Exam 2 ( How the Earth Works)

Alfred Wegner (1915)

Alfred Wegner (1915)

Had a radical hypothesis of continental drift

Evidence for Pangea

Continental Jigsaw, evidence of fossils across sea

lithosphere

A strong, rigid layer that is made up of plates ( older it is, the thicker it is)

Asthenosphere

Weak sphere, near melting temps. It allows Earths rigid outer shell to move

Mesosphere (lower mantle)

Pressure counteracts temperature creating strong rocks

Outer Core

Liquid layer of iron that generates earth’s magnetic field

Inner Core

Solid Iron because of immense pressure

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. Which lead to active margins and passive margins( not plate boundaries)

Divergent Boundaries

Oceanic Ridges and Seafloor Spreading, Continental rifting

Convergent Boundaries

Oceanic- continental convergence, oceanic, and continental

Divergent Plate Boundaries

Two plates move apart as a result of upwelling material from the mantle to creating new oceanic lithosphere, constructive plate margins

Sea Floor Spreading

True divergent plate boundaries occur along mid-ocean ridges, New ocean crust is formed along the ridge, as the plates move away from each other the older crust moves farther away

Sea Floor Spreading

Moves about 5 centimeters per year, no ocean floor exceeds 180 million years old

Convergent Boundaries

Destructive plate margins, Subduction zone ( one plate bends and sinks under another plate)

Convergent Plates Boundaries

Angles of subduction range from 90 averaging about 45, which depends on the density (Old lithosphere is cold and dense with has a steep angle)

Oceanic - Continental Convergence

Downgoing plate (subducted) and overriding plate ( not sinking)

Accretionary Prism ( boundary feature)

A wedge-shaped mass of sediment and rock scraped off the top of a down going plate ( a plow scraping off material

Continental volcanic arc

Volcanoes are associated with the subduction zone because the down plate brings water and the water is heated up and released into the mantle. Which allows it to partially melt, allows magma to form

Partial Melting

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

Oceanic-Oceanic (Convergent zone)

Creates volcanic island arcs, Back-arc Basin-Depression are formed behind a volcanic island arc

Continental-Continental ( Convergent zone)

Cannot be subducted, Subduction ends when two continental plates collide, A collisional mountain belt forms where the tow plates collided

Transform Fault Boundaries

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

Hot Spots

As a plate moves over a hot spot a chain of volcanoes is formed. As these extinct volcanoes sink below sea level, they become seamounts

Earthquake?

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

Fault?

A fracture on which one body of rock slides past another

Focus?

The location where a fault slips during an earthquake ( Hypocenter)

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

Why do Earthquakes occur?

Elastic Rebound and is produced by the rapid release of elastic energy stored in rock that has been subjected to great stress.

Elastic Robound?

Springing back of a rock once an earthquake has occurred and the rock returns back to its original shape

Footwall (Fault)

The rock mass that lies below the fault plane

Hanging wall (Fault)

The rock or sediment above an inclined fault plane

Transform/Strike-Slip Faults

Motion can be left lateral or right lateral. If you stand on one side and the other side moves left, it becomes a left lateral.

San Andreas Fault ( an active Earthquake zone)

A transform plate boundary (right lateral), displacement occurs along discrete segments 100 to 200 kilometers long

Seismic Waves

Surface waves( complex motion/great destruction/ slowest) and Body waves ( travel deep into Earth’s interior)

Body Waves

P-waves: primary, push/pull motion, fastest

S- waves: Shear, slower, only travel through solids

Earthquake Measurement

Seismogram: depicts earthquake wave behavior

Locating the Epicenter

Data from 3 or more stations pinpoints the epicenter

Ricther Scale

Determined by first calculating the interval between the S and P waves, then determining the amplitude of the largest wave produced, the line intersects where the line is formed

Earthquakes

Factors influencing damage: foundation conditions, building standards

Destruction: structural, tsunami, fire

Destruction

Structural damage, fires, ground shaking, tsunami

Ground and Foundation damage

can trigger mass wasting, lose cohesion: due to shaking of ground, water in pore space cause sand to become mobilized, liquefaction

Liquefaction

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

Earth’s interior

P-wave shadow zone which is caused by the refraction of P-waves through the earth’s core and S-waves shadow zone: do not penetrate the liquid outer core

A mountain formed by the accumulation of extrusive volcanic rock

A vent from which melt from inside the Earth spews out onto the planet’s surface

Viscosity

A measure of a material’s resistance to flow

Factors affecting viscosity

Temperature, Composition: Silica content

Gases

dissolved gases increase the fluidity of magma, escaping gases propel the molten rock

Mafic magma

Silica content:Least (-50%), Viscosity: Least, Gas Content: Least(1-2%)

Intermediate magma

Silica content: Intermediate (-60%), Viscosity: Intermediate, Gas Content: Intermediate(3-4%)

Felsic magma

Silica content:Most (-70%), Viscosity: Greatest, Gas Content: Most(4-6%)

Pahoehoe ( basaltic lava flow)

Form relatively smooth skin that wrinkles as the molten subsurface lava continues to advance

lava Tubes: tunnel in hardened lava (horizontal conduit)

Aa ( basaltic lave flow)

Has a surface of rough jagged blocks with sharp edges ( much slower than pahoehoe)

Types of Eruptions and Volcanic Cones

Effusive Eruptions: Shield Volcanoes/Flood Basalts

Explosive Eruptions: Stratovolcanoes/Lava Domes/Cinder Cones

Shield volcanoes

Gentle outpouring of low-silica fluid lavas from a central vent or conduit, Fissure-crack along the flanks of a shield volcano that erupts lava

Ex. Iceland

Strato/ Composite Volcanoes

Combination of effusive and explosive volcanic activity, Occurs landward side of a subduction zone

Ex. Mount Fuji

Stratovolcanoes

Subduction of the Juan de Fuca plate beneath North America has produced the Cascade Range

Lahars

Fast moving volcanic debris flow, Mobilization of debris by water

Ex. Colombia’s nevado del Ruiz

Pyroclastic Debris

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

Tephra

Volcanic rock ejected during an eruption

Nuee Ardente

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

Cinder Cones

Built from ejected lava fragments that take on the appearance of cinders/ small, erupt once, numerous, built of tephra

Calderas

Giant volcanic depressions usually formed after a large eruption, the magma chamber below empties and the volcano collapses into the emptied chamber

Dikes (intrusive igneous activity)

Magma injected into fracture perpendicular to bedding plane

Sills (intrusive igneous activity)

Magma injected into fractures along a bedding plane

Laccoliths (intrusive igneous activity)

Similar to a sill but magma more viscous

Batholith (intrusive igneous activity)

Largest igneous body

Volcanic Hazards

Flows, Ash, Blast, Landslides, and Earthquakes

Mountain Building

True mountains form by convergent plate tectonic activity

Non-tectonic mountains are usually formed by eroding a high plateau

Orogeny

The processes that collectively produce a mountain belt

Rock Deformation

All the changes in the original shape and/or size of the rock body: changes in location or rotation

Brittle (Deformation)

Cracking and fracturing of material subjected to stress

Ductile (Deformation)

The flowing of material subjected to stress with cracking

Folds

Layers of rocks that are deformed by tectonic compression, form geometry (hinge, limbs, axial plane)

Hinge

A line along which curvature is the greatest

Monocline

Result of the reactivation of steeply dipping fault zones in basement rock, caused by a blind fault

Domes

Folded or arched layers with the shape of an overturned bowl that is produced by unwrapping (Black Hills)

Basins

A fold shaped like a right-side bowl that is produced by downwrapping (Bedrock in Michigan)

Normal fault

Associated with fault-block mountains, divergent plate boundaries, tensional forces

Fault Block Mountains

The tensional stress applied to rocks causes a fault system of normal faults called Horst and Graben

Horst

The high block between two grabens

Graben

A down-dropped crustal block bounded on either side by a normal fault dripping toward the basin

Fault Block Mountains

Mountains that are produced by continental rifting or extension of the crust that bounded by high angle normal faults that flatten at depth

Reverse and Thrust Fault

Compressional forces, convergent plate boundaries ( Reverse: > 45o) (Thrust: <45o)

Mountain Building

Volcanic Island Arcs (Oceanic) and Andean( continental volcanic arc)

Accretion and Orgogenesis

Accretion of terranes along a subduction zone can form mountains

Terrane

A crustal block, bounded by faults, whose geologic history is distinct from the history of the adjoining crustal block

The North American Cordillera

Comprised of numerous accreted terranes

Continental- Continental Convergence

Continental collisions are when two tectonic plates made up of continental crust converge on each other, during collision intense compression and shear cause the crust to thicken through folding and faulting

isostasy

Concept of a floating crust in gravitational balance

Isostatic Adjustment

Establishing a new level of gravitational equilibrium, the process of uplift and erosion will continue until the mountain block reaches normal crustal thickness

Mass Wasting

It is the downslope motion of rock, regolith, snow, and ice (Gravity)

Landslide

Is a general term having the same meaning as mass wasting

Slope Stability

mass wasting will occur if the force of gravity pulling on the block exceeds the resistance holding the block in place

Controls and Triggers of Mass Wasting

The role of water, oversteepend slopes, undercutting, planes of weakness, removal of vegetation

The role of water

Mass wasting can occur when heavy rains saturate the soil- saturation reduces the internal resistance of materials

Oversteepend Slopes

Erosion and cut & fill may cause landslides

Removal of Vegetation

Plants protect against erosion because roots bind soil together

Roots help hold rock and soil in place