Exam 2 Flashcards
- Atmospheric water vapor
Unique in our system
- -Water vapor (humidity) can vary from very dry (.01%) to very humid (3%) of the atmosphere
- –Water vapor is important because it : 1 plays a role in precipitation and evaporation 2 TRAPS HEAT, 3 REFLECTS SOLAR RADIATION.
- -Absorbs energy from the sunlight (retains earth’s heat) as well as CO2 and Methane gas/Ozone
- -Temperature in the atmosphere varies with latitude & Altitude. (warmest near equator)
Layers of the atmosphere in order
Troposphere - (Weather clouds) Temperature Decreases with altitude, it has turbulent flow of air and variable humidity
- -lowest layer - where we live
- -zone where all weather phenomena occur
- -80% of atmosphere mass
- -zone where evaporation, condensation, storms occur
Stratosphere- Temperature increases with altitude (because of OZONE) Does not mix with Troposphere
- -solar energy absorbed in ozone
- -no rain - particles here are stuck - rare turbulense - density of air dec. wih height - layers and stratified - no mix
Mesosphere- Temperature Decreases with altitude again.
–ionized gases (middle sphere)
Thermosphere- Temperature increases with altitude it is also where the UV rays are absorbed. (charged ions form)
–warm temp. so bonds broken and charged ions of oxygen and nitrogen form
Magnetosphere-
Air pressure drops rapidly the higher up in the atmosphere you go.
–shield against damaging radiation from space
from geology standpoint which is most important? - the troposphere bc it is where weathering, erosion and life occur
Salinity and circulation of the ocean
Carbon dioxide’s role in climate change
Salinity and circulation of the ocean
Salt increases density and drives water down causing circulation
•Carbon dioxide’s role in climate change
As carbon dioxide increases, so does climate. It’s a greenhouse gas that traps heat.
Salinity
- –TDS - approx. 35 g/kg average 35,000 ppm (<500 in drinking water)
- –Na+ and CI- (approx. 30 g/kg of NaCl)
Temperature
—Water has high heat capacity (influences earth’s climate)
—Layers structure
• Density varies with T
• Warm surface water vs. cold deep water
- types of physical weathering
(ice wedging, sheeting, Talus cones, tree roots, crystal growth, spheroidal)
–minerals most susceptible to weathering (least)
Ice wedging: water seeps into cracks of rocks, freezes and expands, breaking the rock
Sheeting: rocks under crust are under extreme pressure. As the overlying rocks are eroded away, the now exposed rock expands in large sheets/parallel joints
Talus cones: piles of rock debris accumulated at the base of a cliff bc of rockfall
Tree roots: exert tons of pressure on rocks and wreck them; paper beats rock
Crystal growth: mineral water seeps into wood. As the water evaporates the salt mineral crystals grow, expand, and break the wood
Spheroidal: rocks want to be spheres; decomposition most rapid at corners
Minerals MOST susceptible to weathering
–The ones that are high in iron, because it leads to oxidation e.g. Calcite, olivine
LEAST? - Quartz
Subsurface chemical decomposition
The more joints a rock has, the more water can seep in and work its chemical magic
—Soils are more weathered at the top, as dissolved matter travels downwards
- Major types of mass movement
creep, solifluction, slump block, flows, landslide, rock slide, rock fall
Creep: very slow downslope migration of soil/loose rock
Solifluction: special kind of creep in polar regions, bc groundwater in pore spaces of rocks is permanently frozen
Slump block: the mass of displaced rock & soil moving down a slope
Flows: mudflow
Slides
Landslide: slope failure, movement along a well-defined slippage plane
Rock Slide: the rapid movement of a large block of rock
Rock Fall: free fall of rocks, fast
LISTED FROM SLOW TO FAST
Water imp. to mass movement bc - Water affects cohesive strength
- Profile of stream at equilibrium
How does urbanization affect a river
Profile of stream at equilibrium
—Faults (any change of factors) cause imbalance, erosion and deposition occur to bring stream back to equilibrium (think of smoothing out a ridge to make a curve out of a break in the line)
How does urbanization affect a river
–changes the surface runoff and infiltration. surface runoff increases in percentage and velocity, → flooding. infiltration goes down
Threshold velocity and sediment
pointbars
threshold velocity: the minimum velocity required to move grains of a certain size
—in areas of low velocity, the sediment is usually deposited on a floodplain or along the channel
sediment can also be deposited where the velocity is reduced, like where a river meets a lake or ocean
pointbars:
- -the deposit on the inside/point of a meander bend. velocity here is at a minimum, so some of the sediment load is deposited
Processes of stream erosions
- removal of regolith
- –weathering loosens rock debris, debris washed downslope into ocean
- –fresh bedrock is weathered, regolith regenerates - downcutting of stream channel by abrasion
water moves sediment along bottom of channel; sediment acts like a saw and cuts/erodes the channel deeper - headward erosion
- –streams tend to erode upslope (headward), and to increase the lengths of their valleys until they reach the divide. as the water is concentrated, the velocity and volume increase → ability to erode increases
- groundwater
What is the water table
What makes a good aquifer
What happens after excessive pumping of a well
What is the water table
—Upper surface of the Zone of Saturation
What makes a good aquifer
–Being both porous and permeable
What happens after excessive pumping of a well
–It can lower the water table and eventually the well won’t be able to reach any water (cone of depression) or saltwater intrusion
- Glacial systems
Variations in velocity in glaciers
Where are continental glaciers found
Rock debris in lateral moraine
Variations in velocity in glaciers
- –The varying velocity creates tensional stress, results in crevasses
- -crevasses are the most obvious and abundant structures in a glacier - large cracks opened by the fracturing of a brittle. upper layer of ice as the underlying ice continues to flow - early vertical and very deep
- -transverse crevasses form at right angles to the direction of flow
Where are continental glaciers found
—Antarctica and Greenland
Rock debris in lateral moraine
Moraines: big piles of sediment deposited from glaciers
Zone of accumulation, snow line, zone of ablation
Zone of accumulation: usually a big pocket covered in snow
Zone of ablation: where melt begins/occurs
Snow line: boundary between accumulation and ablation (this line moves around)
Types of glacial erosion
Ice flow (rotation of grains, melting/freezing, internal slipping) ← how glaciers move
Cuts u-shaped valley
Ice-wedging smooths surface of the rocks, Plucking pulls up loose fragments and by the time it gets to the bottom of the glacier, it’ll be dust (silt: glacial flour)
- Shoreline systems
Where do waves get their energy from
Why do waves break near the shore
Where do waves get their energy from
—Wind’s energy transferred to water’s surface
Why do waves break near the shore
—They break because of interaction with the ocean floor
Wave erosion
—modifies the shoreline as soon as landscape produced by other agents is submerged. concentrated on headlands, produces wave-cut cliffs/wave-cut platform
Chesapeake Bay
Evolution of reefs in to atolls
—Atolls: death of underwater volcano that create barrier reefs
Spits and longshore drift
spits
–in areas where a straight shoreline is indented by estuaries, bays, etc., longshore drift extends the beach from the mainland to form a spit
longshore drift
–generated as waves hit the shore at an angle, moves sediment up the beach in the direction of the waves. sediment returns partway
- Eolian system
Wind direction and dune shape
How can you tell wind direction from rocks
Transportation of sediment by wind
Wind direction and dune shape
How can you tell wind direction from rocks
Transportation of sediment by wind
- –saltation: in the air, moves a little ways, drops back to —the ground
- –suspension: in the air for a long time and moves a large distance
- –traction/creep: rolling on the ground
Types of dunes
Barchan
—Isolated, crescent shaped, limited supply of sand
Transverse
—Basically a ton of barchans all connected because of large sand supply
Longitudinal
—Even spaced ridges, limited sand availability, strong, bidirectional winds
Star
—Multiple winds converge into one spot, don’t move much
Parabolic
—Look like burchan but instead of the edges moving first, they trail because they’re usually caught in foliage or something (commonly near coast)
ch. 9 class
Atmosphere composition and structure
Atmosphere composition and structure, circulation, climate change
—Climate - long term conditions (long periods)
–Weather (short term - approx. 2 weeks)
Composition of the atmosphere
• Nitrogen, Oxygen and Argon = 99.9%
• Unique in our solar system
◦ Oxygen and water vapor
• Minor gases absorb light energy and help retain heat
◦ Water vapor, CO2, ozone, methane
• CO2 (Carbon dioxide) is ESSENTIAL but an increase is a MAJOR concern
Structure of the atmosphere
• Solar radiation heats the atmosphere
• Temp. varies widely with latitude and altitude
Atmospheric presure and water vapor
atmospheric circulation
Atmospheric pressure
–Air has very low density
–Column of air exerts pressure - at sea level approx. 1 bar
–Atmosphere P drops rapidly with altitude
Water vapor
–Atmospheric moisture varies - evaporation and precipitation
–Traps heat
–Reflect incident solar radiation
Atmospheric circulation
- -Solar radiation produces differential heating of the earth (SPHERE)
- -Air masses move to balance global T - warm air rises/cold air sinks
Water circulation
Atmospheric circulation moves water
- -Evaporation increases with T
- –Warm air holds more water
- –Warm air rises and moves towards poles as cold air sinks
Evaporation - precipitation balance
- –Certain ocean areas evaporation > precipitation
- –Winds carry water vapor
- -Large rivers linked with ocean areas
Rainfall
—Starts hydrologic cycle
Oceanic circulation
Water in the ocean is in constant motion driven by:
◦ Wind
◦ Variations in density (function of T and salinity)
Global oceanic circulation
◦ Entire ocean is slowly mixed
◦ Flow paths may cover the entire globe
Density driven currents
—hermohaline circulation
—T and salinity control DENSITY of seawater
• Cold water > warm water (bc the bonding is tighter in cold??)
• High salinity > low salinity (bc heavier)
—Polar = colder waters, low rainfall, and high salinity
–Dense surface waters in polar regions sinks
–salinity and temp. cause density changes - called Thermohaline circulation - T HAS MORE INFLUENCE THAN SALINITY
–water from surface sinks to freat depths - takes about 1000 years to complete cycle
Wind driven currents
—Wind impacts the surface layer
◦ Prevailing winds push water in one direction
◦ Water is deflected by land
◦ Form roughly circular patterns
–win movement caused by uneven heating of earth’s surface - some more complex bc of continent shapes - Gulf Stream and Kurpsjop
Climate zones
Climate impacts geologic processes ◦ Rates of weathering ◦ Soil development ◦ Types of erosion • Sedimentary rocks record ancient climates
1. Tropical climates ◦ High T ( > 20 C ) ◦ High rain - up to 2 m/yr. ◦ Rain forests ◦ Large rivers ◦ Deeply weathered soils
2. Desert climates ◦ Precipitation < evaporation (total precipitation < 25 cm/yr.) ◦ T varies from very hot to very cold ◦ Slow weathering ◦ Erosion by wind ◦ Evaporate deposits
3. Temperate climates ◦ Btwn 25 and 60 degrees N & S of the equator ◦ T varies throughout the year ◦ Precipitation may fall at any time ◦ Large rivers MAY form ◦ Moderate weathering and rich soils
- Polar climates
◦ Regions N & S of 60 degrees latitude
◦ Average T < 10 C and < 0 C most of the year
◦ Low precipitation, often classified as deserts
◦ Low rates of weathering
◦ Glaciers
Ch. 9 reading - major concepts
—Enormous interconnected system of moving air and water that creates and controls the hydrologic system and entire planet’s climate
–Sediments, rocks, and landscapes record dramatic changes in climate
—Climate controls the river system, wind and waves, the ice cap in Antarctica, deserts, and the soil we grow food in
Climate system driven by SOLAR HEAT and interactions of oceans, atmosphere and circular patterns
• Atmosphere is the envelope of gases that surrounds earth - consists mainly of nitrogen and oxygen ◦ Humidity and temp. variations are caused by uneven distribution of solar radiation and heat • Ocean consists of liquid water, capped at the poles with sea ice - strong vertical temp. gradient in ocean waters creates a thin, warm surface layer and thick mass of cold deep water ◦ Most imp. Dissolved constituents in seawater are salt (NaCl) and calcium carbonate (CaCO3) • Global circulation pattern involving surface and deep waters mixes the entire ocean - circulation of oceans is driven by the wind, by seawater density differences (caused by variations in salinity and temp.) and by coastal upwelling • Global climate change can be caused by changes in solar radiation intensity, volcanism, development of new mountain belts, changes in atmosphere and tectonic position of continents • Concerns about global warming are based on inc. in atmospheric carbon dioxide caused by burning of fossil fuels
composition and structure of atmosphere
unique bc rich in nitrogen and oxygen (.01% of earths mass)
- -temp. variations divide it into layers
- -dynamic open system - transports heat and moderates temp. elsewhere
composition:
- –2 main gasses: nitrogen, oxygen and argon - oxygen allows for life on earth - also reacts with minerals
- -water vapor (humidity)
- –Carbon dioxide makes up .03% but has been increasing bc of burning fossil fuels
- –Gases do little to affect heat balance on earth - but minor gases absorb light and heat up atmosphere…without them earth would be frozen - these gases that absorb solar energy make up less than 1% of atmosphere (water vapor, CO2, ozone, methane)
Thermal structure of atmosphere
- -All heat in atmosphere and oceans comes from nuclear fusion in the Sun - energy is transported by radiation and heat’s the planet’s surface - ave. global temp. of air is 15C and 59F (ranges from -90C to 58C)
- –TEMPERATURE DIVIDES THE ATMOSPHERE INTO LAYERS
atmosphere pressure and water vapor
◦ Air seems to have little density, but if there was not internal fluid pressures in air…we would be crushed
◦ Atmospheric pressure is greatest at sea level and drops rapidly with increasing altitude
• At 8.8km, height of Mount Everest, the air is so thin that humans can’t get enough oxygen in each breath to survive
water vapor
– ◦ Water removed from oceans by evaporation and carried as water vapor in turbulent troposphere
◦ Has a warming influence on atmosphere - called the “Greenhouse effect”
◦ Condenses to form clouds - controls amt. of solar energy that is reflected away from Earth
◦ Cold air can hold much LESS water vapor than warm air
• % of water vapor at poles is 10 times less than at the equator - also water vapor high in atmosphere is much less than at the surface
◦ Precipitation occurs when air is oversaturated with water vapor - occurs when vapor is no longer stable form of water but must be joined by liquid as well - condenses to form droplets of liquid water/ice that falls to the earth
• Most precipitation occurs along the equator - the least falls in deserts N and S of the equator and also in polar zones
energy and motion of atmosphere
Driven by uneven distribution of solar energy - solar heating is greatest in equator and causes water in oceans to evaporate and moist air to rise
—Bordered in middle latitudes by high-pressure zones that are cloud-free and have dry air
Solar radiation and heat balance
- –Large part of sun’s radiation is reflected back to space immediately - 30% reflected by clouds, oceans, ice and snow covered areas (bright areas)
- –As the surface warms - it radiates heat back to space and warms lower atmosphere in the process
- –The amt. of solar radiation absorbed by earth decreases with the distance from equator (bc gets colder closer to poles)
1. Earth is a sphere, angle at which sun’s rays hit surface varies from nearly vertical as the equator to nearly horizontal to the poles
2. Also less energy received at poles bc same amt. of incoming radiation is spread over a large area bc of the angle - the same energy is concentrated in a much smaller area at the equator
3. Sunlight also travels through much greater thickness of atmosphere near poles than at the equator - which diminishes the amt. of heat that reaches surface
4. Also length of the day - tilted 23.5 degrees - length of day varies with the seasons - during winter, days are shorter bc the spin axis is tilted away from the sun
global circulation of atmosphere
◦ Systems try to reach equilibrium - global circulation of atmosphere is an attempt to reach equilibrium by equalizing temp. diff. btwn poles and equator - this movement in the wind causes circulation of oceans and atmosphere - drives climate
◦ Constant movement revealed in clouds and distribution of water vapor
* If movement due to solar heating, hot air would rise at equator and flow toward poles - as cooled, would sink at poles and return to equator - surface winds flor straight from poles to equator * CORIOLIS EFFECT - Newton's 1st law of motion: body in motion keeps speed and direction unless acted on by an outside force - force divides atmosphere circulation into several latitudinal zones - flows in 3 separate loops: tropical, temperate, and polar cells are spiraling convection cells that stretch around the planet
uneven wind patterns caused by uneven ditribution of solar radiation in combo with earth’s rotation
- -neat equator - air heated which reduces density and air rises - at high alititues, air cools and desvends towards equator - trade winds
- -in N, deflected by earth’s rotation and flows s (S moves N)
- -when warm moist air flows from south cools it drops as rain or snow
global patterns of water movement
◦ Two rules of the global transport patterns of water in hydrologic system
1. Evaporation rate increases with temperatures
2. Warm air holds more water vapor than cold air
1. So the water near earth’s equator has higher evaporation - also higher precipitations rates
◦ Circulation model
• In equator, hot, moist air rises bc of low density in warm air - as it rises and cools the moisture condenses - the condensation produces tropical rains which fuel growth in South Am. Africa and Indonesia
▪ The Coriolis effect - Creates trade winds that converge toward the equator and creates intertropical convergence zone
One of the major factors influencing patterns of water movements is balance btwn evaporation and precipitation in oceans
- -Water vapor by evaporation over oceans is major source of water that falls as rain on continents
- –Major sources of water that falls on continents are areas of ocean where evaporation exceeds precipitation (closer to equator - symmetrical on both sides) - most important zone of water for continents and rivers
- –Areas of intense evaporation are the major source of water for the Amazon river
Monsoons - Occur when a wet season is followed by a dry season as prevailing wind directions reverse direction
• Regional not global pattern - controlled by plate tectonics
• During winter, Asian continents become very cold and high pressure zone develops - the cold, dry air push zone over indian ocean - forms dry season - intertropical convergence zone south of equator
• During summer - becomes a hot, low pressure zone - intertropical convergence zone to the North of Equator - warm wet air moves over Himalayas - air cools and heavy rains fall
• Monsoonal rains feed almost half of world’s population
Composition and strcuture of oceans
Oceans cover 70% of earth’s surface and contain 97% of earth’s water - major source of water that evaporates and precipitates on continents - oceans can store heat which moderates seasonal climate changes - oceans help moderate temp. diff. from equator to pole
sea water - NaCl - salnity is measure of all dissolved salts in sea water - varies with amt. of fresh water inputs from rivers or melting glaciers
– ◦ Salinity high in sub-tropical regions bc intense evaporation leaves water rich in salts that cannot evaporate
• At high latitudes, temp. is lower and evaporation rate is lower - fresh rainwater makes surface waters low in salinity
◦ Salinity also greater jus below the surface of sea ice, bc ice rejects the dissolved substances, thus enriching them in the liquid beneath frozen ice
◦ Highly saline waters are more DENSE
◦ Differences in salinity and temp. drive the circulation and flow of seawater
thermal strucure of oceans
• Water has one of the highest heat capacities of any substance - ocean waters can store, transport and release heat - affects earth’s weather and climates
• Ocean temp. decreases with depth (Ave. temp. is 3.5C)
◦ Near surface, seawater almost same temp. as atmosphere - freezing deeper
◦ Diff. btwn temp. btwn surface and bottom water is small at the poles
1. Surface water
◦ Ocean layered bc of temp. differences (like atmosphere)
◦ Warm and less dense - well mixed bc stirred by winds, waves and surface currents - exchanges water vapor and Co2 - bc very mixed, temp. and composition vary only slightly (comparable with troposphere)
2. Deep water
◦ Dramatic temp. drop - almost uniform temp. that changes very little n and S of equator
◦ Very thick and contains most of ocean water - moves slowly - bc so dense, makes it difficult to move upwards and mix with surface water - so stratification is stable - almost completely isolated from atmosphere
• Sea ice - increases the amt. of solar energy that is reflected into space - reflects more solar energy than darker seawater - covers up to 15% of the earth’s surface - permanently present on 7% of ocean
◦ Thin -sea water freezes at colder temp. (-2 degrees C) bc of salt (fresh is 0 C) (thinner in Antarctica than Arctic)
Coastal upwelling
◦ Along shorelines, coastal upwelling of deep-ocean water is imp. - bc of Coriolis effect, winds blowing toward equator and along coast cause seawater to move to right of wind direction in N and to left of wind direction in S - movement of surface water away from shore causes cold deep water to flow upward and take its place - the deep water is rich in nutrients and turns into food for sea animals (Cali)
◦ El Niño - (The Child) - occurs around Christmas - sometimes when wind weakening allows warm currents to approach shore of S Am. Where surface waters are usually cold - causes plankton pop. To diminish and fish pop. To almost disappear (bc surface warm water lacks nutrients) - bird pop. Diminishes and fisherman are out of work - causes flooding in N and S Am. And drought in India, Indonesia and Australia
Climate change
Climate change evident in sedimentary rocks
—Huge temp. changes have not occurred on earth - earth has been cool enough for liquid water to exist for 4 billion years - nearly constant temp.
- Regional change due to continents moving into diff. climate zones
◦ Slow movements of lithosphere (plate tectonics) - over long span of time - move in certain direction over thousands of years, but also obstructed by plate collisions - possible, but earth’s climate has remained relatively unchanged - Global climate change - human disturbance
◦ Most imp. Global climate parameter is temp. - change could be caused by energy output of sun composition of earth’s atmosphere, reflecting of earth and its atmosphere, ocean circulation patterns, blocking of sunlight, or changes in earth’s spin/orbit
◦ Greenhouse effect - Co2 in atmosphere absorbs heat radiated from surface and traps it in troposphere - gases that absorb energy an inc. atmosphere’s temp. called greenhouse gases - CO2 concentrations have been inc. since 1800 - inc. from 275 CO2 to 400 in past 250 years - inc. c02 from fossil fuels (coal, oil gasoline all fossil fuels - burn to release CO2) - inc. dramatically since 1800 industrial revolution - causes global temp. to rise
◦ Ocean acidification - also inc. CO2 in atmosphere bc of increasing acidity of oceans - when co2 is released it accumulates in oceans where it reacts with water to make a weak acid - ph of ocean is 8.1 - causes it to cont. to drop - lower ph makes it diff. for corals, plankton and other sea creatures to precipitate skeletal minerals
- weathering
is the physical and/or chemical alteration of rocks and minerals where the lithosphere, hydrosphere, atmosphere, and biosphere meet
- -breakdown of rock’s at earth’s surface by physical processes and chem. reactions with air and water
- -weathering is process of NATURAL DECAY (buldings deteriorate, wood dries and splits, cement crumbles) - all happens bc rock materials exposed to atmosphere
Physical weathering
- physical breakage of rocks into smaller pieces by phys. processes - no chnge in chemical composition
- Ice wedging
- –Water expands when it freezes - volume increases by 9% (in pic. It looks like the water seeps inside rocks and when it freezes it expands and the rock grows in volume and tends to crack with the new pressure
- –This occurs where daily freeze thaw takes place - at least seasonally
- –Talus cones
- -water from rain or snow penetrates cracks or openings in rocks - as it freezes..it expands and puts pressure on the rock walls - over time the rock is hammered out
- -occurs when lots of moisture exists in env, when there are lots of cracks in rocks, when freq. temp. rise and fall beyond freezing pt.
- -in arid regions, salt crystals grow in pores and cracks to pry apart rocks - grow by evaporation as rocks exposed on salty shores - SLC - Sheeting
- –Release of confining pressure
- –(1) Deeply buried pluton - (2) mass exposed by erosion of overlying soil - (3) pluton expands outward and is exfoliated
- –rocks deep within earth’s crust are under pressure from above rocks - as cover removed by erosion, pressure is released and buried rock tends to expand - causes internal stress that leads to fractuers in rocks - causes them to burst - unloading
talus - product of phys. weathering - best seen in mountains - material accumulates in pile at base of cliffs - called talus cones - built up of isolated blocks loosened by phys. weathering - piles of rock debris that accumulates. at base of cliff as result of rock fall - usually by ice wedgine
Tree roots
—Root tips pressures may exceed 10,000 kg per square meter
–also caused by animals and plants - they mix soil and loose rock particles to cause further chem. breakdown - pressure from growing tree roots
NO CHANGE in chemical composition - just breaking down into small pieces
- Chemical weathering
Proceeds by the removal or addition of chemical components to the minerals, changing the composition and internal structure of rocks
–many scientists believe chem. most imp.
- Dissolution
- –Headstone example over the years - dissolving
- -process where mineral passes intosolution, like salt dissolving in water - some in water and ions are leached (flushed away) - salt (halite) is best ex - extremely soluble - Gypsum also
- -almost all minerals are soluble in water (ionic bonds are easier than covalent) - Acid Hydrolysis
- -most common dissolution reactions involve acidic water
- -H2CO2 common in natural env. and forms when water combines with CO2 - happens in atmosphere or root zones of plants when CO2 is in soil
- -hydrolis is chem. reaction where water and another substance both decompose into ions
- -in pure water, calcite not very soluble, but water in carbonic acid can dissolve more
- -can cause formation of new minerals - new minerals are “hydrated”
- -best Ex. is Feldspar partly altered to a mixture of clay and quartz
- -effect only really seen in microscope - weathering caused feldspar to turn to clay - Oxidation
—Combination of oxygen with one mineral to form a completely diff. mineral where one element has a higher oxidation state (higher ionic charge)
–chem. combo of oxygen in atmosphere or dissolved in water - one mineral to form diff. mineral at higher oxidation state
–iron is most imp. - better in oxidized state
▪ Ex. Fe2+ becomes Fe 3+
LOOK AT TABLE 10.1 - to see which minerals are most susceptible to chemical weathering - Gypsum and halite are quick and easy - Quartz resists dissolution, Pyrite is lowest on table
- mechanicla and chemical weathering linked
Principle: mechanical weathering enhances chemical weathering by producing more surface area - chemical weathering proceeds at the surface of a mineral
–permits deeper penetration of reactive fluids that cause chem decomposition - chem decay facilitates physical disintegration
Spheroidal weathering
Decomposition is most rapid at corners
—Further weathering reduces size
Differential weathering
- -Caused by variations in weathering rate
- –Occurs over a broad range of scales
- -Appalachian mountains, Arches, spindles
- -diff. rock masses or sections of same rock weather at diff. rates - can be seen everywhere - Bryce anyone - white layers erode more rapidly than thicker beds of sand which are more resistant
influences on soil formation
The nature and amount of soil found in a particular place is related to factors affecting weathering rates and the ability of the soil to stay in place
• topography • Parent material •Soil is earth material that is capable of sustaining rooted plant growth • Vegetation • Time • Climate Soil structure ---Soils are more weathered at the top - dissolved matter from the top of a soil column travels downward and is deposited in lower portions
rates of weathering - linked to climate zones - human structures useful gages for measuring rates - thickness of soil profile controlled by weathering rates
joints and fractures
facilitate weathering bc permit water and gases in atmosphere to attack a rock body at considerable depth - also inc. surface area on which chem. reactions can occur
major products of weathering - spheroidal rock forms, blanket or regolith and dissolved ions
–soil is upper part of regolith (mixture of clay minerls, weathered rock partciles and organic matter)
climate and rock type influence type and rate of weathering - also helps control amt. of CO2 in atmosphere and thus climate
Further reading weathering
minerals in rocks are in equilbrium - butwhen exposed to diff. env. the minerals have to adjust to diff. forms that are stable under new conditions
–metamorphic and igneous intrusions most susceptible to weathering
weathering of major rock yypes
influenced by variables: mineral composition, texture, climate in which weathering occurs
–ex. limestone could weather into soil-covered valley in humid climate and form cliff in arid climate
minreal composition imp. - quartz is stable and remains unaltered where olivine and feldspars are unstable and decompose immediately
texutre imp. bc of porosite and permeability - ease at which rock can enter and attack minerals
–precipitation amts. also influence
granite - most homogenous rock - forms at high temp. and under great pressure
- -delspars weather rapidly by chem. reaction with water - altered to various clay minerals
- -calcium is resistant in calcium feldspars
- -basalt - is vesicular and porous - easily broken down pjhyiscally - permeable and easiy composed
- -sandstone - composed of quartz - resistant to chem. weathering
- -shale is fine-grained and soft - composed of clay and has ability to absorbe and expel large amts. of water
products of weathering
1. SPHERICAL SHAPES
LOOK AT PG. 279
major products are
1. rock bodies modified into spherical shapes
-almost all rocks broeken into fractures that influence the weahtering of rucks by cutting blocks of rock to smaller ones (inc. surface area for chem. reactions to take place) - breakdown of rock to joint planes called joint-block separation
–joints also act as system of channels through which water can readily attack a rock from several sides
—tendency for\ spherical (rounded) surfaces to form as decayaing rock breaks - produced bc weatheing attacks all exposed sides of ricks at once - decomposed material falls off and leaves round shape
–exfoliation - type of spheroidal weathering where rock breaks apart by separation along series of concentric shells or layers - layers are parallel to each other and surface - could bring sheeting in granite
products of weathering
2. REGOLITH
- blanket of loose, decayed rock debris called regolith (soil is most imp.)
- -forms a discontinuous cover over solid, bedrock below - loose, soft material formed in place by decomposition of bed rock beneath it - within regolith, the indiv. grains or small groups of mineral
- -transition from bedrock to regolith
- -gravel, sand, silt and mud deposited by streams wind are transported regolith - cover the surface
- -on steep canyon walls, little soil is retained and bedrock is exposed
soil
–uppermost layer of regolith - compose of small particles of rock, new mienrals formed by weathering and amts. of decomposed materials
soil profile - transition from upper surface of soil down to fresh bedrock - shows all the layers (horizons) of soil by compositon, color and texture
- -A horizon - topsoil layer - usually dividied into 3 layers too (A0 thin surface of leaf mold), (A1 humus-rich dark layer), (A2 light, bleached layer)
- -B horizion is subsoil - contains clays washed down from topsoil - Zone of accumulation and reddish in color
- -C HORIZON - zone of partly disintegrated and decomposed bedrock - meets the bedrock
topography - affects soil development bc influences the amt. and rate of erosion and nature of drainage
- -influene is seen from contrast btwn slope soils and veley soil - thick soils from on flat or gently sloping surfaces but steep slopes permit only thin soils to develop
- -time also imp. in soil development - seen in areas of volcanism - thick soils have developed on old lava flows - thin soils on younger flows
products of weathering
3. IONS IN SOLUTION
- ions in solution
- -ions dissolved in water
- -major source of ions in solution is carbonate rock - 45% of dissolved material in rivers is derived from carbonates
climate and wearthering
cliamte is the SINGLE MOST IMP. FACTOR influencing weathering - determines type and rate of weathering but also characteristics of regolith and rock surfaces
- -intense chem. weathering occurs in hot, humid regions and develops thick regolith - it is minimal in deserts/polar regions
- -bc rainfall, temp. and seasonal changes impact weathering style and rate
- -most chem. reactions req. presence of water - precipitation of an area is huge factor!!
physical weathering - most imp. infleunce is temp. changes that produce cycles of freezing and thawing
chemical weathering also controlled by temp. and water acidity (pH level) - from 1 acid to 13 alkaline (iron is MUCH more soluble at pH 6 than pH 8.5) - so forests exp. more chem. weathering than other areas
–physical w. dominates arctic areas (thin soils) and che. in tropical (thick oxidized soils)
soils in diff. regions
OXISOLS - dominate tropical zones in Afica and S Am. - high temp. in tropical areas SPEED chem. reactions
ARIDOSOLS - low-latitude deserts where chem. w. is minimal bc of lack of precipitation - soil is thin
temperate regions - temp. and humidity range so both chem. and phys. w present - soil and regolith develop to depths of diff. meters
–MOLLISOS - organic rich A-horizon thick soils dominate temperate zones
GELISOLS - soil is thin and unproductive - in polar regions - temp. too low for chem. weathering - env. for physical w.
- -climate also affected by weathering - chemical reactions involving carbon create chemical cycles - can remove CO2 from atmosphere - imp. bc co2 is greenhouse gas and when removed it reduces atmosphere’s ability to absorb heat and the planet cools
- -other side - CO2 can be released into atmosphere by weathering - produced by black shales - carbon reacts with oxygen or oxidized groundwater to create co2 - so co2 and temp. rise!!
