Why did my cake crack?

Looking back on a few archived cake photos, I noticed a sponge that I'd made that had pretty noticeable cracks on its surface. It didn't bother me at the time, as I went on to feature its photo in a post, but now, it really bugs me. Why did my cake crack like that?

Three things really:

•  My oven temperature was set too high, and the surface expanded faster than the inside, or
•  Too much baking powder was added, or
•  My cake was placed too high in the oven.

I think I did the latter one, most likely. As when I make a sponge, I have to fight for space for two tins to be next to each other in my oven. So maybe one tin went on the top shelf with the other tin in the middle. That's why they always say to "bake cake in the middle of a pre-heated oven". Middle.