Natural disasters and daily life
Sea-related natural disasters include tsunamis (huge waves caused by an earthquake, volcano or landslide under the sea), cyclones and typhoons (giant storms), storm surges (sea water pushed on to land by a storm) and very high waves or tides.
They change daily life on the coast: houses and boats are damaged, fishing stops, ports close, drinking-water wells turn salty, and people lose income. A disaster is more serious where many people live close to the sea and where buildings are weak.
Natural disasters and safety
Before: know the warning signs and signals, learn the nearest high ground, keep a ready bag (water, food, torch, radio, papers), tie up and check boats, and practise drills.
During: if the ground shakes strongly near the sea, or the sea suddenly pulls far back, or a siren sounds, move at once to high ground or inland. Do not wait to see the wave. A fishing boat that is already far out in deep water is often safer than one in a harbour.
After: stay away until officials say it is safe. Waves can come many times, and the first wave may not be the biggest. Help the injured, avoid broken wires and dirty water.
Speed matters: a tsunami in deep water moves at about 700 km per hour, like a jet. That is why early warnings by radio, phone and siren save lives.
Natural disasters and sustainable production
Fishing and fish farming must continue after a disaster, but in a way that does not harm the sea or put people at risk again.
- Protect natural shields: mangroves, coral reefs and sand dunes slow waves. Plant and protect them.
- Build stronger: strong harbours, sea walls, high fish-landing centres and cold stores on higher ground.
- Spread the risk: more than one kind of income (for example fishing and seaweed farming), savings groups and insurance.
- Restore sustainably: rebuild fish farms and boats without catching too many wild fish, and clear debris and oil from fishing grounds.
- Plan and share information: village disaster plans, marked safe routes, and weather and sea reports on phones.
Try it
Draw a simple map of your area or any coast: mark the sea, the village and the nearest high ground. Draw the shortest safe path from your house. Time yourself walking it. Then use the 3D free play to see why leaving early matters.
Key formulas and definitions
- Tsunami speed in deep water: v = square root of (g x d), where g = 9.8 m/s2 and d = sea depth in metres. For d = 4000 m, v is about 198 m/s, or about 713 km/h.
- Time = distance / speed.
- Water goes over a wall when wave height at the shore is greater than the wall height.
Worked examples
1. An earthquake happens 360 km from the coast. The tsunami moves at 720 km/h. How long before it reaches the coast?
Time = distance / speed = 360 / 720 = 0.5 hour = 30 minutes. That is the time to warn and move.
2. The sea is 4000 m deep. Find the tsunami speed in m/s and km/h.
v = square root of (9.8 x 4000) = square root of 39,200, about 198 m/s. In km/h: 198 x 3.6 = about 713 km/h.
3. A 6 m wave meets a 4 m wall. Mangroves reduce wave height by 40 percent. Does the water go over the wall?
With mangroves the wave is 6 x 0.6 = 3.6 m. This is less than 4 m, so the water stays out. Without mangroves, 6 m is more than 4 m, so it goes over.
4. Why is a boat in deep water often safer in a tsunami than a boat in the harbour?
In deep water the wave is long and low and only lifts the boat. Near the shore the wave piles up and becomes tall and strong, and can throw boats on to land.
Common mistakes
- Going to the shore to watch the sea pull back. This is a sign of a tsunami. Run to high ground at once.
- Thinking the first wave is the biggest and the danger is over. Later waves can be larger.
- Thinking a sea wall alone is enough. Walls can be overtopped, so warnings, high ground and natural shields are also needed.
- Thinking only big disasters matter. Regular storms and surges also damage boats and wells, so preparing every year is important.