This scene, which takes place in the second to last chapter of the book, is one of the most poignant of the entire memoir. The book opens with the death of Eggers' parents and his tone, seemingly throughout, is one of detached maturity, dry humor, and dilligence. Knowing he is responsible for taking care of his siblings, Eggers writes with the strength and courage he probably hopes to embody, and it is clear that he is aware he only pretending to be an adult.
When he returns to Lake Michigan to scatter his mother's ashes, it is almost as if he is finally admitting all of the feelings he has felt all along, but because he has been the "man in charge," he's been hiding them. His thoughts, a reflection of his emotions, are raw, and full of anger, bitterness, and guilt. Yet, amidst these, he also has a rational sense of duty and acceptance.
His anger and bitterness (at himself, at the situation) is evidenced by his recurring use of the f-word in a non-humorous way. He's surprised by how light the ashes are when he begins to throw. He gets angry at himself for dropping some, as if this is a reflection of his inability to do anything right. This subsequently speaks the message, "Why was I put in charge? You should have known I couldn't really handle it." Moments of humor also sprinkle this scene ("I'm stepping on them! Of course I am...how fitting! How expected, a**hole!") to show that Eggers is attempting to avoid becoming overly emotional or taking things too seriously.
Though the scene is real-time was probably short lived, Eggers has so many different things running through his mind, it seems stretched out. He wonders if this moment is "beautiful and noble and right, or small and disgusting." Then, as if he realizes how introspective he's being, he begins throwing the ashes (and now small pebbles) faster, as if to simply get the job done and not make such a big deal out of it.
In short, the entire experience is completely overwhelming, and as a glimpse into the mind of someone experiencing hundreds of emotions all at once, it seems Eggers provides every detail possible. The reader can't help but respond with sadness, respect, and even a little laughter.