Cultural Anthro. Exam 2

Alfred Wegner- 1915

• Radical Hypothesis of continental drift

• Supercontinent called Pangea once existed

• Multiple evidence provided

What evidence of Pangea was provided?

• the Continental Jigsaw Puzzle

• Fossils match across the seas

• Rock types and structures match

• Ancient climates

What are the Earth’s Major plates?

• Lithosphere

• Asthenosphere

• Mesosphere

• Outer Core

• Inner Core

Lithosphere

Strong, rigid later

• Made of broken pieces called plates

  • Oceanic-Basalt max: 100 km thick (thickness is age dependent, older it is, the thicker it is

  • Continental-Granitic generally 100-150 km thick with max being 250km think

Asthenosphere

Weak sphere

• temperature and pressure in upper most portion near melting temperatures

• Allows earths rigid outer shell to move

Mesosphere

Lower mantle, pressure counteracts temperature creating strong rocks

Outer Core

Liquid layer of iron that generates earths magnetic field

Inner Core

Solid iron because of immense pressure

What are the Earths layers in order?

• Crust

• Lithosphere

• Asthenosphere

• Mesosphere

• Outer core

• Inner core

Plate

A distinct piece of the lithosphere that has boundaries on all sides which are called plate boundaries

Continental Margins

Edges of continents where they meet the oceans/seas

• these lead to Active margins and passive margins

Active Margins

Continental margins that are plate boundaries

Passive margins

Continental margins that are not plate boundaries

What are the three main types of Plate Boundaries?

• Divergent Boundaries

• Convergent Boundaries

• Transform Fault Boundaries

Divergent Boundaries

• Two plates move apart as a result of upwelling material from the mantle to creating new ocean int lithosphere

  • Oceanic Ridges and Seafloor spreading

  • Continental rifting

  • Earthquakes and volcanic activity also occur

Divergent Plate Boundaries Picture

Convergent Plate Boundaries

Plate boundaries where the lithosphere is destroyed (destructive plate margins)

• Includes Subduction Zones

• deep-ocean trenches develop as subduction occurs

Convergent Plate Boundaries Picture

Subduction Zones

Where one plate (lithosphere) bends and sinks down (subducted) into the asthenosphere beneath another plate

• Oceanic crust (Mafic) is more dense than continental crust (felsic)

Convergent Plate Boundaries Angles

• angles of subduction range from a few degrees to 90 averaging about 45

• Depends on the density

  • Old Lithosphere is cold and dense (steep angle)

  • Young Lithosphere is warn and buoyant (shallow angle)

Transform Fault Boundaries

Plates slide horizontally past each other without the destruction of the lithosphere

• ex: San Andreas Fault

Transform Fault Boundaries Picture

Sea Floor Spreading

True divergent plate boundaries occur along mid-ocean ridges

• new ocean crust is formed along the ridge in order to “fill in the space” missing as the two plates move away from each other

• As spreading continues, older crust moves farthe

Convergent Plate Boundaries

Includes an Accretionary Prism

• material accreted onto the overriding plate at a convergent plate margin

• Like a plow scraping off material

Convergent Plate Boundary

Accretionary Prism

A wedge-shaped mass of sediment and rock scrapped off the top of a down-going plate

• like a plow scraping off material

Continental Volcanic Arc

Has Partial Melting - the melting of a rock of the minerals with the lowest melting temperatures, while the other minerals remain solid

• Commonly happens at 100-150 km in depth

• Water allows the mangle to partially melt, while allows the magma to form

Partial Melting

The melting of a rock of the minerals with the lowest melting temperatures, while the other minerals remain solid

What are the two types of Convergent Zones?

• Oceaninc

Oceanic - Oceanic Convergent Zone

• Creates volcanic island arcs

  • Aleutians, Mariana, and Tonga

  • Located 100-300 km from a deep-ocean trench

• Back-Arc Basin-Depression formed behind a volcanic island arc

Oceanic - Oceanic Convergent Zon

Continental - Continental Convergent Zone

• Subduction ends when two continental plates collide (collision)

• Continental plate desists is so low that they cannot be subjected, so the former trench becomes a suture (a linear belt of high deformed rocks)

  • A collisional mountain belt forms where the tow plates collided and the down-going plate breaks off (detached)

Suture

A linear belt of highly deformed rocks

Continental - Continental Convergent Zone

Earthquake

A vibration caused by the sudden breaking or frictional sliding of a rock in the earth

Fault

A g

Epicenter

The point on the surface of the earth directly above the focus of an earthquake

Fault trace

The intersection between a fault and the ground surface

Creep

Movement along faults occurs gradually and relatively slowly and smoothly

• Fault displacement without significant earthquake activity

Elastic Rebound

“Springing back” of a rock once an earthquake h

Footwall

The rock mass that lies below the fault plane

Hanging wall

The rock or sediment above an inclined fault plane

Transform/Strike-Slip Faults

Motion can be left lateral or right lateral

• Standing on one side of a fault, and the other side moves to the left, then the fault is a left lateral

• Reversely, standing on one side of a fault, and the other side moves to the right, then the fault is right lateral

  • Does not matter which side of the fault you stand on, the motion is the same

Surface Waves (Rayleigh and Love Waves)

• Complex motion

• Cause greatest destruction eaves exhibit greatest amplitude and slowest velocity

  • Waves have the greatest periods (time interval between crests)

Surface Waves (Rayleigh Waves)

Surface Waves (Love Waves)

Surface Waves (Body Waves)

• Travel deep into the earths interior

• Type types:

  • P-Waves

  • S-Waves

What are the two types of Seismic Body Waves?

• P-Waves

• S-Waves

P-Waves

• Primary Waves

• Compression - push/pull motion

• Fastest

  • Generally, in any solid material, P waves travel about 1.7 times father than S waves

• Travels through liquids, solids, and gases

S-Waves

• Secondary Waves

• Shear

  • Shaking motion at right angles to their direction of travel

• Slower than P-Waves

• Travel only through solids

S-Waves

P-Waves

Seismic Waves

• Different physical properties of waves produced by earthquakes, cause them to travel at different rates

  • P-Wave = Fastest

  • S-Waves = Moderate

  • Surface Wave = Slowest

Which type of Seismic Wave is fastest?

P-Waves

Which type of Seismic Wave is the Slowest?

Surface Wave

Which type of Seismic Wave is moderate/middle speed?

S-Wave

Seismogram

The data record from a seismograph. It depicts earthquake wave behavior, particularly the arrival time of the different waves

• which is used to determine the distance to the epicenter

What is used to record an earthquakes wave data?

Seismograph

Richter Scale

Determined by first calculating the interval between the S- and P- waves

• Then determine the amplitude of the largest wave produced

• Draw a line on special graph paper between these two points

  • The earthquakes magnitude is where the line intersects

What Factors influence destruction in earthquakes?

• local foundation conditions

• Building standards/codes

• Population density

Structural Damage/Destruction in a Earthquake

• the intensity

• Durations of vibrations

• The nature of material upon which the structure rests

• The design

Liquefaction

The process that occurs when the motion of an earthquake causes sand and clay-rich sediment to become a slurry of sand, clay, and water

P-Wave shadow zone

Caused by the refraction of P-Waves through the earths core

• Occurs because seismic velocities are much lower in the liquid outer core than in the overlying mantle, so the Waves are refracted in a way that leaves a gap

S-Waves shadow zone

Differs from the P-wave zone because the physical properties of S-waves do not let them travel through liquids

• therefore, they cannot penetrate the liquid outer core of the earth

• The inner core is solid

Volcano

A mountain formed by the accumulation of extrusive volcanic or a vent from which melt from inside the earth spews out onto the planets surface

• direct consequence of plate tectonics and mantle convection (convergent and divergent boundaries)

What determines how violently a volcano will erupt?

• Temperature

• Magmas composition

• Dissolved gases

Viscosity

A measure of a materials resistance to flow (e.g., higher viscosity materials flow with greater difficulty)

• syrup is more viscous than water

What factors affect viscosity?

Temperature - hotter magmas are less viscous

Composition - Silica content

Gasses

• dissolved gasses increase the fluidity of magma

• Escaping gases propel the molten rock

Felsic Magmas

• Higher silica content, lower Fe and Mg

• Higher viscosity (rhyolite)

Mafic Magmas

• Lower silica content, higher Fe and Mg

• Lower viscosity (basalt)

How do gases affect viscosity?

• dissolved gases increase the fluidity of magma

• Escaping gases propel the molten rock

• Volatiles move upward when an eruption is about to happen

• Gases of most magmas makeup 1-6 percent of the total weight (most water Vapor)

• Help to create a narrow conduit that connects the magma chamber to the surface

Mafic (Basaltic) Magma

• least silica content (~50%)

• Least viscosity

• Least gas content (1-2%)

(Andesitic) Magma I

• intermediate silica content (~60%)

• Intermediate viscosity

• Intermediate gas content (3-4%)

Felsic (Rhyolitic) Magma

• Most silica content (~70%)

• Greatest viscosity

• Most gas content (4-6%)

What are the types of Basaltic Lava Flows?

• Pahoehoe

• Aa

Pahoehoe Basaltic Lava Flow

• congealing of basaltic lavas that form relatively smooth skin that wrinkles as the molten subsurface lava continues to advance

• Lava Tubes - tunnel in hardened lava that acts as a horizontal conduit for lava flowing from a volcanic vent

Pahoehoe Basaltic Lava Flow

Aa Basaltic Lava Flow

• a basaltic lava that has a surface of rough jagged blocks with sharp edges

• Move much slower than a Pahoehoe flow

Aa Basaltic Lava Flow

What are the types of Effusive Eruptions?

• Shield Volvanoes

• Flood Basalts

What are the types of Explosive Eruptions?

• Stratovolcanoes

• Lava Domes

• Cinder Cones

Shield Volcanoes

Gentle outpouring of low-silica fluid lavas from a central vent or conduit

• like a shield laid on the ground

• Formed by hotspots

• Fissure-crack along the flanks of a shield volcano that erupt lava

  • Ex: Iceland, Hawaiian Islands

Shield Volcanoes

Strati / Composite Volcanoes

Combination of effusive and explosive volcanic activity

• Pyroclastic material and lava in alternating layers

• Occur landward side of a subduction zone

  • Ex: Mount Fuji, Mount Vesuvius

Lahars

Fast moving volcanic debris flow

• mobilization of debris by water (precipitation, melting snow, a lake, etc.)

• Ex: Colombias Nevada del Ruiz (17,800 feet high)

  • Reached 30 miles away in minutes

  • 130 foot high Lamar entombed 20,000 people in mud

Pyroclastic Debris

Turbulent mixtures of hot gases and Pyroclastic material that travel with great velocity

• includes Tephra, ash, bombs, blocks

• Various sizes

Tephra

Volcanic rock ejected during an eruption

• ash, bombs, blocks

Pyroclastic Flow - Nuer Ardente (Growing Cloud)

Associated with composite cone volcanoes

• Nuer Ardente- Pyroclastic flow that consist of hot gases infused with incandescent ash and larger rock fragments

  • Full of gases and hot, buoyant air

  • 60 miles from the source

Nuer Ardente

Pyroclastic flow that consists of hot gases infused with incandescent ash and larger rock fragments

• full of gases and hot, buoyant air

Cinder Cones

Built from ejected lava fragments that take on the appearance of cinders

• smallest and most numerous

• Usually erupt once

• Built of Pyroclastic material (tephra)

  • Blocks

  • Bombs

  • Lapilli

  • Ash dust

Calderas

Giant volcanic depression usually formed after a large eruption

• the magma chamber below empties and the volcano collapses into the emptied chamber

• Much larger than a crater

  • Ex: crater lake, oregon

Calderas

Dikes

Magma injected into fracture perpendicular to bedding plane

Sills

Magma injected into fractures along a bedding plane

Laccoliths

Similar to a sill but magma more viscous

Batholith

Largest igneous body