In an atomic explosion why the shock wave goes in horizontal plane instead of a sphere? wht's going up?

Question

In an atomic explosion why the shock wave goes in horizontal plane instead of a sphere? wht's going up?

Answer 1

It is spherical... however, you only see the effects on a horizontal plane - the ground.  

Answer 2

That would be so in water. Air behaves differently and one one side is mother earth upwards there is air and space. Horizontally it's the same in any direction. The blast initially blast outward creating a drop in air pressure then the air rushes back colliding and hence a horizontal pressure wave