Kindly have a look at the given below example which create, clear and load mat file in a MATLAB. The variables x, y, and z are just for reference, you can load/read images by using imread command of matlab:
% Create some variables x = rand(3); y = magic(3); z = eye(3);
% Save the variable x,y,z into one *.mat file save bathymetry.mat x y z