The lagoon - Tour D EarthCache
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Difficulty:
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If you stay in the wonderful area of El Nido, Philippines, you definitely have to visit this "hidden" area: It is the Makaamo Lagoon (or Cadlao Lake) and can be reached with a small hike of 20 minutes. Of course you need a boat (book Tour D or rent a kayak) to go there.
About the area
The island is the largest one in El Nido, occupying a land area of 10.06 square kilometers. Among all islands, it is the closest to town proper and has the highest peak that towers up to 640 meters above sea level. It is known for its white sand beaches, gradually sloping sea floor, hidden lagoons, and nature trails through its lush forest cover.
One of these nature trails leads to the charming Makaamo Lagoon (Cadlao Lake). Surrounded by mangroves, the lagoon is best enjoyed in silence at sunrise or sunset when the birds feed. Wildlife can be experienced here in this beautiful silence.
The rocks around this lagoon are Karst. Karst topography is formed when water forms a mild acid that dissolves the rocks, in this case limestone, and makes small fissures and holes that over time form into the caves, sinkholes, and rock formations that can be found all around the area.
Karst topography
The carbonic acid that carved the karst features into the limestone was formed as rain passed through the atmosphere picking up carbon dioxide (CO2) which dissolved in the water. Once the rain reached the ground, it passed through the soil that provided much more CO2 to the rain water to form a weak acid solution which dissolved the calcium carbonate in the limestone. The mildly acidic water then began to dissolve the surface along fractures or bedding planes in the limestone bedrock. Over time, these fractures enlarged as the bedrock continued to dissolve. Openings in the rock increased in size, and an underground drainage system began to develop, allowing more water to pass through the area, and accelerating the formation of underground karst features.
Makaamo Lagoon
As described above, carbonic acid rain carved the karst features into the limestone. The limestone is formed like a complex crater in this lagoon – an existing depression which was enlarged and deepened by the rain. Now the lagoon is formed like a natural bowl in the landscape.
This natural bowl in the landscape is holding brackish water throughout the year – a mixture of saltwater (which reached the lagoon via holes and channels in the limestone) and rainwater.
Your tasks : On your way to the lagoon you meet a tall "guardian" and national symbol of the Philippines. Near this guardian you have to perform a small climb to reach the crater with the lagoon.
1. There are two types of limestone at the location. One is milky-white/pinkish-white and the other is of a darker colour (reddish-brown). Describe the difference in hardness between the two and the difference between erosion of both types.
2. Take a small Karst sample during your visit in the lagoon and put it in normal household vinegar. Describe how the sample behaves in vinegar. Use your eyes and ears for this experiment!
(You can of course take a small piece home and try out this experiment).
3. (optional) Take a photograph of yourself, your friends or the lagoon to share the experience with other visitors.
IMPORTANT: Unless otherwise noted all caves, cliffs and holes in the area may not be climbed into/onto. The nature of karst rock is that it constantly dissolves and can break at any time.
Sources:
http://en.wikipedia.org/wiki/El_Nido,_Palawan
http://en.wikipedia.org/wiki/Karst
Edited the difficulty from 3.5 to 4.5 on 01 August 2014 because Tour D is currently not served and you have to use a kayak or motorboat. Also added the entry point where you can leave your boat.
Raised the difficulty from 4.5 to 5 due to changes in the terrain / path to the lagoon on 05.June 2022.
Additional Hints
(Decrypt)
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