Volcanic eruptions

Question 1

What is a volcano?

Answer 1

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

Question 2

what are some consequences of euptions?

Answer 2

build mountains
blow mountains to bits
provide productive soils
KILL

Question 3

what are the three products of volcanic eruptions?

Answer 3

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

Question 4

lava flows

Answer 4

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

Question 5

HIGH SILICA

Answer 5

HIGH VISCOSITY

LLL
low silica, low viscosity, liquidy

Question 6

mafic lava

Answer 6

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

Question 7

basaltic pahoehoe lava

Answer 7

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

Question 8

basaltic A’a’ lava

Answer 8

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

Question 9

what causes columnar jointing?

Answer 9

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.

Question 10

pillow basalt

Answer 10

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

Question 11

andesitic lava flow

Answer 11

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

Question 12

rhyolitic lava flow

Answer 12

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

Question 13

describe what happened in mount saint helens

Answer 13

• 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

Question 14

what are in volcaniclastic deposits?

Answer 14

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

Question 15

dramatic fountains of basaltic eruptions

Answer 15

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

Question 16

what types of volcanoes are more prone to explode?

Answer 16

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

Question 17

what debris is generated by explosive eruptions?

Answer 17

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

Question 18

eruption of mt toba

Answer 18

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

Question 19

consequences of mt toba

Answer 19

• 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

Question 20

pyroclastic debris

Answer 20

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

Question 21

what is tephra

Answer 21

deposits of pyroclastic debris of any size

Question 22

what is tuff

Answer 22

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

Question 23

volcanic debris flow

Answer 23

wetted debris that moves downhill
moves like wet concrete downslope

Question 24

what is lahar

Answer 24

water rich debris flow of ash and blocks

Question 25

volcanic gases in decreasing order

Answer 25

water (most) CO2 SO2 and H2S

Question 26

volcanic gas

Answer 26

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

Question 27

basalt vs rhyolite eruption

Answer 27

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

Question 28

vents vs conduits in volcano architecture

Answer 28

vents are for gases and conduits are for leading magma

Question 29

fissure

Answer 29

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.

Question 30

crater

Answer 30

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)

Question 31

caldera

Answer 31

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

Question 32

shield volcanoes

Answer 32

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

Question 33

scoria cones

Answer 33

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

Question 34

stratovolcanoes

Answer 34

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

Question 35

effusive vs explosive eruptions

Answer 35

eff: lava Flow explosive: blow up

Question 36

effusive eruptions

Answer 36

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

Question 37

explosive eruption

Answer 37

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

Question 38

eruptive style and volcano types

Answer 38

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

Question 39

5 eruptions to remember TMVYK

Answer 39

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

Question 40

Tambora

Answer 40

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

Question 41

eruptive hazards

Answer 41

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

Question 42

recurrence intervals

Answer 42

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

Question 43

warning signs of imminent eruption

Answer 43

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

Question 44

lava flows can be diverted

Answer 44

cooling using water building barriers and trenches to channel lava explosives

Question 45

volcanoes and climate

Answer 45

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

Question 46

MOR volcanism

Answer 46

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

Question 47

arc volcanoes develop of overriding plate at convergent boundaties

Answer 47

ring of fire at pacific margins

Question 48

continental rifts

Answer 48

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

Question 49

oceanic hot spot

Answer 49

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.

Question 50

flood basalts

Answer 50

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