waves

Question 1

how do waves work

Answer 1

they propagate energy thru a medium (ocean water)

Question 2

how do water particles move during a wave cycle

Answer 2

forward-circular motions, yet they remain in place

Question 3

generating forces of waves

Answer 3

• wind
• geological events
• gravitational pull of moon

Question 4

restoring forces of waves

Answer 4

• surface tension (L < 1.7cm)
• gravity (L > 1.7cm)

Question 5

what generates seiches?

Answer 5

• changes in atmospheric pressure
• storm surges
• tsunami
• meteor impacts
• seismic forces
• L = 1km

Question 6

what generates tsunamis?

Answer 6

• volcanic eruptions
• landslides
• vertical plate motion at a subduction
  zone
• L = 200km

Question 7

what generates tides?

Answer 7

the rotation of the earth, moons gravitational pull
L = 20,000km

Question 8

deep water waves

Answer 8

d > 1/2L
c = 1.25sqrt(L)
c = 1.56T

Question 9

shallow water waves

Answer 9

d < 1/20 L
c = 3.1sqrt(d)

Question 10

waves break when…

Answer 10

in open ocean: H/L > 1/7
in shallow water: when H/d = 3/4 or H/L > 1/7, whichever happens first

Question 11

factors needed to produce big waves

Answer 11

1. fast wind
2. sustained wind
3. long fetch

Question 12

maximum sea state

Answer 12

fully developed sea

Question 13

rogue waves

Answer 13

• 3-4 times higher than surrounding waves
• generated by constructive interference
• appear and disappear quickly

Question 14

seiche definition

Answer 14

standing wave in a partially or fully enclosed basin

Question 15

longer basin length ->

Answer 15

longer standing wave period

Question 16

natural resonant period

Answer 16

determines period of seiche based on size, depth and contour of lake
T(s) = 0.64L/sqrt(d)

Question 17

tsunamis occur from…

Answer 17

large input of energy affecting water mass
most occur in ring of fire

Question 18

tsunami characteristics

Answer 18

L ~ 200 - 400km
T ~ 10min - 1hr
c ~ 200m/s or 720km/hr
c = 3.1sqrt(d)
H ~ 0.5 - 1m
steepness H/L ~ 0.00002 -> almost flat
tsunamis are always shallow water waves

Question 19

why are tsunamis so destructive?

Answer 19

bc speed decreases and height increases as waves approach shore

Question 20

wind waves vs tsunami

Answer 20

short L & T vs long L & T
water particles rotate in circles vs water flows straight forward

Question 21

when do the effects of a tsunami worse in an enclosed bay?

Answer 21

if wave period is a multiple of natural resonant period

Question 22

types of breakers

Answer 22

spilling: energy released slowly over a wide area
plunging: sudden release of energy, large & violent, forms pipeline
surging: v large & powerful, fast release over small area, waves don’t break but instead surge onto shore

Question 23

longshore drift

Answer 23

waves bend as they approach shore
gradually smooth out coastline

Question 24

mitigation strategies for longshore drift

Answer 24

groins -> trap sediments
jetties -> preserve inlets
breakwaters -> protects shore from erosion
sea walls -> reduce effects of strong waves, wall eventually collapses

Question 25

how are storm surges formed?

Answer 25

1. warm ocean water causes rise of air masses
2. low atmospheric pressure pulls up surface ocean water below, increasing sea surface height
3. storm surges pushed to the coast by hurricane winds

Question 26

maximum storm surges occur…

Answer 26

to the right of the eye in the northern hemisphere