Leaving Cert Geography: Tectonics, Folding, Volcanoes and Earthquakes

Vocabulary flashcards covering core geological concepts including tectonics, mountain folding periods, volcanic activity, and earthquake processes.

Lithosphere

The rigid outer layer of the Earth, made up of the crust and the uppermost part of the mantle. It is broken into tectonic plates.

Asthenosphere

The semi-molten, weak layer of the upper mantle beneath the lithosphere. Tectonic plates move slowly over it.

Moho line

The boundary between the Earth's crust and mantle, where seismic-wave speeds change noticeably.

Convection currents

Circular movements in the mantle caused by heat from the Earth's interior, which help drive the movement of tectonic plates.

Continental drift

The theory that continents have moved over geological time from an earlier joined landmass to their present positions.

Seafloor spreading

The process where magma rises at mid-ocean ridges, cools and forms new oceanic crust, pushing older crust away.

Subduction

The process in which a denser tectonic plate sinks beneath another plate and descends into the mantle.

Slab-pull

A force caused by a cold, dense oceanic plate sinking into the mantle at a subduction zone and pulling the rest of the plate behind it.

Ridge-push

A force caused by gravity acting on raised mid-ocean ridges, helping oceanic plates move away from the ridge.

Tectonic plate

A large, rigid section of the lithosphere that moves slowly over the asthenosphere.

Plate boundaries

The edges where two tectonic plates meet and interact; they may be constructive, destructive or conservative.

Orogeny

The process of mountain building, usually involving the compression, folding and faulting of rock layers.

Anticline

An upward-arching fold in rock layers, with the oldest rocks usually found in its centre.

Syncline

A downward, trough-shaped fold in rock layers, with the youngest rocks usually found in its centre.

Recumbent fold

A fold that has been pushed so far by compression that its axial plane is almost horizontal.

Caledonian folding

A period of mountain building about 490–390 million years ago, which formed mountains in parts of Ireland, Scotland and Scandinavia.

Armorican folding

A period of mountain building about 300 million years ago, which formed or affected mountains in south-west Ireland and parts of Europe.

Alpine folding

A period of mountain building that began about 65 million years ago, caused by the collision of the African and Eurasian plates; it formed the Alps.

Granite intrusion

The emplacement of molten magma into older rock underground, where it cools slowly and solidifies to form granite.

Thrust fault

A low-angle reverse fault where compressional forces push one block of rock up and over another.

Constructive Plate Boundary

A boundary where two plates move apart. Magma rises into the gap, cools and forms new crust, often creating mid-ocean ridges.

Hotspot

A relatively fixed area of unusually hot mantle where magma rises and can create volcanoes as a tectonic plate moves over it.

Basaltic lava

Runny, low-silica lava that is usually hot and flows easily, producing broad, gently sloping volcanoes.

Mantle Plume

A column of unusually hot mantle rock that rises towards the surface and may produce a hotspot and volcanic activity.

Stratovolcano

A steep-sided volcano built from alternating layers of lava and ash; its eruptions can be explosive.

Shield volcano

A broad volcano with gentle slopes, built by repeated flows of runny basaltic lava.

Pyroclastic flow

A fast-moving, extremely hot mixture of volcanic gas, ash and rock fragments that rushes down a volcano's slopes.

Volcanic gas emissions

Gases released from magma and volcanoes, including water vapour, carbon dioxide and sulphur dioxide.

Subduction zone

An area at a destructive plate boundary where one tectonic plate sinks beneath another into the mantle.

Focus

The point inside the Earth where an earthquake begins and seismic energy is first released.

Epicentre

The point on the Earth's surface directly above an earthquake's focus.

Fault line

A fracture or zone of fractures in the Earth's crust along which rocks have moved.

Seismic Waves

Vibrations that carry energy away from an earthquake's focus through the Earth and along its surface.

Aftershock

A smaller earthquake that occurs after the main earthquake in the same general area as the crust adjusts.

Transform boundary

A plate boundary where two plates slide horizontally past each other; crust is neither created nor destroyed.

Megathrust earthquakes

Very powerful earthquakes that occur on large, shallow faults at subduction zones, where one plate is forced beneath another.

Earthquake Early Warning (EEW)

A system that detects the first seismic waves from an earthquake and sends alerts before stronger shaking arrives, where time allows.

Base isolation

A building-design technique that uses flexible bearings or supports between a building and its foundations to reduce the transfer of earthquake shaking.