Lecture 4 Flashcards

Vocabulary flashcards covering key terms related to plate tectonics, boundaries, subduction, and related phenomena.

Plate tectonics

The theory that Earth's lithospheric plates move over the asthenosphere, driven by convection, causing earthquakes, volcanoes, and mountain building.

Lithosphere

The rigid outer layer of Earth, consisting of the crust and upper mantle, broken into tectonic plates.

Asthenosphere

The partially molten, ductile layer beneath the lithosphere that allows plate motion.

Seafloor spreading

The creation of new ocean floor at mid-ocean ridges as tectonic plates move apart. Divergent + mid ocean ridges

Mid-ocean ridge

An underwater mountain chain where seafloor spreading occurs. Divergent

Ridge push

Gravity-driven force that pushes plates away from elevated mid-ocean ridges.(convergent)

Slab pull

A major driving force of plate tectonics, where the dense, cool oceanic lithosphere sinks into the Earth's mantle at a subduction zone under its own weight. This gravitational force pulls the rest of the attached oceanic plate along with it, contributing significantly to plate movement at convergent boundaries.

Subduction zone

A convergent plate boundary where a denser oceanic plate slides beneath another plate (oceanic or continental) and sinks into the mantle, often forming a deep ocean trench, volcanic arcs, and being a site for megathrust earthquakes due to slab pull.

Trench

A deep-sea depression marking the location where subduction begins.

Convergent boundary

A plate boundary where plates collide, forming subduction zones or mountain belts.

Divergent boundary

A plate boundary where plates move apart from each other, driven by mantle convection. As plates separate, magma from the asthenosphere rises to fill the gap, creating new oceanic crust through a process called seafloor spreading. This process commonly forms mid-ocean ridges in oceanic settings (like the Mid-Atlantic Ridge) and rift valleys on continents (like the East African Rift). Volcanic activity and shallow earthquakes are characteristic of these boundaries.

Transform boundary

A plate boundary where two tectonic plates slide horizontally past one another, often in opposite directions or at different rates. This grinding motion creates significant friction, causing stress to build up along the fault line. When this stress is suddenly released, it results in shallow but strong earthquakes. Unlike divergent or convergent boundaries, these boundaries typically do not involve the creation or destruction of lithosphere.

Ring of Fire

A ring-shaped zone around the Pacific Ocean with frequent earthquakes and volcanism due to subduction. (convergent)

Nazca Plate

An oceanic plate subducting beneath South America, forming the Andes.

Cocos Plate

An eastern Pacific oceanic plate subducting under North/Central America; among the fastest plates.

Pacific Plate

A major oceanic plate whose movement contributes to Ring of Fire activity; one of the fastest plates. Moves North West

Himalayas

Mountain range formed by the convergent continental collision of India with Eurasia.

Andes Mountains

Mountains formed by the subduction of the Nazca Plate beneath South America.

Iceland

A location where a spreading ridge rises toward the surface, illustrating seafloor spreading and rifting. Divergent

East Pacific Rise

The fast-spreading mid-ocean ridge in the Pacific Ocean. Divergent

Mid-Atlantic Ridge

The mid-ocean ridge in the Atlantic where seafloor spreading occurs. Divergent

Megathrust earthquakes

The largest, most powerful earthquakes occurring at subduction zones.

Tsunami

A series of large ocean waves generated by sudden seafloor displacement during subduction-zone earthquakes.

San Andreas Fault

A major transform boundary in California where the Pacific Plate slides past the North American Plate moving North West.

Cascadia Subduction Zone

Subduction zone off the Pacific Northwest capable of megathrust earthquakes and tsunamis.

Wallace Creek

A famous exposure of the San Andreas transform boundary showing the relative motion of the plates.

Trenches

Deep-sea trenches marking subduction zones along plate boundaries.

Continental collision

Collision between two continental plates forming high mountain belts (e.g., Himalayas).

Volcanoes along plate boundaries

Volcanic activity concentrates at plate boundaries, especially subduction zones and ridges, including undersea volcanoes.