Because of the addition of whipped eggs whites, this cake rises to the top of the springform pan in the oven, then collapses when it comes out of the oven. The top will have cracks and fissures, just like the ground after an earthquake. Instead of flour, the eggs provide the structure. When mixed with the melted chocolate and butter combo, the result is more fudgy than cakey. Folding in the whipped egg whites is reminiscent of making a souffle, so it's no surprise that it rises in the oven, then cracks and falls. The photo above illustrates why some call it an earthquake cake!