EARTHSC 2GG3 (Post-Midterm)

What are the causes of slope failure?

• Imbalance between friction and gravity forces as object moves downslope

• Slope steepness (gravity overcomes friction)

Joints

• cracks which are common in bedrock near earth’s surface

• create planes of weakness

What causes joints to grow?

• increasing slope angle

• overburden removal

• ice/root wedging

• daily temperature changes

How are joints positioned in sedimentary rocks?

perpendicular to bedding

How are joints positioned in igneous rocks?

can be either perp or parallel to the surface

Exfoliation joint

onion skin-looking joint from erosion bringing igneous rocks to the surface

Planes of weakness

• surfaces with less strength compared to material around it

• e.g. wet clay/sand layers, joints, (Ex)foliation joints (foliation is metamorphic)

• also influenced by slope orientation

Cohesion

• weak electrical charges attracting grains to each other

• promoted by small amounts of water

• overcome by too much water

Angle of repose

• Steepest angle maintained to horizontal by cones of loose material on flat surfaces

• 30 - 37 deg for dry sand/gravel (higher when damp)

• up to 45 deg for irregular gravel

Creep

• slow, gradual downslope movement

• common in temperate areas due to repeated expansion and contraction

Solifluction

• creep in areas with permafrost

• active layer slides downslope in overlapping sheets

• methane and CO2 release

Slump

• mass wasting where rocks/sediment stay mostly coherent during movement

Translational slump

slump where failure surface is planar

Rotational slump

slump where failure surface is concave

Head scarp

exposed, upslope edge of failure surface

Toe

downslope edge of slump rock

Mudflows & debris flows

• Non-coherent flows of rock and sediment (higher water content)

• can move up to 100 km/h

Mudflow

flow containing slurry of mud, and finer materials

Debris flow

flow containing mixture of mud and large rocks

Underwater slides

• sediment dispersing, forming turbulent cloud under water

• caused by earthquakes/large disturbances and hotspot volcanoes

Rockfalls

• a mass free-falling down a cliff/steep slope (often vertical)

• caused by joints/fracturs in rocks

Frost wedging

• splitting of rock through pressure exerted when water freezes

• dominant process causing rockfalls in cold regions

Rock slides & Strurzstroms

• the largest and most destructive landslides

• speeds up to 100-300 km/h

Rock slide

extremely rapid downslope movement of large volumes of rock and debris

Sturzstroms

• aka rock avalanches

• begin as rock slides then break up, taking on air and water

• mechanism unclear

Fluidization

• flowing as a fluid composed of rock fragments suspended in air

• potential theory for Sturzstroms

Leda clay

• aka quick clay

• Water saturated mud deposited in salty water composed of clay flakes with large pore spaces between the flakes

• highly unstable (glacial melting)

• liquifies when disturbed

Weather disasters

• Storms, hurricanes, and floods mainly driven by solar energy instead of energy from within the earth

• main E source is the sun

Watch

• issued when the drivers/signs of an event are present

• high probability that event might happen

Warning

issued when we are sure the event will take place

Lapse rate

change of temp with altitude; ~6.5 °C/km

Troposphere

• part of atm heated by IR radiation from earth's land and water

• where we live

Stratosphere

• part of atm heated by ozone absorbing UV light

• temp increases with heigh

Mesosphere

• part of atm that cools due to lack of ozone

• temp decreases with height

Thermosphere

part of atm where high-energy radiation is absorbed by gases

What happens to air pressure and density with altitude?

They decrease with increasing altitude

Coriolis effect

• shifting of wind movement path to the right due to earth's rotation

• Speed of rotation decreases with latitude

Which direction do air masses curve in the N Hem?

they curve to the right

Which direction do air masses curve in the S Hem?

they curve to the left

Cyclone

air flows upward and counter-clockwise

Anticyclone

air flows downward and clockwise

Hadley cells

• Air rises at 0°C and sinks at ~25° N and S lat

• These cells are when tropical air warms, rises, and flows towards poles

  • Then subtropical air cools, sinks, and flows back towards equator

• Control of rainfall in low latitudes

Trade winds

• Trade winds: result as Hadley cell air flows toward equator

  • N hem surface winds curve southwest

  • S hem surfacer winds curve northwest

Intertropical Convergence Zone (ITCZ)

• where N and S hems trade winds converge

• N hem summer → shifts N of equator

• S hem summer → shifts S of equator

Air pressure zones

• More land mass is in N hem, more water in S hem

• Southern hem has more buffering from water, resulting in less significant seasonal changes

Pressure in Northern winter

cold polar high pressure zones with cold air flowing off continents and rising in Icelandic and Aleutian lows

Pressure in Northern summer

highs pressure over ocean with onshore flow of moist air and monsoons

Front

• When two different air masses meet with different temperature or moisture or both

• Warmer air has potential to hold more moisture than cold air

Cold front

• cold air from north wedges under warmer air, forcing it upwards

• Warm air cools down by force → thunderstorms and rain

Warm front

warm air runs up and over colder air (more gradual since cold air is not 'moving') → cloud formation, rain not likely

How to make a single-cell thunderstorm

• warm, humid air rises, forming clouds

• rain/ice too heavy → condensation

• warm updraft stops when enough has fallen

Supercell thunderstorm

• same as a single cell storm but much larger and can rotate

• Updraft and rotation combined lead to powerful tornadoes

Wall cloud

lower part of column, where updrafts are strongest

Anvil cloud

above the wall cloud, lots of lighting activity

How do tornadoes form?

• Descend from wall cloud within supercell storm

• Most tornadoes are formed within supercell storms

• ~30% of supercell storms produce tornadoes

• Supercell formation -> watch

• Funnel cloud descends -> warning

Tornado track

swath of destruction on the ground (focused destruction); path it takes across the ground

Enhanced Fujita Scale

• Not based on wind speed (hard to track)

• Classed based on worst damage caused by tornado