Divergent (Mid-Atlantic ridge, The Rift Valley), Convergent (The Andes, The Himalayas) and Transform (San Andreas fault, Dead Sea Transform). There are some sub-varieties but these are the main ones. This makes natural sense, so there’s no remembering to do, when you have two contacting plates: they can either be pushing together, pulling apart or rubbing past each other.

Incidentally, the idea that the giant continents move around all the time, enough to pull apart South America and Africa, and thrust up the Himalayas, obvious as it may seem now, was once not at all obvious. And if you stand on the ground in a big landscape, it’s kind of amazing to think of just what an amazing notion it was to propose.

I read about it in Bill Bryson’s, A Short History of Nearly Everything for which I found a relevant excerpt online - The Earth Moves (pdf) - should you be interested in the characters that had the courage to seriously propose it.

Tectonic plate interaction boundaries

Dan Kahneman and Amos Tversky’s behavioural economics theory modeling how we make decisions. It illustrates, among other things, some of the non-rational decisions we make as we are guided by emotion and heuristics in decisions. The sketch points out a few of the key points:

Loss aversion - the different shape of the curves as we make gains or losses (either side of the centre) represents how a loss of £100 annoys us much more than a gain of £100 gives us pleasure.

Diminishing sensitivity - the levelling off of the curves represents that we’ll enjoy winning £100, if we only have £100, much more than we’d enjoy winning £100 if we had £900.

Adaptation level - We don’t evaluate from some absolute level - we evaluate whether something is good or bad from a neutral reference point that we adapt to. So, by the end of a movie the movie theatre doesn’t feel dark, yet walking out feels blinding. Your reaction to the £100 example above was probably affected by whether you think £100 is a lot of money or a little, which is all to do with your adaptation level.

Sales aren’t always the bargain they seem