Hazardous Earth Processes

1
Hazardous Earth Processes

• Some natural hazards are inevitable
• Planning is important
• The impacts of hazardous earth processes are
  enhanced by spatial concentration of population
  and resources
• Should be considered in cost-benefit analysis

2

• Unplanned, rapid urbanization in hazard-prone
  areas.
• El Salvador, 2001 7.6 Mw -1000s
• killed due to poorly sited housing
• Nevado Del Ruiz Volcano - 23,000
• buried alive in 1985 by a lahar
• Absence of effective disaster preparedness
• Evacuation routes
• Disaster response teams
• Early warning systems

• Turkey, 1999 7.4 Mw Earthquake (North Anatolian
  Fault) 17,000 deaths due to ineffective building
  codes (http//pubs.usgs.gov/circ/2000/c1193/)

3
Energy sources for Natural Disasters

• To understand natural disasters, it is important
  to understand the energy sources affecting the
  earth.
• Four primary energy sources make the Earth and
  active body
• The impact of extraterrestrial bodies (asteroids
  and comets)
• Gravity
• Contractions (friction) within the Earth
• Gravitational attractions between the Earth,
  Moon, and Sun (Tidal Energy)
• The Earths internal heat
• The Sun

4
Energy Sources for Natural Disasters

• Earths internal heat (70 from radioactive
  decay, 15 from impacts, 15 from friction)
• Earthquakes (landslides, fire, tsunami)
• Volcanoes (landslides)
• Tsunami Waves
• 90 of the above occur along plate boundaries
• Suns energy
• Severe Weather (floods, landslides, fire)
• Tornadoes
• Thunderstorms
• Hurricanes (floods)
• El Nino (floods)

5
ORIGIN OF SOLAR SYSTEM

• Big Bang origin of Universe 13 to 14 billion
  years ago
• Nebular Hypothesis (Theory) explains origin of
  solar system
• Earth forms from a cloud of gas and dust called a
  nebula
• Nebula cloud is composed of dust and gases 80
  Hydrogen, 15 Helium, few heavier elements
• Nebula likely created by the destruction of one
  or many large stars called supernovae

6

• a) Cloud of gas and dust called a nebula (80
  hydrogen) contracts due
• to gravity around 4.6 billion years ago.
• b) Spinning mass contracts into flattened disk,
  majority of mass in
• the center (sun forms).
• c) Dust grains and gases condense to form
  planets.

7
How old is the earth?

• Oldest rocks on earth are 4.1 Billion Year Old
• The earth is estimated at 4.57 Billion Years Old
• How do we arrive at
• this age?

8
Radioactivity as a Clock

• Radioactive decay
• Half life
• Parent isotope
• Daughter isotope

9
RADIOACTIVITY is main source of heat inside Earth
(Fission Reaction)

• Spontaneous changes (decay) in the atomic nuclei
  of atoms---emission of radiation (energy)

• Parent unstable isotope (decays)
• Daughter isotopes resulting
• from decay
• Isotope different forms of same
• atom (element). Same of
• protons, different of neutrons

10

• Reviewing basic atomic structure
• Nucleus contains
• Neutrons (no charge)
• Protons ( charge)
• Outer shell(s) contain
• Electrons ( charge)

Atomic An elements identifying number.
Number of protons in the nucleus. Atomic mass
(weight) Number of protons and neutrons
in nucleus.
11

• Isotopes example Carbon(C), there are 3
  isotopes
• carbon-12, carbon-13, and carbon-14
• Carbon has 6 protons (atomic is 6), of
  neutrons vary (6, 7, and 8)

12

• Half-life time required for 1/2 (50) of parent
  isotope to decay
• Comparing the ratio of parent to daughter yields
  the age of the sample
• Radioactivity
• Source of heat
• Age of sample

13
Half life varies for each isotope C-14 5,700
years
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17

• a) Early Earth was homogeneous mixture of molten
  rock.
• b) Earth cools and differentiates heavier
  elements (iron) migrate to the center in response
  to gravity, lighter elements form the outer
  layers.

18

• Volcanic outgassing Emission of gases from
  volcanoes
• H2O, CO2, SO2 are the major gases.
• Early atmosphere and oceans

19
Crust

• Inner Core --gt Outer Core --gt Mantle --gt Crust

Mantle
Core
20
solid
Partially molten
solid
solid
liquid
solid
solid
21
Earthquake or seismic waves tell us about
physical nature of Earths interior
Lower mantle
Outer core
22
Plate Tectonics

• Continental Drift

23
Continental
Ocean
Continental
Ocean
Crust
Upper mantle
Partial melt
Upper mantle
Upper mantle

Upper Mantle Asthenosphere and Lithosphere
(excluding crust) Lithosphere Crust and upper
mantle Crust avg. thickness for continental is
35-40 km, ocean is 5-7 km.
24
Isostacy less dense lithosphere (crust is top
layer) is in gravitational balance with the
asthenosphere below.
Gravitational adjustment of Earths crust due to
erosion
For example Scandinavia is rebounding 1
meter per 100 yr. due melting glaciers
25
Earths Internal Heat

• There is an uneven distribution of heat
  throughout Earths interior
• Heat moves by two processes
• Convection physical movement of material (liquid
  and gas)
• Conduction vibration of atoms that make up
  material (solids)
• Sources of heat inside Earth (Earth is slowly
  cooling)
• Radioactive decay (U (uranium Th, thorium K,
  potassium)
• Heat left over from the formation of Earth

26

• Convection in lower and upper mantle is a
  significant driving force of plate tectonics
• Other mechanisms generate forces that contribute
  to plate motion
• Slab-pull
• Ridge-push

27

• Pangaea supercontinent 250 million yr. Ago
• Alfred Wegener, 1915 proposed continental drift
  hypothesis
• Continents "drifted" to present positions
• Evidence supporting hypothesis

28
Fossil evidence
Paleoclimatic evidence
Rock type and structural similarities
29

• Paleomagnetism
• Study of ancient magnetic fields
• Most convincing evidence to support concepts of
  continental
• drift and seafloor spreading
• Caused by convection in the Outer Core
• Last Reversal 780,000 years ago

30
Normal Polarity Magnetic North is located close
to Geographic North