Why do some beaches have black sand? TLDR: Location of recent lava flows and age of the island. Full Explaination: The “White Sandy Beaches of Hawaiʻi” are formed by the broken down shells of marine organisms from the coral reefs. Due to the extensiveness of Hawaiʻi’s reefs, the process of breaking down the organisms is constant. Fun fact: a main contributer in sand formation is the parrot fish. One parrotfish can produce about 90 kg (198 lbs) of sand per year! Black sand beaches are found on Maui and Hawaiʻi island. On Maui these are on the East and Southeastern shores. Why? These are the two youngest islands and the areas with the most recent lava flows. Black sand beaches are created when lava flows into the ocean. The beaches usually only last a few hundred years because the source of the sand stops when the lava flows end. Over the years the ocean erodes the beach, and the waves carry the black sand away. #Kīpahulu #NPS NPS Photo: Kūloa Point, at low tide the black sand is visible.