Have you ever read a fact somewhere
and just… not believed it? This is Newlyn in Cornwall,
in the far south-west of England. When the British government's maps
say that a mountain peak is so many metres above sea level, they are talking about this sea level, the average sea level here. There's a little hut on that harbour wall and underneath it, there is
a narrow, vertical well that connects to the ocean. So the height of the water in that well
is the height of the tide. The waves don't make a difference. So for six years, 1915 to 1921, automatic equipment and
human tidal observers measured the sea level here, and the
average of all those measurements became the Newlyn Datum, the zero point from which all heights
in Britain are measured. The land here is solid granite
stable into deep time, so it seemed like a reasonable
place to use as a baseline. So that's fine. That's all sensible. The fact that I didn't believe is:
this whole part of Britain, the whole Cornish peninsula
for hundreds of miles, rises up and falls down by several
centimetres, twice a day, measurably, because of the weight of the tides. Now if that was true, it'd be
common knowledge, surely? And wouldn't it cause
earthquakes every day? I read that and honestly,
I didn't believe it, even as I looked round and started to find
peer-reviewed papers about it. So I arranged to talk to one of
the authors of one of those papers, a world expert on
ocean tide loading and... yeah. - On some days, Cornwall might
only move up and down by three or four centimetres compared
to its average position. Whereas on other days the movement
might be seven or eight centimetres. So a total range of maybe
even 15 centimetres. There's a horizontal movement
that's about a third or so, typically, of the vertical
movement in most places. So how we've measured
the movement of Cornwall and other places, is using GPS,
the global positioning system. And we can measure that
distance very precisely indeed at something like the two or three
millimetre level of precision. Now there are a lot of errors
that cause a bias in this measurement that we have to deal with,
to deal with the effect of, for example, the change in speed of the radio signal, as it goes through different layers
in the Earth's atmosphere, and so on. But what we can do is we can make
huge numbers of measurements of this. Our measurement of the average
tidal motion becomes very, very accurate and precise indeed. So we measure that tidal signal,
not just over one tidal cycle, but actually over a period
of three or four years, maybe even as much as 10 or 12 years. - It makes sense, I guess,
that the weight of water would compress what's underneath it. A few back-of-the-envelope
calculations and you can work out that there are gigatons
of water moving out there, in and out twice a day. And yeah, at the most extreme
high and low tide this whole area can move as much as six
or seven centimetres up and down. But why does it happen here
and not everywhere else? - The gravitational forces
of the sun and the moon that are what's causing the ocean
to move, and the tides, just happened to synchronise more
or less in their timescale with the way in which the
North Atlantic is able to move. It's just a little bit like
if you have a glass of juice, but if you swirl it around
at just the right speed, you can build up quite a
big slosh around the edges of the glass. Whereas if you swirl it at completely
the wrong speed, as it were, for that glass, then you get a much
smaller amount of motion. Around the coastlines of the major oceans are the places where the tidal
loading is generally larger. So around Western Europe, Greenland, and through to the Bay of Fundy
around the Atlantic coast there around the Gulf of Alaska
and also around New Zealand. So the reason it doesn't start causing big things
like earthquakes is because these movements, although they add up to something
appreciable and measurable by our new modern, accurate techniques
are actually very small relative to the scale of the whole earth. But that's sufficient for the
most accurate engineering work to need to worry about this problem. - Thanks so much to Professor Clarke, I've put links to him and to the
papers that I read in the description.
Tom Scott is one of the most interesting people on YouTube, every video is fascinating and well made. Definitely recommend checking out his other videos
There comes a time in every one of us baldies' lives where you have to accept that the glorified combover isn't convincing anyone any more.
It's time to buzz that hair, Tom
That red shirt is iconic. Put it on a stamp. Thats what happens right?
I see Tom Scott in the thumbnail, i click
Cool 😎
I now have an image of Cornwall being like a geological diving board, flexing up and down a little
The sea behind him looks fucked up due to the framerate of the video, like it's from Morrowind.