Module 4 Flashcards
Magma
define extrusive and intrusive igneous rocks and give an example of a rock type
Magma is molten or partially molten rock beneath the Earth’s surface
We refer to magma as lava (from the Italian, lavare, meaning “stream”) when it erupts onto the Earth’s surface
Extrusive igneous rocks are produced from the cooling and solidification of magma or lava at the Earth’s surface (e.g. basalt)
Intrusive igneous rocks are produced by from the cooling and solidification of magma within the Earth (e.g. granite)
Magma
define extrusive and intrusive igneous rocks and give an example of a rock type
Magma is molten or partially molten rock beneath the Earth’s surface
We refer to magma as lava (from the Italian, lavare, meaning “stream”) when it erupts onto the Earth’s surface
Extrusive igneous rocks are produced from the cooling and solidification of magma or lava at the Earth’s surface (e.g. basalt)
-fine textured rock
Intrusive igneous rocks are produced by from the cooling and solidification of magma within the Earth (e.g. granite)
-coarse textured rock
Basalt= ______ igneous rock
Granite=______igneous rock
extrusive
-fine textured rock
intrusive
-coarse textured rock
How Magma Forms: 3
1.Decompression melting
Occurs at divergent plate boundaries, continental rifts, and hot spots
Great pressures are created at depth due to the weight of overlying rock
Thinning and stretching of the crust at rifts and divergent boundaries causes the mantle to well up towards the surface where pressures are lower
Plumes of hot rock well up to shallow depths at hotspots
A- Decompression melting occurs when the overburden pressure on rocks in the asthenosphere is lowered due to thinning of the overlying lithospheric plate
B- Decompression melting also occurs when superheated rocks well up from deep in the asthenosphere at a hot spot
2.Addition of volatiles
Occurs at subduction zones
Volatiles exist as gases at Earth’s surface (e.g. H2o and Co2)
Volatiles form in minerals within oceanic crust
Volatiles are released when oceanic crust is subducted at depths of 100-150km
The volatiles interact with dry crust, lowering the melting temperature of rocks by breaking chemical bonds within silicate minerals
3.Addition of heat
Occurs when the temperature of rocks exceeds the melting temperature of silicate rocks at that depth
This heat melts adjacent rocks which then melt and change the composition of the melting magma, a process called assimilation
-Magma is hot and as it moves through the surrounding rocks is melts rock and incorporates it in the magma plume
-PROCESS CALLED ASSIMILATION
-becomes increasingly felsic instead of mafic in its composition
Steps in decompression melting forming magma
A- Decompression melting occurs when the overburden pressure on rocks in the asthenosphere is lowered due to thinning of the overlying lithospheric plate
1.Extension at a rift valley
2.Volcanic activity occurs due to decrease in pressure from crustal stretching and thinning
3.Spreading begins at a
new mid-ocean ridge
B- Decompression melting also occurs when superheated rocks well up from deep in the asthenosphere at a hot spot
-lava plumes rising up
Magma at spreading ridges is called _____ magma and creates _____ lava on the ocean floor
mafic, pillow
At spreading ridges, mafic magma derived from the asthenosphere rises to the ocean floor to create new crust
When magma erupts underwater, it forms pillow lava, formed by repeated oozing and quenching of mafic magma
A flexible glass crust forms around the newly extruded lava, forming an expanded pillow
Pressure builds until the crust breaks and new magma extrudes like toothpaste, forming another pillow
-ex:iceland
Magma at continental Rifts is called _____ magma
felsic
Tectonic forces stretch the crust causing Earth’s surface to fracture into normal faults
This results in blocks that tilt and alternatively drop and rise (horst and graben topography)
As the crust thins, the hot mantle can rise closer to the surface, producing magma through decompression melting
Felsic magmas are produced by heating and hydration of the continental crust
The magma travels through fractures in the crust, often along normal faults
horst and graben landscapes are associated with…..
rifting within continental lithosphere
Continental minerals are rich in _____
silica: calcium, alluminum
Hotspot Volcanism
As rising plumes of hot mantle migrate upwards they begin to melt under low pressure (decompression melting) to form magma; the magma rises to the surface and forms a volcano
Hotspots are fixed positions, as the plate carrying the volcano moves away from the hot spot volcanism ceases and a new shield volcano forms in the position over the hot spot producing island arcs (oceanic) or volcanic arcs (continental)
Volcanism associated with hot spots occurs in both the Atlantic and Pacific Oceans but is more common in the Atlantic because it moves at a higher velocity
Oceanic hotspots produce _____ magmas (e.g. Hawaii) whereas continental hotspots produce a mixture of ____ and ____ magmas (e.g. Yellowstone
mafic
mafic, felsic
Yellowstone National park is an example of ____ ____ beneath a continent
hot spot
In Hawaii, because of Hot spot volcanism the volcanic island arc gets older from east to west
- sheild volcanoes are produced over hot spots
- at the same time, weathering and erosion is working down the features and they eventually become submarine features Called SEAMOUNTS
Seamounts
weathering and erosion of shield volcanoes works down features and they eventually become submarine features
Addition of volatiles at subduction zones results in ______ volcanism
RESULTS IN EXPLOSIVE VOLCANISM
.water saturates sediments and is included when it is subducted as well as carbon dioxide
-they assist with the melting of the crust, make it easier
-they then become part of the magama ascending the lithosphere
Where do they occur in terms of plate tectonics?
Stratovolcanoes
Oceanic Island Arcs
Continental Island Arcs
Stratovolcanoes occur at subduction zones around the Pacific Rim
Oceanic island arcs form at oceanic-oceanic convergent plate boundaries
Continental island arcs (e.g. Cascade volcanoes) form at oceanic-continental convergent plate boundaries
Assimilation
Magma is hot and as it moves through the surrounding rocks is melts rock and incorporates it in the magma plume
- becomes increasingly felsic instead of mafic in its composition
- creates stratovolcanoes
Magma Properties:3
1.Composition
Magmas are composed of melted silicate minerals (SiO2; referred to as silica) and dissolved gases
Differentiated on the basis of how much silica the magma contains (see next slide)
2.Viscosity (resistance to flow)
Stickiness factor: low viscosity = high fluidity
Mafic magmas have lower viscosity (higher fluidity) due to their chemical composition (less silica) than felsic magmas (in which silica tends to form strongly bonded chains)
-Differences in viscosity influence the mobility of the magma when it is erupted onto the surface as well as the style of the eruption (effusive vs explosive)
Viscosity is affected by temperature as well as composition:
Basaltic magma: 1000 to 1200° Celsius
Andesitic magma: 800 to 1000° Celsius
Rhyolitic magma: 650 to 800° Celsius
Basaltic lava has a low viscosity when it first is erupted onto the Earth’s surface; as the lava cools away from the vent, its viscosity increases
3.Gases: dissolved gases are referred to as volatiles
The percentage and type of volatiles within a magma influence its buoyancy and explosivity
The main volcanic gases are H2O: water vapor and CO2: carbon dioxide
The volatile content of magma increases with corresponding increases in silica content (e.g.) andesitic and rhyolitic magmas are more prone to explosive eruptions because they contain more dissolved gas (2-5 wt%) than basaltic magmas (<1wt%)
Mafic magmas have _____ viscosity (higher fluidity) due to their chemical composition (____[less/more] silica) than felsic magmas (in which silica tends to form strongly bonded chains)
lower, less
silica content determines how easily the lava will flow once at surface
-low viscosity= flows ____
-high viscosity= flows _____
.really high silica content means ____ VISCOSITY
______(basalt) lava has low viscosity and can flow freely and for long distances
well
like mollasses
HIGh
MAFIC
Viscosity based on igneous rock type:
- Andesite
- Basalt(_____)
- Rhyolite(____)
- Dacite
1.intermediate
-Andesitic magma: 800 to 1000° Celsius
more prone to explosive volcanism
-composite/strato volcano
- (mafic)low viscosity/high fluidity-high in iron
- Basaltic magma: 1000 to 1200° Celsius
- cinder cone or shield volcano - (felsic)high viscosity/low fluidity-low in iron
- Rhyolitic magma: 650 to 800° Celsius
- more prone to explosivve volcanism
- volcanic cone
4.intermediate
.temperature also effects viscosity
The main volcanic gases are ____ and ____
H2O: water vapor
and
CO2_ carbon dioxide
T OR F
The volatile content of magma decreases with corresponding increases in silica content
F
The volatile content of magma increases with corresponding increases in silica content
- ____ viscosity=high volatile gas content
- ____ viscosity=low volatile gas content
high
low
Describe each Type of Volcano with volatile content, temp, viscosity, and silica content: Low, Medium, High for each part
- Volcanic DOME
- SHIELD volcano
- COMPOSITE/strato volcano
Dome:
- High Volotile content
- lower temperature
- higher viscosity
- high silica content
Shield:
- low viscosity
- low silica content
- low volotile content
- high temp
Composite:
- intermediate volitile content
- intermediate viscosity
- intermediate temp
- intermediate silica content
Describe the Internal Workings of a Stratovolcano: 7 parts
1.Magma chamber or reservoir: large underground pool of magma
2.Country rock: surrounding rock that may be heated and mix with the magma
3.Dike/sill: conduits along which magma reaches surface
4.Flank: often refers to the sides of the volcano
5.Fissure: a narrow opening or crack along which magma erupts often on a volcano’s flanks
6.Fumarole: opening through which volcanic gases emerge
7. Pyroclastic: decompression of contained gases literally tears apart magma and realeases it into the atmosphere
-Bongs=biggest
-lippily=pebble gravel size
-ash=sand size travels great distances from vents
.called strato volcanoes because it is built in strata of lava and Pyroclastic
2 types of intrusive igneous rock
Intrusive igneous rocks:
- Dyke=vertically oriented igneous rocks
- Sill=horizontally oriented igneous rocks
Lava erupts through ______ onto _______
fissures onto flanks
Name 3 types of pyroclastics and relative size to one another:
- Bongs=biggest
- lippily=pebble/grvel size
- ash=sand size travels great distances from vents
Why are strato volcanoes called strato
called strato volcanoes because it is built in strata of lava and Pyroclastic
Eruption Styles: 2
The properties of magma control the type of volcano and its eruption style:
Effusive eruptions: are characterized by the outpouring of basaltic lava onto the surface (e.g. Kilaeua, Hawaii). These eruptions tend to be non-explosive because steam bubbles in the rising mafic magma are able to expand and burst.
Explosive eruptions: are characterized by the violent fragmentation of magma (e.g. Mount St. Helens, WA, 1985). These eruptions are explosive because the high viscosity of intermediate or felsic magmas do not allow trapped steam bubbles to escape leading to an increase in pressure. The main products of explosive eruptions are referred to as tephra (unconsolidated) or pyroclastic deposits (consolidated).
_____ magma is non explosive becuase…
____ magma is explosive because
mafic
gas has the ability to rise/expand and be released, releasing pressure
felsic
gas cannot rise and expand, trapped bubbles increase temp
The main products of explosive eruptions are referred to as ______ (unconsolidated) or _______ deposits (consolidated).
tephra
pyroclastic
Effusive erruptions are linked to _____ volcanoes
shield
Explosive erruptions are linked to _____ volcanoes
strato
Cinder cone:
same characteristics as shield volcanoe for viscosity, solica content, and rock type(basalt) yet is explosive not effusive
Volcanic Dome
highly explosive because of high silica content, high viscosity, and rhyolite rock type
Shield Volcanoes
Named for the resemblance to a warrior’s shield
Largest volcanoes on Earth with gently sloping sides (<5-10°) and broad summits
The shape is created from fluid basaltic lava that pours out in all directions from the central summit
Formed mostly from effusive eruptions (contains very little tephra)
Lavas also commonly erupt from vents along fractures (rift zones) that develop on the flanks of the volcano (e.g. Pu’u ‘O’o’ cinder cone on Kilauea, Hawaii)
Examples: Mauna Loa and Kilauea, Hawaii
Composite/Stratovolcanoes
Also referred to as stratovolcanoes
Characterized by a steep, conical shape (6-10° on flanks to 30° near top)
Built mostly from tephra (up to 50%) but characterized by both effusive and explosive eruptions leading to the interlayering of lava flows and tephra
Owing to the higher viscosity of felsic magmas, they are usually more explosive (and dangerous) and erupt less often than shield volcanoes
Characterized by long periods of repose or inactivity lasting for hundreds or thousands of years
Examples: Mt. Vesuvius, Italy; Mt Meager, Mt Garibaldi, Canada; Mount Baker, Mount Rainier, U.S.A.; Volcán Osorno, Chile, Mt. Fuji, Japan
Cinder Cones
These are steep-sided small volume cones (<300 m) with a round to oval surface and a crater on the top that often occur in association with shield volcanoes
They form from the accumulation of pyroclastic debris, usually cinders or scoria
Cinders or scoria form when basaltic or andesitic magma containing abundant volatiles is thrown out explosively from the volcanic vent
Scoria is recognizable from its texture of abundant cavities produced from expanding steam bubbles called vesicles
Cinder cones typically are monogenetic (erupting only once) and therefore have short life spans (decades)
Examples: Mono Craters, California; Sunset Crater, Arizona, Paricutín, Mexico
cinder cones are forms exclusively by _______
pyroclastics
- form very rapidly
- associated with shield volcanoes
Volcanic Domes
Volcanic domes are steep-sided mounds of lava that form around vents from the eruption of highly viscous high volatile felsic magmas (rich in silica) such as rhyolite and dacite
Lava piles up near vent, forming a very rough, spiny dome over the vent that is pushed up from magma below
Very dangerous as domes may produce lateral blasts (e.g. Mount St Helens, 1980) or pyroclastic flows
Examples: Lassen Peak and Mono Craters in California
-Associated with stratovolcanoes
Craters and Calderas
Craters and calderas are both circular to oval depressions at the top of volcanoes that form by the explosive ejecta of magma or from collapse when magma is withdrawn from a shallow magma chamber (see video on caldera formation at http://pubs.usgs.gov/of/2010/1173/)
Craters: less than 1 km in diameter
Calderas: larger (>1km), usually several km in size
.if you empty the magma chamber the result of that is it collapses because of weight of overlying country rocks and creates a depression(ground subsidence)
- called a calderas
- what we see in Yellowstone national park, is a large calderas
Volcanic Vents
Volcanic vents: openings at the summit or flanks of the volcano where lava erupts or tephra or pyroclastic debris is ejected
Some vents are circular and others form along linear cracks known as fissures or rift zones
______ forming eruptions are the largest and most deadly form of volcanic eruption but fortunately they are rare;
caldera
-eruptions that produce calderas several kilometers in diameter occur, on average, once every 200 to 1000 years.
Fumerals:
where toxic gases are being released
Resurgent Calderas
Resurgent calderas: are >24 km in diameter that produce more than 1000km3 of ash and fragmented rock
Produce super eruptions that are larger than any eruptions known in historic times (producing in the range of 1000 km3 of ash and fragmented rock)
supervolcano
Supervolcanoes originate when large volumes of magma rise to shallow depths in the crust above a mantle hot spot; pressure then builds until the eruption occurs
Maars
Maars are broad low relief craters that have formed by the violent interaction of magma and groundwater that form a crater by violent explosion
-Maars, craters, and calderas will often fill with water (groundwater, precipitation or melted ice) to form crater lakes (e.g. Crater Lake, Oregon)
Flood Basalts
Flood basalts: produced by extensive fissure eruptions over millions of years that result in thick, nearly horizontal lava flows covering thousands of km2 (e.g. North Mountain Basalt, Nova Scotia)
- -balsaltic magmas erupting onto oceanic or continental lithosphere can flow for very long distances
ex: giants cossway
giants cossway is an example of
flood basalt
decan and Siberian traps
release of volatile gases caused the acidicfication of the oceans and one of the mass extinctions
Ice-Contact Volcanoes
Many volcanoes erupt subglacially, that is, beneath or against glaciers (e.g. Iceland)
Tuyas form when a basaltic eruption melts part of the overlying ice and produces pillow basalt in the subglacial lake
Water leaks from the lake into the volcano below, destabilizing the magma and resulting in pyroclastic debris explosively ejected by hydrovolcanic eruptions (named for the interaction of water with magma)
Eventually the volcano breaks through the glacier surface and basaltic lava erupts to form the flat-topped tuya
In British Columbia, there is evidence of tuyas that were developed between 10,000-740,000 years ago
tuyas
Tuyas form when a basaltic eruption melts part of the overlying ice and produces pillow basalt in the subglacial lake
hydrovolcanic eruptions
Water leaks from the lake into the volcano below, destabilizing the magma and resulting in pyroclastic debris explosively ejected by hydrovolcanic eruptions (named for the interaction of water with magma)
Different types of magma are produced in different plate tectonic settings:
- Shield Volcanoes
- Stratovolcanoes
- Cinder Cones
- Supervolcanoes
- Shield volcanoes are typically found along divergent plate boundaries where crust is pulling apart (Iceland, East African Rift, Basin and Range) or oceanic hotspots
- Stratovolcanoes occur above subduction zones; lava dome collapse often occurs in final stages of activity
- Cinder cones may occur in a variety of settings- commonly in association with or on the flanks of larger volcanoes
- Supervolcanoes are associated with the eruption of large volumes of felsic magma at continental hotspots
/ of all active volcanoes on land are located along the Ring of Fire surrounding the Pacific Ocean
2/3
Volcanic acitivity is mostly linked to _______ plate boundaries
Volcanic activity is very much linked to convergent plate boundaries(ring of fire)
Describe the Volcanic Explosivety Index
The Volcanic Explosivity Index (VEI) outlines several types of magmatic volcanic eruptions and quantifies their eruption size, volume, and violence
Styles of eruptions can range from frequent and mild (predominantly effusive) to infrequent and violent (predominantly explosive)
Styles are often named after famous volcanoes that exhibit a principal type of behaviour
Some volcanoes change style over the duration of one eruptive event yet others will exhibit the same style over several eruptive events
Describe the Volcanic Explosivety Index
The Volcanic Explosivity Index (VEI) outlines several types of magmatic volcanic eruptions and quantifies their eruption size, volume, and violence
Styles of eruptions can range from frequent and mild (predominantly effusive) to infrequent and violent (predominantly explosive)
Styles are often named after famous volcanoes that exhibit a principal type of behaviour
Some volcanoes change style over the duration of one eruptive event yet others will exhibit the same style over several eruptive events
-measures energy being released like richter
Describe these eruption styles
Magmatic Eruption
Phreatic eruption
Phreatomagmatic eruption
Magmatic eruptions: defined by the VEI based on their eruptive mechanism and strength
Phreatic eruptions: non-magmatic eruptions, driven by the superheating of steam in contact with magma (sources of water may include non-volcanic lakes, crater lakes, or shallow seas)
.Produces maars
Phreatomagmatic eruptions: steam-driven explosions arising from the interaction of magma with ground water
.Hazards include ash falls and base surges
Pyroclastic Flows
Base surge: flaming clouds, what smothered people at vesuvias
Compare Ultra-plinean to Hawaiien eruption styles on Volcanic Explosivety Index(0 to 8)
0.Hawaiien:
.<0.0001 volume of ejected; 100 meter eruption column height
-frequent eruptions
8.Ultra-plinean
.>1000 volume of ejected; >25 km eruption column height
-very infrequent eruptions
.These two represent two ends of a scale with 8 total within the Volcanic Explosivity Index
TOP END OF SCALE:
.high in silica and volatile gases
.eruptive column rises to as high as the tropopause and stratosphere-making it into the global circulation system
VEI FULL INDEX: 0 TO 8
Hawaiian eruptions (VEI 0): very mild effusive eruptions characterized by lava flows (low silica, volatiles, viscosity)
Produces shield volcanoes (e.g. Kilauea, Mauna Loa, Hawaii)
Occur at cinder cones (e.g. Pu’u ‘O’o, on Kilauea has been continuously erupting lava flows since 1983)
Strombolian eruptions (VEI 1-2): mildly explosive eruptions characterized by the production of cinder or scoria Produced from the interaction of fluid magma (intermediate viscosity) with ground or sea water Occur at cinder cones such as Paricutin, Mexico and typically at stratovolcanoes (e.g. Mt. Etna and Stromboli, in Italy)
Vulcanian eruptions (VEI 2-3): more explosive than Strombolian eruptions due to andesitic to dacitic type magmas (high silica, volatiles, viscosity) Produces small/several lava domes and collapse Occur at stratovolcanoes such as Sakurajima, Japan; famous example is Nevado del Ruiz, Columbia (1985)
Peléan eruptions (VEI 4) : characterized by devastating pyroclastic flows and a larger eruption column than seen in Vulcanian events
Named for the 1902 eruption of Mount Pelée in Martinique
Produces a much larger lava dome and collapse
Occur typically at stratovolcanoes such as Mayon Volcano, Philippines; Iceland (2010)
Plinian eruptions (VEI 5-8): highly explosive eruptions produced from dacitic to rhyolitic magmas (high silica, volatiles, viscosity) that generate massive ash fallout in addition to pyroclastic flows An eruptive column is produced in the magma chamber due to the build-up of pressure propelling magma up and out of the volcanic vent into the stratosphere Prevailing winds drive the eruptive column of gases, ash, and fragments away from the volcano (ashfall) covering regions from 0.5-50km3 in size
Plinian eruptions (VEI 5-7): continued….
Pyroclastic flows are generated at speeds up to 700 km/hr and extending hundreds of kilometers from the vent
Hot materials ejected from the summit may mix with snowfall, ice, and other volcanic deposits to form lahars
Named for Pliny the Younger who documented the A.D. 79 eruption of Mount Vesuvius, Italy
Occur typically at stratovolcanoes; famous examples include Mt St. Helens, WA (1980), Hekla, Iceland (1947-1948), Mt. Pinatubo, Phillippines (1991)
Ultra-Plinian eruptions (VEI 8)
Same as Plinian characteristics but produce a much greater volume of eruptive materials (e.g.) Toba, Indonesia, 740,000 years ago
Volcano: Garibaldi in Canada is important because..
it has explosive tendencies
- 0 eruptions in our history, definately before written history
- a stratovolcano in the Garibaldi Volcanic Belt (5)
Volcanic Hazards:
Primary
Secondary
Tertiary
Primary effects
lava flows, ashfalls, volcanic bombs, pyroclastic flows and surges, lateral blasts, and poisonous gases
Secondary effects
lahars, debris avalanches, landslides, groundwater and surface contamination, floods, fires, and tsunamis
Tertiary effects
global cooling, famine, disease
Primary Effects of Lava Flow
May be basaltic (Hawaiian terms: pahoehoe, aa) or felsic (andesitic, dacitic, or rhyolitic) in composition
Basaltic flows are one of the most common but least hazardous processes associated with volcanoes
Usually travel at speeds of a few km/hour or less for distances up to many km from the vent (lava tubes)
Devastating if occurring in a populated region (fire and destruction of any structure in its path (e.g. Kalapana homes in Hawaii, 1990)
Small lava flows may dam rivers and cause upstream flooding (e.g. Tseax Cone, BC)
Lava flows may have durations of many years
Two Main Types of Balsaltic Lava Flows
1.Pahoehoe flows:
Smooth, hummocky, or ropy surface that forms as fluid lava drags cooled skin on the surface into small wrinkles and folds
Higher in temperature and volatiles but less viscous than aa flows
May develop lava tubes
2.Aa flows:
Rubbly surface composed of broken partially crystallized blocks called clinkers
Lower in temperature and volatiles but higher in viscosity; thus are much thicker and slower than pahoehoe flows
Lava’s with high silica content(____)
Lavas with low silica content(____)
felsic
basaltic
Lava Tubes
Lava tubes: develop when the surface of a pahoehoe flow solidifies but molten lava continues to flow in a channel beneath
Often consist of a main tube with several small tubes that supply lava to the front of one or more separate lava flows
Lava tubes may transport lava up to several km from the vent (e.g. in Hawaii, lava tubes carry lava 12 km from a volcanic cone in the east rift of Kilauea volcano to the ocean)
Lava flow which has high viscosity: name it
3.Siliceous lava flows:
Thick stubby flows of andesite, dacite, or rhyolite that do not travel far from volcanic vent because of high viscosity
Hazardous because they induce pyroclastic flows due to lava dome collapse (Vulcanian, Peléan , and Plinian style events)
Define:
Tephra=
Eruption Cloud=
Eruption Column=
Tephra Fall=
3 class sizes of Tephra: name them as their sizes in mm
Tephra: general term for any fragments of rock and ash blasted into the air
Eruption cloud: tephra and gases downwind of the volcano
Eruption column: tephra and gases directly above volcanic vent
Tephra fall: Tephra blown high into the atmosphere as part of the eruption column which then falls over large areas
Ash: <2 mm fragments
Lapilli: 2-64 mm fragments
Blocks and bombs: >64 mm fragments
Secondary Effects of Tephra Falls(6)
Secondary Effects:
Reduction in visibility/causes darkness and atmospheric haze
Buildings may be damaged as tephra piles up on roofs
Health hazards (respiratory illnesses)
Mechanical and electrical equipment can be damaged disrupting electrical power
Aircraft engines can experience failure (e.g. 1989, Mt Redoubt, Alaska; 2010 Eyjafjallajökull)
Tephra Falls Primaryy Effects
Ash fall affects large regions because ash is carried by prevailing winds over thousands of km:Primary effects:
Falling ash may turn daylight into complete darkness and may be accompanied by rain and lightning reducing visibility and leading to disorientation
May cause building collapse, especially if accompanied by rain (1 cm of ash adds an extra 2.3 tonnes of weight on an average house with a 140m2 roof, and this increases if the ash is wet)
Damages mechanical and electrical equipment; fine ash penetrates moving parts and abrades them interrupting transport and communications (power outages, cell phones, cars; airplanes flying at high altitudes)
Tephra Falls Tertiary Effects
Tertiary Effects:
.Atmospheric haze (causing brilliant sunsets)
.Surface water may be contaminated
.Damage to prime agricultural lands (famine)
.Contributes to temporary global cooling (e.g. Laki 1783;
Tambora, 1815; Krakatau, 1883; Pinatubo, 1991)
-Temperature from blocked out sun effects the bottom two bullets together
Mount Baker
Mount Baker is an active volcano
- potential larhars and lava flows are biggest worries
- ash can affect up in BC
Pyroclastic Flows and Surges
Primary Effect:
Flows: avalanches of hot rock, ash, volcanic rock fragments
-Can move at speeds up to 150 km/h
Surges: dense clouds of hot gas and rock debris produced by explosive interaction of water and magma
-Can move at speeds of more than 360 km/h
-Due to their speed surges are better able to overtop topographic barriers and cross bodies of water than pyroclastic flows
Examples: 1902, Mount Pelée, Martinique, 79 A.D., Mount Vesuvius, Italy; Mount Meager, BC 2350 yrs BP (BP = before present)
Due to their speed, _____, are better able to overtop topographic barriers and cross bodies of water than pyroclastic flows
surges
Lateral Blasts
Rock fragments, gas, and ash that are blown horizontally from side of volcano, mixing with avalanche deposits that sweeps down the side of the volcano and reaches up to 25 km away
Example: Mt St. Helen’s, Washington, USA, 1980
Lahars
Lahars - large amounts of loose volcanic ash and other pyroclastic material become saturated with water and rapidly move downslope
-melting snow melted and mixed can create lahars
Lahar is an Indonesian term for a mudflow or debris flow that originates on the slope of a volcano
Primary effect when hot volcanic debris mixes with large volumes of snow and ice or when earthquakes associated with volcanic activity trigger movement (e.g. Nevado del Ruiz, Colombia, 1985)
Secondary effect when lahars occur days, weeks, or years after an eruption (rainfall mixes with volcanic debris)
Examples: Nevado del Ruiz (1985), Mt Rainier, Mt Meager, Garibaldi volcanic belt
-can travel 10’s of km away following river valleys
Poisonous gases associated with volcanoes
-in general not specific gases
Magma chambers may leak gas into overlying crater lakes or limnic eruptions may occur
Volcanoes release sulphur dioxide which mix with water to form acid rain and “vog” (a type of smog)
Volcanoes also release fluorine which may contaminate pastures affecting livestock
Examples of limnic eruptions: Lake Nyos, Cameroon, Africa, 1986 and a volcanic eruption along Nass River in northern BC about 240 years ago
-In lakes occupied by calderas
A limnic eruption,
also referred to as a lake overturn, is a rare type of natural disaster in which dissolved carbon dioxide (CO2) suddenly erupts from deep lake waters, forming a gas cloud that can suffocate wildlife, livestock, and humans
-common in lakes occupied by calderas
City of Aldera, Columbia is an example of
City of aldera
-lahars came from collapse of glaciers which mixed and saturated the pyroclastic material which then flowed down and buried the city in 60 secs
Jökulhaups
Volcanic eruptions that occur subglacially or near glaciers produce jökulhaups
Jökulhaup is an Icelandic term for any sudden burst of water released from subglacial lakes or reservoirs
Jökulhaups may be triggered by melting of snow and ice from a volcanic eruption or geothermal heating
Iceland is at the greatest risk from these types of eruption-triggered floods
How to minimize Volcanic Hazards(5)
Forecasting the probability of a volcanic eruption is determined by information gained by:
1.Monitoring seismic activity
Shallow earthquakes can precede eruptions
May not provide enough time for evacuation
2.Thermal, magnetic, and hydrologic monitoring
Accumulation of hot magma changes temperatures, magnetic properties, and chemical properties of rocks and groundwater
3.Land surface monitoring
Monitoring the growth of bulges or domes
4.Monitoring volcanic gas emissions
Changes in carbon dioxide and sulphur dioxide emission rates may indicate movement of magma toward the surface
5.Geologic history
Mapping of lava flows and pyroclastic deposits can be helpful in predicting future eruptive behaviour
