Tsunamis occur after earthquakes when one tectonic plate subducts or goes below a continental plate. This is generally between an oceanic plate and a continental plate. The deformation that accumulates between the two surfaces causes the tsunami. If you have two pieces of sandpaper and push them against each other, you'll see that at a certain point they'll move apart. That's essentially what happens between two tectonic plates. In the case of a tsunami, it needs a vertical movement of the ground to initiate a disturbance to the surface of the water. There is a plate in that region and it is a subduction zone, so it's possible that there will be a tsunami. However, you can get movements of one plate relative to another without large earthquakes happening and without vertical displacements of the ground below.

I think the problem is that it sounds like an incredible amount, but if you actually weigh that amount up with the weight of the entire globe, then it's an incredibly small amount. You're looking at something that's the size of a pin head compared to the entire volume of the Earth. So I think the answer is no, it's much less than you might think.

They are certainly produced due to volcanic action. Diamonds are formed in diatreme pipes, which are a kind of very steep sided vent down into the Earth. This provides the very high pressure and temperature that diamonds need to form. So it's more of a drilling downwards effect than a coming up and exploding out of a volcano effect. You need the high temperatures, but principally you need the high pressures as well.

The Richter Scale, contrary to popular perception, is actually just derived for California. It's a measurement based on the displacement measured on a seismograph. This measures the displacement of the Earth due to ground motion. It's an empirical measure, and also logarithmic. If you take a magnitude 5 and a magnitude 6 earthquake, the magnitude 6 will be bigger in terms of energy release than a magnitude 5. But a magnitude 7 will be roughly 1000 times bigger than a magnitude 5.

It's essentially the same principle as if you get a cube of sugar and drop it in your cup of tea. It sets up a disturbance in the water surface and it doesn't reach equilibrium again immediately, so you get a lot of oscillations instead of just one. This gives you more than just one wave. They all add together.