What Does the Third Axis Represent in Riemann Zeta Function Zeros Graphs?

[SpaceDreamer]

I was looking at the Wolfram Alpha page on the Riemann Zeta Function Zeros which can be found here, http://mathworld.wolfram.com/RiemannZetaFunctionZeros.html

At the top of the pag there are three graphs each with what looks to be a hole through the graph. Now I know the graph is an Argand Diagram showing the function in bot the real and imaginary axis but what is the third axis? Another question is for the graph on the right the
l ζ(z) l which is the absolute value of the Zeta function correct? If it is not the Zeta function then what is the equation?

Is the hole in the graph a nontrivial zero or just a result of the function?

Thank You.

 

[mfb]

The third axis is the plotted value - the real part, the imaginary part, and the absolute value of the Zeta function.

Is the hole in the graph a nontrivial zero or just a result of the function?

The values are too large to get displayed, that looks like a pole.