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Introduction to Icebergs
Ever since the 6th Century Irish monk Saint Brendan wrote of his voyage to the
West "we passed by towering crystals that rose up to the sky" people have been
fascinated and frightened by icebergs. For 1,400 years people asked the
questions; Where do they come from, Where do they go, How do they move, How
many, How big, How cold.
Nearly 100 years ago peoples interest was once
again focused on icebergs when on the morning of April 15th 1912 the Ocean liner
R.M.S TITANIC hit an iceberg and sank taking 1,500 people to the bottom of the
North Atlantic. Twenty years ago oil exploration started on the Grand Banks of
Newfoundland and off the Coast of Labrador. This activity drove many research
projects to examine these questions along with other questions like; is it
possible to tow icebergs, Is it possible to melt or blowup icebergs. In recent
years interest has peaked with the release of the block buster Movie TITANIC and
today millions of people worldwide are interested in icebergs and are still
asking the same questions that Saint Brendan asked on that day almost two
millennium ago. At PAL Environmental Services we have over 20 years experience
in studying icebergs. We are retained by both private sector and government to
answer these same questions; Where are the icebergs, What they are likely to do,
and how to respond. Even though nowadays we use computers, satellites, and
sophisticated aircraft filled with modern electronics, the individual beauty of
these "towering crystals" is still not lost on us. The following represents some
of our collective knowledge on the subject.
Where do icebergs come
from?
The principle origin of icebergs that reach the Grand Banks are the
Tidewater glaciers along
the West Coast Greenland. Between 10,000 - 15,000 icebergs are calved
each year from 20 major Glaciers between Jacobshaven and the Humbolt Glaciers.
It is estimated that 85% of all icebergs that reach the Grand Banks come from
this area. Other sources of icebergs are the East Greenland Glaciers, which
produce only about half the amount of icebergs as the western ones. East
Greenland glaciers account for about 10% of icebergs reaching the Grand Banks.
The remaining 5% come from the glaciers and ice shelves of Ellesmere Island. By
studying the crystal structure of an iceberg it is possible to tell which
glacier from which it originated.
What shapes do icebergs come
in?
A fantastic variety of shapes result from the deterioration process
of icebergs. Despite the fact that no two icebergs are the same, there are
certain categories of
shapes that are used for iceberg observation. Often the terms; tabular,
blocky, wedge, dome, pinnacle, and dry-dock are used. The large ice shelf in
Melville Bay produces the bulk of the large tabular icebergs while the
Jacobshaven glacier in Disko Bay produces mainly pinnacle icebergs. The
Jacobsheven glacier face is 76m (250') high and 4 miles wide. The average high
of icebergs calved from this glacier is 67m (200')
How many icebergs
are there?
Approximately 40,000 medium to large sized icebergs calve
annually in Greenland and about 1 to 2% (400-800) of those make it as far south
as 48o north latitude. The numbers of icebergs that reach Newfoundland vary
greatly from year to year and are most commonly seen in the spring and early
summer.
How old are icebergs?
The icebergs that reach the east
coast of Newfoundland probably calved from a glacier between 1 - 3 years
before. They often spend a year or more trapped in the pack ice filled
bays of the Arctic islands until eventually passing through the Davis Strait and
into the Labrador current. Rarely do icebergs last more than one year south of
this point. All icebergs start as snow that fell more than 15,000 years
ago!
How are icebergs made?
Glaciers form on land as a result
of an accumulation of snow over thousands of years. Successive layers
compress earlier accumulations until, at depths below 60 to 70 meters,
glacial ice is formed. Glaciers "flow" or "creep" outward under their own weight
like a viscous fluid. When the edge of a glacier advances into the ocean the
pieces that break off are what we call icebergs.
How fast do icebergs
move?
The average drift speed of icebergs off the north east coast of
Newfoundland is around 0.5 Knots. Iceberg drift speed is influenced by many
factors including iceberg size and shape, currents, waves and wind. Speeds
greater than 2.5 Knots have been observed. Icebergs travel eccentric paths
(described as meander) so that the distance traveled by a berg is typically two
- three times the straight line distance.
Where do icebergs
go?
Before some icebergs completely deteriorate they may travel many
thousands of kilometers. Originating at around 75° north latitude in Baffin Bay,
an iceberg may travel up to 4,000 km south to around 40° north latitude (800 km
south of St. John's). Extremely unusual sightings near Bermuda and Ireland have
been reported, which is well outside normal limit.
Why are icebergs
different colours ?
Icebergs are mostly white because the ice is full of
tiny air bubbles. The bubble surfaces reflect white light giving the iceberg an
overall white appearance. Ice that is bubble free has a blue tint which is due
to the same light phenomenon that tints the sky.
The blueish streaks of
clear, bubble free ice often seen in icebergs results from the refreezing of
meltwater which fills crevasses formed in the glacier as it creeps over land.
The ice is blue because of the natural light scattering characteristics of pure
ice. Occasionally airborne dust or dirt eroded from land ends up on the glacier
surface eventually forming a noticeably darkened brown or black layer within the
ice of a floating iceberg.
How much of an iceberg is below
water?
Icebergs float because the density of ice (around 900 kg per cubic
meter) is lower than that of seawater (around 1025 kg per cubic meter). The
ratio of these densities tells us that 7/8ths of the iceberg is
below the water. Usually icebergs are 20% to 30% longer under the
water than above and not quite as deep as they are long at the
waterline.
How do icebergs break up?
Simply put, icebergs melt.
In the process they often calve and fracture into many pieces which can create
trails of smaller floating pieces (Growlers). Usually icebergs melt the fastest
at the waterline this is caused by the action of waves pushing relatively warm
surface water against the iceberg.. This Waterline "notch" which forms induces
calving of overhanging and submerged blocks. Melt and breakup rates change with
water and at temperature. For instance a large berg may take 90 days to fully
deteriorate in water temperatures around 0o whereas the same berg may only last
11 days in 10o water.
How much do icebergs weigh?
Icebergs off
the coast of Newfoundland and Labrador range in size from massive tabular and
blocky bergs in excess of several million tonnes to small bergs weighing 1% of
this. Categories of iceberg sizes which are used for recording iceberg
statistics range from very large (greater than 10 million tonnes and
hundreds of meters long) to large, medium and small bergs and on to bergy bits
then growlers, which are grand piano size pieces. The average iceberg weight for
the Grand Banks area is one to two hundred thousand tonnes. which is physically
about the size of a 15 storey building.
How cold are
icebergs?
The interior temperature of icebergs off the coast of
Newfoundland and Labrador is in the range of -15o to -20o C. Only at the surface
does the temperature increase to 0o C (the melting point). Oddly, icebergs in
warm water appear colder than those in cold water this is caused because the
faster melting, steepens the internal temperature gradient exposing the cold
interior.
Can you tow an iceberg?
Towing icebergs was first
demonstrated in 1971. It is now a common practice in the management of icebergs
for the offshore oil industry. Towing may not be the best term however, as often
massive icebergs are merely deflected slightly from their paths. The tow is
arranged by a vessel navigating around a
berg while paying out a floating tow line. A junction is made so that
the berg is lasooed and then tow tension is applied carefully to avoid rolling
the berg or pulling the line over the top.
What is the largest iceberg
recorded?
The largest Northern Hemisphere iceberg on record was
encountered near Baffin Island in 1882. It was 13 km long, 6 km wide and had a
freeboard (height above water) of about 20 m. The mass of that iceberg was in
excess of 9 billion tonnes. Despite this staggering statistic, icebergs from
Antarctica may be many times larger than this. In 1956 an iceberg 207 miles long
and 62 miles wide broke from the Ross ice shelf. More recently, Iceberg B-10A,
48 miles long by 28 mile wide iceberg is being tracked off
Antarctica
How pure is iceberg ice?
Since glacier ice is formed
from falling snow and snow results from condensed water vapor in the atmosphere,
the water from icebergs is quite pure. Sometimes airborne dust from volcanic
eruptions carried on the wind (thousands of years ago) is deposited on the
surface of a glacier and gradually becomes trapped within the ice so that traces
are found in icebergs. But there are not likely to be many
pollutants!
Are icebergs unstable?
Often icebergs are very
unstable. The highly random shape and non-uniform melting and breakup of an
iceberg leads to frequent shifts in orientation. Tabular bergs are generally the
most stable whereas domed and wedge shaped bergs may roll completely over in
seconds without any apparent provocation.
How hard is iceberg
ice?
The crushing strength of ice is around 1% that of steel or 10% that
of concrete. Though this may not sound very hard, a ship collision with an
iceberg would surely end in disaster. The enormous momentum involved and
potentially huge contact area with the ice can generate hundreds of tonnes of
force on the hull which would cause it to dent and crumple.
Apart from
the TITANIC, have any other ships hit icebergs?
There have been many
recorded events of ships hitting icebergs, prior to the TITANIC there were many
vessels that collided with icebergs. According to IIP, LADY OF THE LAKE sank in
1833 with a loss of 70 lives. Between 1882 and 1890, 14 vessels were lost and 40
seriously damaged due to ice. This does not include the large number of whaling
and fishing vessels lost or damaged by ice.
More recently, the bulk carrier
Canadian Bulker hit a large iceberg at high speed (18+ knots), the impact
destroyed the whole bow section of the vessels. Another incident involved an oil
drilling ship the Pacnorse that was struck by a small iceberg while engaged in
drilling operations off the coast of Labrador. The impact speed was less than
1/2 knot, while there was no visible damage to the vessel, some years later
while on dry dock for inspection it was discovered that several of the vessels
ribs were broken by the iceberg collision.
Do icebergs hit the
bottom?
Yes. Icebergs often "ground" or contact the seabed and get stuck.
This is a frequent occurrence along the coast where icebergs are brought into
shore by irregular tidal currents or strong winds. Sometimes icebergs "scour"
the seabed creating irregular troughs that may be several kilometers in length.
The edges of the Grand Banks are criss-crossed with old and new iceberg scour
marks. In 1984 a large iceberg remained grounded on the edge of the Grand Banks
for 13 days before shedding enough volume to float free again.
How is
global warming affecting icebergs?
There is much debate on this issue and
no clear answers. We have observed a lager number of icebergs calving from the
glaciers of Greenland (fall 1998 saw an ice chart for Baffin Bay with 3/10 of
iceberg coverage) The ice caps of both Greenland and the Canadian Arctic are
melting. However, the warmer air and sea temperatures off the East Coast of
Canada seem to be reducing the number of icebergs that reach Newfoundland, so
one effect seems to be canceling the other.
Do Icebergs have any
commercial applications?
Yes. Icebergs are a valuable asset to the
tourism industry in many places. It is estimated that in Newfoundland alone, the
presents of icebergs close to shore generates millions of tourism dollars
annually. Several companies now bottle iceberg water and it is also distilled
into Iceberg Vodka and Iceberg Wines. There has also been many years of research
and studies into using large icebergs as a source of fresh water for places like
the Middle-East and California. Although, the problems associated with
economically transporting large icebergs over vast distances still has to be
addressed.
Still got questions?
We have been observing,
studying, and researching icebergs for nearly 20 years and are still find things
that amaze us. We don't have all the answers, but e-mail or write us your
questions and we will try our best to answer them.
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