Lecture 10: Volcanic Eruptions Flashcards
Volcano
A mountain constructed by the eruption of molten rock from Earth’s interior and are a direct consequence of plate tectonics and mantle convection
Tallest mountain on earth
Mauna Kea
What do eruptions provide?
Provide highly productive solid to feed a civilization
What are the products of volcanic eruptions?
Volcanic gases
Pyroclastic debris
Lava flows
What is volcanic gas?
Expelled vapour and aerosols
What is pyroclastic debris?
Fragments blown out of a volcano
What is lava flow?
Flowing molten rock with various viscosities
What affects the viscosity of lava?
Due to its composition specifically its silica content
Temperature
Gas content
Runny lava (name, viscosity)
Basaltic lava (low viscosity)
Thick lave (name, viscosity)
Rhyolite lava, high viscosity
Lava in between thick and thin (name?)
Andesite lava
Basaltic lava
Runny-low viscosity, low silica, very hot, long flow distances, rapid speed
Rhyolite lava
Thick-high viscosity, has highest SiO2 content, it rarely flows and plugs the vent creating a lava dome
Andesitic lava
A viscous lava, that flows slower and has a higher silicon oxide content than a basalt. They lava hovers around the vent and its outer crust will fracture into rubble after cooled
Lava tubes
Conduits for basaltic lava, where overtime flow is entirely contained within the tube. Lava tubes are often miles long. Tubes prevent cooling, facilitating flow for miles. After volcanic episodes, lava tubes become caves that can transmit water.
Hawaiian word for describing basalt with a glassy, ropy, twisty texture.
Pahoehoe
Pahoehoe
A basalt with glassy, rope, twisty texture skin which forms when a hot basalt forms a skin.
Hawaiian word describing basalt that solidifies with a jagged, sharp, angular texture.
A’a’
A’a’
A basalt that solidifies with a jagged, sharp, angular texture that forms when hot flowing basalt cools and thickens. With flow the lava crumbles into sharp, jagged shards and fragments that solidify into hard solid rock.
Columnar jointing
Solidified flows that contract with vertical fractures that have cross sections that are hexagonal
Where is columnar jointing most common?
Basalt and other igneous rocks
Pillow basalt
Blobs of basalt that cooled rapidly by quenching in water.
Pillow basalt are a common feature of the
Mid ocean ridge
Mound of pillow basalt
A repeating process of lava pressure rupturing a pillow basalt
QUESTION:
Basaltic vs andesitic vs rhyolitic
SiO2 content, viscosity, pyroclastic debris, difficulty of gas escape:
basaltic
Rhyolitic lava flows
It has the highest SiO2, and is the most viscous. Their lava rarely flows
Lava domes/ volcanic domes
Bulbous mass of congealed lava which are associated with explosive eruptions of gas-poor magma
Explosive eruptions
Occur mostly in rhyolitic and andesitic magmas due to high gas content, they end up creating huge volumes of debris including volcanic ash
Pyroclastic flow
An avalanche made of hot ash, gas, & debris that develops from volcanic eruptions where the ash cloud/column/dome collapses and races down at very high deadly speeds
Volcaniclastic deposits
Large quantities of fragments for volcanic eruption
Materials of volcaniclastic deposits
Pyroclastic debris, preexisting rock, landslide debris, and lahars
Lava fountains
Formed from baslatic eruptions that spew lots of released gases, ejecting clots and drops of molten magma.
Pyroclastic materials size range
From small to large
Tephra
Describes deposits of pyroclastic debris of any size
Tuff
Lithified ash
What type of volcaniclastic deposit accumulates like snow
Air-fall tuff
Ignimbrite
Tuff that is deposited while still hold and welds together
Categories describing volcaniclastic deposits
Pyroclastic: material accumulated from clouds of debris that hasn’t moved since deposition
Volcani-sedimentary: material moved after deposition
Fragmented lava: material from broken lava flows
Volcanic debris flow
Flow of wetted debris, where the volcano is covered with ice/snow/rain
Lahars
A flow of water-rich volcanic debris carrying ash and large blocks: destructive and deadly
Hyaloclastite
Shatters of lava quenched in water
Gas expulsion occurs when
The pressure drops and magma rises
Gas bubbles are called
Vesicles
What controls eruption violence
The way in which gas escapes, difficult=violent
Features of volcanic architecture
Magma chamber, fissures/vents, craters, calderas
What are some distinctive profiles of volcanic architecture, largest to smallest
Shield volcanoes
stratovolcanoes
Cinder volcanoes
Magma chambers
An open cavity or area of highly fractured rock that contains a lots of magma and is located in upper crust and ,may rise through a conduit to reach surface of volcano
Magma that cools in magma chambers turn into
Intrusive rock
Fissures
Magma that erupts along a linear tear
What type of eruption displays a “curtain of fire”?
Fissure eruptions
Fissures evolve to become
discrete vents that erupt from craters
Crater
A bowl shaped depression at the top of a volcano that erupt from pipe-shaped conduits where lava will pile up around the vent
Summit eruptions are located within
The summit crater
What type of eruption/vent occurs at the side of a volcano?
Flank eruptions from flank vents
Caldera
A large volcanic depression (much larger than craters) which form when magma chambers empty causing the volcano to collapse into an evacuated space.
Shield volcanoes
Broad, slightly domed shaped that are formed by lateral flow of basaltic lava
Cinder cones
Cone shaped pile of ejected lapilli-sized fragments with deep crater
Stratovolcanoes
Also called composite volcanoes, cone shaped volcano with steep slopes of alternating felsic lava, tephra, and debris, eruptions are from layered pyroclastic eruptions and very viscous lava flows
What type of volcano is the most violent?
Stratovolcano
What type of volcano produces a nuee ardente?
Stratovolcano
Eruption styles
Effusive eruptions: lava flows that are mostly basaltic can create lava fountains/rivers
Explosive eruptions: lava explodes upward is mainly rhyolitic/andesitic and create pyroclastic flows covering landscape with tephra
Strombolian eruptions: shoot out magma, lapilli and blocks at regular intervals
What factors determine the violence or explosiveness of a volcanic eruption?**
- composition of magma (high sulfur=high viscosity)
- temperature of magma (low temp=high viscosity)
- dissolved gases in the magma (low gas (low gas=high viscosity)
What are the types of magma rock controls the nature of an eruption?
Igneous rocks:
Felsic(granitic/rhyolitic) are high in sulfur/viscosity
Mafic(basaltic): are low in sulfur/viscosity
Why does magma rise to surface
Because magma is less dense than surrounding rock
Viscosity and gas escape
The less viscous = easier escape of gas bubbles
Vulcanian eruption
A moderate-sized explosive eruption
Plinian eruption
An enormous explosion of volcanic material that ejects huge quantities of material into the atmosphere
Eruption styles:
Hawaiian: low-viscosity; fire fountain discharge 1 km high; little pyroclastic material; non-explosive
Strombolian: blasts of lava, including bombs and tephra, create low elevation columns and pyroclastic flows; mildly explosive
Vulcanian: sustained explosions of highly viscous magma; columns reach several km high and collapse to produce pyroclastic flows; very explosive
Pelean: result from collapse of lava dome producing nueé ardente; violently explosive
Plinian: sustained ejection of magma resulting in eruption column up to 45 km high; ash cloud can circle the Earth in days; violently explosive
Phreatic: results when magma mixes with shallow groundwater, which flashes to steam and explosively erupts; no new magma reaches surface
Largest eruption in modern day
Mt. Pinatubo in philippines
Largest eruption documented in all history
Toba in indonesia
What is a dominant control on volcanism?
Tectonic plate motion
Volcanic settings are:
- Mid-ocean ridges: spreading axes
- Convergent boundaries: subduction zones
- Continental rifts: incipient ocean basins
- Oceanic hot spots
- Continental hot spots and flood basalts
Which flow is more deadly?
Pyroclastic flow not lava flow
What is the best defense against volcanic hazards?
Understanding volcanic behaviou
Effect on ashfall in modern day
Kills plants and crops
collapsing roof from heavy tephra
Abrasion of engine from gritty tephra
Tephra can become deadly lahar in flood water
Volcanic blast
Rare hazard since most are vertical not sideways
Landslide in volcanic eruptions
Large masses of material are deopsited quickly near a vent
