Mass Wasting and Tsunamis

What is mass movement/mass wasting?

• The downslope movement of rock, unconsolidated material, soil, and/or ice under the influence of gravity

• Earth’s surface has unstable slopes

• Why is it important?

• Significant loss of life and property

Setting the stage for mass wasting

• Plate tectonics causes uplift (upward movement of the land) and subsidence (downward movement of the land)

• Erosion (via water, ice, and air) can continue to influence the removal or deposition of material and sculpt valleys/mountains/landscapes

This creates relief

Difference in elevation between two points/locationsAnd slopes

And slopes

The tilted surface at two points/locations

Slopes

• Gentle slopes have angles less than 5 degrees

• Moderate slopes have angles that range from 5 degrees to 35 degrees

• Steep slopes exceed 35 degrees

• Cliffs are considered anything greater than 60 degrees

• Vertical slopes make angles of 90 degrees

V shape vs. U shape

V shape = river at the bottom

U shape = glacier at the bottomFactors the affect the stability of a slope

Factors the affect the stability of a slope

• Joints

• Planes of Weakness

• Cohesion

• Angle of Repose

Joints:

• The Earth's surface contains natural cracks in rocks called joints

• Blocks of rocks can break from bedrock along joints

Geologists and Engineers ask three questions when discussing resistance to mass wasting

1. What can cause a joint to grow until it completely separates solid rock from bedrock?

2. What prevents a block of rock from slipping on its surface?

3. What prevents unattached grains in unconsolidated materials from moving relative to their neighbors?

Joints

• Solid bedrock is held together by the chemical bonds in mineral crystals

• Joints occur when there is stress strong enough to break those bonds

  • Stress can be caused from movement of rock due to cooling or contraction during uplift

• More joints = more likely to break

• Factors that can cause joint growth are:

  • Increasing slope angle

  • Overburden removal

  • Ice and root wedging

  • Daily temperature changes

    • Freeze-thaw cycles

Joints in sedimentary rocks …

often occur as rectangular blocks here joints are perpendicular to the beds

Joints in igneous rocks …

may be perpendicular or parallel to the surface

Planes of Weakness

• A surface with less strength compared to the material above it

• Planes of weakness include:

  • Layers of wet clay and sand (i.e. quick clays)

  • Joints in sedimentary and igneous rocks 

  • Exfoliation joints (joins parallel to land surface) in igneous rocks

  • Foliation planes in metamorphic rocks

Cohesion

• Water can play a big role in impacting the ability of a slope 

• Cohesion: the attraction between grains caused by weak electric charges that attract one grain to another

  • Small amounts of water (microscopic films) in grains can provide cohesion

  • Too much water (saturated material) water completely fills pore space, cohesion is no longer present

Angle of Repose

• The angle of the steepest slope that a pile of uncemented/unconsolidated material can attain without collapsing from the pull of gravity 

• Dry, sand or gravel

  • Angle of repose: 30-37 degrees

• Large, irregular gravel:

  • Angle of repose: up to 45 degrees

• Sand’s angle of repose increases when it is damp

1969 - Aberfan, Wales

• Coal spoil heap failed

• Killed 144, predominantly school children

Types of Mass Wasting
Geologists and engineers distinguish mass wasting events based on the following criteria:

1. Type of material (rock, unconsolidated material, mud, ice, or snow)

2. Velocity of movement (slow, intermediate, or fast)

3. Character of the moving mass (coherent, chaotic, or cloudlike)

4. Environment of movement (subaerial(surface of the Earth) or submarine(under water))

Creep

• Slow, gradual, downslope movement

  • Few mm to cm per year

• Caused by repeated expansion and contraction

  • Freezing and thawing

  • Wetting and drying

  • Warming and cooling

• Crepp destroys property but does not cause fatalities

• Common in periglacial areas (i.e. Canadian Arctic)

• Creep that occurs in permafrost areas is called solifluction

• This can occur in the uppermost 0.5m-3m of the permafrost layer

Slump

• Rock and sediments stay mostly coherent during movement

• Translational slump: a planar failure surface

• Rotational slump: concave failure surface

• Head scarp: the exposed, upslope edge of the failure surface

• Toe: the downslope end of the slump block

Portuguese Bend Slump, Southern California

• Clay overlies shale bedrock in this large, translational slump

• 1950s housing boom affects safety:

  • Homes, roads, and septic tanks added weight to slump

  • Clay substrate expanded and weakened due to lawn watering

• Mass movement began in 1956 at 1-2 cm per day

  • Foundations cracked, water mains leaked, power cables snapped

• 150 homes were destroyed, costing millions of dollars

St. Jude, Quebec (May 10, 2010)

Landslide claimed lived of a family of 4

Quick Clays

• Silts and clays deposited in glaciomarine setting

• Salty pore water is leached out by groundwater

• Clay becomes weak and easily fails

• Common in coastal areas covered by sea during past glacial episodes

  • Ottawa region - Champlain Sea

  • Rissa, Norway, Ask, Norway (december 2020)

Rissa Quickclay

• Rissa, Norway

• 1978

• 33 hectares of farmland liquified

• 1 dead

Alta, Norway

• Norway landslide, December 2020

• 7 people killed, 3 missing

• Alta, Norwegian landslide, June 2020

• “Approximately 110,000 people live on more than 2,000 identified quick clay zones all over Norway”

Mudflows/Mudslides

• Debris flows with higher water content

• Can travel up to 100 km/h

• Common in volcanic and arid areas

Mudflows in Rio de Janeiro

• Favelas (shantytowns) have increased in size and number in Rio de Janeiro, Brazil over the last couple of decades

• These are built on unconsolidated material from the erosion of surrounding igneous and metamorphic bedrock

• The lack of public infrastructure (i.e. drainages and proper roads) has caused for the material to become unstable and prone to mudflows

Debris Flows

• Downslope movement of unconsolidated material mixed with and water

• Move at rates of metres to kilometers/hour

• Often triggered by heavy rain, spring thaw

Debris avalanche

• Very destructive flows

• Move at speeds of over 400 km/hr

• Often triggered by earthquakes

• Yungay, Peru 1970, 17,000 killed

Volcanic Hazards - Debris flows (lahars)

• Mudflows (pyroclastic material, debris and water), flow along river valleys

  • Can flow with speeds up to 60 km/hr

Nevado del Ruiz, Colombia (1985)

• Over 23,000 dead

• Lahars reached speed of 50 km/hr

Rockfalls

Free fall of a single block or large mass from a cliff or steep slope

Rockslide/Debris Slide

• Sudden downslope movement of detached masses of bedrock

• Often occurs on dipping surfaces

• Builds talus

• Rockslide: mass is mostly rock

• Debris slides: mass is mostly unconsolidated materials

1903 Frank Slide, Alberta

• Buried town of frank

• Killed 70 people

• Lasted ~ 90 seconds

Avalanches

• Snow avalanche - downslope movement of snow

• Andes flight disaster of 1972

• Uruguay Air Force Flight 571 crashed landed in the Andes containing 45 passengers

Submarine Mass Wasting

Mass wasting that occurs underwater

Submarine Mass Wasting - Three categories:

1. Submarine slumps - semicoherent blocks comprising or sediment slide downslope

2. Submarine debris flows - layers break apart to form a slutty containing larger fragments suspended in mud matrix

3. Turbidity currents - sediment disperses completely to form a turbulent cloud od sediment, suspended in water

Factors the impact Mass Wasting - Shocks and Vibrations

• Earthquakes can cause mass to start moving

• 1970 Yungay, Peru Avalanche

• Strong winds, large transportation vehicles and blasting at constructions can also act as triggers

Factors the impact Mass Wasting - Sediment Liquefaction

• Seismic waves can cause wet (saturated) sediment/soil to turn into slurry and behave like a liquid

• In quick clays, the tension between clay grains is broken

Factors the impact Mass Wasting - Change in Downslope Stress or Resistance Stress

During heavy rains, water can fill pore spaces and the added weight itself of the slope increase the downslope stress

Factors the impact Mass Wasting - Undercutting

Removal of support at the base of a slope will increase the resistance stress

Factors the impact Mass Wasting - Changing of Slope angle

• The steeping (increasing) of a slope cna increase the downslope shear stress

  • I.e. open pit mines

Landslide Potential Maps

Geologists and Engineers can create landslide potential maps to rank regions/areas that may be prone to mass wasting events

Slope Stability - How can we stabilize slopes?

Drain water

• Add drainage pipes

• Lower water table of reservoirs

Add vegetation

• Add drainage pipes

Use rock bolts to secure surface layers

Niagara Escarpment

• Active erosion maintains steep slope

• Problems: failure along roadways in Hamilton

• Focus of current research at McMaster

2004 Indian Ocean earthquake and tsunami

• On December 26, 2004, an earthquake off the coast of the Indonesian island of Sumatra in the Indian Ocean triggered a tsunami

• Waves were up to 30 m high

• ~227,898 casualties in Indonesia, Sri Lanka, India, Thailand

• About 1,600 km of a fault surface slipped about 15m along the subduction zone of where the Indian Plate slides under the overriding Burma Plate (part of the Eurasian plate)

• This caused a displacement of about 30 km of water was displaced

1947 - Hilo, Hawaii

• Waves as high as 12 m

• 159 casualties

• Millions of USD in destruction

• Caused by:

  • An 8.6 M earthquake in the Aleutian Islands (alaska) of a slip of 9 - 12.7m

Tsunamis - Motion of the Ocean

• Currents: circulate water around the global ocean

• Tides: cause the sea surface to rise and fall, generally twice daily

• Wind-driven waves: moving air shares he water surfaces

Tsunami

• Water wave generated by the sudden movement of a mass against water

• This can include:

  • Sea floor (when moved by an earthquake)

  • A submarine landslide

  • A subaerial landslide that falls into a body of water

  • A pyroclastic flow from a volcano

  • Air blast from a volcano

  • Meteorite

Tsunamis are defined by their origin, not their size/magnitude

How do tsunamis form?

• Displacement of sea floor in ‘quake

• Water rushes in and overcorrects

• Creates long, low waves

Tsunamis - waves Trough:

the line along which water depth is lowest

Tsunamis - waves Crest:

the line which water depth is highest

Tsunamis - waves Wave height:

the vertical distance between crest and trough

Tsunamis - waves Wave amplitude

the vertical distance between the equilibrium level and a creat (=half the wave height)

Tsunamis - waves Wavelength:

the horizontal distance between successive crests (or successive troughs)

Tsunamis - waves Wave velocity:

the horizontal speed at which a crest (or trough) moves

Tsunamis Waves

• Wave height can vary depending on the location and distance between the tsunami source and location

• Refraction and  reflection of waves as they encounter islands/seamounts

• Tsunami waves in the open oceans may not even be felt by ships, due to the long wavelengths

• Tsunamis that destroy coastal environments are caused by the changes a wave undergoes as they approach shore and shallow water

  • Process called shoaling

• G represents acceleration of gravity

• Depth = depth of water

• As waves enter shallower water, they slow down

  • As waves approach shallower water they increase in height

  • I.e. a tsunami that was only 10 cm in height over an abyssal plain may rise to 14-40m when it reaches shore

Near-field tsunamis/local tsunamis

reach shore close to the source, tend to have higher wave heights

Far-field tsunamis/distant tsunamis

 waves that cross and ocean and reach shore for from their source, wave heights tend to be lower

Tsunami and Shores Normal shoreline

intersection of sea level before the tsunami arrives

Tsunami and Shores Drawback/drawdown

if a trough of a tsunami arrives first, the drawback will lower the sea surface below sea level

Tsunami and Shores Tsunami elevation

greatest vertical distance between the crest of the tsunami and sea level

Tsunami and Shores Inundation depth

the vertical distance between the ground and the water surface

Tsunami and Shores Inundation limit

the line on land at which water stops

Tsunami and Shores Inundation distance

horizontal distance between the normal shoreline and inundation limit

Tsunami and Shores Run-up elevation

vertical distance between normal shoreline and inundation limit

Tsunami Waves and shores

• The slope of a coast can impact the wave’s height 

  • High relief (i.e. steep cliffs) will cause the water to not flow island

  • Lower relief areas may have water flow kilometers island

• Along shallower water, the wave height will become higher as the waves get narrower and higher

• As waves enter bays or estuaries, the waves get focused into progressively smaller areas so the wave height becomes higher

2018 Sulawesi (indonesia) earthquake and tsunami

• A 7.5 M earthquake near Minahasa Peninsula, Indonesia

• ~4340 casualties

• Major soil liquefactions and mudflows occurred around Palu

Tsunamis vs. Waves

• Waves during a storm can seem high and dangerous but they are very different from tsunami waves

• Wind-drive waves: 100m wavelength

• Tsunami waves: 200 km wavelength (in open ocean) and 10 km wavelength (in shoreline)

Tsunami Damage

• Location dependent

  • Infrastructure (i.e. boats, houses, piers) present

  • Relief of area

  • Substrate (sediment/lithified rock)

2011 Tohoku Tsunami (Japan)

• 8.9 M earthquake

• 4th strongest earthquake recorded in history

• ~19,759 casualties

• Over 220,000 people displaced

• Led to the Fukushima Daiichi nuclear disaster

Quick side note on faults Fault:

 fractures along which movement has taken place

Quick side note on faults Active fault:

movement with last 11,000 years

Quick side note on faults Hanging wall block:

Overlies an inclined fault plane

Quick side note on faults Footwall block:

underlies an inclined fault plane

Quick side note on faults Normal fault:

hanging wall block moves downward relative to footwall block (e.g. rift valleys)

Quick side note on faults Reverse fault:

hanging wall block moves upwards relative to footwall block

Quick side note on faults Thrust fault:

reverse fault with very low angle fault plane (<45 degrees)

Tsunami and Earthquakes

• Fault slips can trigger earthquakes and displace the seafloor

• Often can occur at convergent plate boundaries

• During a normal fault, the hanging wall slides downward and suddenly produces a depression

• During a thrust fault, the hanging wall moves upward and pushes the overlying water up

• Megathrust earthquakes: earthquake caused in large areas of a thrust fault between overriding plate slip in convergent boundaries

• As plates move towards one another, the overriding plate shortens horizontally and thickens vertically causing the land to rise

• When a surface slips, the overriding plate jumps forward and the face is uplifted

Megathrust earthquakes in recent history

• 1960 Chile earthquake with a magnitude of 9.5

  • Casualties ~550

  • Tsunami waves of ~25m

• 2004 Indian Ocean earthquake with a magnitude of 9,3

  • Casualties ~227,898

  • Tsunami wave of ~15m

• 2011 Tohoku earthquake magnitude of 9.1

  • Casualties ~22,312

  • Tsunami waves of 30m

Landslide-generated Tsunamis

• Mass wasting processes such as slumps, rocks, debris slides and rock falls can happen on land or underwater

• Subaerial landslides that fall into the sea push down on this surface, producing large depression, generation tsunami as the sea surface bounces

• Submarine landslides generate tsunamis partly of the downward motion of a solid mass underwater pulls the surface of the ocean down

Ex. Lituya Bay (Alaska) Tsunami

• JUly 9, 1958 had a 7.8 magnitude earthquake released about 30 million m of rock and debris into the bay moving at ~300 km/h

• The water had nowhere to go but the bay itself creating a run-shot of up to 524 metres

Landslide-generated Tsunamis

• Grand banks (NFL)

• Magnitude 7.2 earthquake

• Turbidity current recorded by cable breaks on sea floor - flow velocity 15-60 km/hr

Frank Collapse of Volcanic Islands

The islands of Hawaii are prone to frank collapse, a sudden catastrophic slump that removes part of a volcano

Tsunami due to Volcanic Eruptions - Krakatoa (1883)

Krakatoa (1883)

• Sound heard 3000 miles away

• 40m high tsunami killed over 36,000 people

• Huge ash cloud produced

• Over 18 km of pyroclastic debris fell down and slammed the sea

• Estimated that wave heights were ~15-35m

Effects on climate

• Global temperature reduced 0.5 degrees for 10 years after Krakatoa eruption

Tsunami Relief and Recovery

• Tsunamis are one of the most expensive disasters with heavy economic tolls due to casualties and infrastructure damage

• 2004 Indonesia earthquake and tsunami economic losses

  • 5.6 billion USD was raised through humanitarian response

• 2011 Tohoku earthquake and tsunami economic losses 

  • 235 billion USD