When I was a young lad I had an insatiable thirst for knowledge (actually I still do, but more so back then). I read books on everything I could get my hands on – from insects to spiders to atlases to books about space, science, just about anything. I wanted to see what was outside my door and understand everything around me and in the pre-internet, 3 TV channel age that it was, books were the way to go.

One of the books I read that stuck with me was about tsunami through the eyes of a scientist who investigated them and was trying to design ways to defend against them. I think it was actually called ‘Tsunami’. At the time the word ‘tsunami’ wasn’t particularly well-known with the term ‘tidal wave’ being used in its place. Prior to reading the book my mental picture of a tidal wave (tsunami) was of a giant wave (like the sort of thing a pro surfer rides) breaking over land, carrying with it some boats and debris, then just dumping a load of water where previously there was land – I knew that Britain was once connected to Europe by a landmass that was flooded courtesy of a tsunami in the dim and distant past so figured that was the outcome.

On reading the book it turned out I was completely wrong about virtually everything I thought I knew.

Back then there was pretty much no recorded film of a tsunami. This is long before personal video cameras, never mind mobile phones. So the scientist spent his time visiting places that had just been hit and one of his frustrations was seeing the incredible damage caused but having to rely on eyewitness accounts to try to make sense of what actually happened rather than seeing it for himself. Since tsunami are as likely to strike at night, without warning and kill most of the people who encounter them, his information was sparse.

But the things he found to be consistently reported by all people who survived tsunami were then forever embedded in my psyche and came back to haunt me when watching footage of the Boxing Day tsunami of 2004 and the recent tragedy in Japan. The first thing I learned was what a tsunami actually is.

Most tsunami occur when an earthquake causes a shift in the ground at the bottom of the sea. We’ve all seen pictures of an earthquake at a fault line splitting roads in two and pushing one side metres up in the air. Tectonic plates don’t care if they’re on dry land or at the bottom of the sea so if one occurs down there and a few miles of ocean floor suddenly finds itself raised upwards then a huge volume of water (all the water above the plate that’s shifted upwards) is displaced in a very short place of time. This causes enormous waves to start propagating outwards from the site of the shift. Except it doesn’t look very big to the observer on the surface.

Normal waves out at sea are caused mostly by the weather (either the wind, warm water mixing with cold or other similar actions). Even large waves are only really on the surface so are at most a few metres in height. However the wave generated by an earthquake starts at the sea bed and stretches to the surface. So instead of being a few metres in height it could be a couple of miles in height. Since earthquakes happen very quickly the resulting wave will be moving at serious speed – up to hundreds of miles per hour. Yet at sea you wouldn’t notice a tsunami wave at all – it would appear on the surface to be a normal wave or waves (there are usually multiple waves generated).

Things get scary when the tsunami waves approach land. As a 2 mile high wave reaches land the depth of the water reduces and this causes a huge build up of water while the wave slows down. Think of a bunch of runners sprinting along a road when they hit a deep muddy section. As they do this they slow down and the faster runners still on dry land quickly catch up and pack together with those wading through the mud – the density of people keeps increasing and it gets pretty crowded. Then when runners get clear of the mud they all spill out at once. In the same way the volume of water moving towards shore starts to build up and that’s where the first and only warning sign is.

The book talked about one telltale sign a tsunami was on its way. Suddenly, without warning and without any noise or fuss, all the water on the beach disappears in a matter of minutes. It’s like someone’s pulled the plug and the sea has drained away. When I watched footage from the 2004 tsunami I could see people standing on the beach looking out at shipwrecks suddenly revealed wondering what was going on. The book I read said in no uncertain terms that if you ever found yourself seeing a similar phenomenon then you should run for high ground as fast as you can, because what comes next will kill you for certain.

The reason the water drains away comes back to that huge wave building up as the tsunami slows down. Water starts to pile up and the usual ebb and flow at the beach gets halted so it all runs back out to sea. Shortly afterwards, instead of a huge surfers wave hitting the beach as I’d imagined, water just starts flowing and flowing and flowing carrying huge momentum. It picks up debris and destroys everything in its wake – particularly man-made. It’ll carry boats, ships, trees, cars, houses and it’s relentless. The scientist often found boats deposited several miles inland and he realised that when the water has extended as far inland as it could, gravity would kick in and it would flow back out to sea again. Some of the debris would be left in place, some of it dragged miles back out to the sea.

Until I read the book I’d imagined a single perfect wave crashing down on the shore. Afterwards I understood the mechanics of what was happening and how instead it made sense to think about it as a surge of a huge volume of water destroying everything in its wake. That there was very little you could do to predict or battle against it. And that your only warning is the sea disappearing. That stuck with me for 20 years.

Watching the footage from the 2004 Boxing Day and recent Japanese tsunami was horrifying for obvious reasons. But to actually see what I read about as a child unfold in front of my eyes knowing the damage it was doing was both fascinating and terrifying. Fascinating because as a child I wanted to see what a tsunami looked like. Terrifying because I was actually getting to see what a tsunami looked like. And it was every bit as bad as I’d imagined.