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Roger Weller, geology instructor

wellerr@cochise.edu
                                 

Green Sand
Mike Peters

Physical Geology

Fall 2006 

Is There a Green Sand Beach?!

 

            Throughout the world, beach sand is usually quartz-rich sand. Naturally, there are beaches are on every continents. Most sands comes from mountains and land near oceans or lakes. As we learned in the geology class, there are feldspars, pyroxenes amphiboles, quartz and mica in mountains and lands. None of the minerals are left untouched. They are faced with different weathering aspects such as, physical, chemical and mechanical. The sands are a result from erosion, a chemical weathering and wave action, a mechanical weathering. The wave action force has the capability of breaking and shaping the rock fragment through constant abrasion.


wave action (mechanical weathering)                                        photo courtesy of R. Weller

 

            With the Quartz’s hardness on the Mohs Scale as a seven, it is only three steps below the hardest minerals. The quartz doesn’t react to any chemical weathering. However, the feldspar does and has reacted to chemical weathering, carbonic acid; when water and carbon dioxide are mixed. Feldspar minerals change into a different mineral after having a chemical reaction, which is clay. Mica and feldspar are being eroded by lakes and oceans into the bed and leaving small amounts of themselves on the beach. That leaves you with quartz being the primary mineral in beach sand.

           


sandy beach                                                                               photo courtesy of R. Weller

 

There are three different types of beaches: rocky, gravel and sandy. The rocky beaches are typically when the rocks are dominantly quartz. It does not react to any chemical weathering but does slowly give in to wave action. We won’t live to see rocky beaches become sandy beaches.


rocky beach                                                                                photo courtesy of R. Weller

 

Your first guess on how gravel beaches are formed was probably right. The gravel is in the long process of becoming sandy through chemical weathering and wave action. It will be other hundred years or so for gravel to become tiny sandy particles. Not all of gravel or rocks come from the surface. There are many rocks and gravel on the bed of oceans and lakes. When waves are strong enough, it will pick up the gravel and deposit it on the beaches.

Entry at McMicking PointGravel Beach                                                                       photo courtesy of ShoreDiving.com
   

Now, back to my main point… Is there such a thing as a green sand beach? I would like to share my firsthand experience in my discovery of a green sand beach. Like most people, I have my share of going to many different beaches on the mainland of United States and Mexico. I have seen the color of sands vary from white, tan, black, gray, red or blended. I never knew that a green sand beach existed in this world. In July of 2005, my fiancée and I went to Oahu, Hawaii for a month. During that month, we decided to go to the Big Island to experience a natural untouched beauty and were awed by Kilauea and Mauna Loa Volcanoes. After the intense experience of the Big Island’s unique picturesque wonders, we met some friendly locals and they revealed to us about Pu’u Mahana or Papakolea beach. They are both the same beach but have many different names for Green Sand Beach, southern Big Island. It is the southernmost point in the United States. That particular area was covered with harden lava flow (basalt) for miles and miles. To get there, I recommend either a four wheel drive vehicle or hiking if accompanied with excellent shoes, enough water, snacks and plenty of endurance! It is not very easy place to get to. We decided to hike across the uneven basalt trail. After reaching the destination point, we felt like we have walked for days. Upon the cliff, it was an amazing sight and made all the pain well worth it. It was Papakolea or Pu’u Mahana Beach, the Green Sand beach!  At the top, the Green sand looks like glossy jade painted on the sand. We had to carefully hike down the sandy talus slope. Finally, we were actually standing on the Green Sand beach. This was in a secluded area and was probably half mile in width and 30 yards in length. The waves were pretty rough with a strong riptide. We went in the water with caution to cool ourselves off. We collected a small portion of green sand to show our friends and family back on the mainland. After all, a green sand beach is very rare occurrence in the world.
 

Our own small portion of green sand beach.

How was the green sand beach formed? There are four different types of lava: basalt, andesite, dacite and rhyolite. The olivine is only found in basalt and andesite. Although basalt is olivine-rich, Pu’u Mahana is breached cinder cone that gave the beach unique olivine sand feature. That area had strong wave action and a high concentration of olivine crystal in the magma produced by the Pu’u Mahana volcano. At first, the ocean waves erode the Pu’u Mahana cinder cone and turned it into a small bay. With the wave action, the separation begins from volcanic basalt fragments and green mineral olivine. Like the feldspar, the ocean eroded the lighter basalt fragments and carried it into the ocean bed. The olivine crystal’s density, being heavier, was left behind and formed a beach.

distant view of breached cone                        photo courtesy of Glendale Community College

 
photo courtesy of Glendale Community College   
closer view of breached cone and visible green sand 
           


olivine crystals on the beach                photo courtesy of Arnopole & Associates

Currently, Hawaii earns the right to boast for having the only green sand beach in the world. However, there are other different types of green sand beaches on Talofofo Beach, Guam. So far, they have not disputed Hawaii’s declaration as having the only unique beach. There is also another one which is not of this world. NASA recently found some olivine sand crystals in the icy comet of Tempel 1.  The olivine particles on Tempel 1 are much smaller than the ones on Pu’u Mahana. However, NASA said they are made of the same materials. So how long can Pu’u Mahana keep their status as the only place in the world with green sand? It is a sad occurrence, but as many more people flock to the beauties of the Green Sand Beach; the sand is slowly dwindling due to people taking a piece of such a incredible wonder.

Sources:

http://www.gc.maricopa.edu/earthsci/imagearchive/papakoleki.htm
http://volcano.und.edu/vwdocs/frequent_questions/grp5/question142
http://hvo.wr.usgs.gov/volcanowatch/2005/05_10_27.html
http://www.sease.com/regina/hawaiibeaches/html
http://www.hawaiianstyletravel.com/MauiGuide/Guide350.html
http://www.hawaiiweb.com/hawaii/html/beaches/papakolea_green_sand_beach.html