Week 4- Volcanics and geothermal resources Flashcards
why do people live near volcanoes
- extremely fertile soils
- geothermal energy resources- free green energy
- mineral resources such as cu, zn, fe, au ores
- tourist and economy
what is a volcano
- an erupting vent through which molten rock surfaces
- surface expression of melting processes
- melts are silicate magmas
- often related to plate boundaries
example of a recent major eruption
2022 Hunga tonga- hunga Ha’apai
- major explosive eruption where plume reached heights of 50 km (HALFWAY TO SPACE)
- blast equivalent to 100 million tons of TNT
- pressure wave picked up globally
- intense ferocity from magma- water interaction
what are products of volcanic eruptions
- lava flows- molten rock moving across the ground
- pyroclastic debris- fragments blown out of a volcano
- volcanic gases- expelled vapour and aerosols
what are the two main types og igenous rocks
intusive
extrusive
what are the temperatures needed to melt a rock
- 650- 1100 degrees
what needs to be done in order to melt the mantle
- the geotherm needs to be disturbed
what is a geotherm
- is a gradient, where the rate of increasing temperature changes with respect to increasing depth in earths interior
what changes are needed to disturb the geothem
- add heat
- reduce pressure (most important)
- change the composition
how does decompression (adiabatic) melting occur
- a geological decrease in the pressure
- molecules have more room to move around
- have a high temperature relative to the amount of room that they have
- melting occurs (the solidus is the T and P where a rock will start to melt)
where does adiabatic melting occur
mid-ocean ridges- forms mid-ocean ridge basalt
continental rifts- east Africa will become an ocean over time
what is volatile assisted melting
- change in composition of the system
- new ions increase the complexity of the system which makes the energy needed to break the chemical bonds less
- adding volatiles to earths mantle lowers its melting temperature
- ## c02 release as a result of carbonate water mixing, and then being subducted into the mantle (IN VOLCANIC ARCS)
how are volcanoes linked to plate techtonics
- they disturb the geotherm
- driver of melting can change over time
- majority of magma is erupted at divergent margins
important points to know for surface volcanism
- is the result of mantle melting
- DONT FORGET
submarine volcanism
volcanism on other planets
how is extrusive volcanism influenced
- rheology (viscosity)
how does the rheology of magma operate
- silica polymerisation- network forming, where liquid silica is the most viscous
- high concentration of network former molecules Mgo, CaO, Na2O, K2O means less bonds between oxygen and therefore less energy required to deform the network (basalt)
vice versa with silica and aliminium
how is viscosity (rheology controlled)
- chemical composition
- temperature
- dissolved gas content
- crystal content
flow style also controlled by these factors
what are the qualities of mafic (basaltic lava flows)
- very hot, low silica, low viscosity
- often thin fluid
- flow rapidly up to 30km an hour
- although most flows cant flow more than 10km, these can flow for several hundred km
- this distance is facilitated by lava tubes
examples of mafic (basaltic lava flows)
- ropy (pahoehoe)- when hot basalt forms skin
-blocky (aa) - basalt solidies jaggy
- lava crumbles into shards and fragments
- what you would say if walking barefoot
- forms further from vent
examples of submarine basaltic lava
- pillow basalts- round blobs of basalts cooled underwater, cools forming a pillow
- surface of pillow is cracked quenched glass
- lava pressure rupturesa pillow to form the next blob
- formed a mound thats common at a mid-ocean ridge
qualities of intermediate lava flows
- higher siO2 content and so more viscous
- dont flow rapidly
- fractures into blocky lava
- remains close to the vent
what are the qualities of silicic lava
- high viscosity
- rarely flows- piles up around the vent and intermittent explosive activity
- lava dome formation and spines
main forms of volcanic gases
- 1- 10 percent may be dissolved gases
- water
- CO2
- sulfur dioxide- precipitates at the edge not stable and ignites (can form crystals)
How are gas bubbles formed
- magma rising, paired with pressure decrease causes the gas to become less soluble in the melt and ‘exsolves’
what conditions depend on weather a magma will fragment or not
- volatile concentrations and magma rheology
- lava pours out effusively in non- fragmented bubble lavas
qualities of explosive mafic eruptions
- low viscosity basaltic
- generates fire fountains
- relatively gentle eruptions such as icelandic volcanoes
- gas coalesces and rises as slugs
what are explosive eruptions of vulcanian style magma
- cannon like
- high viscosity so extremely explosive
pressure buildup in silicic magma
- plug of rock on top exsolves gas causing pressure buildup
- plug strength exceeds and erupts violently
- pyroclasts of ash and lapilli erupt next
explosive eruption of silicic example and style name
- plinian
- calbuco volcano in chili in 2015
explosive eruption of silicic example that cannot sustain eruptive column and name
- pelean style
- dome collape at mount Unzen in japan
what is the key factor which explains the transition from plinean to pelean
magma flux (ascent rate)
examples of water volcanic interactions
- phreatic- influenced by magma heat interaction with water
- phreatomagmatic eruption- interaction of new magma water and can be very explosive
when do columnar joints form
- in lava flows, sills, dikes, ignimbrites and shallow intrusions of all compositions
how are entablature columnar joints formed
- ingress of wate in upper parts of lava flow modifies the isotherm and produces these fan like columns
what is pyroclasts
- any material ejected from a volcano, collectively called tephra
different pyroclastic eruption examples
- flow
-fall
-surge
characteristics of pyroclastic fall deposits
- velocity max in core of plume
- at edges not enough velocity so falls down
- tephra falls back down
- parallel bedding
- well sorted
- shows size grading alot
characteristics of pyroclastic flow deposits
- FILL TOPOGRAPHY
- bedding is relatively rare
- poorly sorted
- often graded
BLOCK AND ASH FLOWS
- dense lava fragments derived from collapse of growing lava dome
PUMICE FLOWS
-low density from collapse of an eruption column
characteristics of a pyroclastic surge deposit
- more energetic dilute mixture of searing gas and rock fragments
- move easily over ridges
- topography restrained
- fine grained
-cross bedding - intermediate sorting
- often graded
- may find evidence for volcanic bombs
how can eruption volume be estimated
- tephra dispersal
how have volcanic hazards have an effect on people
- 500 volcanic events in 20th century impacted people
- 6 million evacuated or homeless
- up to 100,000 fatalities
- number injured is much less than killed (12,000)
volcanic hazards of lava flows
- lava flows (basaltic) can cause serious damage to property
- not particularly lethal (1-50km travel rate)
- hawaii big island volcano of kilauea
- evacuation of 2000 and 800 million in damages
hazards of pyroclastic flows
- fast moving and are extremely hot (1000 c)
- devastate anything in their path and can kill by suffocation and burning
hazards of ash clouds
- ash can accumulate to form thick layers of debris- roofs and powerlines can collapse
- ash buries crops, poisons soils and infilrates machinery
- respiratory problems
aviation- ash=glass which sticks to air combustion engines
- acidic aerosols etch windows
such as the flight Eyjafjallajokull which closed european airspace for $200 mill per day
hazards of gas emissions
- C02 is heavier than air at can cause suffocation
- S02 and H2S- combine with water fluid in the air to form sulfuric acid which damages eyes and lungs and irritates soft issues
- HF is highly corrosive and toxic and attacks calcium in the skeletal nervous system
example of a gas emission toxic hazards
- Laki eruption in iceland
secondary volcanic effect (ash)
- lahars which is mixing of volcanic ash and water
- flows like wet concrete
- dangerous when volcanic mixing with snow cap
- ## such as the navado del Ruiz in colombia———– totally e gulfed armero town and killed 20,000
secondary volcanic effect (natural disaster)
- tsunami
- slope failure into water
what happened with the Mount st Helens disaster
- small earthquakes
- outburst of ash and steam
-collapse of north flank due to a large earthquake - one of the largest ever recorded landslides
- removal of mass decompressed the magma chamber
long term example of volcanic destruction
- 1815 tambora
- 10,000 killed by erption
- more than 80,000 killed from starvation
-hazy skies - the years without a summer
- frankenstein
what effect does volcanic aerosols have
- causes global cooling due to reflect but not retaining like greenhouse gases
why is it vital that volcanic soils are fertile
- chlorphyll provide
- fresh volcanic material such as mafic minerals which weather easily
how do volcanic ore deposits
- at seafloor vents, magmatic heat drives circulation of seawater and hydrothermal fluid
- these fluids are rich and dissolved metals and precipitate massive sulfide ores
what eruption site attracts much tourism
- white island
- erupted in 2016
-47 people were on the island t the time of a phreatic eruption
-
what is geothermal energy
- is energy derived from natural heat of the earth
-rainwater seeps down into crust through pores, faults and fractures
in 2021, how much energy came from renewable technology
13%
why is geothermal energy so important
- water can be recycled back
- clean plants emit little co2 matter ect
- continuous reliable base-load in grid
easiest and obvious place to acsess geothermal heat
- yellowstone (supervolcano)
