Geo Waves 2 (Processes)

What is a geomorphic process?

A natural (physical/chemical/biological) mechanism that shapes and modifies the Earth's surface over time.

What is the difference between weathering and erosion?

• Weathering breaks down rocks in situ (without moving them).

• Erosion involves the breakdown and movement of rock material by waves, wind, or water

Physical Weathering: What are the 4 types?

1. Freeze-Thaw (water freezes and expands in cracks)

2. Salt Crystallization (evaporated salt expands in pores)

3. Thermal Expansion (heating and cooling stresses rock)

4. Wetting and Drying (clay swells when wet, shrinks when dry)

DEEPER EXPLANATIONS:

FREEZE THAW:

1. Water enters: Rain or sea spray collects inside a pre-existing crack in the rock.

2. Ice expands: When temperatures drop below freezing, the water freezes into ice and expands by ~9% in volume.

3. Wedge effect: The expanding ice exerts pressure on the surrounding rock walls.

4. Melting & Repeating: When temperatures warm, the ice melts, allowing deeper water into the now-wider crack.

5. Breakage: Over repeated freeze-melt cycles, the crack widens until a chunk of rock completely splits off.

SALT CRYSTALLIZATION:

1. Salty water enters: Seawater enters tiny, microscopic pores inside the rock.

2. Water vanishes: Heat or wind evaporates the liquid water, leaving solid salt behind.

3. Crystals grow: As more salty water enters and evaporates, the remaining salt forms growing solid crystals.

4. Internal pressure: The expanding salt crystals press hard against the tiny pore walls from the inside out.

5. Crumbling: Over time, the internal stress forces the outer layer of rock to crumble and then break off, and leave honeycomb-like pits.

THERMAL EXPANSION:

1. Rock heats up: The sun shines directly on the rock during the day, causing the outer layer to warm up and expand (swell outward) due to +KE form +heat.

2. Rock cools down: At night, the temperature drops and the outer layer cools down and shrinks back.

3. Internal stress: Because rock is a poor conductor of heat, only the outer surface expands and shrinks while the deep inside stays the same size. This constant tug-of-war creates internal stress.

4. Different mineral speeds: Rocks made of different coloured minerals expand at different speeds (dark minerals heat faster than light ones), pushing against each other inside the stone.

5. Peeling & Flaking: Over repeated hot-day and cold-night cycles, the outer surface cracks, weakens, and peels off in thin layers (like peeling an onion).

WETTING AND DRYING:

1. Water gets soaked up: Rocks containing clay (like shale or mudstone) get wet from rain, tide, or sea spray.

2. Clay swells up: The clay minerals absorb the water like a dry sponge, swelling outward.

3. Water evaporates: The sun or wind dries the rock out, making the water vanish.

4. Clay shrinks & pulls apart: As the rock dries, the clay loses its water and shrinks (contracts) rapidly, creating tiny internal cracks.

5. Internal stress: Constant swelling when wet and shrinking when dry causes straining of rock.

6. Cracking & Splitting: Over repeated wet and dry cycles, the rock weakens further, snaps along its cracks, and breaks apart into small flakes or fragments (often called slaking).

Freeze thaw weathering:

1. Water enters: Rain or sea spray collects inside a pre-existing crack in the rock.

2. Ice expands: When temperatures drop below freezing, the water freezes into ice and expands by ~9% in volume.

3. Wedge effect: The expanding ice exerts pressure on the surrounding rock walls from inside.

4. Melting & Repeating: When temperatures warm, the ice melts, allowing deeper water into the now-wider crack.

5. Breakage: Over repeated freeze-melt cycles, the crack widens until a chunk of rock completely splits off.

Salt crystallization:

1. Salty water enters: Seawater enters tiny, microscopic pores inside the rock.

2. Water vanishes: Heat or wind evaporates the liquid water, leaving solid salt behind.

3. Crystals grow: As more salty water enters and evaporates, the remaining salt forms growing solid crystals.

4. Internal pressure: The expanding salt crystals press hard against the tiny pore walls from the inside out.

5. Crumbling: Over time, the internal stress forces the outer layer of rock to crumble and then break off, and leave honeycomb-like pits.

Thermal expansion:

1. Rock heats up: The sun shines directly on the rock during the day, causing the outer layer to warm up and expand (swell outward) due to +KE form +heat.

2. Rock cools down: At night, the temperature drops and the outer layer cools down and shrinks back.

3. Internal stress: Because rock is a poor conductor of heat, only the outer surface expands and shrinks while the deep inside stays the same size. This constant tug-of-war creates internal stress.

4. Different mineral speeds: Rocks made of different coloured minerals expand at different speeds (dark minerals heat faster than light ones), pushing against each other inside the stone.

5. Peeling & Flaking: Over repeated hot-day and cold-night cycles, the outer surface cracks, weakens, and peels off in thin layers (like peeling an onion).

Wetting and Drying:

• Water gets soaked up: Rocks containing clay (like shale or mudstone) get wet from rain, tide, or sea spray.

• Clay swells up: The clay minerals absorb the water like a dry sponge, swelling outward.

• Water evaporates: The sun or wind dries the rock out, making the water vanish.

• Clay shrinks & pulls apart: As the rock dries, the clay loses its water and shrinks (contracts) rapidly, creating tiny internal cracks.

• Internal stress: Constant swelling when wet and shrinking when dry causes straining of rock.

• Cracking & Splitting: Over repeated wet and dry cycles, the rock weakens further, snaps along its cracks, and breaks apart into small flakes or fragments (often called slaking).

Chemical Weathering: What are the 5 types?

1. Carbonation (acidic rain dissolves limestone)

2. Oxidation (oxygen reacts with iron to rust rock)

3. Solution (minerals dissolve directly in water)

4. Hydrolysis (acidic water breaks down silicate minerals)

5. Hydration (minerals absorb water and swell)

CARBONATION (Acid rain melting limestone)

• Acidic rain forms: Rain absorbs carbon dioxide from the air and turns into weak carbonic acid (like plain fizzy water).

• Rain hits the rock: This acidic rain falls onto rocks made of calcium carbonate (like limestone or chalk).

• Chemical reaction: The acid reacts with the rock, changing solid stone into liquid calcium bicarbonate.

• Rock dissolves: The rock completely dissolves into the water and gets washed away, carving out big gaps and underground caves.

OXIDATION (Iron in rock rusting away)

• Oxygen touches rock: Oxygen in the air or water mixes with rocks that contain iron.

• Rust forms: The iron and oxygen react together, turning the iron into iron oxide (literal rust).

• Rock turns brown and weak: The rock changes color to rusty red or brown, making the metal inside crumble.

• Rock collapses: The hard structure crumbles apart, making the whole rock soft and easily broken by waves or rain.

SOLUTION (Minerals melting in pure water)

• Water hits rock: Pure water touches rocks made of easily dissolved minerals/

• Minerals dissolve: The minerals break apart instantly and vanish directly into the liquid

HYDROLYSIS (Acidic water breaking down clay-like minerals)

• Acidic water enters: Slightly acidic water soaks into rocks containing silicate minerals (like granite).

• Chemical swap: Hydrogen in the water reacts with the rock's minerals, completely changing their chemical structure.

• Rock turns to soft clay: The hard minerals break down and weaken, as a result crumbles into loose grains of sand and mud

HYDRATION (Minerals absorbing water and swelling)

• Rock absorbs water: Dry rock minerals soak up liquid water right into their own crystal structure.

• Minerals swell up: As they take in the water, the minerals expand, getting bigger and heavier (like a dry sponge expanding in a bucket).

• Internal stress: The expanding minerals push hard against the rest of the rock from the inside.

• Rock cracks open: The constant stress weakens the rock until it snaps, cracks, and breaks apart into pieces.

Biological Weathering: What are the 2 types?

1. Plant Root Action (roots grow in cracks and split rock as they become bigger, or as tree falls it breaks and rips out rock from ground)

2. Organic Chemical Action (decaying matter releases acids that dissolve rock)

What is Regolith?

The loose layer of un-consolidated soil, weathered rock, and sediment sitting on top of solid bedrock.

Mass Movement: What is Sediment Transfer?

• The gravity-driven downhill movement of regolith from upper cliff sections down to the shoreline; basically what mass movement achieves.

• regolith: The loose layer of un-consolidated soil, weathered rock, and sediment sitting on top of solid bedrock.

Mass Movement: What is a Rockfall?

• Rapid free-fall of individual rock blocks from steep cliff faces, usually triggered by freeze-thaw weathering.

Three types of mass movement:

Rockfall

slide

slump

What is the difference between a Slide and a Slump?

• Slide: Downhill movement of sediment along a flat/straight slip plane.

• Slump: Rotational movement of saturated rock along a curved slip plane.

Wave Processes: What is Abrasion?

• Waves throwing sand, pebbles, and rocks against cliff faces, scraping the rock down like sandpaper.

Wave Processes: What is Attrition?

Rocks and pebbles carried by waves crashing into each other, becoming smaller, smoother, and rounder.

Wave Processes: What is Hydraulic Action?

1. Wave slams in: Wave crashes into a cliff, trapping and compressing air inside cliff cracks.

2. Pressure blasts out: As the wave pulls back, the squeezed air violently expands outward.

3. Rock shatters: This repeated pressure widens the crack until chunks of stone completely break off.

Wave Processes: What is Pounding?

The heavy mass and weight of large breaking waves crashing directly onto cliff faces, exerting huge pressure.

Wave Processes: What is Solution (Corrosion)?

Weakly acidic seawater dissolving soluble minerals within coastal rocks like limestone or chalk.

Sediment Transportation: What are the 4 marine methods?

• Solution (dissolved minerals carried as ions); Acidic seawater dissolves rocks like limestone or chalk, breaking the solid rock down into invisible, charged particles called ions

• Suspension (fine silt/clay held up/float in mid-water)

• Saltation (coarse (rough/raggedy) sand/pebbles bouncing on the sea floor)

• Traction (large boulders rolling along the sea floor)

How does Longshore Drift (LSD) work?

1. Waves arrive at an angle: Prevailing (dominant) winds blow waves towards the beach at an oblique angle (e.g., 45 degrees).

2. Swash pushes sediment up: As the wave breaks, the swash carries sand and pebbles diagonally up the beach at the same angle as the wind.

3. Backwash pulls sediment straight down: Gravity pulls the backwash (and the sediment) straight down the beach slope at a 90-degree angle to the coastline.

4. Zig-zag movement repeats: Over continuous wave cycles, sediment gets transported along the coast in a clear zig-zag pattern, shifting material from one end of the beach to the other.

What are the 5 situations where coastal deposition occurs?

• Entering sheltered bays or coves.

• Sudden drop in water depth (higher seabed friction).

• Reduced wave energy / calmer weather.

• Change in coastline shape (e.g., river mouth forming a spit); As waves reach sheltered water past a bend or river mouth, they lose energy and drop their sediment in a straight line, triggering deposition that builds a spit

• River fresh water meeting ocean salt water (flocculation); Salt forces light clay particles to clump into heavy masses that quickly sink to the seabed, causing heavy deposition of fine mud at the river mouth.

Deposition: What is settling velocity?

The minimum speed water needs to keep a particle moving; below this speed, the particle settles to the seabed.

How does particle size affect settling velocity on a log scale?

Larger, heavier particles (boulders/gravel) have a HIGH settling velocity and drop quickly as wave energy falls. Smaller particles (clay/silt) have a LOW settling velocity and remain suspended longer.

Fluvial Processes: How do rivers impact the coast?

Rivers erode inland rock, transport huge sediment loads, and deposit material when entering the sea to form deltas and mudflats.

Aeolian Processes: How does wind shape dunes?

Wind erodes by abrasion, transports dry sand via saltation/suspension, and deposits sand when wind speed drops or hits marram grass (tall; forms sand dunes as a result; reduces wind blown sand energy so it drops and builds up at marram grass)