The northern-most point of Moreton Bay, between Brisbane and the Sunshine Coast, lies Bribie Island. It's a sand island about 34kms long. People live on the southern part but up in the north, and a large section of it is national park. The beaches on the ocean side are gorgeous with fine, white sand and largely empty. The guide I was with told me that the sand comes from the Blue Mountains in New South Wales, a thousand kilometres south. The mountains erode and make their way into the water systems eventually getting washed out to sea. The eroded material gets rolled around and ground into sand in the ocean and travels up the pacific, depositing on the coast as it goes. By the time it gets up here, it has been ground up so much that the sand is very fine - almost like flour.