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Geology > Volcanic eruptions > Flashcards

Volcanic eruptions Flashcards

1
Q

What is a volcano?

A

vent through which molten rock erupts. mountain built from magmatic eruptions. result of tectonic activity

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2
Q

what are some consequences of euptions?

A

build mountains
blow mountains to bits
provide productive soils
KILL

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3
Q

what are the three products of volcanic eruptions?

A

lava flows (molten rock)
pyroclastic debris (fragments blown out of volcano)
volcanic gases (vapor and aerosols)

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4
Q

lava flows

A

can be thin and runny or thick and sticky
flow style depends on viscosity (silica composition, temp, gas and crystal content)

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5
Q

HIGH SILICA

A

HIGH VISCOSITY

LLL
low silica, low viscosity, liquidy

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6
Q

mafic lava

A

very hot, low silica, low viscosity
basalt flows are thin and fluid, flow rapidly, long distances

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7
Q

basaltic pahoehoe lava

A

glassy, ropy texture
forms when hot basalt forms a skin. skin is rolled into ropy ridges and furrows
(look up picture)

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8
Q

basaltic A’a’ lava

A

basalt that solidifies with sharp angular texture. hot basalt cools and thickens. lava crumbles into shards and fragments.

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9
Q

what causes columnar jointing?

A

produced by cooling of lava flows, ash-flow tuffs, and other bodies of magma or lava.
Cooling causes contraction
which in turn causes fracturing. Fractures propagate from the top and bottom of flows inward towards the center.

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10
Q

pillow basalt

A

round blobs of basalt COOLED IN WATER. pillow surface is cracked, quenched glass. lava pressure ruptures a pillow to form the next blob.
forms a mound of pillow basalts

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11
Q

andesitic lava flow

A

higher SiO2. more viscous. flow slowly. crust fractures into rubble called blocky lava

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12
Q

rhyolitic lava flow

A

highest SiO2 and most viscous. rarely flows far. lava plugs vent as lava dome. lava dome can be blown apart

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13
Q

describe what happened in mount saint helens

A
  • A massive landslide on the north side triggered the eruption.
  • A lateral blast sent hot gas, ash, and rock at high speeds, devastating the area.
  • A 15-mile-high ash plume spread across multiple states.
  • Pyroclastic flows and mudflows (lahars) destroyed forests and infrastructure.
  • left a large crater
  • 1980 to 1986
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14
Q

what are in volcaniclastic deposits?

A
  • pyroclastic debris (lava fragments that freeze in air)
  • preexisting rock (blasted apart by eruption)
  • landslide debris (rolled downslope)
  • lahars (water-rich slurries)
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15
Q

dramatic fountains of basaltic eruptions

A

lapilli = pea-sized fragments
pele’s tears = frozen droplets
pele’s hair = thin glass strands
blocks
bombs = streamlined

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16
Q

what types of volcanoes are more prone to explode?

A

volcanoes with more viscous magmas and more volcanic gases. andesitic or rhyolitic eruptions

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17
Q

what debris is generated by explosive eruptions?

A

pumice (frothy volcanic glass)
ash (small fragments)
pumice lapilli (fragments of pumice)
accretionary lapilli (clumps formed by falling through moist air)

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18
Q

eruption of mt toba

A

during four powerful explosive eruptions beginning 1.2 million years ago
erupted and took away so much of the land that water could accumulate and make a lake

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19
Q

consequences of mt toba

A
  • emitted the equivalent of 3,800 km3 of dense rock then deposited as pyroclastic flow and fall deposits
  • An eruption column of ~32 km high
  • sulphur emitted
  • ash can be found as far away as the Sahara
  • linked to global cooling
  • early population decline
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20
Q

pyroclastic debris

A

avalanches of hot ash
300 km/h
kill everything quickly
nuee ardente

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21
Q

what is tephra

A

deposits of pyroclastic debris of any size

22
Q

what is tuff

A

lithified ash, may or may not contain lapilli
- Air-fall tuff—accumulations of ash that fall like snow
- Ignimbrite—tuff deposited while hot that welds together

23
Q

volcanic debris flow

A

wetted debris that moves downhill
moves like wet concrete downslope

24
Q

what is lahar

A

water rich debris flow of ash and blocks

25
Q

volcanic gases in decreasing order

A

water (most)
CO2
SO2 and H2S

26
Q

volcanic gas

A

gases expelled as magma rises
SO2 reacts with water to form aerosol sulfuric acid
gas bubbles in rock are vesicles

27
Q

basalt vs rhyolite eruption

A

Low viscosity (basalt)—easy escape; mellow eruption
High viscosity (rhyolite)—difficult escape; violent release

28
Q

vents vs conduits in volcano architecture

A

vents are for gases and conduits are for leading magma

29
Q

fissure

A

Magma may erupt along a linear tear called a fissure.
Fissure eruptions may display a “curtain of fire.”
Fissures evolve into discrete vents and craters.

30
Q

crater

A

bowl shaped depression atop volcano formed through explosion
form as erupted lava piles up around the vent
summit eruption at summit crater (other one is flank)

31
Q

caldera

A

larger than a crater
steep sidewalls and flat floors
formed when volcano erupts and then collapses

32
Q

shield volcanoes

A

broad and slightly dome shaped
Constructed by lateral flow of low-viscosity basaltic lava.

33
Q

scoria cones

A

formed after an eruption event
conical piles of tephra; the smallest type of vent
Built of ejected lapilli and blocks piled up at a vent

34
Q

stratovolcanoes

A

steeper slopes formed
built up by layers of lava and tephra and debris

35
Q

effusive vs explosive eruptions

A

eff: lava Flow
explosive: blow up

36
Q

effusive eruptions

A

vast outpour of lava
mafic magma commonly, hot and low viscosity

37
Q

explosive eruption

A

sudden pressure release
gas pressure builds up more in SiO2 rich magma
pyroclastic flows and covers land with tephra
andesitic and rhyolitic (felsic)

38
Q

eruptive style and volcano types

A

effusive – shield volcano
small explosion - scoria cones
alternate effusive explosive - stratovolcanoes
large explsive - calderas

39
Q

5 eruptions to remember
TMVYK

A

Taupo
Mt. Toba
Vesuvius (Naples)
Yellowstone = caldera
Krakatau (huge eruption + tsunami waves)

40
Q

Tambora

A

year-long climate depression
caused global crop failures resulting in the worst famine of the 19th century

41
Q

eruptive hazards

A
  1. lava threats mostly from basalt
    rare for lava flows to kill people
  2. threat of falling ash and lapilli (tephra is heavy)
  3. blast (explosions rarely eject sideways)
  4. landslides (slope failures due to eruptions)
  5. pyroclastic flows (ash clouds)
  6. lahars (mudflows) carries away everything
  7. earthquakes (caused by moving magma) and tsunamis
  8. gas and aerosols
42
Q

recurrence intervals

A

active: erupting, recently erupted or likely to erupt
dormant: hasn’t erupted in hundreds to thousands of years
extinct: not capable of erupting any more

43
Q

warning signs of imminent eruption

A

Earthquake activity—magma flow increases seismicity.
Heat flow— volcanoes “heat up.”
Changes in shape—magma causes expansion.
Emission increases— gas mix

44
Q

lava flows can be diverted

A

cooling using water
building barriers and trenches to channel lava
explosives

45
Q

volcanoes and climate

A

ash and aerosols in stratosphere reflect solar radiation and cause atmospheric cooling

46
Q

MOR volcanism

A

at MOR Basalt erupted from fissures quenches as pillows.
Pillow mounds are pulled apart with plate motion

47
Q

arc volcanoes develop of overriding plate at convergent boundaties

A

ring of fire at pacific margins

48
Q

continental rifts

A

Partial melting of the mantle (mafic magmas)
Partial melting of the crust (felsic magmas)

49
Q

oceanic hot spot

A

plume under oceanic plate eg. hawaii
While the hot spot stays in one place, rooted to its deep source of heat, the tectonic plate is slowly moving above it.
As the plate moves, so does the volcano, and another one forms in its place. The volcano that moved is no longer active.

50
Q

flood basalts

A

Flood basalts are thick successions of basalt erupted onto the continents over short periods of time

Geology (19 decks)

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