Volcanism Flashcards
What are volcanoes?
Fissures at the Earth’s crust that allow hot, molten rock and gasses to escape at the surface
What can volcanic activity form?
Mountains or features like mountains over millions of years (Ma)
What does a volcano start with?
It starts with a fissure and builds up
Which volcanoes are the most dangerous on Earth?
Indonesian volcanoes`
What can subduction of a plate lead to?
Volcanoes
Why doesn’t lava flow very far?
Because of its viscosity
What was a secondary effect of the collapse of a dome of Anak-Krakatau?
It triggered a tsunamii
What is needed in order to prepare for tsunamis?
Effective warming systems
How can tsunamis differ?
This depends on if they were triggered by earthquakes or volcanoes
How many died when Anak Krakatoa erupted in 2019?
At least 430
How many were injured when Anak Krakatoa erupted in 2019?
1495
How far away is Mexico City from Colma?
483km
When did Colma erupt?
29th January and 1st February 2016
How far did the ash plumes from Colma rise in 2016?
4.6-6.7km
How many active volcanoes are on Earth?
1500
How many volcanoes have erupted in the last century?
400
On average how many eruptions are there each year?
50
Where is most volcanic activity concentrated?
Along major plate boundaries
What do the risks of volcanoes depend upon?
The type of volcano
How many people live near volcanoes?
Around 500million
How many volcano related deaths have their been during the last 125 years?
100,000
How many volcano related deaths have there been in the last 20 years?
23,000
Where are some densely populated countries located?
In volcanic zones
Where are some major cities with over 350,000 people located?
Near volcanoes
What can dust from volcanoes cause?
Lightning
In which direction does lava flow?
Downhill only
What happens to the ash plume in the sky after an eruption?
It eventually collapses
In which direction can pyroclastic flow flow?
Uphill as well as downhill
What does the type of volcano depend upon?
The type of magma
When have most volcanoes present today been active?
During the quaternary
What can volcanoes interact with?
The plate boundary
What is one of the first recognised eruptions?
Vesuvius 79AD
What happened when Tambora erupted?
There was a year without summer
Why did Tambora cause cooling?
The ash particles blocked some sunlight
When did Mount St Helen erupt?
1980
When did Soufriere erupt?
1995
When did Vesuvius erupt?
79AD
When did Unzen erupt?
1991
When did Krakatoa erupt?
1883
When did Villarica erupt?
1963-1964
When did Mount Pelee erupt?
1902
When did Tambora erupt?
1815
What was a problem when Mount St Helens erupted?
The US was not prepared for any type of eruption
What 3 things control magma explosivity?
Magma composition
Viscosity of magma
The amount of dissolved gas that the magma contains
What happens if magma contains lots of gas?
It is more explosive
What happens if the magma flows (is quite runny)?
It is less dangerous due to its low viscosity
What happens as magma cools?
It crystalises
What is an issue when magma crystalises?
Some minerals are explosive
What happens to the minerals as they crystalise?
Their composition changes
Different minerals or elements at different temperatures
What is the continuous reaction series?
Minerals don’t change just the elements present
What is the discontinuous series?
The minerals change as the temperature changes
What is olivine rich in?
Calcium
What are characteristics of quartz?
Very viscous and explosive
What happens to the magma as it flows over a continent?
Its composition changes because it is melting other rocks
What is on the continuous branch?
Calcium-rich
Plagioclase
Sodium-rich
What is on the discontinuous branch?
Olivine
Pyroxene
Amphibole
Biotite
Put intermediate, mafic and felsic in order from high temp to low?
Mafic
Intermediate
Felsic
What is felsic magma like?
High viscosity
What is mafic magma like?
Low viscosity
What does the Bowen reaction series show?
Magma composition
It looks like a Y
What does magma viscosity change with?
Temperature
What happens to the explosivity as the magma gets more viscous?
More viscous= more elasticity
What are pillow lavas on continents evidence of?
Mid-oceanic ridges
What is the thermodynamic equilibrium of magma?
Mineral cooling and crystalisation
Why does a magma reaction series take place?
The earlier formed crystals react with the melt to form new crystals
What are the two series that the common minerals of igneous rocks can be divided into?
Continuous reaction series of feldspars
Discontinuous reaction series of ferromagnesian minerals
What does the reaction series imply?
From a single parental magma, various kinds of igneous rocks can be derived by magnetic differentiation
What does high viscosity mean?
There is a great resistance to flow
What happens to the lavas when temperatures are high?
The lavas are more fluid
What happens to the lava as it cools?
It becomes more viscous
What are basaltic lavas like?
They are quite fluid and can therefore are thin and can travel long distances
How far can lava travel?
150km
What are the 3 volcanic landforms from basaltic magma?
Sheild volcanoes
Basalt plateaus
Cinder cones
What is the silica content of basalt like?
It is low, less than 50%
What is the explosivity of basaltic magma like?
Least explosive
What is the gas content of basaltic lava like?
It is small, less than 2%
What are the characteristics of pillow lavas?
Basaltic
Elongated interconnected flow lobes that are elliptical or circular in cross section
What is pahoehoe?
This is the second most abundant type of lava
What is pahoehoe characterised by?
A smooth, billowy or ropy surface
What is the thickness of pahoehoe flows like?
It tends to be relatively thin
What are Aa lavas characterized by?
A rough, jagged, spinose and generally clinkery surface
What is the thickness of aa lava flows like?
Relatively thick compared to pahoehoe flows
What is the thickness of rhyolitic flows like?
They are quite thick because of their viscosity, therefore they travel short distances
What is the silica content of rhyolitic magma like?
It is high, over 70%
What is the viscosity of rhyolitic magma like?
High
What is the gas content of rhyolitic lava like?
It is high, over 4%
What is the tendency for ryholitic lava to explode?
Greatest
What two volcanic landforms are formed by rhyolitic magma?
Volcanic domes
Pyroclastic flows
What is the silica content of andesitic magma like?
Intermediate about 60%
What is the viscosity of andesitic magma like?
Intermediate
What is the gas content of andesitic magma like?
Intermediate
What is the tendency to explode for adesitic lava?
Intermediate
What are two volcanic landforms that are created by andesitic magma?
Composite cones
Straovolcano
What do gases in magmas do?
They migrate upwards and expand during the migration of the magma
What creates lava fountains?
These are created when gases in magma migrate upwards and escape from the vent
What happens to gases in viscous magmas?
They expand during their migration upward of the magma which they do with difficulty. The pressure of gases and magma increases and leads to volcanic eruptions which eject semi-molten rocks and hot gases
What can be found in rhyolitic lava flows?
Quartz
What can be used to date land surfaces?
Pyroclastic flows
What are the 6 types of volcano?
Fissure Shield Dome Ash-cinder Composite Caldera
What is the slope of a fissure volcano like?
It is gentle and made of basaltic lava
What is the slope of a dome volcano like?
It is a steep convex slope from thick, fast cooling lavas
What is the slope of an ash-cinder volcano like?
It has layers of ash and cinder
What is the slope of a shield volcano like?
It is low-angle and built by successive layers of low viscosity lava
What is the material from a shield volcano like?
Only 10% of the erupted material is explosive
Where do shield volcanoes tend to form?
At hot spots or in back-arc volcanic settings
What are stratovolcanoes like?
They have a steep conical edifice built by the alternation of lava flows and pyroclastic deposits
What does the associated magma generally contain for stratovolcanoes?
Up to 10% volatiles and highly viscous
What type of eruption occurs at a stratovolcano?
Explosive eruption
What are 8 eruption products?
Plume Eruption column Bombs Pyroclastic flow Lava flow Lahar Acid rain Ash fall
What is lahar?
Mud or debris flow
What are fumaroles?
Openings near volcanoes through which gases escape
What causes lahars to form?
When pyroclastic flows or lahars mix with ice or water
What is the flow of lahars like?
Fast
When do caldera volcanoes occur?
When the volcano collapses in on itself after an eruption
What is the viscosity like at dome volcanoes?
Quite viscus
What happens to eruptions at volcanoes?
They don’t stay constant, the change and evolve
What occurs when a doe collapses?
Pyroclastic flow
How is eruption classified?
By explosivity
What is VEI?
Volcanic Explosivity Index
What does a VEI score of 0 show?
Non-explosive
What does a VEI of 1 show?
Small
What does a VEI of 2/3 show?
Moderate
What does a VEI of 4 show?
Large
What does a VEI of 5/6 show?
Very large
What is the VEI scale?
0-8
What are the characteristics of a stombolian eruption?
Rhythmic ejection of incandescent cinder, lapilli and bombs to heights of 10-100m
What are stombolian eruptions usually caused by?
Basaltic or andesitic lavas
What is the eruption rate of strombolian eruptions?
Less than 200 m/s
What are the characteristics of a vulcanian eruptions
e.g. Colima, Mexico March 10th 2005
5km high ash cloud
Several pyroclastic flows
Ash and rock fragments as far as 12km
What is the size of the eruption column for plinien eruptions?
20-40 km
What is the ejection velocity for plinien eruptions?
100-400 m/s
What is a characteristic of plinien eruptions?
Bubbles and viscus magma rapidly ascent together, rapid decompression leads to fragmentation and increase explosion
What are the 7 types of eruption?
Hawaiian Strombolian Sub-plinian Vulcanican Surtseyan Ultraplinian and plinian Phreatoplinian
What is the height of the eruption column for hawaiian eruptions?
Less than 2km
What is the height of the eruption column for strombolian eruptions?
Less than 10km
What is the height of the eruption column for vulcanian eruptions?
Less than 20km
What is the height of the eruption column for surtseyan eruptions?
Less than 20km
What was the height of the eruption column for ultraplinian and plinian eruptions?
Less than 55km
What is the height of the eruption column for phreatoplinian eruptions?
Less than 40km
Which is more explosive, phreatoplinian or ultraplinian and plinian?
Phreatoplinian
What separates vulcanian and surtseyan eruptions?
Their explosivity, surtseyan is more explosive
What type of eruption was Vesuvius in 79AD?
Plinien
How high was the eruption column for Vesuvius?
33km high
What was the rate at which hot ash and pumice fell on Pompeii at for Vesuvius?
Hot ash and pumice fell onto Pompeii at a rate of 12-15cm an hour
What areas did ash and pumice from Vesuvius cover?
Pompeii
Herculaneum
Stabiae
At what time was there total darkness after Vesuvius erupted?
1pm
When was Pompeii buried until?
It was buried until excavations began in 1748
Which large city is located near to Mount Vesuvius?
Naples
What was the VEI for Mount St Helens in 1980?
4
When did Mount St Helens erupt?
18th May 1980
What happened just before Mount St Helens erupted?
There was a 5.1 magnitude earthquake
How many miles upward did the erupted material from Mount St Helens rise?
16 miles
What are supervolcanoes?
These are volcanoes that spread ash much further than normal volcanoes
Why do supervolcanoes exist?
They have massive magma chambers that can eject much more material
Where can supervolcanoes be found?
Above hotspots
What causes the magma chamber of the supervolcano to grow?
Partial melting of the asthenosphere.
What happens as the supervolcano’s magma chamber grows?
The magma becomes under high pressure and the surface bulges and cracks. The Earth’s strained surface eventually starts to shatter
What happens once the supervolcano has caused the Earth to shatter?
Large, explosive eruptions take place and there are numerous pyroclastic flows
What happens after a supervolcano eruption?
A crater-like depression forms called the caldera
What is a caldera?
Crust that collapses in an empty magma chamber
What are 8 volcanic hazards?
Lava flows Pyroclastic flows Ash falls Lahars Landslides Fine ashes in the air and on the ground Volcanic gases Climate change
What can latitude affect?
Scale
What can ash in the lower stratosphere lead to?
Ash in the lower stratosphere can lead to warming of the stratosphere and cooling of the troposphere
What is tephra?
This is ash- any airborne pyroclastic
What is ash?
Very fine-grained fragments, generally dominated by broken glass shards but can also contain rock fragments
What is the size requirement for ash?
Less than 2mm
What is lapiilli?
Pea to walnut-size pyroclasts
What is the size requirement for lapilli?
2-64mm
What do lapilli often look like?
Cinders
What causes accretionary lapilli?
In water-rich eruptions, the accretion of wet ash may form rounded spheres
What is the size requirement for blocks and bombs?
Over 64mm
What are blocks?
These are ejected as solid fragments with angular shapes
What are bombs?
These are ejected as incandescent lava fragments which were semi-molten when airborne and therefore inherited streamlined, aerodynamic shapes
What causes pyroclastic flow?
This occurs when the mixture of hot gas and rocks are heavier than the surrounding air, causing the plume to collapse in on itself and flow down the slope of the volcano
At what speed do pyroclastic flows move?
Over 100km/hr
Where are pyroclastic flow deposits usually confined to?
Valleys
What temperatures can pyroclastic flows reach?
Over 400C
What are lahars composed of?
Water, and sediment
What percentage of sediment in a lahar makes it turbulent?
20-60%sediment= turbulent
What percentage of sediment in a lahar makes it smooth?
More than 80% sediment
Which type of lahar moves faster?
The smooth lahar is faster than the turbulent lahar
What can happen to the glaciers and snow caps at the top of the volcano?
They can suddenly melt
How fast can melted snow move downslope?
50km/hour
How far can melted snow move downslope?
It has a long flowing distance, tens of miles from volcanoes
What are landslides?
Large masses of earth that fall, slide or flow rapidly
Why are volcanic edifices prone to instability?
Many volcanoes are steep-sided mountains, often partly constructed from poorly consolidated volcanic deposits
What was the VEI of Krakatoa in 1883?
VEI 6
How many fatalities were there in Krakatoa in 1883?
120,000 or more
How high was the Krakatoa 1883 tsunami?
46m
What happened to the island of Krakatoa in 1883?
It had almost entirely disappeared but it has been growing ever since
Why does the stratosphere warm after an eruption?
The particles in the atmosphere that have been ejected by the volcano absorb the radiation
Why does the troposphere cool after an eruption?
As the stratosphere absorbs more radiation, less gets to the sun
What can a strong, brief impact on climate change be useful for?
It can help to make better predictions of future climate and weather
How long can the strongly enhanced reflection of incoming solar radiation cause global cooling at the surface for?
2-3 years
What effect (greenhouse or haze effect) is more greatly enhanced by volcanic eruptions?
The haze effect is more affected than the greenhouse effect
What does the haze effect cause?
Short term cooling
What happens to cause the haze effect?
Sulfur combines with water vapour in the stratosphere to form a dense cloud of sulfuric acid droplets which take year to settle out and they cool the troposphere because they absorb solar radiation and scatter it back to space
How can volcanic eruptions enhance the greenhouse effect?
The add CO2
Which is a larger input of CO2 into the atmosphere: humans or volcanoes?
Human activities put more CO2 into the atmosphere each year
When did the Laki eruption occur?
1783-1784
Where was the Laki eruption?
Iceland
What percentage of livestock was killed by the Laki eruption?
75%
What percentage of Iceland’s population was killed?
24%
What was the volume of the lava for the Laki eruption?
14.7 km3
What was the volume of tephra at the Laki eruption?
0.4 km3
What climate impacts were there as a result of the Laki eruption?
Summer of 1783 was extremely warm over Europe
Winter of 1783-4 was extremely cold over Europe and North America
What are circulation anomalies produced by?
Volcanic gases and aerosols
Anomalies from which aerosols caused the haze effect?
Sulphate aerosols
What two volcanic gases (not aerosols) act as gases?
CO2 and SO2
When was the Tambora eruption?
1815
What percentage of people died on Sumbawa?
35%
What was the VEI of Tambora?
7
What did the Tambora eruption cause?
The year without a summer
When was the ultra-plinian eruption of Pinatubo?
1991
What was the VEI of the Pinatubo 1991 eruption?
VEI5
What effect did the Toba super-eruption have on climate?
A drop of 10C globally for a few months, cooling lasting several decades
6 years of volcanic winter, followed by 1000 years of the coldest, driest climate of the late Quaternary