Geology: Processes, Hazards, and Soils

Earth’s Structure Core

Inner core: made mostly of iron, solid

Outer core: liquid

Mantle Thick, solid zone surrounds

core Made mostly of iron, but

also contains oxygen, silicon, magnesium

Outermost part is rigid and solid

2 Types of Earth’s Crust Oceanic

Dense, low-lying crust Covers 71% of the earth’s surface

Continental Higher and thicker than oceanic crust Lower density than oceanic crust “floats” higher on the denser mantle

Plate Dynamics:I. Continental Drift Theory:

continents made one supercontinent, approximately 200mya began breaking apart into

smaller continents Continents drifted to present positions

Continental Drift cont’ Evidence for theory:

Similarity between coastlines on opposite sides of the Atlantic

Fossil evidence that matched: Mesosaurus-reptile, and Glossopteris-fern

Matching rock formations: correlation between rock age and type

Paleoclimatic evidence: glacial deposits in southern Africa and South America

Coal Deposits

Continental Drift cont’ Alfred Wegner:

German meteorologist and geophysicist Wrote “The Origin of Continents and Oceans” Proposed the continental drift theory

Downfall of the Theory Inability to explain how continents drifted/the

mechanism or driving force

Pangea

II. Seafloor Spreading Harry Hess:

Developed hypothesis about seafloor spreading in the 1960’s

Proposed ocean ridges are located above upwelling portions of convection cells in the mantle

Newly formed crust at the ridge and older crust moves away from the ridge

Made these findings during WWII while making echo-sounding maps of the ocean

Seafloor Spreading cont’ Evidence:

Magnetic reversals Younger rocks are found near the ridge and older

rocks found near the continent

III. Plate Tectonics Theory of continental drift and seafloor spreading

united into the theory of plate tectonics Theory of Plate Tectonics

Outer, rigid lithosphere consists of several individual moving plates

Each plate moves as a distinct unit in relation to other plates Mobile behavior/plasticity of rock within the asthenosphere

allows movement of plates Interactions between plates occur at plate boundaries Plates are constantly moving at different rates, but a typical

speed is about the rate at which fingernails grow Plate Boundaries

Plate Movement 300 mya Two northern land

masses (Laurasia) collided with two southern land massses (Gondwanaland) to form Appalachian Mountain Chain

Formation of Pangea

Plate Movement cont’ 135 mya

Pangea split into 3 land masses: North America, Eurasia, and Gondwanaland

45 mya Gondwanaland split into 5 continents: South America, Africa, India,

Australia, and Antarctica 100 million years from now if present plate movement

continues: Africa will collide with Europe The Atlantic Ocean will become the largest ocean Africa’s Great Rift Valley will become a sea The Mediterranean Sea will disappear

Natural Hazards

Earthquakes Earthquakes: the faulting or abrupt movement

on an existing fault Focus: the point of initial movement Epicenter: the point on the surface directly above

the focus Magnitude: a measure of the amount of energy

released in the earthquake use an instrument called a seismograph

Earthquakes cont’ Ratings of earthquakes

on the Richter scale Insignificant (less than

4.0) Minor (4.0 - 4.9) Damaging (5.0 – 5.9) Destructive (6.0 – 6.9) Major (7.0 – 7.9) Great (over 8.0)

Earthquakes are most common at all three lithospheric plate boundaries, but can occur away from plate boundaries

Two main groups of seismic waves: Surface waves Body waves

Surface Waves Travel along the outer part of the earth Move up and down and side to side Side to side motion causes most of the

damage to buildings and their foundations Are the last to arrive

Body Waves Primary or P waves:

Push and pull rocks in direction wave is traveling Travel through solids, liquids, & gases Movement is analogous to movement of human vocal cords First waves to arrive

Secondary or S waves: Change only the shape of the material that transmit them Only solids transmit S waves Surface and Body Waves S and P wave demonstration

Effects of Earthquakes Shaking and sometimes permanent vertical or

horizontal displacement of the ground Mass wasting Urban fires Flooding due to subsidence of land Tsunamis

Reduce Damage from Earthquakes Locate active fault zones Make maps of high-risk areas Establish building codes

Volcanoes Volcanic activity is usually concentrated in

the same areas as seismic activity Usually occurs at divergent and convergent

plates, sometimes intraplate sites Eruptions eject large quantities of gases and

particulate matter into the troposphere, sulfur dioxide that’s emitted can remain in the atmosphere up to three years

Benefits of Volcanoes Aesthetically pleasing (mountains, lakes) Geothermal phenomena – geysers and hot

springs Geothermal energy Highly fertile soil produced from the

weathering of lava

Reduce Damage from Volcanoes Land-use planning Better prediction of volcanic eruptions Development of better evacuation plans

Floods Floodplain – the flat valley floor next to a stream

channel Most common type of flooding is caused by heavy

rain or rapid melting of snow People have settled on floodplains for centuries

Soil is fertile Ample water for irrigation Water used for transportation Suitable for cropland

Floods cont’ Flooding is a more common natural disaster.

Deaths caused by natural disasters: 39% by flooding 36% by typhoons and hurricanes 13% by earthquakes 5% by gales and thunderstorms 2% by volcanic eruptions

Floods cont’ Solutions:

Channelization – stream is deepened, widened or straightened to allow more rapid runoff

Artificial levees and embankments – reduce the chances of overflow

Flood control dam Floodplain management – best approach

Mass Wasting Rockfall – frost action forces rocks apart on the face

of a cliff Mudflow – soil saturated by rain, and loss of

vegetation Rockslide – large mass of rock jarred loose by an

earthquake Creep – the soil on a hillside slowly moves downhill

due to frost wedging, burrowing animals, and grazing cattle

Mass Wasting