Tsunami explained: What they are and how much damage they can do
Here are key facts about tsunamis and the damage they can cause:
What is Tsunami and what causes it?
A tsunami is a shock of water that spreads through the sea, usually triggered by a strong earthquake beneath the ocean floor.
The sudden, violent movement of the Earth's crust can thrust up or drive down a section of the seabed -- with the rift displacing vast quantities of water that move as waves.
Tsunamis radiate in all directions from their source and can cover enormous distances, sometimes at the speed of a jet plane. They are a rare phenomenon but can create dangerously powerful currents and cause deadly flooding in coastal areas.
Large quakes are the main driver of tsunamis, but the phenomenon can also be sparked by other cataclysmic geographic events, such as volcanic eruptions and landslides.
In 1883, a volcano shattered the Pacific island of Krakatoa, causing a blast that could be heard 4,500 kilometres (2,800 miles) away, followed by a tsunami that killed around 30,000 people.
Large storms or a meteorite falling into the ocean can also be powerful enough to cause a tsunami, according to the US National Oceanic and Atmospheric Administration.
'Harbour wave'
The word "tsunami" comes from the Japanese words for "harbour" and "wave." Tsunamis are sometimes referred to as "tidal waves" but experts say this is inaccurate because they are not related to tides.
At their point of generation, tsunamis have a relatively small wave height, with peaks far apart.
As the waves approach the shore they are compressed by the shelving of the sea floor, reducing the distance between the peaks and vastly increasing the height. When they hit the coast, tsunami waves can strike repeatedly over several hours, or even days.
Roman historian
To those on the shore, the first sign of something amiss can be the retreat of the sea, which is followed by the arrival of large waves.
"The sea was driven back, and its waters flowed away to such an extent that the deep seabed was laid bare and many kinds of sea creatures could be seen," wrote Roman author Ammianus Marcellinus of a tsunami that struck Alexandria in 365 AD.
"Huge masses of water flowed back when least expected, and now overwhelmed and killed many thousands of people... some great ships were hurled by the fury of the waves onto the rooftops."
How much damage?
Several factors determine the height and destructiveness of a tsunami. They include the size of the quake, the volume of displaced water, the topography of the sea floor and whether there are natural obstacles that dampen the shock.
The Pacific Ocean is particularly prone to earthquakes and therefore to tsunamis, but over the millennia tsunamis have occurred in many parts of the world.
The tsunami of December 2004 in the Indian Ocean was caused by a 9.1 magnitude earthquake off the Indonesian island of Sumatra. It released energy equivalent to 23,000 of the atomic bombs dropped on Hiroshima, according to the US Geological Survey (USGS).
Around 220,000 people in 11 nations were killed, many of them thousands of kilometres from the epicentre.
Hashtags
Try Our AI Features
Explore what Daily8 AI can do for you:
Comments
No comments yet...
Related Articles
New Indian Express
2 hours ago
- New Indian Express
Eyes in the Sky: NISAR to decode Earth's silent warnings
On July 8, a local in Upper Mustang, Nepal, noticed an ominous flood wave rushing down the Chhuhama stream above Chumjung and Lo Manthang, close to the iconic Muktinath temple. The source was a rapidly drained glacial lake high on the Kali Gandaki glacier, located above 5,900 meters altitude. Over preceding weeks, the lake had steadily grown before emptying itself subglacially over 500 meters. Within hours, the floodwaters had ripped apart four downstream bridges, deposited debris across 35 kilometers, and caused substantial damage. This was the third highest Glacial Lake Outburst Flood (GLOF) ever recorded in High Mountain Asia, and a harsh reminder of how rapidly the cryosphere is changing under pressure from rising temperatures. At some places this year, temperatures soared 5°C above long-term seasonal averages. Experts say the frequency of GLOFs is increasing — with at least eight reported this year across Nepal, China, Afghanistan, Pakistan, and Kyrgyzstan —triggered by rapid ice melt, permafrost thawing, and newly formed glacial lakes. Now, all eyes are on NISAR, the joint NASA-ISRO Earth observation satellite launched on July 30, which is being hailed as a game-changer in forecasting such disasters and improving climate resilience. NISAR mission The NASA-ISRO Synthetic Aperture Radar (NISAR) mission is the world's first dual-frequency radar imaging satellite. It combines L-band radar from NASA and S-band radar from ISRO to monitor Earth's surface changes with unmatched precision — day and night, in all weather conditions. The first 90 days post-launch are designated for In-Orbit Checkout (IOC), during which systems will be calibrated and tested before full science operations begin. Once operational, NISAR will image the global land and ice-covered surfaces, including islands, sea-ice and selected oceans every 12 days, which experts say is unprecedented. 'NISAR will allow us to detect subtle movements in Earth's surface — including saturated soils on unstable slopes, deformation from earthquakes, and the slow growth of glacial lakes that might not be visible from above,' said Dr Gerald W Bawden, program manager at NASA's Natural Hazards Research Earth Science Division and a key member of the NISAR launch team, told this newspaper.
Scroll.in
4 hours ago
- Scroll.in
10,000 steps a day isn't the magic number you need to stay healthy
Your fitness tracker might be lying to you. That 10,000-step target flashing on your wrist? It didn't come from decades of careful research. It came from a Japanese walking club and a marketing campaign in the 1960s. A major new study has found that 7,000 steps a day dramatically cuts your risk of death and disease. And more steps bring even greater benefits. People hitting 7,000 daily steps had a 47% lower risk of dying prematurely than those managing just 2,000 steps, plus extra protection against heart disease, cancer and dementia. The findings come from the biggest review of step counts and health ever done. Researchers gathered data from 57 separate studies tracking more than 160,000 people for up to two decades, then combined all the results to spot patterns that individual studies might miss. This approach, called a systematic review, gives scientists much more confidence in their conclusions than any single study could. So where did that magic 10,000 number come from? A pedometer company called Yamasa wanted to cash in on 1964 Tokyo Olympics fever. It launched a device called Manpo-kei – literally '10,000 steps meter'. The Japanese character for 10,000 resembles a walking person, while 10,000 itself is a memorable round number. It was a clever marketing choice that stuck. At that time, there was no robust evidence for whether a target of 10,000 steps made sense. Early research suggested that jumping from a typical 3,000 to 5,000 daily steps to 10,000 would burn roughly 300 to 400 extra calories a day. So the target wasn't completely random – just accidentally reasonable. This latest research paper looked across a broad spectrum – not just whether people died, but heart disease, cancer, diabetes, dementia, depression and even falls. The results tell a fascinating story. Even tiny increases matter. Jump from 2,000 to 4,000 steps daily and your death risk drops by 36%. That's a substantial improvement. But here's where it gets interesting. The biggest health benefits happen between zero and 7,000 steps. Beyond that, benefits keep coming, but they level off considerably. Studies have found meaningful benefits starting at just 2,517 steps per day. For some people, that could be as little as a 20-minute stroll around the block. Age changes everything, too. If you're over 60, you hit maximum benefits at 6,000 to 8,000 daily steps. Under 60? You need 8,000 to 10,000 steps for the same protection. Your 70-year-old neighbour gets 77% lower heart disease risk at just 4,500 steps daily. The real secret of why fitness targets often fail? People give up on them. Research comparing different step goals found a clear pattern. Eighty-five per cent of people stuck with 10,000 daily steps. Bump it to 12,500 steps and only 77% kept going. Push for 15,000 steps and you lose nearly a third of people. One major study followed middle-aged adults for 11 years. Those hitting 7,000 to 9,999 steps daily had 50-70% lower death risk. But getting beyond 10,000 steps? No extra benefit. All that extra effort for nothing. Other researchers watching people over a full year saw the same thing. Step programmes worked brilliantly at first, then people slowly drifted back to old habits as targets felt unrealistic. Most steps happen without realising it Here's something that might surprise you. Most of your daily steps don't come from structured walks or gym sessions. Eighty per cent happen during everyday activities – tidying up, walking to the car, general movement around the house. People naturally build steps through five main routes: work (walking between meetings), commuting (those train station treks), household chores, evening strolls and tiny incidental movements. People using public transport clock up 19 minutes of walking daily just getting around. Research has also found something else interesting. Frequent short bursts of activity work as well as longer walks. Your body doesn't care if you get steps from one epic hike or dozens of trips up the stairs. This matters because it means you don't need to become a completely different person. You just need to move a bit more within your existing routine. So, what does this mean for you? Even 2,500 daily steps brings real health benefits. Push up to 4,000 and you're in serious protection territory. Hit 7,000 and you've captured most of the available benefits. For older people, those with health conditions, or anyone starting from a sedentary baseline, 7,000 steps is brilliant. It's achievable and delivers massive health returns. But if you're healthy and can manage more, keep going. The benefits climb all the way up to 12,000 steps daily, cutting death risk by up to 55%. The 10,000-step target isn't wrong exactly. It's just not the magic threshold everyone thinks it is. What started as a Japanese company's clever marketing trick has accidentally become one of our most useful health tools. Decades of research have refined that original guess into something much more sophisticated: personalised targets based on your age, health and what you can actually stick to. The real revelation? You don't need to hit some arbitrary target to transform your health. You just need to move more than you do now. Every single step counts.
The Hindu
4 hours ago
- The Hindu
SpaceX launches joint astronaut crew to ISS in NASA's Crew-11 mission
An international crew of four astronauts launched toward the International Space Station from Florida on Friday (August 1, 2025) aboard a SpaceX rocket, beating gloomy weather to embark on a routine NASA mission that could be the first of many to last a couple months longer than usual. The four-person astronaut crew— two NASA astronauts, a Russian cosmonaut and Japanese astronaut— boarded SpaceX's Dragon capsule sitting atop its Falcon 9 rocket at NASA's Kennedy Space Center and blasted off at 11:43 am ET (1543 GMT). They will arrive at the ISS on Saturday (August 2, 2025).
