Coastal Hazards - Depositional and Erosional Coastal Landforms Flashcards
Coastlines evolve over time due to the ________ and ________ from breaking waves
erosion and deposition ; breaking waves
This interaction between waves and a landmass can cause the shoreline to slowly move landward, a process referred to as _________
shoreline retreat
Landward migration of a shoreline can also occur when there is a ____________, or when the land itself becomes ____________
rise in sea level ; lower due to subsidence
Accumulations of sediment deposited by waves and longshore currents in the shoreline
Beaches
beaches are deposited by:
waves and longshore currents
t or f: sediments in beaches are well sorted
t
4 main sources for beach sediment:
- Local cliffs and promontories
- The offshore zone
- Calcareous sand and shell fragments from coral and mollusc debris
- Local river bedload material
are elongate deposits of sediment which parallel the
shore and are separated from the mainland by open water, lagoons, tidal mudflats, or saltwater marshes
barrier islands
barrier island are ________ which ________ the shore
deposits of sediments ; parallel
barrier islands are separated from the mainland by:
open water;
lagoons;
tidal mudflats;
saltwater marshes
are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers
tidal flats
is a shallow body of water protected from a larger body of water (usually the ocean) by sandbars, barrier islands, or coral reefs
lagoons
Barrier islands result from the complex interaction between _____, _________, and _________
waves, sea level change, and sediment supply
how does barrier islands form?
wave action causes deposition of sediments offshore forming sand bars, then eventually, enough sand accumulated to form a true island
shoreline retreat is caused by
sea level rise and high erosional processes
Tides move sand within inlets in an ________ manner, creating submerged ________ deltas.
oscillating manner ; ebb-tide
Long narrow ridges of sand
and shingle which project
from the coastline into the
sea.
spit
a beach that is tied to the
coast at one end and free
at the other
spit
spit forms ________ to the longshore sediment drift and ____________ to prevailing wind direction
parallel ; perpendicular
These are depositional
landforms by which an
island becomes attached to
the mainland by a spit or
bar.
tombolo
tombolos are also know as
sandy isthmus
how does tombolo form?
- longshore drift transport material along the coast until the direction changes abruptly or bends
- the materials are then deposited in the same direction seawards, forming a spit
- the spit continues to grow and joins a nearby offshore island, then a tombolo is formed
These are formed when
sand deposited off the
shore dries out and blown
out to the back of the
beach.
coastal dunes
formation of coastal dunes usually need:
large tidal range
broad intertidal zones
large supply of sand
Sites of mud and organic deposition, with quiet waters
lagoons, mudflats, marshes, and mangrove swamps
t or f: lagoons, mudflats, marshes, and mangrove swamps are enclosed by barriers and spits
t
lagoons, mudflats, marshes, and mangrove swamps are formed by combination of _________ and _______
river and coastal processes
are wetlands that form as rivers empty their water
and sediment into another body of water, such as an ocean, lake, or another river
deltas
t or f: deltas cannot empty into land
F (it can but very rare)
Deltas absorb runoff from both ________ and _______
floods (river) and storms (oceans, lake)
t or f: Deltas also filter water as it slowly makes its way
through the delta’s distributary network. This can reduce the impact of pollution flowing from upstream
t
two major ways to classify a delta:
- influences/processes
- shape
four main types of deltas classified by the processes that control the built-up of silt
- wave-dominated delta
- tide-dominated delta
- Gilbert deltas
- Estuarine delta
the movement of waves controls a delta’s size and shape
wave-dominated delta
usually form in areas with a large tidal range, or area between high tide and low tide.
tide-dominated delta
these deltas are formed as rivers deposit large, coarse sediments, are usually confined to rivers emptying into freshwater lakes.
Gilbert deltas
form as a river does not empty directly into the ocean, but instead forms a partly enclosed wetland that contains a brackish water habitat.
estuarine delta
Deltas with this triangular or fan shape are called ________
arcuate (arc-like) deltas
Stronger waves form a _________ , which is more pointed than the arcuate delta, and is tooth shaped.
cuspate delta
A _________ has few, widely spaced distributaries, making it look like a bird’s foot.
bird-foot delta
The distributary network of an ________ is inland, while a single stream reaches the ocean or other body of water.
inverted delta
a type of delta that emptied into a plain, and it extremely rare
inland deltas
An __________ forms as a river develops a new channel, leaving the other to dry up or stagnate. This process is called _________
abandoned delta ; avulsion
a natural process by which flow diverts out of an established river channel into a new permanent course on the adjacent floodplain abandoning the former channel.
avulsion
a rock, sandbar, or other feature lying beneath the
surface of the water
reefs
reef lie how deep below the surface of water?
six fathoms or less beneath low water
a fathom is equal to how many feet?
6
best-known reefs
coral reefs
coral reefs are developed through _______ processes dominated by _______ and __________
biotic ; corals; calcareous algae
underwater structures
made from calcium
carbonate secreted by
corals
coral reefs
coral reefs are often called _____________
rainforests of the sea
Reefs grow best in _____, ______, _______, _____and _______ waters.
shallow, clear, sunny, and agitated waters
Most coral reefs were formed after the _________ when melting ice caused the sea level to rise and
last glacial period
most coral reefs are ___________ years old
<10,000
Coral reefs are found in the_____ away from
__________, ___________ and as
_________
deep sea ; continental shelves; around oceanic islands; atolls
vast majority of oceanic islands that form coral reefs around are ________ in orgin
vocanic
when did Charles Darwin set out his theory about the formation of atoll reefs
1842
charles darwin theorized that ________ and _______ of the Earth’s crust under the oceans formed atolls
uplift and subsidence
3 stages of Atoll Formation (Darwin)
- Fringing Reef
- Barrier Reef
- Atoll Reef
how does atolls form?
Darwin predicted that underneath each lagoons on atoll reefs would be
bed rock base (remains of the original volcano)
Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies and becomes ________________.
white limestone
t or f: Barrier reefs and atolls do not usually form complete circles, but are broken in places by storms.
t
this type of reef is directly attached to a shore, or borders it with an intervening shallow channel or lagoon
fringing reef
a reef separated from a mainland or island shore by a deep channel or lagoon
barrier reef
this more or less circular or continuous barrier reef
extends all the way around a lagoon without a central island.
atoll reef
Marine erosion takes place mainly during
________ and as a result of ________
storms ; wave action
The repetitive _________ slowly breaks the rocks apart and forms a______________ within the cliff face.
hydraulic action ; notch or undercut
t or f: As the notch deepens the overhanging cliff becomes less stable, eventually causing the slope to fail in a mass wasting event
t
In some instances the hydraulic pressure from crashing waves will slowly bore a hole
through a cliff face, forming a____________
sea arch
are points of land that jut seaward and areas where
waves first make contact with land. This causes waves to refract
headlands
observed where a more resistant portion
of the rock remains in the surf, separated from the
retreating cliff
sea stacks
Column of rock standing in the water off a
beach
chimney
where wave erosion has hollowed out a
line of weakness in otherwise resistant promontory
sea arch
are places where waves first
make contact with land and with the
greatest amount of energy
headlands
t or f: in headlands, the energy is high and erosion rate is high
t
As the waves refract around both sides of the
headlands, eroded material is
transported into ________ via ____________ where it is deposited, forming ___________
coves ; longshore current ; isolated beaches
how does an active shoreline transitions into a passive shorelines?
Once tectonic activity ceases, irregular coastlines slowly evolve into passive shorelines with
more low lying terrain and broad, straight beaches. Initially waves break on headlands, forming
longshore current cells that transport eroded material into coves. As the headlands become
smaller, the beaches and longshore cells will eventually merge, forming relatively straight
sections of beach where sediment is transported parallel to shore.
are gently sloping platform of rocks that extend seaward in to a steep drop off.
shore platforms
what are the dominant influences on coastal landforms?
- type of continental margin
- relief, structure, and lithology
- climatic influences
- rates of erosion
- sea level
Edges of actively diverging plates are _________ and ___________, and consequently tend
to be relatively straight with few __________
rifted ; block faulted ; embayments
what type of continental boundaries forms passive margins with continental shelves?
Divergent boundaries
t or f: passive continental margins have thicker sedimentary carapce
t
active continental margin is also called
Pacific Type Boundary
pacific type boundaries are characterized by islands such as
Philippines, Indonesia, and Japan
t or f: pacific type boundaries exhibit continental shelves
F (absent and continental shelf)
in pacific type boundary, structural trend_____________ to the line of convergence
parallel
t or f: pacific type boundary have deep offshore trenches and a line of a mountainous arc
t
passive continental margin is also called
Atlantic-type Margins
atlantic-type margins may have _______ and ______ continental shelves
shallow and broad
Resistant rocks and or tectonically uplifted
blocks form_________with ____________
uplands ; cliffed coastal margins
competent rocks have _________ relief
high
soft rocks exhibit ________ relief
low
The energy available for coastal processes is partially controlled by
- wave height
- wind speed direction
- wind speed duration
High energy coasts tend to have ____________, _____________
rocky beaches ; severely eroded upland coasts
Low energy coasts tend to have _________, _______, or ______
deltas, salt marshes, mangrove swamps
coasts between latitudes of ____________ and _______ facing coasts in the ______________ generally have high storm induced _________
45 to 60 degrees ; east; tradewind belts; swells
energy along waves is influenced by
wind
t or f: high winds = greater wave heights
t
t or f: coastal zone is a rapid zone of change
t
t or f: coasts may advance or retreat in a yearly basis
t
Coastal positions have changed almost constantly through constant cycle of __________ and _____________
glaciation and melting
Present day sea levels can be related into an environment of _______
warm period
