Island Geology

Hawaii is hot and cold volcanoes, clear skies, and open ocean. Like most Pacific islands it is all edge, no center, very shallow, very narrow, a set of green bowls turned upside down in the sea, the lips of the coastline surrounding the bulges of porous mountains. This crockery is draped in a thickness of green so folded it is hidden and softened. Above the blazing beaches were the gorgeous green pleats of the mountains. – Paul Theroux, Hotel Honolulu

The mountains of Kauai. Overlook into Kalalau Valley and the cliffs of the Na Pali Coast.  Photo by Dcrjsr (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

Last year, I wrote about islands for the A to Z challenge, but I guess I’m not quite finished. My focus then was the idea of islands as a cultural icon for Hawaii.  This year, I’d like to talk more about island geology and geography.

Each Hawaiian island starts out underneath the ocean over a hot spot of lava, part of an area geologists call the Ring of Fire. As the lava builds up over millennia, the mountain of lava rises above the ocean and forms an island. This island continues to grow taller and wider. The volcano can become so tall, that some of them even have snow on top!

Because of tectonic shift, the island eventually moves farther northwest away from the hot spot under the ocean. Eventually the volcanic activity slows down and animals and plants start to inhabit the island. Plants break down the hard volcanic rock into soil, supported by the process of erosion and weathering (sun, rain, wind). Lava soil is some of the richest soil in the world. 

There may still be active lava flowing over parts of the island but not others. Slowly, the island’s volcanoes become mountains and then hills and craters.  Around the island, coral reefs grow in the rich waters, providing habitat for ocean species. Beaches become larger and wider as the ocean grinds up coral from older reefs.

Eventually, the islands continue to move northwest and become smaller and more flattened as geologic time, processes and weather take their toll.

Even though we think of Hawaii as the eight major islands, the ones that people live on, there are hundreds of smaller islands and underwater sea mounts farther north, forming an entire archipelago that stretches to the Aleutian Trench off Alaska. 

Other species of birds and plants not commonly found on the human inhabited islands live in these further northern islands. Also, these northwestern islands are often inundated with vast amounts of garbage from the Great Pacific Garbage Patch, a swirling multilevel floating “porous continent” of garbage between Hawaii and California. 

Mountainous Na Pali Coastline of Kauai taken from the ocean. Na Pali means cliffs. Panorama photo taken by "Remember" [Public domain], via Wikimedia Commons

There’s always more to these islands than meets the eye.

P.S. If you are blog hopping from the A to Z challenge, please include your link if you comment! I try to reciprocate comments as quickly as I can, though I did lag behind last year, especially towards the end.

P.P.S. I am running two mini-contests during the A-Z Challenge (and into part of May). Here's how to enter.