Volcanos Flashcards
What are volcanos?
Magma and gas leaking out from earth’s crust and or mantle
How do volcanos form?
magma is melted pre-existing rock below earth’s surface, reaching surface through fractures.
Extrudes as lava
Explodes as pyroclastic material
What are the rocks formed from magam?
Basalt: extrusive rock that cools fast in the outside bits
Granite: plutonic/intrusive rock that cools before reaching surface
What are the two types of igneous rocks?
Volcanic
Plutonic
What is extrusive vs. intrusive?
extrusive: quick cooling, small crystals
intrusive: slow cooling large crystals
What are the 4 parts of the volcanic system?
Source region: deep in mantle or crust
Transport region: bring to storage/surface (i.e. the crust)
Storage region
Eruption
Describe the source region. What is the difference in melted mantle rocks?
Deep, hot, mantle rocks
Mantle (peridotite 33– kgm3)
this melts into..
Magma (basaltic-granite 2700-2500 kgm3)
when this melts density decreases to form magma which is less dense and therefor RISES
Describe the transport region.
magma moves along cracks in earth’s crust forming
DIKES: vertical intrusion that cut through older rock, often basaltic
SILLS: horizontal intrusion of magma
Describe the storage region of the crust?
Where magma accumulates in weak crusty bits
- stored in chambers
Describe the eruptive region
Active volcano! Explosive or Effusive
Why was the Kilauea volcano in hawaii so damaging?
the volume they thought there was going to be was 10x higher because ppl focused on the lake but below there was a huge reservoir
- flowed for 5 months
What are the properties of magma?
- Density: magma is about 3g/cm3
crust: 2.7-3.3
mantle: 3.3-5.7 (we know densities because of earthquakes and velocity of seismic waves are different depending on material that made them)
Magma is often less dense and will rise to crust - Viscosity: 10-10^15 Pas, resistant to flow, causes eruption style
dependant on TEMP, GAS, CRYSTAL content - Silica content: high vs. low
Felsic: high silica
Mafic: low silica - Magma temp:
Hot: low viscosity, low silica (mafic)
Cool: high viscosity, high silica (felsic) - Gas/volitiles: dissolved gas (H20,CO2,SO2)
When magma rises, there is less pressure and less solubility leading to BUBBLES=explosion
Which lava is more viscous? Rhyolite or andeside?
rhyolite
describe mafic and felsic?
felsic: light colour, 65-75% silica, k, na, al, si, high viscosity, 4-6% volitiles
i. e. granite/rhyolite
mafic: 45-55% silica, dark, Mg, Fe, low viscosity, 0.1-1% volitiles
i. e. Gabbro, Basalt
How does composition differ through different rock types? (name 4)
Basalt, Andesite, Dacite, Rhyolite
Dark, mafic, hot, low viscosity, non explosive
»>
Light, felsic (more silica), cooler, high viscosity, explosive
Why does viscosity matter?
Think pahoehoe and a’a, same basalitic composition but different flow!
What determines explosivity?
Mafic: low gas content, low viscosity = effusive
felsic: high gas, high viscosity =explosive
Where do volcanos occur?
Plate boundaries
- spreading ridges, subduction zones
Hotspots
What are volcanos at mid-oceanic ridges like?
Biggest, most volume, not exposed at earth surface (except in iceland because of a hotspot), divergent boundaries
What are the charictaristics of continental volcanic arcs?
how about a oceanic volcanic arc?
subduction volcanos, with mafic magma at the bottom, felsic magma in chambers and felsic/intermediate magmas/lavas closest to the top
local: Subduction of juan de fuca under north american plate (cascadia subduction zone, with Mt Baker, mt. st helens, mazama, mt. shasta)
OCEANIC: two oceanic plates converging, mafic magmas at bottom AND the top
- results in effusive expulsion
i. e. western aleutian arc, cleveland, pavlof
Describe hot spots
Mafic magmas from a plume (stationary, pulsatory) of hot magma
-islands chains are created this way
make a table from volcano settings/mechanisms/magma types from lecture 2!
DO IT
LECTURE 2, HALFWAY DOWN
What are the different types of volcanoes?
- Cinder cones: mafic/explosive
- Shield volcanos: mafic, non explosive
- Stratavolcanos: intermediate, felsic, mixed
- Calderas: felsic, explosive
Describe Cinder Cones
Layers of pyroclastic ejecta from FIRE FOUNTAINING
- 30-40 degree angle of repose, small volcanos that don’t grow up
usually erupt a few years then go dormant
2km by 500m
i.e. paracutin/mexico, elfin lakes/opan cone, garibaldi park
Describe Shield Volcanoes?
Lava erupts from fissure, runs down gentle slopes, cooling erupts ofen, mafic lava flows, not super explosive 100km by 4-10km
i.e. mauna loa hawaii
Describe Stratavolcanos
Interbedded lava flows, pyroclastic flows, lahars, intermediate/felsic
explosive frequently
may erupt many times and stay active for a long time
10 km by 5km
i.e. mt. st. helens, garabaldi, baker
shasta, fuji
Describe Calderas
Large, explosive eruptions of felsic pyroclastic material, created when roof of magma chamber collapses, up to 10 km across, different from a crater!!!!
**
i.e. yellowstone, wyoming, crater lake
What are the two main styles of eruption?
Effusive: outpouring of molten magma from the vent (lavas)
Explosive: gas driven violent eruptions (pyroclastic deposits)
What are the different types of effusive eruptions?
Passive,
- Lava flows: mafic-intermediate
- Lava domes: felsic - intermediate
- Gravitational collapse of lava flows/domes - pyroclastic flows
the higher the silica, higher the viscosity
What are lava flows?
Flows downslope, ponds in topographic lows, outer crust cools and solidifies, insulating molten interior
What are the different types of explosive eruptions?
- Buoyant eruption column of ash
- Pyroclastic airfall
- Pyroclastic flow (column collapse)
- Blocks/bombs close to the vent
Describe pyroclastic falls
10s of kms eruption column
Widespread distribution of ash in downwind direction
Ash blankets everythang
Describe pyroclastic flows
Gas-pyroclast mixtures Gravity driven FLow down slope, channelled in valleys velocity: 40-400 km/h hot as fuck (600degreeccelcius)
What are the keys to explosive volcanism?
Gas content and melt viscosity in the magma
- determines explosive or effusive,
as magma rises, pressure decreases, so bubbles form, but viscosity fights formation of bubbles, pressure rises in the bubbles until the strength of the liquid magma is overcome by the bubbles =producing PYROCLASTIC MATERIAL (tephra)
Why does Gas matter in volcanism?
- Magmas produce bubbles (gas exsolves) during ascent
- Bubbles expand as magma rises with lower pressure
- Foaming = explosivity
Depends on amount of bubbles, rate of rise, bubble retention
What is pumice?
Light, full of air bubbles, volcanic plume fragments
How is pyroclastic ash formed?
Liquid magma containing dissolved gas is suddenly decompressed
Gas bubbles expand rapidly and blow up liquid magma
Freezes in mid air to form ash
How is gas different in mafic/felsic magmas?
mafic: low gas content, fluid, gas escapes and pressure is released
felsic: high gas content, gooey, gas is kept under increasing pressuer
What are the ranges of explosive eruptions?
Hawaiian Strombolian Vulcanian Plinian Phreatomagmatic
Describe Hawaiian Eruptions.
Low viscosity Basaltic Low explosivity - lava flows - fire fountaining
important bits: lava fountain, lava lake, lava flow
(ash plume, fumaroles, ash plume)
Describe Strombolian Eruptions
Basaltic/andesitic magma
Intermediate composition/silica content
Mildly explosive
- bombs/lava
important parts: lava fountain, volcanic bomb, lava flow
Describe Vulcanian Eruptions
Viscous andesitic/rhyolitic magma (high silica)
Very explosive
Sustained ash
important parts: ash plume, lapilli, volcanic ash rain, volcanic bomb
Describe Plinian eruptions
Andesitic/rhyolitic ash Violently explosive Sustained ash colums Pyroclastic flows Can erupt for days
important parts: ash plume, volcanic ash rain
What is the trend of increasingly devastating eruptions?
Higher viscosity, more felsic, higher gas content
Describe Phreatomagmatic eruptions
Contact between water and magma
Water flashes to steam
Violently explosive
Surtseyan and Phreatoplinian
important parts: water vapour cloud, compressed ash, crater, water
How are eruption sizes scaled?
Volume of ash Height of eruption above vent Duration - mostly total volume erupted EXPLOSIVELY -1 unit = 10x more volume erupted
VEI Scale 0-8
Interval represents a factor increase of 10 (logarithmic scale)
What are some examples of VEI 1, 3, 5? 6?
1: hawaiian
3: vulcanian (montserrat)
5. plinian (mt. st. helens)
6. ultra plinian (mt pinatubo)
What was the impact of the 1991 pinatubo eruption
22000000 tons of SO2
global temp decreased, ozone hole size incrased
sulfer dioxide could be traced globally
What would a VEI 8 volcanic eruption look like
100 pinatubos erupting at once
TOBA an Ultraplinan 75ka, caldera forming eruption. 3 degree decrease in global temp
possibly yellowstone??\
TOBA, long valley caldera, yellowstone
what is a hazard? what is a risk?
HAZARD: any event or situation that could cause human or economic harm
RISK: probability that any given hazardous event might occur (chance of loss)
-includes vulnerability
Describe Lava Flows
Slow Not usually dangerous (usually) Mafic + low viscosity Hazards: burning, destruction Don't often kill but are hard to stop
i.e. Heimaey, Iceland
Nyiragongo: killed ppl
Describe Fire fountaining
If Basalitic lava is gas rich
small explosions
As liquid drops back, they can form a lava flow
-forming spindle bombs
Describe pyroclastic falls.
Hot gas and ash fall
Hazards: breathing ash, total darkness, rooftops collapse* ppl trying to shelter, die!
Ash getting in plane entines (suck it in) Windshields are scratched/broken
turbulence
- now satelites check for volcanic ash!
i.e. Krakatoa
Shiveluch volcano,russia
Describe pyroclastic flows
Avalanche of pyroclastic material/air/gas
Gravity driven
40-400km/hour
(mt. st. helens, vesouvious)
MOST COMMON CAUSEcollapse of volcanic column
sustained fountaining in a plinian column
NEXT MOST COMMON CAUSE: explosive collapse of lava domes - silica rich magma, highly viscous, steep sided, glowing at night
If they are big enough, they move out of the valleys and can even more over water!
What is dome collapse?
often followed by pyroclastic flows down a slope, with dense core of boulders hidden by ash billows
Describe Lahars?
volcanic mud flows
-debris flows with the water
Lahar: indonesian for volcanic debris flow
Lahars are water and loose volcanic debris
snowclad/ice clad volcanos i.e. mt baker
What are some hazards at mt. baker?
lava flows, pyroclastic flows, tephra (ash), lahars
Describe sector collapse
A volcanic landslide!
-volcanic edifice is weakened, and collapse of part of the volcnao might happen, causing a debris avalanche!
When was a key eruption for mt. st. helens? Describe it
1980 May 18th
Landslide triggered an eruption
Lateral blast of 100-300 degrees, speed of 500 km /hour, desvastating to a large area, trees blown down by the blast
Describe volcanic gases
Volcanic gases: hot, high acidity (pH 1), burn instantly
h20, c02, hcl, so4, hf
fumarole -
examples: cameroon aftrica, crater lake in dormant volcano
1986, 1700 ppl killed by breathing it in (asphyxiation)
What are the types of monitoring and prediction?
Geology and Mapping (hazard maps)
Monitering (seismology, ground deformation, gas, thermal imaging, lahar flow detection, satellite obervation)
Prediction and Hazard analysis
What are hazard maps?
Map volcanic deposits
Determine deposit type (lava flow, mud flow, pyroclastic flow) and distribution
Determine age and frequency
Consider the risk (hazard/vulnerability)
What are different monitering types and methods used by USGS volcanic hazards program?
Gas (airborn and ground)
Remote sensing (thermal imaging, satellite - ash hotspots and inSAR)
Ground vibration (eathquake and lahar sensors)
Deformation (tiltmeter, GPS, surveying)
Describe seismology and how it is helpful for earthquakes
Most important tool for monitering and forcasting
baseline monitoring is essential to recognize changes so you know normal from abnormal behavior
when magma rises, rocks crack, causing little quakes and cracks
deep quakes are shown before big explosion
Describe ground deformation techniques
As volcano bulges with magma, measure its change of shape
GPS: measure changes in position
TM: tiltmeter- measures changes in angle of slope
inSAR: interferometric synthetic aperture rador - measurements by satellites to detect changes in elevation (equation creates a time delay) volcanos change shape during intrusion of magma
often equiptment is destroyed but you get info and rate of change
**MSH interferometry - measures surface deformation (inflated/deflated)
Describe gas emission techniques?
Fumaroles!
either 1) direct sampling
2) from a distance using spectrometers that measure c02 and s02
COSPEC: correlation spectrometer
FTIR: fourir transform infrared spectrometer
Describe thermal imaging
Monitering of temp range and change
- on ground
- in helicopter
How do we detect lahars?
Moniter lahar and debris flow channels
- seismic/motion sensing systems ( real time warning, hours to flow from vent to city)
Describe satellite obervation techniques and what they can show us
Thermal pulse, ash tracking SO2 tracking - global coverage - rapid repeat measurements (15mins) -good for early warning and air routes -good for remote areas without a lot of other coverage
What can we do to protect against volcanos?
Zoning/regulation for where we put stuff, safe distance from hazards…but not much
What are the eruption warning levels?
VAN
normal: typical background, noneruptive state OR changed down from a higher level to this
advisory: signs of elevated unrest above known background level or downgraded from higher level
watch: volcano exhibiting heightened or escalating unrest with potential of eruption, timeframe unknown, eruption is underway but hazards are limited
WARNING: hazardous eruption is imminent /underway/ suspected
green/yellow/orange/red!
What is our local stratovolcano?
Mt. Baker
- dormant but hot, small eruption 1872, last major one 7000 years ago
Dominantly intermediate magma, explosive potential
Glacier covered: lahar potential
greatest risk is to abbosford in LAHAS, lava and pyroclastic flows won’t reach us!
