Plate tectonics and mass movements

Lithosphere

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

Asthenosphere

A semi-molten layer beneath the lithosphere that allows plate movement due to its plasticity.

Mantle

The thick layer between Earth's crust and core, composed of silicate rocks rich in iron and magnesium.

Core

The innermost part of Earth, divided into a liquid outer core and solid inner core, primarily iron and nickel.

Tectonic Plates

Large segments of the lithosphere that move over the asthenosphere, causing geological activity.

Plate Tectonic Theory

The scientific theory explaining the movement of Earth's plates and associated phenomena like earthquakes and volcanoes.

Continental Drift

The hypothesis that continents move across Earth's surface over geological time.

Sea Floor Evidence

Data such as magnetic striping and age of rocks that support plate tectonic theory.

Ridge Push

A tectonic force where newly formed oceanic crust at mid-ocean ridges pushes older crust away.

Convective Drag

Movement of tectonic plates driven by convection currents in the mantle.

Slab Pull

A force where a subducting plate pulls the rest of the plate along as it sinks into the mantle.

Plate boundaries

Zones where tectonic plates meet, including divergent, convergent, and conservative types.

Convection Currents

Circular movements in the mantle caused by heat from the core, driving plate motion.

Convergent

A boundary where plates move toward each other, often forming mountains or subduction zones.

Divergent

A boundary where plates move apart, creating new crust at mid-ocean ridges.

Conservative

A boundary where plates slide past each other, causing earthquakes.

Collision

A type of convergent boundary where two continental plates meet, forming fold mountains.

Compression

Forces that squeeze rocks together, often forming folds.

Tension

Forces that pull rocks apart, common at divergent boundaries.

Shearing

Forces that cause rocks to slide past each other horizontally.

Fold mountains

Mountains formed by the folding of Earth's crust due to compression.

Ocean trenches

Deep underwater valleys formed at subduction zones.

Island arcs

Chains of volcanic islands formed above subduction zones.

Ocean ridges

Elevated regions on the ocean floor formed at divergent boundaries.

Anticlines

Upward-arching folds in rock layers.

Synclines

Downward folds in rock layers.

Accretionary wedge/prism

Sediments scraped off a subducting plate and accumulated at a convergent boundary.

Subduction

The process where one plate sinks beneath another into the mantle.

Orogenesis

The process of mountain formation through tectonic forces.

Benioff Zone

A zone of earthquake activity along a subducting plate.

Rift Valley

A valley formed by the downward displacement of a block of Earth's surface at a divergent boundary.

Transform fault

A fault where plates slide past each other horizontally.

Sea floor spreading

The formation of new oceanic crust at mid-ocean ridges and its outward movement.

Oceanic crust

Dense, basaltic crust beneath the oceans.

Continental crust

Less dense, granitic crust forming continents.

Palaeomagnetism

The study of Earth's past magnetic field recorded in rocks.

Seamount

An underwater mountain formed by volcanic activity.

Mantle plume

A column of hot rock rising from deep within the mantle, often forming hotspots.

Regolith

A layer of loose, heterogeneous material covering solid rock.

Freeze-thaw

A weathering process where water freezes in cracks, expands, and breaks the rock.

Scree

Loose rock debris found at the base of cliffs or slopes.

Ergs

Large areas of shifting sand dunes in deserts.

Unloading

Expansion and fracturing of rock due to removal of overlying material.

Pseudo-bedding planes

False layering in rocks caused by processes like weathering or deposition.

Hydrolysis

A chemical weathering process where minerals react with water.

Hydration

Weathering caused by water absorption into minerals, causing expansion.

Dehydration

Loss of water from minerals, often reversing hydration.

Carbonation

Weathering caused by carbonic acid reacting with minerals like limestone.

Minerals

Naturally occurring inorganic substances with a definite chemical composition.

Basalt

A dark, fine-grained volcanic rock forming much of the oceanic crust.

Quaternary period

The most recent geological period, spanning the last 2.6 million years.

Creep

Slow, gradual downslope movement of soil or debris.

Plastic flow

Movement of ice or soil behaving like a viscous fluid.

Solifluction

Slow flow of water-saturated soil down a slope, common in periglacial areas.

Terracettes

Small step-like features on slopes formed by soil movement.

Lahars

Volcanic mudflows formed by mixing volcanic material with water.

Mass Movements

Downslope movement of soil, rock, or debris under gravity.

Loading

Addition of weight to a slope, increasing instability.

Consolidated / unconsolidated

Refers to whether sediments are compacted and cemented (consolidated) or loose (unconsolidated).

Ploughing

Human activity that can destabilize slopes and contribute to erosion.