Morgan McCulloughSummer is in full swing, and because Chapel Hill is sadly not a beach town (despite the oppressing humidity!), I’ve been reminiscing about the most unique beach I ever visited. In the winter of 2019, I went on a trip to Hawaii. With my family, I spent this vacation exploring the Big Island of Hawaii, called Hawai’i. In planning the trip’s itinerary, I discovered that Hawai’i is home to one of the only beaches in the world with green sand.
This beach is called Papakōlea beach, which means “plover flats” (called this because of the Pacific golden plover birds that migrate to this beach), or simply Green Sand beach. Papakōlea beach is also named Mahana beach, which comes from the name of the volcano next to the beach, Pu’u Mahana. Pu’u Mahana was formed approximately 49,000 years ago, during an eruption of Mauna Loa, the world’s largest active volcano.
All of this was interesting to me, but I didn’t even consider why the sand was green when I drove to a remote parking lot in southern Hawai’i. I hiked for several miles across dusty, dry, hot hills and finally came to the top of what seemed to be a half-crater that looked down into the most peculiar-looking beach I’d ever seen. While the sand wasn’t exactly the vibrant green that I’d seen in photos, the in-person effect was striking. Now, 5 years later and dreaming of an escape to the beach, I finally decided to learn why the sand of Papakōlea beach is green.
Why is the Green Sand beach green?
The answer to this geological phenomenon, like many phenomena in Hawaii, is volcanoes. As mentioned, Pu’u Mahana is a smaller volcano that formed during a long-ago eruption of the gigantic volcano Mauna Loa. The exact origin of Pu’u Mahana is disputed, with some scholars believing that the volcano formed when flowing lava from Mauna Loa interacted with seawater and solidified (called a littoral volcanic cone), and others believing that Pu’u Mahana is its own independent volcano and the source of the magma itself.
Regardless of the nature of the formation of Pu’u Mahana, the erosion of the volcano is the source of the mineral responsible for Papakōlea beach’s green color. This mineral, olivine, is an abundant mineral that may be composed of manganese, iron, calcium, and/or magnesium in different combinations. Compared to other volcanic debris such as ash, olivine is much denser, so while sand, shells, and other minerals are brought out to sea by the continual waves of the ocean, olivine remains at the shore and gives the beach its green color. Although olivine is not rare, the bay that comprises Papakōlea beach is exceptionally narrow due to the volcano that formed it, which allows olivine to effectively settle and accumulate along its shores instead of being washed out to sea.
Like many of the arresting vistas in Hawai’i, the phenomenon of the Green Sand beach is attributed to volcanic eruptions. These eruptions deposit a unique combination of minerals that, when given enough time, become the beautiful beach we can appreciate today.
Peer Editor: Amie Solosky