Waves are influenced by wind, tides, and swell, and while the ocean floor also plays a role, it’s minor at best.
Simply put, in deep water, the sea floor is unable to influence the formation of waves on the surface.
But this changes in shallow water, at which point the structure of the floor (known as “bathymetry”, from the Greek word for “deep”) determines the nature of the breaking waves.
The bathymetry impacts the wave through a process known as refraction.
Let’s explore what happens to an ocean wave when it is refracted.
Ocean Wave Refraction Defined In A Nutshell
Ocean wave refraction occurs when ocean waves approach a coastline or a change in the ocean floor’s depth.
As waves encounter variations in the ocean floor’s contour, their speed and direction change, resulting in a bending of the wave fronts. This bending is known as refraction.
Refraction happens due to the change in wave speed as the waves move from deeper water to shallower water or vice versa.
When waves approach shallower areas, their lower portion encounters friction with the seabed, causing the waves to slow down.
Meanwhile, the upper portion of the waves continues to move at a faster speed, leading to a change in the direction of the wave crest.
This bending effect can cause waves to converge or diverge along the coastline.
Ocean Wave Refraction Explained: what causes a wave to refract & Bend
This video gives an example of the behavior of ocean wave refraction.
As waves travel over the sea floor at different speeds, they bend and contort, with the bend essentially turning toward its slowest point.
And because shallower water creates slower waves, they bend or “refract” toward that shallow water.
This diagram of ocean wave refraction shows how wave energy is pushed in a different direction when ocean swell energy meets shallow water. Image from hawaii.edu.
This is wave refraction, and it means that the shape of the waves above the surface can be heavily dependent on the topography below the surface.
The unique bathymetry of different surf spots creates equally unique breaking waves.
At Nazare, for instance, the waves are pushed into an A-frame, sending immense wave energy upwards to create monster wave crests and produce some of the biggest surf on the planet.
Ocean wave refraction can also be caused by the shape of a bay or coastline where waves diverge because of refraction which results in calmer ocean water in the bay and rougher water at the land points or headlands that jut out from the uneven coastline.
This diagram of ocean wave refraction shows how wave energy is pushed in a different direction when ocean swell energy converges and concentrates wave energy on the headlands that reside on either side of the bay . Image from hawaii.edu.
Two Examples of Wave Refraction In California
You can find two examples of ocean wave refraction in California at 1) The Wedge in Newport Beach and 2) at South Ocean Beach in San Francisco.
The Wedge In Newport Beach, California
See the results of ocean wave refraction at the Wedge in Newport Beach, CA.
In the summertime, south swells run north and break at beaches that are south facing in California.
Newport Beach is one of those beaches.
However, Newport Beach has a very long jetty that extends out into the ocean from the inlet/bay at a surf spot known as The Wedge.
The south swell push north at The Wedge, some of which hit the beach directly, but some of the swell hits the jetty first and combines with the swell that is aiming to land on the beach.
The two swells combine to form one massive, mutant wave that can reach upwards of 20 feet and can break in a just a few feet of water.
Surfers, bodyboarders and bodysurfers test their skills on these waves knowing that 9 out of 10 times the wave will closeout on them.
South Ocean Beach In San Francisco, California
See the results of ocean wave refraction at San Francisco’s Ocean Beach, CA.
When winter arrives, swells from Alaska travel south down the coast of California.
South Ocean Beach, located just southwest of the Golden Gate Bridge, is open to all open-ocean swells that run north to south.
It is one big swell magnet.
The winter swell energy that hits Ocean Beach in San Francisco bounces off the coastline and collects again at South Ocean Beach all but a quarter to a half mile away resulting with waves that can be twice the size as those that break at neighboring Ocean Beach.
That’s right, a 5 to 6 foot wave at Ocean Beach could easily be 10 feet a half mile away at South Ocean Beach.
Focusing and Defocusing
There are two main factors to consider when talking about ocean wave refraction: focusing and defocusing.
Focusing ocean wave refraction can occur when the swell reaches a jutting coral reef with deep water on either side.
The wave bends inwards and concentrates all of the energy into a central spot, similar to what we see at Nazare, as well as the unforgiving breaks seen at Teahupoo in Tahiti.
Defocusing occurs when the wave rapidly approaches a shallow water depth, such as a bay.
At this point, it begins to slow down.
The wave changes and starts to bend outwards.
Depending on the bathymetry, some locations may produce both types of wave refraction.
Mawimbi huathiriwa na upepo, mawimbi, na mawimbi, na ingawa sakafu ya bahari pia huchangia, ni ndogo sana. Kwa ufupi, katika maji ya kina kirefu, sakafu ya bahari haiwezi kuathiri kuundwa kwa mawimbi juu ya uso. Lakini hii hubadilika katika maji yasiyo na kina kirefu, ambapo muundo wa sakafu (unaojulikana kama <unk>bathymetry<unk>, kutoka neno la Kigiriki kwa <unk>deep<unk>) huamua asili ya mawimbi ya kuvunja. Bathymetry huathiri wimbi kupitia mchakato unaojulikana kama refraction. Hebu tuchunguze kinachotokea kwa wimbi la bahari linapovunjika. Refraction ya Wimbi la Bahari Inatokea wakati mawimbi ya bahari yanapokaribia pwani au mabadiliko katika kina cha sakafu ya bahari. Mawimbi yanapokutana na mabadiliko katika umbo la sakafu ya bahari, mwendo na mwelekeo wao hubadilika, na kusababisha mapindo ya mbele za mawimbi. Mzunguko huo huitwa refraction. Refraction hutokea kutokana na mabadiliko katika kasi ya wimbi kama mawimbi kusonga kutoka maji ya kina kirefu kwa maji ya kina kirefu au kinyume chake. Mawimbi yanapokaribia maeneo yasiyo na kina kirefu, sehemu yake ya chini hukutana na msuguano na sakafu ya bahari, na kusababisha mawimbi kupungua. Wakati huohuo, sehemu ya juu ya mawimbi huendelea kusonga kwa mwendo wa kasi zaidi, na hivyo kubadilisha mwelekeo wa mwinuko wa mawimbi. Mageuzi hayo yanaweza kusababisha mawimbi yakutanike au kutofautiana kando ya pwani. Mzunguko wa mawimbi ya bahari: nini husababisha mawimbi ya bahari kuanguka na kugeuka? Mawimbi yanapopiga bahari kwa kasi tofauti, yanapindika na kugeuka-geuka, na kwa kweli mwinuko huo huelekea mahali pake pa polepole zaidi. Na kwa sababu maji yasiyo na kina kirefu hutokeza mawimbi yasiyo na kina kirefu, mawimbi hayo hupindika au "kupinduka" kuelekea maji hayo yasiyo na kina kirefu. Mchoro huu wa refraction ya mawimbi ya bahari inaonyesha jinsi nishati ya wimbi ni kusukumwa katika mwelekeo tofauti wakati bahari swell nishati hukutana maji ya kina kirefu. Picha kutoka hawaii.edu. Hii ni refraction wimbi, na ina maana kwamba umbo la mawimbi juu ya uso inaweza kuwa sana kutegemea topography chini ya uso. Vipimo vya maji vya pekee vya maeneo tofauti ya kuogelea hutokeza mawimbi ya kipekee pia. Kwa mfano, katika eneo la Nazareth, mawimbi huingia kwenye mviringo wa A, na kusafirisha nishati kubwa ya mawimbi juu ili kuunda miamba mikubwa na kutokeza baadhi ya mawimbi makubwa zaidi duniani. Mvuke wa bahari unaweza pia kusababishwa na umbo la ghuba au pwani ambapo mawimbi yanatofautiana kwa sababu ya kuvunjika, na kusababisha maji ya bahari kuwa ya utulivu katika ghuba na maji makali zaidi katika sehemu za ardhi au nyanda ambazo hutoka kwenye pwani isiyo sawa. Mchoro huu wa refraction ya mawimbi ya bahari inaonyesha jinsi nishati ya wimbi ni kusukumwa katika mwelekeo tofauti wakati bahari swell nishati converges na kuzingatia nishati ya wimbi juu ya nyuso kwamba kuishi katika pande zote mbili za ghuba. Picha kutoka hawaii.edu. Mfano wa kuanguka kwa mawimbi ya bahari ni katika eneo la Newport Beach, California, na katika eneo la South Ocean Beach, San Francisco. The Wedge In Newport Beach, California Angalia matokeo ya refraction bahari wimbi katika Wedge katika Newport Beach, CA. Wakati wa kiangazi, mawimbi ya kusini huelekea kaskazini na kuvunjika kwenye fuo zinazoelekea kusini huko California. Newport Beach ni mojawapo ya fukwe hizo. Newport Beach ina bandari ndefu sana ambayo inaenea nje katika bahari kutoka inlet bay katika surf mahali inajulikana kama Wedge. Wimbi la kusini huelekea kaskazini kwenye The Wedge, baadhi ya mawimbi hayo huanguka kwenye ufuo wa bahari, lakini mengine huanguka kwenye bandari kwanza na kuungana na mawimbi ambayo yana lengo la kutua kwenye ufuo wa bahari. Mlipuko huo unaunganishwa na kuunda wimbi moja kubwa ambalo linaweza kufikia urefu wa mita 20 na linaweza kuvunjika kwa mita chache tu za maji. Surfers, bodyboarders na bodyboarders kujaribu ujuzi wao juu ya mawimbi haya, akijua kwamba 9 kati ya 10 mara wimbi itakuwa closeout juu yao. South Ocean Beach Katika San Francisco, California Angalia matokeo ya mawimbi ya bahari refraction katika San Francisco Ocean Beach, CA. Wakati wa majira ya baridi kali, mawimbi kutoka Alaska husafiri kuelekea kusini kwenye pwani ya California. South Ocean Beach, iliyoko kusini magharibi tu ya Golden Gate Bridge, ni wazi kwa mawimbi yote ya bahari iliyo wazi ambayo huelekea kaskazini hadi kusini. Ni sumaku moja kubwa ya mawimbi. Mvua ya majira ya baridi kali ambayo huanguka kwenye pwani ya San Francisco, hupiga pwani na kukusanya tena katika pwani ya South Ocean, karibu na nusu maili mbali, na kusababisha mawimbi ambayo yanaweza kuwa na ukubwa mara mbili kuliko wale wanaovunja pwani ya Ocean. Wimbi la futi 5 hadi 6 katika pwani ya Ocean Beach linaweza kuwa na futi 10 kwa nusu maili mbali katika pwani ya South Ocean. Kuna mambo mawili makuu ya kuzingatia wakati wa kuzungumza juu ya refraction mawimbi ya bahari: kuzingatia na defocusing. Mvuke wa bahari unapofikia mwamba wa matumbawe wenye maji ya kina kirefu upande mmoja au ule mwingine, unaweza kusababisha mawimbi ya bahari ya bahari yawe na mwamba wa matumbawe. Mlipuko huo unazunguka ndani na kukusanya nishati yote katika sehemu moja ya katikati, sawa na kile tunachokiona huko Nazareth, na vilevile mapumziko yasiyo na huruma yanayoonekana huko Teahuku huko Tahiti. Kupoteza mwelekeo hutokea wakati wimbi linapokaribia kwa haraka kina cha maji yasiyo na kina kirefu, kama vile ghuba. Katika hatua hii, huanza kupunguza mwendo. Wimbi hubadilika na kuanza kukunjika kuelekea nje. Ikitegemea bathymetry, baadhi ya maeneo inaweza kuzalisha aina zote mbili za refraction wimbi.