Refer to this answer, which also elaborates how to find the max value and its (1D) index, you can use argmax()
>>> a = array([[10,50,30],[60,20,40]])
>>> maxindex = a.argmax()
>>> maxindex
3
You can then use unravel_index(a.argmax(), a.shape)
to get the indices as a tuple:
>>> from numpy import unravel_index
>>> unravel_index(a.argmax(), a.shape)
(1, 0)