·        long-term atmospheric and surface conditions for area

·        warm climate=hot house

·        cold climate=ice house or Ice Age

·        the time scale for global climate change is decades/centuries to thousands/millions of years

·        Early Earth (first 1-2 billion years) was very warm

·        end of Paleozoic (~300 m.y.a) was very cold (glaciers)

·        end of Mesozoic (~100-50 m.y.a) was very warm

·        end of Cenozoic (Quarternary, past 2 m.y) had climate oscillations from very hold to warm

climate change-- effect on sea level

o       if current glaciers were to melt, that water (now on land) would drain into oceans causing the sea level or rise which would result in flooding of many costal cities

o       On the other hand, if glaciers were to become larger (as in Ice Age), water from the oceans would get transferred to ice on land, causing a drop in the sea level

o       During Ice Age (past 2 m.y) glaciers covered ~1/3 of the area of continents, reducing sea level by ~100 m compared to today

o       East Coast of USA was 100km east of NYC, France and Britain joined by land (now English channel) and Alaska and Siberia were joined by land

·        Large change in climate (major warming or cooling)

o       has an impact on agricultural productivity/ecosystems and even population migration

o       If significant global warming occurs, some areas will become much drier (others wetter), causing deserts

§         this means greater irrigation or lower agricultural productivity

§         greater severe weather and greater disease (sleeping sickness, malaria, yellow fever)

o       if glaciers or deserts advance over large areas, people will have to move and agricultural productivity will lower

·        Glaciers’ effect on landscapes/floods

o       carves spectacular mountain peaks in some areas (Rocky Mountains and Alps)

o       form Great Lakes

o       flattens landscapes  (most of Illinois)

§         rich soil of Midwest is due to deposition of glacial debris

o       Catastrophic floods (as glaciers melt)—large lakes were created (Lake Missoula in Montana)

§         Dam of ice or glacial sediment was holding water and suddenly dam gave away, resulting in huge amounts of water racing across states of WA or IL

§         WA flood created topography called channeled scablands

·         rough, soil free land, created ripples and moved enormous boulders

§         IL flood carved large river valley on Illinois river

·        Predict Future Climate

o       understand geologic past to help predict future (inverse uniformitarianism)

General Controls on Climate

·        Atmospheric Composition-Role of Greenhouse Gases/Greenhouse effect

·        Composition of Earth’s current atmosphere (excludes water, which varies 0-4%)

o       Nitrogen: 78%

o       Oxygen: 21%

o       Argon: .9%

o       Carbon Dioxide: .04%

o       Others: <.01%

·        Solar energy is electromagnetic radiation distinguished by its wavelength

o       Electromagnetic spectrum is a collection of all wavelengths of electromagnetic radiation from long radio waves to very short x-rays and cosmic rays

·        All objects emit e-m radiation, nature of which depends on their temperature

o       greater temperature, object emits greater amount of radiation (greater intensity) which is a shorter wavelength

o       Sun emits must of its energy as visible light

o       Earth is much cooler and emits much less radiation (lower intensity), ~entirely as longer wavelength infrared radiation

Greenhouse effect

·        some of incoming sunlight (visible light with short wavelength) gets absorbed by earth, and then is reradiated as long wavelength infrared (heat) radiation which is trapped by greenhouse gases (H₂0 vapor and C0₂ but also methane/CH₄, nitrous oxide/N₂0, ozone/0₃ and chlorofluorocarbons/CFC) in atmosphere, causing heating (greenhouse effect)

·        Heat absorption raises the average temperature of the earth and makes earth a habitable planet

·        without the Greenhouse Effect (no atmosphere), the average temperature on earth would be ~33 degrees Celsius colder and water would be frozen

·        We would also see enormous swings in daily temperatures similar to those on the moon

o       on the sunlit side, Earth’s temperature would be close to boiling but the dark side would be far below freezing

·        Abundance of C0₂ has a major effect on global temperature

What processes affect abundance of C0₂ in the atmosphere?

·        Volcanism is where volcanic eruptions release gases (mostly H₂0, C0_2, CO, and N₂) as well as lava and volcanic ash

o       Volcanic eruptions were source of most gases in our atmosphere (except O₂)

·        Chemical weathering reaction of silicate or carbonate is C0₂ + H₂0 + silicate/carbonate material-àdissolved ions + HC0₃^-

o       weathering removes Co₂ gas from atmosphere and adds it to oceans (as HC0₃) which increases chemical weathering of rock causes greater C0₂ in the atmosphere

·        Burning fossil fuels is the burning of any carbon-based fuel (coal, oil, natural gas, wood, leaves and ethanol) and it involves the production of C0₂ gas

o       C (organic matter) + oxygen-à C0₂ gas + heat

·        Photosynthesis (removes C0₂) using light energy. Plants convert C0₂ gas into food (chemical) energy

·        Photosynthesis reaction: C0₂ gas + sunlightà C (organic matter in form of sugar) + 0₂

o       this reaction if the reverse of the fossil fuel combustion reaction

o       increasing the amount of plant life means lowering C0₂ in atmosphere

·        Respiration is the reverse of a photosynthesis reaction, plants and animals used stored chemical energy to carry out life functions

Scientific Writing Goals

·        Effective Communication

o       communicate clearly

o       community efficiently

·        Recommendations for Effective Writing

o       Identity audience and pose questions your audience might ask

o       answer above questions in controversial way

o       have a good hook

§         starling fact, vivid example, paradox

o       put yourself in shoes of reader (editing)

o       get feedback

o       have a central theme (thesis) and good topic sentences

o       put most important ideas first

o       do not plagiarize

o       pick a good title

§         brief, interesting, captures attention

o       proper grammar

o       brevity and clarity

o       concrete words

o       use active tense (not passive tense); verbs are stronger clearer and shorter

Effect of greenhouse gases on climate: Geologic examples

·        Early Earth (4.6-3.5 or 3 b.y.a., early Precambrian)

o       C0₂ abundance of early earth: 98% vs. current earth of .039%

o       P (bars) of early earth: 60 vs. current earth of 1

o       Temperature of early earth: 290 vs current earth of 16 (Celsius)

·        Mesozoic/beginning of Cenozoic (100-50 m.y.a)

o       very warm interval, which resulted in flooding of much land on continents (glaciers melt, sea level rises)

o       The major reason for the warming is greater levels of C0₂ gas from greater volcanism by rapid sea floor spreading associated with opening of Atlantic Ocean

·        Cenozoic cooling (50-2 m.y.a)

o       after hothouse climate, earth cooled progressively

o       occurred because of plate tectonics  which began ~45 m.y.a.

o       creation of mountain ranges exposed enormous amount of silicate and carbonate rock to chemical weathering and the steep slopes were erode quickly exposing new fresh rock

o       chemical weathering of silicate and carbonate rock lowered levels of C0₂ gas which in turn caused global cooling

o       greater marine plants cause greater photosynthesis and lower C0₂ gas also

·        Atmospheric composition: role of dust particles from volcanism

o       large explosive volcanic ash (ash-fall) eruptions can send enormous amounts of volcanic ash (dust sized) into stratosphere for months to years

o       the dust (and associated S0₂ gas which oxidizes to sulfate aerosol reflect sunlight and can cause short term cooling

o       Tambora (Indonesia): volcanic eruption in 1815

§         largest historic volcanic eruption that sent huge amounts of volcanic ash and SO₂ gas  into stratosphere and caused global cooling

§         1816 was a year without summer

§         Crops failed with cold temperatures and worldwide famine resulted in ~90,000 deaths

o       Mt. Pinatubo, Philippines eruption in 1991

§         caused some global cooling

§         Only year of 1990s that wasn’t warmest ever recorded during historical times up to the 1990s

·        Sun intensity

o       Sun’s energy is the dominant source of heat to Earth’s surface

o       Variable amount of solar energy received by Earth can greatly affect global climate

o       Solar energy varies by

§          changes in sunspot activity

·         greater sunspots=slight warming

§         changes in overall reflectivity of Earths surface

·         dark surfaces (dark soil), deep blue equatorial seawater and green leaves absorb more solar energy

·         light surfaces such as snow, ice, polar seawater reflect more solar energy)

o       Variations in Earth’s orbit and spin/rotation (eccentricity, tilt and precession)

§         End of Cenozoic/Pleistocene (last 2 m.y)

·         this effect on solar energy is used to explain regular oscillations of icehouse and warmhouse climates that have occurred over the past 2 m.y.

·         Continental glaciers (thick ice sheets) repeatedly covered much larger part of the Earth’s surface

o       Periodic minor variations in Earth’s orbit area and spin/rotation

§         Shape (eccentricity) of Earth’s orbit

·         varies from ~circular to elliptical (eccentric) on 100,000 year cycle

·         Greater the temperature variation in seasons with elliptical orbit

§         Wobble (precession) or Earth’s axis

·         Earth wobbles on its spin axis with 23,000 year cycle; with eccentricity, wobble affects climate

·         when northern hemisphere winter is farthest from the sun and summer is nearest to the sun, it gets the largest temperature extremes in the northern hemisphere

§         Tilt (orientation, obliquity) of spin axis

·         tilt of spin axis varies from 21.2-24.5 degrees from Sun with 41,000 year cycle

·         Greater variation in seasons with highest tilt because of less direct sunlight at high latitudes in winter

§         These 3 periodic variations combine to produce episodes of mild summers in northern latitudes that prevent snow and ice melting on 100,000 year cycle (Milankovitch cycle) which coincides with 20 glacial advances observed over the past 2 m.y.

§         Although these variations are small, they seem to be enough to trigger regular Ice Ages of Pleistocene

·        Distribution of land and water masses (plate tectonics control)

o       if continents are located over polar latitudes, they can develop continental glaciers due to colder temperatures (can’t develop thick ice sheets over ocean)

o       End of Paleozoic (~250 m.y.a)

§         Ice Age-extensive glaciers in continents of Southern Hemipshere because they were centered over South Pole in single landmass

§         Pangea-largest temperature extremes due to long distance from moderating effect of ocean

·        Wind/atmospheric circulation, Ocean circulation

o       controlled by global wind patterns, but also influenced by land and water mass distribution

o       Current ocean circulation patterns keep some areas relatively warm and other areas relatively mild

o       if warm, equatorial waters are prevented from circulating to polar latitudes and those areas will get much colder

·        Mountains (plate tectonics influence)

o       high altitude=colder temperature and a greater chance of mountain glaciers (if enough precipitation)

Current and Future Global Climate Change-Global Warming

·        Greenhouse Effect is a process of trapping reradiated solar energy by greenhouse gases in atmosphere

·        The problem is that human activities have a greater amount of greenhouse gases in atmosphere which may lead to the problem of global warming (greater average temperature of Earth)

o       Carbon Dioxide

§         recording stations on Hawaii and gas bubbles in glacial ice indicates level of carbon dioxide in atmosphere have steadily increased over the last two centuries from ~280 ppm to ~380 ppm due to fossil fuel combustion, deforestation, fewer plants mean less photosynthesis which removes carbon dioxide gas

§         burning carbon-based fuel produces carbon dioxide gas

§         C (organic matter) + 0₂ -à C0₂ gas +heat + light

§         as more fossil fuel is burned, level of C0₂ gas in atmosphere could increase steadily

§         USA leads world in fossil fuel combustion (and energy use) and associated production of C0₂ gas

§         methane from organic decay (landfills), extracting fossil fuels and agricultural activities (rice fields and raising cattle and sheep)---other greenhouse gases are being steadily added to atmosphere

·         N0₂ from fossil fuel combustion and fertilizers

·         CFC from Freon in refrigeration units and as aerosol in propellant

·         03 from fossil fuel combustion (lower atmosphere only)

§         greater levels of greenhouse gases may cause global warming

o       Over the past century, only small rise in average earth temperatures (~1 celsius)

o       The 10 warmest years have been in the past 15 years

o       Indicators of global warming

§         small mountain glaciers are almost all shrinking now compared to a few decades ago

§         Artic ice cap has thinned by ~1.5 m and are greater in volume by 40% compared to previous measurements

§         animals have modified their range of habitat (birds and butterflies have moved northward) and plants in mountain habitats have colonized higher elevations

§         over past 100 years sea level has steadily increased by about ~20 cm

o       Many climate models predict future global warming of 2-5 degrees which would have drastic effects on global climate

§         more natural disasters are likely to occur

§         warmer weather may cause disease

§         warming would heat and expand seawater and melt glacial ice creating an increase in sea level—many of the world coastal cities would be flooded

o       Solutions to Greenhouse effect

§         Due to economic concerns, USA rejected 1997 Kyoto Protocol which required lower C0₂ production

§         future Ice Age-would help develop relatively rapidly in ~10-20 years based on study of past climates in Greenalnd ice core

§         In 1300-1800 (Little Ice Age), temperatures were ~1-2 degrees cooler than today, which resulted in much larger alpine glaciers, Delaware River froze over and Viking population in Greenland declined due to frozen water routes

Coastlines

·        where land meets an ocean or a large lake

·        includes beaches (surf zones) and estuaries (semi enclosed bodies of mixed fresh and salt water that attract many organisms)

·        beaches are the Earth’s most dynamic environment due to continuous erosion, transport and deposition of sediment by waves or tides

·        Beaches can undergo great changes (in shape, location or both) during single storm or gradual continuous change due to rising sea level

·        Even stable beach has continuous sediment transport

Coastal hazards

·        hurricanes/storms, tsumamis and coastal erosion

·        human intervention often occurs to protect developed areas from coastal erosion

o       often transfers problem to a different location

Coastal processes

·        most important process in coastal areas is action of waves

·        tides are of lesser importance

o       Waves

·        mechanical energy moving through water

·        waves release energy at shoreline when they break

·        wave size=f (wind velocity, duration of wind activity, distance over which wind blows)

·        Ocean waves that form in one area and travel 100s to 1000s of km to another area are called swells

·        Wave Terms

·         Crest=the top of a wave

·         Trough=lowest point of a wave

·         Wave length (L)=horizontal distance from crest to crest (commonly 40-400m for ocean waves)

·         wave height (H)=vertical distance from crest to trough (2-5 m in normal ocean, up to 15 m in storms)

·         Wave period (P)=amount of time for one to complete wavelength to pass given point

·        waves with large L and P are most powerful and erosive

·        In open water, water molecule in wave moves in circular trajectory (no net forward movement) that lowers with depth

·        Water is motionless at depths greater than .5 X L

·        Near the coastline, friction between the floor bottom and wave causes elliptical wave trajectories, asymmetrical wave shape, lowers velocity, lowers L due to lower velocity and great H

·        Eventually the wave top outruns the bottom and collapses into a surf zone, where forward and backward motion occurs, which drives sediment movement

·        Wave fronts are lines along the crest

·        Wave normals are lines perpendicular to wave fronts (show direction wave is moving)

·        Wave refraction is the bending of wave fronts as one part of wave reaches shallow water (lowers velocity) before another part

·         Even with wave refraction, water surges up the beach at small angle to coastline (due to wave energy) and retreats directly backward (due to gravity) which creates zig-zag motion that is swash and backwash

·        Typical angle of approach is <5 degrees (not parallel to coast) and is enough to create longshore current

·        Transported sediment is longshore drift

·        Curved coastlines are common

·        Wave refraction will focus wave energy at protruding headlands, causing erosion and cliff formation

·        Wave energy will be dispersed (lower) at intervening bays, where sediment deposition occurs

·        The effect of wave refraction straighten coastlines

o       Beaches

·        strip of sediment (usually sand or gravel) accumulated by waves at coastlines

·        Beaches occur between average low water level and cliff, dune or vegetated zone

·        Berm-flat zone

·        Beach face=more steeply sloping area below bern

·        Offshore bar=underwater ridge of wave deposited sediment (where waves break)

·        Features of beaches

·         Spit-finger like ridege of sediment that extends into deeper water; due to longshore currents

o       cape cod

·         Barrier islands-elongate, low relief, very long (up too 100 km) islands of sand parallel to coast

o       Common along US Atlantic coast; in front of Long Island, NJ, MD, VA, NC (outer banks) and FL and in Gulf of Mexico

o       Great for recreation but bad for permanent development

·         Sea cliffs

o       wave erosion can undermine cliff, causing landslides

o       Avoid building near sea cliffs (potential for erosion and property loss)

Coastal erosion- Causes and Mitigation

Problem

·         Many nations in the world have coastal zones

·         30 of our 50 states have coastlines along major water body

o       Atlantic and Pacific Oceans, Gulf of Mexico and Great Lakes

·         ~50% of USA population lives in coastal counties and population density is increasing

·         Coastal erosion is an ongoing, gradually developed geologic hazard in USA and world

·         In USA, much of Atlantic and Gulf coast are severely eroding and other coasts

·         Storms and hurricanes can cause great erosion at specific localities but by themselves cannot account for continuous, large scale erosion

Causes of large scale coastal erosion

·         Global rise in sea level

o       sea level rose through last century by 2-3 mm per year due to global warming

o       small rise in sea level can cause large change in position of coastlines for flat areas

o       predict greater rises in sea level due to enhanced Greenhouse effect and great possibility of flooding of major cities

·         Dams

o       loss of sediment supply

o       sediment for longshore drift is supplied mainly by rivers that enter the lake or ocean

o       dam construction traps sediment before it reaches coastline

o       many of America’s rivers have been dammed, therefore greater sediment is supplied from eroding cliffs, resulting in greater coastal erosion

·         very complex, involves prediction of future sea levels and knowing many processes over large zone of coastline: nature and amount of sediment supply (rivers, sea cliffs)

·         nature of wave energy (predominant direction, size)

·         nature of coastline (straight, curved)

·         offshore topography

·         nature of sediment transport (amount of longshore drift, direction of longshore currents)

·         nature of sediment loss (amount of sediment loss, directions of offshore currents)

Mitigation of Coastal Erosion

·         accelerating coastal erosion has lead to many efforts (costly)  to prevent erosion and save property

·         many efforts have failed or have transferred the problem to another location

·         Sea walls

o       onshore wall of concrete or rock debris parallel to coastline

§         Purpose: to protect land behind wall from wave energy but it commonly fails because wave energy comes around sides and is reflected downwards, causing erosion and the sediment supply is cut off

o       Galveston, Texas is a city developed on barrier island

§         in 1900, a large topical storm washed away 2/3 of city buildings and killed 6,000

§         in 1902 Galyeston build largest seawall ever on barrier island and the sea wall protected the city from later storms but the beach gradually eroded

o       Daufuskie Island, SC

§         sued state to build seawall to protect their property (seawalls are banned in SC)-state won

o       wall of concrete, rock, wood or sandbags built perpendicular to beach to trap moving sand and widen beach

o       usually successful on upcurrent side but sediment supply for downcurrent side of beach is cut off and erosion occurs there

o       downcurrent erosion can lower by artificially filling beach soon after groin construction or engineering capability for allowing sediment to bypass groin

o       pair of long groins that protect harbor channel from sedimentation

o       Because of size, jetties completely cut off longshore sediment transport, problem of upcurrent deposition and downcurrent erosion lower than for groins

o       Ocean City, MD located on highly developed barrier island next to jetty protected harbor

§         barrier island on downcurrent side (little development) has retreated landward by ~500 m

o       offshore wall parallel to coast to absorb wave energy and provide quiet water for harbors

o       problem=quiet water means deposition occurs and endless cycle of dredging or sediment bypass begins

Coastal erosion-Case histories

Chicago area lakeshore

• ~100 km along southwest coastline of Lake Michigan
• borders most densely populated area in Great Lakes region and includes some of the most highly engineered and human altered settings in region
• Lake plain (flat)
  • extends for ~50 km from IN border to Wilmette, most of the area is used for city parks
  • located on silt and mud that formed from glacial Lake Chicago
• Glacial till cliffs (steep)
  • extends for ~35 km from Wilmette to Waukegan, IL
  • ~all if developed with expensive homes
  • located on hills of unsorted sediment deposited directly by glacial ice
• Beach ridges (flat)
  • extends for ~15 km from WI border to Waukegan, Il
  • mostly within IL Beach State Park
  • Small dunes formed over past several thousand years due to build up of longshore drift

Lake levels and coastline changes

• lake levels are more variable than sea level and depend on regional precipitation (heavy rains=high lake levels) and human controls (dams)
• From 1920 to 2000 total variation in level of Lake Michigan is ~2 m; historic high in 1986 and historic low in 1964
• Before mid 1800s, much of IL shoreline was highly vulnerable to wave erosion but now must of the shore is “protected” but erosion remains a problem especially during high lake water levels
• In Chicago, biggest change in shoreline was from lake filling, which began in mid 1800s but must occurred from 1920-1940

Coastal erosion Control Measures along Southwestern Lake Michigan

• Revetments
  • ~seawall/lakewall
  • Chicago coastline
  • rock filled cribs designed to absorb wave energy; many built in late 1800s and early 1900s
  • deteriorating and need repair
• Bluffs area
  • although much of bluffs area is protected by revetments (lakewalls) and some groins, wave energy is reflected downward and beginning to undermine protective barriers
  • potential for massive erosion is those structures are lost
• Groins
  • examples in Chicago: North Ave-Fullerton Beach
• Jetties
  • Waukegan harbor
• Breakwaters
  • Lake Forest
• Beach nourishment
  • IL Beach State Park is experiencing major beach erosion because sand supply is cut off from north

Cape Hatteras Lighthouse Controversy

• located on North Carolinas outer banks, 200 km line of barrier islands
• known for “capes” (seaward projections of land)
• known as “graveyard of Atlantic” due to many ship groundings on nearby shoals during storms
• tallest brick lighthouse in the world (~60+ m)
• rising sea level and flat slops greatly reduced distance—all attempts to fix were unsuccessful
• Options include
  • build very large seawall
  • do nothing and lose lighthouse
  • move lighthouse to new area ~500 m inland

• build seawall in attempt to save historic lighthouse commissioned by George Washington but seawall was opposed

River

• flowing water at Earth’s surface usually confined to channel
• water derived from rain or melted snow that runs over Earth’s surface or through ground into river
• river flows downhill due to gravity, eroding and transporting sediment, eventually to ocean
• sediment carried by the river is the river’s load which consists of grains (clay through boulders) that are carried up in water or near bottom (bed load) by grain hopping or rolling
• With greater velocity, a river can carry greater load and larger grains

River-

Streamflow characteristics

• Velocity (v)-water speed, 5 km/hr is a fast river. Maximum velocity is in river center, just below surface
• Discharge (Q)-volume of water passing point over period of time (m3/sec or commonly ft3/sec)
  • Discharge=v x A= velocity x width x depth
  • A=cross sectional area of river (m²), width=horizontal distance from bank to bank, depth=vertical distance from water surface to river bottom
  • discharge normally is higher after rainstorms because of greater velocity and greater cross sectional area and downstream where tributaries add to main river
  • characterizes flood size
  • gradient (downhill slope, rise/run in m/km or ft/mile)

River Channel Characteristics

• Rivers tend to have characteristic downhill shape called longitudinal profile
  • river elevation vs. distance along flow direction
• usually begin in steep, actively eroding areas, with fast moving water that carries all but boulders
• eventually landscape flattens out and river slows down, depositing sand and gravel
• when river reaches base level (lowest elevation), it deposits the remaining sediment (silt and mud) at river mouth
• Velocity of major rivers is usually greater downstream

• Mountain rivers

•  
  • valley has characteristic v-shape and channel occupies nearly all of valley bottom
  • tends to flow relatively straight pathways due to steep topography
  • typical gradient= 10-40 m/km

• Meandering rivers

•  
  • rivers that wander back and forth across broad valley and flat plain called floodplain
    • broad, flat area consisting of sediment that is deposited during food, when river overflows its channels
  • Typical of rivers in plans (near mouth) where typical gradient= .1 m/km
  • natural levees are low wedge shaped lenses of sediment along river channel that commonly form due to deposition during flooding
  • change their course with time due to constant erosion and deposition that occurs along meanders
  • outer part of meander has higher velocity, therefore erosion occurs
  • inner part of meander has lower velocity, therefore deposition occurs
  • differences in velocity are due to inertia (mass), water wants to move in a straight line
  • area of maximum water velocity is shifted to outer part of meander forming a straight channel leaving oxbow lake (abandoned river meander)
  • area drained by river and its tributaries (small rivers that drain into larger ones) are called drainage basins
  • usually high ground separates one drainage basin from another
  • Dendritic drainage is a pattern of river and tributaries that resemble branches of a tree
  • When river enters body of standing water (lake or ocean), flow stops and remaining sediment load is deposited in delta
    • Shape is often like a triangle

• river overflows its channel due to excessive discharge
• for average river in humid climate, flooding occurs every ~1-2 years
• floods are a widespread geologic hazard, affecting more people than all other geologic hazards
• In USA, ~22,000 communities, 6 million homes are located on flood-prone land, resulting in ~$6 billion damage and ~140 deaths per year

Cause of floods

• Heavy rain (most common cause)-water runs quickly over land into river rather than infiltrating into ground, where it moves slowly
• Rapid snow melt-heavy snow and then quick warming causes large input of water directly into rivers because ground is still frozen and resists infiltration
  • PA
• Coastal storm surge-hurricanes and tropical storms affect coastal areas with winds blowing onshore plus tremendous rainfall amounts
  • Tropical storm Alberto hit FL and GA in July 94 with ~90 cm of rain and $250 damage
  • Hurricane Mitch poured 2-6’ of rain on central America
• Dam failure-occurred at Johnstown, PA in 1889 killing 2,200 people

• typical of flood in mountain rivers; brief but severe flood usually due to sudden intense rainstorm, floodwaters rise and then fall rapidly
  • affects small areas and can be devastating
  • water cant infiltrate ground quickly enough so it goes directly into river
  • flood severity is worsened by impermeable soil, steep slopes and lack of vegetation
  • Big Thompson River Flood of 1976 in CO involved 8” of rain in 1 hour, causing 139 deaths and $35 million in damage in a few hours
  • Black Hills of S. Dakota got 15” of rain in ~6 hours which caused damn failure
  • Rapid Creek-238 deaths and $160 million in damage

• -large meandering river spreads over floodplain; due to prolonged rainfall and snow melt over large area
  • water levels rise more slowly but it takes longer for them to fall
  • ground is saturated with water, so there is nowhere else for the water to go
  • Upper Mississippi River floods if 1993 summer

• Two parameters describe stream flow and flood size
  • stream stage-height above reference elevation (measured at gaging station)
  • stream discharge-volume of water flowing past point of time
    • measured by velocity and cross sectional area at different stage values
    • Q (discharge)= ft3/sec= Velocity x cross sectional area= ft/sec x ft2
    • discharge and stage are closely related by rating curve (graph that shows specific relationship between Q and stage at given location along river)
• Hydrograph-depicts flood data recorded at river gaging station (well dug next to river and connected by pipe, used to monitor stream velocity and stage or height)
  • show Q vs. time although stage is also used
• time between maximum rainfull and maximum flood stage is the lag time
  • upstream flood has short lag time and sudden rise and fall of floodwaters
  • downstream flood has longer lag time and longer flood duration

Prediction of floods

• Flood frequency analysis=determine how often you can expect flood of particular size; use records of size (maximum Q or stage) of historic floods. Gives recurrence = average number of years between occurrence of certain size flood.
  • R=(N+1)/M
  • R=recurrence
  • N=total number of years of record
  • M=ranking of year under consideration (1=biggest, N=smallest)
  • probability (risk of certain size flood in any year)
  • plot of discharge (or stage) vs. recurrence can be used to extrapolate to different flood sizes
• Problems with Flood frequency analysis
  • size of small frequent floods is well constrained but size of very large floods is usually poorly constrained
  • land use changes in drainage basin (dam construction or urbanization also makes it harder to determine size of all floods (large and small)
• Flood hazard map
  • uses stage vs. recurrence data and topographic map to plot 50 year floodplain or 100 year floodplain on map

Effects of Urbanization

• development of cities around rivers can intensify effects of flooding
• greater flood size and frequency means lower lag time
• Effects of flooding are intensified
  • Creation of impermeable barriers-concrete, pavement and buildings prevent infiltration and enhance runoff
  • street sewers-underground tunnels that sent water from streets directly to nearest river
  • Buildings in floodplain take up space
  • Construction (clearing vegetation cover)-easily eroded sediment can fill river channel
• effects are greatest for smaller rainstorm events
• for big storms, urbanization effect is limited (system is overwhelmed)

• Preserve wetlands (swamps)-excellent locations for rainwater infiltration into ground, rather than running off into river
  • ~50% of worlds wetlands have been lost over past 200 years
• Public education-about risks of flood, floodplain, flood frequency, etc
• Mapping and zoning-determine areas of risk and restrict land use (allow only parks, golf courses, agriculture); most effective approach
• Mandatory insurance-require those who live on floodplain to have insurance (for homes and crops)
• Relocate-give government aid for high risk communities to move

• Channelization
  • involves changing channel characteristics (straightening, deepening, widening, clearing debris of channel, or lining channel with concrete
    • boneyard creek in campustown and urbana
      • allows more water to be funneled through river
• Floodway
  • transports floodwaters away from plpulated areas
    • Winnipeg, Canada constructed 47 km floodway around city in 1968 which lowers flooding from Red River
• Dam/Reservoir
  • dam blocks flow of river and creates reservoir which can be filled during heavy rainfall
    • Hoover Dam
    • Grand Coulee Dam
    • Aswan Dam
    • Three Gorges Dam
• Artificial levees
  • human made walls of sand and mud built along sides of channel to increase height of riverbank and allows for greater flow without flooding
  • Floodwalls=concrete river channel walls (more expensive)

Mississippi River Flood of 1993

• During summer of 1993, record floods plagued upper portion of Mississippi River.
• Worst flood disaster in history of USA (+ costliest + most widespread natural disaster in history of IL) in terms of area affected, number of rivers which recorded record stage + discharge (~150 rivers involved), amount of damage, + flood duration (weeks to months).
• Property damage $12 - 20 billion + ~50 deaths. > 50,000 homes were seriously damaged or destroyed, 54,000 people were evacuated from home at some point. Worst hit areas were Iowa, Missouri, + Illinois.
• Many gaging stations measured record discharge, 46 stations recorded >100 year
• Many levee failures (85% of those built by US Army Corps of Engineers held, but only 22% of those built by local communities held - ~1,000 failed levees).
•  Damage to agricultural land (sand eroded from river channel + deposited over crops in floodplain, also massive soil erosion), impact on transportation (bridges over Miss. River were closed, Interstate highways, river barges, railroads, + airports were all closed).

Flood relief involved attempts to save levees with support from sandbags

Valmeyer + Prairie Du Rocher, IL

·         levee district - area (in shape of letter c) protected by single levee. Individual districts are in shape of letter c.

·         Levee broke on upstream side, floodwaters picked up speed + overtopped next levee. Wall of water crashed into Valmeyer, causing major damage

·         broke levee at southern point to send floodwaters northward and slow down onrushing water from north.

Quincy, IL

• 5-mile wide floodplain that was filled, couldn't cross bridge over Mississippi River into Missouri

• protected by 52-ft high floodwall, which almost collapsed + came close to being overtopped.

Grafton, IL

• town with no protection, frequent flooding, supposed to be relocated with government aid (FEMA), but didn't.

Alton, IL

• most of town is above floodplain, except for downtown business district, grain elevator, + water treatment plant. Alton constructed emergency levee out of sandbags (700 ft long, 9 ft high) which spared downtown area.

Red River of the North Flood, Spring 1997

• begins near where North Dakota, South Dakota + Minnesota meet + flows north, forming border between ND + MN. Eventually empties into Lake Winnipeg in Manitoba, Canada.
• During April of 1997, area experienced worst flood disaster for area due to heavy winter snowfall (3.5 times average), then blizzard in April (~25 cm) + quick warming caused snow melt to fill river.
•  Frozen ground enhanced runoff + farther north, Red River was still frozen so nowhere else for floodwater to go.
• >24,000 homes in Grand Forks were partially or completely destroyed by flooding + flood-induced fire; 50,000 people were evacuated + damage = several $ billion

·         Origin of Earth/Solar System (lithosphere, hydrosphere + atmosphere)

o        4.6 billion years ago. Earth (+ solar system) formed by collisions of many meteorites (pieces of rock + metal, photo) + comets (dirty ice balls, photo).

o       Scars from those ancient collisions (craters = bowl-shaped depressions produced from meteorite collision) are still clearly visible on the Moon

·          Role in evolution

o       meteorite impacts caused several mass extinctions (global dyings) during Earth history and perhaps even origin of life because some meteorites (carbonaceous chondrites) contain protein-related amino acids, building blocks of life

·         Economic Resource - certain metallic ore deposits

·         Potentially catastrophic future natural disaster

o       Meteorite impacts can potentially produce most catastrophic consequences of any natural disaster, potential to cause mass extinction of many organisms including human beings

·         Meteorites have played important role in human history

o       Islam religion has sacred rock in Mecca, Saudi Arabia, thought to be iron meteorite.

·         On June 30, 1908, mysterious explosion occurred in Tunguska region, central Siberia. Massive fireball streaked across sky, causing incredible blast of heat and exploded ~8 km above ground; sound from explosion heard up to 1,000 km away. No deaths only because closest human was tens of km away; trees in area >1,000 km2 were destroyed + charred on one side; no crater. Explanation = 30 - 50 m comet (or stony meteorite) exploded above Earth's surface; comets (weak bodies) can easily disintegrate in Earth's atmosphere without striking Earth, producing no crater.

·         Greek, meteoron = phenomenon of sky, piece of rock or metal (large or small) that has collided with Earth.

·         stony meteorites resemble igneous rocks of Earth's mantle

·         carbonaceous chondrites=type of stony meteorite with round blebs of rock , i.e., chondrules (photo), + abundant dark, fine-grained carbon-rich material, including organic compounds + other volatile compounds, requires formation in cold/outer regions of solar system

·         Iron (metallic) meteorites resemble Earth's core, (stony-iron meteorites include rock + iron metal). Meteorites typically have blackened outer crust from frictional heating + melting during entry into Earth's atmosphere.

·         meteoroid = piece of rock or metal floating in space (on collision course with Earth).

·         meteoritics = scientific study of meteorites + meteoroids.

·         meteor = very small (commonly ~1 mm, but ~always <1 m) pieces of rock or metal that vaporize (due to frictional heating) upon entering Earth's atmosphere.

·         meteor shower = large numbers of meteors all coming from ~same direction.

·         asteroid= usually, but not always large (dust-size - ~1,000 km) piece of rock or metal that is usually in orbit around Sun, located in Asteroid Belt, between Mars + Jupiter; ~100,000 asteroids in Asteroid Belt probably represent rocky fragments that failed to accumulate into planet (due to gravitational pull of Jupiter + relatively small volume); some asteroids are similar to Earth with iron core separated from rocky outer layer.

• Asteroid belt - Gravitational attraction of nearby Jupiter disrupts asteroids from regular orbit, causing them to crash into each other. Collisions can send ~large asteroids or smaller pieces into orbits toward inner planets (Apollo objects/Earth-crossing asteroids). 150 Apollo objects are > 1 km + could cause massive destruction during impact. (Small number of meteorites consist of rock from our Moon or Mars; produced when asteroid collides with Moon or Mars, breaking off pieces of that body + sending them to Earth.)
•  Comets- bright objects consisting of dust + frozen gases (mostly loose snow, i.e., frozen H2O but also NH3, CH4, CO2, + CO), similar in composition to outer planets, with long tail that always points away from Sun; comets originate beyond margins of our solar system + approach Sun in wide elliptical orbits. Sublimating ice (solid to vapor) + dust are carried away by solar wind (stream of nuclear particles from Sun) as comet approaches Sun, forming characteristic tail.
  • Halley's Comet, 76 year orbit cycle + last seen from Earth in 1986. Most regularly occurring meteor showers (e.g., Perseid + Leonid) consist of swarms of small, glowing pieces of comet (break apart easily) entering Earth's atmosphere.

• Each day ~100 tons of meteorites strike Earth's atmosphere but most are small enough (<1 m) to be vaporized by frictional heating as they fall through atmosphere (very small, <1µm, pieces are slowed greatly + fall like snow). Larger objects (>1 m + >350 tons) are not slowed + hit Earth with very high speed (80,000 km/hr), releasing huge force + produce impact crater. Jet stream of rock + dust (ejecta), is sent in all directions from impact point, producing blanket of ejecta, which thins away from crater. Such events are simulated in laboratory experiments.
• Force from collision compresses + fractures underlying rock + sends shock waves + heat into ground. Due to intense pressure, minerals can convert to denser forms, e.g., quartz to stishovite + coesite. Intense heat from impact can cause melting of rock on crater floor. Meteorite is usually pulverized by collision but small pieces may be preserved. Rock along crater walls slides into hole, enlarging crater size to ~10 - 20 x meteorite size. For collision of large (>100 - 200 m) meteorite, get uplifted area in middle of crater (photo #1 vs. #2 with no uplift) due to complex interactions of shock waves, gravity, + strength of rocks. Shock waves rebound upward sending molten rock into air, where it cools quickly to form impact-derived glass particles
• ~150 known impact craters on Earth, most are < 200 m.y. in age + > 5 km wide. Why mostly relatively young + large ones?
• world famous crater ~100 miles NE of C-U (Kentland, IN). Buried impact craters at Des Plaines, IL (near Chicago O'Hare airport) + Glasford, IL (near Peoria)

Other effects of very large (>10 km) meteorite =

• tsunamis (if impact in ocean); massive earthquakes; melting of large part of crust (+ some mantle) + asteroid; molten rock sent skyward + falls like rain, igniting global fires, + sending soot into upper atmosphere, dust (ejecta) + soot in atmosphere form thick, dark cloud to block sunlight around globe for months, causing global cooling ("nuclear winter scenario") + death of plants (no photosynthesis) + animals up food chain; eventually atmospheric dust (+ tektites + soot) settles on ground providing global "signature" of impact; longer term effects = acid rain (due to heating, N2 + O2 in atmosphere combine to produce nitric acid) + if impact occurred in ocean, get global warming due to enhanced greenhouse effect (> H2O vapor).

Geologic Record of Mass Extinction

• Extinction - disappearance of plants or animals on global scale, fossil evidence indicates that extinction has occurred ~continuously over geologic time, but during certain time periods there were very high rates of extinction, e.g., several times during Paleozoic, end of Paleozoic (90 - 95% of all species of marine organisms + many terrestrial organisms), end of Mesozoic (50% of all life on Earth), today (past 50 - 100 yrs). These events are called mass extinctions.

Examples of causes of mass extinction

• Disruption of food chain or disease
• Change in climate - can be caused in many ways such as:
• Movement of continents (gradual effect) Tectonic
• Mountain building (gradual effect) Tectonic
• Meteorite collision with Earth (sudden effect) Extraterrestrial
• Dinosaur ("terrible lizard")-Group of extinct reptiles that lived during Mesozoic Era, had upright posture, most were land-dwellers, included herbivores (which walked on all 4 feet or back legs only) + carnivores (most of which walked on back legs).

Dinosaurs include largest land animals ever + are considered to be most successful land animal. Lived for 160 m.y. (from 225 m.y. to ~65 m.y.).

Causes for Dinosaur Extinction

• Impact by large meteorite/asteroid (photo) - Proposed in 1979 by Nobel physics laureate Luis Alvarez + his son (geologist) Walter Alvarez. Idea explains dinosaur extinction by collision with Earth of very large meteorite or comet (~10 km) that occurred ~65 m.y. ago.
• Because of large size (millions of megatons) + high speed (80,000 km/hr), force released upon impact is equivalent to detonation of ~1,000x entire nuclear arsenal of world at single point (animation of asteroid impact + crater formation). Most important effects = impact sent large amounts of dust into upper atmosphere; melting of crust + asteroid; shock waves reflected upward, sending molten rock skyward, igniting global fires, + sending soot into upper atmosphere. Dust + soot in atmosphere formed thick, dark cloud that blocked out Sun around globe for months; cloud blocked photosynthesis + caused global cooling. Plants died, disrupting food chain. Dinosaurs + other organisms starved + froze to death.

How do we know?

• Evidence from clay layer deposited at end of Mesozoic Era - Distinctive thin clay layer at end of Mesozoic/beginning of Cenozoic (photo) (K/T boundary). Layer is rich in elements (iridium) normally abundant only in meteorites, + it contains metamorphosed quartz grains (with lineations called shock lamellae) only found in known meteorite impact sites (or nuclear explosions), tektites (glassy blebs produced by melting of rock during impact) + pieces of carbon (from fires).
•  Large, buried impact crater in southeast Mexico - ~200 km (right size), formed at 65 m.y. (right time)
• Volcanic Eruptions - Many Hawaiian-type volcanoes erupted at ~65 m.y. They would also eject dust into atmosphere + block sunlight. Possibly meteorite impact triggered volcanic eruptions, which further blocked sunlight. Or they may have just happened to coincide in time.

Future Risk - Meteorite Impacts

• Collision of 10-km meteorite with Earth would be ULTIMATE global catastrophe/disaster + result in mass extinction, perhaps including human beings. However, collision of 10-km meteorite probably occurs only every 100 m.y. (see figure) (determined by frequency of impact craters on Moon, where weathering + subduction don't erase them over time). 1-km meteorite can devastate most nations + 50 - 100 m objects could level whole cities.
• In March 1989, 500 m meteorite crossed Earth's orbit + missed us by 6 hours (<700,000 km)! There are 1,000 large (>1 km) near Earth objects (NEOs = asteroids or comets that come relatively close to Earth) + ~1,000,000 small (>50 m) NEOs. Over 50 years, risk of dying from meteorite collision estimated at 1 in 20,000. Although event itself (>1 km meteorite impact) has low probability (every 100,000 years), there will be huge number of deaths (~1.5 billion).

Mitigation - Meteorite Impacts

•  Meteorite collisions are only natural disaster that we can potentially PREVENT by deflecting or destroying (e.g., with nuclear bomb explosion on object), but we would need much advance warning (~10 years). First step (link #2) = detect + track most dangerous objects; done for ~half of large (>1 km) NEOs + none of small (<1 km) NEOs (too many + too difficult to find).
• Five-year Near Earth Asteroid Rendezvous mission (NEAR) placed spacecraft in close orbit with asteroid known as 433 Eros to learn more about geology + physical properties of NEOs. Eros is large rocky, peanut-shaped asteroid, ~33 km long by 13 km around with cratered surface, some up to 6 km (4 miles) across. NEAR mission ended dramatically with spacecraft landing on surface of Eros in February 2001.