmas from a plume (stationary, pulsatory) of hot magma
-islands chains are created this way

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22
Q

make a table from volcano settings/mechanisms/magma types from lecture 2!

A

DO IT

LECTURE 2, HALFWAY DOWN

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23
Q

What are the different types of volcanoes?

A
  1. Cinder cones: mafic/explosive
  2. Shield volcanos: mafic, non explosive
  3. Stratavolcanos: intermediate, felsic, mixed
  4. Calderas: felsic, explosive
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24
Q

Describe Cinder Cones

A

Layers of pyroclastic ejecta from FIRE FOUNTAINING
- 30-40 degree angle of repose, small volcanos that don’t grow up
usually erupt a few years then go dormant
2km by 500m

i.e. paracutin/mexico, elfin lakes/opan cone, garibaldi park

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25
Q

Describe Shield Volcanoes?

A 
Lava erupts from fissure, runs down gentle slopes, cooling
erupts ofen, 
mafic lava flows, 
not super explosive
100km by 4-10km

i.e. mauna loa hawaii

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26
Q

Describe Stratavolcanos

A

Interbedded lava flows, pyroclastic flows, lahars, intermediate/felsic
explosive frequently
may erupt many times and stay active for a long time
10 km by 5km

i.e. mt. st. helens, garabaldi, baker
shasta, fuji

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27
Q

Describe Calderas

A

Large, explosive eruptions of felsic pyroclastic material, created when roof of magma chamber collapses, up to 10 km across, different from a crater!!!!
**

i.e. yellowstone, wyoming, crater lake

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28
Q

What are the two main styles of eruption?

A

Effusive: outpouring of molten magma from the vent (lavas)

Explosive: gas driven violent eruptions (pyroclastic deposits)

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29
Q

What are the different types of effusive eruptions?

A

Passive,

  1. Lava flows: mafic-intermediate
  2. Lava domes: felsic - intermediate
  3. Gravitational collapse of lava flows/domes - pyroclastic flows

the higher the silica, higher the viscosity

30
Q

What are lava flows?

A

Flows downslope, ponds in topographic lows, outer crust cools and solidifies, insulating molten interior

31
Q

What are the different types of explosive eruptions?

A
  1. Buoyant eruption column of ash
  2. Pyroclastic airfall
  3. Pyroclastic flow (column collapse)
  4. Blocks/bombs close to the vent
32
Q

Describe pyroclastic falls

A

10s of kms eruption column
Widespread distribution of ash in downwind direction
Ash blankets everythang

33
Q

Describe pyroclastic flows

A 
Gas-pyroclast mixtures
Gravity driven
FLow down slope, channelled in valleys
velocity: 40-400 km/h
hot as fuck (600degreeccelcius)
34
Q

What are the keys to explosive volcanism?

A

Gas content and melt viscosity in the magma
- determines explosive or effusive,
as magma rises, pressure decreases, so bubbles form, but viscosity fights formation of bubbles, pressure rises in the bubbles until the strength of the liquid magma is overcome by the bubbles =producing PYROCLASTIC MATERIAL (tephra)

35
Q

Why does Gas matter in volcanism?

A
  1. Magmas produce bubbles (gas exsolves) during ascent
  2. Bubbles expand as magma rises with lower pressure
  3. Foaming = explosivity

Depends on amount of bubbles, rate of rise, bubble retention

36
Q

What is pumice?

A

Light, full of air bubbles, volcanic plume fragments

37
Q

How is pyroclastic ash formed?

A

Liquid magma containing dissolved gas is suddenly decompressed
Gas bubbles expand rapidly and blow up liquid magma
Freezes in mid air to form ash

38
Q

How is gas different in mafic/felsic magmas?

A

mafic: low gas content, fluid, gas escapes and pressure is released
felsic: high gas content, gooey, gas is kept under increasing pressuer

39
Q

What are the ranges of explosive eruptions?

A 
Hawaiian
Strombolian
Vulcanian
Plinian
Phreatomagmatic
40
Q

Describe Hawaiian Eruptions.

A 
Low viscosity
Basaltic
Low explosivity
- lava flows
- fire fountaining

important bits: lava fountain, lava lake, lava flow
(ash plume, fumaroles, ash plume)

41
Q

Describe Strombolian Eruptions

A

Basaltic/andesitic magma
Intermediate composition/silica content
Mildly explosive
- bombs/lava

important parts: lava fountain, volcanic bomb, lava flow

42
Q

Describe Vulcanian Eruptions

A

Viscous andesitic/rhyolitic magma (high silica)
Very explosive
Sustained ash

important parts: ash plume, lapilli, volcanic ash rain, volcanic bomb

43
Q

Describe Plinian eruptions

A 
Andesitic/rhyolitic ash
Violently explosive
Sustained ash colums
Pyroclastic flows
Can erupt for days

important parts: ash plume, volcanic ash rain

44
Q

What is the trend of increasingly devastating eruptions?

A

Higher viscosity, more felsic, higher gas content

45
Q

Describe Phreatomagmatic eruptions

A

Contact between water and magma
Water flashes to steam
Violently explosive
Surtseyan and Phreatoplinian

important parts: water vapour cloud, compressed ash, crater, water

46
Q

How are eruption sizes scaled?

A 
Volume of ash
Height of eruption above vent
Duration
- mostly total volume erupted EXPLOSIVELY
-1 unit = 10x more volume erupted

VEI Scale 0-8
Interval represents a factor increase of 10 (logarithmic scale)

47
Q

What are some examples of VEI 1, 3, 5? 6?

A

1: hawaiian
3: vulcanian (montserrat)
5. plinian (mt. st. helens)
6. ultra plinian (mt pinatubo)

48
Q

What was the impact of the 1991 pinatubo eruption

A

22000000 tons of SO2
global temp decreased, ozone hole size incrased
sulfer dioxide could be traced globally

49
Q

What would a VEI 8 volcanic eruption look like

A

100 pinatubos erupting at once

TOBA an Ultraplinan 75ka, caldera forming eruption. 3 degree decrease in global temp
possibly yellowstone??\

TOBA, long valley caldera, yellowstone

50
Q

what is a hazard? what is a risk?

A

HAZARD: any event or situation that could cause human or economic harm

RISK: probability that any given hazardous event might occur (chance of loss)
-includes vulnerability

51
Q

Describe Lava Flows

A 
Slow
Not usually dangerous
(usually) Mafic + low viscosity
Hazards: burning, destruction
Don't often kill but are hard to stop

i.e. Heimaey, Iceland
Nyiragongo: killed ppl

52
Q

Describe Fire fountaining

A

If Basalitic lava is gas rich
small explosions
As liquid drops back, they can form a lava flow
-forming spindle bombs

53
Q

Describe pyroclastic falls.

A

Hot gas and ash fall
Hazards: breathing ash, total darkness, rooftops collapse* ppl trying to shelter, die!
Ash getting in plane entines (suck it in) Windshields are scratched/broken
turbulence
- now satelites check for volcanic ash!
i.e. Krakatoa
Shiveluch volcano,russia

54
Q

Describe pyroclastic flows

A

Avalanche of pyroclastic material/air/gas
Gravity driven
40-400km/hour
(mt. st. helens, vesouvious)

MOST COMMON CAUSEcollapse of volcanic column
sustained fountaining in a plinian column
NEXT MOST COMMON CAUSE: explosive collapse of lava domes - silica rich magma, highly viscous, steep sided, glowing at night

If they are big enough, they move out of the valleys and can even more over water!

55
Q

What is dome collapse?

A

often followed by pyroclastic flows down a slope, with dense core of boulders hidden by ash billows

56
Q

Describe Lahars?

A

volcanic mud flows
-debris flows with the water
Lahar: indonesian for volcanic debris flow
Lahars are water and loose volcanic debris
snowclad/ice clad volcanos i.e. mt baker

57
Q

What are some hazards at mt. baker?

A

lava flows, pyroclastic flows, tephra (ash), lahars

58
Q

Describe sector collapse

A

A volcanic landslide!

-volcanic edifice is weakened, and collapse of part of the volcnao might happen, causing a debris avalanche!

59
Q

When was a key eruption for mt. st. helens? Describe it

A

1980 May 18th
Landslide triggered an eruption
Lateral blast of 100-300 degrees, speed of 500 km /hour, desvastating to a large area, trees blown down by the blast

60
Q

Describe volcanic gases

A

Volcanic gases: hot, high acidity (pH 1), burn instantly
h20, c02, hcl, so4, hf
fumarole -

examples: cameroon aftrica, crater lake in dormant volcano
1986, 1700 ppl killed by breathing it in (asphyxiation)

61
Q

What are the types of monitoring and prediction?

A

Geology and Mapping (hazard maps)
Monitering (seismology, ground deformation, gas, thermal imaging, lahar flow detection, satellite obervation)
Prediction and Hazard analysis

62
Q

What are hazard maps?

A

Map volcanic deposits
Determine deposit type (lava flow, mud flow, pyroclastic flow) and distribution
Determine age and frequency
Consider the risk (hazard/vulnerability)

63
Q

What are different monitering types and methods used by USGS volcanic hazards program?

A

Gas (airborn and ground)
Remote sensing (thermal imaging, satellite - ash hotspots and inSAR)
Ground vibration (eathquake and lahar sensors)
Deformation (tiltmeter, GPS, surveying)

64
Q

Describe seismology and how it is helpful for earthquakes

A

Most important tool for monitering and forcasting
baseline monitoring is essential to recognize changes so you know normal from abnormal behavior

when magma rises, rocks crack, causing little quakes and cracks

deep quakes are shown before big explosion

65
Q

Describe ground deformation techniques

A

As volcano bulges with magma, measure its change of shape
GPS: measure changes in position
TM: tiltmeter- measures changes in angle of slope
inSAR: interferometric synthetic aperture rador - measurements by satellites to detect changes in elevation (equation creates a time delay) volcanos change shape during intrusion of magma

often equiptment is destroyed but you get info and rate of change

**MSH interferometry - measures surface deformation (inflated/deflated)

66
Q

Describe gas emission techniques?

A

Fumaroles!
either 1) direct sampling
2) from a distance using spectrometers that measure c02 and s02

COSPEC: correlation spectrometer
FTIR: fourir transform infrared spectrometer

67
Q

Describe thermal imaging

A

Monitering of temp range and change

  • on ground
  • in helicopter
68
Q

How do we detect lahars?

A

Moniter lahar and debris flow channels

- seismic/motion sensing systems ( real time warning, hours to flow from vent to city)

69
Q

Describe satellite obervation techniques and what they can show us

A 
Thermal pulse,
ash tracking
SO2 tracking
- global coverage
- rapid repeat measurements (15mins) 
-good for early warning and air routes
-good for remote areas without a lot of other coverage
70
Q

What can we do to protect against volcanos?

A

Zoning/regulation for where we put stuff, safe distance from hazards…but not much

71
Q

What are the eruption warning levels?

A

VAN
normal: typical background, noneruptive state OR changed down from a higher level to this
advisory: signs of elevated unrest above known background level or downgraded from higher level
watch: volcano exhibiting heightened or escalating unrest with potential of eruption, timeframe unknown, eruption is underway but hazards are limited
WARNING: hazardous eruption is imminent /underway/ suspected

green/yellow/orange/red!

72
Q

What is our local stratovolcano?

A

Mt. Baker
- dormant but hot, small eruption 1872, last major one 7000 years ago
Dominantly intermediate magma, explosive potential
Glacier covered: lahar potential

greatest risk is to abbosford in LAHAS, lava and pyroclastic flows won’t reach us!

EOSC 114 (6 decks)

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