Typical Hawaiʻi Shoreline

Picture postcard beaches of white sand with turquoise blue water are what so many tourists imagine when Hawaiʻi is mentioned. Add a few coconut palm trees and you have the ideal beach of song and legend.

Mauna Kea Beach
The ideal Hawaiian beach represented by Mauna Kea beach on the Kohala Coast.
What surprises many tourists is that this postcard ideal is not the reality of our island. Black rock shorelines are the norm. Once under water you will find the sandy areas are interspersed with coral reef, the rocky shorelines usually supporting extensive coral reef rather than sand.

It is the coral that is the source of the white sand beaches here in Hawaiʻi, ground coral chewed and digested by the many coral eating fish. The pretty triggerfish and parrotfish chew the coral constantly, crushing the coral into a fine grained sand. Our pretty sandy beaches are literally fish shit.

Old Airport beach
Typical shoreline along the Kona coast, if there is sand, it usually becomes rock and coral at the waterline
While not exactly rare, there are quite a few, beaches where the sand continues into the water are not the rule along the Kona coastline. Most of the coastline feature black lava shorelines where the water crashes against bare rock. This rocky shoreline accounts for something like 90% or more of the coastline of the Island of Hawaii.

This stands as a stark contrast to other tropical shorelines around the world, where miles upon miles of beach are not uncommon, sand as far as the eye can see. Here on the Big Island the few truly good beaches are treasured and well used parks.

Coconuts are not the usual shoreline tree either, that role belongs to either the kiawe tree or what is locally called ironwood. Both names are not what you would find in the botanical texts. Kiawe is the island name for what the rest of the world calls mesquite or Prosopis pallida, a drought tolerant tree that covers much of the dry leeward shorelines. Likewise the local ironwood is actually the beach she-oak or Casuarina equisetifolia. The rather confusing name ‘ironwood’ is used for over thirty different species around the world.

Another surprise to many is that this island has black sand beaches. In place of ground coral these beaches are ground up lava, often created by the interaction of hot lava and cold water shattering the rock into a deep black sand. There is even a green sand beach, where the sand is in large part made up of the semi-precious gemstone olivine.

Hawaiʻi is the youngest island in the chain, the forces of erosion, coral growth, and hungry fish, have not had enough time to create the long sandy beaches. These beaches become more common as you jump northward from island to island. Oahu or Kauai have extensive beaches along a much large percentage of shoreline. The islands in the northwest Hawaiʻian islands, places like Kure and Midway are pretty much nothing but sandy beach.

We do have beaches, and they are pretty good.

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on Mauna Kea, Hawai'i.

Leave a Reply