Coastal Landforms & Deserts

atoll (WOWOWWOWOWO)

pacific circular reef enclosing a lagoon

how are coastal landforms formed?

tides + ocean currents transport huge amounts of solid material that have been eroded from land

reg

a hamada (desert pavement) that has a covering of pebbles + gravel on the top
→ lowkey just looks like a bunch of rocks on flat ground

what is a key feature when determining coastal features?

nature of the rock
→ e.g. hard rock resists erosion

wave action

slope of coast

change in sea lavel

coral formations

glaciers (fjords)

volcanic activity (determines rock type + mass wasting?)

human actions

what causes a wave to form

the wind blowing on the surface on the ocean

arches

formed by 2 caves on opposite sides of a headland

sea caves

formed by waves eroding a line of weakness along the headland

• corrasive action + hydraulic action

• opens up to form a large hole in the headland

offshore bar

a submarine bar built above surface of water

• hinders commercial ships

• made up of sand, gravel

• formed by wave deposition in emergent coastlines

  • the more gradual slope allows waves to break far off from shore; thus sediment is deposited in the ocean before it hits the beach. over time, this builds an underwater ridge until it reaches the surface

raised beach

land that used to be below sea level (due to eustatic rise in sealevel after glacial retreat), and is now above the sea level (due to isostatic rebound)

lagoon

an enclosed “lake” of salt water

→ lies behind an offshore bar

shorelines of emergence

land is rising, water is becoming more shallow

significance of shorelines of emergence to humans

• not good for deep harbours for ports

• lots of sand bars inhibit commercial shipping

• raised beaches + newly emerged coastal plains are good for agriculture or beaches

  • lagoons great for tourism & resorts!

what are these landforms? (1, 2, 3)

1. off-shore bar

2. lagoon

3. submarine bar

submarine bar

• made up of sand, gravel

• formed by wave deposition

ria coastline

a drowned, V-shaped valley

→ narrow, long, deep inlet

shoreline of submergence

land is sinking + water is rising

fjord coastline

a drowned U-shaped valley
→ narrow, long, deep inlet

eg. coast of BC or Norway

spit

a low, narrow ridge of sand or pebbles that is connected at one end to the land

• occurs bc of longshore drift

• may occur along bays or at the mouth of a river

  • become hooked over time if the waves come to the shore at an oblique angle

  • if this extends across the mouth of a river, the river either is diverted around this ridge or the river forms a lagoon

tombolo (image depicted is NOT geo, it’s a bolo bun)

a sandbar that connects an island to the mainland

bay mouth bar

spit that goes all the way across a bay
(we rhyming wow)

significance of submerged shorelines for humans

• irregular coastline/features

  • hinders land transportation along the coast

  • deep harbours good for shipping + ports

• rough terrain hinders human settlement

coral reef

• occurs in warm tropical waters

• living creatures produce exterior skeletons

  • skeleton is made of calcium carbonate

    • when these creatures die, the next generation can grow on top of the old skeletons

      • → cycle of continual growth

• these skeletons are a superb habitat to encourage biodiversity

give an example of a coral reef

The Great Barrier Reef of Australia

longitudinal coastline

folded mountains are parallel to the coastline

what type of coastline is this

longitudinal

what type of coastline is this

ria

bajada

coalesced alluvial fans at base of a mountain/mouth of a canyon

playa lake

small lakes underlain with alluvium & crusted with salts

• usually formed at outer edge of an alluvial fan

• the water runs past the alluvial fan to fill up a depression & create the lake

• usually salty (brackish) water due to rapid evaporation in the desert

  • Note: a playa is a dry lake bed

why are alluvial fans often found in deserts

during flood stage, rivers in the desert are full of sediment & alluvium.

• when this fast moving river suddenly moves from a steep mountain to a flat and open plain, it drops its load and creates an alluvial fan

• a continuous group of merged alluvial fans is called a bajada

erg

an expanse of sand-dune topography

• i.e. sandy parts of deserts

• not all deserts are fully erg, bc some parts can have exposed bedrock bc the sand was stripped away by the wind

  • e.g. only 30% of Sahara Desert is covered with dunes (erg)

mesa

flat-topped elevated platform

• has protective layer of limestone

• separated from the main plateau (eroded remnant?)

butte

smaller isolated mesa

• formed due to erosion

what is a desert

• <250 mm annual precipitation per year

• large difference btwn rate of evaporation and rate of precipitation

  • i.e. “the annual rainfall is not sufficient to maintain a continuous cover of vegetation” - Mleziva, Resource Binder

sandblasting or windblasting

• when strong desert winds pick up tiny rock fragments and carrthem with great force, producing unique rock structures

  • aeolian transport

• requires a lack of vegetation which usually:

  • restricts air movement

  • anchors the soil

• effectiveness influenced by:

  • wind speed

  • hardness + quantity of sand

  • hardness of rock being eroded

dune synonym

drift

what is a dune

a pile of sand formed by an obstacle that blocks the wind

• obstacle causes the accumulation of sand next to it

synonym for drift

barkhan/barchan

a crescent shaped dune

• most common dune shape

why are some parts of the desert not covered with sand dunes?

wind action (aka aeolian erosion? aeolian transport??) can strip sand away from a large area along the desert.

→ this exposes the bedrock

→ creates hamadas

hamada

a large area of rough rock “pavement”
similar to reg but not entirely the same (regs have a layer of pebbles on top)

True or False: Deserts receive very little rain, but if it happens it is in the form of light showers

FALSE.

Although deserts rarely receive rain, when they do, it is often in the form of very strong torrents that produce thunderstorms + flash floods

• lack of vegetation also increases the intensity of these flash floods bc there is no barrier to slow down runoff

  • lack of vegetation also causes the water rapidly flowing down desert slopes to tear large gashes

what is a drift

a pile of sand formed by an obstacle that blocks the wind

• obstacle causes the accumulation of sand next to it

synonym for dune

wadis

wide, dry ditches

• formed after rainstorm water evaporates

• aka a wide, flat DRY river valley

  • only has water after infrequent storms

bajada

a continuous, broad, band of alluvium

• formed from multiple alluvial fans merging into one

salt flat

a dried up playa lake

• e.g. Salt Flats of Utah

bolson

a large desert basin that is slowly filling up with debris

plateau

a region that has a protective cap rock layer that prevents the rock underneath from being eroded by wind

• eg. limestone, granite are both resistant to physical weathering!

canyon

deep river valley

• formed by a large permanent river eroding through the protective cap of a plateau

• lack of tributaries causes an absence of gullies/rills along the sides of the valley

  • eg. Grand Canyon, Colorado River

the bAdLaNdS

heavily eroded plateau after the protective limestone cap has been worn away

• underlying layers are soft so highly susceptible to erosion

• forms gullies, ridges, ravines, tall pillars of resistant rock

• eroded by water in semi-arid climate

talus synonym + context in a desert?

scree
the rock fragments left at the base of a cliff

loess (desert context?)

wind-blown piles of finely-sorted rock sediment

• mostly silt + clay

• found on leeward/rainshadow side

• e.g great loess deposits of Northern China + Argentina

deflation

a gradual lowering of the land due to the removal of materials by wind in the desert

saltation (desert context?)

sands move by leaping and skipping across surface of sand, when pushed by the wind

surface creep

sands bump into one another, causing each other to move forward

• analogous to attrition except the sands are not eroding each other, but merely moving each other

suspension (desert context)

so ppl know how most sediment is transported in the difficult climate of the desert

corrasion

dust particles or rocks hit each other to speed up process of erosion

exfoliation

• needs large range of temperature

• rapid fluctuations btwn day and night temps

  • minerals in separate layers expand at dif. rates → layers separate → layers peel off

stack

an isolated pillar of the cliff face that forms when an arch collapses

• formed in hard rock

• corrasion + hydraulic action

• waves refract (bend) to target this protruding piece of rock → there so much more erosive power

define load and describe what it is composed of

the mix of materials carried by breaking waves on a beach.

• sand

• shingles

• mud

what are the sources of load

• rivers leading into the sea

• wave erosion

• mass wasting off of cliffs

undertow

an underwater current that pulls water from the shore back into the ocean

• occurs during high tides to balance out the piling up of water

  • not the same as a rip tide bc its not as strong

  • not the same as a backwash bc its under the surface of the water

wave cut platform

the flat landform formed by deposits from the cliff face as it is undercut by the waves (thru attrition, abrasion, hydraulic action)

**note: if this land is uplifted, it creates a ______ ____ _________

wave refraction

when a wave approaches a headland that is protruding from the shoreline, the waves slow down and bend to concentrate around this point

• occurs bc headlands have shallower water around them compared to the rest of the bay at that distance from the shore

  • waves slow down in shallow water + wave length shortens only in the area around the headland

  • the waves in the middle of the bay continue at the same speed as before → bending around headland

sheet flooding

occurs during heavy precipitation where the water covers the entire ground surface and flows as one body

• carries a vast amount of sediment rapidly

pediments

a bedrock plain with little to no soil cover

• starts at the base of steep mountains and gently slopes into the center of desert basins

• formed by erosion

define coast

the piece of land before the highest water level

define shore

the region between the highest and lowest water level of waves

define beach

the assortment of sand & pebbles along a coastline that were deposited there by waves

top of wave

crest

bottom of wave

trough

what factors determine the power of a wave

• fetch (distance of open water that the wind travels)

• strength of wind (aka wind speed)

fetch

the distance of open water that a wind blows over to create a wave

• bigger fetch = bigger waves

TRUE OR FALSE: Waves in the open sea are formed by currents of moving water

False.

1. Waves don’t actually move water - they move energy.

→ The water only actually moves forward when it crashes near land.

2. Currents do not form waves

→ the wind blowing across the water creates waves

This diagram depicts wind blowing over the surface of the sea, forming a wave. At which of the layers of air is friction the lowest?

the top layer has the lowest friction

this wave is increasing in height. what does that say about the water depth at this location?

the water depth is getting shallower, thus:

• the circular motion of the wave is flattened and slows down

  • waves behind this one catch up to the slowing wave and amplify its height

    • a taller wave is formed, which eventually falls forward on itself and crashes

what are 3 types of coastal erosion

• attrition

• hydraulic action

• corrasion/abrasion

desricbe how hydraulic action erodes away at cliffs

the force of the water pushes into cracks in the cliff face

• air inside these cracks is compressed

  • then, the water exits and the air rapidly expands from the decrease in pressure → shatters rock on cliff face

describe how attrition erodes away at cliffs

boulders and pebbles in the waves are dashed against each other + the beach.

• this weathers them into finer particles

describe how corrasion/abrasion erodes away at cliffs

waves carrying pebbles, boulders, and sand slam into the cliff

• these rocks undercut the cliff

destructive vs constructive waves

destructive:

• backwash » swash

• erosional

• >9 waves/min

• tall waves crash down on beach

• steep, rocky beach

constructive:

• swash » backwash

• depositional

• <=9 waves/min

• short waves break on beach

• gradually sloped sandy beach

groyne

perpendicular to coastline; blocks longshore drift
- must be able to tell which side wind came from by looking at distribution of sand btwn these sections

breakwater

parallel to coastline, in the water

→ blocks strong tides + protects moored boats behind it

seawall

reduces coastal erosion; parallel and adjacent to coastline
→ downsides: no beach

which direction is longshore drift moving in?

away from the camera

features common to submerging coastlines

drowned valleys

• u-shaped = fjord

• v-shaped = ria

headlands

bay beaches

stacks

caves

arches

spits (common to both)

features common to emerging coastlines

offshore bars (forms bc the beach gradient is so gradual that waves crash long before reaching the shore → sediment is deposited where the wave crashes)

lagoons

raised beaches

wave-cut platforms & terraces

spits (common to both)

mud flat vs salt flat

mud flat:

• coastal feature

• created in an enclosed or partially enclosed area of water

• made of silt + clay

• regularly flooded by ocean tides (so it has salt water)

• eg. estuary of a ria or in a lagoon

salt flat (aka salt pan)

• desert feature

• formed by a dried out playa

• leaves behind a flat, salt-encrusted layer

synonym for salt flat

salt pan

what is this

salt flat

bolson

the term for the entire desert basin that is slowly filling up with debris

wadis

a dried up desert valley; only has water during flash floods

hamada

aka reg
desert pavement

made up of large stones + boulders after all of the smaller pebbles have been blown away by the wind
(aeolian action)

what kind of weathering is this?

abrasion/corrasion

how to tell if smth if butte or mesa?

butte is taller than it is wide, mesa is wider than it is tall

why are the badlands so easily eroded?

they don’t have a cap rock to protect the softer rock underneath

synonym for hamada

reg

canyon

a deep and wide river valley formed by a massive, permanent river cutting through the cap rock

• sides are uneroded and relatively smooth due to lack of tributaries

• deserts only have large rivers passing through bc of flash floods, no regular rainfall

what direction is the wind originating from? thus, what would the name of this wind be if u name it according to the direction it came from?

explain which side of a barchan receives deposition, and which receives erosion, and why

the windward side receives erosion because the wind moves sand up the slope constantly

on the lee side, the wind slows down and drops/deposits some of its load because this side is slightly shielded from the wind. the horns are formed curved bc the wind moves sand faster at the edges where there is less sand.

TRUE OR FALSE: abrasion can refer to wind erosion

TRUE.

although wind is not the most powerful form of erosion in the desert, it can pick up sand and use the sand to erode at rocks.

eg. pedestal rocks