Waves & Tsunamis

Question 1

All waves

Answer 1

T = period (S) one wave crest to the next
steepness = H / L
speed = L / T

Question 2

Deep water wave speed

Answer 2

speed S = 1.25 * swrt(L)
S = 1.56 * T
Longer wavelengths travel faster

Question 3

Shallow water wave speed

Answer 3

speed S = sqrt(gd)
S = 3.1 * swrt(d)
g = gravitational constant, d = water depth
waves travel faster in deeper water (no dependence on wave length)
examples: tides & tsunamis

Question 4

Generation of wind-driven waves

Answer 4

Wave energy imparted to ocean depends:
- wind speed
- duration (longer the wind blows)
- fetch (area over which the wind blows)

Question 5

Wave height plot

Question 6

Beaufort scale

Answer 6

Relates wind energy and wind speed to appearance of sea surface

Question 7

How do waves go from chop to swell?

Answer 7

• storm puts more energy into ocean, waves move away from storm
  Wave dispersion:
• waves with longer wavelengths travel faster
• waves are sorted by wavelength/speed
• longer wavelengths reach the shore first

Question 8

Deep water wave train speed

Answer 8

Wave energy travels more slowly than each wave crest (for deep water waves)
- leading wave dies out, new wave forms behind
- wave train (and wave energy) travels at 1/2 speed of individual wave

Question 9

Interference - what happens when two wave systems (swells) collide?

Answer 9

Destructive interference
Constructive interference

Question 10

Mixed wave inteference

Answer 10

Patterns of small and tall eaves along coast

Question 11

Non-linear affects

Answer 11

• Linear: The combined height equals the sum of the individual waves
• Non-linear: create rogue waves that are tller than the sum of the individual waves

Question 12

Rogue waves

Answer 12

• an anomalously large wave that is over twice as big as the significant wave height of the surrounding sea state
• caused by a combination of multiple waves and non-linear effects
• occur in open ocean with multiple swells

Question 13

Onshore progression

Answer 13

Deep waves become shallow
- wave speed decreases as become shallow-water waves
- wavelength decreases
- wave height increases
- waves break when height: wavelength ratios exceeds ~1.7
- speed goes doen bc dependent on water depth

Question 14

Types of breakers

Answer 14

• spilling breakers: foam, not a dramatic break
• plunging breakers: steeper beach, drmatic steepening of waves, depth changes fast = speed changes fast
• surging breakers: too steep, lots of foam, not a clean break

Question 15

What makes the world’s biggest waves surfable?

Answer 15

The underwater canyon focuses wave energy like a magnifying glass focuses light energy

Question 16

Wave refraction

Answer 16

• waves usually appraoch the coast at an angle
• one end of the wave shoals before the other = refraction

Question 17

Tsunamis

Answer 17

• long wavelength ocean waves generated by submarine earthquakes, landslides, volcanic eruptions, and meteor impacts
• shallow water waves, wave orbitals smushes at the bottom (long wavelength and low wave period)
• behaves as a shallow water wave (depth is <1/20 wavelength)
• they can pass unoticed at sea (not very tall compared to its long wavelength)

Question 18

Which waves are the most deadly?

Answer 18

• rogue waves: abnormally large waves in the open ocean observed by mariners
• tidal waves: the wave that creates the twice-daily up and down motion of the tides (often incorrectly used to describe a rogue wave)
• seiches: large-scale sloshing of water in lakes
• tsunamis: large waves creates by earthquakes or landslides
• sneaker waves: multiple waves crashing together on a beach
• wind-driven waves: the most common type of wave ___

Question 19

Why are tsunamis so destructive?

Answer 19

• energy compresses into smaller area, creating larger wave with steeper crest
• small amplitudes in the deep ocean, but as they approach land they slow down and create waves up to 40 m

Question 20

Tsunami detection

Answer 20

Bottom pressure recorder: detects tsunamis with amplitudes as small as 30 mm in 6,000 m of water
-DART: record pressure

Question 21

How fast do tsunamis travel?

Answer 21

example:
propogation speed: 196

Question 22

Pacific ring of fire

Answer 22

80% of tsunamis occure in Pacififc ocean