Transcript

INSTRUCTOR

Open the file that you just downloaded from the course website, and Google Earth will open. Now, the picture you get of the screen may be different to the one that you're used to seeing. On the top left-hand side, there's a box, and that box contains Google Earth layers. And these layers are information which we're going to use.

What I would like you to do is to left-click and so select the one which says Depth Section Across. And you can't see the rest of it, but you will in a moment. Then right-click and go to the drop-down menu and say Show Elevation Profile. Now when that happens, you can see that the picture in the main screen reorientates itself. The top of the screen has a yellow line, and the bottom has a graph.

Now I would like to make sure that you've got turned off the water surface effect. So go up to the View menu, left-click, and you can see I've got it selected as a tick. Click with your left mouse button, and you can see that the picture in the main window has now got much, much clearer.

Now that yellow line is a transect which runs from shallow water, light blue, across in the region in which we call the continental slope into deep water. The graph at the bottom represents the water depth along that profile.

And now the really good bit. We can use that transect and that graph to work out the water depth along the line in yellow, and also to work out the average water depth at particular locations. So if you put your mouse on that bottom plot, you can see that straightaway in the view picture we have a red arrow.

Now the minus 124 metres is the water depth. So the water depth is 124 metres at that point. The 2.72 kilometres is the distance from the beginning of the transect, the yellow line. And the minus 0.2% is the gradient of the sea floor at that location.

Now as I move my mouse along this plot in the bottom, you can see that the arrow actually moves water depths, the distance along the transect, and the slope for those particular locations. You can see now that as I go over the continental slope region, it gets much, much steeper. And the water depth's increasing.

And then finally we get to the bottom section. And you can see that the water is much deeper. At that location, 185 kilometres from the start of the section, it's 4563 metres deep. Really quite deep.

And the last thing we can do with this elevation plot is we can actually use it to find the average water depth at a particular location. So if we go back over the continental shelf region with our arrow by moving our mouse, now if I left-click with my mouse button and drag the mouse across, you can see that I've got now a red line on either side of my yellow line in the top picture. That means that I've got the average depth along that bit that's shaded in red.

If you look at the numbers in the bottom window, you can see that the area of shading, it gives us the minimum, the average, and the maximum elevation. So the first thing to look at is the minimum elevation. That's minus 167 metres. Then the average water depth along that section is minus 147 metres. And the maximum is minus 127 metres.

So along that bit that's shaded, the shallowest water depth is 127 metres. The deepest water depth is 167 metres. And the average water depth is 147 metres. And finally, when you look at the range totals just underneath those numbers, you can see that the length that I highlighted was 45.9 kilometres.