I. Structure of the Earth

I. Structure of the Earth

1. Inhomogeneous accretion

2. Lithosphere - solid
   a. continental crust - granite, gneiss, diorite
       density - 2.8 - 2.9 gm/cm3
   b. oceanic crust - basalt, gabbro
       density - 2.7 - 3.0 gm/cm3
   

3. Mohorovicic discontinuity

4. Asthenosphere - plastic
   a. peridotite
   b. density - 3.3 - 3.4 gm/cm3
   

5. Isostasy

6. Mantle
   a. solid oxide & silicates
   b. density - 5 - 6 gm/cm3
   

7. Gutenberg discontinuity

8. Outer core
   a. liquid iron & nickel
   b density - 9 - 10 gm/cm3
   c. Liquid innner core and solid outer core
   

9. Lehmann discontinuity

10. Inner core
    a. solid iron & nickel
    b. density - 13 gm/cm3
    

B. Temperature, pressure

1. geothermal gradient 30š C/km

2. pressure increases with depth

C. How do we know this?

1. seismic waves and their characteristics

II. Plate Tectonics

A. Importance - interrelated with:

1. mountain building
   
2. origin of ore deposits
   
3. location of oil fields
   
4. evolution of life forms
   
5. origin of stratigraphic sequences
   
6. salinity of the oceans
   
7. earthquakes
   
8. volcanic activity
   
9. state of the atmosphere
   

B. History of the theory

1. Pre-Wegener
   a. Francis Bacon
   b. Pelligrini
   c. Suess
   

2. Wegener - "continental drift"
   
   a. match of continents along continental slopes
   b. mountains are compressions along leading edge
   c. paleoclimates
   
   1.) glacial deposits
   2.) coral reefs
   
   d. structures
   
   1.) mountain chains
   
   e. fossil plants and animals
   

3. Geophysical evidence after World War II
   a. oceanography
   
   1.) mid-oceanic ridges
   2.) rift valleys
   3.) sea mounts
   4.) sediment thickness
   5.) age of oceanic crust
   6.) paleomagnetism
   7.) sea floor spreading
   8.) magnetic reversals
   

4. Plate tectonics
   

5. Satellite laser ranging
   

C. Plates - location, direction of motion, speed

D. Plate boundaries - types, locations, and characteristics -
TASA CD ROM

1. transform - plates sliding past each other
   a. San Andreas Fault
   

2. divergent - plates moving away from each other
   a. mid-oceanic ridges
   b. rises
   c. rifts - on land
   

3. convergent - plates colliding with each other
   a. oceanic to oceanic crust collision
   b. oceanic to continental crust collision
   c. continental to continental crust collision
   

E. Hot spots

1. location and characteristics
   a. oceanic
   b. intracontinental
   

2. Importance

F. Exotic Terrain

1. huge pieces of continental and oceanic crust that did not originate where it is now found
   a. Alaska
   b. San Francisco
   c. Northwest coast of North America
   d. New Zealand
   

G. Driving force

1. most likely is convection currents

III. Minerial Resources and Rocks

A. Definition of a mineral (Power Point presentation)

1. naturally occurring
2. homogeneous solid
3. definite but not fixed chemical composition
4. ordered atomic arrangement
5. formed from inorganic processes

B. Environmentally significant minerals - examples (samples in class)

1. quartz
2. mica
3. feldspar
4. pyrite
5. asbestos
6. halite
7. calcite

C. Rock Cycle

D. Rock types and their formation -samples in class

1. Igneous - environmentally significant
   
   a. intrusive - granite
   b. extrusive - basalt
   

2. Sedimentary - environmentally significant
   
   a. clastic - sandstone, shale, limestone
   b. non-clastic - limestone, salt, coal
   

3. Metamorphic - environmentally significant
   
   a. foliated - schist, gneiss, slate
   b. non-foliated - marble, quartzite
   

E. Resources vs reserves

1. economics

2. discovered vs undiscovered

IV. Earthquakes

1. Shaking or vibration of the ground

2. Deforming rocks suddenly break along a fault

3. Elastic rebound - aftershocks

B. Seismic waves

1. P waves
   
2. S waves
   
3. L waves

C. Locating the epicenter and focus

D. Measuring the size of the earthquake

1. Modified Mercalli Earthquake Intensity Scale -
   effects on people and structures

2. Richter Scale -
   measures the magnitude (size) of an earthquake; for each unit of magnitude, the amplitude of ground motion (or seismic waves) increases by a factor of 10. The energy released increases by a factor of 33 for each unit of magnitude.

3. Moment - Magnitude Scale -
   measures total energy released, more precise

E. Earthquakes and plate tectonics

Earthquakes, Volcanism and Plate Boundaries

F. Earthquake destructiveness

1. resonance
   video clip from "The Mechanical Universe"
   video - "When the Bay Area Quakes" - University of California Extension Media Center

2. ground motion

3. tsunamis

G. Prediction

1. paleoseismology
2. global positioning system
3. seismicity gaps
4. radon in well water
5. swarms of small earthquakes
6. surface deformation
7. animal behavior

V. Volcanic Activity

A. Magma

1. Origin of magma
   a. &#gt 20 km
   b. melting of rock
   

2. Composition
   a. molten rock
   b. gases - water vapor with some CO2 - as much as 14%
   
   also N, SO2, Cl, H, and Ar
   
   c. elements - O2, Si, Al, Mg, Ca, Na, K, Ti - abundant
   d. basaltic magmas - 40% - 50 % silica
   e. granitic magmas - 60% - 70 % silica
   f. andesitic magmas - 50% - 60% silica
   g. single volcano can extrude lavas with a wide range of chemical composition
   
   (1). incorporation of country rock
   (2). fractional crystallization - some never reaches the surface
   

3. Movement
   Expanding body of molten magma forced upward through fractures or faults

B. Products of volcanic or fissure eruptions

1. Liquids - lava
   basaltic lavas are very fluid and flow in thin, broad sheets

   a. flood or plateau basalt - not associated with volcanoes

   Washington and Oregon - 3000 meters thick
   b. pahoehoe
   c. a'a
   d. pillow basalt - lava flows entering ocean or originating in the ocean
   
   can cause a phreatic explosion when the hot lava comes in contact with the cooler ocean waters

2. gases
   a. 70% - 95% water vapor
   b. 14% CO2
   c. plays a role in violent eruptions vs quiet ones
   

3. solids
   pyroclastics

   a. upon release, the superheated gases expand - up to 75X - and blow pulverized rock and lava from the vent

   b. differ in size from dust and ash to cinders to volcanic bombs and blocks weighing many tons

   dust and ash - so many gas bubbles that lava resembles a froth - very fine fragments

   c. pyroclastic flow - (nuee ardente)
   

   Language of the Earth pg. 77
   (1.) cushion of gases creates an almost frictionless environment
   (2.) can move at speed of up to 150 km/hr
   

C. Volcanic eruptions and volcanoes

1. Components of a typical volcano
   • magma chamber
   • vent
   • crater or caldera
   • rift zones
   • secondary or side vents - form parasitic cones

   Size and shape of the volcano reflect the nature of the erupted material.

2. Shield volcanoes
   a. tall, gently-sloped sides - 15š slope or less
   b. successive lava flows with little pyroclastics included
   c. Mauna Loa -
   
   (1). base is 5000 meters below sea level and 4170 meters above water
   (2). covers 5271 km2
   (3). tholeiitic basalt
   
   d. quiet eruptions - low silica, low gas content

3. cinder cones
   a. pyroclastics
   b. 30š - 40š slope
   c. &#lt 300 meters high
   d. may be a parasitic cone
   e. occur in groups
   f. may be last phase of activity because magma has cooled and become more viscous
   g. Paracutin - 300 km west of Mexico City
   

4. Stratovolcano - composite
   a. steep-sided
   b. alternating lava and pyroclastics
   c. most violent type
   
   (1). higher in silica content
   (2). higher in gas content
   
   d. phreatic explosion - heat melts snow cap of volcano and creates a steam explosion -
   Mt. St. Helens
   

5. volcanic domes
   lava solidifies in or immediately above a volcanic vent
   a. highly viscous
   b. in caldera of Mt. St. Helens
   

D. Other volcanic happenings

1. Earthquakes

2. volcanic lightning

E. Relationship to plate tectonics

Plate Boundaries and Volcanic Activity

1. Subduction zones - 80% of volcanic activity
   a. basaltic oceanic crust with marine sediments
   (1). water-laden sediments increases melting by lowering the melting point
   (a). these sediments are clays and silica-rich materials
   (b). gives rise to magma with high silica content
   (2). Mt. Fujiyama - Japan - andesitic cone
   b. continental crust - oceanic convergence
   
   (1). continental crust is more felsic than oceanic crust
   (2). Andes mountains
   (3). Cascade Range
   

2. divergent boundaries - 15% of volcanic activity
   a. Iceland
   b. Mt. Kilamanjaro - east African rift zone
   c. lavas of Isle Royal - failed rift of N. Am. continent
   

3. Intraplate
   1. hot spots - Hawaii, Yellowstone
   2. Columbia River Plateau - unexplained
   

F. Volcanic Hazards

G. Prediction

1. swelling of volcano
2. SO2
3. earthquake activity
4. ground surface temperatures
5. preliminary ash emissions

VI. Floods

Notes Table of Contents

Introduction to Environmental Science Home Page

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Created and maintained by
Jim Ferguson
Revised 10/5/95.