What is the difference between Elsa's attacks?

Elsa has two attack modes, one where she shoots a spiral of cold and another where she shoots a smaller spiral with a snowball on the end.

What is the difference between these two attacks?
They both appear to work at range, so what makes them different from one another?


As an aside, why can't Elsa make an ice shield when she blocks?
You'd think if you could make ice from thin air (or the water in the air?), you'd generate a icy barrier in front of you to block incoming attacks.