Module 4

Question 1

Magma

define extrusive and intrusive igneous rocks and give an example of a rock type

Answer 1

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)

Question 2

Magma

define extrusive and intrusive igneous rocks and give an example of a rock type

Answer 2

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

Question 3

Basalt= ______ igneous rock

Granite=______igneous rock

Answer 3

extrusive
-fine textured rock

intrusive
-coarse textured rock

Question 4

How Magma Forms: 3

Answer 4

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

Question 5

Steps in decompression melting forming magma

Answer 5

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

Question 6

Magma at spreading ridges is called _____ magma and creates _____ lava on the ocean floor

Answer 6

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

Question 7

Magma at continental Rifts is called _____ magma

Answer 7

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

Question 8

horst and graben landscapes are associated with…..

Answer 8

rifting within continental lithosphere

Question 9

Continental minerals are rich in _____

Answer 9

silica: calcium, alluminum

Question 10

Hotspot Volcanism

Answer 10

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

Question 11

Oceanic hotspots produce _____ magmas (e.g. Hawaii) whereas continental hotspots produce a mixture of ____ and ____ magmas (e.g. Yellowstone

Answer 11

mafic

mafic, felsic

Question 12

Yellowstone National park is an example of ____ ____ beneath a continent

Answer 12

hot spot

Question 13

In Hawaii, because of Hot spot volcanism the volcanic island arc gets older from east to west

Answer 13

• 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

Question 14

Seamounts

Answer 14

weathering and erosion of shield volcanoes works down features and they eventually become submarine features

Question 15

Addition of volatiles at subduction zones results in ______ volcanism

Answer 15

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

Question 16

Where do they occur in terms of plate tectonics?
Stratovolcanoes

Oceanic Island Arcs

Continental Island Arcs

Answer 16

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

Question 17

Assimilation

Answer 17

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

Question 18

Magma Properties:3

Answer 18

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%)

Question 19

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)

Answer 19

lower, less

Question 20

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

Answer 20

well

like mollasses

HIGh

MAFIC

Question 21

Viscosity based on igneous rock type:

1. Andesite
2. Basalt(_____)
3. Rhyolite(____)
4. Dacite

Answer 21

1.intermediate
-Andesitic magma: 800 to 1000° Celsius
more prone to explosive volcanism
-composite/strato volcano

2. (mafic)low viscosity/high fluidity-high in iron
   - Basaltic magma: 1000 to 1200° Celsius
   - cinder cone or shield volcano
3. (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

Question 22

The main volcanic gases are ____ and ____

Answer 22

H2O: water vapor
and
CO2_ carbon dioxide

Question 23

T OR F

The volatile content of magma decreases with corresponding increases in silica content

Answer 23

F

The volatile content of magma increases with corresponding increases in silica content

Question 24

• ____ viscosity=high volatile gas content

- ____ viscosity=low volatile gas content

Answer 24

high

low

Question 25

Describe each Type of Volcano with volatile content, temp, viscosity, and silica content: Low, Medium, High for each part 1. Volcanic DOME 2. SHIELD volcano 3. COMPOSITE/strato volcano

Answer 25

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

Question 26

Describe the Internal Workings of a Stratovolcano: 7 parts

Answer 26

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

Question 27

2 types of intrusive igneous rock

Answer 27

Intrusive igneous rocks: 1. Dyke=vertically oriented igneous rocks 2. Sill=horizontally oriented igneous rocks

Question 28

Lava erupts through ______ onto _______

Answer 28

fissures onto flanks

Question 29

Name 3 types of pyroclastics and relative size to one another:

Answer 29

1. Bongs=biggest 2. lippily=pebble/grvel size 3. ash=sand size travels great distances from vents

Question 30

Why are strato volcanoes called strato

Answer 30

called strato volcanoes because it is built in strata of lava and Pyroclastic

Question 31

Eruption Styles: 2

Answer 31

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).

Question 32

_____ magma is non explosive becuase... ____ magma is explosive because

Answer 32

mafic gas has the ability to rise/expand and be released, releasing pressure felsic gas cannot rise and expand, trapped bubbles increase temp

Question 33

The main products of explosive eruptions are referred to as ______ (unconsolidated) or _______ deposits (consolidated).

Answer 33

tephra pyroclastic

Question 34

Effusive erruptions are linked to _____ volcanoes

Answer 34

shield

Question 35

Explosive erruptions are linked to _____ volcanoes

Answer 35

strato

Question 36

Cinder cone:

Answer 36

same characteristics as shield volcanoe for viscosity, solica content, and rock type(basalt) yet is explosive not effusive

Question 37

Volcanic Dome

Answer 37

highly explosive because of high silica content, high viscosity, and rhyolite rock type

Question 38

Shield Volcanoes

Answer 38

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

Question 39

Composite/Stratovolcanoes

Answer 39

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

Question 40

Cinder Cones

Answer 40

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

Question 41

cinder cones are forms exclusively by _______

Answer 41

pyroclastics - form very rapidly - associated with shield volcanoes

Question 42

Volcanic Domes

Answer 42

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

Question 43

Craters and Calderas

Answer 43

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

Question 44

Volcanic Vents

Answer 44

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

Question 45

______ forming eruptions are the largest and most deadly form of volcanic eruption but fortunately they are rare;

Answer 45

caldera -eruptions that produce calderas several kilometers in diameter occur, on average, once every 200 to 1000 years.

Question 46

Fumerals:

Answer 46

where toxic gases are being released

Question 47

Resurgent Calderas

Answer 47

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)

Question 48

supervolcano

Answer 48

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

Question 49

Maars

Answer 49

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)

Question 50

Flood Basalts

Answer 50

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

Question 51

giants cossway is an example of

Answer 51

flood basalt

Question 52

decan and Siberian traps

Answer 52

release of volatile gases caused the acidicfication of the oceans and one of the mass extinctions

Question 53

Ice-Contact Volcanoes

Answer 53

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

Question 54

tuyas

Answer 54

Tuyas form when a basaltic eruption melts part of the overlying ice and produces pillow basalt in the subglacial lake

Question 55

hydrovolcanic eruptions

Answer 55

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)

Question 56

Different types of magma are produced in different plate tectonic settings: 1. Shield Volcanoes 2. Stratovolcanoes 3. Cinder Cones 4. Supervolcanoes

Answer 56

1. Shield volcanoes are typically found along divergent plate boundaries where crust is pulling apart (Iceland, East African Rift, Basin and Range) or oceanic hotspots 2. Stratovolcanoes occur above subduction zones; lava dome collapse often occurs in final stages of activity 3. Cinder cones may occur in a variety of settings- commonly in association with or on the flanks of larger volcanoes 4. Supervolcanoes are associated with the eruption of large volumes of felsic magma at continental hotspots

Question 57

_/_ of all active volcanoes on land are located along the Ring of Fire surrounding the Pacific Ocean

Answer 57

2/3

Question 58

Volcanic acitivity is mostly linked to _______ plate boundaries

Answer 58

Volcanic activity is very much linked to convergent plate boundaries(ring of fire)

Question 59

Describe the Volcanic Explosivety Index

Answer 59

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

Question 60

Describe the Volcanic Explosivety Index

Answer 60

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

Question 61

Describe these eruption styles Magmatic Eruption Phreatic eruption Phreatomagmatic eruption

Answer 61

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

Question 62

Pyroclastic Flows

Answer 62

Base surge: flaming clouds, what smothered people at vesuvias

Question 63

Compare Ultra-plinean to Hawaiien eruption styles on Volcanic Explosivety Index(0 to 8)

Answer 63

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

Question 64

VEI FULL INDEX: 0 TO 8

Answer 64

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

Question 65

Volcano: Garibaldi in Canada is important because..

Answer 65

it has explosive tendencies - 0 eruptions in our history, definately before written history - a stratovolcano in the Garibaldi Volcanic Belt (5)

Question 66

Volcanic Hazards: Primary Secondary Tertiary

Answer 66

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

Question 67

Primary Effects of Lava Flow

Answer 67

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

Question 68

Two Main Types of Balsaltic Lava Flows

Answer 68

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

Question 69

Lava’s with high silica content(____) Lavas with low silica content(____)

Answer 69

felsic basaltic

Question 70

Lava Tubes

Answer 70

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)

Question 71

Lava flow which has high viscosity: name it

Answer 71

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)

Question 72

# Define: Tephra= Eruption Cloud= Eruption Column= Tephra Fall= 3 class sizes of Tephra: name them as their sizes in mm

Answer 72

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

Question 73

Secondary Effects of Tephra Falls(6)

Answer 73

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)

Question 74

Tephra Falls Primaryy Effects

Answer 74

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)

Question 75

Tephra Falls Tertiary Effects

Answer 75

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

Question 76

Mount Baker

Answer 76

Mount Baker is an active volcano - potential larhars and lava flows are biggest worries - ash can affect up in BC

Question 77

Pyroclastic Flows and Surges

Answer 77

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)

Question 78

Due to their speed, _____, are better able to overtop topographic barriers and cross bodies of water than pyroclastic flows

Answer 78

surges

Question 79

Lateral Blasts

Answer 79

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

Question 80

Lahars

Answer 80

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

Question 81

Poisonous gases associated with volcanoes | -in general not specific gases

Answer 81

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

Question 82

A limnic eruption,

Answer 82

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

Question 83

City of Aldera, Columbia is an example of

Answer 83

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

Question 84

Jökulhaups

Answer 84

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

Question 85

How to minimize Volcanic Hazards(5)

Answer 85

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