May 24, 2022 — Yesterday I did a hike to Ponolu Beach. I set off by myself in Penni’s car, a 90 minute drive from Kona, to a steep hike down to a small black sand and vesicular basalt boulder beach shouldered by steep cliffs. Driving around Hawaii (we had previously done a limniscate around the island) and now up over the mountain to Ponolu, you become hyper aware of how little soil there is. It has simply not had time to develop. That’s why natural beaches are rare except on Kauai, the oldest of the islands. The Ponolu hike was short and steep (only 1 mile round trip) and the black gem of a beach was again, a rare thing, as beaches haven’t had time to develop either. Apparently the white and golden sand beaches around most of the hotels are all shipped in!
Hike to Ponolu Beach, a rare natural black sand beach, can’t recommend it enough! Even in the rain, it is lovely.
Here’s a great article about the imported sands.
Walk along Waikiki’s famed beach and you’ll find golden sand that is soft, inviting and picture perfect. The secret is that most of that sand is imported. During the 1920s and 1930s, barges brought tons of California sand to transform the swampy coast into the playground it is today. Periodic facelifts are needed thanks to beach erosion. While Waikiki’s sand may be largely imported, other island beaches are homegrown. Island age, types of erosion and sand composition determine the texture and color of Hawaii’s beaches.
Birth of the Hawaiian Islands
The Hawaiian Islands are of volcanic origin, formed when the Pacific Plate moved over a stationary hot spot. A hot spot is created when molten lava, or magma, punches through a weak spot in the Earth’s crust. The eruption creates an island. As the Pacific Plate moves northwest, the old volcanoes stop erupting and new ones pop up. That hot spot now sits under the southeast corner of the Big Island. Eruptions still add real estate to that island and are creating a new island, Loihi, which has yet to breach the ocean’s surface.
Sand Creation by Erosion
Islands surrounded by reefs, such as Kauai, have beaches created by both physical and bio-erosion. Physical erosion occurs when waves or currents pound against the reef, breaking off tiny bits that are churned about, something like rocks in a tumbler. The more the bits are rolled and pounded in the waves, the finer they become. Bio-erosion is caused by marine creatures that either bore into or graze on the reef. In Hawaii, one grazer is the colorful parrotfish. They use their hard, parrot-like jaws to scrape off seaweed or to feed on the coral itself. The fish cannot digest the coral shell and it is expelled. Sea urchins, sponges and boring worms all chip away at the coral reef, leaving tiny grains of sand behind. On the volcanically active parts of the Big Island, reefs are scarce or entirely absent. In this case, sand is formed mostly by the physical erosion of waves on lava rock.
The composition of Hawaii’s sand varies almost as much as the islands themselves. Mainland beach sand is composed of large amounts of quartz, creating the white color. In Hawaii, that mineral is rarely found. The white beaches are made up mostly of eroded shells, marine-life skeletons and corals. Kauai, for example, is framed with some 50 miles of beaches, most covered with finely grained white or lightly colored sand. The Big Island, youngest of the group other than subsurface Loihi, tends to have beaches with sand that is coarser grained, sometimes made up of pebbles. On the Big Island’s southern end, some beaches are jet black, formed by the waves pounding on hardened lava.
Other Colors of Hawaii’s Beaches
The Big Island is home to the green sands of Papakolea Beach, located on Mahana Bay. The green comes from olivine, otherwise known as peridot. This volcanic crystal sometimes is used in jewelry. In Maui, on the Hana coast, Kaihalulu Beach sports a combination of red and black sand, created by the erosion of older, crumbly, iron-rich lava. Glass Beach, on the southern end of Kauai, is a bit of an anomaly. Located near Port Allen Harbor, the beach is filled with tiny bits of polished sea glass. Glass Beach once was a dumping ground for broken auto glass and bottles. Thanks to Mother Nature’s waves, it now is a magnet for beachcombers looking for the unusual.