The sentence in question is:
Everyone always talks about the process of grief, which is as much the activity that is going on below the surface as above.
As far as I know, this should mean that the activity that is going on below the surface has the same amount as the activity that is going on above the surface.
However, it's not logical and definitely not what the author states immediately after the sentence, which is:
The image often used to illustrate it is an iceberg: what we see above the waterline -- our words, our appearance, our expressions -- is only a third of the whole.
Is it that I misinterpret the first sentence?