More adventures
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Welcome
to our Nature Guide
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Science
bored many of us in school-it wasn't taught properly. Forget
all that!
Today, your movie is much more than just "sight-seeing".
Today, you expand horizons.
For 13 years, we've been having fun with field science. It's
great. You live and feel miracles from simple encrusting sponges
to the world's most sophisticated aviators. Watch Mother Earth
grow, and understand water's influence on our Planet. Feel
our world, ask questions-and ponder concepts. Consider"
Systems Theory ," a nuclear physics concept that says
everything in Nature is interconnected, andinterdependent. Change one element and you change the entire
system.
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Geology Section
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Formation
of the Bay
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Limestone karst gives Phang Nga its complicated beauty. And anything this beautiful is always complicated. The first important geology happened 300 million years ago when South East Asia was 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 biggest ridge became the Isthmus of Kra (Malay Peninsula), one of the World's Classic "land bridges"
that wildlife used to migrate all the way to Bali and Borneo.
When all the large islands were connected into one land mass it was a subcontinent called the "Sunda Shelf''. Look closely at the
channels between the islands, and you can see that many ridge lines were actually connected before the elements eroded them apart.
The overhang is created by tidal erosion. Often made by wave action as well, this notch is called the "Nape", the same name as the area where your head and neck join.
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Tidal currents running down the Bay hit North Panak head-on. Their power ate away two galleries of sea level, creating a nape that is both high and wide. The 1 top level was created first, allowing the exterior stalactites to form. It all makes for a great paddle in the shade. |
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Limestone is brittle, but it is also easily dissolved by rainwater. The fine silt that runs from the islands is called "alluvium." Because it is colored red by high iron content, this alluvium forms the red mud banks so common around Thailand's coastlines.It is quite likely that when sea levels were lower, Phang Nga Bay was a giant valley peppered with limestone pinnacles. As the alluvium ran from the limestone ridges, it created the jagged structures called "karst". The alluvium flowed into the deepest parts of the valley. Ever since the tides submerged the valley, tidal friction
regulates the level of the mud banks, keeping them just below the lowest low tide. |
The rivers carry alluvium (silt) down from the North to the mangroves,whose roots hold the mud banks together. Finally, look at how the islands run North-South.This is where the Earth folded during plate movements, creating the limestone ridges that are now islands.
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Changing tides eat away the waterline. These layers are not strata, which is usually on an angle, but it shows napes created by tidal erosion at different geologic periods. |
Limestone is almost 20% of the Earth's surface, but it only forms bizarre and
grotesque formations in areas of heavy rainfall. There is karst in the Balkans, but most
karst is at least tropical or Equatorial (like Phuket at Latitude 8,), where heavy rains
create jagged surfaces and honeycomb caverns. Originally coral, the hard and brittle
karst is "porous". Water almost never pools on the surface -streams actually disappear
into the Earth, and we paddle throught river caves from 2-10K long high up in the
mountains. This land is usually rolling hills and valleys, with few pinnacle towers.
You will also see sedimentary strata mixed in with the coral-based karst. This is
classic sea-bed strata that intruded into the karst when it was on the ocean floor. This
thick, sedimentary strata forms some of the oldest rock in the Bay. |
With its origins in coral, limestone is brittle.You see countless cracks or faults in the rock created by pressure.When large faults slip, the limestone breaks off in blocks, often big enough to become these islands.Imagine huge limestone blocks floating on the Earth's crust
like a cube of ice
floating in a glass of water. When continental plates drift, the limestone spins and bobs up and down just like ice does when you put your finger on the cubes. These cracks collect oxide before the rock rotates again, taking the iron ore high above sea level. Percolation enlarges the cracks, depositing particulates "downstream" as flowstone. Caves form along these cracks when water percolates downhill, filling the cavern with stalactites. Some cave roofs have holes leading to either sunlight or another cave, the earliest point of Hong creation. Eventually, the cavern will collapse, one way of forming a "Hong", which is Thai for chamber or room.
(More on this later.)
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The top photo shows exterior stalactites created by percolation, and a long, deep Hong created by a collapsed semi-tidal cavern. The cavern remains at the back of the 2K "overnighter" Hong, relentlessly percolating away.
The bottom cave sits in mountains at the top of the Peninsula. It's easy to see how this river cave runs along a fault line, and how water seeping down the fault formed these stalactites.
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Limestone
and Percolation
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Water is today's theme. You are obviously surrounded by sea water, but it's rain
water that creates the bizarre karst that attracts people to Phang Nga Bay. Even in thedry season, rainwater drips down inside the cave in a never-ending process that eatsaway the islands.
Heavy rainfall creates karst, so these grotesque shapes are usually found in the
Tropics. The combination of raised reef limestone in a tropical monsoon region
creates this great karst region. |
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The process that dissolves particles in the water that flows down through the island is called "Percolation" - in the same way as percolating water goes through coffee grounds. Clear water picks up the coffee molecules as it runs through the grounds, and drips brown-colored coffee into the pot.
Phang Nga's islands are sculpted by the same percolation process. The rainwater "on top of the islands is slightly acidic, boosted by acids in decaying vegetation on top of the islands. Since limestone and seawater are both alkaline, percolation corrodes the rock faster that the seawater. With gravity on its side, rainwater finds cracks (faults) in the rocks and fills them. The difference in Ph (acid/alkaline) corrodes the rock, slowly dissolving molecules into the water. This enlarges the cracks until they find their way completely down through the rockto sea level, the water table in small limestone islands. These cracks
enlarge into drainage tubes which become
caves and "Hongs," today's big attraction! |
Both interior and exterior stalactites are created by percolation.In fact, many exterior stalactites were born in total darkness. When the fault line that created them enlarged and fellaway, the stalactites became exposed so we can see them.
Some of South Thailand's largest stalactites are these 20 meter columns in a Far South expedition sea cave. |
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| Percolation creates this stalactite's oxide stains. |
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The oxide (iron) is carried down the three rivers that empy into the Bay from deposits high in mountains to the North. But we see oxide stains hundreds of meters above sea level, and the seas never rose more than 75 meters above today's heights
How did the oxide get up there?
It didn't -the islands spun down
to the sea. That rotation took millions
of years, but you can see evidence of
that spin from the Strata in the cliff
faces. Right now, most of Phang Nga's
strata sits at an angle of 45%-60%. In
Ha Long Bay, Vietnam, strata can sit
at 75%-85%. This drops the islands
into the sea and the mud, allowing red
oxide to intrude into the cracks and
cavities in the coral-based limestone. |
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