They say that a movie is only as good as its villain, and the new movie Titanic, now packing people into theatres all over the world, has a whopper: a giant block of ice that tears open the “unsinkable” ship’s hull and, a couple of hours later, send it to the bottom.
Icebergs have bedevilled ships in the North Atlantic since the earliest crossings. You might say they automatically have right of way: they don’t move for nobody, not even the mightiest passenger liner ever to set sail. But you can hardly blame them for that: after all, the iceberg that the Titanic hit, like every other iceberg in the ocean, began forming thousands of years ago, long before humans had even dreamed of sailing across the ocean.
Of course, icebergs don’t occur just in the North Atlantic: they’re also common around Antarctica and a few appear in the North Pacific. But the ones in the North Atlantic get the most attention because of a tendency to drift into shipping lanes. Shortly after the Titanic disaster, the International Ice Patrol (IIP) was formed to monitor icebergs and warn shipping, and I highly recommend that anyone interested in icebergs pay a visit, like I did, to their web page at http://www.rdc.uscg.mil/iippages.
Today’s iceberg was born about 1,000 B.C. as snow that fell on the glaciers of Greenland. Over several months, that snow became firn, old, granular snow. As decades passed, more snow fell on top of it and became firn in its turn. The weight of the continually accumulating snow compressed the lower layers of snow into very dense ice. Eventually, the weight grew so great on it that it began to flow: in other words, it had become part of a glacier.
Greenland’s glaciers flow at impressive rate of up to sixty-five feet a day. When they reach the sea, huge slabs of ice are “calved” from them, broken off by the action of the rising and falling tides. These slabs of ice are what we call icebergs.
More than 10,000 icebergs–perhaps as many as 30,000–are produced by Greenland’s glaciers every year. The shape and size of those icebergs is largely determined by which glacier spawned them. Icebergs from some glaciers, for instance, meet water away from the coast, at the head of a narrow fjord, which limits the size of the icebergs that can escape into open water. Glaciers that calve icebergs directly into the sea probably produce the largest ones.
Once they’re in the water, icebergs are moved not so much by surface currents and wind as by subsurface currents. One of the first things most people learn about icebergs is that there’s more of them underwater than above water–about seven-eighths below to one-eighth above. That’s because, although ice floats (unusual in itself; no other solid substance floats in a liquid version of itself) its density is still very close to that of liquid water. Archimedes’ Principle states that objects float when they’re able to displace an amount of water equal to their own weight. Since ice’s density is so close to water’s density, most of it has to be submerged before it displaces its own weight in water.
That means that there’s much more surface area for subsurface currents to push against than there is for wind and waves to push against–which is why it’s not uncommon to see icebergs moving directly into the teeth of strong winds.
In order to make it to the shipping lanes off Newfoundland’s Grand Banks, icebergs from Greenland have to ride the currents from Baffin Bay through the Davis Strait and Labrador Sea. Most melt before they ever get that far. Those that do are just hastening their demise: the waters are much warmer in the Atlantic and so they melt that much faster–on average, within about two months.
Nevertheless, a large iceberg can take a lot of melting, which is why icebergs sometimes show up amazingly far south, riding the warm waters of the Gulf Stream. In 1926, the southernmost known iceberg was spotted just 150 nautical miles from Bermuda. Icebergs have also been known to travel as far east as the Azores.
The fact that so much of an iceberg is underwater also increases the hazard they pose to shipping. The Titanic, for example, didn’t hit the part of the iceberg that showed above water; it looked to those on board like it would miss it, right up until the last minute. The ship was apparently done in by a large spur of ice under the surface.
The iceberg the Titanic hit was estimated at the time to be 50 to 100 feet high and 200 to 400 feet long. (One of the first ships to reach the scene after the disaster, the S.S. Mackay Bennett, photographed an iceberg that may have been the one the Titanic struck (bodies and debris were floating around it) although no one can be certain.) The Titanic may have been the largest moving man-made object to that time, but it was done in by a very average iceberg; the International Ice Patrol considers that a “medium” iceberg. Its size classification system ranges from “growlers,” which are less than 17 feet high and less than 50 feet long, through small, medium and large to very large, which are more than 240 feet tall and more than 670 feet long–in other words, approaching (and in many cases surpassing) the size of the Titanic itself. Some are the size of small–or even not-so-small–islands.
The largest icebergs are found in the Antarctic, where, a few years ago, the Larsen Ice Shelf sapwned an iceberg roughly the size of the U.S. state of Rhode Island.
Icebergs are also lumped into two shapes: tabular (steep sides with a flat top), and non-tabular, which includes such sub-categories as dome shaped, sloping, blocky and pinnacle. (The tallest pinnacle-type iceberg on record had a tower of ice more than 500 feet high–in other words, about the size of a 50-story building.)
As noted earlier, there’s nothing you can do to stop an iceberg from drifting wherever it wants to–it simply weighs too much. From time to time experiments have been conducted to see if there’s a way to accelerate the disintegration of icebergs. Gunfire, mines, torpedoes, depth charges, thermite and bombing have all been tried–and failed.
Calculations indicate it would require 1,900 tons of TNT to break-up an average-sized iceberg of 70,000 cubic feet. Melting it would require the heat produced by burning 2.4 million gallons of gasoline. Obviously, neither choice is practical.
Instead, the International Ice Patrol, and the various national ice agencies (such as the Canadian Ice Service), concentrate on tracking icebergs. The IIP coordinates reports of icebergs from commercial shipping and aerial reconnaisance by a variety of both public and public organizations, as well as conducting its own aerial reconnaissance.
No ship that has followed the IIP’s iceberg warnings has ever suffered a fatal collision with an iceberg.
It’s a shame they weren’t around in 1912.
