Natural Hazards

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Natural Hazards

• Impacts and Extinctions
• Chapter 14

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1972 Great Daylight FireballEarth-Grazing
Meteoroid partially vaporized by continued on
to a subsequent close approach in 1999
Sourceshttp//science.slashdot.org/story and
http//www.phys.ncku.edu.tw/astrolab/mirrors/apod
_e/image/0903/earthgrazer_ansmet_big.jpg
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If it partially burned in the atmosphere, then
shouldnt it be called a meteor instead?I
observed a smoke and debris trail that lasted for
many seconds.Various Web sites also noted
that.
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Ok, now lets review our learning objectives

• Know the difference between asteroids,
  meteoroids, and comets
• Understand physical processes associated with
  airbursts and impact craters
• Understand possible causes of mass extinction
• Understand the process of mass extinction caused
  by extra-terrestrial collisions with earth

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More learning objectives

• Know the likely physical, chemical, and
  biological consequences of impact from a large
  asteroid or comet
• Understand the risk of impact or airburst of
  extraterrestrial objects
• Understand how impact risk might be minimized

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Earths Place in Space

• The universe may have begun with a Big Bang 14
  billion years ago
• First stars probably formed 13 billion years ago.
• Lifetime of stars depends on mass
• Large stars burn up more quickly 100,000 years
• Smaller stars, like our sun may last 10 billion
  years
• Supernovas signal death of star
• Releases energy and shock waves

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Earths Place in Space

• 5 billion years ago, supernova explosion
  triggered the formation of our sun.
• Sun grew by buildup of matter from solar nebula
• Pancake of rotating hydrogen and helium dust
• Hydrogen fuses into helium, releasing
  electromagnetic energy, some of which is visible
  light.
• After formation of sun, other particles were
  trapped in rings (orbits).
• Particles in rings attracted other particles and
  collapsed into planets
• Earth was hit by inter-stellar debris,
  adding/subtracting its mass
• Bombardment continues today

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Anthropocene (human) epoch now?
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Asteroids, Meteoroids, and Comets

• Asteroids (10m 1000 km) - asteroid belt between
  Mars and Jupiter
• Composed of metals
• Meteoroids are broken-up asteroids
• Meteors are meteoroids that enter Earths
  atmosphere
• Meteorites actually hit the earths surface
• Chondrite a meteorite with more stone than
  metal - 85 of all meteorites
• Comets -
• have glowing tails dirty snowball
• composed mostly of frozen water or carbon dioxide
  
• May have originated in Oort cloud far from our
  solar system

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Comets are soft - gas and/or ice.Asteroids are
rocky or metallic.
Meteors and meteorites travel at relatively high
speed collision with Earth atmosphere causes
immediate combustion intense heat and
flame. The energy of colliding with earth is
converted to heat and flame.
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Meteorfully or partially vaporized on
atmospheric entry
Asteroid - larger

• Meteoroid smaller fragments

Meteorite Very small remnants that survive
re-entry and land on earth
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Oort cloud is extremely far away most knowledge
of it is inferential or theoretical
Figure 13.3
Pluto has been relegated to association with the
Kuiper belt
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Airbursts and Impacts

• Objects enter Earths atmosphere at 27,000 to
  161,000 mph
• Metallic or stony
• Flash to flame on striking the atmosphere -
  bright light
• Meteorites
• Small pieces that did not vaporize but instead
  survive to hit the earth
• Airbursts
• Meteor explodes on striking the atmosphere at
  high speed (Tunguska 1908)
• Chelyabinsk (2013) included hundreds of
  meteorites large enough to be collected by people
  on the ground.

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Impact Craters

• Provide evidence of meteor impacts.
• Bowl-shaped depressions with upraised rim
• Rim is overlain by ejecta blanket of debris
• Broken rocks cemented together into breccia
• Features of impact craters are unique from other
  craters.
• Impacts involve high velocity, energy, pressure,
  and temperature.
• Kinetic energy of impact produces shock wave into
  earth.
• Compresses, heats, melts, and excavates
  materials
• Soil and water may vaporize from vast heat
  produced by collision
• Other rocks may metamorphose or melt.

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A half-ton iron meteorite was found near Delta
Utah. The Upheaval Dome site south of Moab may
be the dot on the map.
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• Utahs Upheaval Dome
• Circular, with center uplift typical of an impact
  structure.
• Or, could it just be a collapsed salt dome?

http//www.hohmanntransfer.com/cg/upheaval/dome.ht
m
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• Severity of meteorite impact
• Worst vaporize into basic elemental gases
• Very bad completely melt into new rocks
• Bad metamorph into a modified rock
• Not bad be thrown into the air and broken apart
• Note Being blown into the air and broken into
  pieces is similar to a student not finishing an
  ePortfolio before the final exam.

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Simple Impact Craters

• Typically small
• less than 6 km
• Arizonas Barringer Crater

A shatter cone may form under the impact zone.
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Complex Impact Craters

• Larger in diameter
• than 6 km
• Rim collapses more completely
• Center uplifts following impact leaving a peak

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Impact Rebound
Source joerenaissanceman.blogspot.com
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Impact Crater Details

• Craters are much more common on the Moon because
• Moon has no atmosphere to incinerate incoming
  objects
• On earth, most impacts are in the ocean, buried,
  or eroded

Impact alteration of rocks can occur in
collisions between asteroids as well - - they
hit each other - - a few are bumped toward the
earth. Intense heat and pressure may
metamorphose rocks. Contact metamorphosis can
also occur on earth by tectonic force, including
volcanism and pyroclastics.
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Add Chelyabinsk 2013 estimated 20-meters wide
before exploding - arrived at speed of 12 miles
per second 12 x 60 x 60 43,200 mph
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• Estimates of energy released vary widely, but
  include
• A 7-meter (22 feet) wide meteorite striking the
  atmosphere releases energy equivalent to an
  atomic bomb.
• 5-meter meteors arrive about every year.
• 50-meter rocks arrive once a thousand years.
• (Source en.wikipedia.org/wiki/Impact_event

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• The Chelyabinsk meteorite event knocked people
  off their feet. Others were seriously burned or
  even blinded by the bright light of combustion.
• The effects were much more than just breaking
  glass.
• Scientists are now considering that impacts of
  that size may occur more frequently than
  previously believed.
• (Sourcewww.theguardian.com/science?across-the-uni
  verse/2013/feb/15/russian-meteorite . . )

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Mass Extinctions

• Sudden loss of large numbers of plants and
  animals
• Sudden climate change
• Define the boundaries of geologic periods or
  epochs
• Mass extinctions can also be caused by meteorites
  and
• Plate tectonics
• Moves habitats to different locations
• Volcanic activity
• Large eruptions release CO2, warming Earth
• Volcanic ash reflects radiation, cooling Earth
• Changes in solar energy can also be attributed to
  weather and/or catastrophic effect.

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Six Major Mass Extinctions

1. Ordovician, 446 million years ago (mya),
   continental glaciation in Southern Hemisphere
2. Permian, 250 mya, volcanoes causing global
   warming and cooling
3. TriassicJurassic boundary, 202 mya, volcanic
   activity associated with breakup of Pangaea
4. CretaceousTertiary boundary (K-T boundary), 65
   mya, meteorite impact
5. Eocene period, 34 mya, plate tectonics
6. Pleistocene epoch, initiated by airburst meteor,
   continues today, more recently enhanced by human
   activity

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Now, consider that aside from earth change
caused by meteorites and volcanoes, human power
arose when the Pleistocene ice age withdrew.
The earth warmed enough to provide space for
people to start farming and burning fossil
fuel.So, the Anthropocene epoch makes sense.
We are human bulldozers powered by ancient
solar energy stored for millions of years as oil,
coal and natural gas.
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Lets look a little more at the K-T Boundary
Mass Extinction 65 million years ago.

• Dinosaurs disappeared with many plants and
  animals.
• 70 of all genera died
• Set the stage for evolution of mammals (humans
  are mammals)
• What does geologic history tell us about K-T
  Boundary?
• Walter and Luis Alvarez decided to measure
  concentration of Iridium in clay layer at K-T
  boundary in Italy.
• Fossils found below layer were not found above.
• How long did it take to form the clay layer?
• Iridium deposits indicate that layer formed
  quickly.
• Extinction probably caused by a single meteorite
  impact.

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K-T Boundary Mass Extinction

• Alvarez did not have a crater to prove the
  theory.
• But we later found a crater in Yucatan Mexic0.
• Diameter approx. 180 km (112 mi)
• Nearly circular
• Semi-circular pattern of sinkholes on land define
  the edges
• Possibly as deep as 3040 km (1825 mi)
• Slumps and slides filled crater
• Drilling located breccia under the surface
• Glassy, indicating intense heat

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Notice the center uplift consistent with large,
complex crater.
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Iridium is part of the platinum group it is
more common in meteorites than in native
earth.Iridium rivals Osmium as the most dense
natural element known in the universe and the
most resistant to heat and corrosion.Most of
our Iridium may have come from a meteorite. The
Iridium layer of rock points toward a meteorite
strike.
Some evidence suggests that the element nickel
may also have an extra-terrestrial origin.
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Considering Iridium and possibly Nickel, and the
origin of the Earths Moon, can we say?1. The
earth has accreted (added) mass from meteorite
strikes.2. The Earth has lost mass due to
meteorite strikes.
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Can we also surmise that after billions of years
of hard meteor strikes and planet formation,
there may be less mass available for strikes in
the future?
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Iridium metalBeautiful, strong, expensive
Source en.wikipedia.org/wiki/Iridium
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Sequence of Events

1. Asteroid moving at 30 km (19 mi) per second
2. Asteroid hit the Earth, producing a crater 200 km
   (125 mi) diameter, 40 km (25 mi) deep
3. Shock waves crushed, melted and vaporized rocks

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Sequence of Events, cont.

• Seconds after impact
• Ejecta blanket forms
• Mushroom cloud of dust and debris
• Fireball sets off wildfires around the globe
• Sulfuric acid enters atmosphere
• Dust blocks sunlight
• Tsunamis from impact reach over 300 m (1000 ft)

Ask yourself What role would nitrogen play?
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Sequence of Events, cont.

• Month later
• No sunlight, no photosynthesis
• Continued acid rain
• Food chain stopped
• Several months later
• Sunlight returns
• Acid rain stops
• Ferns restored on burned landscape

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K-T Extinction, summary

• Impact caused massive extinction of plants and
  animals, but allowed for evolution of mammals.
• Another impact of this size would mean another
  mass extinction probably for humans and other
  large mammals.
• However, impacts of this size are very rare.
• Occur once ever 40100 million years
• Smaller impacts are more probable and have their
  own dangers.

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Linkages with Other Natural Hazards

• Tsunamis
• Wildfires
• Earthquakes
• Mass wasting
• Climate change
• Volcanic eruptions

All of these events can result from a major
meteorite strike on earth
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Event Frequency and Risk

• Risk related to probability and consequences
• Large events have consequences, will be
  catastrophic
• Worldwide effects
• Potential for mass extinction
• Return period of 10s100s millions of years
• Smaller events may create regional catastrophe
• Effects depends on site of event
• Return period of 1000 years
• Likelihood of an urban area hit every few 10,000
  years
• Local events every 100 years (Tunguska,
  Chelyabinsk)
• Micro events many daily

This outlook is from the textbook and is being
re-evaluated by scientists.
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Risk Related to Impacts, cont.
Emerging risk assessment may be altered
upward Meteorite hazards to humans may be
greater than we thought.

• Risk from impacts is relatively high.
• Probability that you will be killed by
• Impact 0.01-0.1
• Car accident 0.008
• Drowning 0.001
• However, that is AVERAGE probability over
  thousands of years.
• Events and deaths are very rare.

Meanwhile, if the chances of getting hit by a
meteorite are greater than drowning, then why
dont we have reports of human deaths from
meteorites?
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Minimizing the Impact Hazard

• Identify nearby threatening objects.
• Spacewatch
• Inventory of objects with diameter larger than
  100 meters in Earth-crossing orbits
• 85,000 objects found so far
• Near-Earth Asteroid Tracking (NEAT or NEO)
  project
• Identify objects diameter of 1 km or larger
• Use telescopes and digital imaging devices
• Most objects threatening Earth will not collide
  for thousands of years from discovery.

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Minimizing the Impact Hazard

• Consider our options once a hazard is detected
• Use nuclear explosion to fragment the object in
  space
• Small pieces could rain radioactivity down on
  earth
• Nudge it out of Earths orbit
• Much more likely because we will have time to
  prepare
• Technology can change orbit of asteroid
• Expensive process will require coordination of
  world military and space agencies
• Evacuation
• A good idea only if we can predict impact point
• Could be impossible depending on how large an
  area would need to be evacuated
• Notice that no personal preparation options are
  provided -

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Bolide (fireball) Meteor Perhaps large enough
to cause a sonic boom
Note the debris trail. The 1972 event also
included visible flame and smoke
Source Astronomy.wonderhowto.com/inspiration/soni
c-boom
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Do regular meteor showers occur? Yes.

• Lyrid, Geminid, Leonid and other regular meteor
  showers occur, based on routine intersection of
  orbits about the sun.
• Comets exhibit similar habits.

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Clark Planetarium at the Gatewaylt The
planetarium has a selection of meteorites and
vast other resources for ePortfoliosgt
The planetarium also has very cool light shows
set to rock music -- no pun intended.
Impact craters
Source clarkplanetarium.org/venue/cosmic-light-sh
ows
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Why does the dark side of the moon have much
more cratering?

• Because the moons rotation is
• earth-synchronous,
• so that it keeps the same face to the earth at
  all times.
• So, the side facing away from the earth is not
  shielded from meteorites.

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Chelyabinsk 2013a major meteorite strike in
Russia
This meteor was tracked en-route to earth,
supporting the concept of prediction and
protection NEO and NEAT space programs are
tracking other dangerous asteroids and comets
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• Conclusion
• Current science suggests that if an asteroid is
  large enough to cause world-wide damage,
• then there is probably enough time to identify
  the hazard and take action at least 100 years
  before the collision.