What you are looking at are a series of caves which seemingly contains tints of blue, along
with the colors orange, white, and black.
These are known as the Marble Caves, and can be found just above the water level of General
Carrera Lake in southern Chile.
Since people are highly curious about what exactly caused these colors I will rapid fire
explain each color's origin.
Orange occurs due to iron oxide inclusions, which due to weathering naturally have a rust
like appearance.
The black represents what was once fossil rich limestone with abundant carbon from organic
material before it turned to marble.
The white represents marble with very few impurities as this represents the default
color of calcium carbonate or CaCO3.
And, the blue is not actually a true color as it instead appears due to the reflection
of light on blue glacial sediment rich waters.
But, how did this geologic formation originate?
Before I answer this question we need to first establish what exactly marble as a rock type
is.
Marble is defined as a typically low grade metamorphic rock of a generally white color
which forms when typically low degrees of heat and pressure transform a rock that was
once more than a combination of 90% limestone and dolostone to a harder more dense rock.
This causes the calcium carbonate to recrystallize during this process which generally occurs
at a temperature of about 200 degrees Celsius or 392 degrees Fahrenheit.
Taking this into account, the Marble Caves were once a rich limestone environment which
got deformed after hundreds of millions of years.
The origin of this fascinating cave system which could be classified as a karst terrain
type landform can be traced back to a period of time 320 million years ago when the Earth
was in the midst of the the Carboniferous period.
During this period, widespread rainforests covered the land while large fish or sharks
dominated the oceans and seas.
And, what was to become the Marble Caves was the site of a temperature coral reef which
had numerous creatures with hard shelled parts.
As these creatured died, their hard calcium carbonate rich parts fell to the bottom of
the ocean.
Over a lengthy period of time, this eventually built up a thick limestone rock unit which
was likely once more 100 meters thick.
This limestone eventually rose above sea level due to not only uplift but also because the
regional sea level dropped as significant volumes of water were locked in ice caps that
formed at the planet's poles.
Now permanently above sealevel, separate sedimentary rock and breccia rock layers piled on top
of the limestone.
This rock unit was eventually buried by a significant extent of perhaps as much as 2,000
meters.
Then, around 30 million years ago, a major mountain building event occurred known as
the Andean Orogeny.
As an oceanic plate subducted into the mantle below, it transferred compressional forces
into the South American plate, causing rocks to deform, fold, and be uplifted.
It was during this process that the limestone turned into marble while also retaining significant
folds which can be seen in the Marble Caves.
Then, 20 million years ago, a large graben developed, causing a lengthy block of north-northeast
facing land to sink while the surrounding rock units rose in comparison.
After millions of years of erosion and weathering, the marble rock units became exposed on the
surface.
When the last ice age ended, meltwater poured into the low valley, eventually forming the
massive General Carrera Lake.
Although this water had a fairly neutral pH, we must take into account that calcium carbonate
which made up more than 95% of the marble has a pH of 9.9.
Thus, when wave action from the lake began colliding with sections of the marble, chemical
weathering caused large sections of it to dissolve.
Some of the tilted layers were slightly harder then surrounding rock, causing harder pillars
to remain while softer bits became large caves.
This weathering has occurred at a fairly rapid pace, with the caves forming completely within
the last 10,000 years.
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