The shape of an icicle is determined by the way it grows. Icicles grow from water that drips off a surface, such as the edge of a roof or a tree branch. As the water drips, it freezes and forms a thin layer of ice. This layer of ice is called the "axial core" of the icicle.

As more water drips onto the icicle, it freezes onto the axial core and builds up the icicle's shape. The water freezes in layers, and each layer is called a "lamella." The lamellae are separated by thin layers of air, which are called "interlamellar spaces."

The ripples on an icicle are caused by the way the water freezes onto the axial core. When water drips onto the icicle, it does not freeze evenly. Instead, it freezes first at the edges of the icicle and then slowly works its way inward. This creates a series of ridges and valleys on the surface of the icicle. The ridges are where the water has frozen, and the valleys are the interlamellar spaces.

The ripples on an icicle can also be affected by the weather conditions. If the weather is very cold, the water will freeze more quickly and the ripples will be smaller. If the weather is warmer, the water will freeze more slowly and the ripples will be larger.

The shape of an icicle is also affected by the surface that it is growing from. If the surface is smooth, the icicle will be smooth. If the surface is rough, the icicle will be rough.