Physical Description of the Iceberg
One of the significant failings of research into the sinking of Titanic has been the lack of attention paid to the other large floating object involved: the iceberg. Yet the size, shape, density and hardness of that floating mountain of ice were all factors in creating the fatal damage to the ship. No honest assessment of the sinking can avoid the necessity of investigating the fatal iceberg.
The Size and Shape of Titanic's Iceberg
Icebergs come in a variety of sizes and shapes that vary with the locations where they were calved and their ages. No two icebergs have the same shape. Also, all icebergs are continually changing shape as they decompose by melting. Scientists who study icebergs have created descriptive names for bergs based on their characteristics:
Tabular A flat-topped iceberg with steep or vertical sides. Most show horizontal banding. Very solid. Length to height ratio less than 5:1.
Blocky A flat-topped iceberg with steep vertical sides.
Non-Tabular This category covers all icebergs that are not tabular as described above. This includes bergs that are dome-shaped, sloping, blocky, and pinnacle.
Drydocked An iceberg which is eroded so that a U-shaped slot has formed.
Pinnacled An iceberg with a central spire, or with more than one spire.
Wedged An iceberg that is flat on top and with steep vertical sides on one end and sloping on the other.
In addition to names describing their shapes, icebergs can also be described by their size. At the top on the size charts are the very large bergs that tower 46 to 75 meters above the water and are more than two football fields in length. The smallest true icebergs are growlers, which are less than a meter high and only 5 meters or so in length.
The berg in Titanic's path most likely broke off the Jacobshaven glacier on the west coast of Greenland. More than 85% of all the icebergs on the North Atlantic are thought to originate with that glacier or with the nearby Humbolt glacier. Approximately 40,000 medium- to large-sized bergs calve annually in Greenland. New bergs may spend a year or more in the waters of their berth before moving south through the Davis Strait. Seldom do more than 2% of them make it as far south as latitude 48 North. In April of 1912, however, a significant amount of ice had been carried much further south on the Labrador current. Titanic was a bit south of 42 North when it struck.
Icebergs from the Jacobshaven glacier have characteristically pointed shapes. There were few eyewitnesses to Titanic's iceberg. However, the descriptions that do exist seem to agree that the fatal iceberg had at least one towering point, and perhaps more. Quartermaster Thomas Rowe pacing Titanic's poop deck than night first thought he saw the masts and sails of a sailing ship. Another Quartermaster, Alfred Olliver, was not in a position to see any more than the highest portions of the iceberg. He described the "tip" of the berg gliding past where he walking on the Boat Deck. Lookout Frederick Fleet remembered the berg having a large, pointed top. On the morning after the tragedy, the chief steward on the German ship Prinz Adelbert snapped a picture of an iceberg with a large smear of red paint along the bergs waterline. That iceberg had a large central point with two smaller flanking points. In the dark, it could have been confused for a moment with the three masts of a sailing ship.
No clear-cut evidence exists as to the horizontal length of the fatal iceberg. Estimates have ranged from 200 to 400 feet. This range is in keeping with the approximate 60 to 100 foot height estimates of eyewitnesses. When combined, it appears that Titanic was the victim of a rather ordinary medium-size iceberg. It was probably a pinnacle berg that had started to erode into the drydock configuration.
Icebergs float because the dense ice in their cores is less dense (about 900 kg per cubic meter) than sea water (about 1025 kg per cubic meter. When an iceberg is first calved, as much as 20% of it may extend above the waterline. The reason for this is that the upper portions are often comprised primarily of snow, which is much less dense (lighter) than the core of the berg. Icebergs are quite unstable. As a result, they roll over frequently during their lifetimes. After a few rolls, the middle-aged berg has lost its topping of snow, leaving only the dense, hard-frozen core. The result is that less berg is exposed above the waterline. Older bergs float with only about 1/8th of their bulk exposed to the air.
The most significant factor with regard to understanding what happened to Titanic is that icebergs are typically 20% to 30% longer under the water than above. Thus, a berg that has a length of 100 feet above the waterline can be expected to be 120 to 130 feet wide under the water. The sloping ice shelves that extend outward beneath the water pose a significant threat to ships operating near icebergs. This is made clear in H.O. Pub 9, The American Practical Navigator ("Bowditch"):
Another danger is from underwater extensions, called rams, which are usually formed due to melting or erosion above the waterline at a faster rate than below. Rams may also extend from a vertical ice cliff, also known as an ice front, which forms the seaward face of a massive ice sheet....In addition to rams, large portions of an iceberg may extend well beyond the waterline at greater depths.
American Practical Navigator, 1995
Icebergs are the subject of continuous study at the Center for Cold Ocean Resource Engineering (C-CORE) in St. John's, Newfoundland. Richard F. McKenna, Ph.D., P. Eng, is Director of Ice Engineering for C-CORE. He confirmed for the authors of this paper the dangers of ice rams or other underwater extensions of icebergs. "Iceberg shapes are highly irregular," he wrote. "From a technical standpoint, we are cautious about making conclusions from above water shapes. That said, underwater shapes are quite variable and underwater protrusions beyond the water line extend (rams) are quite common."
The practical aspects of handling ships around ice are also discussed in Bowditch. Vessel operators are cautioned that if they must make contact with an ice floe:
...never strike it a glancing blow. This maneuver may cause the ship to veer off in a direction which will swing the stern into the ice. If possible...hit it head-on at slow speed....
...Keep clear of corners and projecting points of ice, but do so without making sharp turns which may throw the stern against the ice, resulting in a damaged propeller, propeller shaft, or rudder. The use of full rudder in non-emergency situations is not recommended because it may swing either the stern or mid-section of the vessel into the ice.
American Practical Navigator, 1995
Although this advice comes from a recent navigation text (1995), the dangers of ice rams were well known in 1912. More specifically, they were well known to Captain Edward J. Smith, who was Master of Titanic on her fatal voyage. Eerily, the captain appears to have predicted Titanic's accident to some American friends, Mr. and Mrs. W. P. Wills, and a Dr. Williams in 1910. At that time, Smith was Master of the White Star liner Adriatic.
"...the big icebergs that drift into warmer water melt much more rapidly under water than on the surface, and sometimes a sharp, low reef extending two or three hundred feet beneath the sea is formed....If a vessel should run on one of these reefs half her bottom might be torn away....Some of us would go to the bottom with the ship."
Captain E.J. Smith, as quoted in The New York Times, April 18, 1912
Stability of Icebergs
One piece of universal advice to navigators is to avoid approaching icebergs because they have a tendency to capsize with little or no warning. "It is dangerous to approach an iceberg because it can calve or roll, creating a huge disturbance in the water which can upset a boat," is the warning from Dr. Stephen E. Bruneau, Ph.D., P. Eng. of Tatham Offshore Canada Ltd., Bain Johnston Centre in St. John's, Newfoundland. According to Dr. Bruneau, "It is even more dangerous to attempt to get on an iceberg. Falling ice is a threat and a rolling berg can dump you in the very cold water before collapsing over on top of you."
The notorious instability of icebergs is the result of their random shapes, coupled with non-uniform melting that can cause bergs to suddenly reorient themselves in the water. Another cause of rolling is a large portion of the berg breaking off to form a growler. Tabular icebergs are considered the most stable. The least stable are dome and wedge-shaped berges, which can roll over within seconds for no apparent cause.
Color of Icebergs
Icebergs that originate in Greenland are comprised of compacted snow. It is estimated that this compaction takes 10,000 to 15,000 years to accomplish. The resulting ice is full of tiny air bubbles, which reflect sunlight, giving icebergs their characteristic white color. Blue bands are usually the result of meltwater that has re-frozen and is bubble-free. Ice that does not have trapped air is bluish in color. Dark streaks through an iceberg can be caused by dirt and rocks picked up while the berg was part of its mother glacier. Lighter colored streaks may result from layers of airborne dust. Antarctic explorer, Sir Ernest Shackleton, testified about icebergs before the British Board of Trade:
"There are many bergs I have seen that appear to be black, due to the construction of the berg itself. Again...if it is not of close construction it is more porous and taking up the water does not reflect light in any way."