Lecture 7 Flashcards
What happens to the shallow wave circles in deeper waters
- the circles are getting elongated
- >in deep water they get shorter and smaller
What happens to shallow water waves as they enter shallow water
- they slow
- > C decreases
- > their period does not change
- > their wavelength does decrease, as T does not change
- kinetic energy is converted to potential
- > so wave height increases
- > wave steepness also increases
- > until we get to a point to where waves are breaking on the shores
What is wave refraction
-the bending of shallow water waves due to changes in water depth
- as wave crests approach shore parallel to each other, the waves bend and conform to the shape of the coast line
- > the first segment of the wave reaches the land before the other part and this segment slows down first
- > the segment of the wave closest to the headland slows down before the rest of the wave
- > eventually, the wave bends and breaks parallel to the shore regardless of original direction of approach
What happens to the headland over time as waves hit it again and again
- wave energy is concentrated on the headland
- > over time, headlands wear back due to erosion while deposits of sediments tend to build in coasts
- > over time an irregular coast line generally becomes straighter due to this combination of erosion and deposition
Do waves approach at an angle
- yes waves usually approach the shore at an angle
- > one part of the wave in in shallow water while the rest of the wave is in deeper water
- waves refract or bend around a point
- > so that on one side they are parallel and on the other side they are also parallel
Is wave refraction as complicated as topography
-yes
What is going to occur if a wave approaches a bay flanked by headlands
- normally it is shallow in front of the headlands
- > this first slows the wave in these areas
- > while the waves deeper in the center of the bay are slowed down last
- > in the end, we get the wave breaking almost parallel to the coast
- note as the wave is refracted in the bay
- > the total length of the crest increases, lowering its height
- > thus the wave energy is spread along the beach with gentler waves
- > this process also transports sand towards the shore where it builds the beach
- as the wave is refracted at the headland, refraction reduces the lengths of the wave crest, increasing the height
- > thus one will generally see more energetic and higher waves breaking in these areas
- > the same wave can also hit the headland from both sides at once
- > this leads to lots of erosion and carrying away of sand
What is the surf zone
-the area offshore within which waves are breaking
What are the 4 different types of breaking waves
1) Spilling breaker
- >peak becomes ov
- >breakers have low overall energy and break over a long distance
- >gives surfers a longer but less exciting ride
- >occurs on gentle underwater beach slopes which gradually extract energy from the wave and cause it to break over extended distance
2) Plunging breakers
- >peak travels fast enough to outrun the rest of the wave
- >the crest curls over and smashes down in the water
- >best type of wave for surfing
- >forms on medium underwater beach slope and breaks over moderate distance
- >have curling crest that forms an air pocket
3) Collapsing breakers
- >base of the front side becomes unstable before the crest and the base of wave collapses
4) Surging breaker
- >it never really breaks
Why are wave conditions for surfing generally better on the west coast than the east coast of North America
1) Pacific is bigger than the Atlantic
- >so bigger waves can develop
2) Onshore winds
- >winds generally onshore(westerlies) enhancing waves on west coast and weakening them on the east coast
3) Steep beaches
- >beach slopes are generally steeper on Pacific coasts, creating plunging breakers
