Physical Geography - Landforms and Processes

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The scientific theory that Earth's lithosphere is divided into large plates that move slowly (a few cm/year) over the asthenosphere. Their interactions cause earthquakes, volcanoes, and mountain building.

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Convergent: Plates move toward each other (subduction or collision). Divergent: Plates move apart (ocean ridges, rifts). Transform (conservative): Plates slide past each other horizontally (e.g., San Andreas Fault).

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Plates collide. If oceanic meets continental: oceanic plate subducts (sinks), forming a trench and volcanic arc. If continental meets continental: fold mountains form (e.g., Himalayas).

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Plates move apart, creating a gap. Magma rises to fill it, creating new oceanic crust. Forms mid-ocean ridges (e.g., Mid-Atlantic Ridge) or rift valleys (e.g., East African Rift).

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Where a denser oceanic plate sinks beneath a less dense plate into the mantle. Creates deep ocean trenches, volcanic arcs, and earthquakes. Example: Pacific Ring of Fire.

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A 40,000 km horseshoe-shaped zone around the Pacific Ocean with ~75% of Earth's volcanoes and ~90% of world's earthquakes. Caused by multiple subduction zones surrounding the Pacific Plate.

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Both measure earthquake magnitude. Richter scale: Older system, each unit = 10× more ground motion. Mw (Moment Magnitude): More accurate modern scale used for large earthquakes. Both are logarithmic.

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Focus (hypocentre): The underground point where the earthquake originates. Epicentre: The point on the surface directly above the focus — where shaking is usually strongest.

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Shield: Low, broad, gentle slopes. Basaltic lava, non-explosive. Example: Mauna Loa, Hawaii. Composite: Steep-sided, cone-shaped. Alternating lava and ash layers, violent eruptions. Example: Mount Fuji, Vesuvius.

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Hydraulic action: Force of water breaks rock. Abrasion: Rock particles scrape and wear the channel. Attrition: Rocks collide and break into smaller pieces. Solution (corrosion): Water dissolves soluble rocks.

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Traction: Large boulders rolled along the bed. Saltation: Pebbles bounced along the bed. Suspension: Fine particles carried within the water. Solution: Dissolved material carried invisibly.

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Forms when a river flows over a band of hard rock overlying softer rock. The softer rock erodes faster, creating a step. Hydraulic action undercuts the hard rock, forming an overhang that collapses — the waterfall retreats upstream.

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A crescent-shaped lake formed when a river meander is cut off. As a meander tightens, the river breaks through the neck during a flood, taking a shorter path. The old loop is sealed by deposition, forming an ox-bow lake.

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A landform at the mouth of a river where sediment is deposited as the river slows entering the sea. Arcuate (fan-shaped): e.g., Nile Delta. Bird's foot: e.g., Mississippi Delta. Cuspate (tooth-shaped): e.g., Ebro Delta.

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Waves trap and compress air in cracks in the cliff face. When the wave retreats, the compressed air expands explosively, breaking off rock fragments. Also called wave quarrying.

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The zigzag movement of sediment along a coastline. Waves approach at an angle (driven by prevailing winds), carrying sediment diagonally up the beach. Backwash returns sediment straight back down the beach.

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A long, narrow ridge of sand or shingle extending from the coast into the sea or across a river mouth. Forms by longshore drift depositing material beyond a headland or change in coastline direction. Example: Spurn Head, UK.

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Plucking: Meltwater freezes around rock fragments, which are pulled away as the glacier moves. Abrasion: Rock fragments embedded in the glacier's base scratch and grind the valley floor, smoothing it.

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A wide, flat-bottomed, steep-sided valley formed by a glacier. Glaciers erode by plucking and abrasion, transforming a V-shaped river valley into a U-shape. Example: Yosemite Valley, USA.

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Physical (mechanical): Rock broken without chemical change (e.g., freeze-thaw, thermal expansion). Chemical: Rock altered by chemical reactions (e.g., carbonation dissolving limestone). Biological: Organisms break down rock (e.g., tree roots, lichens).

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Water enters cracks in rock and freezes, expanding by ~9%, widening the crack. Repeated freezing and thawing progressively breaks the rock into angular fragments (scree). Common in mountain and periglacial environments.

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A long, narrow, deep inlet carved by a glacier that has since retreated and been flooded by the sea. Characterized by steep cliff walls. Famous examples in Norway, New Zealand (Milford Sound), and Chile.

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The downhill movement of rock, soil, or debris under gravity. Types include: rockfall (free fall), landslide (sliding along a plane), slump (rotational sliding), mudflow (fluid movement of saturated debris).

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A threshold beyond which a system rapidly shifts to a new state that may be difficult to reverse. Example: Arctic ice melting reduces albedo, causing more warming — a positive feedback loop.

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All the land that drains into a particular river system. Separated from adjacent drainage basins by a watershed (ridge of high land). Includes the river and all its tributaries.