Fix the height of a column

Question

I have several similar slides in beamer. Each slide has 2 parts side by side. On the left hand, there is a tikzpicture in a minipage, it is same for all the slides; On the right hand, there are several blocks, some slides have more blocks, some have less. What I notice is, due to the different length of the blocks of the different slides, the position of the left hand changes - This is not what I want. I would like the height of the left hand to remain for all the slides, which is independent of the length and height of the right hand. Does anyone know how to do it?

Here are 2 typical slides, one could notice that the position of the left rectangle is not same between the 2 slides...

\documentclass{beamer}
\usetheme{Boadilla}
\usepackage{color}
\usepackage{tikz}
\usepackage{framed}
\usepackage{multicol}
\usepackage{xifthen}% http://ctan.org/pkg/xifthen
\begin{document}

\begin{frame}
  \begin{columns}
    \begin{column}{0.32\textwidth}
      \resizebox{0.66\textwidth}{!}{%  
        \begin{minipage}[t][10cm][t]{\linewidth-2\fboxsep-2\fboxrule}% Remove fbox rule/sep width
          \hspace*{-1em}{\begin{tikzpicture}[thick, scale=0.4]
              \filldraw[fill=white!20] (2,2) rectangle (6,12);
            \end{tikzpicture}}
        \end{minipage}}
    \end{column}
    \begin{column}{0.64\textwidth}
      \begin{alertblock}
        a \vspace{2cm} b
      \end{alertblock}
    \end{column}
  \end{columns}
\end{frame}

\begin{frame}
  \begin{columns}
    \begin{column}{0.32\textwidth}
      \resizebox{0.66\textwidth}{!}{%  
        \begin{minipage}[t][10cm][t]{\linewidth-2\fboxsep-2\fboxrule}% Remove fbox rule/sep width
          \hspace*{-1em}{\begin{tikzpicture}[thick, scale=0.4]
              \filldraw[fill=white!20] (2,2) rectangle (6,12);
            \end{tikzpicture}}
        \end{minipage}}
    \end{column}
     \begin{column}{0.64\textwidth}
      \begin{alertblock}
        a \vspace{7cm} b
      \end{alertblock}
    \end{column}
  \end{columns}
\end{frame}
\end{document}

Answer 1

You can achieve a consistent top alignment, if you set the optional parameters for both the frame and the columns environment:

\begin{frame}[t] % align frame content to top
  \begin{columns}[T] % align all columns to top of first line
    % definition of individual columns
  \end{columns}
\end{frame}