Natural Selection® Nature Photography
By Mark J. Thomas
That belief may come from what people say about blue icebergs,
'because they are old they predate all manmade contamination therefor
they are clean' and simply giving the same characteristics to snow.
Below an explanation for 'blue icebergs' taken from
http://www.blueiceberg.com/stories/blueice.htm
----------------------------
Why is this iceberg blue?
The short answer: This ice has been under extreme pressure from deep
within a glacier for hundreds of thousands, if not millions of years.
The interesting shapes are caused from wave action below and wind
erosion above, where the waves cannot reach. When viewing one of the
wider angle shots of this iceberg, it is easy to see where the high
point of the wave action is (where the iceberg is no longer smooth).
The more detailed answer: To understand why this iceberg is blue, it
might be helpful to learn a little bit about where icebergs come from
and why most appear to be white.
Most icebergs come from glaciers, which are huge, slowly moving fields
of ice and snow. They are formed through the continual accumulation of
falling snow. Glaciers are influenced by gravity in two ways. Gravity
causes the glacier to move in a downhill direction and it is also
responsible for the compression of the snow that is deeper inside the
glacier. If a glacier is near a coastal area, gravity usually causes
it to move in the direction of the sea. Where the glacier meets the
sea, huge chunks of ice continually break off from the face of the
glacier in a process known as "calving." This is where icebergs are
born. Once adrift, icebergs are at the mercy of the ocean currents and
the winds.
The vast majority of icebergs familiar to most people appear as huge
chunks of white ice. So why is this one blue? Remember, icebergs come
from glaciers and glaciers are formed as a result of snowfall. As
water freezes into snow, it becomes crystallized. A close examination
of a snowflake reveals a many-faceted crystal, not unlike a cut
diamond. These facets, or surfaces are capable of reflecting light.
Snow appears white for this very reason. As snow accumulates, the
structure of snowflakes trap a great deal of air. This is easily seen
if you fill a glass to the top with snow, then bring it inside and
allow it to melt. You quickly notice that most of what you thought was
frozen water, was actually air. Because snow contains a lot of trapped
air, light hitting it is able to reflect off the many internal
surfaces and we see this as white.
So why do most icebergs look white but this one is brilliant blue?
Now that we know a little bit about why snow looks white, we can
tackle this question. Most icebergs look white for the exact same
reason that snow looks white, and for a very good reason. Icebergs are
made from snow. Icebergs that come from relatively shallow or young
glaciers have not undergone very much compression. Therefore, there is
still a great deal of air trapped within them and they reflect back
much of the light that hits them as white light.
The blue color only occurs in very old ice from a very deep glacier
and is the result of hundreds of thousands of years of compression. As
you go deeper and deeper into a glacier, the weight of the ice and
snow above increases dramatically. As this pressure increases, the air
that was originally trapped by the falling snow is forced out. As this
happens, the reflective surfaces of our "snowflakes" disappear. The
ability to reflect light exists only when there is air between the
surfaces of the ice crystals. This very, very old, and very, very
dense ice is no longer capable of reflecting light. So it no longer
appears white.
That explains why it is not white, but that still doesn't explain why
it looks blue?
To understand this phenomenon, simply look into the deep end of a
swimming pool. Doesn't the water look blue? But if you fill a glass
with this same pool water, it isn't blue at all. It's clear. What
gives?
First, daylight or "white light," is not actually white at all. If you
have ever seen a rainbow then you know this to be true. Light that is
visible to us is actually a combination of many different wavelengths
of light. Each different wavelength has a different amount of energy
associated with it. If light is refracted through a prism, such as
raindrops, all the colors of our visible spectrum can be seen (a
rainbow). These colors always appear in the same order,
RED ORANGE YELLOW GREEN BLUE INDIGO VIOLET
(ROY G BIV) in direct relation to the energy associated with each
wavelength. The red end of the spectrum contains lower energy
wavelengths while the blue end contains higher energy wavelengths.
As light travels through water, which is much denser than air, the
weaker wavelengths of light, from the red end of the spectrum, quickly
filter out while those from the blue end penetrate the deepest. This
phenomenon is very familiar to SCUBA divers. At the surface, all the
colors are visible. But as the diver goes deeper, the colors start to
disappear. First red disappears, then orange, then yellow, right down
the spectrum. Finally, at the limit of most divers, everything appears
as some shade of blue. The water above the diver has filtered out most
of the sunlight. Eventually, if one goes deep enough into the ocean,
even the blues disappear and you are left in total blackness.
A blue iceberg is blue for this exact same reason. Since this ice has
been under enormous pressure for eons, most of the air, and therefore,
most of the reflective surfaces within this iceberg have been
eliminated. Light hitting this iceberg no longer "bounces" off of it.
Instead, it is absorbed into it. The weaker wavelengths of light are
quickly filtered out. The blue wavelength, however, has enough energy
to penetrate deep enough to either find some internal surface to
reflect back from or penetrate all the way through this dense iceberg.
Thus giving it its blue color. |
