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|REALLY STRANGE ICEBERGS
(Icebergs in the Gerlache Strait)
PICTURE AT THE TOP OF THE PAGE: I took this on January 15, 2009 in Paradise Bay, which is an inlet
off of the Gerlache Strait (see the map below). That big iceberg on the left side was grounded in the
channel through which we wanted to get in and out of Paradise Bay, but fortunately there was another way.
The ship in the picture is the cruise ship Marco Polo, which we saw several times during our cruise. Look
just to the left of the Marco Polo. That is an ordinary sized building, part of an Antarctic research station
operated by Chile, the rest of which is hidden behind the ship. That gives the picture and the iceberg some
scale, doesn't it?
On the second day, Jan 15, we cruised around the Gerlache Strait
and nearby bays and channels as suggested by the constantly turning
path labeled Jan 15 to the left. Paradise Bay, mentioned above, is
the last little zig into the mainland just before leaving the area.
This region was full of deeply weathered icebergs taking on many
strange shapes. Besides that, it was full of penguins and other
wildlife including whales, although I didn't get very good pictures of
the whales here. Down below, there are many iceberg pictures and
a few penguins. You will find more penguins in another gallery, not
In Gallery 1, there is a lot of talk about how the big tabular bergs had no good way to get in here at least
as of Jan, 2009. Some fragments from the disintegrating Wilkins Ice Shelf might find there way in here
sometime, but at least not yet. So we didn't see that type of iceberg. But we did see these:
These probably came from nearby glaciers as they reach the water and calve. All this weathering
suggests that they have been in the water for a long time.
The two pictures below both show the same iceberg from different directions (as we passed it).
I hate to speculate about something that looks like this, but I wonder if this surface was once on the
bottom where it became smooth (see a description of this is Gallery 6), then rolled over, then was so
affected by weathering by the wind that it took on this mottled appearance. Just a suggestion.
OK, actually just a guess.
Check out the underwater part of the iceberg above in the left-hand picture. More on that below.
|About all I can say
about these is that this
whole weathering thing
is mighty chaotic and
can make a whole lot of
|I decided to to call this one the "sea
monster". It is one of my favorite icebergs.
Again, notice the mottled appearance, which is
supposed be caused by weathering by the wind.
The water was clear and still enough that day that I got a few
pictures showing more than "the tip of the iceberg". You can
look through the water to part of the underwater portion, which
usually seems to look blue (picture to the right, 5 more below it,
and several others on this page). Now, here is a question: Does
that underwater blue color come from the removal of other colors
as the light comes through the water? Or has the water melted
the ice in the berg down to the blue glacier ice? (See more
explanation of the blue color in Gallery 3.)
I think it is more the second one -- that there is blue glacier ice
down there. Look at the third and fourth pictures in the column,
and you will see white areas as well as blue suggesting that when
the ice is not blue, you can tell. Also, in many pictures, you can
see where waves have worn the bergs down to blue ice just above
the water line, especially in Gallery 7.
|Now, if you are
but here is a
box with math
in it. You can
enlarge it by
clicking in it
just like any
skip it, if you
want, but it
explains how to
figure how much
of the iceberg
The last 2 lines
in it give the
If ordinary ice is floating in fresh water, the densities are 0.9168
for ice and 1 for water (the densities are in grams per cubic
centimeter - how many grams you can stuff into a cube one
centimeter on a side). Divide the densities, ice by water, and you
get 0.9168 -- 91.68% underwater. Subtract from 100%, and you
get 8.32% above water.
But the seawater is more dense, about 1.025 because of the salt
content. Divide 0.9168 by 1.025 and you get 0.8944 - 89.44%
underwater and 10.56% above water. That is usually rounded off,
and people say that 10% (one tenth) is above water and the other
90% (nine tenths) is below water.
But there are a couple more complications. For one thing, that
10% and 90% refer to volume, not depth. You need to refer to
the math box if you want to see why. If the top of the berg is
100 feet above water level, the bottom is probably not 900 feet
deep, although that might be true for a big tabular berg that has
not weathered much. But some irregular shaped berg can have a
great variety of depths depending on its shape. See the picture to
the right (and click it to enlarge it) for more explanation about this.
But the iceberg is probably not pure ice. There is likely to be
snow piled on top, and the snow is light and fluffy with many air
spaces. So it lowers the average density, and the whole thing
rides higher in the water than 10%/90%. And the original glacier
ice is made of compacted snow, and some of it might not be as
compacted as the rest. So the glacier ice itself can have a
variable density. If it were all pure blue gloacier ice, it would ride
a little lower than 10%/90%, but that would be very rare. So the
10%/90% is just an approximation anyway.
|There are a couple of larger ones, and a
big rock on the shore. Quite a bit of blue
ice is showing through on one of them.
|There are many small bits of ice here. The smallest
of icebergs are called "Growlers" (less than 3 feet
tall and less than 16 feet long). The next smallest
category is the "Bergy Bit" (really!). There were
plenty of each here, (MORE on classification - go
about half-way down the page after taking the link.)
|One of those has a smooth look as if
it has turned over. See Gallery 6.
|There are often stripes and dark layers on icebergs
which can be read to give clues to their history.
Usually, they start out flat but can become distorted
through partial melting, weathering, and tilting of the
iceberg. See Gallery 6.
Of course, you can see a danger to ships in all
this. The underwater ice can stick out to the
side farther than the visible part. So if you
think you are guiding your ship around it, you
might be surprised by a "crunch"!
On our ship, they said they only needed to worry
about the first 9 meters (29.5 feet) underwater
because that is how deep the ship went. Below
that, the berg can stick out all it wants.
Maybe you noticed the penguins in the picture just above. The penguins certainly did like to ride on bergs,
and the little dots in the second picture above are also penguins. There is more on penguins in Gallery 9,
not yet built.
Speaking of wildlife, there is a seal taking a nap on an
iceberg just to the left.
Here is an example of weathering digging into icebergs and striking
blue ice. Also, that is a glacier front in the background with a
near vertical ice wall and snow on top. It has, sometime in the
past, calved off icebergs that later floated away. Probably none
of these bergs came from this wall. They look pretty weathered
and have probably been in the water for a long time. So they
probably have floated in from some other glacier.
This is another iceberg with a glacier front behind it. The berg
has some nice, fine detail weathered into it, though.
Before leaving icebergs, lets just think for a minute about one other little detail about them. You
have probably heard it. Anyway here it is:
When an iceberg -- or any other floating ice such as an ice shelf, sea ice, or an ice cube -- melts,
that does not raise the sea level. The water it melts into just fits the same volume formerly taken
up by the underwater part of the ice.
However, most of the ice in the Antarctic (and in Greenland) is not floating. It is on land, and if
that melts or spills into the water some other way, then the sea level goes up. That is the problem
with ice shelves breaking up. They are holding back the glaciers that made them in the first place.
So when they break up, the glaciers are free to slide into the water and bring up the sea. That is
the way the Antarctic has to lose ice -- sliding it into the sea. Except for the Peninsula and a few
coastal areas in the summer, it is far too cold to melt. But a bit of extra warmth along a coast
containing an ice shelf can release a lot of extra sliding ice.
** WARNING ** WARNING ** WARNING ** MATH AHEAD MATH AHEAD
Want to know why the melted ice just fits into the underwater portion of the former iceberg?
Referring to what is in the math box above, the mass of the iceberg is
density of ice x volume of the whole iceberg = mass of iceberg
When it melts, it takes on a new density, the density of water. But it still has the same mass. So
density of water x new volume of water = mass of iceberg
But from the material in that box, the weight of the water in the underwater portion has to equal
the weight of the whole iceberg. That is what floats it. So they also have the same mass. So
density of water x new volume of water = mass of water that would fit into underwater portion
And that makes the new volume of water the same as the volume of the underwater portion. So it
would just fit.
Isn't that cool? (Har! Har!)