Tectonic Plates and Volcanic Activity

Flashcards covering key vocabulary related to tectonic plates, plate boundary processes, landforms, and volcanic activity, based on the provided lecture notes.

Tectonic Plates

Large sections of the Earth's lithosphere that move across the globe, driving geological processes.

Convection Currents (Old Theory)

Huge currents of semi-molten rocks within the asthenosphere that were once thought to upwell, diverge, and drag tectonic plates along.

Asthenosphere

The semi-molten, ductile layer of the upper mantle beneath the lithosphere, where rock can flow over geological timescales.

Ridge Push (Gravitational Sliding)

A mechanism at mid-ocean ridges where the elevated, hotter, and less dense lithosphere slides away from the ridge due to gravity, exerting a force on spreading plates.

Slab Pull

A primary mechanism for plate movement where the edge of a denser, colder subducting plate sinks into the mantle, pulling the rest of the plate along.

Decompression Melting

The process where a hot plume of material rises to an area of lower pressure at the outer edge of the mantle, causing it to melt despite no increase in temperature.

Rift Valley

A linear depression formed by the stretching and fracturing of continental crust as plates begin to spread apart at a constructive margin.

Linear Sea

A narrow sea that forms when a newly created rift valley, as plates continue to move apart, is filled with ocean water.

Mid-Ocean Ridge

Continuous ranges of submarine volcanic mountains that encircle the globe, marking constructive or divergent plate margins where new oceanic crust is formed.

Transform Faults (Ocean Ridge)

Fractures that offset sections of mid-ocean ridges, allowing for even spreading of the seafloor.

Mid-Atlantic Ridge

A specific example of a slow-spreading mid-ocean ridge that runs along the north-south axis of the Atlantic Ocean, characterized by seafloor spreading, volcanic activity, and earthquakes.

Horst and Graben Structures

Distinctive landforms within rift valleys, where crustal blocks are uplifted (horst) or downdropped (graben) due to tensional forces and faulting.

Mantle Plumes

Upwellings of hot material from the Earth's mantle that can cause heating, expansion, and fracturing of overlying continental crust, initiating rifting.

Rift Volcanoes

Volcanoes that form when magma rises into the gap between diverging plates, often exhibiting complex characteristics in continental locations due to assimilation of crustal material.

Destructive Margin (Convergent Boundary)

A plate boundary where two plates are forced towards each other, resulting in subduction and often characterized by trenches, volcanoes, and earthquakes.

Atacama Trench

A long, narrow, deep ocean trench off the western coast of South America, marking the subduction zone of the Nazca Plate beneath the South American Plate.

Subduction

The geological process in which one tectonic plate sinks beneath another and into the Earth's mantle at a convergent plate boundary.

Accretionary Wedge

A mass of sediments and oceanic crustal material that is scraped off the subducting plate and accumulates against the edge of the overriding plate at a destructive margin.

Fold Mountains

Mountain ranges formed when continental crust is subjected to intense compressional forces, causing rock layers to buckle, fold, and uplift.

Benioff Zone

A dipping seismic zone that corresponds to the region of shallow to deep-focus earthquakes along the contact plane of a subducting oceanic plate.

Hydration-activated Melting

The process where water released from the subducting oceanic plate lowers the melting temperature of the surrounding mantle, leading to the generation of magma.

Island Arc System

A chain of volcanic islands formed parallel to an oceanic trench at an oceanic-oceanic convergent boundary, resulting from magma rising from the subducting plate.

Aleutian Trench

An example of an oceanic-oceanic convergent boundary where the Pacific Plate is being subducted beneath the North American Plate.

Aleutian Island Arc

A chain of volcanic islands formed north of the Aleutian Trench due to the melting of the crust caused by the descending Pacific Plate.

Collision Margin (Continental-Continental)

A plate boundary where two continental plates converge and collide, resulting in intense folding, faulting, and the formation of high mountain ranges without significant subduction.

Orogeny

A geological term referring to a period of intense mountain building, involving the deformation and uplift of the Earth's crust.

Himalayan Fold Mountains

A prominent example of fold mountains formed by the ongoing continental-continental collision between the Indian and Eurasian plates.

Conservative Plate Margin (Transform Fault)

A plate boundary where two tectonic plates slide horizontally past each other, resulting in shallow earthquakes but typically no volcanic activity.

San Andreas Fault

A major transform fault in North America, marking the strike-slip boundary between the Pacific Plate and the North American Plate.

Volcano

An opening or fissure on the Earth's surface (land or sea) that allows lava, gases, and other volcanic material to escape.

Lava Viscosity

A measure of how 'sticky' or 'runny' lava is, primarily determined by its silica content, influencing eruption style and volcano shape.

Basaltic Lava

Low-viscosity, fluid lava with low silica content, capable of flowing long distances and associated with effusive eruptions.

Andesitic Lava

Lava with intermediate viscosity and silica content, which tends to break up as it flows and is associated with more explosive eruptions than basaltic lava.

Rhyolitic Lava

Very high-viscosity lava with high silica content, which often piles up in a dome shape near the vent and is associated with highly explosive eruptions.

Pahoehoe Lava

A type of basaltic lava flow characterized by a smooth, billowy, or 'ropy' surface, forming from slower, less outwardly cooling flows.

Aa Lava

A type of basaltic lava flow characterized by a rough, jagged, and blocky surface composed of angular chunks called clinkers, forming from rapid flows with significant heat loss.

Pillow Lava

Distinctive rounded, sack-like lava forms that create during submarine eruptions as lava extruded into water cools rapidly.