GEOG 101 Ch. 14 Study Guide: Internal Processes

What were some of the reasons that Alfred Wegener's theory of "continental drift" was rejected for so many decades?

He couldn't provide evidence of a mechanism that would move the plates

Describe and explain the formation of landforms that result from strike-slip faulting (such as linear fault troughs, sag ponds, and offset streams).

- A linear fault trough is a valley marking a strike-slip fault; it occurs by repeated movement and fracturing of rock. A sag pond is a pond caused by the collection of water from springs and/or runoff into sunken ground, resulting from the jostling of Earth in the area of fault movement. An offset stream, or offset drainage channel, is perhaps most conspicuous landform. Offset streams are produced by strike-slip faulting where a stream's course runs perpendicular to a fault line, and then has its flow redirected by a lateral shift in the fault blocks.

What is a hot spot? Name at least one present-day example of a hot spot location.

- Areas of volcanic activity within the interior of a lithospheric plate associated with magma rising up from the mantle below; Hawaiian Islands

What is a terrane and how does one form?

- Def: A Mass of lithosphere, bounded on all sides by faults, and has grown together with a lithospheric plate margin with different lithologic characteristics. - a piece of lithosphere is carried along a plate until it converges with another, but is bouyant and does not subduct.

What are the differences in origin of a hot spot trail and a volcanic island arc? Provide one example of each.

- Hot spot trail: associated with a plate depositing features in a linear fashion relative to its movement over a plume; Hawaii - Island arc: created by an ocean-ocean convergent plate boundarycreating a parrallel island arc; Aleutian Islands

Define the following terms: magma, lava, and pyroclastics.

- Magma: Molten rock beneath the surface of the Earth - Lava: Molten magma that is extruded onto the surface of Earth, where is cools and solidifies. - Pyroclastics: The totality of materials ejected from a volcano, including liquid material, ashes and dust

Explain the general differences in silica content and style of volcanic eruption (i.e., effusive ["quiet"] lava flows vs. explosive eruptions of pyroclastics)

- Quiet Lava flows: lowest amount of silica, very fluid and flowing. - Explosive eruptions of pyroclastics: Highest amount of silica, thick and viscous, pasty. Explosive eruptions

In what ways have hot spots been used to verify that plate motion is taking place?

- The plate above the plume is moving, causing the older to newer line of features to illustrate the direction of the plate

Why are deep-focus earthquakes (those originating many hundreds of kilometers below the surface) associated with subduction zones, but not with divergent boundaries and transform boundaries?

- The subduction plates are diving deep below the surface in the subduction zones, divergent and transform zones are close to the surface where the spreading is happening.

How does the idea of a mantle plume explain the existence of hot spots?

- There are locations of narrow plumes of magma that rise up through the surface and as the plate moves/shifts it creates a line of volcanoes and possible islands

In what ways don't hot spots fit in with the basic model of plate tectonics and plate boundaries?

- They are not associated with plate boundaries

Describe and explain the origin and characteristics of volcanic mudflows ("lahars") and pyroclastic flows.

- Volcanic Mudflows (Lahars): when the loose mantle of ash and pyroclastic flow deposits on the slopes of a volcano are mobilized by heavy rain or by the melting of snow and glaciers during an eruption - Pyroclastic flows: High speed dense avalanche of hot gases, ash, and rock fragments emitted from a volcano during an explosive eruption.

Why is there such a concentration of volcanoes and earthquakes around the margin of the Pacific Ocean (a region referred to as the Pacific Ring of Fire)?

- because of subduction zones along with the segments of transform and divergent boundaries. The pacific rim has plate boundarys all the way around it.

Describe and explain the tectonic activity, volcanic activity and general topographic features of the two kinds of divergent plate boundary: midocean ridges and continental rift valleys.

- mid-ocean ridges: slow sloping grade ridges diverging, underwater volcanoes, shallow focus earthquakes; mid-Atlantic ridge - continental rift valleys: divergence within a continent down drop blocks, rift valleys, shallow earthquakes, volcanoes; great east African rift valley

Describe and explain the tectonic activity, volcanic activity and general topographic features of the three kinds of convergent plate boundary: oceanic-to-continental plate subduction, oceanic-to-oceanic plate subduction, and continental plate collision. Mention at least one present-day example of each of these kinds of convergent boundary.

- oceanic-to-continental plate subduction: ocean crust dives under continent because its more dense, creates ocean trench, mountains, shallow and deep earthquakes along the edge of subducting plate: peru-chile trench. - oceanic-to-oceanic plate subduction: one ocean crust dives under other ocean crust creating trench, volcanoes are formed in island arcs parallel to the trench, shallow and deep earthquakes; Mariana trench - continental plate collision: no subduction because the crust is too buoyant, huge mountain ranges, volcanoes rare, shallow focus earthquakes; Himalayas, India into Asia.

Describe the fundamental differences among divergent, convergent and transform plate boundaries.

-- Divergent: (spread) Plates move away from each other - Asthenosphere wells up in the plate opening - Represented by a midoceanic ridge - Associated with shallow-focus earthquakes and volcanic activity - Constructive-crust created - Continental rift valley (divergence on continent) --Convergent: -(collide) Collisions between plates - Destructive = removal or compression of surface crust - Three primary collisions: 1.) Oceanic-continental : oceanic plate sinks since more dense; subduction. Subducting slab pulls the rest of the plate "slab pull" - Oceanic trench - Continental mountains (e.g., Cascades, Andes) - Continental volcanic arc Earthquakes - Subducting oceanic plate metamorphosed 2.) Oceanic-oceanic - Deep and shallow earthquakes - Island volcanic arc 3.) Continental-continental - No subduction since two plates are highly buoyant - Builds huge mountain ranges (Ex. Alps, Himalayas) - Volcanoes are rare - Shallow earthquakes are relatively common - Regional metamorphism is common --Transform: - (slip past) Two boundaries slip past each other laterally - Transform faults - Neither create nor destroys crust - Commonly produce shallow focus earthquakes

Describe and explain the general formation, shape and structure of the following kinds of volcanic peaks: shield volcanoes, composite volcanoes, and plug domes ("lava domes").

-- Shield volcanoes: - Layer upon layer of solidified lava flows - Little pyroclastic material - Broad, can be massive -- Composite volcanoes: - Emit higher silica lavas (andesite lava) - Form symmetric, steepsided volcanoes - Pyroclastics (ash and cinders) from explosive lava flows alternate with nonexplosive flows - Pyroclastic flows produce steep slopes, lava holds it together -- Plug domes ("lava domes"): - Usually small, with irregular shape - Solidified magma that was thick and viscous when molten-explosive eruptions - Dome grows from expansion of lava from within - Frequently occur within the crater of composite volcano

What general process taking place within Earth's mantle is responsible for lithospheric plate movement?

Convection

What is the general relationship of global earthquake activity to plate boundaries?

Earthquakes generally happen along the borders, where spreading, slipping, and convergence happens with the plates

Why can oceanic lithosphere be subducted while continental lithosphere cannot?

Oceanic crust is more dense and the continental crust is more buoyant.

What lines of evidence confirm that seafloor spreading has been taking place and that the positions and configuration of continents and ocean basins changes over geologic time? You should be able to describe and explain at least one line of evidence found on the ocean floors that verifies seafloor spreading.

The mid atlantic ridge shows seafloor spreading and the alignment of continents such as south america to Africa show that the continents "fit" together, or the animals dispersed across them. Or the mountain ranges such as the appalachians to the brittsh Isles and Caledonian mountains

How does the San Andreas Fault system fit in with plate tectonics?

it sits on a transform boundary between the Pacific and North America.

In the context of plate tectonics, describe the differences between the lithosphere (the "plates") and the asthenosphere.

lithosphere is the continent sized slabs called plates that shift and that the asthenosphere is hot and soft. The lithosphere slides over the asthenosphere