Eosc 114 Volcanos & Landslides

Front 1

What is the 'Holy Grail' for Volcanologists?

Back 1

Prediction

Front 2

What are two ways in which Volcanologists study volcanoes?

Back 2

Studying & Monitoring Active Systems and Forensic Reconstruction

Front 3

Define Magma, and what are its three components?

Back 3

Melted rock below the Earth’s surface.

melt + crystals + bubbles

Front 4

Define Lava, and what are its three components?

Back 4

Melted rock exposed at the Earth’s surface.

melt + crystals + bubbles

Front 5

How do Volcanoes form? [two parts]

Back 5

1). Magma is created by the melting of pre-existing rock in the Earth’s interior (mantle & crust).

2). It reaches the surface through fractures and erupts as lava or as pyroclastic material (tephra).

Front 6

What are the four regions of The Volcanic System? (order from top to bottom)

Back 6

1. Eruption Region

2. Storage Region

3. Transport Region

4. Source Region

Front 7

In The Volcanic System, where is the Source Region located and what occurs there?

Back 7

Occurs in the Mantle, where Mantle (Peridotite) melts to form Magma (Basaltic granitic).

Front 8

In The Volcanic System, where is the Transport Region located and what occurs there?

Back 8

Occurs in the Crust, where Magma moves along cracks (magma channels) in the Earth’s crust - forming dikes and sills.

Front 9

In The Volcanic System's Transport Region, what are Dikes and Sills?

Back 9

Dikes - Vertical intrusion of magma

Sills - Horizontal intrusion of magma

Front 10

In The Volcanic System, where is the Storage Region located and what occurs there?

Back 10

Occurs in the Crust, where Magma ponds below the Earth’s surface in large Magma chambers.

Front 11

In The Volcanic System's Storage Region, what is Intrusive Rock?

Back 11

Magma that is not erupted, and freezes slowly in the crust, forming large crystals.

Front 12

What are the two different types of igneous rocks, and how are they formed?

[each rock has two terms]

Back 12

1. Extrusive/Volcanic - (Cooled at the surface, Small crystals/fine grained)

2. Intrusive/Plutonic - (Cooled below the surface, Large crystals/course grained)

Front 13

Which two basic locations do volcanoes occur?

Back 13

1. Plate boundaries [Convergent & Divergent]

2. Hotspots

Front 14

Which two types of Plate Boundaries can cause Volcanoes, and which direction do these plates move?

Back 14

1. Convergent --> <--

2. Divergent <-- -->

Front 15

Is Mafic Lava more or less viscous than Felsic lava, does it have a high silica content, does it have a high gas content, and is it generally more or less explosive than Felsic lava?

Back 15

Mafic lava has a low viscosity in comparison to Felsic lava, due to its lower silica content [45-55% SiO2]. It has a low gas content. Eruptions of volcanoes made of Mafic lavas are less explosively violent than Felsic lava eruptions.

Front 16

Is Felsic Lava more or less viscous than Mafic lava, does it have a high silica content, does it have a high gas content, and is it generally more or less explosive than Mafic lava?

Back 16

Felsic lava has a high viscosity in comparison to Mafic lava, due to its higher silica content [65-75% SiO2]. It has a high gas content. Eruptions of volcanoes made of Felsic lavas are more explosively violent than Mafic lava eruptions.

Front 17

Which Volcanic sites do you expect to find Felsic lava?

[Clue, the type of crust is important]

Back 17

Divergent boundaries, Convergent boundaries, and Hot Spots - all beneath Continental Crust.

Front 18

What are the four main types of Volcanoes?

Back 18

1. Cinder cones

2. Shield volcanoes

3. Stratovolcanoes

4. Calderas

Front 19

What type of lava do Cinder Cones eject, how explosive are they, what are they made from, and how often do they erupt?

Back 19

They eject Mafic (basalt) lava. They are usually explosive. They are formed from layers of pyroclastic ejecta. They usually erupt for a few years then never again.

Front 20

What type of lava do Shield Volcanoes eject, how explosive are they [What volcanic phenomena do they produce?], and how often do they erupt?

Back 20

They eject Mafic lava. They are usually not very explosive [flows of Pahoehoe followed by A’a]. They erupt often.

Front 21

What type of lava do Stratovolcanoes eject, how explosive are they [What volcanic phenomena do they produce?], and how often do they erupt?

Back 21

They eject Intermediate or Felsic lava. They are frequently explosive [Interbedded lava flows, pyroclastic flows, lahars]. May erupt many times and stay active for 100,000 years.

Front 22

What type of lava do Calderas eject, how explosive are they, and how often do they erupt?

Back 22

They eject Felsic pyroclastic material. They are very explosive, but erupt rarely.

Front 23

How is a Caldera created?

Back 23

When the roof of a large magma chamber collapses.

Front 24

What is the definition of Pahoehoe, and what type of Volcano creates them?

Back 24

A low viscosity lava flow with a smooth, ropy surface - they are created by Shield Volcanoes

Front 25

What is the definition of A'a, and what type of Volcano creates them?

Back 25

A high viscosity lava flow with a rough, blocky surface - they are created by Shield Volcanoes

Front 26

What is the definition of Lahars, and what type of Volcano creates them?

Back 26

A volcanic mudflow comprised of unconsolidated volcanic debris and water - they are created by Stratovolcanoes

Front 27

What three conditions can be changed to increase the rate of rock melting into magma?

Back 27

Lowering the pressure [decompression melting]

Increasing its water content

Raising the temperature

Front 28

Arrange Andesite magma, Basalt (Gabbro) magma, Dacite magma, and Rhyolite (Granite) magma from most to least silica content

Back 28

1. Rhyolite (Granite) <-- Felsic [Explosive]

2. Dacite [This magma is rarely mentioned, btw]

3. Andesite

4. Basalt (Gabbro) <-- Mafic [Less Explosive]

Front 29

Which is formed at higher temperatures, Mafic or Felsic lava?

Back 29

Mafic lava (1200-1400 C)

Front 30

What three factors affect Magma viscosity?

Back 30

Temperature, gas content, and crystal [silica] content

High Viscosity Magma is formed through colder temperatures, and has higher gas and crystal content.

Front 31

What are the two main styles of Volcanic eruptions?

Back 31

Effusive - Passive outpouring of molten magma from the vent

Explosive - gas driven violent eruptions

Front 32

Which style of eruption is characterized by lava flows [Mafic] and lava domes [Felsic]

Back 32

Effusive eruption

Front 33

Which style of eruption is characterized by buoyant columns of ash, Pyroclastic airfall [Hot ash and gas], and Pyroclastic flows (column collapse)

Back 33

Explosive eruption

Front 34

What are Pyroclastic flows made from, and what's its collective name?

Back 34

Gas-pyroclast mixtures of hot gas and rock, collectively known as Tephra

Front 35

What two factors are the key to explosive volcanism

Back 35

Gas Content + Melt Viscosity

Front 36

What three factors of Magma Foaming affect Explosivity?

Back 36

Amount of bubbles, rate of rise [bubbles expand as the magma rises], and bubble retention

More bubbles, slow rate of rise, and high retention means more explosivity

Front 37

Does Viscosity fight or aid bubble growth?

Back 37

Viscosity fights bubble growth

Front 38

When does Fragmentation occur during a volcanic eruption?

Back 38

When the strength of the liquid magma is overcome by the rising pressure inside its air bubbles.

Front 39

How explosive are Strombolian eruptions and what is the composition of their magma?

Back 39

They are mildly explosive with Basaltic/andesitic magma

Front 40

How explosive are Vulcanian eruptions and what is the composition of their magma?

Back 40

They are very explosive with Viscous andesitic/rhyolitic magma

Front 41

What style of eruption are Hawaiian eruptions, how explosive are they, and what is the composition of their magma?

Back 41

They are effusive, with low explosivity and low viscosity basaltic magma

Front 42

How explosive are Pelean eruptions and what occurs during them?

Back 42

They are violently explosive and are characterized by large dome collapses

Front 43

How explosive are Plinian eruptions and what is the composition of the columns of ash that they produce?

Back 43

They are violently explosive with Andesitic/rhyolitic ash

Front 44

How explosive are Phreatomagmatic eruptions and where do they occur?

Back 44

They are violently explosive, and they occur underwater.

Front 45

Arrange these types of eruptions from most to least explosive:

Hawaiian, Pelean, Plinian, Strombolian, and Vulcanian

Back 45

1). Plinian

2). Pelean

3). Vulcanian

4). Strombolian

5). Hawaiian

Front 46

Why does high viscosity promote high explosivity?

Back 46

Highly viscous magma lets bubbles grow, as it is very difficult for gas to escape. This increases the pressure of the gas, which increases the intensity with which the magma is ejected out of a volcano

Front 47

What does adding external water to magma do to the explosivity of an eruption - and what causes the change in explosivity?

Back 47

Increases it due to rapid heating of water

Front 48

What are the three key characteristics that define the Volcanic Explosivity Index (VEI) - and how high does the VEI's scale go?

Back 48

1. Volume of ash produced

2. Height of eruption cloud above the vent

3. Duration of eruption

The VEI goes to a maximum of 8

Front 49

Increase in 1 unit on the VEI equals how many times more volume of volcanic material erupted?

Back 49

Ten

Front 50

What is the definition of a Volcanic Hazard?

Back 50

Any potentially dangerous volcanic process (e.g. lava flows, pyroclastic flows, ash fallout, lahars)

Front 51

What is the definition of a Volcanic Risk?

Back 51

Any potential loss or damage as a result of Volcanic Hazard.

Front 52

What formula can be used to calculate Volcanic Risk?

Back 52

Risk = Vulnerability x Hazard / Mitigation

Hazard = size, frequency, type of damage

Vulnerability = what is impacted and value

Mitigation = $ invested to reduce Vulnerability or to control hazard

Front 53

What are Lava Flows generally hazardous towards?

Back 53

Buildings & infrastruture.

Front 54

What conditions are ideal for Fire Fountaining (Small explosive eruptions)?

Back 54

If Basaltic lava (Mafic) is gas-rich

Front 55

What are three Hazards for people from Pyroclastic Falls - and what is the most dangerous?

Back 55

• Breathing in ash

• Total darkness

• Roofs collapse – most dangerous problem

Front 56

What are three potential weather effects from Pyroclastic Falls?

Back 56

1). Fine ash and gas blasted into stratosphere and interfering with incoming sunlight, causing a cooling effect

2). SO2 picks up oxygen and water to form sulphuric acid, causing acid rain

3). Excess CO2 creates a greenhouse warming effect

Front 57

What are the two most common origins of Pyroclastic flows?

Back 57

1). Collapse of a volcanic ash column [Most common] <-- generally Explosive

2). Explosive Collapse of highly viscous, silica-rich Lava domes <-- generally Effusive [Felsic]

Front 58

What causes a Volcanic Sector collapse?

Back 58

A volcanic edifice is weakened during eruption, causing a collapse of part of the volcano, and a debris avalanche

Front 59

What are the five major components of highly acidic and toxic volcanic gas?

Back 59

H2O, CO2, HCl, SO2, and HF

Front 60

What three things do Hazard Maps do?

Back 60

1). Map volcanic deposits

2). Determine deposit type (lava flow, mud flow, pyroclastic flow, etc.) and distribution

3). Determine age of deposits and eruption rate

Front 61

Fill out the simplified Hazard Map Key

Back 61

A – Ash fall

B – Pyroclastic flow

C - Lahar

D - Bombs

E – Lava flows

Front 62

What Hazards does the Stratovolcano Mt. Baker pose for the surrounding area?

Back 62

Lahar hazard (due to Glaciers) in surrounding valleys including Abbotsford, with a low risk Intermediate Lava & pyroclasticflow hazard in uninhabited areas close to Mt. Baker

Front 63

What is the Return period of large landslides in BC?

Back 63

25 to 70 years

Front 64

What three factors are used to classify (name) landslides?

Back 64

1) Type of material

2) Type of movement

3) Rate of movement

Front 65

Name four types of Landslide material that could be used to classify (name) them

Back 65

1) Rock

2) Soil/Earth

3) Mud

4) Debris (mixture of rock, earth,trees, water etc.)

Front 66

Name four types of Landslide movement that could be used to classify (name) them

Back 66

a) Falls

b) Slides – Cohesive block moves on a failure surface

c) Flows – fluid motion

d) Complex movements

Front 67

What are the two types of Landslide 'Slide' movements and what differentiates them?

Back 67

Rotational slide -- occurs on a Curved/bowl shaped failure surface

Translational slide -- occurs on a Flat/planar failure surface

Front 68

If a landslide's rate of movement is slow, what are two ways that they can be generally classified (named)?

Back 68

Creep, or Soil/Earth flow

Front 69

Definition of a slope's Angle of Repose

Back 69

Steepest angle a slope can maintain without collapsing [The exact angle varies depending on material]

Front 70

What is the Driving Force affecting the stability of a slope?

Back 70

Gravity, which manifests as Shear stress (τ) [“Shearing” is gravitational motion from side to side across a plane]

Front 71

What are the two Resisting Forces affecting the stability of a slope?

Back 71

Friction – Resistance to sliding (proportional to normal force/stress)

Cohesion – How the material holds together

these both manifest as Shear strength (τf) [the slope’s ability to resist shearing motion]

Front 72

We can model the stability of any slope by comparing ____(A)______ forces (Shear _____(B)______ / more stable) to _____(C)______ forces (Shear _____(D)______ / less stable)

Back 72

A). Resisting

B). Strength

C). Driving

D). Stress

Front 73

What are the five External causes of landslide Mass Movement?

Back 73

1) Slope angle

2) Undercutting

3) Overloading

4) Vegetation

5) Climate

Front 74

What is the definition of Undercutting, one of the External factors of Mass Movement?

Back 74

When the supporting material of the lower part of a slope is removed [Caused by roads, rivers, buildings, etc.]

Front 75

What is the definition of Overloading, one of the External factors of Mass Movement?

Back 75

Adding weight at the top of a slope [Caused by buildings, roads, landslides, trees etc.]

Front 76

What are two ways in which Vegetation affects landslide Mass Movement?

Back 76

Roots bind loose material, so the removal of vegetation can make slopes unstable.

Heavy trees can cause Overloading

Front 77

How does Climate contribute to Mass Movement as an External factor?

Back 77

More water causes Increased weathering of rocks, more fractures, more soil, etc.

Front 78

What are the three Internal causes of landslide Mass Movement?

Back 78

1) Water content

2) Inherently weak materials

3) Adverse geologic structures

Front 79

What are four ways the Internal cause of Water Content increases Mass Movement in all slopes

Back 79

–Adds weight (overloading)

–Decreases normal stresses, which decreases friction and Shear Strength [Resisting Forces]

–Increases weathering

–Acts as a medium for flows

Front 80

How do varying levels of Water Content affect the Angle of Repose/cohesion of a slope in sediment (loose rocks, sand, silt, and clay)

Back 80

No water - low angle of repose

Some water - high angle of repose

Too much water - very low angle of repose

Front 81

What are two ways the Internal cause of Water Content increases Mass Movement in solid rock

Back 81

– Water reduces Shear strength along planes of weakness (fractures)

– Causes Frost wedging/Freeze thaw, where water gets into cracks and fractures (joints), freezes, and expands, forcing the fractures apart.

Front 82

Clay, an inherently weak material, is affected by Van Der Waals forces. What therefore increases cohesion between clay particles?

Back 82

Salt water content.

Front 83

What can lower the salt content (therefore lowering the cohesion) of Clay?

Back 83

Percolating groundwater

Front 84

What is the definition of a Trigger?

Back 84

A force or event that disrupts the equilibriumof a slope and initiates mass movement [e.g. Earthquakes, Snow melt, Heavy Rainfall]

Front 85

Could the Oso Landslide have been predicted?

Back 85

Yes, landslide warnings went back decades, but a buyout program [Avoidance] was unsuccessful

Front 86

What is the highest rank for Landslide Velocity Class? - and which ranks are dangerous to humans?

Back 86

7 - Extremely rapid

6-7 are dangerous to humans

Front 87

What are some techniques you can use to Investigate whether a slope will fail or not, and if it fails where it will go?

Back 87

1) Looking at historical records to develop GeoStatistics for a region

2) Geologic Mapping of materials and properties on site

3) Hazard Mapping

4) Modeling

Front 88

What are the three paths, after Investigation, to Mitigate landslides?

Back 88

1) Avoidance

2) Prevention

3) Protection

Front 89

What is the definition of Avoidance, one of the paths to mitigate Landslide effects? -- And what is its main drawback?

Back 89

Move to a different area, avoid problem

In almost all cases Avoidance is too expensive

Front 90

What is the definition of Prevention, one of the paths to mitigate Landslide effects?

Back 90

Do something to make sure landslides don’t occur, or don’t occur when people are there

Front 91

What is the definition of Protection, one of the paths to mitigate Landslide effects?

Back 91

Armour or strengthen the area that might be affected if landslide happens [minimize Hazard]

Front 92

What are four ways of applying Prevention, one of the paths to mitigate Landslide effects?

Back 92

1. Removing material before it slides [includes scaling].

2. Applying a resisting force at the bottom of a slope such as retaining walls or gabions, to counter undercutting

3. Tensioning - anchoring unstable layers using cables tightened by nuts at surface, and anchored to stable rock underground

4. Draining excess water

Front 93

What are five structures that can be built to minimize the Hazard of landslides? [utilizing Protection, one of the paths to mitigate Landslide effects]

Back 93

1. Rock Barrier

2. Rock Net

3. Rockfall Shed - shields roads

4. Rock Fences, that catch falling/rolling rocks and dissipate kinetic energy

5. Debris flow retention structures, that remove debris from water

Front 94

What tree shape indicates that landslides occur?

Back 94

Pistol Butt Trees

Front 95

What is the definition of Scaling?

Back 95

A method of landslide Prevention Mitigation where pieces ('scales') of rock are taken off a mountainside in a controlled, safe way.

Front 96

How does Tensioning, a method of landslide Prevention Mitigation, stop landslides from occurring ?

Back 96

Steel cables increase stress perpendicular to the plane of weakness

Front 97

With regard to landslides, shear strength is _____.

A. the cohesion between grains in a rock or sediment sample

B. the degree to which the surface tension of water holds material together

C. a combination of all the factors causing geologic materials to resist shear stress

D. a combination of composition, density, and electromagnetic attraction within geologic materials

E. slope steepness plus composition

Back 97

C. A combination of all the factors causing geologic materials to resist shear stress

Front 98

What would be MOST likely to trigger a landslide on the coast of BC?

Back 98

Heavy Rainfall

Front 99

Shear strength directly depends on which of the following?

A. slope composition

B. slope gradient

C. shear stress

D. earthquake frequencies

E. gravity

Back 99

A. slope composition

Front 100

What is the Fs (factor of safety), and what amount does it have to be for a landslide to occur?

Back 100

The factor of safety is the shear strength of a slope/the average shear stress. Slope failure will occur when the factor of safety is less than 1.0