Earth & Planetary Science III

How We Determine Structure of the Earth

Use propagation of seismic waves that reach stations (if same wave arrives to equidistant stations at diff times then the material on one path was harder to get through - faster in colder material and slower in warmer), or use high pressure mineral physics to push diamond piston/laser to get to mantle P/T

Convection in Mantle

Can have full mantel convection (subduction to 2900 km then up) or upper vs lower cells based on rayleigh number… plate can go down to 660 km and phase change to allow for full mantle cell but some material can’t pass through the P/T change

Geoid

Gravitational potential = the more mass there is a given distance from a pole the more pull there is, geoid is imaginary equipotential surface covering earth close to man sea level (reveals variation density in earth, since rotating sphere wants to redistribute mass), topography is not the same as geoid and is expression of underlying heating processes

Heat Profile of the Earth

All rocks can flow, all have some visco-elasticity which doesn’t need melting but is dependent on T, buoyancy forces drive convection, material is goo conductor if T increases faster, greatest heat at mid ocean ridges, west US very hot from a lot of tectonic activity, eastern turns older/more carbonate, driven by ridge push and slab pull and convection coupling

Magnetic Field

Mostly dipole, solar wind reflection makes field lines asymmetric and they periodically reverse, declination = angle between magnetic north and true north, inclination = angle between surface and field lines, magnetism lost when material gets to 500-700 degrees C (nothing gets permanently magnetized below 30 km), properties in mineral align w/ magnetic field if cools below its Curie T, reversals last about 1000 years (last one 30,000 years ago)

Paleomagnetic Records

Indicate field has excited for 3 million years, outer core generates field through small bits of iron whirling around at slow speeds releasing energy, field currently changing at an accelerating rate, bacteria/birds have magnetoreceptors to detect chemical gradients/light

Causes of Mass Movement

Steeper slopes = greater slide (certain materials can hold steeper slope - granite), water content (little bit creates cohesion but too much = liquefaction), earthquakes, anisotropy (parallel bedding creates foliation fractures that rocks fall in), undercutting slopes (adding load on top or eroding underneath), loss of vegetation through wildfires/deforestation increases erosion and can create a turbidite flow

Angle of Repose

Electrostatic forces between grains creates cohesion to resist sliding (depends on grain size/angularity/water content), σshear = cohesion + (σnormal - Ppore) tanφ (basically amonton’s law)… inherent strength + (weight of sliding mass - water pressure which counteracts the load) \* internal friction… angle for sand = 35 degrees and angular pebbles = 45

Consolidated Rock Mass Wasting

Rockslides: medium velocity/whole block movement, rockfall: high velocity/failure on steep slopes and exposed bedrock, avalanche: high velocity/movement of broken material riding on cushion of trapped air

Unconsolidated Rock Mass Wasting

Creep: slow steady soil movement due to trapped water, Solifluction: flow of water saturated soil over frozen soil, Earthflow: moderate slope/soil and shales shaken to liquefy, Debris Flow: movement of bigger waterlogged material, Mudflow: movement very fine saturated grains

Predicting Volcanoes

Eruptions >12 in process at any time and 100 per year, can have months to decades of precursors and actual event can last years, best at predicting volcanoes out of all disasters, monitor plumes/batholiths/sills/dikes

Magma Reservoir

Crystals differentiate so what erupts is different from chamber, molten rock has to be less dense to rise by adding gas to dissolve and bubble - when pressure low enough (closer to 1 atmosphere) bubbles form, as move up start coming together and expanding until fragment and blow out when can’t escape fast enough

Eruptive Quality

Depends on amount of volatiles (CO2, SO2, H2O) and their viscosity, higher viscosity (felsic - rhyolitic) harder for bubbles to escape… effusive where no fragmentation and gasses escape easily, crystallized rind from rapid quenching like water, explosive where ash flows like turbidite (hot air + debris), rhyolitic like toothpaste

Basaltic Lava

Mafic so low viscosity, very fluid and rarely explosive, form at highest T, black, plumes form plateaus, in past 20 million years have had great capacity affect climate, hawaiian: Aa (viscous granular masses) and Pahoehoe (Ropy twists), mid ocean ridges: pillow basalts (blow out then quenching seals then blows out again), Vesicular: formed by bubbles nucleating and creating holes (diff from water erosion - depends on altitude)

Andesitic and Rhyolitic Lava

Intermediate silica, explosive, common in subduction zones; felsic, light color, high viscosity, explosive

Pyroclastic Flow

Hot rocks mixing with air to create fluid-like flow, can travel long distances, suspend over water and jump rocks, extremely dangerous and the cause of most volcanic casualties

Index of Volcanoes

Energetic classification from 0-8 (based on volume and height of erupted tephra), Hawaiian - Strombolian - Vulcanian - Plinian - Ultra Plinian (most named after Italian islands - lots of subduction), last 10,000 years 3477 M2 eruptions and 4 M7

Shield Volcano

Accumulation thousands thin sheets of basalt flows above water

Volcanic Dome

More viscous so steeper, bulbous masses rhyolitic/andesitic lava piling up (not flowing)

Cinder-Cone Volcanoes

Smaller forms from central eruptive event dominantly pyroclastic flow

Stratovolcanoes

Built from alternating layers of pyroclastic debris and lava flow

Caldera

After volcano has blown out and the magma chamber is emptied the column collapses, erosion occurs above and lake fills, phreatic eruptions: hot gaseous lava encounters water to form steam

Fissure Eruptions

Fissures in rocks allows highly fluid basaltic lava to flow through underground and spread

Volcanic Hazards

Lahars: Torrential mudflow (wet volcanic debris - lava encounters river or glacier), eruption cloud, pyroclastic flow, volcanic bombs, ash fall, landslide, fumaroles, acid rain, lava dome collapse, 1500 - today >10,000 deaths from volcanoes

Global Pattern of Volcanism

New basalt production 4 km3 per year mostly at mid ocean ridges, all active volcanoes on convergent boundaries which only create 1 km3, primarily on Ring of Fire subduction zones bordering Atlantic Ocean, occurs commonly but at random cadence

Intraplate Volcanism

Heat rises from core creating instabilities in the mantle to cause buoyant nonmolten material to rise in plume then pools at lithosphere where starts partially melting and spreading into sills/dikes/batholiths, plate moves over hotspot to create mountains or plateaus

Aerosols

Sulfuric volcanic clouds (SO2 sulfates) that reaches stratosphere can spread throughout atmosphere, SO2 reflects sunlight and cools earth’s surface, geoengineering idea to inject sulfates (frequently bc short lifespan) into atmosphere to buy around 50 years (will make our sky white and dim and question of how to globally decide who/how/when)

Basics of Water

4\.04% of Earth’s water is freshwater, 2.97% is ice, 1.05% underground (.009% in lakes/rivers and .001% in atmosphere), highest heat capacity compared to other solids, highest conduction of liquids, highest latent heat of vaporization, high surface tension, expands 9% when frozen

Global Weather Systems

Determined by latitudinal variation in evaporation/precipitation/major wind belts/oceanic salinity, Hadley - Ferrel - Polar Cells (0 - 30 - 60 - poles), air heated at equator and rises to tropopause where decreased pressure cools and spreads away from equator, sinks at certain latitude and heats up creating deserts (odd # of cells bc desert at poles, ancient salt deposits at evaporation zones at 30 degrees), rainforests create their own weather systems from absorbing/storing/reemitting water

Orographic Effects

90% humidity saturated wind comes off ocean and cools/precipitates then loses saturation/increases pressure on the way down so dries/heats

Runoff

Amount of water flowing over land, forms streams of which rivers are the larger branches, bigger drainage basin = more runoff regardless of precipitation, continental divides break up/determine direction of runoff drainage

Porosity

Percent void space in rock, depends on cementing minerals/grain size and distribution (sorting)/fracturing, decreases with depth bc more diagenesis w/ pressure, foliated rocks low porosity bc layers stretched/bent/bound

Permeability

Interconnection between the void space, depends on porosity though not always directly correlated, increases with fracturing

Darcy’s Law

Formula for amount of water flow, Q = A\[K\*(ha-hb)/1\], Volume = Area(Distance/Time), or the Volume is proportional to the cross-sectional area or the river through which the water flows during a given time period, looking at a hydraulic gradient (ha-hb) between two wells, volume of water increases if the hydraulic head increases (which also increases with hydraulic conductivity aka permeability)

Groundwater Aquifers

Unsaturated topsoil layer (weathered bedrock/evaporating soils) until the water table (typically reflects topography which creates head for darcy’s law) then a saturated layer of soil (permanently contains water year-round)

Confined vs. Unconfined Aquifers

Plains/salt deposit landscapes that don’t let water through/permeable sedimentary layer that’s over and underlain by impermeable rock (shale) - artesian well is where elevation of ground surface is below the average water table of the area then water will flow out on its own out of pressure of well; Permeable layer extends to surface and only indicator change from saturated to unsaturated zone is water table

Water Table Variations

Effluent river where groundwater feeds river (gaining water as flows downriver) and influent river where river feeds groundwater (losing water as flows downriver, water table gets depressed), stream can be completely disconnected from water table

Human Modification of Recharge and Discharge

Overpumping wells can create cone of depression (water can’t fill in area drafted immediately around well quick enough), overpumping creates fissures and air pockets that can collapse and lead to subsidence, when pump along coast saltwater normally under freshwater bc denser but overdraft blurs gradient and brings saltwater/other pollutants (from landfills/lagoons/chemical spills) into well… if stopped pumping ground won’t bounce back w/o fracking

Sacramento - San Joaquin River Delta

Lots subsidence through peat compaction - delta islands formed of organic anaerobic material that gets exposed and aerobic through overdraft which encourages microbial digestion of land material causing it to sink, causing levee to be exposed and erodes

Carbonate Rich Systems

Rivers can incise into carbonate systems, cave creation through nutrient depleted groundwater weathering away Calcite/Aragonite in rock, can create stalactite/stalagmites (calcite + carbonic acid = calcium ion + bicarbonate) which is easily soluble & creates sinkholes

Global Network of Streams

Globally streams carry 16 billion tons of sediment and 3 billion tons of dissolved matter every year, ag and deforestation doubled sediment flows compared to prehistoric times, in CA comes from Sierras

Laminar Flow

Sheet-like flow at low velocity where everything moving at effectively same pace, mostly at tops or edges of streams, uncommon in major rivers

Turbulent Flow

Chaotic irregular swirling flow, occurs at elevated rates of flow, suspends particles

Stream Discharge

Depends on velocity/gradient/bed roughness/channel width/depth, Q = V *A or Discharge (m/s3) = width (m) * depth (m) * velocity (m/s)*, where continuity of flow maintained by increasing cross section area by decreasing volume or vice versa, where velocity influenced by slope/roughness

Flow Competence

Measure of maximum particle size that can be transported by a stream, proportional to velocity squared where higher speed lets transport bigger things

Flow Capacity

Total volume of sediment that can be transported, proportional to both velocity and volume (total particle material flowing compared to total water + particle material flowing), deeper streams have higher capacity but most flow at low capacity

Dissolved Load

Adding Na2+/Ca2+/Cl-/sulfate molecules to water from chemical weathering and erosion

Suspended Load

Fine grained sediment transported throughout body of river through turbulence where particles don’t settle

Bed or Traction Load

Coarser sediments transported on bed of stream through rolling and sliding

Saltation

Sand particles intermittently jump along bed (phase between bed load and suspended load), creates increased weathering

Stream Erosion

Streams further weather eroded material, sediment grinds inside eddies to form potholes, waterfalls create headward erosion where bedrock erodes away underneath stream by water hitting ground beneath

Longitudinal Profile of Rivers

Rivers attempt to achieve grade (equilibrium - steady curved slope) through erosion/deposition along concave up profile, erosion dominates top of slope from fast rainfall and no sediment yet, deposition dominates bottom where encounters larger body of water, base level controls elevation of grade, dams create new profiles

Knickpoints

Abrupt breaks in slope from fault/tributaries/dams where rapids develop, gradient higher downstream of knickpoint and creates a lot of erosion bc no longer saturated with sediments (and deposition upstream - lake)

Meandering Streams

Imperfectly straight river propagates into sinuous back and forth shaped river, moderate slope and higher coarse load, flow is maintained throughout all points along river, flows faster to get through bend and slower along straits, erodes along outside of bend and deposits (point bar) along inside for low velocity rivers (deposition can cut across bend in a river to create oxbow lake), little bumps of deposition form along side of riverbanks that when floods deposits on top and creates natural levee

Braided Streams

Multiple channels with diverging sand bars to create interlacing formation (from steep gradient/variable discharge rate/abundant coarse load/easily eroded bank)

Drainage Networks

Series of hills/gullies/channels that flows into basin, dendritic: fractal geometric river network, jointed: road-like system on flatter ground, extensional (self-termed): lightning-like network on less easily rock of anticlines/synclines, or spiderweb-like network sprawling out from central mountain-peak

Superimposed Streams

Folding occurs then sediments deposit on top that river cuts through, or river pre-existing and folding occurs under it and it incises deeper to follow grade

Hydrographs

Precipitation x axis and discharge y, increase precipitation increases river depth (after a time delay since precipitation isn’t immediately incorporate), reaches peak volume (Q) then decreases

Floodplains and Levees

Area low lying land adjacent to river formed through flooding sediments, many major cities built in floodplains, levees protect from frequent floods but prevents meandering and creates backup/constriction increases velocity until water tops levees, will open spillways upstream to prevent city flooding

Components of Climate System

Climate = average conditions of region based on T/humidity/cloud cover/rain/wind, atmosphere is thermally stratified: up troposphere T decreases then increases in stratosphere then cools in outer atmosphere, hydrosphere based on thermohaline circulation (takes a thousand years to overturn), cryosphere (reflective ice), biosphere (

Radiative Balance

Energy in = energy out, sun emits at 6000 kelvin in visible light and earth at 300 kelvin in infrared, Flux (watts/m2) = σ \* T^4 where T is kelvin and σ = 5.67 \* 10^-8 watts (boltzmann constant), increase temperature you increase flux, amount of energy earth receives from sun at any given moment is S0 = 1368 watts/m2 (aka σ ** T^4 * (*4πr2 of the sun/4πr2 distance of earth from sun) where times 4 to get total 24 hour period of energy hitting surface…. then Energy In = S0 \* πr2 \* 1 - a where 1-a = albedo (33%) which gives you 250 kelvin or -21 degrees c… we are emitting -21 degrees but our surface is on average 15 degrees bc of GHG effect

Composition of the Atmosphere

78% N, 21% O, 1% Argon, trace gasses: CO2/Ne/He/Kr/Xe/H/CH4/N2O, water vapor between .1-4% and is most potent GHG but not anthropogenic (water gets high enough and H2 and O split and can leave atmosphere but clouds prevent), proportion of biggest GHGs: 49% CO2, 18% CH4, 14% CFCs, 6% N2O

Water Vapor Positive Feedback Loop

Increasing T increases evaporation, that increase in water vapor increases T (high GWP)

Albedo Positive Feedback Loop

T increase then decreases ice/snow, which decreases albedo, which increases energy absorption increasing T

Radiative Damping Feedback Loop

Increasing T increases infrared energy emitted to space, which decreases overall T

Short vs Longer Timescale Climate Variations

Daily and seasonal changes, ENSO 3-7 year variations, high pressure system pushes low pressure zone back to Americas for warm storms and La Nina is exaggerated version of it… Worldwide weather stations established in 1880s and WWII increased tidal gages and GRACE looks at gravitational pull of region to determine groundwater/ice melt, Mauna Loa graphs show CO2 oscillations

Ice Cores

Air bubbles preserve ancient atmospheres, oldest ones around 800,000 years, highest amount CO2 ppm was 400,000 years ago at 300 ppm, measure relative amounts of Deuterium compared to H

How to Relate CO2 Emissions to Human Activity

CH4(g) + 2O2(g) -> CO2(g) + 2H2O + energy … CO2 will always be released from burning, age of C14 in modern plants should be 0 bc half life is 5000 years so fossil fuels should have -1000% , can measure in glaciers and tree rings, beyond the ice cores the world about 12 degrees warmer

Representative Concentration Pathways

Future of how we emit CO2/CH4 and how will react in atmosphere, based on exposure/sensitivity/adaptation, have concrete ideas of what ocean/land/ice will do but plants are up to debate, 2.6… 4.5… 6… 8.5, current policies on track for 2.5-2.9 degrees c increase, to get below 1.5 degree we need to get to negative emissions by 2100, deal w/ T events and variable weather

5 Degree C Increase; Lower Degree Increase

Falling yields/sea level threatening major cities/species extinction/intensity storms/forest fire/droughts/flooding/heat wave increase; vs falling yields in high latitudes/small mountain glacier disappearance/threatened water supplies/coral reef damage

Adaptation

Engineering ways out of climate change, rich countries can adapt, actions to compensate for climate change, disaster management and business continuity… solutions: increase urban green spaces/water retention/cool roofs/wetlands/stormwater capture

Mitigation

Actions in societal behavior to reduce CO2, solutions: low emissions and energy transit/renewable energy/building retrofits/sulfates in atmosphere (geoengineering)/storing carbon back in ground/ocean fertilization to promote photosynthesis then die and eaten by microbes to store carbon in ocean floor