Geology midterm 3

Volcanism

Go with the flow vs crack under the pressure

1. Formation of magma

a. Magma = molten rock

b. Increased temperatures means melting molten rock

c. Decreased temperature means hardened crust and solidified rocks

d. Most magmas come from the partial melting of the asthenosphere (mantle)

i. Underground where temperature and pressure is high

e. Three major mechanisms:

i. Decompression

1. At a divergent plate boundary at the rift because the asthenosphere/lithosphere is weakened with less pressure

2. The melting temperature of mantle silicate rocks at the Earth's surface: 1200°C

3. This temperature is reached in the first 100 km

4. Increase in pressure means mantle at the solid state

5. A decrease in pressure without a change in temperature=melting

6. Divergent boundaries, continental rifts, hot spots

ii. Addition of volatiles

1. Addition of volatiles = lowers the melting temperature (helps to break chemical bonds within silicate minerals)

2. Volatiles (e.g. H2O and CO2) are incorporated into minerals, and released at subduction zones

3. H2O also released from subducting sediment

4. Interaction with “dry” asthenosphere = melting

5. Subduction zones

iii. Addition of heat

1. Addition of heat = melting, if the temperature of the rock is greater han the melting temperature at the depth

2. Rising of magma through crust can melt the surrounding rocks (transfer of heat)

3. Assimilation/mixing of the two magmas

2. Magma properties

a. Composition

i. Molten silicate minerals (silicate solution)

ii. Volatiles (dissolved gases): H2O and CO2

iii. Major elements: O, Si, Al, Fe, Mg, Ca, Na, K

iv. Si and O combined: SiO2 (silica)

v. SiO2 content influences magma properties

b. Viscosity, dissolved gases and style of eruption

i. Silica content is proportional to the viscosity

ii. Viscosity: resistance to flow, stickiness, thickness

iii. A magma with a high silica content has a high viscosity;

1. Flows slowly (not easily)

2. Lavas are restricted to the vent region

3. Forms steed-sided volcanoes

4. Contains more volatiles

a. Two glasses, one with water, one with cold molasses, put a straw in each of them, in the water the air will bubble and move to the surface quickly, in the molasses it will take a very long time to do the same

b. So high silica content magma is the molasses in that example

5. Causes explosive eruptions (champagne...) and pyroclastic flows

a. The “molasses” type magma cant release the gases enough so it builds up pressure so high that it has explosive eruptions

b. Pyroclastic flows: pyro (fire) + clast (fragments)

c. Ashes, gases (toxic), rock fragments come from the eruption

i. Deadly, super-fast up to 3-400km /hr, super-hot up to 1000°C (T that hot, one breath destroys your lungs)

6. Super high viscosity: it will just build up and build up and build up like a spine or needle (or jenga tower) and the higher it gets the more unstable it is until it tumbles and triggers the eruption

7. Ex:

a. Soufriere Hills, Montserrat

i. High viscous content

b. Colima Volcano, Mexico

i. High column of ash

c. Mount St. Helens, US

i. Even higher column of ash, super explosive volcano

d. Volcanic bomb: giant rock thrown 100s of m away from the crater

e. Pyroclastic flows: Sinabung Volcano, Indonesia

i. Like a dragon of smoke rushing down the side, gigantic smoke cloud

iv. A magma with a low silica content has a low viscosity:

1. Flows rapidly (but distance from volcano, temperature)

a. The further the lava flows from the surface of the volcano, the lower the temperature, and the slower it flows

2. Lavas can travel 10s and 100s of km

3. Forms gently sloping volcanoes

4. Contains little volatiles

5. Causes effusive (non-explosive) eruptions of fluid lavas

6. Ex:

a. Hawaii

b. Piton de la Fournaise, Reunion Island

3. Types of volcanoes

a. Four types of volcanoes

i. Volcanic domes

1. Rhyolitic

a. Form from rhyolitic magmas:

i. Very high silica content and very high viscosity

b. The very high viscosity prevents lava from flowing

c. The lava thus forms dome-shaped steep-sided mounds, where lava slowly cools in situ (in place)

d. Explosive eruptions (accumulation of gases) or pyroclastic flows (if dome collapses while still hot/molten)

i. Higher chance of huge ash clouds (pyroclastic flows)

ii. Volcanic dome:

1. Mono Craters, US

a. Crater mountain, california

b. Volcanic dome and lava dome.

2. Paoha Island in Mono Lake, US

3. Chaiten Volcano, Chile

4. Paluweh Volcano, Indonesia

ii. Stratovolcanoes

1. Rhyolitic/andesitic

a. Form from rhyolitic to andesitic magmas:

i. High silica content and high viscosity

b. The high viscosity prevents lava fromfowing far from the vent

c. The alternating layers (or strata) of hardened lavas an pyroclastic deposits form steep-sided cones

d. Explosive eruptions and/or pyroclastic flows

i. Stratovolcano:

1. Mount Fuji, Japan

2. Mount St. Helens, US

3. Mount Adams, US

iii. Shield volcanoes

1. Basaltic

a. Form from basaltic magmas:

i. Low silica content and low viscosity

b. The low viscosity allows the lava to flow far from the vent, for 10s and 100s of km

c. The successive lavas thus form broad domes with gentle slopes resembling a soldier’s shield

d. Effusive eruptions, i.e. flows of fluid lavas (non-explosive eruptions)

i. Shield volcano

1. Mauna Kea, Hawaii

2. Skjaldbreiour, Iceland

3. Piton de la Fournaise, Reunion Island

iv. Cinder cones

1. Basaltic

a. Form from basaltic magmas:

i. Low silica content, low viscosity, and rich in volatiles

b. The volatile-rich magma “explodes” and is blown out into the air as fragments that quickly cool and fall back onto the ground as scoria

c. The fallout of scoria froms cones with slopes between 30-40° (angle of repose)

d. Towards the end of the eruption, the fluid lava may drain from the base of the scoria cone

i. Cinder cones

1. SP Crater, US

2. Paricutin Volcano, Mexico

3. Chaine des Puys, France

4. Distribution of magmatism

a. most magmatism/volcanism occurs along divergent and convergent tectonic plate boundaries

b. Magmatism also occurs in the interior of tectonic plates rather than at their margins; it is termed intraplate magmatism, or hot spots

1) Divergent boundaries

a) Mid-ocean ridges magmatism

i) Located at mid-ocean ridges, where two newly-formed oceanic plates move away from each other

ii) Basaltic magma

iii) Produces new oceanic crust

iv) On the sea floor, the lava cools quickly and forms pillow lavas (or pillow basalts)

b) Continental rifts magmatism

i) Located at continental rifts, where a continent is pulled apart and thinned by a system of faults

ii) Rising basaltic magma can lead to a partial melting of the continental crust (of andesitic to rhyolitic composition)

iii) Magma can therefore vary from basaltic to rhyolitic

iv) Eruptions are diversified: shield volcanoes, basaltic fissure eruptions (curtains of fluid effusive lavas), cinder cones, stratovolcanoes and volcanic domes (explosive)

(1) Shield Volcano, Erta Ale (East African Rift)

(2) Stratovolcano, Mount Meru (East African Rift)

2) Convergent boundaries

a) Ocean-ocean subduction (island arc)

i) Located at ocean-ocean subduction zones

ii) Mainly andesitic magma

(1) But can vary from basaltic to rhyolitic

iii) Eruptions mainly explosive (stratovolcanoes)

(a) Caribbean

(i)

(b) Soufriere Hills, Montserrat

(i) Pyroclastic flows, explosive nature of these volcanoes

1. 1995, 97, 06, 08, 10

2. Video: Lava dome collapsed, pyroclastic flow cascaes down the northern side, 3 eruptions of pyroclastic flows, up to 128km/hr, part of the pyroclastic flows divides and called a surge invades out of the valley into farmland and after 22 min 12 people are dead (?)

(i) New village after last eruption

(ii) Village was 6 km away from the volcano, took 30sec-1min for the village of 30,000 people to be dead

(iii) All the walls in the city parallel to the pyroclastic flows are still standing, but all the perpendicular walls were laid flat

(iv) City of 30,000 people and only one survivor, a man who stabbed someone and was in a prison cell, thick walls, insulated, had 3rd degree burns but only one who survived because he was in the cell

(d) Sumatra, Indonesia

(i) Tsunami that was hard enough to alter the tilt of the earth, in the context to the ocean-ocean plate boundary

(ii) Earthquakes, tusnamis and volcanoes here

(e) Sinabung Volcano, Indonesia

(i) After 400yrs of dormant, it erupted in 2014, 16, 21

(ii) Pyroclastic flow on the side

(iii) Ocean-ocean, explosive, andesitic

(f) Luzon Island, Philippines

(i) Philippine plate subducted under other one created Pinatubo Volcano

(g) Pinatubo Volcano, Indonesia

(i) 34 km high ash plume, something strong enough to propel the ash that high

(ii) dropped temperature of .5 degrees from the amount of ash blocking the sun

b) Ocean-continent subduction (continental arc)

i) Located at ocean-continent subduction zones

ii) Rising basaltic magma can lead to a partial melting of continental crust (of rhyolitic to andesitic composition)

iii) Mainly andesitic magma, but generally higher silica content than in island arcs

(1) But can vary from basaltic to rhyolitic

(2) Continental plate is richer in silica

iv) Eruptions mainly explosive (stratovolcanoes)

(a) Mount St. Helens (Cascade Range)

(i) 25-30 km high ash plume

(ii) 1980 eruption, more domes starting forming inside the dome in the crater

(b) Mount Mazama and Crater Lake (Cascade Range)

(i) Connection between lake and volcano, caldera

(ii) Mazama volcano way back when, 7700 years ago erupted, emptied it out from the inside, mountain structure above collapsed into the empty space, became a caldera (depression in cauldron shape, then filled with water became a lake

(iii) Eruption so explosive it emptied itself out completely

(iv) Andesitic, silica rich magma

(v) Cinder cone volcano inside the crater lake/caldera

(vi) What caused the caldera was andesitic, but after that something that was basaltic erupted causing wizard island in the middle of the caldera of crater lake

(i) Super rapid pyroclastic flows, covered them during their sleep

3) Hot spots

a) Oceanic

i) Located in the interior of an oceanic plate, above a fixed mantle plume

ii) Somewhere in the middle of the plate, nothing to do with the plate boundaries

iii) The hot rock transported from the base of the mantle up to the base of the lithosphere is decompressed and experiences partial melting

iv) Basaltic magma

v) Effusive eruptions of fluid lavas (shield volcanoes)

(a) Hawaii

(b) Mauna Kea, Hawaii

b) Continental

i) Located in the interior of a continental plate, above a fixed mantle plume

ii) Rising basaltic magma causes the partial melting of the continental crust (of rhyolitic to andesitic composition)

iii) Rhyolitic magma

iv) Very explosive eruptions leading to caldera formation

(a) Yellowstone, US

4) Special Cases-

a) Iceland

i) Mid-ocean ridge + hot spot

ii) Mainly basaltic magma

(1) But also rhyolitic and andesitic

iii) Mainly effusive eruptions of fluid lavas:

(1) Fissure eruptions (curtains of lava)

(2) Shield volcanoes

(3) Cinder cones (aligned)

b) Flood basalts

i) Continental rift + hot spot

ii) Basaltic magma

iii) Partial melting at the rift of the very hot asthenosphere from the mantle plume (hotter than normal asthenosphere)

iv) Low-viscosity lavas spread out over vast areas, forming vast plateaus called Large Igneous Provinces (LIPs)

v) “Traps” = stairs (swedish)

(1) after eruption, these successive flows erode, the interfaces of erosion at each flow causing dropping and stair-like edges

(a) Columbia River Basalts, US

(b) Deccan Traps, India

5. Volcanic hazards

a. Lava flows (e.g. Hawaii)

b. Pyroclastic flows (e.g. Montserrat, Sinabung)

c. Lateral blast (e.g. Mount St. Helens)

d. Ashes (e.g. Pinatubo, Iceland)

i. Roof collapse (weight, especially if wet)

ii. Toxic chemical substances (humans, crops)

iii. Climate (volcanic winters)

iv. Crops buried/destroyed

v. Aircraft

e. Landslides (Mount St. Helens)

f. Toxic gases

i. Nyos Lake, Cameroon, Africa, 1986

1. Lake is within a crater, somewhere underneath somewhere there is a magmatic chamber containing CO2 gases in the magma

2. Very deep lake, the top water wouldnt mix with the bottom water

3. The co2 dissolved in the water from below, and since the top and bottom dont mix, there was a lot of co2 in the bottom layer of water and didnt mix with the surface, and then it kept filling and filling until there was too much and it bubbled up to the surface, but because it is more dense than air, it stayed close to the surface, travelled through the valley and filled the crater and valley, replacing all the oxygen with co2 gases, killing thousands of people and livestock in that valley

g. Lahars

i. Cars, homes buried in ash/water mix

1. When ashes mixes with water, it becomes a muddy mixture, rushes down the slope, and becomes a hazard because it is much more dense than mud because of the ash, can carry boulders and trees, etc., making it very hazardous

ii. Lahar in Semeru 2003

1. Sudden lahar happening, following an eruption and a sudden heavy rainfall, creates a lahar, a very hot dense temporary river

h. Jokulhlaup

i. Breach following a volcanic eruption in a glacier

6. Products of magmatism

a. Texture of igneous rocks

i. Magma can crystallize:

1. Underground (inside the Earth’s crust):

a. Intrusive igneous rock

b. Slow cooling

c. Big crystals --> phaneritic texture

2. On the surface of the Earth’s crust:

a. Extrusive igneous rock

b. Rapid cooling

c. Small/tiny/microscopic crystals --> aphanitic texture

3. Intrusive rocks:

a. Basaltic slow cooling:

b. Andesitic slow cooling:

c. Rhyolitic slow cooling: Granite

4. Extrusive rocks:

a. Basaltic fast cooling: Basalt

b. Andesitic fast cooling: Andesite

c. Rhyolitic fast cooling: Rhyolite

b. Some structures

i. Batholith:

1. Very large (vast) body of intrusive igneous rock (> 100km^2)

a. Mont St-Hilaire

i. Sedimentary strata

ii. Igneous rock (batholith) in between sedimentary rock

iii. Differential erosion (different rocks erode at different rates)

iv. Mont st hilaire is just the batholith that didnt get eroded as fast as the surrounding sedimentary rocks, meaning the underground igneous rock structure (batholith) became an above ground surface

v. Magmatic chamber that cooled underground

b. Monteregian Hills

ii. Dyke:

1. Tabular intrusion of igneous rock that cuts through the surrounding rocks

a. Subvertical cross-cutting relationship in relative dating

iii. Sill:

1. Tabular intrusive igneous body emplaces parallel to the layering of the surrounding rock

a. Horizontal injection of magma that cooled between two layers of rocks

iv. Laccolith:

1. Dome-shaped intrusive igneous body between two layers of sedimentary rock

v. Plateau basalt:

1. Vast area of superimposed sheets/layers of successive basaltic lava flows (area 100s km squared, 1-2 km thick)

a. Columbia River Basalts, US

b. Giant’s Causeway, Ireland

c. Devil’s Postpiles, US

d. Could form columnar joints

vi. Volcanic neck:

1. Resistant steep-sided volcanic pipe standing above the surrounding terrain following erosion of the volcanic cone

a. Agathla Peak, US

b. Devil’s Tower, US

Are there volcanoes elsewhere in the Solar System?

· Venus

o Yes, some volcanic systems, some volcanic flows on the surface

· Mars

o Mount Olympus on Mars, one volcano, 600km wide, 27km high

o What type of volcanism is responsible for this single volcano, and why is it so big?

§ Hotspot volcano

§ But we have hotspot volcanism on earth, but not as big as on mars, why?

· Could it be erosion?

o No

· Hotspot volcanism with no plate tectonics on mars so doesnt have to go through the plate like it does on earth

· Io

o Jupiters moon

o Extreme gravitational pull from jupiter and the other satellites, therefore a lot of pushing and pulling in its core, keeping the rocks always moving and hot and tidal heating, causing more intense volcanic activity on Io

Mass Movements: A moving experience

1. Introduction

a. Most expensive natural hazard in Canada:

i. 1000s of small “landslides” every year; mostly in the Spring and Fall... why?

ii. 200-400 M$/ year

iii. Growing population (630 deaths since 1840)

b. Materials are constantly pulled downslope... by what?

i. Gravity, always trying to pull everything down so that the earth would be flattened

c. How come then there are still topography and mass movements today?

i. Plate boundaries, volcanism, etc.

d. Mass movements vs Landslides

i. Landslide is misleading, not just slides, other movements too, mass movements is the better term for it

e. Travel speeds are very variable (e.g. creep vs rockslide and debris flow)

i. Creep is very slow

1. Sign of creep is when on the side of mountains, the tree trunks curve at the bottom to make sure they can still grow straight up

2. Takes years and years for creep to occur

ii. Debris flows and rockslides are much faster

1. Rockslide is like cartoon movie landslide, everything comes crumbling down really fast, like an avalanche

2. Forces on slopes

a. Stability of the slope: driving force vs resistance force:

i. Driving force > Resistance = Movement

ii. The gravity pulls straight down to the center of the earth, the bigger the slope, the higher the gravitational pull

b. Driving force (main):

i. Gravity: causes the downslope movement; it operates at all times 24/7

ii. Pulling things down

c. Resistance force:

i. Cohesion of material (chemical bonds, cement, interlocking crystals, electrical charges

ii. Friction

iii. Keeping things in place

d. Earthquakes and heavy rainfalls are examples of what can provide the initial energy needed to overcome the resistance force and cause a movement

e. Angle of repose:

i. Maximum angle at which debris can accumulate (beyond this angle, the resistance force is generally not strong enough to hold the particles together)

3. Conditions of slope instability

a. What is the main force pulling materials down to decrease the inclination of the slope, and controlling the mass movement?

i. Gravity?

b. The driving and resistance forces are not static

c. Some factors/variables tend to increase slope instability (changing Fd and Fr) to facilitate the work: they are the conditions of slope instability

i. How can they affect the driving force to increase the odds of a slope failure? Example...

1. Increase driving force

2. Decrease resistance force

3. Cliffside view over the ocean, building roads and houses and towers on the top of the slope, creating instability

4. Time, nothing lasts forever, over time the rock cliff could open cracks and fissures and decrease the instability

ii. How can they affect the resistance force? Example...

1. ^^

d. Conditions of slope instability (factors affecting Fd and Fr):

i. Type of material

1. The material composing a slope can affect both the type and the frequency of mass movements

2. Speed/rate of movement

a. Slow

b. Rapid

3. Main material characteristics to consider:

a. Mineral composition

i. Rock vs Regolith

1. Regolith: soil, sediment, etc.

ii. Clays (clay minerals) (more susceptible to mass movements):

1. Expansion (wet) / contraction (dry) (e.g., creep)

2. Liquefaction (e.g., quick/sensitive clays)

a. Quick clay

i. Super fine sediment, on which you can build stuff on top of, super sturdy, BUT, once disturbed it liquifies (liquefaction)

ii. Comes from glacial sediment, as glaciers move, they grind on the rock below and create a rock powder, comes from glacial erosion

iii. Deposits in a marine setting, among these particles, there are clay minerals with a resulting negative charge around them, if it is deposited in a marine setting with positive ions like sodium for example, it attracts the clay sheets, and neutralizes the negative charge with the saline water in the marine setting

iv. *Glacial sediment that can liquify/flow if disturbed and create a mass movement

b. Rissa Landslide, Norway, 1978

i. At some point there was a trigger event that caused the original liquefaction of the ground and backtracked (retrogressive) into the rest of the ground dropping it all into the hole that formed

ii. Covered an area of 25-35 sq m

b. Cementation / consolidation

i. Decrease in cohesion due to the dissolution of the cement that binds the grains together or the chemical alteration of the rocks (making the rocks more friable)

1. Thin section image, fossils 440Ma

a. Cement holding all those fossils together

b. Fresh water (slightly acidic) comes along and dissolves the cement, the whole thing falls apart

2. Granite (intrusive version of Rhyolite, intrusive igneous rock)

a. When it comes to the surface, it's not happy because granite is an intrusive rock, it goes through chemical alteration

c. Planes of weakness

i. Fracture (e.g. frost/thaw, exfoliation)

1. Periglacial environment? - frost/thaw example

a. When water freezes it expands, 9% volume increase

b. If theres a tiny crack in the cliff, and a bit of water comes in, overnight it freezes and widens the crack a bit. Then it thaws during the day, sinks further in the rock, and freezes again, furthering the widening of the crack in the cliff face

c. Spectacular Rockslide in Switzerland (two angles) video on youtube

i. Most likely an example of frost and thaw

2. Exfoliation

a. When the granite is initially 5-10 km down, eventually given enough time will slowly make its way up to the surface. As it comes up, it is no longer covered with the pressure of 5km of rock, 4, 3, 2, 1, at the surface and no more pressure and it can expand. At the surface it is brittle, and as it expands, it cracks open and forms peals or slabs of rock that is parallel to the surface, Yosemite National Park, USA, granite cracked open with exfoliation joints

b. Exfoliation joints= planes of weakness

ii. Bedding plane

1. Sedimentary rocks are made of sediment that is typically deposited horizontally, but if its got to move somewhere, it will go into the bedding planes, making it a plane of weakness

iii. Metamorphic foliation

1. When all the different elements in a rock realign perpendicular to the maximum pressure

2. Creates a preferable alignment in the rock

iv. Soft rock

1. Layer of clay underground and for some reason it receives water, becomes mushy mushy and the other top rocks can slide over the wet expanded layer

v. Old failure surface (landslide or fault)

1. Especially if high angle

ii. Slope angle and topography

1. Slope: steep slope = larger component parallel to the slope

a. How can it get steeper?

i. River at the base of a slope, during spring, the river might erode and make it steeper

ii. Building a house, cut out the bottom of a slope to make more room, just made it steeper

2. Topography: mountainous relief = high relied = steep slopes (cliffs, narrow river valleys)

iii. Climate

1. Determines and affects:

a. Temperature

b. Quantity and type of precipitation (rain/snow, sudden)

c. Timing of water that infiltrates the ground

d. Type and abundance of vegetation

e. All of this determines how much water goes into the ground

iv. Vegetation

1. Protective cover against falling rain

2. Roots stabilize the ground (~reinforced concrete)

3. However, weight, and fracturing of the rock

a. Trees are heavy so having a lot of them would weigh down on the slope, and if it is a rocky slope, the tree roots will help in fracturing the rock

4. What will be the effect of forest fires and deforestation?

a. Would be devastating, removing the protective layer of the slope and can make it fail, it will cause slope instability

v. Water

1. Water plays many roles promoting mass movements:

a. Erosion of the base of the slopes (undercutting)

i. East Sussex Coast, England

1. Made of chalk

2. Sedimentary rock, made of tiny microorganisms on the sea floor, then make their way to the surface and get eroded

ii. Holderness Coast, England

1. Glacial teal, sediment deposited by ice, coastal erosion is the fastest on earth 2m/year gone, when the tide goes up, it undercuts the bottom of the slope and drops and moves back about 2m/year

b. Weight

i. Water is heavier than air

ii. What is the effect of its weight on the driving force?

iii. Filling the rock pores with water instead of air increases the weight and increases the driving force

1. Sea-to-Sky Highway, BC, 2008

a. There was a drought, then a few days of heavy rain, and its thought that the weight of the water is what triggered the mass movement

b. This one relatively small mass movement could have possibily costed a couple million dollars

c. Saturation

i. Decrease in cohesion between grains because water fills pore spaces entirely (keeps grains apart): debris flow

ii. Can also result in the liquefaction of the sediment

iii. Destabilizes the slope

1. Anchorage, Alaska, 1964

a. Megathrust earthquakes in Alaska convergent plate boundary

b. Also, an example of mass movement

c. Ground was made of sediment, earthquake happened around end of march/springtime, ground was saturated with water, the earthquake was the trigger for liquefaction to occur and the sediment was disturbed turning to liquified sediment and the ground fell apart

d. Earthquake caused a mass movement; the mass movement was a slide and all that material slid into the sea. As it did that, it displaced the water column. As a result, a tsunami initiated. Earthquake triggered mass movement triggered tsunami all at the same time in Anchorage, Alaska in 1964.

d. Freezing

i. The volume increase when water freezes in fractures can destabilize the slopes and result in rock falls

e. Thawing of the active layer (permafrost)

i. Sediment slides/flows at the permafrost interface following thaw of the “active layer” and sediment saturation

1. NWT, Canada

f. Chemical alteration

i. Water moving on and through the rocks alters the rock-forming minerals into other minerals, thus decreasing the cohesion of the rock

1. Ex: Feldspar to clay minerals

ii. Water can also dissolve the cement holding the grains together, also resulting in a decrease in cohesion

4. Triggers

a. What is the force that constantly pulls material downslope?

i. Gravity, driving force

b. Is there a condition of slope instability that seems most important, decreasing substantially the internal strength of slopes?

i. Water

ii. Frost and thaw, chemical alteration, saturation, etc

c. All of the conditions of slope instability will push the slops to the brink of failure; the slopes ALMOST fail

d. A trigger is needed to initiate the mass movement

e. Common triggers:

i. Heavy rains

1. Condition of slope instability and a trigger, can be both

ii. Snowmelt

iii. Increasing of the slope angle

iv. Earthquakes and other sudden vibrations

v. Thawing of frozen ground

vi. Construction projects of humans

vii. Bird on the top of a slope...

f. Summary

i. Gravity is the main driving force

ii. Several conditions of instability make the slopes more vulnerable/unstable and close to failure

g. Triggers are the immediate cause that finally initiate mass movements

5. Types of mass movements

a. Mass movements are classified based on:

i. Type of movement:

1. Fall: free fall

a. Rockfall and debris fall

i. Freefall of rocks or debris

ii. <300km/h

iii. Can turn into rock/debris avalanche

iv. Violent blast of wind upon impact: air blast

v. Impact ~earthquake

1. Rockfall- Yosemite National Park, USA, 1996

a. Rockslide to free fall, created seismic waves equivalent to a magnitude 2 earthquake, also created an air blast that was strong enough to knock down trees and a cabin

2. Slide: ~coherent mass, failure surface

a. Slump

i. Slide along a curved failure surface

ii. Driving mass decreases and resistance mall increases --> new equilibrium

iii. However, head scarp ~vertical

b. Rockslide and debris slide

i. Slide along a planar failure surface corresponding to a plane of weakness

ii. <300 km/h

iii. Can turn into rock/debris avalanche

1. Rockslide- Point Fermin, Los Angeles

2. ***Rockslide and rock avalanche – Frank Slide, Alberta

a. 29th april 1903, springtime, 4am, km long block, 1/2km wide

b. First it slid down the slope for about a km then turned into a rock avalanche and continued for 3 km, km of different sediments and particles mixing with air and sliding down really fast down the slope, on turtle mountain, slide happened on one side of the mountain, slid down so fast it went upwards on the slope of the neighboring mountain 100s of m up the slope, 70+ ppl died, they didnt even look for the bodies because they were probably put up the mountain from the slide

c. Coal bed under the mountain, mining activity, night in april, 20 miners went at night to mine, 3 went home and went to bed, 17 miners were inside the mine when the rockslide happened, the 17 survived and the 3 that went home died in the rockslide

d. How did it happen geologically?***

i. Type of material: it was made of limestone-type of rock, overtime limestone can be dissolved by acidic fluids, rainwater is naturally slightly acidic, once the limestone was at the surface, it was being dissolved by rainfall, thus losing its cohesion overtime. Planes of weakness, it was an anticline, meaning that the bedding planes are moved towards one side/angle, turtle mountain bedding plane was at an anticline angle bending towards the ground. Also had fractures in the mountain from repeated frost and thaw over the years, decreased resistance, increasing the potential for slope failure.

ii. Slope angle and topography: steep slope means higher driving force. Side rocks are much softer than the limestone in the middle of the mountain, glacial erosion created the steep slope by eroding around the limestone

iii. Climate: relatively humid, precipitation, water seeping in the ground, also cold, so with humid and cold climate, opens up the mountain to frost and thaw, decreasing the resistance of the mountain, initially also responsible for the glaciers in the area 20000 years ago. Loss of cohesion, more planes of weakness

iv. Water: dissolution of the limestone, fractures from frost and thaw, glacial ice long time ago

v. ^all conditions of slope instability. What is the trigger? It was a very cold night between 28-29th of april, the month had been pretty mild, so everything was wet and damp, but that night was –18 degrees and everything froze more and was most likely responsible for the freezing/expanding/breaking of the rock overnight on an already highly unstable slope

3. Flow: behaves like a fluid, material deformed

a. Mudflow and debris flow

i. Degree of saturation of sediment with water; slurry + viscous

ii. Big blocks, trees, cars, houses

iii. River valleys and channels

iv. Speed = water content and slope

1. Depends on viscosity: very viscous=slow flow=fast momentum=higher damage

2. Flows in preexisting valleys and slopes

v. Lahar

1. Debris flow- Ladakh, Himalayas, 2010

a. Starts with the starting zone, down to the track, then the deposition zone (triangle/fan-like section at the bottom)

2. Debris flow- Caraballeda city, Venezuela, 1999

a. 1m of rain in 2 days, venezuela is known for its debris flows so they had channels made for it, but 1m of rain in 2 days is way too much and it was overflowing over the edges of the channel

3. Lahar – Mount St. Helens, USA, 1980

a. Lahar: mudflow made from volcanic ash

b. Super explosive eruption, tons of ash, lahar started at the slope of Mount St. Helens, joined with the river and inflated with the amount of lahar/rocks/debris joining the river

c. Took out a logging camp and a bridge

b. Creep

i. Very slow

ii. Mechanism: expansion/contraction due to:

1. Wet/dry

2. Frost/thaw

c. Gelifluction

i. Areas of permafrost

ii. Thawing of the active layer -> soil saturation -> soil flow

1. In the winter the active layer freezes, in the summer it thaws, the permafrost is an impermeable layer so the water in the active layer saturates the soil in the active layer, which can cause a gelifluction soil flow, or overlapping sheets, or sometimes can cause active-layer detachment, where the entire slab of the active layer falls off the permafrost, exposing it to a thaw flow slide

iii. Overlapping sheets (little ridges in a hill where they overlap on each other)

iv. Can lead to an active-layer detachment slide (not gelifluction)

d. Thaw flow slide

i. When the permafrost is exposed, it starts melting and creates a thaw flow slide that takes minutes to hours for it all to collapse and flow

4. Snow avalanches

a. Cause: weight >internal strength

b. Internal strength: density, thickness, H2O, temperature

c. Heterogeneous piling of distinct layers: rain, melt/freeze, wet/dry snow, hoar

d. Planes of weakness/ weak layer

i. Avalanche will be triggered in a plane of weakness

e. Triggers: weight, cornice collapse, rockfall, earthquake, explosives, skier/animal

f. Loud sounds and screams

1. Studies been done saying that shouting in a mountain is not sufficient enough to cause a snow avalanche

ii. Trigger:

iii. Cornice collapse

1. Wind always blows same way and the snow piles up and piles up until it forms a cornice (overhanging pile of snow), and eventually something could trigger it to fall causing an avalanche

iv. Skier

1. As the skier jumps down the mountain, he lands, and the snow forms a big crack around him and starts a slab avalanche (he's faster so he out-skiis it)

g. 2 major types of avalanches:

i. Powder snow avalanche

1. Dry snow, non-cohesive, very cold, lightweight

2. Powder snow flows and brings more powder snow down with it causing giant clouds of snow and air blasts

3. Accelerates and entrains more snow

4. Mixes with air

5. 60-100 km/h but <300km/h

6. Air blast

ii. Slab avalanche

1. Wet snow, cohesive, more dense (heavier)

2. Slab of snow detaches and slides down

3. Disintegration of slab -> flow

4. 30-65 km/h but <140km/h

5. High momentum

a. Crown fracture

h. Morphology very similar to that of debris flows; often along avalanche chutes

i. Also has starting zone, track where it speeds up, and deposition zone where it expands and slows down, like a debris flow

ii. Slide 78 shows avalanche chutes

i. Few factors to consider:

i. Slope angle

ii. Orientation of slope (sun, wind)

1. Downwind direction, might have snow cornices forming and when they fall it causes an avalanche

iii. Surface of slope (rough vs smooth)

iv. Vegetation (trees)

1. Trees can prevent snow avalanches because it could slow or stop an avalanche, unless the avalanche starts higher up, then comes down and plows through the trees (but it could still slow it possibly)

j. Risks associated with avalanches

i. Asphyxia (videos on youtube)

1. Can't just dig out of it, it's very compacted when it lands, and you're stuck under the surface of the snow

ii. Hypothermia

1. Die of cold

iii. Physical injuries (fractures)

iv. Psychological trauma

1. Very scary

v. Destruction (house, infrastructures, forests)

6. Prevention

a. Revegetation

i. Roots stabilize the potential failure plane

b. Grading

i. Terrace steps remove load and catches debris

c. Drainage control

i. Potential failure plane dries and becomes stronger

d. Preventing undercutting

i. Fill the channel where the stream or river was and make a new diverted channel so the stream is away from the cliff and can’t undercut it

e. Construction of safety structures

i. Riprap absorbs wave energy and slows undercutting,

ii. Building a retaining wall in front of the cliff to catch/block the falling debris

iii. Rock bolts

iv. Avalanche shed

v. Fencing along a cliff to catch debris as it starts to fall

vi. Metal mesh covering the cliff so as the rocks fall within the cliff and the mesh net

vii. Shocrete? Shooting concrete on the surface of the cliff to make it more cohesive

viii. Catchment basin in Charles Creek, BC to direct the debris flows

f. Controlled blasting of unstable slopes

i. Triggering the rock falls/avalanches on purpose in a controlled space rather than it happening on people down below unsuspecting it

7. Mass movements in Canada

a. Frank Slide, AB (1903): Rockslide to rock avalanche

b. Hope Slide, BS (1965): rockslide to rock avalanche

c. St-Jean Vianney, QC (1971): slide and mudflow (sensitive clays)

i. Mudflow from clay coming from glacial erosion

ii. Quick clay or sensitive clays

iii. Ground liquefied and started a mudflow

d. Lemieux, ON (1971 and 1993): slide and mudflow (sensitive clays)

i. After St-Jean Vianney, researchers found that Lemieux also was built on sensitive clays and in 1991 they relocated everyone living there at the time to somewhere else, and 2 years later in 1993, the mudflow happened there

e. St-Jude, QC (2010): slide and mudflow (sensitive clays)

f. Mount Meager, BC (2010): Rockslide -> Debris flow

i. Started as rockslide at the top, turned into debris avalanche as it rushed down, then hit a wall at the bottom near the river and mixed with the river to become a debris flow

At the Champlain lookout, half of the area below used to be filled with saline water from the glacial melting and deposition of sediment from the glaciers melting into that body of water and now has quick clays in the water at Champlain Lookout.

Midterm 3: Wednesday March 26th at 1pm DON’T BE LATE

Need to know examples of volcanoes

Need to know the Frank Slide and Lemieux landslide

15 multiple choice

Some short answer- diagrams, figures, complete the figure

Long answer:

Possible choice between 2 questions

One on volcanism:

Highlighting the similarities and differences, compare the volcanism of the following 4 locations: Hawaii, Yellowstone, Iceland, and the Columbia River Plateau (i.e. Columbia River Basalts). Be sure to discuss the tectonic contexts (cf. Distribution of magmatism), types of magmas and thei rorigin, types of eruptions and/or types of volcanoes. Finally, despite the differences that exist, identify the major common point between these four locations. Illustrate your explanations.

· Example based on the 4 locations talked about in class

· Say something about:

o tectonic context (hotspot, ocean-continent, convergent, etc)

o Types of magma (viscosity, silica content)

o Origin of magma

o Types of eruptions

o Types of volcanoes

· Then say the ONE MAJOR SIMILARITY between all four (that is not the fact that they are all volcanoes)

One on mass movements:

Name the type (or types) of mass movement involved in the “Frank Slide” in Alberta, and briefly explain your answer. Next, name and explain (as discussed in class) the different conditions of slope instability that gradually made this flank of Turtle Mountain more and more unstable over time. Then, identify and explain the trigger that caused the mass movement on that specific date in 1903 (April 29th, 1903). Illustrate your explanations.

· 3 parts

o Name the type of mass movement at frank slide

o Why is it that? What is the definition of that mass movement?

o Name and explain the conditions of slope instability at frank slide

o Identify and explain what the trigger was that caused frank slide

o Illustrate your explanations

Long answer question 1:

Comparison of Volcanism in Hawaii, Yellowstone, Iceland, and the Columbia River Plateau

Tectonic Context
- Hawaii:
  - Located in the middle of the Pacific Plate.
  - Formed by a hotspot, where a fixed mantle plume creates magma that rises to the surface.
  - The islands are formed as the tectonic plate moves over the hotspot, resulting in a chain of volcanic islands.
- Yellowstone:
  - Located in the interior of the North American tectonic plate.
  - Another hotspot, related to mantle plumes, this volcanic region is not located at a plate boundary.
  - The Yellowstone hotspot is responsible for a massive caldera that has formed from explosive eruptions over the last several million years.
- Iceland:
  - Situated on the Mid-Atlantic Ridge, where the North American and Eurasian tectonic plates are diverging.
  - Also influenced by a hotspot, resulting in both volcanic and geothermal activity.
  - The presence of both a tectonic plate boundary and a hotspot contributes to the substantial volcanic activity.
- Columbia River Plateau:
  - Not located at a plate boundary but formed from a series of flood basalt eruptions.
  - Relates to the creation of vast basaltic lava flows due to a mantle plume that caused the lithosphere to weaken and allow magma to rise.
Types of Magmas and Their Origin
- Hawaii:
  - Primarily basaltic magma.
  - Characterized by low viscosity and low silica content (approximately 50% SiO2), allowing it to flow easily and producing gentle, effusive eruptions.
- Yellowstone:
  - A range of magmas, primarily rhyolitic, due to the melting of the continental crust, enriched in silica (over 70% SiO2).
  - The higher viscosity leads to explosive eruptions, often creating large calderas.
- Iceland:
  - Basaltic magma is most common due to the geology of the oceanic crust.
  - Similar to Hawaii, it features low viscosity, allowing for effusive eruptions though also displays trends of more explosive activity due to its tectonic setting.
- Columbia River Plateau:
  - Composed predominantly of basaltic lava flows as a result of flood basalt volcanism.
  - The magma is characterized by low viscosity, enabling flows to cover vast areas during massive eruptions.
Types of Eruptions and Volcano Characteristics
- Hawaii:
  - Dominated by effusive eruptions, characterized by lava flows that create shield volcanoes (e.g., Mauna Kea, Mauna Loa).
  - These volcanoes generally have gentle slopes due to the fluidity of the basaltic lava.
- Yellowstone:
  - Exhibits explosive eruptions leading to caldera formations due to the high silicic magma.
  - The volcanic activity results in unique geothermal features like geysers and hot springs.
- Iceland:
  - Eruptions are both effusive and explosive, forming various volcanic structures (e.g., stratovolcanoes, shield volcanoes, and fissure eruptions).
  - The diverse eruption styles arise from the interaction of basaltic magma and the dynamic tectonic environment.
- Columbia River Plateau:
  - Features extensive flood volcanic eruptions, with vast sheets of basaltic flows.
  - Largely non-explosive in nature, it lacks the typical volcanic structures due to the nature of its eruptions.
Common Point
- Despite the differences in tectonic settings, magma compositions, and eruption styles, a major common point among Hawaii, Yellowstone, Iceland, and the Columbia River Plateau is their connection to mantle plumes or volcanic hotspots. Each of these locations is influenced by underlying mantle plumes that provide a source of heat and magma generation. In Hawaii, the hotspot creates basaltic magma that leads to the formation of shield volcanoes. Yellowstone, while also a hotspot, generates more silicic magmas that result in explosive volcanic activity and caldera formation due to the melting of continental crust. Iceland's volcanic activity is a unique intersection of a hotspot and a divergent tectonic plate boundary, resulting in both effusive and explosive eruptions. The Columbia River Plateau, associated with a mantle plume, has produced extensive flood basalt flows. This commonality underscores how mantle plumes drive volcanic activity across varied geological settings, despite the differing compositions and eruption behaviors observed in each area.

Long answer 2:

The Frank Slide, which occurred in Alberta on April 29, 1903, is primarily classified as a rockslide that transitioned into a rock avalanche.

Type of Mass Movement:
- Rockslide: This type of mass movement involves the rapid downward movement of rock along a plane of weakness. In the case of the Frank Slide, large volumes of limestone and shale slid down the slope of Turtle Mountain. The mass of the rock, combined with its speed, signifies a rockslide.
- Rock Avalanche: The rockslide rapidly transformed into a rock avalanche due to the increase in speed and volume of the debris as it descended. During the avalanche, the material became highly fluid, mixing air with the debris, allowing it to travel quickly across the landscape. This phase was characterized by the chaotic movement of rocks, gravel, and soil, reaching significant velocities and covering extensive distances.
Conditions of Slope Instability:
- Geological Composition: The primary material of Turtle Mountain is limestone, which can lose its cohesion over time due to erosion, weathering, and chemical alteration from rainwater. As limestone is dissolved by slightly acidic water, its structural integrity decreases, contributing to slope instability.
- Frost-Thaw Cycles: The region experiences freeze-thaw cycles, leading to expansion and contraction within the rocks. The freezing of water in cracks can gradually widen them, facilitating further rock fragmentation and promoting instability.
- Water Accumulation: Heavy rains or snowmelt can saturate the soil and rock, increasing the weight on the slope and decreasing the frictional resistance. Water also fills pore spaces between soil particles, leading to a condition known as liquefaction under certain circumstances, which can significantly destabilize the slope.
- Geological Fractures and Faults: The presence of existing fractures and faults in the rock create planes of weakness. As these fractures are exploited by weathering and other factors, the stability of the entire slope can be compromised, making it more susceptible to sudden movements.
- Anthropogenic Factors: Human activity, such as mining, can alter the stability of slopes by removing lateral support and increasing the potential for landslides. In the case of Turtle Mountain, past mining operations may have affected the physical properties of the slope, increasing vulnerability to mass movement.
Trigger for the Frank Slide:
- The trigger event for the Frank Slide was a rapid drop in temperature leading to a heavy snowfall followed by an equally rapid thaw. On April 29, 1903, conditions were exacerbated by a rain event that increased saturation in the soil. The additional moisture from the melting snow and rain increased pore water pressure within the slope, leading to a loss of friction along the failure surface.
- As the weight of the saturated material increased and the supporting structures of the rock began to fail, the combination of these factors reached a critical point where the forces driving the material downslope (gravity) outweighed the resisting forces (friction and cohesion), resulting in a catastrophic failure, known as the Frank Slide. According to reports, over 30 million cubic meters of rock moved during this event, resulting in complete destruction of a part of the town of Frank and the loss of 70 lives.