The Twin Lagoon is located in a large bay with a multitude of limestone rocks, also known as a Karst area. This area is a part of Caron Island.
The geologic orgin:
The first important geologic event happened 300 million years ago, when South East Asia was still the largest coral reef in history. Obviously formed under the sea, the crescent-shaped reef ran from Bali and Borneo north off Australia and drifted past Thailand, creating incredible pressures that rippled the landscape into giant ridges running North and South.
The consistently humid warm temperatures and the surface water which seeped into the porous subsoil let the lime sediments weather. Funnel-shaped valleys where formed, so-called dolinas and gigantic limestone caves. With progressive erosion the dolinas increased more and more in the depth, while the cave covers often collapsed. Thus originated the tower and cone mattocks which are typical today for many regions of South-East Asia. There are similar bizarr sceneries, for example, in Guilin in China or in the Halong bay in the north of Vietnam.
The fact that the mattock towers are in the water in this area, is the result of an other tectonic movement. The sea scenery originated from a overturning of the Malayan peninsula at which the western part sank and the eastern was lifted however.
Formation:
A karst landscape can appear only where there are water-soluble rocks like limestone and dolomite. Another name for them is carbonate rocks, after the main mineral they contain – calcium carbonate. Both rocks appeared as sea sediment. Karst stone has been used by man for building since prehistoric times. In some areas of the Kras, the traditional karst houses are built almost fully from stone cut by hand.
Limestone is a rock primarily made up of water soluble calcium carbonate, CaCO3. One litre of pure rainwater can dissolve a few milligrams of lime. A similar rule applies to dolomite rock. The solubility increases when carbon dioxide (CO2) from the air or the soil also dissolves in the water, creating a mild carbonic acid (H2CO3). The acid dissolves the carbonate rock, resulting in the appearance of calcium (Ca2+) and hydrogen carbonate ions (HCO3). This process takes place in both directions. One litre of rainwater percolating through the soil to the limestone can thus dissolve up to a few hundred milligrams of calcium carbonate.
H2O + CO2 = H2CO3
CaCO3 + H2CO3 = Ca2+ +2(HCO3)-
Ca2+ + 2(HCO3)- = CO2 + CaCO3 + H2O
The coastal area of Coron Island known as Twin Lagoon is undoubtedly one of the most impressive geological features in the region, especially when viewed from above.
Some of these large sunken blue holes formed by karst limestone are nearly perfect circles, and the shallow, rocky reefs that surround them are full of marine life. The collapsed areas of limestone form deep pools of blue, differentiating themselves from the shallower surrounding waters.
Atention: New! EarthCache Guideline Updated 10 June, 2019
Your tasks:
1) Have a look to the rocks right between the two lagoons. Are there any signs of errosion? Which ones?
2) What difference you can feel between the temperature of the two lagoons? What is the reason for this?
3) What do you think looks these two lagoons in 10000 years? Please explain your answer based on some of the observations you made during your visit.
4) Add a photo of you or a personal thing (like your GPS or thomething else) on the steps between the two lagoons.
Any logs that does not have the required photo will be deleted without notice. No excuses/reasons will be accepted, just simply log this earthcache when you have a photo to include into your log and then email answers. Do not log a find without it.
Mail me your answers 1.) - 3.) , attach the photo at your log and feel free to log this cache. If there will be a wrong answer, I will contact you.
source: http://www.karstmuseum.com/geology , https://www.unofficialguide.ph/twinlagoons/