Nelson & His World

Flicking through volume one of 'The Naval Chronicle', I came across an interesting recollection of a curious event which happened at Plymouth:

On the morning of July 17, 1793, between seven and eight o'clock, the tide flowed into the harbour in a very unusual and rapid manner. It rose two feet perpendicular in nine minutes, and as rapidly receded again : this it did three times in the space of less than an hour. It ran so very swift in the pool, that it was impossible for a fast rowing boat to make head against it; one vessel lost her bowsprit by being run fowl of by another, and became perfectly unmanagable, owing to the rapidity of the current. Nothing of the kind had been observed since the great earthquake at Lisbon, when the tide ebbed and flowed in the same extraordinary manner.

I'm assuming there was no earthquake at Plymouth, does anyone know what might have caused the strange tide?
Or are tide movements such as this not uncommon?

I have access to the Times archive so I took a quick look to see if/how they reported it.

On 20th July they included a brief article and the wording was identical to the Naval Chronicle. So it looks as if the NC just "lifted" their report from the Times. That was quite normal back then.

I couldn't see any follow-up as to the reason for this incident. But it does sound like a sort of "mini tsunami" doesn't it.

Something at the back of my mind tells me there was something similar early in the 18th century (not certain about the date). I seem to recall a Time Team programme where they found evidence of an extraordinarily high tide with flooding etc. etc. - maybe on the Severn or somewhere like that. Sorry if this is a bit garbled - grateful if somebody can properly refresh my memory.

MB

A 'tsunami' in Britain, while exceedingly rare, is not entirely unknown. I live in a village at the foot of the Mendip Hills, overlooking the Somerset Levels, a stretch of very low-lying land that used to be flooded in winter before drainage ditches (called 'rhynes' locally) were made. Here is a link to the Somerset tsunami of 1607:


http://www.safecoast.org/editor/databan ... f-1607.pdf

Well, tsunami's in Britain, I would never have thought it! Many thanks for the link Anna, it was a real revelation.
When reading the description tsunami or similar came to mind, I just never identified them as a potential danger to these shores.
Really quite alarming!

Thanks Anna,

I got the wrong century and the wrong TV programme but I was thinking vaguely along the right lines.

MB

Don't go having nightmares - but there has been a theory around for years that one day a massive area of rock will part company with the island of La Palma in the Canary Islands. And that it will set off tsunamis which will wreak havoc all round the Atlantic including the U.K. and the eastern sea board of the United States.

Here is an article from the Guardian: http://www.guardian.co.uk/uk/2004/aug/10/science.spain

I doubt it will happen in our lifetimes - if at all - so I am pretty sure we can all rest easy.

MB

However, it could just be a tidal phenomenon which could have a variety of causes, rather than a tsunami.

I'm no expert, but have sailed a bit, and one of the most important, and first, requirements of the day was to study the tide tables! Many coasts have two high tides and two low tides a day, roughly six hours apart, caused of course by the movement of the moon and the sun, but there are local variations. Besides spring and neap tides, equinoctal tides, diernal tides, etc., they can be inflenced by barometric pressure and even the shape of the local coastline, which in turn affects the movement of the water. This can manifest itself in many ways, such as delaying the time of high tide, making it run faster than it normally would, or perhaps as here, the tide coming in increments. Of course we say that the tide 'comes in' or 'goes out', but it is actually a vertical movement – it just doesn't appear that way to the uninitiated!

Many tidal phenomina are well known, such as the Severn Bore as it is called, partly caused by the shape of the Severn estuary (and which might actually be what Mark referred to); and the Bay of Fundy in Canada, which I think has sone of the highest tides in the world, but there are others. The tides on the French coast and in the Channel Islands, are also normally higher than on the British side. I lived for many years in Poole, Dorset, which has a well-known harbour that is said to be the second largest in the world after Sydney, Australia. Although it has the usual double high tides, the size and shape of the harbour and its narrow entrance, means that the water doesn't have enough time to run out on the first ebb, before the next high tide. This resulted in what was called a 'stand', and the second high water when it came, was thus usually higher than the first. On the other hand I have seen the harbour with virtually no water at all, when it really ebbed, bar only a small stream in the centre of the channels – and all the moored boats and the channel buoys were high and dry. That was an amazing sight and you can understand why boats with double fin keels, or one on either side of the boat, were the very popular! On occasion, one could see single keel yachts right over on their sides – and I bet their owners had problems when the next tide came in!

So, I'm not convinced this was a tsunami – just an average day in the tidal world. Trimmer, I think the last sentence of your post is probably nearer the truth!

Many thanks for the second instalment Mark (I have just finished blowing up my water wings!)
Living in Croydon does reassure me a little, at 53 miles Brighton is the nearest stretch of coast. The Thames is a bit more of a worry though. I must stop this!

Devenish, I appreciate your views about tidal phenomenon. One small query: are the examples you give recurring, is there a pattern to them?
I admit I haven't as yet checked this, but as far as I know this is the only incident of its kind at Plymouth. Would this make it more likely to be a tsunami, or can the tidal movements you mention be unique incidents?

My vote is still for a tsunami. If it was a local tidal phenomenon, then I'm sure it would have been recognised as such - as perhaps Trimmer is suggesting... And the description is too specific for a ride rising incrementally, which is not that unusual.

Richard,

In so far as tidal movements are affected by the earth’s rotation, the influence of heavenly bodies such as the moon and sun, and other natural factors then, yes, to all intents and purposes, these are normally of a regular pattern, are of course measurable, but hardly unique. The earth’s tidal movements, as well as the effects of planetary orbits on them, have been well-documented over the centuries – to a large extent by the captains of naval and other vessels.

Other factors, however, come into play which affect this regular pattern including, as I think I mentioned, weather and pressure systems, and the shape of coastlines. To what extent they have influence of course varies greatly, but the effects can be marked and may be seen in the ways that I previously mentioned.

As regards the tsunami at Plymouth, I am perhaps now coming round to the general way of thinking on this forum – in that it may have been one! I largely say this due to the fact that, coincidentally, there appears to have been a small one near Plymouth only yesterday, or the day before. How strange is that – but I read it on the BBC website, so it must be true! Well, actually they had some film of it, as well!

Incidentally, I did come across another report of a similar phenomena off Plymouth in the nineteenth century, whilst googling yesterday – but now I can’t find it! It would seem, though, as if the area is prone to this sort of thing.

Kester,
considering the number of factors governing tidal movement, the unpredictable nature of the subject is not surprising. Although, I suppose some coastlines will always be more susceptible than others.
I too loooked at the BBC website and found record of a mild tsunami at Plymouth, 29th June 2011:

http://www.bbc.co.uk/news/uk-england-devon-13955321

Richard.

Well, actually that was the one I was thinking of – although I've only just noticed the date was in June, which you have given. Recent, but not that recent!