Coastal Flashcards Preview

Geo 101 > Coastal > Flashcards

Flashcards in Coastal Deck (64):
1

Neap Tide

Less tidal range than Spring Tide
& 1/2 and 22 day marks
Sun and moon are in quadrature (90 degrees out of phase)

2

Spring tide

Larger tidal range than Neap tides (lower low and higher high tides)
1 and 15 day marks
Occurs when sun and moon are in conjunction or opposition

3

Diurnal Inequality

Two high tides and two low tides of unequal sizes in the same day
Measured in difference of height between two successive low or high tides

4

Apogee

When the moon is furthest from the earth

5

Perigee

When the moon is closest to the Earth

6

Tidal Range

The vertical distance between the high tide and the succeeding low tide.

7

Wave Base

equals half the wave length.
wave motion affects water particles up to this depth
WB not in contact with sea floor = deep water
WB in contact = shallow water

8

Surf Beat

the alternating arrival of higher and lower sets
(can either result in long lulls or rouge waves when crests and troughs align)

9

Stokes' Drift

something sitting on the surface will move forward along the wave

10

Wave Length

Distance between successive waves

11

Wave Period

Time between successive waves
(easiest to measure

12

Spilling Waves

Shallow flat beach (piha)
Waves break a long way out
Wide surf zone

13

Surging Waves

Very steep beach (Napier)
Waves dont encounter sea floor until last minute

14

Infragravity Waves

Water trapped in the swash zone (btw 1st breaking wave and swash zone)
long period, low frequency (100 secs wave period)
moving back and forth, sea surface going up in down like when you hop into a bath tub
Results in the odd wave that travels further up the beach

15

Wave Refraction

Waves bending in response to different wave depths
Affects the distribution of wave energy on the shoreline
As a wave refracts more it becomes more parallel to the shore

16

Wave Diffraction

Wave crests are broken into segments and redirected by an obstacle
Wave shadow (quiet water) is created behind the obstacle some wave energy may leak into shadow area
After obstacle wave segments may recombine

EG: Rabbit island and A frame

17

Wave Reflection

Waves bounce or reflect off a shoreline
may result in an edge wave that travels along the shore (backwards waves colliding with wave then travelling parallel to shore)

18

Longshore Feeder Currents

carry water along beach into rips

19

Longshore Currents

Wave induced current flowing parallel to shore in breaker zone
velocity of longshore current increases as the angle of the wave approach increases and wave height increases
Can skew rip systems

20

Mass Transport

Slow onshore movement of water

21

Rip Head

seaward end of rip current

22

Bed return flow

transports sediment offshore / undertow
always present under breaking waves
fed by water carried to the shore by breakers

23

Swash Zone

upper part of the beach that is alternatively wet and dry

24

Dissipative beach

High energy
Flat gradient
Wide surf zone
Smaller sediment
Spilling waves

25

Reflective beach

Low energy
Steep gradient
Very narrow surf zone
Larger sediment
Surging waves

26

Winter (storm) profile

High storm waves
Offshore Sand transport
Beach erosion
Longshore Bar Accretion
Low beach gradient

27

Summer (swell) profile

Regular, low wave conditions (swell)
Onshore sand transport
beach construction
Berm build up
Steep beach gradient

28

Percolation

the rate at which water will pass through a sediment
Greatest for coarse materials and less for finer materials

29

Berm

swash deposition
nearly horizontal
often slopes away from sea opposite to beach face

30

Angle of repose

angle at which loose material can maintain a slope (due to internal friction)
Dry sand = 30 - 34 degrees

31

Storm Surge

pressure set up + wind set up (most damaging when combined with high tide)

32

Flocculation

-clay and silt particles have negative ions
-remain individual ions in fresh water
-saltwater has positive ions (Ca, Mg, Na)
-the particles bind together in salt water due to the electrical attraction
-thus come out of suspension and sink to the floor creating mud

33

Residual Current

more dominant in a partially mixed estuary where there is a lot of mixing
(potentially look at lab material and assessment to find more)

34

Turbidity maximum

Suspended fine sediment from both directions/ sources meeting in the middle
Occurs at the limit of salt water

35

Shore platform

Rock surface that forms at mean tidal level
is foot of the cliff
is left behind as rocky coast erodes
Erodes quickly due to the tides causing water-layer weathering (alternate wetting and drying = expansion, contraction, break up of rock)

36

Bio-erosion

Caused by marine organisms (invertebrates)
either Chemical (dissolving)
or Mechanical (burrowing)

37

Mass movement

The erosion of the a rocky coast can take place over a long period of time but mass failure can occur changing the coast suddenly

38

Salt water PPT

35 ppt

39

Fresh Water PPT

0-0.5 ppt

40

Thermal expansion

surface of ocean expands due to heat
hence the water at the equator is elevated as it is warmer

41

Glacio-eustasy

global rise and fall in sea level caused by melting and expansion of ice sheets

42

Glacio-isostasy

rise and fall in land caused by melting/expansion of thick ice sheets
Isostatic rebound
(weight of ice on land depresses land into fluid mantle (sinks) ... when ice melts weight is lifted and the crust moves/ rebounds back up)
Rebound is greatest in the centre and decreases towards the coastline
coast effectively sink which means sea level rises

43

Transgression

Coastal retreat
as the sea level rises the coastline retreats landwards taking sediment with it. New beaches forming and old coastal features left behind

44

Regression

Coastal advance
As sea level falls the coastline is able to advance
(also occurs when sea level is stable when there is an abundance of sediment)

45

Pleistocene

10,000 to 1.8 million years ago

46

Holocene

present to 10,000 years ago

47

Key dates and facts?

-1870 we started recording sea level
-Auckland sea level has risen 16cm in last century
-18000 yrs ago the sea level was 120 meters lower than today
NZ and Aus sea level has risen 1.3m per century since the last glacial period
Sea level reached it current positon 6000 yrs ago (sea level stillstand)

48

Wind set up

results in surface tension between air and water over a distance (fetch) will produce a wave (longer distance = longer wave)

49

Pressure set up

Storm = low pressure system
low = less weight pressure holding down water = elevated sea
high = more weight/ pressure = calmer less elevated sea

50

Storm surge

wind set up + pressure set up
most damaging at high tide

51

Sea wall

to build a large wall to protect the land behind the beach (hard structure approach)
rubble is often put in front of wall to prebreak the waves
Work by reflecting destructive wave energy
Problems:
can result in beach loss reducing deposition of sediment in normal conditions

52

Groyne

The construction of a structure perpendicular to the shore
Designed to catch sediment moving alongshore (hard structure)
Slow longshore currents that carry sand = less sediment carried = sand is trapped and deposited.
Problems:
While sand collects on the updrift side, the downdrift side is deprived of sand

53

Breakwater

To protect the shoreline by creating a structure that reduces incident wave energy (also used to create artificial harbours, surfing reefs)
hard option

54

Beach Replenshment

To replace lost sediment by placing new sediment on the beach (soft option)
however it is only
Problems:
Temporary, needs to be carried out periodically
Expensive
Sand has to come from somewhere and needs to be a constant supply
(can be cost effective when paired with existing estuary dredging programmes)

55

Dune Rehabilitation

Replanting sand dunes to help recreate natural dune systems
have fences and access tracks to protect dune vegetation
Vegetation stops sand from blowing away
Popular soft form of CM as it involves communities

56

Accommodation (in the context of coastal management)

learning to live with sea level rise and coastal inundation (elevating buildings, coastal warning systems)

57

Set back zone

minimum distance from the shoreline for infrastructure to be built
Problems:
difficult to do in already developed land also not very popular

58

Mixed Layer

the upper part of the ocean (in direct contact with the atmosphere)
Approx 50 meters deep (varies, seasonal changes)

Characterised by nearly uniform properties (temperature, salinity etc)
Dramatic increase in salinity and decrease in temperature as you travel deeper

seasonal variation has consequences on marine life. During summer they thrive but in winter there are more storms = more wind = more mixing = deeper mixed layer = phaeto plankton sink too deep and get less sunlight.

59

Coriolis Force

created by the earths rotation whereby moving objects (winds, tides, ocean currents) are deflected left or right
Northern Hemisphere = deflect to the right
Southern Hemisphere = deflected to the left
only appears on large bodies of water

60

Subtropical gyre

huge circular surface currents
-North Pacific
-North Atlantic
-South Pacific
-South Atlantic
-Indian Ocean
Ekman Transport and winds (trades and westerlies) piles up water approx 2m high = subtropical gyre
returns warm water towards poles

61

Gulf Stream

an example of a western boundary current
Water in subtropical gyres is returned to poles along westen boundary currents
they are strong (1-2 m/s)
narrow (100 - 200 km)
and warm (moving water from tropics to the poles

this explains why places like the UK are warmer than Alaska despite being at a similar latitude. Due to gulf stream going past UK radiating heat to surroundings

62

Antarctic Circumpolar Current

Flows clockwise around Antarctica
Keeps warm water away from Antarctica (vital to prevent ice melting)
Connects all oceans and is principle pathway of exchange

63

Thermohaline circulation

deep ocean current (influence 90% of ocean)
returns oxygen to deep water and brings nutrients to the surface
very slow 10 - 20 km per year

hIgh salinity water cools and sinks in north atlantic
flows along deep ocean currents
upwells and returns to surface in indian and pacific oceans

64

Bathymetry

Under water topography
eg affects deep water currents