Green Sand, Red Lava

As a general rule, I’ll take the mountains over a beach any day. That said, I’ve seen my share of sand: tan, grey, white, and even black. Green sand, however, has until very recently managed to elude me and for good reason. There are only four green sand beaches in the world: in Norway, the Galapagos Islands, Guam, and Hawaii. It was to the latter – Hawaii’s Papakolea Beach – that we set off, armed with a rather worthless map and a distinct lack of information.

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Had we done our research, we would’ve quickly realized that our idea of “let’s leave the car and take a short walk down to the beach” should rather have been phrased as “let’s walk 3 miles along the shore until we find the intricately hidden cove”. Not that I’d turn down a 3-mile hike, but knowing which direction to walk in would’ve been an asset. Having hiked half a mile along the shore and with no green sand in sight, we began to doubt the success of our venture. But just as we were thinking of turning back, we were passed by a local in a pick-up truck headed in the same direction.

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Now while I have fairly broad definitions of the words ‘truck’ and ‘driving’, the battered rig in the back of which we hitched a ride doesn’t fall into either. But a ride is a ride, and we were grateful for it. Along the way, we stopped to pick up two more lost families, and the truck slowly wound its way over the rocky, steep terrain, bouncing and leaning precariously every which way. At last, driving over the top of the last hill, the hidden cove stretched out before us.

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I’ll be honest – from a distance, it doesn’t look that green. But when you pick up a handful of sand and let the light shine through it, the color comes out a lot more clearly.

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So, why it it green? And why is the cove surrounded by layered cliffs that seem out of place when compared to the jagged black basalt that forms the rest of the coastline? In fact, the cove is what’s left of a cinder cone volcano that formed roughly 50,000 years ago. Over time, waves have eroded much of the cinder cone, forming the beach and the cove we see today. As the basalt of the volcano erodes, the lighter material – including glass, ash, and the black mineral pyroxene – is washed away, leaving behind heavier crystals of olivine – a beautiful green mineral referred to by locals as Hawaiian diamond.

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Because of scratches and imperfections on the surfaces of the crystals, the dry sand only seems dull green. It is only when water fills in these gaps and light passes through that the bright green color can be seen. As the cinder cone continues to erode, it provides an ongoing source of olivine crystals. Eventually the volcano will be weathered away completely, and the beach will be washed away by the waves, disappearing without a trace.

And because no post about Hawaii would be complete without photos of volcanoes…

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This has been your daily dose of mostly harmless science.

If you enjoyed this article, please comment below and check out more of my posts! I’d love for you to follow me on WordPress or on Twitter @harmlessscience (just click Follow on the right sidebar). Thanks for reading!

Olivine crystal close-up photo courtesy of Orbital Joe, Flickr Creative Commons.

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4 responses to “Green Sand, Red Lava

  1. Fantastic! How wonderful to find that incredible beach. I have little bottles of sand from unique places that we’ve been. Have you visited the pink sand beach at Big Sur, California? Great pics – makes me want to visit Hawaii again.

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