Ko e fetukutuku mei he peaukula ki he ngaahi taulanga, ngaahi taulanga, mo e ngaahi vaka¶

‘Oku ‘omai ‘e he ngaahi peakulá ha fakatu‘utāmaki fakatu‘utāmaki ki he kau toutaí, kau pule ‘o e ngaahi taulangá, mo e kau fakalele vaka ‘i he matātahí. ‘I he taimi ‘oku fakafetongi ai ‘e he ngaahi mofuike ‘i he sone subduction, ngaahi holo ‘a e kelekele ‘i lalo tahí, pe ko e ngaahi holo ‘a e caldera ‘a e kiupiki mita ‘e laui piliona ‘o e vai tahí, ‘oku ‘alu atu ‘a e ngaahi peau kalāvite vaha‘a taimi lōloá ‘i he ngaahi ‘oseni ‘i he vave ‘o e ngaahi vakapuna ‘oku laka hake ‘i he kilomita ‘e 800 ‘i he houa (maile ‘e 500 ‘i he houa). ʻI he ʻoseni ʻataʻataá, ʻoku meimei ʻikai ke ʻiloʻi ʻa e ngaahi peau ko ʻení ʻi lalo ʻi he ngaahi vaká, ʻo siʻi hifo ʻi he mita ʻe 1 (fute ʻe 3) ʻenau māʻolungá ʻi he ngaahi peau ʻoku kilomita ʻe 100 ki he 200 (maile ʻe 62 ki he 124).

‘I he hū atu ha peaukula ki he ngaahi vai ‘o e matātahí ‘oku ‘ikai fu‘u loloto, ‘oku fakamālohi‘i ai ‘e he fepakipaki ‘a e konitinēnití ‘a e lōloa ‘o e peá, ‘o fakatuai‘i fakaofo ‘a e vave ‘o e peá lolotonga ia ‘oku fakamālohi‘i ‘a e ma‘olunga ‘o e peá ke skyrocket ‘o fakafou ‘i he shoaling. ‘I loto ‘i he ngaahi taulanga ‘oku tāpuni‘í, ngaahi halanga vaka fāsi‘í, mo e ngaahi taulanga ‘oku ‘ikai fu‘u lolotó, ‘oku liliu ai ‘a e peaukulá ki he ngaahi peaukula fakamālohi, ngaahi ‘aofi tu‘u, mo e ngaahi tō fakatu‘utāmaki ‘o e vaí. ʻOku hoko ʻa e ngaahi tauʻanga vaká ko ha ngaahi mīsini fufulu vai fakatupu mate ʻa ia ʻoku haeʻi ai ʻe he ngaahi taulangá mei he ngaahi pou ʻo e vaká, motuʻa fakataha ʻa e ngaahi vaka ʻoku ʻi he kelekelé, pea ʻoku laka hake ʻi he noti ʻe 15 (kilomita ʻe 28 ki he houá pe maile ʻe 17 ki he houá) ʻo laiki ha taha pē ʻoku maʻu ʻi he ngaahi tauʻanga vaká pe feinga ke fakahaofi ʻa e vaká ʻi he miniti fakaʻosí.

Fai ʻeni he taimí ni .¶

1. Faka'auha 'a e ngaahi vaka kuo tau ki he kelekele ma'olunga 'i he va'e 'i he taimi pe ko ia 'i ha fakatokanga fakalotofonua:
   • Liʻaki ʻa e ngaahi vaka ʻoku haʻi ki he ngaahi tauʻanga vaká, ngaahi ʻaá, pe ngaahi tauʻanga vaká ʻi he momeniti ʻoku hoko ai ha lulululu mālohi ʻa e kelekelé pe ongo mai ha fakatokanga peaukula.
   • Lele ki ʻuta pea ʻalu hake ʻi he taimi pē ko iá, ʻo aʻu ki ha ngaahi māʻolunga ʻoku ʻikai siʻi hifo he mita ʻe 30 (fute ʻe 100) ʻi ʻolunga ʻi he levolo ʻo e tahí pe ʻunu ʻi ha kilomita ʻe 3 (maile ʻe 2) ki ʻuta.
   • ʻOua naʻá ke teitei fakamoleki ha taimi ʻi he feinga ke kamata ʻa e ngaahi mīsiní, liʻaki ʻa e ngaahi laine tauʻangá, pe fakahaofi ha koloa fakafoʻituitui ʻi he tahí ʻi he taimi ʻoku aʻu mai ai ʻa e peá ʻi loto ʻi ha houa ʻe ua.
2. Fakahokohoko 'a e ngaahi ngaue 'a e vaka 'o fakatatau ki he loloto 'o e vai kapau 'oku 'osi lolotonga 'i tahi:
   • Kapau ‘oku ngāue ‘i ha vai loloto ‘oku laka hake ‘i he mita ‘e 183 (100 fathoms pe fute ‘e 600), nofo pē ‘i he matātahí pea fakalele hangatonu ki he ngaahi ‘uha ‘oku ha‘u ‘i ha taimi lōloa.
   • If operating in shallow coastal waters between 20 meters and 100 meters (66 feet and 328 feet), motor immediately toward deep water if at least two hours remain before wave impact.
   • If operating within a narrow bay, harbor approach, or shallow inlet with less than one hour of warning, beach the boat in a safe cove and run uphill on foot.
3. Never attempt to pilot through narrow harbor entrances during a warning:
   • Refrain from entering or exiting confined jetties, harbor mouths, or breakwaters once a tsunami alert is issued.
   • Avoid narrow harbor bottlenecks where hydraulic suction and compressed incoming surges create lethal standing bores and breaking waves.
   • Stand off in open, deep water beyond the continental shelf break until port authorities issue an official all-clear directive.
4. Monitor emergency marine telecommunications continuously:
   • Tune your marine VHF transceiver to Channel 16 (156.800 megahertz) and monitor National Oceanic and Atmospheric Administration weather radio broadcasts.
   • Coordinate offshore staging positions with the United States Coast Guard, port authorities, and regional rescue coordination centers.
   • Transmit your position, crew count, and vessel status to maritime safety networks before offshore cellular coverage drops.
5. Prepare for multi-day offshore isolation if remaining at sea:
   • Throttle back engines to minimum steerageway once in deep water to conserve diesel and gasoline supplies.
   • Ration drinking water and food provisions, anticipating that shore infrastructure, fuel docks, and harbor piers will be destroyed upon return.
   • Establish an anchor watch and maintain active radar sweeps to avoid floating shipping containers, detached marina docks, and drifting derelict hulls.

flowchart TD
    A["Tsunami Warning Issued: Earthquake Felt or Siren Sounds"] --> B{"Where Is Your Vessel Currently Located?"}
    B -- "Moored at Dock or Slip" --> C{"Time to First Wave Impact"}
    C -- "Less Than 2 Hours" --> D["Abandon Boat Immediately: Run Inland to 30m / 100ft Elevation"]
    C -- "More Than 2 Hours & Open Harbor" --> E["Evaluate Port Authority Directives & Evacuate if Mandated"]
    B -- "Underway Inside Harbor or Shallow Bay" --> F{"Can You Reach 183m / 100 Fathoms in Time?"}
    F -- "No: Less Than 1 Hour" --> G["Beach Vessel in Safe Cove, Evacuate to High Ground on Foot"]
    F -- "Yes: Open Deep Water Ahead" --> H["Motor Full Speed to Deep Water Beyond 183m / 600ft Depth"]
    B -- "'Oku lolotonga lele 'i he Tahi 'i he tafa'aki 'o e 183m / 100 Fathoms" --> I["Nofo Matahi 'i he Vai Loloto: Faka'uli ki he Ngaahi Puna Loloa"]

Fisiki 'o e ngaahi peaukula fakatahi: 'Oseni loloto vs fata 'oku 'ikai loloto¶

Ko hono tokanga‘i malu ha vaka lolotonga ha peaukula ‘oku fiema‘u ke mahino‘i ‘a e ngaahi mīsini ‘o e vai ‘oku nau pule‘i ‘a e ngaahi peau ‘i he vai ‘oku ‘ikai fu‘u lolotó ‘i ha vaha‘a taimi lōloa. Neongo ‘oku fononga ‘a e ngaahi peaukula ‘i he ngaahi ‘oseni ‘oku mita ‘e lauiafe hono lolotó, ‘oku fakakalasi kinautolu ‘e he ‘oseni fakasinó ko e ngaahi peau ‘oku ‘ikai fu‘u loloto koe‘uhi ‘oku lahi ange ‘aupito honau lōloá ‘i he loloto ‘o e ‘oseni.

‘I he vai loloto ‘o e ‘oseni, ‘oku fakatu‘unga hangatonu ‘a e vave ‘o e peaú ‘i he loloto ‘o e vaí, ‘a ia ‘oku pule‘i ia ‘e he vave ‘o e kalāvité. ʻI he ngaahi teleʻa ʻo e ʻataʻataá ʻoku mita ʻe 4,000 nai hono lolotó (fute ʻe 13,120), ʻoku fononga ai ha peaukula ʻi ha vave fakafuofua ki he mita ʻe 200 ʻi he sekoni (kilomita ʻe 720 ʻi he houa pe maile ʻe 447 ʻi he houa). Neongo ‘a e vave ko ení, ‘oku si‘isi‘i ‘a e steepness ‘o e peá. Ko ha peau ‘oku mita ‘e 0.5 ki he mita ‘e 1 (fute ‘e 1.6 ki he fute ‘e 3.3) ‘a hono mā‘olungá ‘oku tufaki ‘i ha peau ‘oku kilomita ‘e 150 (maile ‘e 93) ‘okú ne fakatupu ha heke ‘oku fu‘u māmālie ‘o ‘ikai ke ‘ilo‘i ai ‘e he ngaahi vaka ‘i tahí ‘a e peau ‘oku fakalaka atu ‘i lalo ‘i honau ngaahi ‘aá.

Ko e liliu mei he benign open-ocean swell ki he peau faka'auha 'o e matātahi 'oku hoko ia 'o fakafou 'i he shoaling 'i he fetaulaki 'a e peau mo e fata konitinēniti:

• Lao 'a Green mo e Fakalahi 'o e Peau: 'I he holo hifo 'a e loloto 'o e vai, 'oku tuai 'a e vave 'o e peau 'o fakatatau hangatonu ki he square root 'o e loloto 'o e vai. Koe‘uhi ‘oku kei tu‘u ma‘u pē ‘a e vaha‘a taimi ‘o e peá, ‘oku fononga vave ange ai ‘a e tafa‘aki ki mui ‘o e peá ‘i he tafa‘aki ki mu‘á, ‘o ne fakamālohi‘i ‘a e lōloa ‘o e peá. Ke fakatolonga 'a e kinetic mo e malava 'o e ivi 'o e flux, 'oku tupulaki 'a e ma'olunga 'o e peau 'o fakatatau ki he loloto 'o e vai 'oku hiki hake ki he malohi kovi 'o e vahe fa 'e taha, ko ha fehokotaki'anga fakafika 'oku 'iloa ko e lao 'o Green.
• Ko e Fakafefeka'i 'o e Peau: 'I he vai loloto, 'oku 'i he kilomita 'e 100 ki he 200 (maile 'e 62 ki he 124) 'a e tumutumu 'o e peaukula. ʻI he taimi ʻoku holomui ai ʻa e peá mei he kilomita ʻe 720 ki he houa (maile ʻe 447 ki he houa) ʻi he vai lolotó ki he kilomita ʻe 36 ki he houa (maile ʻe 22 ki he houa) ʻi he ngaahi feituʻu ʻoku ʻikai fuʻu loloto ʻi he matāfangá, ʻoku fakamālohiʻi ʻa e lōloa ʻo e peá ʻo siʻi hifo ʻi he kilomita ʻe 5 (maile ʻe 3), ʻo ne fakatoka ʻa e vaí ki ha ngaahi tumutumu tuʻu hangatonu lahi.
• Kinetic ki he malava 'o e malohi 'o e liliu: 'I he lalo 'o e kolomu 'o e vai 'oku toho ki he funga tahi 'oku 'ikai loloto, 'oku hiki 'a e vave 'o e ngaahi momo'i me'a fakahosite ki 'olunga, 'o liliu 'a e ivi kinetic lahi 'aupito ki he hydrostatic 'ulu 'o e 'omi. Ko e founga ko ení ‘okú ne liliu ha fetukutuku ‘oku ngingila mo fakatakataka ‘i he ‘oseni lolotó ki ha nga‘unu ‘i ‘uta.

'I loto 'i he ngaahi sino 'o e vai 'oku semi-faka'ata, ngaahi taulanga, mo e ngaahi matātahi, hydrodynamics hono ua amplify 'a e faka'auha:

• Resonance 'o e Taulanga (Seiche Dynamics): 'Oku ma'u 'e he taulanga kotoa pe 'oku tapuni ha tu'o lahi 'o e oscillation fakanatula 'o makatu'unga 'i hono siometi, loloto, mo e laulahi 'o e hū'anga. 'I he taimi 'oku fe'unga ai 'a e vaha'a taimi 'o e ngaahi lēlue peau peaukula 'oku ha'u mo e tu'o lahi 'o e resonant fakanatula 'o e pesini 'o e taulanga, 'oku hoko 'a e fakalavea 'o e peau langa. 'Oku faka'uli 'e he resonance 'a e ngaahi tu'unga 'o e vai ke oscillate fakamālohi 'i he houa 'e 24 ki he 48, 'o fakatupu 'a e ma'olunga 'o e 'uha 'i loto 'oku liunga ua 'a e ma'olunga 'i he matātahi 'ata'ataa.
• Ko e Bore Formation in Shallow Estuaries: Ko e taimi 'oku hu ai ha peaukula ki ha 'aofi vaitafe 'oku 'ikai loloto pe ko ha 'aofi 'oku 'ikai fu'u loloto, 'oku vave 'a e 'alu hake 'a e tafa'aki ki mu'a 'o e peau 'oku ha'u, 'o ne fa'u ha 'ā fakahangatonu 'o e vai 'oku moveuveu mo foaming 'oku 'iloa ko e tidal bore pe tsunami bore. ‘Oku laka atu ‘a e ngaahi fo‘i ava ‘i he noti ‘e 15 ki he 30 (kilomita ‘e 28 ki he 56 ‘i he houa pe maile ‘e 17 ki he 35 ‘i he houa), ‘o fakahoko ai ‘a e fu‘u tenge faka‘auha lahi ‘o e ram ki he ngaahi fu‘u ‘akau ‘i tahí mo e ngaahi vaka ‘oku tau‘angá.

Ko e Tu'utu'uni 'o e 100-Fathom mo e Ngaahi Ngaue 'a e Vaka 'i he Vai Loloto .¶

Ko e ngaahi kautaha malu’i ‘o e tahi ‘i mamani kotoa, kau ai ‘a e Pule’anga Fakafonua ki he ‘Oseni mo e ‘Atakai, Kau Le’o ‘o e ‘Otu Motu ‘o e ‘Iunaiteti Siteiti, mo e Potungaue ‘Ea ‘a Siapani, ‘oku nau tauhi ha tu’unga fakavaha’apule’anga ki he mo’ui ‘a e ngaahi vaka ‘i ‘uta: ko e 100-fathom (183-mita pe 600-fute) loloto ‘o e contour rule.

Ko e ngaue 'i he tafa'aki 'o e laine contour bathymetric 'o e 100-fathom 'oku ne hiki ho'o vaka 'i he tafa'aki 'o e mavahe 'a e fata konitinēniti, 'a ia 'oku liliu vave ai 'a e loloto 'o e funga 'o e 'oseni ki he ngaahi tele'a 'o e abyssal. 'I he tafa'aki 'o e loloto ko 'eni, 'oku te'eki ke kamata 'a e liliu 'o e peaukula:

Ko e taimi 'oku fakalele ai ha vaka 'i he vai loloto lolotonga ha fakatokanga peaukula 'oku lolotonga ngaue:

• Faka'uli Hangatonu Ki he Swell: Tauhi 'a e kaufana 'o ho'o vaka ke fakahangatonu ki he ngaahi peau 'oku ha'u. Na‘a mo e ‘i he vai lolotó, ‘oku lava ke fakatupu ‘e he tafa‘aki mu‘a ‘o ha peaukula ‘a e ngaahi pupula mā‘olunga ‘i he‘ene kolosi ‘i he ngaahi ‘otu ‘i lalo tahí. Ko hono to'o 'o ha fula 'i he 'akau 'oku ne fakafe'iloaki mai 'a e tafe lahi pea 'oku fakatu'utamaki 'a e broaching pe capsizing.
• Throttle Foki ke Fakahaofi 'a e Penisini: 'Oua 'e tutu 'a e lolo ta'e fie ma'u 'aki hono tauhi 'a e vave 'o e folau vakapuna ma'olunga 'i he taimi 'e taha 'i he tafa'aki 'o e laine 100-fathom. Throttle hifo ki he steerageway si'isi'i taha, tauhi 'a e ivi fe'unga pe ki mu'a ke tauhi 'a e mafai 'o e rudder mo e orientation 'o e kaufana ki he tahi 'oku ma'u.
• Disengage Autopilot Systems: Deactivate automated steering systems and maintain manual control of the helm. Tsunami wave trains produce long-period orbital water movements that can confuse fluxgate compasses and gyrocompass inputs, causing erratic steering maneuvers.
• Tauhi Hokohoko atu 'a e Ngaahi Le'o Radar: 'Oku tafi'i 'e he backwash 'o e peaukula 'a e ngaahi toni metric 'e laui miliona 'o e ngaahi veve 'o e fonua ki he ngaahi vai 'o e matātahi 'oku 'ata'ataa. Fakaʻaongaʻi ʻa e lēta tahi ʻoku fakatonutonu ki he ngaahi founga nounou-pulse, resolution maʻolunga ke muimuiʻi ʻa e ngaahi fakatuʻutāmaki ʻoku ʻikai ke ulo, kau ai ʻa e ngaahi vaka kuo mafuli, ngaahi konga ʻo e taulanga kuo motuhi, ngaahi koniteina vaka fakakomesiale, mo e ngaahi ʻakau kuo taʻaki ʻoku tafe ʻi ʻuta.

Marina mo e Taulanga Dynamics: Ko e Faingata'a'ia 'o e Vaka Moored¶

‘Oku fehangahangai ‘a e ngaahi vaka ‘oku tau‘angá mo ha faka‘auha fakatu‘utāmaki lolotonga ha peaukula. Ko e feinga ke heka ki tu‘a ‘i ha ‘uha ‘i ha vaka ‘oku ha‘i ki ha taulanga ko e taha ia ‘o e ngaahi fehālaaki fakatupu mate anga-maheni taha ‘oku fai ‘e he kau toutaí ‘i he ngaahi feitu‘u ‘i he matātahí.

Ko e faka'auha 'o e ngaahi langa fakalakalaka 'o e taulanga 'oku hoko atu ia 'i he ngaahi konga fakatu'asino vave:

flowchart TD
    A["Tu'uta mai 'a e Sunami Crest ki Taulanga"] --> B["'Oku 'Alu Hake 'a e Levolo 'o e Vai 'i he Mita 'e 1 ki he 3 'i he Miniti"]
    B --> C["Ngaahi Taulanga 'oku 'alu holo 'oku 'alu holo 'i 'olunga 'i he ngaahi tumutumu 'o e ngaahi pilings fakafa'unga"]
    C --> D["Haeʻi ʻo e Ngaahi Cleats ʻo e Mooring; Laine Synthetic Snap 'i lalo 'i he ngaahi kavenga 'o e 'ohovale"]
    D --> E["Fakatu'utamaki 'a e Ngaahi Taulanga mo e Ngaahi Vaka 'oku 'Alu Tau'ataina 'i he 'Otu Motu 'i he Tangled Flotilla"]
    E --> F["Violent Drawdown Empties Basin: Vessels Ground and Roll on Bilges"]
    F --> G["Peau Ua 'oku ne taa'i 'a e ngaahi vaka 'oku 'i he kelekele: Fakakatoa 'o e hull fakatu'asino Crushing"]

1. Piling Overtopping and Dock Failure¶

Modern marinas use floating pontoon docks held in lateral position by vertical steel, concrete, or wooden pilings. These pilings are engineered to accommodate historical astronomical high tides plus a standard storm surge safety margin, typically 2 to 3 meters (7 to 10 feet) above mean higher high water.

When a major tsunami surge enters a harbor, water levels rise at vertical rates exceeding 1 to 3 meters per minute (3 to 10 feet per minute). As the water level exceeds the height of the pilings, floating docks detach from their vertical guide sleeves. Once freed from their pilings, docks, gangways, utility lines, and hundreds of moored vessels become an unguided, multi-thousand-ton floating mass driven by high-velocity currents into shoreward breakwaters and bridges.

2. Mooring Line Snapping and Cleat Tear-Out¶

Even in harbors where pilings remain un-topped, the horizontal water velocity generated by tsunami surges exerts catastrophic drag forces on vessel hulls. Standard three-strand nylon or braided polyester dock lines are engineered to absorb gentle tidal surges and minor wind chop.

A 10-knot current rushing past a moored 12-meter (40-foot) displacement vessel generates thousands of kilograms of static lateral force. When turbulent surges alternate direction every 10 to 15 minutes, mooring lines experience violent cyclic shock loading. Synthetic lines stretch beyond their elastic limits, snapping with explosive force, while aluminum dock cleats tear out of fiberglass decks, launching metal projectiles across docks.

3. Rapid Water Drawdown and Keel Grounding¶

Tsunami wave physics dictates that if the leading wave of a tsunami train is a trough, the arrival of the wave is preceded by a dramatic, rapid withdrawal of water from coastal harbors. Water recedes at rates that can drain an entire harbor basin in less than 5 to 10 minutes, exposing the sea floor, anchor chains, and subsea pipelines.

Vessels moored in slips drop violently to the seabed, landing on their keels, rudders, and propellers. Deep-draft sailboats and twin-engine motor yachts heel over on their bilges, filling with mud and trapping crew members below decks. When the returning tsunami crest strikes the drained harbor basin minutes later, it acts as a breaking wall of water that slams into the rolled, grounded hulls before they can re-float, crushing cabins and drowning trapped occupants.

Real-World Case Studies and Nautical Lessons¶

Analyzing historical maritime tsunami disasters provides clear lessons regarding the lethal nature of harbor surges and the practical survival margins achieved by vessels that moved offshore.

The Great Alaska Earthquake on March 27, 1964, generated a trans-oceanic tsunami that traveled across the Pacific. Crescent City, California, situated over 2,500 kilometers (1,550 miles) south, experienced catastrophic harbor destruction due to bathymetric focusing across the Mendocino Fracture Zone.

The harbor was struck by four primary wave crests spaced roughly 40 minutes apart. The first three waves caused substantial flooding, but the fourth wave was the largest, measuring over 6 meters (20 feet) in height. The surge lifted docks off pilings, broke vessels free from moorings, and deposited large fishing trawlers into city streets.

Sixteen commercial vessels were sunk directly in the basin, while dozens were crushed against harbor rock jetties. Those who attempted to enter the harbor between the second and third waves to save their boats were caught by the fourth surge, resulting in numerous maritime fatalities.

The magnitude 9.1 Tohoku earthquake on March 11, 2011, generated a massive local tsunami along the Sanriku coast of Japan, alongside destructive trans-Pacific surges. In Kamaishi, Japan, the world's deepest tsunami breakwater failed to stop the immense wave energy. Inside the commercial port, large cargo freighters were lifted over seawalls and deposited inland into urban neighborhoods. Conversely, vessels operated by the Japan Coast Guard that immediately stood out to sea beyond the 200-meter (656-foot) depth contour rode over the tsunami waves with zero damage or hull stress.

Across the Pacific Ocean in Santa Cruz, California, 8,000 kilometers (5,000 miles) away, the tsunami arrived 10 hours after the earthquake. Harbor resonance triggered violent water surges oscillating at 15-minute intervals. Currents inside the narrow entrance channel exceeded 12 knots (22 kilometers per hour or 14 miles per hour). The surges tore 18 commercial docks from their moorings, sank 15 vessels, and damaged approximately 100 others, causing over 28 million dollars in maritime infrastructure losses in a harbor that was thousands of kilometers away from the seismic epicenter.

On December 26, 2004, a magnitude 9.1 megathrust earthquake ruptured off northern Sumatra. In coastal resort harbors throughout Phuket, Thailand, and southern Sri Lanka, vessels tied to docks or anchored in shallow bays were pulverized. Liveaboard dive boats operating in deep offshore waters near the Similan Islands experienced the wave only as a slight vertical swell followed by unusual surface water ripples. The crew only became aware of the catastrophe when they attempted to contact shore bases and observed terrestrial debris fields drifting out to sea.

Decision Matrix: Evacuate On Foot vs Transit Offshore¶

When a tsunami alert is issued, vessel owners and commercial operators face a life-or-death choice: should you take the vessel out to sea, or should you abandon the vessel and evacuate inland on foot?

This decision must be made using a strict, objective assessment of water depth, transit time, and harbor entrance geometry:

flowchart TD
    A["Tsunami Alert Triggered"] --> B{"Is Your Vessel Moored at a Dock or Marina?"}
    B -- "ʻIo" --> C{"Time to Impact >= 2 Hours AND Open Channel?"}
    C -- "No: Less Than 2 Hours" --> D["DO NOT ATTEMPT TO MOTOR OUT"]
    D --> E["Tie Emergency Spring Lines If Time Permits (2 mins max)"]
    E --> F["Abandon Boat: Sprint Inland and Uphill to Safe Elevation"]
    C -- "Yes: >= 2 Hours Warning" --> G{"Can You Reach 183m / 100 Fathoms Before Arrival?"}
    G -- "ʻIkai" --> D
    G -- "ʻIo" --> H["Motor Directly Offshore to Deep Water Beyond 100 Fathoms"]
    B -- "No: Vessel Underway" --> I{"Are You in Deep Water (>183m / 100 Fathoms)?"}
    I -- "ʻIo" --> J["Stay in Deep Water; Steer Bow Into Swells"]
    I -- "No: Shallow Shelf" --> K{"Can You Clear Shallows Before First Wave?"}
    K -- "ʻIo" --> H
    K -- "ʻIkai" --> L["Head to Nearest Deep Cove or Beach Boat, Evacuate Uphill"]

The Golden Rule of Harbor Evacuation¶

If your vessel is tied to a dock, slip, or harbor mooring, and the estimated time of tsunami arrival is less than two hours, you must abandon the vessel immediately and evacuate on foot.

Do not attempt to ready the vessel, untie frozen lines, start cold engines, or steer through congested harbor channels. In every major tsunami event, mariners who died attempting to save their vessels were either trapped in their slips as water levels rose, crushed between boats and docks, or grounded in shallow harbor entrance channels during rapid drawdowns.

Criteria for Offshore Evacuation¶

You should attempt to pilot your vessel into deep water only if all of the following conditions are met simultaneously:

1. Official tsunami warnings confirm that the arrival of the first wave is more than two to three hours away (typical for distant or teletsunami events originating across the ocean basin).
2. Your vessel is completely operational, fully fueled, with engines warm and running without mechanical hesitation.
3. The harbor channel is completely clear of congestion, drawbridges are fully raised, and you can maintain a transit speed of at least 10 to 15 knots.
4. Bathymetric navigation charts confirm that your vessel can transit beyond the 100-fathom (183-meter or 600-foot) contour line at least 45 minutes before the predicted wave arrival time.
5. Port authority officials and the local Coast Guard have explicitly authorized outbound maritime traffic and have not closed the harbor entrance.

Port Authority, Marina Management, and Harbor Hardening¶

Maritime facility managers, harbor masters, and port authorities carry institutional responsibility for mitigating life safety hazards and infrastructure collapse before, during, and after a tsunami impact.

Standard operating procedures for commercial ports and marinas during a tsunami alert include structured protocol phases:

Konga 1: Fakama’a Vave ‘a e Ngaahi Taulanga Tahi (T-Minus Fakatokanga Window)¶

• Le'o 'a e Ngaahi Fafangu 'o e Taulanga pea Tu'utu'uni ke Fetuku Vave: Fakalele 'a e ngaahi sisitemi lea ki he kakai, ngaahi saileni 'o e taulanga, mo e ngaahi fakatokanga fakamafola tahi VHF 'o fekau'i 'a e kau vakapuna kotoa pe, kau toutai fakakomesiale, mo e kau nofo 'i he liveaboard ke nau fakama'a vave 'a e ngaahi slips mo e ngaahi taulanga.
• Tapuni 'a e Ngaahi Ngaue'anga 'o e Tahi: Fakamavahe'i to'oto'o 'a e ngaahi fafanga tufaki'anga 'o e ngaahi ngaue'anga ki he ngaahi taulanga kotoa pe. Ko hono motuhi 'o e ngaahi fafanga 'o e ivi 'o e 'uta 'i he ngaahi panel 'o e breaker terrestrial tefito 'oku ne ta'ofi 'a e ngaahi vela 'uhila mo e ngaahi fakatu'utamaki 'o e 'uhila 'i he vai 'i he taimi 'oku ngoto ai 'a e ngaahi slips. Tāpuni ‘a e ngaahi me‘a fakatonutonu pamu lolo, pea tāpuni‘i ‘a e ngaahi valve fakavavevave ‘i he ngaahi tangikē tauhi‘anga lolo ‘i tahí ke ta‘ofi ‘a e malingi ‘a e lolo ki he peisiní.
• Ta’ofi ‘a e Fefononga’aki ‘a e Vaka Hu Mai: Kuo pau ke ta’ofi vave ‘e he kau pailate ‘o e Taulanga mo e ngaahi sevesi fefononga’aki ‘a e ngaahi vaka ‘oku hu mai, ‘o fakahinohino’i ‘a e ngaahi vaka koniteina, ngaahi vaka uta lolo, mo e ngaahi vaka uta koloa lahi ki he ngaahi taulanga pukepuke ‘i ‘uta ‘oku tu’u ‘i he ngaahi vai ‘oku loloto ange ‘i he mita ‘e 200 (fute ‘e 656).

Konga 2: Fakafefeka'i 'o e Fa'unga ki he Ngaahi Fale¶

'E lava ke fakahoko 'e he ngaahi taulanga 'oku tu'u 'i he ngaahi sone 'o e peaukula 'oku lolotonga ngaue 'a e ngaahi fakalelei faka'enisinia ke fakasi'isi'i 'a e ta'elavame'a 'o e ngaahi langa lolotonga 'a e ngaahi 'uha fakafuofua:

• Ngaahi Piling Fakahinohino Ma’olunga ange: Fakalahi ‘a e ma’olunga ‘o e ngaahi piling ‘o ‘ikai si’i hifo he mita ‘e 4 ki he 6 (fute ‘e 13 ki he 20) ‘i ‘olunga ‘i he ngaahi tu’unga fakahisitolia ‘o e ‘uha ‘o e matangi. Ko hono fokotu'u 'o e ngaahi pulou 'o e piling mo e ngaahi me'a faka'ai'ai ukamea mamafa 'oku ne ta'ofi 'a e ngaahi taulanga mei he 'alu holo mei he tumutumu 'o e ngaahi pilings lolotonga 'a e ngaahi puna ta'e'amanekina 'o e vai tu'u.
• Heavy-Duty Piling Guides: Replace standard aluminum or plastic dock roller guides with reinforced ductile steel collar guides capable of withstanding lateral shear loads exceeding 50 kilonewtons.
• Breakaway Gangways: Install articulated gangways with mechanical breakaway pins on the dock side, so that when floating docks rise or tilt violently, gangways disconnect cleanly rather than buckling docks or ripping shore bulkheads.

Vessel Recovery, Re-Entry Protocols, and Navigation Hazards¶

The danger to mariners does not end when the initial tsunami surge passes. The post-tsunami marine environment remains hazardous for days, characterized by long-period seiche waves, destroyed aids to navigation, and dense fields of floating debris.

+----------------------------------------------------------------------------------------------------+
|                                  POST-TSUNAMI RE-ENTRY CHECKLIST                                   |
+----------------------------------------------------------------------------------------------------+
| [ ] Maintain offshore holding pattern until Port Authority issues an official All-Clear.           |
| [ ] Verify harbor entrance channel is hydrographically surveyed before attempting passage.         |
| [ ] Post a dedicated forward bow watch to identify submerged logs, containers, and debris.         |
| [ ] Transit at dead slow speed (<5 knots) to prevent hull impact with unlit obstructions.          |
| [ ] Do not rely on navigation buoys or channel markers; anchors and chains are likely displaced.   |
| [ ] Prepare emergency tow lines and confirm bilge pumps operate prior to entering shallow waters.  |
| [ ] Assume shore facilities lack electrical power, fuel delivery, and potable water hookups.       |
+----------------------------------------------------------------------------------------------------+

The Multi-Wave Hazard Window¶

Tsunamis are not single, isolated waves; they are a train of successive waves spanning 12 to 24 hours. The initial wave is rarely the largest. Secondary or tertiary crests, arriving hours after the initial impact, are frequently amplified by bathymetric resonance within harbor basins.

Vessels holding offshore must remain in deep water beyond the 100-fathom line until official all-clear advisories are transmitted across marine VHF Channel 16 by the Coast Guard or local port authorities. Returning to harbor prematurely has led to numerous fatal groundings and collisions with secondary surges.

Post-Impact Navigation Hazards¶

When port authorities finally grant permission for vessels to re-enter coastal waterways, mariners must travel with extreme caution:

• Displaced Navigation Buoys and Beacons: Tsunami surges rip multi-ton concrete sinkers and anchor chains across the sea floor. Lateral channel marker buoys, daybeacons, and lighted hazard markers are routinely displaced hundreds of meters into active channels or stripped away entirely. Do not rely on visual buoys; steer strictly using calibrated GPS chartplotters and forward-looking depth sounders.
• Shoaling and Channel Infilling: Tsunami backwash transports immense volumes of terrestrial soil, roadbed material, and beach sand into navigation channels. Harbor channels that previously maintained 10 meters (33 feet) of draft may be choked with silt bars reducing depths to less than 2 meters (6 feet).
• Derelict and Submerged Flotsam: Millions of metric tons of wreckage litter the water surface and water column. Submerged shipping containers floating flush with the surface, tangled mooring lines, submerged structural beams, and fuel tanks present catastrophic hull-breach hazards to fiberglass and aluminum vessels. Post a dedicated watchstander on the bow, reduce vessel speed below 5 knots, and maintain immediate readiness to reverse propulsion.

Maritime Emergency Communications and Coordination¶

Effective communication during a maritime tsunami emergency supports rapid vessel tracking, timely distribution of safety alerts, and coordinated offshore holding maneuvers.

Vessel operators must maintain disciplined telecommunications practices:

• VHF Marine Channel 16 Priority: Channel 16 (156.800 megahertz) is the international maritime distress, safety, and calling frequency. Maintain continuous listening watches. Keep transmissions brief and formal, reserving airtime for life-threatening distress calls (MAYDAY) and urgent safety broadcasts (SECURITE).
• Automated Identification System (AIS) Operations: Keep your vessel Class A or Class B AIS transponder active at all times. In dense fog or heavy ashfall accompanying volcanic tsunamis, AIS allows neighboring commercial vessels, Coast Guard cutters, and vessel traffic services to track your position, speed, and heading, preventing catastrophic offshore collisions during mass harbor evacuations.
• Digital Selective Calling (DSC): Verify your VHF marine radio is connected to an active GPS receiver and registered with a valid Maritime Mobile Service Identity (MMSI) number. In an acute emergency, activating the red distress button transmits an automated digital distress burst containing your vessel's precise coordinates and emergency nature directly to regional maritime rescue coordination centers.
• Satellite Communications and EPIRBs: For vessels operating beyond VHF line-of-sight range (typically 30 to 50 kilometers or 20 to 30 miles from shore stations), satellite messengers, satellite phones, and 406-megahertz Emergency Position Indicating Radio Beacons (EPIRBs) provide reliable global emergency signaling. Confirm your EPIRB battery and hydrostatic release unit are within their certified operational dates.

Fakamo'oni ki he tokoni 'uluaki¶

Surviving maritime disasters, capsizings, and violent harbor surges frequently results in severe physical trauma, acute hypothermia, near-drowning, and crush injuries. When offshore vessels are cut off from shore-based medical clinics and municipal emergency medical services cannot access destroyed port facilities, crew members must possess the knowledge, training, and equipment necessary to provide advanced bystander medical care.

Completing comprehensive, accredited first aid, CPR, and automated external defibrillator certification through established providers, such as the American Red Cross, St. John Ambulance, the Canadian Red Cross, or specialized maritime medicine academies, provides critical life-saving skills. Hands-on medical training teaches you how to manage severe saltwater inhalation, clear obstructed airways, perform prolonged cardiopulmonary resuscitation on hypothermic drowning victims, immobilize compound fractures sustained from violent vessel collisions, apply arterial tourniquets to traumatic limb injuries, and treat secondary shock until maritime search and rescue teams arrive.

Ngaahi fehu'i 'oku toutou 'eke .¶

Kuo vakaiʻi ʻa e ngaahi maʻuʻanga fakamatalá¶

• National Oceanic and Atmospheric Administration (NOAA) National Tsunami Warning Center (NTWC, United States): Tsunami Safety Protocols for Mariners, Deep-Water Navigation Guidelines, and Shoaling Hydrodynamics.
• United States Coast Guard (USCG, United States): Navigation and Vessel Inspection Circulars, Marine Safety Alerts on Tsunami Preparedness, and Harbor Evacuation Directives.
• International Tsunami Information Center (ITIC, UNESCO / IOC): Global Tsunami Warning and Mitigation System Guidelines, Maritime Hazard Mapping, and Post-Event Port Assessments.
• Japan Meteorological Agency (JMA, Japan): Marine Tsunami Warning Scales, Sanriku Coast Maritime Survival Studies, and Deep-Water Vessel Staging Protocols.
• California Geological Survey (CGS, United States): Maritime Tsunami Response Playbooks, Harbor Resonance Dynamics, and Marina Infrastructure Hardening Guidelines.
• Federal Emergency Management Agency (FEMA, United States): Coastal Port Resiliency and Tsunami Evacuation Planning Guidelines.

Ngaahi fakahinohino fekau'aki¶

• Tsunami safety and coastal evacuation
• Meteotsunamis and sudden harbor seiches
• Seiche waves and harbor resonance surges
• Glacial calving megatsunamis and small boat evasion
• Waterspouts and marine vortex evasion
• Ngaahi fika fakavavevave 'i he fonua